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Stage-dependent fate determination of neural precursor cells in mouse forebrain
Abstract
Cortical neural precursor cells (NPCs) sequentially undergo expansion, neurogenic and gliogenic phases during development, although the underlying mechanisms are poorly understood. Recent studies have identified a number of extrinsic factors that regulate the fate of NPCs. For example, we have shown that Wnt signaling induces neuronal differentiation of NPCs in an instructive manner. Importantly, Wnt signaling does so in late stage (neurogenic phase) of NPCs but not in early stage (expansion phase) of NPCs. Instead, Wnt signaling promotes proliferation of early NPCs. Likewise, STAT3-activating ligands induce astrocytic differentiation in late (gliogenic phase) but not in early (expansion and neurogenic phases) NPCs. These stage-dependent responses of NPCs might play a central role in determining the timing of differentiation and the size of final population of each differentiated cell type.
... However, the abovementioned studies in neuronal cells stably expressing SCD5 underscore the possibility that this enzyme is integral to the intertwined modulation of cell replication and differentiation, processes whose balance determines the fate of cells. Moreover, exit from cell cycle is a prerequisite for the differentiation of neurons [57], therefore, a more active cycle of cell replication could explain the delay, or even failure, in fully developing into differentiated neurons of those cells expressing ectopic SCD5. This view is supported by the observation that although retinoic acid in neuronal cells markedly halted cell proliferation in both SCD5-expressing and controls cells the anti-differentiation effect of the retinoid was less prominent in the SCD5 overexpressors [38]. ...
... The changes in the biological phenotype of neuronal cells promoted by the expression of SCD5, such as alterations in cell proliferation and neurite outgrowth, could be traced, at least in part, to a modification of signaling mechanisms, such as Akt, ERK1/2, and Wnt [38]. In this study, it was observed that in cells conditioned for differentiation SCD5 blunted the EGF-induced phosphorylation and activation of EGFR, as well as its downstream signals ERK and Akt, which are central players in neuronal replication and functional maturation [57,58]. In light of the findings showing that SCD1 activity is required for the full induction of Akt and ERK pathways [32,59,60], the observation that SCD5 modulates these two signaling systems in an opposite manner suggests that human SCD isoforms may exhibit divergent functions in human cells, at least in certain cell types. ...
A large body of research has demonstrated that human stearoyl-CoA desaturase 1 (SCD1), a universally expressed fatty acid Δ9-desaturase that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), is a central regulator of metabolic and signaling pathways involved in cell proliferation, differentiation, and survival. Unlike SCD1, stearoyl-CoA desaturase 5 (SCD5), a second SCD isoform found in a variety of vertebrates, including humans, has received considerably less attention but new information on the catalytic properties, regulation and biological functions of this enzyme has begun to emerge. This review will examine the new evidence that supports key metabolic and biological roles for SCD5, as well as the potential implication of this desaturase in the mechanisms of human diseases.
... Bcl6 Functionally Alters b-Catenin/Tcf Signaling to Promote Neurogenesis Given the importance of the Wnt pathway in the regulation of self-renewal versus differentiation balance in the cortex (Chenn and Walsh, 2002;Fang et al., 2013;Hirabayashi and Gotoh, 2005;Hirabayashi et al., 2004;Kuwahara et al., 2010;Munji et al., 2011;Mutch et al., 2010;Wrobel et al., 2007;Zhang et al., 2010) and the number of downregulated genes belonging to this pathway, we tested the global impact of Bcl6 on the Wnt pathway in vivo. Axin 2, a classical Wnt/b-catenin-dependent target gene, was found to be upregulated in Bcl6 À/À mouse embryonic cortex using in situ hybridization. ...
... Moreover, in relation with b-catenin transcriptional activity, our data indicate that Tcf7l1 is a key mediator of Wnt signaling that is directly downstream of Bcl6. Wnt activation has been reported to have differential effects on neurogenesis (Chenn and Walsh, 2002;Fang et al., 2013;Hirabayashi and Gotoh, 2005;Hirabayashi et al., 2004;Kuwahara et al., 2010;Munji et al., 2011;Mutch et al., 2010;Wrobel et al., 2007;Zhang et al., 2010), and Tcf7l1 was previously proposed to act either as a repressor or an activator of transcription of Wnt-specific genes (Cole et al., 2008;Kim et al., 2000;Lu et al., 2015;Shy et al., 2013;Wu et al., 2012;Yi et al., 2011). However, our data indicate that, in the context of Bcl6 effects on neurogenesis, Tcf7l1 acts mostly as a blocker of neurogenesis, in line with previous findings (Ohtsuka et al., 2011), and thereby likely as an activator of pro-proliferative genes, such as Ccnd1/2 identified in this study. ...
During neurogenesis, progenitors switch from self-renewal to differentiation through the interplay of intrinsic and extrinsic cues, but how these are integrated remains poorly understood. Here, we combine whole-genome transcriptional and epigenetic analyses with in vivo functional studies to demonstrate that Bcl6, a transcriptional repressor previously reported to promote cortical neurogenesis, acts as a driver of the neurogenic transition through direct silencing of a selective repertoire of genes belonging to multiple extrinsic pathways promoting self-renewal, most strikingly the Wnt pathway. At the molecular level, Bcl6 represses its targets through Sirt1 recruitment followed by histone deacetylation. Our data identify a molecular logic by which a single cell-intrinsic factor represses multiple extrinsic pathways that favor self-renewal, thereby ensuring robustness of neuronal fate transition.
... They can differentiate into neuronal precursor cells and glial precursor cells, and each progenitor cell differentiates into neurons, astrocytes, and oligodendrocytes. The neural stem cells that do not differentiate into neurons differentiate into glial cells before and after birth, at which point differentiation into neurons is complete ( Figure 5) [43]. ...
... They can differentiate into neuronal precursor cells and glial precursor cells, and each progenitor cell differentiates into neurons, astrocytes, and oligodendrocytes. The neural stem cells that do not differentiate into neurons differentiate into glial cells before and after birth, at which point differentiation into neurons is complete ( Figure 5) [43]. Neuronal progenitor cells differentiate into neurons, while glial progenitor cells differentiate into astrocytes and oligodendrocytes [44]. ...
Vitamin K is classified into three homologs depending on the side-chain structure, with 2-methyl-1,4-naphthoqumone as the basic skeleton. These homologs are vitamin K1 (phylloquinone: PK), derived from plants with a phythyl side chain; vitamin K2 (menaquinone-n: MK-n), derived from intestinal bacteria with an isoprene side chain; and vitamin K3 (menadione: MD), a synthetic product without a side chain. Vitamin K homologs have physiological effects, including in blood coagulation and in osteogenic activity via γ-glutamyl carboxylase and are used clinically. Recent studies have revealed that vitamin K homologs are converted to MK-4 by the UbiA prenyltransferase domain-containing protein 1 (UBIAD1) in vivo and accumulate in all tissues. Although vitamin K is considered to have important physiological effects, its precise activities and mechanisms largely remain unclear. Recent research on vitamin K has suggested various new roles, such as transcriptional activity as an agonist of steroid and xenobiotic nuclear receptor and differentiation-inducing activity in neural stem cells. In this review, we describe synthetic ligands based on vitamin K and exhibit that the strength of biological activity can be controlled by modification of the side chain part.
... Neocortical cells isolated from mouse embryos at 11.5 days postcoitum (dpc) were cultured in suspension with FGF2 and epidermal growth factor (EGF) for 0, 3, or 9 days in vitro (DIV). Under these conditions, 0 and 3 DIV cultures correspond to the neurogenic phase, whereas 9 DIV cultures correspond to the astrogliogenic phase (Hirabayashi and Gotoh, 2005;Qian et al., 2000). Reverse transcription (RT) and quantitative polymerase chain reaction (qPCR) analysis confirmed that the expression levels of neurogenic genes were reduced, whereas that of the astrogliogenic gene for glial fibrillary acidic protein (GFAP) was increased at 9 DIV compared to 0 or 3 DIV ( Figures 1A-1E). ...
... We prepared neocortical NPCs from Ring1A À/À ;Ring1B flox/flox ;Rosa26::CreER T2 mouse embryos at 12.5 dpc, cultured the cells in suspension with FGF2 and EGF for 6 DIV, and then infected them with various retroviruses before culture for an additional 3 days in the absence or presence of 4-hydroxytamoxifen (4-OHT) to induce Cre-mediated deletion of the floxed Ring1B alleles ( Figure 1J). Under these conditions, 10 DIV cultures correspond to the astrogliogenic phase (Hirabayashi and Gotoh, 2005;Qian et al., 2000). The addition of 4-OHT indeed resulted in the depletion of Ring1B protein in these Ring1A-deficient NPCs as well as in the down-regulation of total H2Aub to an undetectable level . ...
Polycomb repressive complex (PRC) 1 maintains developmental genes in a poised state through monoubiquitination (Ub) of histone H2A. Although Ub-independent functions of PRC1 have also been suggested, it has remained unclear whether Ub-dependent and -independent functions of PRC1 operate differentially in a developmental context. Here, we show that the E3 ubiquitin ligase activity of Ring1B, a core component of PRC1, is necessary for the temporary repression of key neuronal genes in neurogenic (early-stage) neural stem or progenitor cells (NPCs) but is dispensable for the persistent repression of these genes associated with the loss of neurogenic potential in astrogliogenic (late-stage) NPCs. Our results also suggest that histone deacetylase (HDAC) activity of the NuRD/MBD3 complex and Phc2-dependent PRC1 clustering are necessary for the transition from the Ub-dependent to -independent function of PRC1. Together, these results indicate that Ub-independent mode of repression by PRC1 plays a key role in mammalian development during cell fate restriction.
... It is also reported that LIF is secreted by grafted NSCs and provides protective effects in animal model of multiple sclerosis by promoting survival, differentiation, and the remyelination capacity of both endogenous oligodendrocyte precursors and mature oligodendrocytes [32,33]. However, in the early neurogenic phase when NSCs mainly give rise to neurons, LIF and CNTF can modulate neuron-astrocyte transition by promoting astrocytic differentiation from NSCs [34]. There is a similar, posttransplantation transition of neurons into astrocytes [35]. ...
... There is a similar, posttransplantation transition of neurons into astrocytes [35]. It is believed that inhibition of LIF and CNTF signals can reduce astrocytogenesis and enhance neuronal generation from NSCs [34]. ...
Background
Neural stem/precursor cells (NSCs) are of particular interest because of their potential application in cell therapy for brain damage. However, most brain injury cases are followed with neuroinflammatory stress, which affects the lineage selection of grafted NSCs by promoting astrocytogenesis, thus hampering the potential for neural replacement. The present study investigated the role of miR-17-92 in protecting against detrimental effects of neuroinflammation on NSC differentiation in cell therapy. MethodsNSCs were treated with conditioned medium from lesioned astrocytes with/without neutralizing antibodies of leukemia inhibitory factor (LIF) or/and ciliary neurotrophic factor (CNTF), respectively. Afterward, the levels of p-STAT3 and p-JAK2 were determined by western blotting while expression of glial fibrillary acidic protein (GFAP) and β-tubulin III was assessed by immunostaining. The activation of JAK-STAT pathway and cell differentiation were also evaluated after we overexpressed miR-17-92 in NSCs under different neuroinflammatory conditions. After the transplantation of miR-17-92-overexpressing NSCs into injured mouse cortex, PH3, nestin, GFAP, and NeuN were analyzed by immunostaining. In addition, motor coordination of mice was evaluated by rotarod test. ResultsConditioned medium from lesioned astrocytes activated JAK-STAT pathway and facilitated astrocytic differentiation in NSCs while neutralizing antibodies of LIF and CNTF remarkably attenuated such effects. miR-17-92 cluster repressed the expression of multiple proteins including GP130, CNTFR, JAK2, and STAT3 in JAK-STAT pathway. Overexpression of miR-17-92 in NSCs systematically blocked the activation of JAK-STAT pathway mediated by LIF and CNTF, which facilitated neuronal differentiation in vitro. Furthermore, miR-17-92 increased neuronal generation of grafted NSCs and reduced astrogliosis, which resulted in the improvement of motor coordination of brain-injured mice. Conclusions
Our results suggest that miR-17-92 promotes neuronal differentiation of grafted NSCs under neuroinflammatory condition via inhibition of multiple proteins in JAK-STAT pathway.
... Wnt signaling also promotes NPC differentiation (Kléber and Sommer, 2004;Muroyama et al., 2004). Wnt3 and Wnt7a specif-ically favor neuronal differentiation of late, but not of early, cortical NPCs (Hirabayashi et al., 2004;Hirabayashi and Gotoh, 2005;Yu et al., 2006), and Wnt5a stimulates the differentiation of dopaminergic neurons (Castelo-Branco and Arenas, 2006;Andersson et al., 2008). As Wnt ligands elicit such a variety of responses, their functions need to be determined in a cell type-and context-dependent manner. ...
... However, a general rule cannot be drawn as yet. In fact, and surprisingly, the activation of the -catenin pathway can induce neuronal differentiation of cortical NPCs derived from late developmental ages (Hirabayashi et al., 2004;Hirabayashi and Gotoh, 2005). To explain this apparent paradox, it has been proposed that the cellular response to a Wnt signal relies to a limited extent on the identity of the ligand and to a larger extent on the cell type, developmental stage, receptor context/availability, and the presence of concomitant signals (Viti et al., 2003;Israsena et al., 2004;Kléber and Sommer, 2004;Mikels and Nusse, 2006;Li et al., 2009). ...
During brain development, neurogenesis, migration, and differentiation of neural progenitor cells are regulated by an interplay between intrinsic genetic programs and extrinsic cues. The Dlx homeogene transcription factors have been proposed to directly control the genesis and maturation of GABAergic interneurons of the olfactory bulb (OB), subpallium, and cortex. Here we provide evidence that Dlx genes promote differentiation of olfactory interneurons via the signaling molecule Wnt5a. Dlx2 and Dlx5 interact with homeodomain binding sequences within the Wnt5a locus and activate its transcription. Exogenously provided Wnt5a promotes GABAergic differentiation in dissociated OB neurons and in organ-type brain cultures. Finally, we show that the Dlx-mutant environment is unfavorable for GABA differentiation, in vivo and in vitro. We conclude that Dlx genes favor interneuron differentiation also in a non-cell-autonomous fashion, via expression of Wnt5a.
... The FGF pathway also seems to be involved in stem cells renewal (Yoon et al., 2004). In the cortex, Wnt/β-catatenin pathway is both implicated in selfrenewal (Chenn and Walsh, 2002) and neuronal differentiation (Hirabayashi et al., 2004), however, the type of response seems to be dependent on the stage of cortical development (Hirabayashi and Gotoh, 2005). Cross-talk between FGF and Wnt/β-catatenin pathways can also determine if cells undergo (in the absence of FGF) or not (in the presence of FGF) differentiation (Israsena et al., 2004). ...
... The signaling mediated by of Notch, FGF and Wnt involve transcription activators (Hirabayashi et al., 2004;Israena et al., 2004;Miyata et al., 2004) as well as transcription repressors, such as REST/NRSF that represses neuronal genes in non-neuronal cells (Ballas et al., 2005). When stem cells differentiate in neurons there is a decrease of the binding of REST to neuronal promoters (Ballas et al., 2005).The generation of astrocytes occurs after neuronal generation and it also requires instructive signals and activation of signaling pathways such as bone morphogenic protein BMP/ Sma and Mad related proteins (Smad), JAK/STAT and Notch (Kamakura et al., 2004;Hirabayashi and Gotoh, 2005). ...
... This study was designed to reveal whether neurogenesis occurs in the hippocampus throughout the lifespan. (2) The results indicate that low-intensity exercise or exposure to bright light increases neurogenesis in the hippocampal dentate gyrus of adult rats and the combined treatment does not have an additive effect. ...
... The mammalian brain produces neuronal precursor cells throughout development [1][2][3] . Neurogenesis occurs in the hippocampus during both periods of neuron generation and after active growth, and the hippocampus is critically involved in learning and the formation of memories [4][5] . ...
The hippocampus is a brain region responsible for learning and memory functions. The purpose of this study was to investigate the effects of low-intensity exercise and bright light exposure on neurogenesis and brain-derived neurotrophic factor expression in adult rat hippocampus. Male Sprague-Dawley rats were randomly assigned to control, exercise, light, or exercise + light groups (n = 9 per group). The rats in the exercise group were subjected to treadmill exercise (5 days per week, 30 minutes per day, over a 4-week period), the light group rats were irradiated (5 days per week, 30 minutes per day, 10 000 lx, over a 4-week period), the exercise + light group rats were subjected to treadmill exercise in combination with bright light exposure, and the control group rats remained sedentary over a 4-week period. Compared with the control group, there was a significant increase in neurogenesis in the hippocampal dentate gyrus of rats in the exercise, light, and exercise + light groups. Moreover, the expression level of brain-derived neurotrophic factor in the rat hippocampal dentate gyrus was significantly higher in the exercise group and light group than that in the control group. Interestingly, there was no significant difference in brain-derived neurotrophic factor expression between the control group and exercise + light group. These results indicate that low-intensity treadmill exercise (first 5 minutes at a speed of 2 m/min, second 5 minutes at a speed of 5 m/min, and the last 20 minutes at a speed of 8 m/min) or bright-light exposure therapy induces positive biochemical changes in the brain. In view of these findings, we propose that moderate exercise or exposure to sunlight during childhood can be beneficial for neural development.
... The expression profiles of genes from the GDS3442 dataset were consistent with our results. Most NPCs are undifferentiated at E9.5, and start to differentiate into neurons at E11.5, and at E13.5 when neurogenesis peaks [40]. In the GDS3442 dataset, numerous gene expression changes occurred during mouse embryonic brain development, in which metabolism and cell cycle-related gene were downregulated when precursor cells switched from proliferation to neuronal differentiation (E9.5-E11.5), ...
MicroRNAs have been studied extensively in neurodegenerative diseases. In a previous study, miR-153 promoted neural differentiation and projection formation in mouse hippocampal HT-22 cells. However, the pathways and molecular mechanism underlying miR-153-induced neural differentiation remain unclear. To explore the molecular mechanism of miR-153 on neural differentiation, we performed RNA sequencing on miR-153-overexpressed HT-22 cells. Based on RNA sequencing, differentially expressed genes (DEGs) and pathways in miR-153-overexpressed cells were identified. The Database for Annotation, Visualization and Integrated Discovery and Gene Set Enrichment Analysis were used to perform functional annotation and enrichment analysis of DEGs. Targetscan predicted the targets of miR-153. The Search Tool for the Retrieval of Interacting Genes and Cytoscape, were used to construct protein-protein interaction networks and identify hub genes. Q-PCR was used to detect mRNA expression of the identified genes. The expression profiles of the identified genes were compared between embryonic days 9.5 (E9.5) and E11.5 in the embryotic mouse brain of the GDS3442 dataset. Cell Counting Kit-8 assay was used to determine cell proliferation and cellular susceptibility to amyloid β-protein (Aβ) toxicity in miR-153-overexpressed cells. The results indicated that miR-153 increased cell adhesion/Ca²⁺ (Cdh5, Nrcam, and P2rx4) and Bdnf/Ntrk2 neurotrophic signaling pathway, and decreased ion channel activity (Kcnc3, Kcna4, Clcn5, and Scn5a). The changes in the expression of the identified genes in miR-153-overexpressed cells were consistent with the expression profile of GDS3442 during neural differentiation. In addition, miR-153 overexpression decreased cellular susceptibility to Aβ toxicity in HT-22 cells. In conclusion, miR-153 overexpression may promote neural differentiation by inducing cell adhesion and the Bdnf/Ntrk2 pathway, and regulating electrophysiological maturity by targeting ion channels. MiR-153 may play an important role in neural differentiation; the findings provide a useful therapeutic direction for neurodegenerative diseases.
... Research on the JAK/STAT pathway has shown that the stimulation of CNTF receptors in embryonic cells activates JAK1, STAT1, and STAT3, promoting the differentiation of neural stem and neural progenitor cells into astrocytes [55,56]. Studies utilizing conditional knockout mice have demonstrated that a STAT3 deficit significantly reduces astrocyte proliferation and viability, supporting the maintenance of the astrocyte population's homeostasis [57]. ...
Spinal cord injury (SCI) leads to significant functional impairments below the level of the injury, and astrocytes play a crucial role in the pathophysiology of SCI. Astrocytes undergo changes and form a glial scar after SCI, which has traditionally been viewed as a barrier to axonal regeneration and functional recovery. Astrocytes activate intracellular signaling pathways, including nuclear factor κB (NF-κB) and Janus kinase-signal transducers and activators of transcription (JAK/STAT), in response to external stimuli. NF-κB and STAT3 are transcription factors that play a pivotal role in initiating gene expression related to astrogliosis. The JAK/STAT signaling pathway is essential for managing secondary damage and facilitating recovery processes post-SCI: inflammation, glial scar formation, and astrocyte survival. NF-κB activation in astrocytes leads to the production of pro-inflammatory factors by astrocytes. NF-κB and STAT3 signaling pathways are interconnected: NF-κB activation in astrocytes leads to the release of interleukin-6 (IL-6), which interacts with the IL-6 receptor and initiates STAT3 activation. By modulating astrocyte responses, these pathways offer promising avenues for enhancing recovery outcomes, illustrating the crucial need for further investigation into their mechanisms and therapeutic applications in SCI treatment.
... Pregnant mice were anesthetized on embryonic day 15 (E15), corresponding to the second trimester with intensive neurogenesis [22]. These mice were placed in an enclosed box that allowed the convection of anesthetic gases. ...
An increasing number of studies reveal the deleterious effects of isoflurane (Iso) exposure during pregnancy on offspring cognition. However, no effective therapeutic strategy for Iso-induced deleterious effects has been well developed. Angelicin exerts an anti-inflammatory effect on neurons and glial cells. This study investigated the roles and mechanism of action of angelicin in Iso-induced neurotoxicity in vitro and in vivo. After exposing C57BL/6 J mice on embryonic day 15 (E15) to Iso for 3 and 6 h, respectively, neonatal mice on embryonic day 18 (E18) displayed obvious anesthetic neurotoxicity, which was revealed by the elevation of cerebral inflammatory factors and blood–brain barrier (BBB) permeability and cognitive dysfunction in mice. Angelicin treatment could not only significantly reduce the Iso-induced embryonic inflammation and BBB disruption but also improve the cognitive dysfunction of offspring mice. Iso exposure resulted in an increase of carbonic anhydrase (CA) 4 and aquaporin-4 (AQP4) expression at both mRNA and protein levels in vascular endothelial cells and mouse brain tissue collected from neonatal mice on E18. Remarkably, the Iso-induced upregulation of CA4 and AQP4 expression could be partially reversed by angelicin treatment. Moreover, GSK1016790A, an AQP4 agonist, was used to confirm the role of AQP4 in the protective effect of angelicin. Results showed that GSK1016790A abolished the therapeutic effect of angelicin on Iso-induced inflammation and BBB disruption in the embryonic brain and on the cognitive function of offspring mice. In conclusion, angelicin may serve as a potential therapeutic for Iso-induced neurotoxicity in neonatal mice by regulating the CA4/AQP4 pathway.
Graphical Abstract
... Later on, during mid-gestation they undergo asymmetric cell division and receive cues to differentiate into neurons. Lastly, from late-gestation to perinatal periods they enter the gliogenic phase and differentiate into astrocytes and oligodendrocytes [1,2]. Importantly, undifferentiated NSCs still reside in two niches of the adult brain, namely the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus [3]. ...
Astrocytes arise from multipotent neural stem cells (NSCs) and represent the most abundant cell type of the central nervous system (CNS), playing key roles in the developing and adult brain. Since the differentiation of NSCs towards a gliogenic fate is a precisely timed and regulated process, its perturbation gives rise to dysfunctional astrocytic phenotypes. Inflammation, which often underlies neurological disorders, including neurodevelopmental disorders and brain tumors, disrupts the accurate developmental process of NSCs. However, the specific consequences of an inflammatory environment on the epigenetic and transcriptional programs underlying NSCs’ differentiation into astrocytes is unexplored. Here, we address this gap by profiling in mice glial precursors from neural tissue derived from early embryonic stages along their astrocytic differentiation trajectory in the presence or absence of tumor necrosis factor (TNF), a master pro-inflammatory cytokine. By using a combination of RNA- and ATAC-sequencing approaches, together with footprint and integrated gene regulatory network analyses, we here identify key differences during the differentiation of NSCs into astrocytes under physiological and inflammatory settings. In agreement with its role to turn cells resistant to inflammatory challenges, we detect Nrf2 as a master transcription factor supporting the astrocytic differentiation under TNF exposure. Further, under these conditions, we unravel additional transcriptional regulatory hubs, including Stat3, Smad3, Cebpb, and Nfkb2, highlighting the interplay among pathways underlying physiological astrocytic developmental processes and those involved in inflammatory responses, resulting in discrete astrocytic phenotypes. Overall, our study reports key transcriptional and epigenetic changes leading to the identification of molecular regulators of astrocytic differentiation. Furthermore, our analyses provide a valuable resource for understanding inflammation-induced astrocytic phenotypes that might contribute to the development and progression of CNS disorders with an inflammatory component.
... Later, during midgestation, NSCs switch to asymmetric divisions and differentiate only into neurons. However, in late-gestation and perinatal periods, NSCs acquire a gliogenic capacity producing astrocytes and later oligodendrocytes (Hirabayashi and Gotoh, 2005). DNAm has a role in the regulation of this neurogenesis-gliogenesis switch, critical for producing a balanced number of each cell type. ...
Neural induction, both in vivo and in vitro , includes cellular and molecular changes that result in phenotypic specialization related to specific transcriptional patterns. These changes are achieved through the implementation of complex gene regulatory networks. Furthermore, these regulatory networks are influenced by epigenetic mechanisms that drive cell heterogeneity and cell-type specificity, in a controlled and complex manner. Epigenetic marks, such as DNA methylation and histone residue modifications, are highly dynamic and stage-specific during neurogenesis. Genome-wide assessment of these modifications has allowed the identification of distinct non-coding regulatory regions involved in neural cell differentiation, maturation, and plasticity. Enhancers are short DNA regulatory regions that bind transcription factors (TFs) and interact with gene promoters to increase transcriptional activity. They are of special interest in neuroscience because they are enriched in neurons and underlie the cell-type-specificity and dynamic gene expression profiles. Classification of the full epigenomic landscape of neural subtypes is important to better understand gene regulation in brain health and during diseases. Advances in novel next-generation high-throughput sequencing technologies, genome editing, Genome-wide association studies (GWAS), stem cell differentiation, and brain organoids are allowing researchers to study brain development and neurodegenerative diseases with an unprecedented resolution. Herein, we describe important epigenetic mechanisms related to neurogenesis in mammals. We focus on the potential roles of neural enhancers in neurogenesis, cell-fate commitment, and neuronal plasticity. We review recent findings on epigenetic regulatory mechanisms involved in neurogenesis and discuss how sequence variations within enhancers may be associated with genetic risk for neurological and psychiatric disorders.
... Neurogenesis is the process of new cell formation from neural stem/ progenitor cells (NSCs), which have the ability to proliferate and differentiate into astrocytes, oligodendrocytes, or neurons (Akkermann et al., 2017;Bond et al., 2020;Hirabayashi and Gotoh, 2005;Mira and Morante, 2020;Taupin and Gage, 2002). After the nervous system development in the embryonic stage, neurogenesis remains physiologically active in specific cerebral regions of mammals (Altman and Das, 1965;Eriksson et al., 1998;Kaplan and Hinds, 1977). ...
The subgranular zone of the dentate gyrus is an adult neurogenic niche where new neurons are continuously generated. A dramatic hippocampal neurogenesis decline occurs with increasing age, contributing to cognitive deficits. The process of neurogenesis is intimately regulated by the microenvironment, with inflammation being considered a strong negative factor for this process. Thus, we hypothesize that the reduction of new neurons in the aged brain could be attributed to the age-related microenvironmental changes towards a pro-inflammatory status. In this work, we evaluated whether an anti-inflammatory microenvironment could counteract the negative effect of age on promoting new hippocampal neurons. Surprisingly, our results show that transgenic animals chronically overexpressing IL-10 by astrocytes present a decreased hippocampal neurogenesis in adulthood. This results from an impairment in the survival of neural newborn cells without differences in cell proliferation. In parallel, hippocampal-dependent spatial learning and memory processes were affected by IL-10 overproduction as assessed by the Morris water maze test. Microglial cells, which are key players in the neurogenesis process, presented a different phenotype in transgenic animals characterized by high activation together with alterations in receptors involved in neuronal communication, such as CD200R and CX3CR1. Interestingly, the changes described in adult transgenic animals were similar to those observed by the effect of normal aging. Thus, our data suggest that chronic IL-10 overproduction mimics the physiological age-related disruption of the microglia-neuron dialogue, resulting in hippocampal neurogenesis decrease and spatial memory impairment.
... In mid-gestation, they start to produce neurons, and then generate glial cells from late gestation until the perinatal period. 2 This sequential acquisition of differentiation potential is essential for generating a balanced number of each cell type at the right timing to produce the elaborate brain structure. ...
The brain consists of three major cell types: neurons and two glial cell types (astrocytes and oligodendrocytes). Although they are generated from common multipotent neural stem/precursor cells (NS/PCs), embryonic NS/PCs cannot generate all of the cell types at the beginning of brain development. NS/PCs first undergo extensive self-renewal to expand their pools, and then acquire the potential to produce neurons, followed by glial cells. Astrocytes are the most frequently found cell type in the central nervous system (CNS), and play important roles in brain development and functions. Although it has been shown that nuclear factor IA (Nfia) is a pivotal transcription factor for conferring gliogenic potential on neurogenic NS/PCs by sequestering DNA methyltransferase 1 (Dnmt1) from astrocyte-specific genes, direct targets of Nfia that participate in astrocytic differentiation have yet to be completely identified. Here we show that SRY-box transcription factor 8 (Sox8) is a direct target gene of Nfia at the initiation of the gliogenic phase. We found that expression of Sox8 augmented leukemia inhibitory factor (LIF)-induced astrocytic differentiation, while Sox8 knockdown inhibited Nfia-enhanced astrocytic differentiation of NS/PCs. In contrast to Nfia, Sox8 did not induce DNA demethylation of an astrocyte-specific marker gene, glial fibrillary acidic protein (Gfap), but instead associated with LIF downstream transcription factor STAT3 through transcriptional coactivator p300, explaining how Sox8 expression further facilitated LIF-induced Gfap expression. Taken together, these results suggest that Sox8 is a crucial Nfia downstream transcription factor for the astrocytic differentiation of NS/PCs in the developing brain.
... The E10 cerebral cortex mainly consists of proliferating neural progenitors, whereas cortical neurogenesis is completed by E17 (Takahashi et al., 1999). After neurogenesis, astrocyte production (gliogenesis) begins (Hirabayashi and Gotoh, 2005). We confirmed that nestin, a marker for neural progenitors, was expressed at E10 and E18, neurogenic and gliogenic periods, respectively, and that expression of MAP2, a marker for mature neurons, was increased at E18 (Supplementary Figures 1A,B). ...
Proper regulation of neuronal morphological changes is essential for neuronal migration, maturation, synapse formation, and high-order function. Many cytoplasmic proteins involved in the regulation of neuronal microtubules and the actin cytoskeleton have been identified. In addition, some nuclear proteins have alternative functions in neurons. While cell cycle-related proteins basically control the progression of the cell cycle in the nucleus, some of them have an extra-cell cycle-regulatory function (EXCERF), such as regulating cytoskeletal organization, after exit from the cell cycle. Our expression analyses showed that not only cell cycle regulators, including cyclin A1, cyclin D2, Cdk4/6, p21cip1, p27kip1, Ink4 family, and RAD21, but also DNA repair proteins, including BRCA2, p53, ATM, ATR, RAD17, MRE11, RAD9, and Hus1, were expressed after neurogenesis, suggesting that these proteins have alternative functions in post-mitotic neurons. In this perspective paper, we discuss the alternative functions of the nuclear proteins in neuronal development, focusing on possible cytoplasmic roles.
... Neocortical NPCs can be propagated in suspension culture with FGF2 and EGF, during which they form cell aggregates known as neurospheres. The cells cultured for 0 or 3 days in vitro (DIV) correspond to the neurogenic phase of development, whereas those cultured for 9 DIV correspond to the astrogliogenic phase (Hirabayashi and Gotoh, 2005;Qian et al., 2000). ...
Dynamic changes in histone modifications mediated by Polycomb group proteins can be indicative of the transition of gene repression mode during development. Here, we present methods for the isolation of mouse neocortical neural progenitor-stem cells (NPCs) and their culture, followed by chromatin immunoprecipitation quantitative PCR (ChIP-qPCR) techniques to examine changes in histone H2A ubiquitination patterns at various developmental stages. This protocol can be applied for both in vitro NPCs and NPCs directly isolated from mouse neocortices.
For complete details on the use and execution of this protocol, please refer to (Tsuboi et al., 2018).
... En revanche, si le plan de clivage est parallèle au ventricule (ou horizontal), une division asymétrique prend place pour produire deux types de cellules différentes qui hériteraient pour chacune d'entre elles des constituants apicaux ou des constituants basaux ( Figure 19) (Chenn et McConnell, 1995). Ainsi, au début du développement embryonnaire, la division verticale serait majoritairement présente afin d'augmenter le stock de précurseurs neuraux, tandis qu'à l'âge adulte, la scission horizontale serait prédominante (Hirabayashi et Gotoh, 2005). Ce modèle qui repose sur le plan de clivage n'est cependant pas complètement confirmé par d'autres équipes (Noctor et coll., 2008). ...
La régulation de la neurogenèse embryonnaire implique de nombreux facteurs intrinsèques et extrinsèques délivrés avec une séquence temporelle stricte. Parmi ces facteurs, l’oxygène joue un rôle important dans la maintenance et la différenciation des cellules souches neurales (CSN). Dans ce contexte, le facteur de transcription HIF-1α, un des principaux intervenants dans les réponses adaptatives aux variations d’oxygène, pourrait jouer un rôle majeur dans la neurogenèse embryonnaire notamment au niveau des CSN. Dans ce but, nous avons évalué les conséquences de la perte de HIF-1α sur la neurogenèse en développant un modèle de souris transgénique Glast-YFP-CreERT2 ; HIF-1α flox/flox dans lequel HIF-1α est spécifiquement inhibé dans les cellules de la glie radiaire GLAST+, cellules faisant office de CSN chez l'embryon. Dans ce modèle HIF-1α CKO, une altération importante et rapide de l’angiogenèse corticale associée à une diminution de l’épaisseur du néocortex est observée. Ces changements ne sont pas corrélés à une mort cellulaire corticale mais sont associés à une diminution significative du nombre de mitoses et de la prolifération cellulaire au niveau des régions ventriculaire et sous-ventriculaire. Cette perte fonctionnelle de HIF-1α provoque également une diminution du nombre des cellules Sox2+ et Pax6+ et une augmentation des progéniteurs intermédiaires (Tbr2+). Ces données suggèrent donc que HIF-1α dans les CSN joue un rôle essentiel sur la neurogenèse embryonnaire. Parallèlement, j’ai participé à l’identification d’acteurs moléculaires impliqués dans la migration/invasion radio-induite des cellules souches de gliomes (CSG) précédemment mise en évidence au laboratoire. Nos résultats démontrent que la migration radio-induite des CSG est dépendante de HIF-1α qui intervient en régulant positivement la protéine JMY qui, de par son activité de polymérisation des filaments d’actine favorise la migration cellulaire. A l’instar des CSG, des expériences de vidéo-microscopie montrent que la migration radio-induite observée dans les CSN est également dépendante de HIF-1α. En conclusion, le développement d’un modèle transgénique knockout conditionnel inductible Glast-YFP-CreERT2 ; HIF-1αflox/flox nous a permis de caractériser l’importance de HIF-1α dans les CSN au cours de la neurogenèse. Son utilisation devrait également nous permettre d’identifier de nouveaux acteurs moléculaires dépendants de HIF-1α impliqués dans la migration radio-induite des CSN et des CSG. De par leurs caractéristiques communes avec les CSG, l’identification de ces nouveaux acteurs identifiés dans les CSN pourrait représenter de nouvelles cibles thérapeutiques afin d’améliorer à plus long terme l’efficacité des traitements des patients atteints de glioblastomes par l’inhibition de mécanismes moléculaires stimulant la migration radio-induite des CSG au cours de la radiothérapie.
... Fittingly in the context of AD, Wnt signalling is also required for the development of brain structures including the hippocampus among others, which is integral for memory [60]. There, Wnt3a regulates both neuronal progenitor cell (NPC) expansion and neuronal differentiation via canonical signalling [61][62][63][64][65]. Wnt3a is further accompanied by Wnt5a and Wnt7b, which respectively regulate axonal and dendritic differentiation (axon specification, axon growth, and dendritic tree formation) via non-canonical Wnt/PCP signalling [66][67][68][69][70]. ...
The Wnt signalling system is essential for both the developing and adult central nervous system. It regulates numerous cellular functions ranging from neurogenesis to blood brain barrier biology. Dysregulated Wnt signalling can thus have significant consequences for normal brain function, which is becoming increasingly clear in Alzheimer’s disease (AD), an age-related neurodegenerative disorder that is the most prevalent form of dementia. AD exhibits a range of pathophysiological manifestations including aberrant amyloid precursor protein processing, tau pathology, synapse loss, neuroinflammation and blood brain barrier breakdown, which have been associated to a greater or lesser degree with abnormal Wnt signalling. Here we provide a comprehensive overview of the role of Wnt signalling in the CNS, and the research that implicates dysregulated Wnt signalling in the ageing brain and in AD pathogenesis. We also discuss the opportunities for therapeutic intervention in AD via modulation of the Wnt signalling pathway, and highlight some of the challenges and the gaps in our current understanding that need to be met to enable that goal.
... Astrocytes originate from radial glial cells, and through a series of steps they mature and migrate to the designated position in the brain [12]. There they begin to assume their final spongy stellate morphology, which involves, among other things, extensive changes in their cytoskeleton. ...
Glioblastoma multiforme (GBM) represents approximately 60% of all brain tumors in adults. This malignancy shows a high biological and genetic heterogeneity associated with exceptional aggressiveness, leading to a poor survival of patients. This review provides a summary of the basic biology of GBM cells with emphasis on cell cycle and cytoskeletal apparatus of these cells, in particular microtubules. Their involvement in the important oncosuppressive process called mitotic catastrophe will next be discussed along with select examples of microtubule-targeting agents, which are currently explored in this respect such as benzimidazole carbamate compounds. Select microtubule-targeting agents, in particular benzimidazole carbamates, induce G2/M cell cycle arrest and mitotic catastrophe in tumor cells including GBM, resulting in phenotypically variable cell fates such as mitotic death or mitotic slippage with subsequent cell demise or permanent arrest leading to senescence. Their effect is coupled with low toxicity in normal cells and not developed chemoresistance. Given the lack of efficient cytostatics or modern molecular target-specific compounds in the treatment of GBM, drugs inducing mitotic catastrophe might offer a new, efficient alternative to the existing clinical management of this at present incurable malignancy.
... The WNT signaling pathway is an evolutionarily conserved pathway that plays a crucial role during embryogenesis and adult stem cells by controlling several mechanisms such as cell polarity, cell specification, and tissue homeostasis. In the brain, besides its critical role during its development, this pathway is involved in neurogenesis as well as in controlling the homoeostatic proliferation and self-renewal of NSPCs in the adult subventricular zone [122][123][124]. Taking this into account, it is not surprising that this pathway has been described to be deregulated in cancer, including GBM, and to have an important role in CSC maintenance as well as in resistance to chemotherapy and radiotherapy [125]. ...
The discovery of glioblastoma stem cells (GSCs) in the 2000s revolutionized the cancer research field, raising new questions regarding the putative cell(s) of origin of this tumor type, and partly explaining the highly heterogeneous nature of glioblastoma (GBM). Increasing evidence has suggested that GSCs play critical roles in tumor initiation, progression, and resistance to conventional therapies. The remarkable oncogenic features of GSCs have generated significant interest in better defining and characterizing these cells and determining novel pathways driving GBM that could constitute attractive key therapeutic targets. While exciting breakthroughs have been achieved in the field, the characterization of GSCs is a challenge and the cell of origin of GBM remains controversial. For example, the use of several cell-surface molecular markers to identify and isolate GSCs has been a challenge. It is now widely accepted that none of these markers is, per se, sufficiently robust to distinguish GSCs from normal stem cells. Finding new strategies that are able to more efficiently and specifically target these niches could also prove invaluable against this devastating and therapy-insensitive tumor. In this review paper, we summarize the most relevant findings and discuss emerging concepts and open questions in the field of GSCs, some of which are, to some extent, pertinent to other cancer stem cells.
... Astrocytes are generated from the same population of multipotent neural progenitor cells (NPCs) as neurons (Taupin & Gage, 2002), with astrogenesis following neurogenesis (Bayer & Altman, 1991;Forscher & Smith, 1988;Hirabayashi & Gotoh, 2005;Miller & Gauthier, 2007). ...
Astrocytes, a highly heterogeneous population of glial cells, serve as essential regulators of brain development and homeostasis. The heterogeneity of astrocyte populations underlies the diversity in their functions. In addition to the typical mammalian astrocyte architecture, the cerebral cortex of humans exhibits a radial distribution of interlaminar astrocytes in the supragranular layers. These primate‐specific interlaminar astrocytes are located in the superficial layer and project long processes traversing multiple layers of the cerebral cortex. However, due to the lack of accessible experimental models, their functional properties and their role in regulating neuronal circuits remain unclear. Here we modeled human interlaminar astrocytes in humanized glial chimeric mice by engrafting astrocytes differentiated from human‐induced pluripotent stem cells into the mouse cortex. This model provides a novel platform for understanding neuron‐glial interaction and its alterations in neurological diseases. We engrafted RFP‐expressing astrocytes differentiated from hiPSCs into the cortex of immunodeficient mice neonatally. Nine months post engraftment, the human astrocytes in the superficial cortex developed into interlaminar astrocytes that mimicked the interlaminar astrocytes architecture of the adult human cortex. This chimeric mouse model will enable the study of human‐specific interlaminar astrocytes in vivo.
... In order to speed up the information conduction, axons are ensheathed and insulated with multi-spiral myelin membranes synthesized by oligodendrocytes (OLs) [3][4][5]. During neocortical development in Homo sapiens, early neural progenitor cell (NPC) differentiation into neuronal cell types, through the so-called "neurogenic phase" is temporally followed by the "gliogenic phase" during which multipotent NPCs differentiate into different glial cell types such as oligodendrocyte precursor cells (OPCs) [6,7]. OPCs migrate to developing white matter and divide a limited number of times until reaching their target axon [8]. ...
Background
New insights on cellular and molecular aspects of both oligodendrocyte (OL) differentiation and myelin synthesis pathways are potential avenues for developing a cell-based therapy for demyelinating disorders comprising multiple sclerosis. MicroRNAs (miRNA) have broad implications in all aspects of cell biology including OL differentiation. MiR-184 has been identified as one of the most highly enriched miRNAs in oligodendrocyte progenitor cells (OPCs). However, the exact molecular mechanism of miR-184 in OL differentiation is yet to be elucidated.
Methods and results
Based on immunochemistry assays, qRT-PCR, and western blotting findings, we hypothesized that overexpression of miR-184 in either neural progenitor cells (NPCs) or embryonic mouse cortex stimulated the differentiation of OL lineage efficiently through regulating crucial developmental genes. Luciferase assays demonstrated that miR-184 directly represses positive regulators of neural and astrocyte differentiation, i.e., SOX1 and BCL2L1, respectively, including the negative regulator of myelination, LINGO1. Moreover, blocking the function of miR-184 reduced the number of committed cells to an OL lineage.
Conclusions
Our data highlighted that miR-184 could promote OL differentiation even in the absence of exogenous growth factors and propose a novel strategy to improve the efficacy of OL differentiation, with potential applications in cell therapy for neurodegenerative diseases.
Electronic supplementary material
The online version of this article (10.1186/s13287-019-1208-y) contains supplementary material, which is available to authorized users.
... During the fetal expansion phase, NSCs self-replicate via symmetric cell division, whilst later, during mid-gestation, they undergo asymmetric cell division and receive cues to differentiate into neurons. Lastly, in late-gestation to perinatal periods they enter the gliogenic phase and differentiate into astrocytes and oligodendrocytes (Hirabayashi and Gotoh, 2005;Fig. 1. Depiction of key epigenetic mechanisms. ...
Astrocytes play a significant role in coordinating neural development and provide critical support for the function of the CNS. They possess important adaptation capacities that range from their transition towards reactive astrocytes to their ability to undergo reprogramming, thereby revealing their potential to retain latent features of neural progenitor cells. We propose that the mechanisms underlying reactive astrogliosis or astrocyte reprogramming provide an opportunity for initiating neuronal regeneration, a process that is notably reduced in the mammalian nervous system throughout evolution. Conversely, this plasticity may also affect normal astrocytic functions resulting in pathologies ranging from neurodevelopmental disorders to neurodegenerative diseases and brain tumors. We postulate that epigenetic mechanisms linking extrinsic cues and intrinsic transcriptional programs are key factors to maintain astrocyte identity and function, and critically, to control the balance of regenerative and degenerative activity. Here, we will review the main evidences supporting this concept. We propose that unravelling the epigenetic and transcriptional mechanisms underlying the acquisition of astrocyte identity and plasticity, as well as understanding how these processes are modulated by the local microenvironment under specific threatening or pathological conditions, may pave the way to new therapeutic avenues for several neurological disorders including neurodegenerative diseases and brain tumors of astrocytic lineage.
... The -Catenin is a critical downstream component of the Wnt pathway, which plays essential role in the regulation of mammalian neural development [87]. In vitro and in vivo studies demonstrate that the Wnt/ -catenin pathway regulates the proliferation and differentiation of neural progenitor cells [88]. Neuronal differentiation is induced by overexpression of -catenin or the pharmacological inhibition of GSK3 (the phosphorylating enzyme of -catenin) [89,90]. ...
Objectives:
Xuefu Zhuyu decoction (XFZYD), a traditional Chinese medicine (TCM) formula, has been demonstrated to be effective for the treatment of traumatic brain injury (TBI). However, the underlying pharmacological mechanisms remain unclear. This study aims to explore the potential action mechanisms of XFZYD in the treatment of TBI and to elucidate the combination principle of this herbal formula.
Methods:
A network pharmacology approach including ADME (absorption, distribution, metabolism, and excretion) evaluation, target prediction, known therapeutic targets collection, network construction, and molecule docking was used in this study.
Results:
A total of 119 bioactive ingredients from XFZYD were predicted to act on 47 TBI associated specific proteins which intervened in several crucial pathological processes including apoptosis, inflammation, antioxidant, and axon genesis. Almost each of the bioactive ingredients targeted more than one protein. The molecular docking simulation showed that 91 pairs of chemical components and candidate targets had strong binding efficiencies. The "Jun", "Chen", and "Zuo-Shi" herbs from XFZYD triggered their specific targets regulation, respectively.
Conclusion:
Our work successfully illuminates the "multicompounds, multitargets" therapeutic action of XFZYD in the treatment of TBI by network pharmacology with molecule docking method. The present work may provide valuable evidence for further clinical application of XFZYD as therapeutic strategy for TBI treatment.
... Like neurons, astrocytes originate from radial glial cells, which, despite their uniform appearance, form different progenitor domains within the ventricles of the developing brain, and generate cell subtypes with distinct morphological, functional and positional identities. Neurogenesis and gliogenesis from radial glial cells follow a step-like arrangement during development (Hirabayashi and Gotoh, 2005). In the mouse brain, neurogenesis starts at day E11 of prenatal development. ...
Astrocytes are the most prevalent glial cells in the brain. Historically considered as “merely supporting” neurons, recent research has shown that astrocytes actively participate in a large variety of central nervous system (CNS) functions including synaptogenesis, neuronal transmission and synaptic plasticity. During disease and injury, astrocytes efficiently protect neurons by various means, notably by sealing them off from neurotoxic factors and repairing the blood-brain barrier. Their ramified morphology allows them to perform diverse tasks by interacting with synapses, blood vessels and other glial cells. In this review article, we provide an overview of how astrocytes acquire their complex morphology during development. We then move from the developing to the mature brain, and review current research on perisynaptic astrocytic processes, with a particular focus on how astrocytes engage synapses and modulate their formation and activity. Comprehensive changes have been reported in astrocyte cell shape in many CNS pathologies. Factors influencing these morphological changes are summarized in the context of brain pathologies, such as traumatic injury and degenerative conditions. We provide insight into the molecular, cellular and cytoskeletal machinery behind these shape changes which drive the dynamic remodeling in astrocyte morphology during injury and the development of pathologies.
... Given the importance of the Wnt pathway in the regulation of self- renewal/differentiation balance in the cortex ( Chenn and Walsh, 2002;Fang et al., 2013;Hirabayashi and Gotoh, 2005;Hirabayashi et al., 2004;Kuwahara et al., 2010;Munji et al., 2011;Mutch et al., 2010;Wrobel et al., 2007;Zhang et al., 2010) and the number of down-regulated genes belonging to this pathway, we tested the global impact of Bcl6 on the Wnt pathway in vivo. Axin 2, a classical Wnt/?-catenin-dependent target gene, was found to be up- regulated in Bcl6 -/-mouse embryonic cortex using in situ hybridization. ...
During neurogenesis, progenitors switch from self-renewal to differentiation through the interplay of intrinsic and extrinsic cues, but how these are integrated remains poorly understood. Here we combine whole genome transcriptional and epigenetic analyses with in vivo functional studies and show that Bcl6, a transcriptional repressor known to promote neurogenesis, acts as a key driver of the neurogenic transition through direct silencing of a selective repertoire of genes belonging to multiple extrinsic pathways promoting self-renewal, most strikingly the Wnt pathway. At the molecular level, Bcl6 acts through both generic and pathway-specific mechanisms. Our data identify a molecular logic by which a single cell-intrinsic factor ensures robustness of neural cell fate transition by decreasing responsiveness to the extrinsic pathways that favor self-renewal.
... The b-catenin molecule then enters the nucleus and forms a complex with T-cell factors (TCFs) and lymphocyte enhance factors (LEFs) [29]. b-Catenin-TCF-LEF complex increases expression of basic helix-loop-helix (bHLH) proteins family, neurogenin 1 (Ngn 1) and Ngn 2, by activating the promoter of Ngn 1 and Ngn 2, and ultimately increase neurogenesis [30][31][32][33]. When the Wnt signalling pathway is not active, b-catenin is phosphorylated by the axin-APC-GSK3b-conductin complex and degrades by the ubiquitin-proteasome system [31,33]. ...
CD133 (prominin-1), a pentaspan membrane glycoprotein, is one of the most well-characterized biomarkers used for the isolation of cancer stem cells (CSCs). The presence of CSCs is one of the main causes of tumor reversal and resilience. Accumulating evidence has shown that CD133 might be responsible for CSCs tumorigenesis, metastasis, and chemoresistance. It is now understood that CD133 interacts with the Wnt/β-catenin and PI3K-Akt signaling pathways. Moreover, CD133 can upregulate the expression of FLICE-like inhibitory protein (FLIP) in CD133-positive cells, inhibiting apoptosis. Additionally, CD133 can increase angiogenesis by activating the Wnt signaling pathway and increasing the expression of vascular endothelial growth factor-A (VEGF-A) and interleukin-8. Therefore, CD133 could be considered to be an “Achilles’ heel” for CSCs, because by inhibiting this protein, the signaling pathways that are involved in cell proliferation will also be inhibited. By understanding the molecular biology of CD133, we can not only isolate stem cells, but can also utilize it as a therapeutic strategy. In this review, we summarize new insights into the fundamental cell biology of CD133 and discuss the involvement of CD133 in metastasis, metabolism, tumorigenesis, drug-resistance, apoptosis, and autophagy.
... it promotes terminal differentiation of IPC into neurons [9][10][11][12]. Transition of radial glial cells to IPCs is accompanied with the loss of adherens junctions and neuroepithelial identity [3]. ...
Generation of neurons in the embryonic neocortex is a balanced process of proliferation and differentiation of neuronal progenitor cells. Canonical Wnt signalling is crucial for expansion of radial glial cells in the ventricular zone and for differentiation of intermediate progenitors in the subventricular zone. We detected abundant expression of two transcrtiption factors mediating canonical Wnt signalling, Tcf7L1 and Tcf7L2, in the ventricular zone of the embryonic neocortex. Conditional knock-out analysis showed that Tcf7L2, but not Tcf7L1, is the principal Wnt mediator important for maintenance of progenitor cell identity in the ventricular zone. In the absence of Tcf7L2, the Wnt activity is reduced, ventricular zone markers Pax6 and Sox2 are downregulated and the neuroepithelial structure is severed due to the loss of apical adherens junctions. This results in decreased proliferation of radial glial cells, the reduced number of intermediate progenitors in the subventricular zone and hypoplastic forebrain. Our data show that canonical Wnt signalling, which is essential for determining the neuroepithelial character of the neocortical ventricular zone, is mediated by Tcf7L2.
Electronic supplementary material
The online version of this article (10.1186/s13064-018-0107-8) contains supplementary material, which is available to authorized users.
... System. Expression of mouse IGF2BP2 during the early embryonic development and its decrease after birth [74] correlate with its regulatory role in the differentiation of neural precursor cells into neurons or glial cells [16], but with dwindling neurogenic potential with brain development [75][76][77][78]. IGF2BP2 is expressed at a high level in neocortical NPCs at the early stage when these cells are proliferative and pluripotent, but to a less extent at the later stage when the cells lose their self-renewal ability [16]. ...
RNA-binding proteins (RBPs) mediate the localization, stability, and translation of the target transcripts and fine-tune the physiological functions of the proteins encoded. The insulin-like growth factor (IGF) 2 mRNA-binding protein (IGF2BP, IMP) family comprises three RBPs, IGF2BP1, IGF2BP2, and IGF2BP3, capable of associating with IGF2 and other transcripts and mediating their processing. IGF2BP2 represents the least understood member of this family of RBPs; however, it has been reported to participate in a wide range of physiological processes, such as embryonic development, neuronal differentiation, and metabolism. Its dysregulation is associated with insulin resistance, diabetes, and carcinogenesis and may potentially be a powerful biomarker and candidate target for relevant diseases. This review summarizes the structural features, regulation, and functions of IGF2BP2 and their association with cancer and cancer stem cells.
... Moreover, STAT3 signaling has been found to induce Hes1 and Hes5 expression in cultures of neuroepithelial cells prepared from E12.5 mice, thus supporting the existence of a positive feedback loop (Yoshimatsu et al., 2006). Furthermore, Hes1 and Hes5 functionally suppress proneural genes and promote astrogliogenesis in E14.5 neural progenitor cells (Hirabayashi and Gotoh, 2005;Bertrand et al., 2002) (Fig. 10.1). A loss of function of these proneural genes has been shown to result in premature glial differentiation at the expense of neuronal differentiation (Nieto et al., 2001;Sun et al., 2001;Tomita et al., 2000). ...
Astrocytes exert pivotal functions in the brain ranging from homeostasis to plasticity and their malfunctioning may contribute to neurodegenerative diseases. With increased recognition of their importance, more efforts are being dedicated to decoding the molecular mechanisms that control the generation of astrocytes from neural stem cells, a process referred to as astrogliogenesis. In this chapter, we highlight the discoveries that have shed light on the role of transcription factors, DNA methylation, histone modifications, and microRNAs in driving the transcriptional programs that underlie astrocyte generation. We further discuss the current understanding of gene regulatory pathways that control the switch from neurogenesis to astrogliogenesis during development.
... During early gestation, NSCs divide symmetrically to expand their own pool, and then switch to asymmetric divisions to give rise to each cell type: (1) NSCs acquire the potential to differentiate into neurons at mid-gestation, (2) they obtain the gliogenic capacity to generate astrocytes and oligodendrocytes in the late-gestation to perinatal periods. 6) Tight regulation of neurogenesis-to-astrogenesis switching is critical for the generation of a balanced number of each neural cell type, and proper neuronal circuit formation. Many studies have shown that extracellular factors such as Notch (for NSC maintenance), Wingless/int (Wnt, for neurons), leukemia inhibitory factor (LIF, for astrocytes), bone morphogenetic protein (BMP, for astrocytes), and sonic hedgehog (Shh, for oligodendrocytes) are required for differentiation of NSCs into each cell type. ...
In the developing brain, the three major cell types, i.e., neurons, astrocytes and oligodendrocytes, are generated from common multipotent neural stem cells (NSCs). In particular, astrocytes eventually occupy a great fraction of the brain and play pivotal roles in the brain development and functions. However, NSCs cannot produce the three major cell types simultaneously from the beginning; e.g., it is known that neurogenesis precedes astrogenesis during brain development. How is this fate switching achieved? Many studies have revealed that extracellular cues and intracellular programs are involved in the transition of NSC fate specification. The former include growth factor- and cytokine-signaling, and the latter involve epigenetic machinery, including DNA methylation, histone modifications, and non-coding RNAs. Accumulating evidence has identified a complex array of epigenetic modifications that control the timing of astrocytic differentiation of NSCs. In this review, we introduce recent progress in identifying the molecular mechanisms of astrogenesis underlying the tight regulation of neuronal-astrocytic fate switching of NSCs.
... BIO has been shown to reduce GSK3β kinase activity and signals in the canonical Wnt pathway by causing an increase in β-catenin levels (Meijer et al., 2003). Both in vitro and in vivo studies have demonstrated that the Wnt/β-catenin pathway regulates the proliferation and differentiation of neural progenitor cells (Hirabayashi and Gotoh, 2005;Polakis, 2000;Skardelly et al., 2011). The β-catenin signaling promotes proliferation of progenitor cells in the adult mouse SVZ, and an inhibitor of GSK3β promotes the proliferation of Mash1 cells (Adachi et al., 2007). ...
Glycogen synthase kinase 3β (GSK3β) was originally identified as a regulator for glycogen metabolism and is now an important therapeutic target for a variety of brain disorders including neurodegenerative diseases due to it's pivotal role in cellular metabolism, proliferation and differentiation. In the development of stroke therapies focusing on tissue repair and functional recovery, promoting neurogenesis is a main approach in regenerative medicine. In the present investigation, we explored the effects of a GSK3β specific inhibitor, 6-Bromoindirubin-3′-oxime (BIO), on regenerative activities of neuroblasts in the subventricular zone (SVZ) and functional recovery after focal cerebral ischemia. Adult C57/BL mice were subjected to occlusion of distal branches of middle cerebral artery (MCA) supplying the sensorimotor barrel cortex. Three days later, BIO (8.5 μg/kg, i.p.) was administered every 2 days until sacrificed at 14 or 21 days after stroke. The BIO treatment significantly increased generation of neuroblasts labeled with BrdU and BrdU/doublecortin (DCX) in the SVZ. Comparing to vehicle controls, increased number of neuroblasts migrated to the peri-infarct region where they differentiate into mature neurons. Along with the elevated BDNF expression at the peri-infarct area, the number of newly formed neurons was significantly increased. BIO treatment significantly enhanced sensorimotor functional recovery after the focal ischemia. It is suggested that the GSK3 signaling may be a potential therapeutic target for regenerative treatment after ischemic stroke.
... Moreover, STAT3 signaling has been found to induce Hes1 and Hes5 expression in cultures of neuroepithelial cells prepared from E12.5 mice, thus supporting the existence of a positive feedback loop (Yoshimatsu et al., 2006). Furthermore, Hes1 and Hes5 functionally suppress proneural genes and promote astrogliogenesis in E14.5 neural progenitor cells (Hirabayashi and Gotoh, 2005;Bertrand et al., 2002) (Fig. 10.1). A loss of function of these proneural genes has been shown to result in premature glial differentiation at the expense of neuronal differentiation (Nieto et al., 2001;Sun et al., 2001;Tomita et al., 2000). ...
Astrocytes are a heterogeneous class of glial cells in the brain that fulfil an ever increasing list of functions important for the formation, maintenance, and plasticity of the brain (Bayraktar et al., 2014). In particular, astrocytes play key roles in regulating the neuronal microenvironment by contributing to ion and neurotransmitter homeostasis (Walz, 2000, Rothstein et al., 1996) and are important for neuronal energy supply (Choi et al.). Moreover, astrocytes sense neuronal activity through neurotransmitter receptors on their surface and release so-called gliotransmitters, which in turn act on neurons, thereby contributing to synaptic processing and perhaps even plasticity (Henneberger et al., 2010, Jourdain et al., 2007, Pascual et al., 2005, Wang et al., 2006). In some instances, astrocytes serve as chemosensors, as shown for CO2-sensitive astrocytes in respiratory control centers (Gourine et al., 2010). Furthermore, astrocytes, together with pericytes, play a fundamental role in the maintenance of the blood-brain-barrier by interacting with microvessels through their astrocytic endfeet (Abbott et al., 2006, Daneman et al., 2010). Finally, astrocytes are a critical component of the so called neurovascular unit, which couples neural activity to local cerebral blood flow (Petzold and Murthy, 2011, Attwell et al., 2010). Given their important functions, astrocytes have recently been implicated in many neurological diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer’s disease (AD), Huntington’s disease (HD) and Parkinson’s disease (PD) (Maragakis and Rothstein, 2006, Molofsky et al., 2012). Although this remarkable plethora of specialized functions suggests a high degree of specification and molecular and functional heterogeneity, little is known regarding how these functions are controlled on a molecular level during the development of the nervous system. Therefore, it is important to understand the molecular mechanisms underlying the differentiation of astrocytes from neural stem cells, a process referred to herein as astrogliogenesis which commences largely after the end of neurogenesis (Kriegstein and Alvarez-Buylla, 2009). Throughout the last two decades, interest into the role of transcription factors (TFs) and epigenetic mechanisms in astrogliogenesis has markedly risen. The goal of this chapter is to provide an overview of our current knowledge regarding the transcriptional and epigenetic mechanisms underlying astrogliogenesis
... In the embryonic forebrain, Wnt serves to promote a cortical identity for the dorsal telencephalon (Wilson et al. 2000;Backman et al. 2005). Beginning at E11 in the SVZ, Wnts are responsible for maintaining an actively proliferating stem cell pool that will populate the cortex with neurons (Chenn et al. 2002;Sato et al. 2004;Hirabayashi et al. 2005). During mid to late corticogenesis, Wnt signaling through β-catenin stimulates the expression of Neurod1, Ngn1 and Ngn2, thereby promoting neuronal differentiation (Hirabayashi et al. 2004). ...
Cell type-specific gene expression is a tightly controlled process which is facilitated by several classes of proteins including transcription factors, histone modifying enzymes and ATP-dependent chromatin remodeling enzymes. The CHD class of chromatin remodelers is important for development and maintenance of mammalian stem cell populations and their progeny. In humans, haploinsufficiency for the CHD family member CHD7 results in a multiple congenital anomaly disorder called CHARGE syndrome. Defects of the eye, ear, heart, brain, olfactory organs and craniofacial features are commonly observed in CHARGE syndrome. Notably, CHARGE individuals display decreased or absent sense of smell (hyposmia or anosmia) and small or absent olfactory bulbs (OB) and tracts (arrhinencephaly). The OB is populated by neurons born in a neural stem cell niche located along the lateral walls of the lateral ventricles in a region termed the subventricular zone (SVZ). The process of neuronal migration from the SVZ to the OB begins during late embryogenesis and continues into adulthood, implying that CHD7 deficiency in the SVZ neural stem cell niche may play a role in the olfaction. In order to study the role of CHD7 in SVZ neural stem cell function, I generated conditional Chd7 knockout mice using a Chd7flox allele and ubiquitous or neural stem cell-specific Cre recombinases. In adult mice, Chd7 deficiency leads to decreased SVZ proliferation, ventriculomegaly, fewer neuroblasts and mature OB interneurons, and increased glial cells. Conditional adult and perinatal knockout mice display defects in proliferation, self-renewal and neuronal differentiation which can be rescued by modulation of retinoic acid signaling. By chromatin immunoprecipitation, CHD7 binds to the promoters of retinoic acid receptors and pro-neural genes in neural stem cells. Additionally, microarray analysis of SVZ gene expression from control and Chd7 conditional knockout mice shows that neuronal differentiation, migration and maturation genes are down-regulated upon loss of Chd7. Together, these data suggest that CHD7 plays a critical role in the development and maintenance of the SVZ neural stem cell niche. My research has helped to identify molecular mechanisms of CHD7 function in neural stem cells could improve diagnostic and therapeutic approaches for individuals with CHARGE syndrome and related disorders.
... La voie de signalisation Wnt/ catenine est impliquée dans la régulation de la prolifération des CSN lors du développement embryonnaire (Hirabayashi and Gotoh, 2005). Très conservée au fil de l'évolution, la voie Wnt/ catenine assure lors du développement de l'embryon chez les mammifères la différenciation de la zone dorsale du télencéphale à l'origine du néocortex et de l'hippocampe (Lee and Jessell, 1999). ...
Quiescent neural stem cells (NSCs) are considered the reservoir for adult neurogenesis, generating new neurons throughout life. However, neurogenesis decreases during aging, causing a progressive decline that is currently untreatable. To study the regulatory mechanisms of NSCs proliferation, we set up a new technique allowing the isolation of quiescent NSCs and their progeny. We show that GABAAR directly regulates NSCs quiescence in vivo as the depletion of GABA-producing neuroblasts or GABAAR pathway pharmacological blockade provoked NSCs cell cycle entry in the SVZ. During aging, the stock of NSCs is not perturbed, but we show that an over-production of TGFβ1 by brain endothelial cells directly lengthens activated NSCs G1 phase, strongly decreasing the production of new neurons. These findings highlight GABAAR and TGF-β/Smad-3 as two major pathways controlling NSCs proliferation. In line with a future therapeutic application, we also prove that their blocking stimulates endogenous neurogenesis in vivo.
... Within the early phase of mouse embryonic nervous system development, between E8.5-E10.5, there is massive expansion of neuroprogenitor cells [33] and CPE-DN might be involved in this proliferation phase, as was demonstrated for cancer cell proliferation [21]. At E11.5, neuroprogenitor cells begin to switch to neurogenesis, peaking at E13.5-E14.5 [34,35]. Whether the surge in CPE-DN expression from E13.5-E14.5 is involved in this differentiation event remains to be determined. ...
Neuroprotective proteins expressed in the fetus play a critical role during early embryonic neurodevelopment, especially during maternal exposure to alcohol and drugs that cause stress, glutamate neuroexcitotoxicity, and damage to the fetal brain, if prolonged. We have identified a novel protein, carboxypeptidase E-ΔN (CPE-ΔN), which is a splice variant of CPE that has neuroprotective effects on embryonic neurons. CPE-ΔN is transiently expressed in mouse embryos from embryonic day 5.5 to postnatal day 1. It is expressed in embryonic neurons, but not in 3 week or older mouse brains, suggesting a function primarily in utero. CPE-ΔN expression was up-regulated in embryonic hippocampal neurons in response to dexamethasone treatment. CPE-ΔN transduced into rat embryonic cortical and hippocampal neurons protected them from glutamate- and H2O2-induced cell death. When transduced into embryonic cortical neurons, CPE-ΔN was found in the nucleus and enhanced the transcription of FGF2 mRNA. Embryonic cortical neurons challenged with glutamate resulted in attenuated FGF2 levels and cell death, but CPE-ΔN transduced neurons treated in the same manner showed increased FGF2 expression and normal viability. This neuroprotective effect of CPE-ΔN was mediated by secreted FGF2. Through receptor signaling, FGF2 activated the AKT and ERK signaling pathways, which in turn increased BCL-2 expression. This led to inhibition of caspase-3 activity and cell survival.
... In addition to spatial information, which confers a dorsoventral and rostrocaudal identity upon neuronal populations, temporal information contributes to this diversity. Throughout the central nervous system (CNS), neural progenitor cells (NPCs) produce subtypes of neurons in a defined order before astrogliogenesis is initiated, and astrocytes are formed before most oligodendrogenesis is initiated (Walsh and Cepko 1992, Qian, Shen et al. 2000, Hirabayashi and Gotoh 2005, Shen, Wang et al. 2006, Noctor, Martinez-Cerdeno et al. 2008, Costa, Bucholz et al. 2009). ...
In the developing mammalian nervous system, common progenitors integrate both cell extrinsic and intrinsic regulatory programs to produce distinct neuronal and glial cell types as development proceeds. This spatiotemporal restriction of neural progenitor differentiation is enforced, in part, by the dynamic reorganization of chromatin into repressive domains by Polycomb repressive complexes, effectively limiting the expression of fate-determining genes. Here, we review the distinct roles that Polycomb repressive complexes play during neurogenesis and gliogenesis, while also highlighting recent work describing the molecular mechanisms that govern their dynamic activity in neural development. Further investigation of the way in which Polycomb complexes are regulated in neural development will enable more precise manipulation of neural progenitor differentiation facilitating the efficient generation of specific neuronal and glial cell types for many biological applications.
... As shown above ( Figure 3F), suppression of let-7s with antagomirs increased neurogenesis and decreased gliogenesis in Tissue-NPCs, but when HES5 induction was simultaneously blocked by siRNA ( Figure 6G), this effect was lost ( Figure 6H). This result was consistent with the described role for HES5 in murine neural development in the absence of LIF, whereas, in the presence of LIF, HES5 has a progliogenic role (Chambers et al., 2001;Chenn, 2009;Hirabayashi and Gotoh, 2005). ...
It is clear that neural differentiation from human pluripotent stem cells generates cells that are developmentally immature. Here, we show that the let-7 plays a functional role in the developmental decision making of human neural progenitors, controlling whether these cells make neurons or glia. Through gain- and loss-of-function studies on both tissue and pluripotent derived cells, our data show that let-7 specifically regulates decision making in this context by regulation of a key chromatin-associated protein, HMGA2. Furthermore, we provide evidence that the let-7/HMGA2 circuit acts on HES5, a NOTCH effector and well-established node that regulates fate decisions in the nervous system. These data link the let-7 circuit to NOTCH signaling and suggest that this interaction serves to regulate human developmental progression.
Phospholipase D1 (PLD1) plays a crucial role in cell differentiation of different cell types. However, the involvement of PLD1 in astrocytic differentiation remains uncertain. In the present study, we investigate the possible role of PLD1 and its product phosphatidic acid (PA) in astrocytic differentiation of hippocampal neural stem/progenitor cells (NSPCs) from hippocampi of embryonic day 16.5 rat embryos. We showed that overexpression of PLD1 increased the expression level of glial fibrillary acidic protein (GFAP), an astrocyte marker, and the number of GFAP-positive cells. Knockdown of PLD1 by transfection with Pld1 shRNA inhibited astrocytic differentiation. Moreover, PLD1 deletion (Pld1−/−) suppressed the level of GFAP in the mouse hippocampus. These results indicate that PLD1 plays a crucial role in regulating astrocytic differentiation in hippocampal NSPCs. Interestingly, PA itself was sufficient to promote astrocytic differentiation. PA-induced GFAP expression was decreased by inhibition of signal transducer and activation of transcription 3 (STAT3) using siRNA. Furthermore, PA-induced STAT3 activation and astrocytic differentiation were regulated by the focal adhesion kinase (FAK)/aurora kinase A (AURKA) pathway. Taken together, our findings suggest that PLD1 is an important modulator of astrocytic differentiation in hippocampal NSPCs via the FAK/AURKA/STAT3 signaling pathway.
Phospholipase D1 (PLD1) plays a crucial role in cell differentiation of different cell types. However, the involvement of PLD1 in astrocytic differentiation remains uncertain. In the present study, we investigate the possible role of PLD1 and its product phosphatidic acid (PA) in astrocytic differentiation of hippocampal neural stem/progenitor cells (NSPCs) from hippocampi of embryonic day 16.5 rat embryos. We showed that overexpression of PLD1 increased the expression level of glial fibrillary acidic protein (GFAP), an astrocyte marker, and the number of GFAP-positive cells. Knockdown of PLD1 by transfection with Pld1 shRNA inhibited astrocytic differentiation. Moreover, PLD1 deletion ( Pld1 −/− ) suppressed the level of GFAP in the mouse hippocampus. These results indicate that PLD1 plays a crucial role in regulating astrocytic differentiation in hippocampal NSPCs. Interestingly, PA itself was sufficient to promote astrocytic differentiation. PA-induced GFAP expression was decreased by inhibition of signal transducer and activation of transcription 3 (STAT3) using siRNA. Furthermore, PA-induced STAT3 activation and astrocytic differentiation were regulated by the focal adhesion kinase (FAK)/aurora kinase A (AURKA) pathway. Taken together, our findings suggest that PLD1 is an important modulator of astrocytic differentiation in hippocampal NSPCs via the FAK/AURKA/STAT3 signaling pathway.
Background:
Bisphenol A (BPA), an endocrine disruptor, may be involved in the etiology of autism spectrum disorders (ASD); however, the mechanism of neuronal and astrocytic damage remains ambiguous. A possible role of altered expression of p21 in autistic-like behavior in rat offspring was examined with prenatal and postnatal BPA exposure.
Methods:
Wistar albino dams were exposed to BPA (5 mg/kg) intraperitoneally throughout pregnancy and until the third postnatal day (PND). Pups were examined on 21st PND for behavioral test. Blood samples were collected for serum lactate levels and pups were sacrificed. Right frontal cortices were dissected out and processed for H&E, immunohistochemical analysis, and gene expression.
Results:
Anxiety like behavior and thigmotaxis along with reduction in serum lactate concentrations were observed in pups exposed to BPA. Decline in neuronal number and decreased astrocytic population with reduced dendritic spines were revealed by H&E and immunohistochemical analysis, respectively, in right frontal cortices. Over expression of p21 was also detected in BPA-exposed offspring.
Conclusions:
Over expression of p21 may be associated with autistic behavior. Further studies are recommended to explore the structural alterations in other white matter pathways in frontal cortices.
The nervous system consists of several hundred neuronal subtypes and glial cells that show specific gene expression and are generated from common ancestors, neural stem cells (NSCs). As the experimental techniques and molecular tools to analyze epigenetics and chromatin structures are rapidly advancing, the comprehensive events and genome‐wide states of DNA methylation, histone modifications, and chromatin accessibility in developing NSCs are gradually being unveiled. Here, we review recent advances in elucidating the role of epigenetic and chromatin regulation in NSCs, especially focusing on the acquisition of glial identity and how epigenetic regulation enables the temporal regulation of NSCs during murine cortical development. Main Points: Recent studies have unveiled the roles of epigenetics and chromatin during neural development. Global and local regulation of histone and DNA modifications and chromatin accessibility orchestrate transcription of neuronal and glial genes for glial identity.
Most clinically used general anesthetics have demonstrated neurotoxicity in animal studies, but the related mechanisms remain unknown. Previous studies suggest that anesthetics affect neuronal development through neuroinflammation, and significant effects of neuroinflammation on neurogenesis and neuronal disease have been shown. In the present study, we treated pregnant mice with 2% sevoflurane for 3 h at gestational day 15.5 and analyzed the expression of proinflammatory cytokines, including IL-6 and IL-17, in fetal mice brains. Sevoflurane induced IL-6 mRNA significantly, but did not upregulate IL-17. Other volatile anesthetics, including isoflurane, enflurane, and halothane, induced IL-6 mRNA in fetal brains as well as sevoflurane, but propofol did not. Sevoflurane and isoflurane showed the same effects in cultured microglia and astrocytes, but not in neurons. Because IL-6 induction in fetal brains may affect neuronal precursor cells (NPCs), numbers of NPCs in the subventricular zone were studied, revealing that maternal sevoflurane treatment significantly increases NPCs in offspring at 8 weeks after birth (p8wk). But this effect was absent in IL-6 knockout mice. Finally, behavioral experiments also revealed that maternal sevoflurane exposure causes learning impairments in p8wk offspring. These findings collectively demonstrate that maternal exposure to volatile anesthetics upregulates IL-6 in fetal mice brains, and the effects could result in long-lasting influences on neuronal development.
Early disruptions to neurodevelopment are highly relevant to understanding both psychiatric risk and underlying pathophysiology that can be targeted by new treatments. Much convergent evidence from the human literature associates inflammation during pregnancy with later neuropsychiatric disorders in offspring. Preclinical models of prenatal inflammation have been developed to examine the causal maternal physiological and offspring neural mechanisms underlying these findings. Here we review the strengths and limitations of preclinical models used for these purposes and describe selected studies that have shown maternal immune impacts on the brain and behavior of offspring. Maternal immune activation in mice, rats, nonhuman primates, and other mammalian model species have demonstrated convergent outcomes across methodologies. These outcomes include shifts and/or disruptions in the normal developmental trajectory of molecular and cellular processes in the offspring brain. Prenatal developmental origins are critical to a mechanistic understanding of maternal immune activation-induced alterations to microglia and immune molecules, brain growth and development, synaptic morphology and physiology, and anxiety- and depression-like, sensorimotor, and social behaviors. These phenotypes are relevant to brain functioning across domains and to anxiety and mood disorders, schizophrenia, and autism spectrum disorder, in which they have been identified. By turning a neurodevelopmental lens on this body of work, we emphasize the importance of acute changes to the prenatal offspring brain in fostering a better understanding of potential mechanisms for intervention. Collectively, overlapping results across maternal immune activation studies also highlight the need to examine preclinical offspring neurodevelopment alterations in terms of a multifactorial immune milieu, or immunome, to determine potential mechanisms of psychiatric risk.
Severe intrauterine ischemia is detrimental to the developing brain. The impact of mild intrauterine hypoperfusion on neurological development, however, is still unclear. We induced mild intrauterine hypoperfusion in rats on embryonic day 17 via arterial stenosis with metal microcoils wrapped around the uterine and ovarian arteries. All pups were born with significantly decreased birth weights. Decreased gray and white matter areas were observed without obvious tissue damage. Pups presented delayed newborn reflexes, muscle weakness, and altered spontaneous activity. The levels of proteins indicative of inflammation and stress in the vasculature, i.e., RANTES, vWF, VEGF, and adiponectin, were upregulated in the placenta. The levels of mRNA for proteins associated with axon and astrocyte development were downregulated in fetal brains. The present study demonstrates that even mild intrauterine hypoperfusion can alter neurological development, which mimics the clinical signs and symptoms of children with neurodevelopmental disorders born prematurely or with intrauterine growth restriction.
Since embryonic stem cells (ESC) and the epiblast share a gene expression profile and an attenuated cell cycle, ESC are an attractive model system to study lineage choice at gastrulation. We have employed mouse ESC as a model system to examine the role of Wnt signaling in the transition from pluripotency to neural precursors and have identified a new function for the Geminin gene in mesendodermal differentiation.
Wnt signaling is required for differentiation of both epiblast and ESC to the mesendodermal lineage. To test the hypothesis that blocking Wnt signaling in the absence of BMP signaling would promote differentiation of mESC to neural precursors, we developed a mESC line that inducibly expresses a dominant negative Tcf4 (dnTcf4) protein to block canonical Wnt signaling. Cells expressing the dnTcf4 protein differentiated largely to Sox3 positive neural precursors but were unable to progress to beta-III tubulin positive neurons unless Wnt signaling was de-repressed. This cell line will provide an important resource
for other investigators studying the role of Wnt signaling in embryonic development.
Geminin has been described as a bi-functional protein that inhibits endoreduplication during cell division and promotes neural differentiation by inhibiting BMP signaling. Geminin also binds transcription factors and chromatin remodeling proteins in the nucleus to inhibit their function. In mESC over-expression of Geminin induced mesendodermal differentiation and an epithelial to mesenchymal transition (EMT) via increasing Wnt signaling. We hypothesize that Geminin binds to Groucho/TLE proteins in the nucleus thereby dis-inhibiting Wnt target gene transcritption by Tcf/Lef proteins. Germinin is frequently over-expressed in cancer cells and EMT is an integral part of cancer metastasis. These observations make Geminin an attractive candidate for cancer therapy; reduction of Geminin protein could reduce metastasis as well as induce cell death due to endoreduplication. Overall, this work demonstrates that Wnt signaling is required for mesendodermal differentiation, EMT, and the transition from proliferative neural precursor to primitive neurons during lineage allocation of mESC.
Differentiation of neural stem/precursor cells (NS/PCs) into neurons, astrocytes and oligodendrocytes during mammalian brain development is a carefully controlled and timed event. Increasing evidences suggest that epigenetic regulation is necessary to drive this. Here, we provide an overview of the epigenetic mechanisms involved in the developing mammalian embryonic forebrain. Histone methylation is a key factor but other epigenetic factors such as DNA methylation and noncoding RNAs also partake during fate determination. As numerous epigenetic modifications have been identified, future studies on timing and regional specificity of these modifications will further deepen our understanding of how intrinsic and extrinsic mechanisms participate together to precisely control brain development.
Cell cycle progression and exit must be precisely patterned during development to generate tissues of the correct size, shape and symmetry. Here we present evidence that dorsal-ventral growth of the developing spinal cord is regulated by a Wnt mitogen gradient. Wnt signaling through the β-catenin/TCF pathway positively regulates cell cycle progression and negatively regulates cell cycle exit of spinal neural precursors in part through transcriptional regulation of cyclin D1 and cyclin D2. Wnts expressed at the dorsal midline of the spinal cord, Wnt1 and Wnt3a, have mitogenic activity while more broadly expressed Wnts do not. We present several lines of evidence suggesting that dorsal midline Wnts form a dorsal to ventral concentration gradient. A growth gradient that correlates with the predicted gradient of mitogenic Wnts emerges as the neural tube grows with the proliferation rate highest dorsally and the differentiation rate highest ventrally. These data are rationalized in a ‘mitogen gradient model’ that explains how proliferation and differentiation can be patterned across a growing field of cells. Computer modeling demonstrates this model is a robust and self-regulating mechanism for patterning cell cycle regulation in a growing tissue.
Supplemental data available on-line
Our understanding of early human development has been impeded by the general difficulty in obtaining suitable samples for study. As a result, and because of the extraordinarily high degree of evolutionary conservation of many developmentally important genes and developmental pathways, great reliance has been placed on extrapolation from animal models of development, principally the mouse. However, the strong evolutionary conservation of coding sequence for developmentally important genes does not necessarily mean that their expression patterns are as highly conserved. The very recent availability of human embryonic samples for gene expression studies has now permitted for the first time an assessment of the degree to which we can confidently extrapolate from studies of rodent gene expression patterns. We have found significant human-mouse differences in embryonic expression patterns for a variety of genes. We present detailed data for two illustrative examples. Wnt7a, a very highly conserved gene known to be important in early development, shows significant differences in spatial and temporal expression patterns in the developing brain (midbrain, telencephalon) of man and mice. CAPN3, the locus for LGMD2A limb girdle muscular dystrophy, and its mouse orthologue differ extensively in expression in embryonic heart, lens and smooth muscle. Our study also shows how molecular analyses, while providing explanations for the observed differences, can be important in providing insights into mammalian evolution.
Mutations in the adenomatous polyposis coli (APC) tumour-suppressor gene occur in most human colon cancers. Loss of functional APC protein results in the accumulation of beta-catenin. Mutant forms of beta-catenin have been discovered in colon cancers that retain wild-type APC genes, and also in melanomas, medulloblastomas, prostate cancer and gastric and hepatocellular carcinomas. The accumulation of beta-catenin activates genes that are responsive to transcription factors of the TCF/LEF family, with which beta-catenin interacts. Here we show that beta-catenin activates transcription from the cyclin D1 promoter, and that sequences within the promoter that are related to consensus TCF/LEF-binding sites are necessary for activation. The oncoprotein p21ras further activates transcription of the cyclin D1 gene, through sites within the promoter that bind the transcriptional regulators Ets or CREB. Cells expressing mutant beta-catenin produce high levels of cyclin D1 messenger RNA and protein constitutively. Furthermore, expression of a dominant-negative form of TCF in colon-cancer cells strongly inhibits expression of cyclin D1 without affecting expression of cyclin D2, cyclin E, or cyclin-dependent kinases 2, 4 or 6. This dominant-negative TCF causes cells to arrest in the G1 phase of the cell cycle; this phenotype can be rescued by expression of cyclin D1 under the cytomegalovirus promoter. Abnormal levels of beta-catenin may therefore contribute to neoplastic transformation by causing accumulation of cyclin D1.
β-Catenin plays a dual role in the cell: one in linking the cytoplasmic side of cadherin-mediated cell–cell contacts to the actin cytoskeleton and an additional role in signaling that involves transactivation in complex with transcription factors of the lymphoid enhancing factor (LEF-1) family. Elevated β-catenin levels in colorectal cancer caused by mutations in β-catenin or by the adenomatous polyposis coli molecule, which regulates β-catenin degradation, result in the binding of β-catenin to LEF-1 and increased transcriptional activation of mostly unknown target genes. Here, we show that the cyclin D1 gene is a direct target for transactivation by the β-catenin/LEF-1 pathway through a LEF-1 binding site in the cyclin D1 promoter. Inhibitors of β-catenin activation, wild-type adenomatous polyposis coli, axin, and the cytoplasmic tail of cadherin suppressed cyclin D1 promoter activity in colon cancer cells. Cyclin D1 protein levels were induced by β-catenin overexpression and reduced in cells overexpressing the cadherin cytoplasmic domain. Increased β-catenin levels may thus promote neoplastic conversion by triggering cyclin D1 gene expression and, consequently, uncontrolled progression into the cell cycle.
Neurons destined for the cerebral neocortex are formed in the pseudostratified ventricular epithelium (PVE) lining the ventricular cavity of the developing cerebral wall. The present study, based upon cumulative S-phase labeling with bromodeoxyuridine, is an analysis of cell cycle parameters of the PVE. It is undertaken in the dorsomedial cerebral wall of mouse embryos from the eleventh to the seventeenth gestational day (E11-E17, day of conception = E0) corresponding to the complete period of neuronogenesis. The growth fraction (fraction of cells in the population which is proliferating) is virtually 1.0 from E11 through E16. The length of the cell cycle increases from 8.1 to 18.4 hr, which corresponds to a sequence of 11 integer cell cycles over the course of neuronal cytogenesis in mice. The increase in the length of the cell cycle is due essentially to a fourfold increase in the length of G1 phase which is the only phase of the cell cycle which varies systematically. Thus, the G1 phase is most likely to be the phase of the cell cycle which is modulated by extrinsically and intrinsically acting mechanisms involved in the regulation of neuronal cytogenesis.
Identifying the signals that regulate stem cell differentiation is fundamental to understanding cellular diversity in the brain. In this paper we identify factors that act in an instructive fashion to direct the differentiation of multipotential stem cells derived from the embryonic central nervous system (CNS). CNS stem cell clones differentiate to multiple fates: neurons, astrocytes, and oligodendrocytes. The differentiation of cells in a clone is influenced by extracellular signals: Platelet-derived growth factor (PDGF-AA, -AB, and -BB) supports neuronal differentiation. In contrast, ciliary neurotrophic factor and thyroid hormone T3 act instructively on stem cells to generate clones of astrocytes and oligodendrocytes, respectively. Adult stem cells had remarkably similar responses to these growth factors. These results support a simple model in which transient exposure to extrinsic factors acting through known pathways initiates fate decisions by multipotential CNS stem cells.
Many types of vertebrate precursor cells divide a limited number of times before they stop and terminally differentiate. In no case is it known what causes them to stop dividing. We have been studying this problem in the proliferating precursor cells that give rise to postmitotic oligodendrocytes, the cells that make myelin in the central nervous system. We show here that two components of the cell cycle control system, cyclin D1 and the Cdc2 kinase, are present in the proliferating precursor cells but not in differentiated oligodendrocytes, suggesting that the control system is dismantled in the oligodendrocytes. More importantly, we show that the cyclin-dependent kinase (Cdk) inhibitor p27 progressively accumulates in the precursor cells as they proliferate and is present at high levels in oligodendrocytes. Our findings are consistent with the possibility that the accumulation of p27 is part of both the intrinsic counting mechanism that determines when precursor cell proliferation stops and differentiation begins and the effector mechanism that arrests the cell cycle when the counting mechanism indicates it is time. The recent findings of others that p27-deficient mice have an increased number of cells in all of the organs examined suggest that this function of p27 is not restricted to the oligodendrocyte cell lineage.
A mechanism by which members of the ciliary neurotrophic factor (CNTF)–leukemia inhibitory factor cytokine family regulate
gliogenesis in the developing mammalian central nervous system was characterized. Activation of the CNTF receptor promoted
differentiation of cerebral cortical precursor cells into astrocytes and inhibited differentiation of cortical precursors
along a neuronal lineage. Although CNTF stimulated both the Janus kinase–signal transducer and activator of transcription
(JAK-STAT) and Ras–mitogen-activated protein kinase signaling pathways in cortical precursor cells, the JAK-STAT signaling
pathway selectively enhanced differentiation of these precursors along a glial lineage. These findings suggest that cytokine
activation of the JAK-STAT signaling pathway may be a mechanism by which cell fate is controlled during mammalian development.
In the developing vertebrate CNS, members of the Wnt gene family are characteristically expressed at signaling centers that pattern adjacent parts of the neural tube. To identify candidate signaling centers in the telencephalon, we isolated Wnt gene fragments from cDNA derived from embryonic mouse telencephalon. In situ hybridization experiments demonstrate that one of the isolated Wnt genes, Wnt7a, is broadly expressed in the embryonic telencephalon. By contrast, three others, Wnt3a, 5a and a novel mouse Wnt gene, Wnt2b, are expressed only at the medial edge of the telencephalon, defining the hem of the cerebral cortex.
The Wnt-rich cortical hem is a transient, neuron-containing, neuroepithelial structure that forms a boundary between the hippocampus and the telencephalic choroid plexus epithelium (CPe) throughout their embryonic development. Indicating a close developmental relationship between the cortical hem and the CPe, Wnt gene expression is upregulated in the cortical hem both before and just as the CPe begins to form, and persists until birth. In addition, although the cortical hem does not show features of differentiated CPe, such as expression of transthyretin mRNA, the CPe and cortical hem are linked by shared expression of members of the Bmp and Msx gene families.
In the extra-toesJ(XtJ) mouse mutant, telencephalic CPe fails to develop. We show that Wnt gene expression is deficient at the cortical hem in XtJ/XtJmice, but that the expression of other telencephalic developmental control genes, including Wnt7a, is maintained. The XtJmutant carries a deletion in Gli3, a vertebrate homolog of the Drosophila gene cubitus interruptus (ci), which encodes a transcriptional regulator of the Drosophila Wnt gene, wingless. Our observations indicate that Gli3 participates in Wnt gene regulation in the vertebrate telencephalon, and suggest that the loss of telencephalic choroid plexus in XtJmice is due to defects in the cortical hem that include Wnt gene misregulation.
The adenomatous polyposis coli gene (APC) is a tumor suppressor gene that is inactivated in most colorectal cancers. Mutations of APC cause aberrant accumulation of beta-catenin, which then binds T cell factor-4 (Tcf-4), causing increased transcriptional activation of unknown genes. Here, the c-MYC oncogene is identified as a target gene in this signaling pathway. Expression of c-MYC was shown to be repressed by wild-type APC and activated by beta-catenin, and these effects were mediated through Tcf-4 binding sites in the c-MYC promoter. These results provide a molecular framework for understanding the previously enigmatic overexpression of c-MYC in colorectal cancers.
Neocortical neurons begin to differentiate soon after they are generated by mitoses at the surface of the ventricular zone (VZ). We provide evidence here that bone morphogenetic protein (BMP) triggers neuronal differentiation of neocortical precursors within the VZ. In cultures of dissociated neocortical neuroepithelial cells, BMPs increase the number of MAP-2- and TUJ1-positive cells within 24 hr of treatment. In explant cultures, BMP-4 treatment leads to an increase in the number of TUJ1-positive cells within the ventricular zone. Furthermore, truncated, dominant-negative, BMP type I receptor, introduced into neocortical precursors by retrovirus-mediated gene transfer, blocks neurite elaboration and migration out of the VZ. Finally, immunocytochemistry indicates that BMP protein is present at the VZ surface. Together, these results indicate that BMP protein is present within the VZ, that BMP is capable of promoting neuronal differentiation, and that signaling through BMP receptors triggers neuronal precursors to differentiate and migrate out of the VZ.
beta-Catenin plays a dual role in the cell: one in linking the cytoplasmic side of cadherin-mediated cell-cell contacts to the actin cytoskeleton and an additional role in signaling that involves transactivation in complex with transcription factors of the lymphoid enhancing factor (LEF-1) family. Elevated beta-catenin levels in colorectal cancer caused by mutations in beta-catenin or by the adenomatous polyposis coli molecule, which regulates beta-catenin degradation, result in the binding of beta-catenin to LEF-1 and increased transcriptional activation of mostly unknown target genes. Here, we show that the cyclin D1 gene is a direct target for transactivation by the beta-catenin/LEF-1 pathway through a LEF-1 binding site in the cyclin D1 promoter. Inhibitors of beta-catenin activation, wild-type adenomatous polyposis coli, axin, and the cytoplasmic tail of cadherin suppressed cyclin D1 promoter activity in colon cancer cells. Cyclin D1 protein levels were induced by beta-catenin overexpression and reduced in cells overexpressing the cadherin cytoplasmic domain. Increased beta-catenin levels may thus promote neoplastic conversion by triggering cyclin D1 gene expression and, consequently, uncontrolled progression into the cell cycle.
The mechanisms that regulate patterning and growth of the developing cerebral cortex remain unclear. Suggesting a role for Wnt signaling in these processes, multiple Wnt genes are expressed in selective patterns in the embryonic cortex. We have examined the role of Wnt-3a signaling at the caudomedial margin of the developing cerebral cortex, the site of hippocampal development. We show that Wnt-3a acts locally to regulate the expansion of the caudomedial cortex, from which the hippocampus develops. In mice lacking Wnt-3a, caudomedial cortical progenitor cells appear to be specified normally, but then underproliferate. By mid-gestation, the hippocampus is missing or represented by tiny populations of residual hippocampal cells. Thus, Wnt-3a signaling is crucial for the normal growth of the hippocampus. We suggest that the coordination of growth with patterning may be a general role for Wnts during vertebrate development.
Neurogenin1 (Ngn1), Neurogenin2 (Ngn2), and Mash1 encode bHLH transcription factors with neuronal determination functions. In the telencephalon, the Ngns and Mash1 are expressed at high levels in complementary dorsal and ventral domains, respectively. We found that Ngn function is required to maintain these two separate expression domains, as Mash1 expression is up-regulated in the dorsal telencephalon of Ngn mutant embryos. We have taken advantage of the replacement of the Ngns by Mash1 in dorsal progenitors to address the role of the neural determination genes in neuronal-type specification in the telencephalon. In Ngn2 single and Ngn1; Ngn2 double mutants, a population of early born cortical neurons lose expression of dorsal-specific markers and ectopically express a subset of ventral telencephalic-specific markers. Analysis of Mash1; Ngn2 double mutant embryos and of embryos carrying a Ngn2 to Mash1 replacement mutation demonstrated that ectopic expression of Mash1 is required and sufficient to confer these ventral characteristics to cortical neurons. Our results indicate that in addition to acting as neuronal determinants, Mash1 and Ngns play a role in the specification of dorsal-ventral neuronal identity, directly linking pathways of neurogenesis and regional patterning in the forebrain.
The olfactory bulb, neocortex and archicortex arise from a common pool of progenitors in the dorsal telencephalon. We studied the consequences of supplying excess Notch1 signal in vivo on the cellular and regional destinies of telencephalic precursors using bicistronic replication defective retroviruses. After ventricular injections mid-neurogenesis (E14.5), activated Notch1 retrovirus markedly inhibited the generation of neurons from telencephalic precursors, delayed the emergence of cells from the subventricular zone (SVZ), and produced an augmentation of glial progeny in the neo- and archicortex. However, activated Notch1 had a distinct effect on the progenitors of the olfactory bulb, markedly reducing the numbers of cells of any type that migrated there. To elucidate the mechanism of the cell fate changes elicited by Notch1 signals in the cortical regions, short- and long-term cultures of E14.5 telencephalic progenitors were examined. These studies reveal that activated Notch1 elicits a cessation of proliferation that coincides with an inhibition of the generation of neurons. Later, during gliogenesis, activated Notch1 triggers a rapid cellular proliferation with a significant increase in the generation of cells expressing GFAP. To examine the generation of cells destined for the olfactory bulb, we used stereotaxic injections into the early postnatal anterior subventricular zone (SVZa). We observed that precursors of the olfactory bulb responded to Notch signals by remaining quiescent and failing to give rise to differentiated progeny of any type, unlike cortical precursor cells, which generated glia instead of neurons. These data show that forebrain precursors vary in their response to Notch signals according to spatial and temporal cues, and that Notch signals influence the composition of forebrain regions by modulating the rate of proliferation of neural precursor cells.
Identifying external signals involved in the regulation of neural stem cell proliferation and differentiation is fundamental to the understanding of CNS development. In this study we show that platelet-derived growth factor (PDGF) can act as a mitogen for neural precursor cells. Multipotent stem cells from developing CNS can be maintained in a proliferative state under serum-free conditions in the presence of fibroblast growth factor-2 (FGF2) and induced to differentiate into neurons, astrocytes, and oligodendrocytes on withdrawal of the mitogen. PDGF has been suggested to play a role during the differentiation into neurons. We have investigated the effect of PDGF on cultured stem cells from embryonic rat cortex. The PDGF alpha-receptor is constantly expressed during differentiation of neural stem cells but is phosphorylated only after PDGF-AA treatment. In contrast, the PDGF beta-receptor is hardly detectable in uncommitted cells, but its expression increases during differentiation. We show that PDGF stimulation leads to c-fos induction, 5'-bromo-2'deoxyuridine incorporation, and an increase in the number of immature cells stained with antibodies to neuronal markers. Our findings suggest that PDGF acts as a mitogen in the early phase of stem cell differentiation to expand the pool of immature neurons.
Transgenic mice expressing a stabilized β-catenin in neural precursors develop enlarged brains with increased cerebral cortical
surface area and folds resembling sulci and gyri of higher mammals. Brains from transgenic animals have enlarged lateral ventricles
lined with neuroepithelial precursor cells, reflecting an expansion of the precursor population. Compared with wild-type precursors,
a greater proportion of transgenic precursors reenter the cell cycle after mitosis. These results show that β-catenin can
function in the decision of precursors to proliferate or differentiate during mammalian neuronal development and suggest that
β-catenin can regulate cerebral cortical size by controlling the generation of neural precursor cells.
Beta-catenin plays a pivotal role in cadherin-mediated cell adhesion. Moreover, it is a downstream signaling component of Wnt that controls multiple developmental processes such as cell proliferation, apoptosis, and fate decisions. To study the role of beta-catenin in neural crest development, we used the Cre/loxP system to ablate beta-catenin specifically in neural crest stem cells. Although several neural crest-derived structures develop normally, mutant animals lack melanocytes and dorsal root ganglia (DRG). In vivo and in vitro analyses revealed that mutant neural crest cells emigrate but fail to generate an early wave of sensory neurogenesis that is normally marked by the transcription factor neurogenin (ngn) 2. This indicates a role of beta-catenin in premigratory or early migratory neural crest and points to heterogeneity of neural crest cells at the earliest stages of crest development. In addition, migratory neural crest cells lateral to the neural tube do not aggregate to form DRG and are unable to produce a later wave of sensory neurogenesis usually marked by the transcription factor ngn1. We propose that the requirement of beta-catenin for the specification of melanocytes and sensory neuronal lineages reflects roles of beta-catenin both in Wnt signaling and in mediating cell-cell interactions.
The G1 phase of the cell cycle of neuroepithelial cells, the progenitors of all neurons of the mammalian central nervous system, has been known to lengthen concomitantly with the onset and progression of neurogenesis. We have investigated whether lengthening of the G1 phase of the neuroepithelial cell cycle is a cause, rather than a consequence, of neurogenesis. As an experimental system, we used whole mouse embryo culture, which was found to exactly reproduce the temporal and spatial gradients of the onset of neurogenesis occurring in utero. Olomoucine, a cell-permeable, highly specific inhibitor of cyclin-dependent kinases and G1 progression, was found to significantly lengthen, but not arrest, the cell cycle of neuroepithelial cells when used at 80 microM. This olomoucine treatment induced, in the telencephalic neuroepithelium of embryonic day 9.5 to 10.5 mouse embryos developing in whole embryo culture to embryonic day 10.5, (i) the premature up-regulation of TIS21, a marker identifying neuroepithelial cells that have switched from proliferative to neuron-generating divisions, and (ii) the premature generation of neurons. Our data indicate that lengthening G1 can alone be sufficient to induce neuroepithelial cell differentiation. We propose a model that links the effects of cell fate determinants and asymmetric cell division to the length of the cell cycle.
Wnt signaling has recently emerged as a key factor in controlling stem cell expansion. In contrast, we show here that Wnt/β-catenin
signal activation in emigrating neural crest stem cells (NCSCs) has little effect on the population size and instead regulates
fate decisions. Sustained β-catenin activity in neural crest cells promotes the formation of sensory neural cells in vivo
at the expense of virtually all other neural crest derivatives. Moreover, Wnt1 is able to instruct early NCSCs (eNCSCs) to
adopt a sensory neuronal fate in a β-catenin–dependent manner. Thus, the role of Wnt/β-catenin in stem cells is cell-type
dependent.
Neural precursor cells (NPCs) have the ability to self-renew and to give rise to neuronal and glial lineages. The fate decision of NPCs between proliferation and differentiation determines the number of differentiated cells and the size of each region of the brain. However, the signals that regulate the timing of neuronal differentiation remain unclear. Here, we show that Wnt signaling inhibits the self-renewal capacity of mouse cortical NPCs, and instructively promotes their neuronal differentiation. Overexpression of Wnt7a or of a stabilized form of beta-catenin in mouse cortical NPC cultures induced neuronal differentiation even in the presence of Fgf2, a self-renewal-promoting factor in this system. Moreover, blockade of Wnt signaling led to inhibition of neuronal differentiation of cortical NPCs in vitro and in the developing mouse neocortex. Furthermore, the beta-catenin/TCF complex appears to directly regulate the promoter of neurogenin 1, a gene implicated in cortical neuronal differentiation. Importantly, stabilized beta-catenin did not induce neuronal differentiation of cortical NPCs at earlier developmental stages, consistent with previous reports indicating self-renewal-promoting functions of Wnts in early NPCs. These findings may reveal broader and stage-specific physiological roles of Wnt signaling during neural development.
The caudomedial margin of the medial pallium, known as the cortical hem, expresses several Wnt genes that have been shown to be crucial for cortical development. We examined the expression of members of the Frizzled (mFz) family of Wnt receptors and the Secreted Frizzled Related Protein (SFRP) family of Wnt inhibitors during telencephalic development. We found that mFz-5 and mFz-8 are specifically expressed in the neocortical neuroepithelium and excluded from the hippocampal neuroepithelium in early telencephalic development, whereas mFz-9 and mFz-10 have expression domains confined to the medial pallium. In addition, SFRP-1 and SFRP-3 are expressed in opposing anterolateral to caudomedial gradients within the telencephalic ventricular zone throughout corticogenesis.
The differentiation of multipotential progenitor cells in the vertebrate retina into photoreceptors, neurons and glial cells is regulated in part by cell-cell signalling. Transforming growth factor (TGF)-alpha is one of the extracellular signals implicated in the control of several aspects of retinal development, including proliferation and cell fate. The way cells interpret pleiotropic signals such as TGF-alpha is influenced by the level of expression of epidermal growth factor receptor (EGF-R) in some cell lines. To address the influence of receptor level on responses of retinal progenitor cells to TGF-alpha, additional copies of EGF-Rs were introduced in vitro and in vivo with a retrovirus. Normally in vitro, low concentrations of TGF-alpha stimulated proliferation whereas high concentrations biased choice of cell fate, inhibiting differentiation into rod photoreceptors while promoting differentiation into Müller glial cells. We report here that introduction of extra EGF-Rs into progenitor cells in vitro reduced the concentration of TGF-alpha required for changes in rod and Müller cell differentiation but did not enhance proliferation. Introduction of extra EGF-Rs in vivo increased the proportion of clones that contained Müller glial cells, suggesting that receptor level is normally limiting. These findings demonstrate that responsiveness to extracellular signals during development can be modulated by the introduction of additional receptors, and suggest that the level of expression of receptors for these signals contributes to the regulation of cell fate.
Glial fibrillary acidic protein (GFAP) is an intermediate filament protein specifically expressed in astrocytes in the CNS. To examine the function of GFAP in vivo, the Gfap gene was disrupted by gene targeting in embryonic stem cells. Mice homozygous for the mutation were completely devoid of GFAP but exhibited normal development and showed no obvious anatomical abnormalities in the CNS. When inoculated with infectious scrapie prions, the mutant mice exhibited neuropathological changes typical of prion diseases. Infectious prions accumulated in brains of the mutant mice to a degree similar to that in control littermates. These results suggest that GFAP is not essential for the morphogenesis of the CNS or for astrocytic responses against neuronal injury. The results argue against the hypothesis that GFAP plays a crucial role in the pathogenesis of prion diseases.
Mutation and expression studies have implicated the Wnt gene family in early developmental decision making in vertebrates and flies. In a detailed comparative analysis, we have used in situ hybridization of 8.0- to 9.5-day mouse embryos to characterize expression of all ten published Wnt genes in the central nervous system (CNS) and limb buds. Seven of the family members show restricted expression patterns in the brain. At least three genes (Wnt-3, Wnt-3a, and Wnt-7b) exhibit sharp boundaries of expression in the forebrain that may predict subdivisions of the region later in development. In the spinal cord, Wnt-1, Wnt-3, and Wnt-3a are expressed dorsally, Wnt-5a, Wnt-7a, and Wnt-7b more ventrally, and Wnt-4 both dorsally and in the floor plate. In the forelimb primordia, Wnt-3, Wnt-4, Wnt-6 and Wnt-7b are expressed fairly uniformly throughout the limb ectoderm. Wnt-5a RNA is distributed in a proximal to distal gradient through the limb mesenchyme and ectoderm. Along the limb's dorsal-ventral axis, Wnt-5a is expressed in the ventral ectoderm and Wnt-7a in the dorsal ectoderm. We discuss the significance of these patterns of restricted and partially overlapping domains of expression with respect to the putative function of Wnt signalling in early CNS and limb development.
The embryonic cerebral cortex contains a population of stem-like founder cells capable of generating large, mixed clones of neurons and glia in vitro. We report that the default state of early cortical stem cells is neuronal, and that stem cells are heterogeneous in the number of neurons that they generate. In low fibroblast growth factor (FGF2) concentrations, most maintain this specification, generating solely neuronal progeny. Oligodendroglial production within these clones is stimulated by a higher, threshold level of FGF2, and astrocyte production requires additional environmental factors. Because most cortical neurons are born before glia in vivo, these data support a model in which the scheduled production of cortical cells involves an intrinsic neuronal program in the early stem cells and exposure to environmental, glia-inducing signals.
Early cortical progenitor cells of the ventricular zone (VZ) differ from later progenitor cells of the subventricular zone (SVZ) in cell-type generation and their level of epidermal growth factor receptors (EGFRs). To determine whether differences in their behavior are causally related to EGFR number/density, we introduced extra EGFRs into VZ cells with a retrovirus in vivo and in vitro. This results in premature expression of traits characteristic of late SVZ progenitor cells, including migration patterns, differentiation into astrocytes, and proliferation of multipotential cells to form spheres. The choice between proliferation and differentiation depends on ligand concentration and progenitor cell age and may reflect different thresholds of stimulation. The level of EGFRs expressed by progenitor cells in the cortex may therefore contribute to the timing of their maturation and choice of response to pleiotropic environmental signals.
The cytokines LIF (leukemia inhibitory factor) and BMP2 (bone morphogenetic protein–2) signal through different receptors
and transcription factors, namely STATs (signal transducers and activators of transcription) and Smads. LIF and BMP2 were
found to act in synergy on primary fetal neural progenitor cells to induce astrocytes. The transcriptional coactivator p300
interacts physically with STAT3 at its amino terminus in a cytokine stimulation–independent manner, and with Smad1 at its
carboxyl terminus in a cytokine stimulation–dependent manner. The formation of a complex between STAT3 and Smad1, bridged
by p300, is involved in the cooperative signaling of LIF and BMP2 and the subsequent induction of astrocytes from neural progenitors.
p27Xic1, a member of the Cip/Kip family of Cdk inhibitors, besides its known function of inhibiting cell division, induces Müller glia from retinoblasts. This novel gliogenic function of p27Xic1 is mediated by part of the N-terminal domain near but distinct from the region that inhibits cyclin-dependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p27Xic1 work within the context of an active Notch pathway. The gradual increase of p27Xic1 in the developing retina thus not only limits the number of retinal cells but also increasingly favors the fate of the last cell type to be born in the retina, the Müller glia.
Whereas vertebrate achaete-scute complex (as-c) and atonal (ato) homologs are required for neurogenesis, their neuronal determination activities in the central nervous system (CNS) are not yet supported by loss-of-function studies, probably because of genetic redundancy. Here, to address this problem, we generated mice double mutant for the as-c homolog Mash1 and the ato homolog Math3. Whereas in Mash1 or Math3 single mutants neurogenesis is only weakly affected, in the double mutants tectal neurons, two longitudinal columns of hindbrain neurons and retinal bipolar cells were missing and, instead, those cells that normally differentiate into neurons adopted the glial fate. These results indicated that Mash1 and Math3 direct neuronal versus glial fate determination in the CNS and raised the possibility that downregulation of these bHLH genes is one of the mechanisms to initiate gliogenesis.
Multipotent stem cells that generate both neurons and glia are widespread components of the early neuroepithelium. During CNS development, neurogenesis largely precedes gliogenesis: how is this timing achieved? Using clonal cell culture combined with long-term time-lapse video microscopy, we show that isolated stem cells from the embryonic mouse cerebral cortex exhibit a distinct order of cell-type production: neuroblasts first and glioblasts later. This is accompanied by changes in their capacity to make neurons versus glia and in their response to the mitogen EGF. Hence, multipotent stem cells alter their properties over time and undergo distinct phases of development that play a key role in scheduling production of diverse CNS cells.
Notch1 has been shown to induce glia in the peripheral nervous system. However, it has not been known whether Notch can direct commitment to glia from multipotent progenitors of the central nervous system. Here we present evidence that activated Notch1 and Notch3 promotes the differentiation of astroglia from the rat adult hippocampus-derived multipotent progenitors (AHPs). Quantitative clonal analysis indicates that the action of Notch is likely to be instructive. Transient activation of Notch can direct commitment of AHPs irreversibly to astroglia. Astroglial induction by Notch signaling was shown to be independent of STAT3, which is a key regulatory transcriptional factor when ciliary neurotrophic factor (CNTF) induces astroglia. These data suggest that Notch provides a CNTF-independent instructive signal of astroglia differentiation in CNS multipotent progenitor cells.
We have addressed the role of the proneural bHLH genes Neurogenin2 (Ngn2) and Mash1 in the selection of neuronal and glial fates by neural stem cells. We show that mice mutant for both genes present severe defects in development of the cerebral cortex, including a reduction of neurogenesis and a premature and excessive generation of astrocytic precursors. An analysis of wild-type and mutant cortical progenitors in culture showed that a large fraction of Ngn2; Mash1 double-mutant progenitors failed to adopt a neuronal fate, instead remaining pluripotent or entering an astrocytic differentiation pathway. Together, these results demonstrate that proneural genes are involved in lineage restriction of cortical progenitors, promoting the acquisition of the neuronal fate and inhibiting the astrocytic fate.
Neural stem cells, which differentiate into neurons and glia, are present in the ventricular zone of the embryonal brain.
The precise mechanism by which neural stem cells are maintained during embryogenesis remains to be determined. Here, we found
that transient misexpression of the basic helix-loop-helix genes Hes1 and Hes5 keeps embryonal telencephalic cells undifferentiated although they have been shown to induce gliogenesis in the retina. These
telencephalic cells later differentiate into neurons and astroglia when Hes expression is down-regulated, suggesting that
Hes1- andHes5- expressing cells are maintained as neural stem cells during embryogenesis. Conversely, in the absence of Hes1and Hes5, neural stem cells are not properly maintained, generating fewer and smaller neurospheres than the wild type. These results
indicate that Hes1 and Hes5 play an important role in the maintenance of neural stem cells but not in gliogenesis in the embryonal telencephalon.
Bone morphogenetic proteins (BMPs) have diverse and sometimes paradoxical effects during embryonic development. To determine the mechanisms underlying BMP actions, we analyzed the expression and function of two BMP receptors, BMPR-IA and BMPR-IB, in neural precursor cells in vitro and in vivo. Neural precursor cells always express Bmpr-1a, but Bmpr-1b is not expressed until embryonic day 9 and is restricted to the dorsal neural tube surrounding the source of BMP ligands. BMPR-IA activation induces (and Sonic hedgehog prevents) expression of Bmpr-1b along with dorsal identity genes in precursor cells and promotes their proliferation. When BMPR-IB is activated, it limits precursor cell numbers by causing mitotic arrest. This results in apoptosis in early gestation embryos and terminal differentiation in mid-gestation embryos. Thus, BMP actions are first inducing (through BMPR-IA) and then terminating (through BMPR-IB), based on the accumulation of BMPR-IB relative to BMPR-IA. We describe a feed-forward mechanism to explain how the sequential actions of these receptors control the production and fate of dorsal precursor cells from neural stem cells.
The discovery of stem cells that can generate neural tissue has raised new possibilities for repairing the nervous system. A rush of papers proclaiming adult stem cell plasticity has fostered the notion that there is essentially one stem cell type that, with the right impetus, can create whatever progeny our heart, liver or other vital organ desires. But studies aimed at understanding the role of stem cells during development have led to a different view - that stem cells are restricted regionally and temporally, and thus not all stem cells are equivalent. Can these views be reconciled?
Astrocyte differentiation, which occurs late in brain development, is largely dependent on the activation of a transcription factor, STAT3. We show that astrocytes, as judged by glial fibrillary acidic protein (GFAP) expression, never emerge from neuroepithelial cells on embryonic day (E) 11.5 even when STAT3 is activated, in contrast to E14.5 neuroepithelial cells. A CpG dinucleotide within a STAT3 binding element in the GFAP promoter is highly methylated in E11.5 neuroepithelial cells, but is demethylated in cells responsive to the STAT3 activation signal to express GFAP. This CpG methylation leads to inaccessibility of STAT3 to the binding element. We suggest that methylation of a cell type-specific gene promoter is a pivotal event in regulating lineage specification in the developing brain.
Cell cycle progression and exit must be precisely patterned during development to generate tissues of the correct size, shape and symmetry. Here we present evidence that dorsal-ventral growth of the developing spinal cord is regulated by a Wnt mitogen gradient. Wnt signaling through the beta-catenin/TCF pathway positively regulates cell cycle progression and negatively regulates cell cycle exit of spinal neural precursors in part through transcriptional regulation of cyclin D1 and cyclin D2. Wnts expressed at the dorsal midline of the spinal cord, Wnt1 and Wnt3a, have mitogenic activity while more broadly expressed Wnts do not. We present several lines of evidence suggesting that dorsal midline Wnts form a dorsal to ventral concentration gradient. A growth gradient that correlates with the predicted gradient of mitogenic Wnts emerges as the neural tube grows with the proliferation rate highest dorsally and the differentiation rate highest ventrally. These data are rationalized in a 'mitogen gradient model' that explains how proliferation and differentiation can be patterned across a growing field of cells. Computer modeling demonstrates this model is a robust and self-regulating mechanism for patterning cell cycle regulation in a growing tissue. Supplemental data available on-line
A complex orchestration of stem-cell specification, expansion and differentiation is required for the proper development of the nervous system. Although progress has been made on the role of individual genes in each of these processes, there are still unresolved questions about how gene function translates to the dynamic assembly of cells into tissues. Recently, stem-cell biology has emerged as a bridge between the traditional fields of cell biology and developmental genetics. In addition to their potential therapeutic role, stem cells are being exploited as experimental 'logic chips' that integrate information and exhibit self-organizing properties. Recent studies provide new insights on how morphogenic signals coordinate major stem cell decisions to regulate the size, shape and cellular diversity of the nervous system.
Vascular endothelial growth factor (VEGF) is an angiogenic protein with neurotrophic and neuroprotective effects. Because VEGF promotes the proliferation of vascular endothelial cells, we examined the possibility that it also stimulates the proliferation of neuronal precursors in murine cerebral cortical cultures and in adult rat brain in vivo. VEGF (>10 ng/ml) stimulated 5-bromo-2'-deoxyuridine (BrdUrd) incorporation into cells that expressed immature neuronal marker proteins and increased cell number in cultures by 20-30%. Cultured cells labeled by BrdUrd expressed VEGFR2/Flk-1, but not VEGFR1/Flt-1 receptors, and the effect of VEGF was blocked by the VEGFR2/Flk-1 receptor tyrosine kinase inhibitor SU1498. Intracerebroventricular administration of VEGF into rat brain increased BrdUrd labeling of cells in the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG), where VEGFR2/Flk-1 was colocalized with the immature neuronal marker, doublecortin (Dcx). The increase in BrdUrd labeling after the administration of VEGF was caused by an increase in cell proliferation, rather than a decrease in cell death, because VEGF did not reduce caspase-3 cleavage in SVZ or SGZ. Cells labeled with BrdUrd after VEGF treatment in vivo include immature and mature neurons, astroglia, and endothelial cells. These findings implicate the angiogenesis factor VEGF in neurogenesis as well.
In the developing central nervous system (CNS), Notch signaling preserves progenitor pools and inhibits neurogenesis and oligodendroglial differentiation. It has recently been postulated that Notch instructively drives astrocyte differentiation. Whether the role of Notch signaling in promoting astroglial differentiation is permissive or instructive has been debated. We report here that the astrogliogenic role of Notch is in part mediated by direct binding of the Notch intracellular domain to the CSL DNA binding protein, forming a transcriptional activation complex onto the astrocyte marker gene, glial fibrillary acidic protein (GFAP). In addition, we found that, in CSL-/- neural stem cell cultures, astrocyte differentiation was delayed but continued at a normal rate once initiated, suggesting that CSL is involved in regulating the onset of astrogliogenesis. Importantly, although the classical CSL-dependent Notch signaling pathway is intact and able to activate the Notch canonical target promoter during the neurogenic phase, it is unable to activate the GFAP promoter during neurogenesis. Therefore, the effect of Notch signaling on target genes is influenced by cellular context in regulation of neurogenesis and gliogenesis.
beta-Catenin plays a pivotal role in Wnt signaling during embryogenesis and is a component of adherens junctions. Since targeted disruption of the beta-catenin gene is lethal at gastrulation we have used a D6-Cre mouse line for conditional inactivation of beta-catenin in the mouse cerebral cortex and hippocampus after embryonic day (E) 10.5. In D6-Cre floxed beta-catenin mice, hippocampal CA1-CA2 fields are disrupted in similar manner as in Wnt-3a and LEF-1 mutants. The cortex of D6-Cre floxed beta-catenin mutants is strongly affected which contrasts with the normal cortex observed in Wnt-3a and LEF-1 mutants. Severe abnormalities in the organization of the neuroepithelium are observed that include disrupted interkinetic nuclear migration, loss of adherens junctions, impaired radial migration of neurons toward superficial layers and decreased cell proliferation after E15.5. At newborn stage, a premature disassembly of the radial glial scaffold and increased numbers of astrocytes are found in the cortex.
Wnt signaling is implicated in the control of cell growth and differentiation during CNS development from studies of mouse and chick models, but its action at the cellular level has been poorly understand. In this study, we examine the in vitro function of Wnt signaling in embryonic neural stem cells, dissociated from neurospheres derived from E11.5 mouse telencephalon. Conditioned media containing active Wnt-3a proteins are added to the neural stem cells and its effect on regeneration of neurospheres and differentiation into neuronal and glial cells was examined. Wnt-3a proteins inhibit regeneration of neurospheres, but promote differentiation into MAP2-positive neuronal cells. Wnt-3a proteins also increase the number of GFAP-positive astrocytes but suppress the number of oligodendroglial lineage cells expressing PDGFR or O4. These results indicate that Wnt-3a signaling can inhibit the maintenance of neural stem cells, but rather promote the differentiation of neural stem cells into several cell lineages.
The generation of distinct cell types during development depends on the competence of progenitor populations to differentiate along specific lineages. Here we investigate the mechanisms that regulate competence of rodent cortical progenitors to differentiate into astrocytes in response to ciliary neurotrophic factor (CNTF). We found that fibroblast growth factor 2 (FGF2), which by itself does not induce astrocyte-specific gene expression, regulates the ability of CNTF to induce expression of glial fibrillary acidic protein (GFAP). FGF2 facilitates access of the STAT/CBP (signal transducer and activator of transcription/CRE binding protein) complex to the GFAP promoter by inducing Lys4 methylation and suppressing Lys9 methylation of histone H3 at the STAT binding site. Histone methylation at this site is specific to the cell's state of differentiation. In progenitors, the promoter is bound by Lys9-methylated histones, and in astrocytes, it is bound by Lys4-methylated histones, indicating that astrocyte differentiation in vivo involves this switch in chromatin state. Our observations indicate that extracellular signals can regulate access of transcription factors to genomic promoters by local chromatin modification, and thereby regulate developmental competence.
Neural stem cells proliferate and maintain multipotency when cultured in the presence of FGF2, but subsequent lineage commitment by the cells is nevertheless influenced by the exposure to FGF2. Here we show that FGF2 effects on neural stem cells are mediated, in part, by beta-catenin. Conversely, the effects of beta-catenin in neural stem cells depend in part upon whether there is concurrent fibroblast growth factor (FGF) signaling. FGF2 increases beta-catenin signaling through several different mechanisms including increased expression of beta-catenin mRNA, increased nuclear translocation of beta-catenin, increased phosphorylation of GSK-3beta, and tyrosine phosphorylation of beta-catenin. Overexpression of beta-catenin in the presence of FGF2 helps to maintain neural progenitor cells in a proliferative state. However, overexpression of beta-catenin in the absence of FGF2 enhances neuronal differentiation. Further, chromatin immunoprecipitation (ChIP) assays demonstrate that both beta-catenin and Lef1 bind directly to the neurogenin promoter, and luciferase reporter assays demonstrate that beta-catenin is directly involved in the regulation of neurogenin 1 and possibly other proneural genes when neural stem cells are cultured in the presence of FGF2. We suggest that the balance between the mitogenic effects and the proneural effects of beta-catenin is determined by the presence of FGF signaling.
The functions of Wingless-Int (Wnt) signaling, studied intensely in embryonic brain development, have been comparatively little investigated in the postnatal brain. We report remarkably patterned gene expression of Wnt signaling components in postnatal mouse cerebral cortex, lasting into young adulthood. Wnt genes are expressed in gene-specific regional and lamina patterns in each of the major subdivisions of the cerebral cortex: the olfactory bulb (OB), the hippocampal formation, and the neocortex. Genes encoding Frizzled (Fz) Wnt receptors, or secreted Frizzled-related proteins (sFrps), are also expressed in regional and lamina patterns. These findings suggest that Wnt signaling is active and regulated in the postnatal cortex and that different cortical cell populations have varying requirements for a Wnt signal. The OB, in particular, shows gene expression of a large variety of Wnt signaling components, making it a prime target for future functional studies. The penultimate components of the canonical Wnt pathway are the Tcf/Lef1 transcription factors, which regulate transcription of Wnt signaling target genes. Surprisingly, we found little Tcf/Lef1 expression in the postnatal neocortex. These observations suggest that noncanonical Wnt pathways predominate, which will require functional testing. However, Lef1 is widely expressed in the dorsal thalamus, and Wnt ligands and receptors are expressed, respectively, in cortical areas and thalamic nuclei that are interconnected. Thus, canonical Wnt signaling could be utilized in a major cortical input by Fz- and Lef1-expressing thalamic cells that innervate the Wnt-expressing cortex.
Although the Notch and JAK-STAT signalling pathways fulfill overlapping roles in growth and differentiation regulation, no coordination mechanism has been proposed to explain their relationship. Here we show that STAT3 is activated in the presence of active Notch, as well as the Notch effectors Hes1 and Hes5. Hes proteins associate with JAK2 and STAT3, and facilitate complex formation between JAK2 and STAT3, thus promoting STAT3 phosphorylation and activation. Furthermore, suppression of endogenous Hes1 expression reduces growth factor induction of STAT3 phosphorylation. STAT3 seems to be essential for maintenance of radial glial cells and differentiation of astrocytes by Notch in the developing central nervous system. These results suggest that direct protein-protein interactions coordinate cross-talk between the Notch-Hes and JAK-STAT pathways.
beta-Catenin is an essential component of the canonical Wnt signaling system that controls decisive steps in development. We employed here two conditional beta-catenin mutant alleles to alter beta-catenin signaling in the central nervous system of mice: one allele to ablate beta-catenin and the second allele to express a constitutively active beta-catenin. The tissue mass of the spinal cord and brain is reduced after ablation of beta-catenin, and the neuronal precursor population is not maintained. In contrast, the spinal cord and brain of mice that express activated beta-catenin is much enlarged in mass, and the neuronal precursor population is increased in size. beta-Catenin signals are thus essential for the maintenance of proliferation of neuronal progenitors, controlling the size of the progenitor pool, and impinging on the decision of neuronal progenitors to proliferate or to differentiate.
Synergistic signaling in fetal brain by STAT3–Smad1 complex bridged by p300
- Nakashima