Fig 2 - uploaded by Klaus Schughart
Content may be subject to copyright.
Neural tube defect in brain regions of opb mutant embryos. (A,B) Head region of wild-type and opb mutant embryos, respectively, at day 10.5 p.c. The rostral boundary of the open neural tube in opb mutant embryos (B) extended into the region of the lamina terminalis between the two telencephalic hemispheres (arrow). The most rostral region of the forebrain was closed. (C) opb mutant (left) and wildtype embryos (right) at day 9.5 p.c. of development. The neural tube defect was apparent from the forebrain region to the posterior region of the hindbrain (arrows). DI, diencephalon; FB, forebrain; HB, hindbrain; MB, midbrain; MS, mesencephalon; MT, metencephalon; MY, myelencephalon; TE, telencephalon.
Source publication
We describe a new mouse mutation, designated open brain (opb), which results in severe defects in the developing neural tube. Homozygous opb embryos exhibited an exencephalic malformation involving the forebrain, midbrain and hindbrain regions. The primary defect of the exencephaly could be traced back to a failure to initiate neural tube closure a...
Contexts in source publication
Context 1
... exen- cephaly was apparent in the brain of day 12.5 p.c. opb mutant embryos (Fig. 1B,D). The affected region involved the Open brain mutation forebrain, midbrain and hindbrain. This defect in the closure of the neural tube was already evident at day 9.5 p.c., at a time when the cephalic neural tube had completely closed in normal littermates ( Fig. 2C). At day 10.5 p.c., opb embryos exhibit an open neural tube extending from the developing diencephalon into the future myelencephalon, to about the level of the otic vesicle ( Figs 2B, 3A). The most rostral regions of the forebrain were closed (Fig. ...
Context 2
... defect in the closure of the neural tube was already evident at day 9.5 p.c., at a time when the cephalic neural tube had completely closed in normal littermates ( Fig. 2C). At day 10.5 p.c., opb embryos exhibit an open neural tube extending from the developing diencephalon into the future myelencephalon, to about the level of the otic vesicle ( Figs 2B, 3A). The most rostral regions of the forebrain were closed (Fig. 2B). ...
Context 3
... 9.5 p.c., at a time when the cephalic neural tube had completely closed in normal littermates ( Fig. 2C). At day 10.5 p.c., opb embryos exhibit an open neural tube extending from the developing diencephalon into the future myelencephalon, to about the level of the otic vesicle ( Figs 2B, 3A). The most rostral regions of the forebrain were closed (Fig. ...
Citations
... (204,205). Mutation in many other genes of the Shh signaling pathway contributes to exencephaly (206)(207)(208)(209)(210)(211)(212)(213)(214)(215)(216)(217)(218). Some studies also implicated the mutation in the genes (Ptch1, Rab23, and Tulp3) of the Shh signaling pathway in the development of spina bifida and CRN (209-212, 217, 218). ...
Neural tube defects (NTDs) are serious congenital deformities of the nervous system that occur owing to the failure of normal neural tube closures. Genetic and non-genetic factors contribute to the etiology of neural tube defects in humans, indicating the role of gene-gene and gene-environment interaction in the occurrence and recurrence risk of neural tube defects. Several lines of genetic studies on humans and animals demonstrated the role of aberrant genes in the developmental risk of neural tube defects and also provided an understanding of the cellular and morphological programs that occur during embryonic development. Other studies observed the effects of folate and supplementation of folic acid on neural tube defects. Hence, here we review what is known to date regarding altered genes associated with specific signaling pathways resulting in NTDs, as well as highlight the role of various genetic, and non-genetic factors and their interactions that contribute to NTDs. Additionally, we also shine a light on the role of folate and cell adhesion molecules (CAMs) in neural tube defects.
... CS causes a wide spectrum of defects, such as OPEN ACCESS EDITED BY craniosynostosis, congenital heart defects, obesity, polydactyly, and multiple skeletal abnormalities including decreased hip mobility, spina bifida occulta, kyphoscoliosis, short muscular neck, genu valgum, and lateral displacement of the patella and mandibular defects (Cohen et al., 1987;Jenkins et al., 2007). Rab23 open brain mutant mice exhibit abnormalities in the neural tube, vertebral column, and axial skeleton, such as the ribs, limbs, and skull (Gunther et al., 1994;Eggenschwiler and Anderson, 2000;Hasan et al., 2020). ...
RAB23 is a small GTPase which functions at the plasma membrane to regulate growth factor signaling. Mutations in RAB23 cause Carpenter syndrome, a condition that affects normal organogenesis and patterning. In this study, we investigate the role of RAB23 in musculoskeletal development and show that it is required for patella bone formation and for the maintenance of tendon progenitors. The patella is the largest sesamoid bone in mammals and plays a critical role during movement by providing structural and mechanical support to the knee. Rab23 −/− mice fail to form a patella and normal knee joint. The patella is formed from Sox9 and scleraxis (Scx) double-positive chondroprogenitor cells. We show that RAB23 is required for the specification of SOX9 and scleraxis double-positive patella chondroprogenitors during the formation of patella anlagen and the subsequent establishment of patellofemoral joint. We find that scleraxis and SOX9 expression are disrupted in Rab23 −/− mice, and as a result, development of the quadriceps tendons, cruciate ligaments, patella tendons, and entheses is either abnormal or lost. TGFβ-BMP signaling is known to regulate patella initiation and patella progenitor differentiation and growth. We find that the expression of TGFβR2, BMPR1, BMP4, and pSmad are barely detectable in the future patella site and in the rudimentary tendons and ligaments around the patellofemoral joint in Rab23 −/− mice. Also, we show that GLI1, SOX9, and scleraxis, which regulate entheses establishment and maturation, are weakly expressed in Rab23 −/− mice. Further analysis of the skeletal phenotype of Rab23 −/− mice showed a close resemblance to that of Tgfβ2 −/− mice, highlighting a possible role for RAB23 in regulating TGFβ superfamily signaling.
... On the contrary, Gli1 or Gli2 negative mice, two mediators of the Shh signalling, do not develop NTDs (Ding et al., 1998;Matisse et al., 1998). In open-brain or Zic2 mutant mice, two mutations where negative regulators of the Shh signalling are disrupted (Eggenschwiler et al., 2001;Nakata et al., 1998), the neural tube fails to close both in the brain and the lower spine area (Günther et al., 1994;Nagai et al., 2000). Interestingly, the dorsal and dorsolateral cells do not seem to differentiate (Eggenschwiler et al., 2000). ...
Despite recent advances leading to the suppression of the auto-immune attack during Multiple Sclerosis, efficient remyelinating therapies are still lacking. In MS, the spontaneous remyelination from oligodendrocyte precursor cells (OPCs), present all over the brain, is inefficient and diminishes with age. We identified Tns3 (Tensin 3) as a target of key oligodendrogenic factors (Chd7, Chd8 or Olig2) and showed that it was strongly induced at the onset of oligodendrocytes (OLs) differentiation while downregulated in mature OLs, constituting a good marker for immature OLs (iOLs). I characterized Tns3 expression in oligodendroglia as: 1) mainly restricted to the iOLs, 2) localized in the OLs cytoplasm and processes, and 3) overlapping with known iOLs markers (Itpr2 and Nkx2.2). Tns3 expression is also found during adult brain remyelination after LPC injection, especially in newly formed OLs, therefore constituting a novel marker for iOLs.In vivo Tns3 loss-of-function (LOF) by CRISPR/Cas9 technology in neonatal neural stem cells (NSCs) of the subventricular zone blocks OL differentiation without affecting OPC survival or proliferation. It seems that a total deletion of the locus and the frameshift of the full-length isoform induces similar effects on the OL population. Moreover, OPCs specific deletion of Tns3 in a floxed Tns3 model also impair OL production without affecting the OPC population and the Nkx2.2 positive iOLs. Finally, preliminary data on MACSorted OPCs for Tns3flox mice suggest that Tns3 KO in OPCs delay iOLs differentiation and decrease their survival on the first 72h.All of these data show the involvement of Tns3 in the oligodendrocyte generation
... The basal ganglia arise from the ventral telencephalon, an anterior extension of ventral neuraxis, which is patterned by the sonic hedgehog (SHH) signaling pathway in normal vertebrate development. This dynamic protein serves a multitude of functions in a contextdependent manner, both as a mitogen to promote cellular proliferation, and a morphogen to direct cellular and regional specification towards ventral fates [34][35][36][37]. Embryological investigation has exposed many of the multifaceted roles that SHH plays in development, adding insight into the disorders observed with deficits in SHH expression [35,[38][39][40]. ...
... This dynamic protein serves a multitude of functions in a contextdependent manner, both as a mitogen to promote cellular proliferation, and a morphogen to direct cellular and regional specification towards ventral fates [34][35][36][37]. Embryological investigation has exposed many of the multifaceted roles that SHH plays in development, adding insight into the disorders observed with deficits in SHH expression [35,[38][39][40]. ...
... Herein lies the initial guide to the central nervous system's rise to cellular diversity. context-dependent manner, both as a mitogen to promote cellular proliferation, and a morphogen to direct cellular and regional specification towards ventral fates [34][35][36][37]. Embryological investigation has exposed many of the multifaceted roles that SHH plays in development, adding insight into the disorders observed with deficits in SHH expression [35,[38][39][40]. ...
The complexities of human neurodevelopment have historically been challenging to decipher but continue to be of great interest in the contexts of healthy neurobiology and disease. The classic animal models and monolayer in vitro systems have limited the types of questions scientists can strive to answer in addition to the technical ability to answer them. However, the tridimensional human stem cell-derived organoid system provides the unique opportunity to model human development and mimic the diverse cellular composition of human organs. This strategy is adaptable and malleable, and these neural organoids possess the morphogenic sensitivity to be patterned in various ways to generate the different regions of the human brain. Furthermore, recapitulating human development provides a platform for disease modeling. One master regulator of human neurodevelopment in many regions of the human brain is sonic hedgehog (SHH), whose expression gradient and pathway activation are responsible for conferring ventral identity and shaping cellular phenotypes throughout the neural axis. This review first discusses the benefits, challenges, and limitations of using organoids for studying human neurodevelopment and disease, comparing advantages and disadvantages with other in vivo and in vitro model systems. Next, we explore the range of control that SHH exhibits on human neurodevelopment, and the application of SHH to various stem cell methodologies, including organoids, to expand our understanding of human development and disease. We outline how this strategy will eventually bring us much closer to uncovering the intricacies of human neurodevelopment and biology.
... The SHH signaling pathway plays a crucial role in neurulation and neuronal differentiation along the dorsoventral axis of the neural tube via an SHH concentration gradient. [6] Interestingly, mutations related to the upregulation of the SHH pathway, such as gain-of-function mutations in Shh [7] and GLI2 [8] or loss-of-function mutations in Shh suppressor genes, including Fkbp8, [9] Rab23, [10,11] Tulp3, [12,13] Ptch1, [14] Luzp, [15] and Sufu, [16] can lead to NTDs in mouse models. In humans, several reports have demonstrated that single-nucleotide polymorphisms (SNPs) in the SHH pathway genes PKA, [17] PTCH1, [18] SMO, [19] and SUFU [20] increase the risk of NTDs. ...
rs3738880 was a risk factor for NTDs in the Han Chinese population.
... Subsequently, there have been increasing number of studies focusing on genetic function of Rab23.In mammals, Gunther et al [33]. identified the mouse open brain (opb) gene based on two recessive mutations(spontaneous and induced by N ethyl N nitrosourea, respectively). ...
... identified the mouse open brain (opb) gene based on two recessive mutations(spontaneous and induced by N ethyl N nitrosourea, respectively). Next, homozygous opb embryos showed an exencephalic monstrosity affecting the forebrain, midbrain and hindbrain regions [33]. However, the definite relationship between mouse opb gene and Rab23 has remained unclear. ...
Rab23, has been proven to play a role in membrane trafficking and protein transport in eukaryotic cells. Rab23 is also a negative regulator of the Sonic hedgehog signaling pathway in an indirect way. The nonsense mutation and loss of protein of Rab23 has been associated with neural tube defect in mice and aberrant expression in various diseases in human such as neural system,breast, visceral and cutaneous tumor. In addition, Rab23 may play joint roles in autophagosome formation during anti-infection process against Group A streptococcus. In this paper, we give a brief review on the functions of Rab23, summarize the involvement of Rab23 in genetic research, membrane trafficking and potential autophagy pathway, especially focus on tumor promotion,disease pathogenesis and discuss the possible underlying mechanisms that are regulated by Rab23.
... The SHH signaling pathway plays a crucial role in neurulation and neuronal differentiation along the dorsoventral axis of the neural tube via an SHH concentration gradient. [6] Interestingly, mutations related to the upregulation of the SHH pathway, such as gain-of-function mutations in Shh [7] and GLI2 [8] or loss-of-function mutations in Shh suppressor genes, including Fkbp8, [9] Rab23, [10,11] Tulp3, [12,13] Ptch1, [14] Luzp, [15] and Sufu, [16] can lead to NTDs in mouse models. In humans, several reports have demonstrated that single-nucleotide polymorphisms (SNPs) in the SHH pathway genes PKA, [17] PTCH1, [18] SMO, [19] and SUFU [20] increase the risk of NTDs. ...
Background: The sonic hedgehog (SHH) pathway is an important signaling pathway for neural tube closure. GLI family zinc finger 2 (GLI2) is the major activation mediator of the SHH pathway; however, no single-nucleotide polymorphisms (SNPs) in GLI2 have been reported to be associated with human neural tube defects (NTDs) to date. Here, we evaluated a mutation in GLI2 in the Han Chinese population.
Methods: We used SNPscan to genotype rs3738880 in the GLI2 coding region. We then investigated the function of this gene by Western blotting and dual-luciferase assays.
Results: In this study, we found that the GLI2 missense variant rs3738880 significantly increased the risk of NTDs in the Han Chinese population via association studies in a cohort of 254 patients and 277 controls from Shanxi Province (odds ratio [OR] = 1.89, 95% confidence interval [CI] = 1.28–2.80, P = 0.0012). Additional stratified analyses demonstrated that rs3738880 was significantly related to spina bifida (114 cases, OR = 2.01, 95% CI = 1.19–3.38, P = 0.0067). Functional analysis revealed that rs3738880 did not affect GLI2 protein stability and significantly increased SHH activity because of the introduction of a potential phosphorylation site in GLI2.
Conclusion: rs3738880 was a risk factor for NTDs in the Han Chinese population.
... The dorso-ventral neural tube patterning defects seen in Ehd1-null embryos resemble the phenotypes associated with increase in SHH signaling. For example, the phenotypes we observed resemble those of mutants with functional disruption of negative regulators of SHH signaling, including Rab23, Gpr161, Thm1, Ptch1, TULP3 and PKA 97,[103][104][105][106][107][108][109][110] . This similarity suggests that the primary function of EHD1 in the early embryo is to restrain the activity of the SHH pathway. ...
Members of the four-member C-terminal EPS15-Homology Domain-containing (EHD) protein family play crucial roles in endocytic recycling of cell surface receptors from endosomes to the plasma membrane. In this study, we show that Ehd1 gene knockout in mice on a predominantly B6 background is embryonic lethal. Ehd1-null embryos die at mid-gestation with a failure to complete key developmental processes including neural tube closure, axial turning and patterning of the neural tube. We found that Ehd1-null embryos display short and stubby cilia on the developing neuroepithelium at embryonic day 9.5 (E9.5). Loss of EHD1 also deregulates the ciliary SHH signaling with Ehd1-null embryos displaying features indicative of increased SHH signaling, including a significant downregulation in the formation of the GLI3 repressor and increase in the ventral neuronal markers specified by SHH. Using Ehd1-null MEFS we found that EHD1 protein co-localizes with the SHH receptor Smoothened in the primary cilia upon ligand stimulation. Under the same conditions, EHD1 was shown to co-traffic with Smoothened into the developing primary cilia and we identify EHD1 as a direct binding partner of Smoothened. Overall, our studies identify the endocytic recycling regulator EHD1 as a novel regulator of the primary cilium-associated trafficking of Smoothened and Hedgehog signaling.
... Ectopic expression of Shh and mutations in negative regulators of Shh signalling, e.g. Ptch1, Sufu, Rab23, and Tulp3, result in exencephaly and/or spina bifida (Echelard et al., 1993, Goodrich et al., 1997, Cooper et al., 2005, Gunther et al., 1994, Eggenschwiler et al., 2001, Ikeda et al., 2001, Murdoch and Copp, 2010. This indicates that increased activation of Shh signalling, resulting in an expansion of ventral markers, prevents neural tube closure. ...
The glycine cleavage system (GCS) is a multi-enzyme complex localised in the mitochondria and serves as the main catabolic pathway for glycine. It contributes to supply of one-carbon units into folate one-carbon metabolism (FOCM) which utilises them for vital processes such as purines and thymidylate biosynthesis and methylation reactions. This thesis focuses on the role of glycine decarboxylase (Gldc), a member of the GCS, in embryonic development of the brain. It utilises two loss-of-function mouse models for Gldc which were found to exhibit two distinct disease phenotypes: non-ketotic hyperglycinemia (NKH) and neural tube defects (NTDs). The aims of this project are to investigate what effects GCS deficiency has on FOCM, the developmental mechanisms underlying NTDs caused by loss of Gldc expression, and suitability of the Gldc mice models as animal models for classical NKH. NKH is a rare metabolic disease caused by mutations of GCS genes (mainly GLDC) and characterised by accumulation of glycine in body fluids, resulting in severe neurological dysfunction and poor survival. Gldc-deficient mice exhibited features of NKH including elevated glycine, early post-natal lethality, and hydrocephalus. Enlargement of the brain ventricles was found to already be present at late-foetal stage, while glycine levels in whole embryos were already elevated shortly after neurulation. Gldc-deficient embryos also displayed NTDs, a common birth defect of the central nervous system that result from failure of the neural tube to close. Gldc-deficient embryos displayed abnormal folate metabolism, growth retardation and reduced cell proliferation. Supplementation with one-carbon units through dietary means was able to normalise folate profiles, completely rescue the NTDs, and normalise proliferation and growth in Gldc-deficient embryos. Diet-induced folate deficiency and interactions with the Mthfr mutation (which results in a methylation defect) did not exacerbate the NTDs caused by the Gldc mutation. This study provides the first mouse model for classical NKH and suggests that the pathology of NKH begins earlier in development than suspected. It also suggests that Gldc deficiency causes NTDs by reducing the supply of glycine-derived, mitochondrial one-carbon units for FOCM reactions.
... The first insight into the function of Rab23 came from cloning of the mouse open brain (opb) allele (Eggenschwiler and Anderson, 2000;Gunther et al., 1994;Sporle et al., 1996) of Rab23 (Eggenschwiler et al., 2001). In vertebrate embryonic patterning, Rab23 is required for dorsalization and acts antagonistically to Shh, which is essential for ventral cell type specification (Chiang et al., 1996;Sporle et al., 1996). ...
... Successful sequential activation of both genes is crucial in Shh-dependent patterning of the neural tube, and normal development of the brain and spinal cord. Rab23 mutant mouse embryos exhibit exencephalic malformation of the forebrain, midbrain and hindbrain regions, and do not survive beyond the second half of gestation (Eggenschwiler et al., 2001;Gunther et al., 1994). How exactly Rab23 silences the Shh pathway in dorsal neural cells and how Rab23 controls Shh target genes, is unknown. ...
The small GTPase Rab23 is an antagonist of Sonic hedgehog (Shh) signaling during mouse development. Since modulation of Shh signaling depends on the normal functioning of the primary cilium, and overexpression of Rab23's putative RabGAP, Evi5L, led to reduced ciliogenesis, Rab23 could have a role at the primary cilium. Rab23 wild-type and constitutively active Rab23 Q68L mutant were found enriched at the primary cilium. In testing Rab23's role in the ciliary targeting of known cargoes, ciliary localization of a kinesin-2 motor protein Kif17 was disrupted in Rab23 silenced cells. Co-immunoprecipitation and affinity binding studies revealed that Rab23 exists in a complex with Kif17 and Importin β2 (Kif17's putative ciliary import carrier), implying that Kif17 requires binding to regulatory proteins like Rab23 for its ciliary transport. Although a ciliary-cytoplasmic gradient of nuclear Ran is necessary in regulating Kif17's ciliary transport, Rab23 and Ran appear to have differing roles in ciliary entry of Kif17. Our findings have uncovered a hitherto unknown effector of Rab23 and demonstrated how Rab23 could mediate Kif17's transport to the primary cilium.
© 2015. Published by The Company of Biologists Ltd.
