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Neural tube closure defects are limited to the cranial region of Gcn5 hat/hat embryos. (A) Scanning electron micrographs showing dorsal views of E9.5 wild-type or Gcn5 hat/hat embryos. The neural tube is completely closed in the wild-type embryo, but it is open from the hindbrain-
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Gcn5 was the first transcription-related histone acetyltransferase (HAT) to be identified. However, the functions of this
enzyme in mammalian cells remain poorly defined. Deletion of Gcn5 in mice leads to early embryonic lethality with increased apoptosis in mesodermal lineages. Here we show that deletion of
p53 allows Gcn5−/− embryos to survive lo...
Citations
... Moreover, in Gcn5 +/À p300 +/À mice embryos, embryos are smaller in size and show retardation in organ formation and increased apoptosis (Phan et al., 2005). Also, alteration in expression of GCN5 and point mutation targeted to its catalytic activity cause deficiency in neural tube closure in mouse embryos (Bu, Evrard, Lozano, & Dent, 2007;Lin et al., 2008;Xu et al., 2000). However, Pcaf À/À mouse embryos are viable, and they do not show any developmental abnormality (Yamauchi et al., 2000). ...
Dynamic epigenetic regulation is critical for proper oogenesis and early embryo development. During oogenesis, fully grown germinal vesicle oocytes develop to mature Metaphase II oocytes which are ready for fertilization. Fertilized oocyte proliferates mitotically until blastocyst formation and the process is called early embryo development. Throughout oogenesis and early embryo development, spatio-temporal gene expression takes place, and this dynamic gene expression is controlled with the aid of epigenetics. Epigenetic means that gene expression can be altered without changing DNA itself. Epigenome is regulated through DNA methylation and histone modifications. While DNA methylation generally ends up with repression of gene expression, histone modifications can result in expression or repression depending on type of modification, type of histone protein and its specific residue. One of the modifications is histone acetylation which generally ends up with gene expression. Histone acetylation occurs through the addition of acetyl group onto amino terminal of the core histone proteins by histone acetyltransferases (HATs). Contrarily, histone deacetylation is associated with repression of gene expression, and it is catalyzed by histone deacetylases (HDACs). This review article focuses on what is known about alterations in the expression of HATs and HDACs and emphasizes importance of HATs and HDACs during oogenesis and early embryo development.
... Knockout mice of p300 (histone acetyltransferase enzyme) exhibited cranial NTDs, suggesting that it is essential for the closure of the neural tube (142). Studies have found that mutations in Gcn5 and Cited2 disrupt HAT activity and elevate the risk of NTDs (143,144). Pharmacological inhibitors such as valproic acid and trichostatin-A demolish the regulation of acetylation that causes NTDs (145,146). Mutations in histone deacetylase (hdac4 and sirt1) cause cranial NTDs (147,148). ...
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.
... Supporting the neuroprotective role of GCN5, a study showed that GCN5-mediated acetylation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), protects neuronal cells against MPP + -induced oxidative stress [20]. GCN5 −/− mice died during embryogenesis due to a combination of excessive apoptosis [21,22] and loss of GCN5 transcriptionally upregulated BH3-only protein (Bim) and caspasedependent neuronal apoptosis [17]. ...
α-synuclein (αS) is a β-sheet intracellular protein that has been implicated as a major pathological hallmark of Parkinson's disease (PD). Several studies have shown that overexpression of αS causes dopaminergic cell loss; however, the role of αS in apoptosis remains not fully known. Therefore, this study aims to address the mechanisms of the αS overexpression model in apoptosis and to its correlation with PD pathogenesis. Here, we used a human αS (hαS) plasmid to characterize the role of ectopic αS in neuronal apoptosis in sporadic PD in vitro. We found that overexpression of αS transcriptionally upregulated Bim-mediated apoptosis in neuronal SH-SY5Y cells. Interestingly, αS overexpression inhibited general control non-depressible 5 (GCN5), a histone acetyltransferase (HAT), and promoted transcriptional upregulation of Bim. Consequently, co-overexpression of GCN5 in the αS overexpressed model showed a reversal of αS toxicity in neuronal cells. These in vitro findings support the hypothesis of αS-mediated histone deacetylation and dopaminergic neuronal loss in PD. Moreover, our study indicates that therapeutic activation/homeostasis of GCN5 may benefit PD and other α-synucleinopathies.
... Importantly, Supt3 deletion in mice indicated that SUPT3H is important for mouse embryogenesis as embryos die between E9.5 and E14.5 (50). This observation suggests Nucleic Acids Research, 2022 17 that SUPT3H is not essential for early mouse development, similarly to other SAGA subunits, such as GCN5, PCAF, SUPT20H, USP22 and ATXN7L3 (47,(51)(52)(53)(54)(55). ...
Coactivator complexes regulate chromatin accessibility and transcription. SAGA (Spt-Ada-Gcn5 Acetyltransferase) is an evolutionary conserved coactivator complex. The core module scaffolds the entire SAGA complex and adopts a histone octamer-like structure, which consists of six histone-fold domain (HFD)-containing proteins forming three histone-fold (HF) pairs, to which the double HFD-containing SUPT3H adds one HF pair. Spt3, the yeast ortholog of SUPT3H, interacts genetically and biochemically with the TATA binding protein (TBP) and contributes to global RNA polymerase II (Pol II) transcription. Here we demonstrate that (i) SAGA purified from human U2OS or mouse embryonic stem cells (mESC) can assemble without SUPT3H, (ii) SUPT3H is not essential for mESC survival, but required for their growth and self-renewal, and (iii) the loss of SUPT3H from mammalian cells affects the transcription of only a specific subset of genes. Accordingly, in the absence of SUPT3H no major change in TBP accumulation at gene promoters was observed. Thus, SUPT3H is not required for the assembly of SAGA, TBP recruitment, or overall Pol II transcription, but plays a role in mESC growth and self-renewal. Our data further suggest that yeast and mammalian SAGA complexes contribute to transcription regulation by distinct mechanisms.
... Loss of the catalytic subunit Gcn5 causes defects in mesoderm formation and early embryonic lethality, whereas Pcaf null embryos are viable and fertile (Bu et al., 2007;Koutelou et al., 2020;Xu et al., 2000;Yamauchi et al., 2000). Studies of SAGA and ATAC HAT functions in Drosophila revealed that Ada2a or Ada2b mutants have lethal phenotypes, but at different stages of development, suggesting that Ada2a and Ada2b have different functions in development. ...
... Earlier studies on Gcn5 null ESCs demonstrated a requirement of the HAT activities of SAGA and ATAC during differentiation of mouse ESCs (Lin et al., 2007;Wang et al., 2018). This suggests that the histone-modifying activities of SAGA and ATAC have a more critical role during differentiation than for ESC self-renewal, consistent with the requirement of Gcn5 catalytic activity during mouse embryonic development (Bu et al., 2007;Xu et al., 2000;Yamauchi et al., 2000). Similarly, catalytic inactivation of the histone-modifying activities of TIP60 did not impair mouse ESC growth or self-renewal, but resulted in defects during mouse embryonic development (Acharya et al., 2017). ...
... Inactivation of Atac2, an ATAC-specific subunit, was shown to lead to defects in embryonic development at the post-gastrulation stage (Guelman et al., 2009). Similarly, inactivation of genes encoding catalytic subunits of SAGA, Gcn5, Pcaf, Atxn7l3 or Usp22 resulted in embryonic lethality at stages beyond gastrulation (Bu et al., 2007;Koutelou et al., 2019;Xu et al., 2000;Yamauchi et al., 2000;Wang et al., 2021). These phenotypes do not argue for a crucial role of SAGA or ATAC in the inner cell mass of the blastocyst, from which ESCs are derived. ...
SAGA (Spt-Ada-Gcn5 acetyltransferase) and ATAC (Ada-two-A-containing) are two related coactivator complexes, sharing the same histone acetyltransferase (HAT) subunit. The HAT activities of SAGA and ATAC are required for metazoan development, but the role of these complexes in RNA polymerase II transcription is less understood. To determine whether SAGA and ATAC have redundant or specific functions, we compare the effects of HAT inactivation in each complex with that of inactivation of either SAGA or ATAC core subunits in mouse embryonic stem cells (ESCs). We show that core subunits of SAGA or ATAC are required for complex assembly and mouse ESC growth and self-renewal. Surprisingly, depletion of HAT module subunits causes a global decrease in histone H3K9 acetylation, but does not result in significant phenotypic or transcriptional defects. Thus, our results indicate that SAGA and ATAC are differentially required for self-renewal of mouse ESCs by regulating transcription through different pathways in a HAT-independent manner.
... Thalamus and amygdala are among the top five tissues for expression of both GCN5 and PCAF. Correspondingly, GCN5, PCAF, as well as other SAGA members have critical developmental functions in the central nervous system (further discussed in the following section) [44,45]. ...
... SAGA members are involved in neural development of the central and peripheral nervous systems, and aberrations in a single component could lead to detrimental consequences. Mice with Gcn5-deficient neural stem and precursor cells have a microcephaly phenotype caused by reduction of brain mass, whereas mice homozygous for a catalytic-dead allele of Gcn5 are defective in cranial neural tube closure, resulting in exencephaly [44,91]. Although Pcaf null mice do not display developmental defects, they exhibit impaired memory and learning ability, as well as an overreactive emotional response to acute stress [45]. ...
The SAGA complex is an evolutionarily conserved transcriptional coactivator that regulates gene expression through its histone acetyltransferase and deubiquitylase activities, recognition of specific histone modifications, and interactions with transcription factors. Multiple lines of evidence indicate the existence of distinct variants of SAGA among organisms as well as within a species, permitting diverse functions to dynamically regulate cellular pathways. Our co-expression analysis of genes encoding human SAGA components showed enrichment in reproductive organs, brain tissues and the skeletal muscle, which corresponds to their established roles in developmental programs, emerging roles in neurodegenerative diseases, and understudied functions in specific cell types. SAGA subunits modulate growth, development and response to various stresses from yeast to plants and metazoans. In metazoans, SAGA further participates in the regulation of differentiation and maturation of both innate and adaptive immune cells, and is associated with initiation and progression of diseases including a broad range of cancers. The evolutionary conservation of SAGA highlights its indispensable role in eukaryotic life, thus deciphering the mechanisms of action of SAGA is key to understanding fundamental biological processes throughout evolution. To illuminate the diversity and conservation of this essential complex, here we discuss variations in composition, essentiality and co-expression of component genes, and its prominent functions across Fungi, Plantae and Animalia kingdoms.
... Transactivation of viral RNA synthesis of HIV [201] Malaria Plasmodium falciparum H3K9 acetylation Regulate antigenic variation and gametogenesis Antigenic variation and gametogenesis [202] Protective Cranial neural tube closure Mouse embryos p53 HAT-independent function Embryonic development and cranial neural tube closure [195] Continued over [198] transcriptional factor is abundantly present in these two cell lines which are directly linked with the granulopoiesis and leukemogenesis [174,175]. The E2A-PBX1, a fusion chimeric protein involved in leukemogenesis and oncogenesis has been reported to directly interact with GCN5. ...
... These findings suggest two contrary roles of GCN5 in apoptotic cell death. Its HAT-independent function is required for embryonic development and cranial neural tube closure in mice, and a decrease in its activity leads to defects in neural tube closure and exencephaly [195]. ...
General control non-depressible 5 (GCN5) or lysine acetyltransferase 2A (KAT2A) is one of the most highly studied histone acetyltransferases. It acts as both histone acetyltransferase (HAT) and lysine acetyltransferase (KAT). As an HAT it plays a pivotal role in the epigenetic landscape and chromatin modification. Besides, GCN5 regulates a wide range of biological events such as gene regulation, cellular proliferation, metabolism and inflammation. Imbalance in the GCN5 activity has been reported in many disorders such as cancer, metabolic disorders, autoimmune disorders and neurological disorders. Therefore, unravelling the role of GCN5 in different diseases progression is a prerequisite for both understanding and developing novel therapeutic agents of these diseases. In this review, we have discussed the structural features, the biological function of GCN5 and the mechanical link with the diseases associated with its imbalance. Moreover, the present GCN5 modulators and their limitations will be presented in a medicinal chemistry perspective.
... In mouse embryos, inactivation of the Atac2 subunit of ATAC was reported to lead to lethality around the gastrulation stage (Guelman et al., 2009). Loss of the catalytic HAT subunits, Gcn5 and Pcaf, shared by SAGA and ATAC were found to cause embryonic lethality in mice also around the gastrulation stage (Bu et al., 2007;Xu et al., 2000;Yamauchi et al., 2000). ...
... As earlier studies on Gcn5 -/-ESCs demonstrated a requirement of the HAT activities of SAGA and ATAC during differentiation of mouse ESCs (Lin et al., 2007;Wang et al., 2018), the histone modifying activities of ATAC and SAGA appear to have a more critical role during differentiation than for ESC self-renewal. This agrees with the requirement of Gcn5 catalytic activity during mouse embryonic development (Bu et al., 2007;Xu et al., 2000;Yamauchi et al., 2000). Similarly, catalytic inactivation of the histone modifying activities of TIP60 did not impair mouse ESC growth or self-renewal, but resulted in defects during mouse embryonic development (Acharya et al., 2017). ...
... Homozygous inactivation of Supt20h (also called p38IP) in mice was reported to cause severe gastrulation defects with abnormalities in mesoderm migration (Zohn et al., 2006). Similarly, inactivation of genes encoding catalytic subunits of SAGA, Gcn5, Pcaf or Usp22 resulted in embryonic lethality at stages beyond gastrulation (Bu et al., 2007;Koutelou et al., 2019;Xu et al., 2000;Yamauchi et al., 2000). ...
Recent studies from my host laboratory indicate that the histone modifying complex SAGA acts as a general cofactor for RNA polymerase II transcription in budding yeast in contrast to its previously assumed specific functions. SAGA is evolutionarily well conserved, from yeast to mammals, and has a histone acetyltransferase (HAT) function. In metazoans, the HAT activity of SAGA is shared with another complex, the ATAC complex. New approaches have allowed me to demonstrate that SAGA and ATAC have crucial roles in maintaining stemness of mouse embryonic stem cells. Newly synthesized RNA analyses revealed that inactivation of the SAGA and ATAC complexes influences the expression of different groups of genes and results in relatively distinct phenotypes in these cells. Finally, I was able to show that the transcriptional anomalies and the observed phenotypes do not seem to be linked to the HAT activity shared by these two complexes. Therefore, our data indicate that SAGA and ATAC have important, HAT-independent roles in mammalian cells.
... It remains to be seen whether the molecular functions of the bromodomain in vertebrates hold true to those in yeast. Gcn5 −/− mice have a more severe phenotype than Gcn5 hat/hat mice [15], indicating that GCN5 has functions outside of its HAT activity, and at least some of those functions may be mediated by the bromodomain. The GCN5/ PCAF bromodomain could provide a targetable domain in disease states, following the precedent of BET domain inhibitors used to combat specific human cancers. ...
... Analysis of the affected mesodermal tissues revealed elevated levels of apoptosis that could be responsible for the disappearance of these lineages [4]. Subsequent studies support this idea, as elimination of p53 in Gcn5 null mice prevented apoptosis and allowed embryos to survive until mid-gestation [15]. ...
... While the early embryonic lethality of Gcn5 null embryos [5,24] precludes the study of Gcn5 functions in later developmental processes, hypomorphic mutations that substantially lower Gcn5 expression or KAT function result in axial skeleton defects in lower thoracic regions, including rib fusions and homeotic transformations, along with spina bifida and exencephaly [15,25,26]. These rib fusions and homeotic transformations of lumbar L1 to thoracic T14 vertebrae are preceded by posterior shifts in the anterior boundary of Hoxc8 and Hoxc9 expression [25]. ...
A wealth of biochemical and cellular data, accumulated over several years by multiple groups, has provided a great degree of insight into the molecular mechanisms of actions of GCN5 and PCAF in gene activation. Studies of these lysine acetyltransferases (KATs) in vitro, in cultured cells, have revealed general mechanisms for their recruitment by sequence-specific binding factors and their molecular functions as transcriptional co-activators. Genetic studies indicate that GCN5 and PCAF are involved in multiple developmental processes in vertebrates, yet our understanding of their molecular functions in these contexts remains somewhat rudimentary. Understanding the functions of GCN5/PCAF in developmental processes provides clues to the roles of these KATs in disease states. Here we will review what is currently known about the developmental roles of GCN5 and PCAF, as well as emerging role of these KATs in oncogenesis.
... Out of 19 total embryos, we identified 3 embryos with the genotype Wnt1-Cre; Gcn5 hat/flox(neo) at the expected frequency (Supplemental Table 2). Wnt1-Cre; Gcn5 hat/flox(neo) embryos had a neural tube closure defect and a less severe craniofacial defect than Wnt1-Cre; Gcn5 Δ3−18/flox(neo) mutant embryos, which we expected as the HAT allele still generates full-length protein [6]. Gross observation of Wnt1-Cre; Gcn5 hat/flox(neo) embryos did not show obvious craniofacial defects nor cleft of the nasal prominence or the palatal shelves ( Figure 1F). ...
... GCN5 was first described in Tetrahymena and yeast as a histone acetyltransferase, participating in active transcription [37,38]. GCN5 has been shown to preferentially acetylate H3K9 [6,18] and acetylation of H3K9 on histone tails is considered an active transcription mark and is necessary for transcriptional machinery to access DNA during transcription [39]. Therefore, we hypothesized that GCN5 acetylates H3K9 at the Acan locus to turn on Acan expression during chondrocyte maturation. ...
... The results from mammalian studies yield discrepancies in the requirement for GCN5 to globally acetylate histones. For instance, in murine development, knock-out of GCN5 HAT activity does not cause a global loss of H3K9ac [5,6]. In fact, knock-out of both Gcn5 and Pcaf is required to globally ablate H3K9 acetylation [51]. ...
Development of the craniofacial structures requires the precise differentiation of cranial neural crest cells into osteoblasts or chondrocytes. Here, we explore the epigenetic and non-epigenetic mechanisms that are required for the development of craniofacial chondrocytes. We previously demonstrated that the acetyltransferase activity of the highly conserved acetyltransferase GCN5, or KAT2A, is required for murine craniofacial development. To further test the potential cell autonomous function, we hypothesize that GCN5 is required for chondrocyte development following the arrival of the cranial neural crest within the pharyngeal arches. Here, we show that Gcn5 is required cell autonomously in the cranial neural crest. Using a combination of in vivo and in vitro inhibition of GCN5 acetyltransferase activity, we demonstrate that GCN5 is a potent activator of chondrocyte maturation, acting to control chondrocyte maturation and size increase during pre-hypertrophic maturation to hypertrophic chondrocytes. Rather than acting as an epigenetic regulator of histone H3K9 acetylation, our findings suggest GCN5 primarily acts as a non-histone acetyltransferase to regulate chondrocyte development. Here, we investigate the contribution of GCN5 acetylation to the activity of the mTORC1 pathway. Our findings indicate that GCN5 acetylation is required for activation of this pathway, either via direct activation of mTORC1 or through indirect mechanisms. We also investigate one possibility of how mTORC1 activity is regulated through RAPTOR acetylation, which is hypothesized to enhance mTORC1 downstream phosphorylation. This study contributes to our understanding of the specificity of acetyltransferases, and the cell type specific roles in which these enzymes function.
