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Centromere instability and micronuclei formation following fertilization of ATRX-deficient oocytes. (A) Transmission of aneuploidy from the oocyte to the pre-implantation embryo in chromosome spreads obtained from transgenic zygotes analyzed by CREST (green) immunochemistry. Upper panel: transgenic zygote spread with hypoploid karyotype (2N = 39); lower panel: hyperploid karyotype showing 41 chromosomes (micrographs of chromosome complements of this zygote were taken individually (white line) to display at a comparable magnification with the panel above). (B) Partial chromosome spreads from zygotes undergoing the first mitotic division. Chromosomes were immunostained with CREST (green) and subsequently subjected to fluorescence in situ hybridization using a pan-centromeric DNA probe (red). Transgenic zygotes frequently presented chromosomal breaks at pericentric heterochromatin as indicated by detachment of a chromosomal fragment exhibiting a CREST signal and presence of major satellite DNA (red) at the proximal as well as at the distal fragment (arrow, right inset). Note that satellite DNA sequences in some chromosomes exhibit excessive stretching (arrowhead). (C) High incidence (P<0.005) of illegitimate centromere mitotic recombination in transgenic parthenogenetic zygotes as indicated by changes in lateral asymmetry of major satellite sequences (arrow). A centromeric break within the same chromosome complement is marked by an arrowhead. (D) Proportion of zygotes that exhibit centromeric breaks at the first mitotic division. (E) Pan-centromeric FISH revealed that chromosomal instability in transgenic zygotes results in the formation of centromeric DNA-containing micronuclei (arrow, insets) in ATRX deficient 2-cell embryos. (F) Distribution of kinetochore domains in 2-cell stage embryos. CREST signals (green) are detectable at perinuleolar regions in the nuclei of control and transgenic embryos (arrowheads, insets). In contrast, micronuclei in transgenic 2-cell stage embryos are CREST-signal negative (arrow, inset), therefore originating from DNA fragmentation and subsequent missegregation of acentric chromosomal material. Scale bars = 10 µm.
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The α-thalassemia/mental retardation X-linked protein (ATRX) is a chromatin-remodeling factor known to regulate DNA methylation at repetitive sequences of the human genome. We have previously demonstrated that ATRX binds to pericentric heterochromatin domains in mouse oocytes at the metaphase II stage where it is involved in mediating chromosome al...
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... gain further insight into the potential mechanisms of aneuploidy, we analyzed in vitro fertilized zygotes during the first mitotic division by CREST immunochemistry (green). Transmis- sion of aneuploidy was clearly evident in transgenic zygotes as indicated by the presence of numerical chromosome abnormalities ( Figure 7A). Moreover, immuno-FISH experiments with CREST antiserum (green) and subsequent visualization of pericentric heterochromatin using a pan-centromeric DNA probe (red) revealed the presence of centromeric breaks ( Figure 7B lower panel, arrow and inset) in a high proportion of in vitro fertilized transgenic zygotes (41.2%; n = 105) compared to controls (6.6%; n = 100) (P,0.001; Figure 7-D). ...
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... sion of aneuploidy was clearly evident in transgenic zygotes as indicated by the presence of numerical chromosome abnormalities ( Figure 7A). Moreover, immuno-FISH experiments with CREST antiserum (green) and subsequent visualization of pericentric heterochromatin using a pan-centromeric DNA probe (red) revealed the presence of centromeric breaks ( Figure 7B lower panel, arrow and inset) in a high proportion of in vitro fertilized transgenic zygotes (41.2%; n = 105) compared to controls (6.6%; n = 100) (P,0.001; Figure 7-D). Moreover, we observed extensive stretching of centromeric heterochromatin domains in transgenic zygotes (Figure 7-B, lower panel, arrowhead), indicating that chromosome breaks and structural aberrations occur within constitutive heterochromatin. ...
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... immuno-FISH experiments with CREST antiserum (green) and subsequent visualization of pericentric heterochromatin using a pan-centromeric DNA probe (red) revealed the presence of centromeric breaks ( Figure 7B lower panel, arrow and inset) in a high proportion of in vitro fertilized transgenic zygotes (41.2%; n = 105) compared to controls (6.6%; n = 100) (P,0.001; Figure 7-D). Moreover, we observed extensive stretching of centromeric heterochromatin domains in transgenic zygotes (Figure 7-B, lower panel, arrowhead), indicating that chromosome breaks and structural aberrations occur within constitutive heterochromatin. ...
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... immuno-FISH experiments with CREST antiserum (green) and subsequent visualization of pericentric heterochromatin using a pan-centromeric DNA probe (red) revealed the presence of centromeric breaks ( Figure 7B lower panel, arrow and inset) in a high proportion of in vitro fertilized transgenic zygotes (41.2%; n = 105) compared to controls (6.6%; n = 100) (P,0.001; Figure 7-D). Moreover, we observed extensive stretching of centromeric heterochromatin domains in transgenic zygotes (Figure 7-B, lower panel, arrowhead), indicating that chromosome breaks and structural aberrations occur within constitutive heterochromatin. This notion was further substanti- ated by a significant increase in the incidence (44.7%; n = 65) of illegitimate recombination events within centromeric heterochro- matin in parthenogenetic ATRX-RNAi zygotes compared to controls (20.9%; ...
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... = 85), which was reflected by the presence of sister chromatid exchanges (red) during the first DNA replication cycle (P,0.005; Figure 7C, arrow). Interestingly, we also found evidence for the presence of centromeric breaks within the same chromosomal spreads (arrowhead), which might give rise to acentric chromosomal fragments and the formation of micronu- clei. ...
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... we also found evidence for the presence of centromeric breaks within the same chromosomal spreads (arrowhead), which might give rise to acentric chromosomal fragments and the formation of micronu- clei. Notably, compared to controls (5.6%; n = 90), a higher proportion of in vitro fertilized transgenic 2-cell embryos (39.6%; n = 102) exhibited micronuclei ( Figure 7E, lower panel, arrow and inset). Moreover, virtually all micronuclei observed at this stage contained major satellite DNA corresponding to pericentric heterochromatin (red) along with euchromatic chromosomal fragments ( Figure 7E). ...
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... compared to controls (5.6%; n = 90), a higher proportion of in vitro fertilized transgenic 2-cell embryos (39.6%; n = 102) exhibited micronuclei ( Figure 7E, lower panel, arrow and inset). Moreover, virtually all micronuclei observed at this stage contained major satellite DNA corresponding to pericentric heterochromatin (red) along with euchromatic chromosomal fragments ( Figure 7E). However, in contrast to blastomere nuclei (arrowheads, inset), kinetochore domains (CREST, green) were not detectable in micronuclei of transgenic 2-cell embryos (Figure 7-F, arrow, inset) demonstrating that most micronuclei originate from acentric chromosomal fragments rather than whole chromosomes. ...
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... virtually all micronuclei observed at this stage contained major satellite DNA corresponding to pericentric heterochromatin (red) along with euchromatic chromosomal fragments ( Figure 7E). However, in contrast to blastomere nuclei (arrowheads, inset), kinetochore domains (CREST, green) were not detectable in micronuclei of transgenic 2-cell embryos (Figure 7-F, arrow, inset) demonstrating that most micronuclei originate from acentric chromosomal fragments rather than whole chromosomes. These findings provide strong evidence that lack of ATRX results in the transmission of aneuploidy and the occurrence of centromeric breaks leading to a high incidence of structural and numerical chromosome aberrations in the pre- implantation embryo. ...
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Citations
... In contrast, the vast majority of studies in ATRX-deficient mouse cell lines or tissues such as the brain, mESCs, and oocytes showed that defects like DSBs at telomeres or loss of PH3 at pericentromeric heterochromatin occur across all chromosomes. 8,12,50 The reason is that the chromosomal sites, the telomeres and pericentromeric heterochromatin, where ATRX binds to and is important in these other tissues, are highly conserved in mouse chromosomes. 35 Therefore, loss of ATRX in these tissues will lead to chromosome-wide defects. ...
... 6,11 Moreover, in mouse oocytes, loss of ATRX leads to reduced phosphorylation of histone H3 at pericentromeric heterochromatin associated with incomplete chromosome condensation and centromeric breaks. 50 In Sertoli cells, we found that ATRX is expressed not only at the HP1a-positive pericentromeric heterochromatin as expected but also strongly at the HP1a-positive heterochromatin region at the GATA4 foci on Yp. Strikingly, this region is often in very close association with one of the chromocenters. ...
ATR-X (alpha thalassemia, mental retardation, X-linked) syndrome features genital and testicular abnormalities including atypical genitalia and small testes with few seminiferous tubules. Our mouse model recapitulated the testicular defects when Atrx was deleted in Sertoli cells (ScAtrxKO) which displayed G2/M arrest and apoptosis. Here, we investigated the mechanisms underlying these defects. In control mice, Sertoli cells contain a single novel “GATA4 PML nuclear body (NB)” that contained the transcription factor GATA4, ATRX, DAXX, HP1α, and PH3 and co-localized with the Y chromosome short arm (Yp). ScAtrxKO mice contain single giant GATA4 PML-NBs with frequent DNA double-strand breaks (DSBs) in G2/M-arrested apoptotic Sertoli cells. HP1α and PH3 were absent from giant GATA4 PML-NBs indicating a failure in heterochromatin formation and chromosome condensation. Our data suggest that ATRX protects a Yp region from DNA damage, thereby preventing Sertoli cell death. We discuss Y chromosome damage/decondensation as a mechanism for testicular failure.
... Available experimental data prove the importance of ATRX for the formation of a new organism. In particular, ATRX is required for the maintenance of chromosome stability during meiosis, since RNAi-derived ATRX-deficient mouse oocytes show abnormal chromosome morphology at the MII stage, as well as defects in chromosome segregation leading to aneuploidy [15,16]. In embryos, known epigenetic asymmetry of pericentric heterochromatin before the onset of the first cleavage division is largely conferred by an ATRX-dependent silencing of major satellite transcripts. ...
The chromatin-remodeling protein ATRX, which is currently recognized as one of the key genome caretakers, plays an important role in oogenesis and early embryogenesis in mammals. ATRX distribution in the nuclei of mouse embryos developing in vivo and in vitro, including when the embryos are arrested at the two-cell stage—the so-called two-cell block in vitro—was studied using immunofluorescent labeling and FISH. In normally developing two- and four-cell embryos, ATRX was found to be closely colocalized with pericentromeric DNA sequences detected with a probe to the mouse major satellite DNA. The association of ATRX with pericentromeric heterochromatin is mediated by nuclear actin and reduced after the treatment of embryos with latrunculin B. When culturing embryos in vitro, the distribution pattern of ATRX changes, leading to a decrease in the association of this protein with major satellite DNA especially under the two-cell block in vitro. Taken together, our data suggest that the intranuclear distribution of ATRX reflects the viability of mouse embryos and their probability of successful preimplantation development.
... The chromatin remodeling protein ATRX associates with highly condensed, DAPI-bright chromocenters in GV stage oocytes ( Supplementary Figures 2a-d) and is required for centromere stability in mouse oocytes 16,19 . SR-SIM analysis revealed that γ-irradiation results in a striking chromocenter decondensation after 24 h in oocytes that exhibit the NSN configuration, Notably, ATRX remained bound to decondensed chromocenter chromatin fibers in irradiated oocytes (Supplementary Figure 2e and Supplementary Figures 3a-c). ...
... in mouse oocytes 16,19,54,55 . However, ATRX remained associated with PCH fibers in irradiated oocytes suggesting that unfolding of major satellite DNA takes place in spite of ATRX localization. ...
... We analyzed chromatin dynamics in live oocytes, using recombinant Histone H2B-RFP and a TALEN vector specific for centromeric major satellite sequences. Briefly, GV stage oocytes were microinjected with capped mRNAs encoding fluorescently labeled histone H2B-fusion proteins (H2B-RFP, red) as well as transcription activator-like effector (TALE)-mClover transcripts against repetitive major satellite genomic sequences (green) following vitro transcription from plasmids pGEMHE-H2B-RFP (Euroscarf, cat# P30517) 63 and pTALYM3B15 (Addgene cat# 47878) 14,19 . In brief, 10 pl capped mRNA were microinjected into the cytoplasm of GV-intact oocytes in MEM medium containing 1 μg/ml milrinone using an electronic FemtoJet microinjector (Eppendorf) and Eppendorf micromanipulators on a Nikon Eclipse Ti-U inverted microscope. ...
The mechanisms leading to changes in mesoscale chromatin organization during cellular aging are unknown. Here, we used transcriptional activator-like effectors, RNA-seq and superresolution analysis to determine the effects of genotoxic stress on oocyte chromatin structure. Major satellites are organized into tightly packed globular structures that coalesce into chromocenters and dynamically associate with the nucleolus. Acute irradiation significantly enhanced chromocenter mobility in transcriptionally inactive oocytes. In transcriptionally active oocytes, irradiation induced a striking unfolding of satellite chromatin fibers and enhanced the expression of transcripts required for protection from oxidative stress (Fermt1, Smg1), recovery from DNA damage (Tlk2, Rad54l) and regulation of heterochromatin assembly (Zfp296, Ski-oncogene). Non-irradiated, senescent oocytes exhibit not only high chromocenter mobility and satellite distension but also a high frequency of extra chromosomal satellite DNA. Notably, analysis of biological aging using an oocyte-specific RNA clock revealed cellular communication, posttranslational protein modifications, chromatin and histone dynamics as the top cellular processes that are dysregulated in both senescent and irradiated oocytes. Our results indicate that unfolding of heterochromatin fibers following acute genotoxic stress or cellular aging induced the formation of distended satellites and that abnormal chromatin structure together with increased chromocenter mobility leads to chromosome instability in senescent oocytes.
... Chromosome spreads were prepared following chemical removal of the zona pellucida using Tyrode's solution (Sigma Aldrich). Zona free oocytes were placed on glass slides and lysed in a fixative solution of 1% PFA, 0.15% Triton X-100 before airdrying [5]. ...
... Time-lapse image acquisition was performed as previously described [29] following co-microinjection of a capped messenger RNA (cRNA) cocktail encoding PLK1-mCherry and MAP4-EGPF fusion proteins with or without MajSat-mers into the cytoplasm of fully grown prophase-I arrested (GV-stage) oocytes in order to visualize the PLK1 (red) and MTs (green), respectively. Capped mRNAs were synthesized from vectors pGEMHE-EGFP-MAP4 and pCS2-PLK1-mCherry (Addgene) using the mMESSAGE mMACHINE Kit (Thermo-Fisher) as previously described [5]. Following cRNA microinjection, the oocytes were cultured at 37°C overnight in MEM/BSA with 10 µM milrinone to allow recombinant protein expression during prophase-I arrest. ...
In somatic cells, mitotic transcription of major satellite non-coding RNAs is tightly regulated and essential for heterochromatin formation and the maintenance of genome integrity. We recently demonstrated that major satellite transcripts are expressed, and chromatin-bound during mouse oocyte meiosis. Pericentric satellite RNAs are also expressed in human oocytes. However, the specific biological function(s) during oocyte meiosis remain to be established. Here, we use validated locked nucleic acid gapmers for major satellite RNA depletion followed by live cell imaging, and superresolution analysis to determine the role of pericentric non-coding RNAs during female meiosis. Depletion of satellite RNA induces mesoscale changes in pericentric heterochromatin structure leading to chromosome instability, kinetochore attachment errors and abnormal chromosome alignment. Chromosome misalignment is associated with spindle defects, microtubule instability and, unexpectedly, loss of acentriolar microtubule organizing centre (aMTOC) tethering to spindle poles. Pericentrin fragmentation and failure to assemble ring-like aMTOCs with loss of associated polo-like kinase 1 provide critical insight into the mechanisms leading to impaired spindle pole integrity. Inhibition of transcription or RNA splicing phenocopies the chromosome alignment errors and spindle defects, suggesting that pericentric transcription during oocyte meiosis is required to regulate heterochromatin structure, chromosome segregation and maintenance of spindle organization.
... Moreover, human oocytes with a similar chromatin pattern show some ultrastructural signs of cytoplasmic degeneration [28]. It has been experimentally shown that chromatin remodeling defects in oogenesis also cause aneuploidies, leading to preand post-implantation developmental arrest, implantation disorders, and spontaneous abortions [29]. Such widely-used morphological and morphometric indicators as the state of the nucleoplasm, the position of the GV, the shape of the nuclear envelope, and the size of the oocyte are associated with chromatin condensation [30]-a potential marker of oocyte quality in IVM cycles. ...
... Nevertheless, we can assume that the condensation of chromatin around the atypical nucleolus and the formation of the karyosphere contribute to the spatial organization of meiotic chromosomes. Impaired formation of the karyosphere, including due to impaired expression of key heterochromatinization proteins, can lead to an increase in the frequency of errors in chromosome behavior during meiotic divisions and, as a result, to the formation of aneuploid oocytes/embryos, as shown, for example, for mice with impaired expression of chromatin remodeling protein ATRX [29]. ...
The search for simple morphological predictors of oocyte quality is an important task for assisted reproduction technologies (ARTs). One such predictor may be the morphology of the oocyte nucleus, called the germinal vesicle (GV), including the level of chromatin aggregation around the atypical nucleolus (ANu)—a peculiar nuclear organelle, formerly referred to as the nucleolus-like body. A prospective cohort study allowed distinguishing three classes of GV oocytes among 135 oocytes retrieved from 64 patients: with a non-surrounded ANu and rare chromatin blocks in the nucleoplasm (Class A), with a complete peri-ANu heterochromatic rim assembling all chromatin (Class C), and intermediate variants (Class B). Comparison of the chromatin state and the ability of oocytes to complete meiosis allowed us to conclude that Class B and C oocytes are more capable of resuming meiosis in vitro and completing the first meiotic division, while Class A oocytes can resume maturation but often stop their development either at metaphase I (MI arrest) or before the onset of GV breakdown (GVBD arrest). In addition, oocytes with a low chromatin condensation demonstrated a high level of aneuploidy during the resumption of meiosis. Considering that the degree of chromatin condensation/compaction can be determined in vivo under a light microscope, this characteristic of the GV can be considered a promising criterion for selecting the best-quality GV oocytes in IVM rescue programs.
... ATRX recruits DAXX to the pericentromeric regions during the NSN-SN transition, resulting in both proteins being predominantly concentrated in the ANu-associated heterochromatin compartment of SN oocytes [73,74]. The lack of ATRX leads, in particular, to centromere instability and aneuploidy in mouse embryos [75]. ...
In the oocyte nucleus, called the germinal vesicle (GV) at the prolonged diplotene stage of the meiotic prophase, chromatin undergoes a global rearrangement, which is often accompanied by the cessation of its transcriptional activity. In many mammals, including mice and humans, chromatin condenses around a special nuclear organelle called the atypical nucleolus or formerly nucleolus-like body. Chromatin configuration is an important indicator of the quality of GV oocytes and largely predicts their ability to resume meiosis and successful embryonic development. In mice, GV oocytes are traditionally divided into the NSN (non-surrounded nucleolus) and SN (surrounded nucleolus) based on the specific chromatin configuration. The NSN–SN transition is a key event in mouse oogenesis and the main prerequisite for the normal development of the embryo. As for humans, there is no single nomenclature for the chromatin configuration at the GV stage. This often leads to discrepancies and misunderstandings, the overcoming of which should expand the scope of the application of mouse oocytes as a model for developing new methods for assessing and improving the quality of human oocytes. As a first approximation and with a certain proviso, the mouse NSN/SN classification can be used for the primary characterization of human GV oocytes. The task of this review is to analyze and discuss the existing classifications of chromatin configuration in mouse and human GV oocytes with an emphasis on transcriptional activity extinction at the end of oocyte growth.
... ddm1 hira double mutants exhibited delayed growth phenotypes, but these were comparable to ddm1 siblings and were also viable ( Figure 2C). ATRX encodes a conserved Snf2-like remodeler specifically required for H3.3 deposition in heterochromatin just before mitosis [58][59][60][61][62] . By contrast with ddm1, double mutants between atrx and hira are inviable while atrx fas2 CAF1 double mutants are viable 62 and we found that atrx ddm1 double mutants were also fully viable ( Figure 2D). ...
... ; https://doi.org/10.1101/2023.07.11.548598 doi: bioRxiv preprint phase, but DDM1 was lost during mitosis when histone H3.3 accumulates instead ( Figure 6; Videos S1 and S2). The reverse is true for ATRX, which deposits H3.3 in heterochromatin in mammals [58][59][60][61] , and removes macroH2A 83 likely promoting heterochromatic transcription in G1 84 . In Arabidopsis, ATRX is also required for H3.3 deposition in heterochromatin 62,85 and may have a reciprocal function to DDM1 in mitosis (Graphical abstract). ...
Epigenetic inheritance refers to the faithful replication of DNA methylation and histone modification independent of DNA sequence. Nucleosomes block access to DNA methyltransferases, unless they are remodeled by DECREASE IN DNA METHYLATION1 (DDM1 Lsh/HELLS ), a Snf2-like master regulator of epigenetic inheritance. We show that DDM1 activity results in replacement of the transcriptional histone variant H3.3 for the replicative variant H3.1 during the cell cycle. In ddm1 mutants, DNA methylation can be restored by loss of the H3.3 chaperone HIRA, while the H3.1 chaperone CAF-1 becomes essential. The single-particle cryo-EM structure at 3.2 Å of DDM1 with a variant nucleosome reveals direct engagement at SHL2 with histone H3.3 at or near variant residues required for assembly, as well as with the deacetylated H4 tail. An N-terminal autoinhibitory domain binds H2A variants to allow remodeling, while a disulfide bond in the helicase domain is essential for activity in vivo and in vitro . We show that differential remodeling of H3 and H2A variants in vitro reflects preferential deposition in vivo . DDM1 co-localizes with H3.1 and H3.3 during the cell cycle, and with the DNA methyltransferase MET1 Dnmt1 . DDM1 localization to the chromosome is blocked by H4K16 acetylation, which accumulates at DDM1 targets in ddm1 mutants, as does the sperm cell specific H3.3 variant MGH3 in pollen, which acts as a placeholder nucleosome in the germline and contributes to epigenetic inheritance.
... Our previous work identified ATRX as a protein with a potential to phaseseparate (Guthmann et al. 2019). ATRX is required for heterochromatin integrity in oocytes, and a lack of ATRX in female gametes leads to chromosomal instability in preimplantation embryos (De La Fuente et al. 2004Baumann et al. 2010;Liu et al. 2020 Figure S8B. All statistical analyses were performed using the two-sided Mann-Whitney U-test. ...
... 3A, 4D) depend on weak hydrophobic interactions, and that ATRX is subsequently required for the morphological changes that lead to chromocenter formation. The lack of partitioning into smaller heterochromatin domains in the absence of ATRX that we observed is in line with the known defects in aneuploidy resulting from maternal depletion of ATRX (Baumann et al. 2010;De La Fuente et al. 2015). While all our observations are compatible with embryonic heterochromatin displaying condensate features, it is also likely that ATRX may contribute additional roles through its ability to bind and remodel chromatin (Xue et al. 2003;Eustermann et al. 2011;Iwase et al. 2011) by biochemical rather than biophysical means. ...
The majority of our genome is composed of repeated DNA sequences that assemble into heterochromatin, a highly compacted structure that constrains their mutational potential. How heterochromatin forms during development and how its structure is maintained are not fully understood. Here, we show that mouse heterochromatin phase-separates after fertilization, during the earliest stages of mammalian embryogenesis. Using high-resolution quantitative imaging and molecular biology approaches, we show that pericentromeric heterochromatin displays properties consistent with a liquid-like state at the two-cell stage, which change at the four-cell stage, when chromocenters mature and heterochromatin becomes silent. Disrupting the condensates results in altered transcript levels of pericentromeric heterochromatin, suggesting a functional role for phase separation in heterochromatin function. Thus, our work shows that mouse heterochromatin forms membrane-less compartments with biophysical properties that change during development and provides new insights into the self-organization of chromatin domains during mammalian embryogenesis.
... ATRX is required for chromosomal stability throughout both mitosis and meiosis. ATRX is necessary for centromere stabilization and epigenetic regulation of heterochromatin function throughout meiosis and the transition to the first mitosis [48]. During prophase I arrest, ATRX is necessary to bind the transcriptional regulator DAXX to pericentric heterochromatin. ...
Simple Summary
ATRX is one of the most frequently mutated tumor suppressor genes in human cancers. ATRX protein is a chromatin remodeler and transcriptional regulator that is essential for normal development. ATRX plays a crucial role in several essential cellular pathways, such as cooperating with DAXX to deposit histone variant H3.3 at repetitive regions, participating in chromatin remodeling, and responding to replication stress and DNA damage repair. ATRX mutations have been identified in several cancers and are considered important markers of clinical behavior, especially in glioma. The disruption of ATRX may contribute to cancer development and resistance to treatment. However, its role in tumorigenesis and the details of its mechanisms remain unclear. In this review, we will summarize the function of ATRX in normal biology and cancer and discuss the potential future direction of ATRX’s role in tumorigenesis. Understanding the functions of ATRX in cancers will help to develop more efficient and targeted anticancer therapies.
Abstract
The alpha-thalassemia mental retardation X-linked (ATRX) syndrome protein is a chromatin remodeling protein that primarily promotes the deposit of H3.3 histone variants in the telomere area. ATRX mutations not only cause ATRX syndrome but also influence development and promote cancer. The primary molecular characteristics of ATRX, including its molecular structures and normal and malignant biological roles, are reviewed in this article. We discuss the role of ATRX in its interactions with the histone variant H3.3, chromatin remodeling, DNA damage response, replication stress, and cancers, particularly gliomas, neuroblastomas, and pancreatic neuroendocrine tumors. ATRX is implicated in several important cellular processes and serves a crucial function in regulating gene expression and genomic integrity throughout embryogenesis. However, the nature of its involvement in the growth and development of cancer remains unknown. As mechanistic and molecular investigations on ATRX disclose its essential functions in cancer, customized therapies targeting ATRX will become accessible.
... Similar observations have been reported in fibroblast cell lines in which Brg1 deletion increased the appearance of micronuclei and aberrant mitosis [49] and using siRNA targeting Brg1 in HeLa cells, which resulted in mitotic abnormalities [50]. Interestingly, knockdown of ATRX in oocytes, another member of the SWI/SNF2 family, was associated with higher incidence of micronuclei and chromosome segregation defects during embryo development [51]. These data suggest that SWI/SNF complexes in granulosa cells are essential for controlled cell cycle and appear to support the proper acquisition of oocyte quality and capacity for embryonic development, although how granulosa cells convey that impairment to oocytes remains to be elucidated. ...
Mammalian folliculogenesis is a complex process that involves regulation of chromatin structure for gene expression and oocyte meiotic resumption. The SWI/SNF complex is a chromatin remodeler using either BRG1 or BRM (encoded by Smarca4 and Smarca2, respectively) as its catalytic subunit. SMARCA4 loss of expression is associated with a rare type of ovarian cancer; however, its function during folliculogenesis remains poorly understood. In this study, we describe the phenotype of BRG1 mutant mice to better understand its role in female fertility. Although no tumor emerged from BRG1 mutant mice, conditional depletion of Brg1 in the granulosa cells of Brg1fl/fl;Amhr2-Cre mice caused sterility, while conditional depletion of Brg1 in the oocytes of Brg1fl/fl;Gdf9-Cre mice resulted in subfertility. Recovery of cumulus-oocyte complexes after natural mating or superovulation showed no significant difference in the Brg1fl/fl;Amhr2-Cre mutant mice and significantly fewer oocytes in the Brg1fl/fl;Gdf9-Cre mutant mice compared to controls, which may account for the subfertility. Interestingly, the evaluation of oocyte developmental competence by in vitro culture of retrieved two-cell embryos indicated that oocytes originating from the Brg1fl/fl;Amhr2-Cre mice did not reach the blastocyst stage and had higher rates of mitotic defects, including micronuclei. Together, these results indicate that BRG1 plays an important role in female fertility by regulating granulosa and oocyte functions during follicle growth and is needed for the acquisition of oocyte developmental competence.
