Polycomb repressive complexes 1 and 2 are each essential for maintenance of X inactivation in extraembryonic lineages
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE168140 | GEO | 2022/10/12
REPOSITORIES: GEO
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Project description:During X-inactivation, Xist RNA spreads along an entire chromosome to establish silencing. However, the mechanism and functional RNA elements involved in spreading remain undefined. By performing a comprehensive endogenous Xist deletion screen, we identify Repeat B as crucial for spreading Xist and maintaining Polycomb repressive complexes 1 and 2 (PRC1/PRC2) along the inactive X (Xi). Unexpectedly, spreading of these three factors is inextricably linked. Deleting Repeat B or its direct binding partner, HNRNPK, compromises recruitment of PRC1 and PRC2. In turn, ablating PRC1 or PRC2 impairs Xist spreading. Therefore, Xist and Polycomb complexes require each other to propagate along the Xi, suggesting a positive feedback mechanism between RNA initiator and protein effectors. Perturbing Xist/Polycomb spreading causes failure of de novo Xi silencing, with partial compensatory downregulation of the active X, and also disrupts topological Xi reconfiguration. Thus, Repeat B is a multifunctional element that integrates interdependent Xist/ Polycomb spreading, silencing, and changes in chromosome architecture.
2019-03-01 | GSE107217 | GEO
Project description:X-chromosome inactivation (XCI) is a global silencing mechanism by which XX and XY mammals equalize X-linked gene dosages. XCI begins with an establishment phase during which Xist RNA spreads and induces de novo heterochromatinization across a female X chromosome, and is followed by a maintenance phase when multiple epigenetic pathways lock down the inactive X (Xi) state. Involvement of Polycomb repressive complexes 1 and 2 in XCI has been intensively studied, but with conflicting conclusions regarding their recruitment and role in Xi silencing. Here we reveal that establishment of XCI has two phases and reconcile the roles that Xist Repeats A and B play in gene silencing and Polycomb recruitment. Repeat A initiates both processes, whereas Repeat B bolsters or stabilizes them thereafter. Once established, XCI no longer requires Repeat A during maintenance. These findings integrate disparate studies and present a unified view of Xist?s role in Polycomb-mediated silencing.
2020-06-15 | GSE135389 | GEO
Project description:Polycomb group (PcG) proteins are highly conserved from flies to mammals and many of these factors have essential roles in early embryonic development. PcG proteins comprise two multimeric complexes, the Polycomb Repressive complexes 1 and 2 (PRC1 and 2), which have been shown to repress transcription through epigenetic modification of chromatin structure. To gain insight into the role of Polycomb in early development, we have identified PRC1 and PRC2 target genes in mouse embryonic stem (ES) cells using genome-scale location analysis. We found that PRC2 occupies many genes that encode key regulators of development including those encoding transcription factors and components of signaling pathways. These genes are repressed and contain nucleosomes methylated at lysine 27 on histone H3. The majority of PRC2 bound and methylated target genes are co-occupied by PRC1 indicating that these complexes function at a similar set of genes in ES cells. Lack of PRC1 or PRC2 subunits in ES cells results in derepression of target genes and loss of pluripotency. These results provide insight into how PcG proteins contribute to the maintenance of stem cell identity.
2006-05-09 | E-WMIT-12 | biostudies-arrayexpress
Project description:During development, transcriptional and chromatin modification changes co-occur but the order and causality of events often remain unclear. We explore the interrelationship of these processes using the paradigm of X-chromosome inactivation (XCI). We initiate XCI in female, mouse embryonic stem cells by inducing Xist expression and monitor changes in transcription and chromatin by allele-specific TT-seq and ChIP-seq respectively. An unprecedented temporal resolution enabled identification of the earliest chromatin alterations during XCI. We demonstrate that HDAC3 interacts with both NCOR1 and NCOR2 and is pre-bound on the X chromosome where it deacetylates histones to promote efficient gene silencing. We also reveal the choreography of polycomb accumulation following Xist RNA coating, with PRC1-associated H2AK119Ub preceding PRC2-associated H3K27me3. Furthermore, polycomb-associated marks accumulate initially at large, intergenic domains and then spreads into genes but only in the context of gene silencing. Our results provide the hierarchy of chromatin events during XCI and demonstrate that some chromatin changes play key roles in mediating transcriptional silencing.
2019-01-17 | PXD011344 | Pride
Project description:Polycomb Repressive Complexes 1 and 2 (PRC1, PRC2) are conserved epigenetic regulators that promote transcriptional silencing. PRC1 and PRC2 converge on shared targets, catalyzing repressive histone modifications. In addition, a subset of PRC1/PRC2 targets engage in long-range interactions whose functions in gene silencing are poorly understood. Using a CRISPR screen in mouse embryonic stem cells, we discovered that the cohesin regulator PDS5A links transcriptional silencing by Polycomb and 3D genome organization. PDS5A deletion impairs cohesin unloading and results in derepression of subset of endogenous PRC1/PRC2 target genes. Importantly, derepression is not associated with loss of repressive Polycomb chromatin modifications. Instead, loss of PDS5A leads to aberrant cohesin activity, ectopic insulation sites and specific reduction of ultra-long Polycomb loops. We infer that these loops are important for robust silencing at a subset of Polycomb target genes and that maintenance of cohesin-dependent genome architecture is critical for Polycomb regulation.
2023-11-10 | GSE194268 | GEO
Project description:Polycomb Repressive Complexes 1 and 2 (PRC1 and PRC2) are histone-modifying and -binding complexes that mediate the formation of facultative heterochromatin and are required for silencing of developmental genes and maintenance of cell fate. Multiple pathways of RNA decay work together to establish and maintain heterochromatin in fission yeast, including a recently identified role for a conserved RNA degradation complex called the rixosome or RIX1 complex. Whether RNA degradation also plays a role in the stability of mammalian heterochromatin remains unknown. Here we show that the rixosome contributes to silencing of many Polycomb targets in human cells. The rixosome associates with human PRC complexes and is enriched at promoters of Polycomb target genes. Importantly, depletion of either the rixosome or Polycomb results in accumulation of paused and elongating RNA polymerase at Polycomb-target genes. We identify point mutations in the RING1B subunit of PRC1 that disrupt the interaction between PRC1 and the rixosome and result in diminished silencing, suggesting that direct recruitment of the rixosome to chromatin is required for silencing. Finally, we show that the RNA kinase activity of the rixosome and the XRN2 exoribonuclease, which degrades RNAs with 5’ mono-phosphate groups generated by the rixosome, are required for silencing. Our findings suggest that rixosome-mediated degradation of nascent RNA is conserved from fission yeast to human, although in human cells the rixosome degrades RNA in facultative rather than constitutive heterochromatin.
2022-01-20 | PXD029403 | Pride
Project description:Polycomb Repressive Complexes 1 and 2 (PRC1 and PRC2) are histone-modifying and -binding complexes that mediate the formation of facultative heterochromatin and are required for silencing of developmental genes and maintenance of cell fate. Multiple pathways of RNA decay work together to establish and maintain heterochromatin in fission yeast, including a recently identified role for a conserved RNA degradation complex called the rixosome or RIX1 complex. Whether RNA degradation also plays a role in the stability of mammalian heterochromatin remains unknown. Here we show that the rixosome contributes to silencing of many Polycomb targets in human cells. The rixosome associates with human PRC complexes and is enriched at promoters of Polycomb target genes. Importantly, depletion of either the rixosome or Polycomb results in accumulation of paused and elongating RNA polymerase at Polycomb-target genes. We identify point mutations in the RING1B subunit of PRC1 that disrupt the interaction between PRC1 and the rixosome and result in diminished silencing, suggesting that direct recruitment of the rixosome to chromatin is required for silencing. Finally, we show that the RNA kinase activity of the rixosome and the XRN2 exoribonuclease, which degrades RNAs with 5’ mono-phosphate groups generated by the rixosome, are required for silencing. Our findings suggest that rixosome-mediated degradation of nascent RNA is conserved from fission yeast to human, although in human cells the rixosome degrades RNA in facultative rather than constitutive heterochromatin.
2022-01-19 | PXD027966 | Pride
Project description:The Xist long noncoding RNA (lncRNA) is essential for X-chromosome inactivation (XCI), the process by which mammals compensate for unequal numbers of sex chromosomes. During XCI, Xist coats the future inactive X (Xi) and recruits Polycomb Repressive Complex 2 (PRC2) to the X-inactivation center (Xic). Currently unclear is how Xist spreads silencing on a 150 Mb scale. Here we generate high-resolution maps of Xist binding across a developmental time course using CHART-seq. In female cells undergoing XCI de novo, Xist follows a two-step mechanism in which it initially targets gene-rich islands before spreading to intervening gene-poor domains. Xist is depleted from genes that escape XCI but frequently concentrates near escapee boundaries. Xist binding was linearly proportional to PRC2 density and H3 lysine 27 trimethylation (H3K27me3), suggesting co-migration of Xist and PRC2. Interestingly, when the Xi is acutely stripped of Xist in post-XCI cells, Xist recovers quickly within both gene-rich and -poor domains on a time scale of hours instead of days, suggesting a previously primed Xi chromatin state. We conclude that Xist spreading takes on distinct stage-specific forms: During initial establishment, Xist follows a two-step mechanism, but during maintenance, Xist spreads rapidly to both gene-rich and -poor regions. Capture hybridization analysis of RNA targets (CHART) and input samples of (differentiating) mouse embryonic stem (ES) cells and immortalized mouse embryonic fibroblasts (MEF) using paired-end 75 nt reads on Illumina HiSeq2500, with 2 replicates per sample (# of samples). RNA-seq of the same cell lines with 50 nt reads on Illumina HiSeq2000, with 2 replicates per sample (2 samples, 4 datasets total). CHIP-seq: Data from GSE36905 was aligned and processed as CHART-seq samples. Resulting coverage tracks (EZH2/K27me3) are linked directly to GSE48649 (bedGraphs linked below).
2013-11-04 | E-GEOD-48649 | biostudies-arrayexpress
Project description:The Xist long noncoding RNA (lncRNA) is essential for X-chromosome inactivation (XCI), the process by which mammals compensate for unequal numbers of sex chromosomes. During XCI, Xist coats the future inactive X (Xi) and recruits Polycomb Repressive Complex 2 (PRC2) to the X-inactivation center (Xic). Currently unclear is how Xist spreads silencing on a 150 Mb scale. Here we generate high-resolution maps of Xist binding across a developmental time course using CHART-seq. In female cells undergoing XCI de novo, Xist follows a two-step mechanism in which it initially targets gene-rich islands before spreading to intervening gene-poor domains. Xist is depleted from genes that escape XCI but frequently concentrates near escapee boundaries. Xist binding was linearly proportional to PRC2 density and H3 lysine 27 trimethylation (H3K27me3), suggesting co-migration of Xist and PRC2. Interestingly, when the Xi is acutely stripped of Xist in post-XCI cells, Xist recovers quickly within both gene-rich and -poor domains on a time scale of hours instead of days, suggesting a previously primed Xi chromatin state. We conclude that Xist spreading takes on distinct stage-specific forms: During initial establishment, Xist follows a two-step mechanism, but during maintenance, Xist spreads rapidly to both gene-rich and -poor regions.
2013-11-04 | GSE48649 | GEO
Project description:The established hierarchical model explaining co-occupancy of Polycomb repressor complexes 1 and 2 (PRC 1 and 2) at target loci proposes that the chromodomain of the polycomb protein, a core PRC1 subunit, recognises the H3K27me3 histone modification catalysed by PRC2. We used chromatin immunoprecipitation to analyse PRC1 occupancy at target loci in Eed-/- mouse embryonic stem cells (ESCs) that lack H3K27me3. Occupancy of the core PRC1 proteins Ring1B and Mel18 was strongly reduced, consistent with the hierarchical model. However, levels of H2A ubiquitylation (H2AK119u1), the histone modification catalysed by PRC1, were similar to wild-type cells, suggesting PRC1 recruitment is independent of H3K27me3. ChIP-sequencing analysis of Ring1B occupancy genome wide substantiated this conclusion, demonstrating significant Ring1B levels at polycomb target loci in Eed-/- ESCs. Thus PRC1 and PRC2 are recruited independently to sites that they co-occupy. We conclude that the primary function of H3K27me3 is to increase the residency of PRC1 at target loci and thereby to contribute to the stability of PRC1 mediated silencing. Examination of Ring1B binding in WT, Eed ko and Input of ESCs Examination of CBX7 in WT and Eed ko of ESCs
2011-11-30 | E-GEOD-23716 | biostudies-arrayexpress