Polycomb Repressive Complex 1 regulates transcription of active genes [ChIPseq]
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ABSTRACT:
ORGANISM(S): Drosophila melanogaster
PROVIDER: GSE100544 | GEO | 2017/06/28
SECONDARY ACCESSION(S): PRJNA392099
REPOSITORIES: GEO
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Project description:Polycomb repressive complex 1 (PRC1) and PRC2 are chromatin regulators maintaining transcriptional repression by depositing H2A mono-ubiquitination (H2Aub) or H3 lysine 27 tri-methylation (H3K27me3), respectively. While PRC1 is known to be required for transcriptional repression, the contribution of H2Aub in the Polycomb repressive system remains unclear in plants. Here, we directly test the requirement of H2Aub for gene repression in Marchantia polymorpha by generating point mutants in H2A that fail to be ubiquitinated by PRC1. These mutants show reduced H3K27me3 levels on the same target sites as mutants in PRC1 subunits MpBMI1 and the homolog MpBMI1L, revealing that PRC1-catalyzed H2Aub is essential for Polycomb system function. Furthermore, we demonstrate that H2Aub contributes to the PRC1-mediated silencing of genes and transposable elements. Together, our data provide evidence that H2Aub plays indispensable roles in the PRC1-initiated repressive system in Marchantia.
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Project description:Polycomb Group (PcG) proteins regulate gene expression through changes to chromatin structure and are essential for development. PcG proteins function together with the Trithorax Group (TrxG) proteins, which affect diverse steps in transcription activation. The PcG and TrxG are genetically and functionally antagonistic, and current understanding suggests a balance of their activities can maintain a wide range of transcription states. PcG and TrxG proteins assemble into a series of complexes. How these complexes work together, how PcG complexes are recruited to target genes, and whether other proteins are involved in their regulation of gene expression remain open questions. We carried out tandem affinity purification followed by mass spectrometry (TAP-MS) on two core components of Drosophila Polycomb Repressive Complex 1 (PRC1). Our data reveal a network of interactions among PcG complexes, and extensive co-purification of TrxG complexes with PRC1. We co-purified >50 transcription factors with PRC1 that were not previously linked to the PcG. Finally, we identify novel co-purifying complexes, including HP1c and PCNA handling complexes. Our resource of candidate PRC1 interacting proteins generate new hypotheses for PRC1 function.
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Project description:This study examines the role of Polycomb repressive complex 1 (PRC1) at active genes. The PRC1 and PRC2 complexes are crucial for epigenetic silencing during development of an organism. They are recruited to Polycomb response elements (PREs) and establish silenced domains over several kilobases. Recent studies show that PRC1 is also directly recruited to active genes by the cohesin complex. Cohesin participates broadly in control of gene transcription, but it is unknown whether cohesin-recruited PRC1 also plays a role in transcriptional control of active genes. We address this question using genome-wide RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq). The results show that PRC1 influences transcription of active genes, and a significant fraction of its effects are likely direct. The roles of different PRC1 subunits can also vary depending on the gene. Depletion of PRC1 subunits by RNA interference alters phosphorylation of RNA polymerase II (Pol II) and occupancy by the Spt5 pausing-elongation factor at most active genes. These effects on Pol II phosphorylation and Spt5 are likely linked to changes in elongation and RNA processing detected by nascent RNA-seq, although the mechanisms remain unresolved. The experiments also reveal that PRC1 facilitates association of Spt5 with enhancers and PREs. Reduced Spt5 levels at these regulatory sequences upon PRC1 depletion coincide with changes in Pol II occupancy and phosphorylation. Our findings indicate that, in addition to its repressive roles in epigenetic gene silencing, PRC1 broadly influences transcription of active genes and may suppress transcription of nonpromoter regulatory sequences.
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Project description:Polycomb repressive complex 2 (PRC2) catalyzes histone H3K27 trimethylation (H3K27me3), a hallmark of gene silencing. Here we report the crystal structures of an active PRC2 complex of 170 kilodaltons from the yeast Chaetomium thermophilum in both basal and stimulated states, which contain Ezh2, Eed, and the VEFS domain of Suz12 and are bound to a cancer-associated inhibiting H3K27M peptide and a S-adenosyl-l-homocysteine cofactor. The stimulated complex also contains an additional stimulating H3K27me3 peptide. Eed is engulfed by a belt-like structure of Ezh2, and Suz12(VEFS) contacts both of these two subunits to confer an unusual split active SET domain for catalysis. Comparison of PRC2 in the basal and stimulated states reveals a mobile Ezh2 motif that responds to stimulation to allosterically regulate the active site.
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Project description:Huntington's disease (HD) is caused by expansion of the polymorphic polyglutamine segment in the huntingtin protein. Full-length huntingtin is thought to be a predominant HEAT repeat alpha-solenoid, implying a role as a facilitator of macromolecular complexes. Here we have investigated huntingtin's domain structure and potential intersection with epigenetic silencer polycomb repressive complex 2 (PRC2), suggested by shared embryonic deficiency phenotypes. Analysis of a set of full-length recombinant huntingtins, with different polyglutamine regions, demonstrated dramatic conformational flexibility, with an accessible hinge separating two large alpha-helical domains. Moreover, embryos lacking huntingtin exhibited impaired PRC2 regulation of Hox gene expression, trophoblast giant cell differentiation, paternal X chromosome inactivation and histone H3K27 tri-methylation, while full-length endogenous nuclear huntingtin in wild-type embryoid bodies (EBs) was associated with PRC2 subunits and was detected with trimethylated histone H3K27 at Hoxb9. Supporting a direct stimulatory role, full-length recombinant huntingtin significantly increased the histone H3K27 tri-methylase activity of reconstituted PRC2 in vitro, and structure-function analysis demonstrated that the polyglutamine region augmented full-length huntingtin PRC2 stimulation, both in Hdh(Q111) EBs and in vitro, with reconstituted PRC2. Knowledge of full-length huntingtin's alpha-helical organization and role as a facilitator of the multi-subunit PRC2 complex provides a novel starting point for studying PRC2 regulation, implicates this chromatin repressive complex in a neurodegenerative disorder and sets the stage for further study of huntingtin's molecular function and the impact of its modulatory polyglutamine region.
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Project description:Polycomb repressive complexes (PRC) 1 and 2 are essential chromatin regulators of cell identity. PRC1, a dominant executer of Polycomb-mediated control, functions as multiple sub-complexes that possess catalytic-dependent H2AK119 mono-ubiquitination (H2AK119ub) and catalytic-independent activities. Here, we show that despite its well-established repressor functions, PRC1 binds to both silent and active genes. Through in vivo loss-of-function studies, we show that global PRC1 function is essential for skin development and stem cell (SC) specification.
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