Project description:The Polycomb group proteins are repressive chromatin modifiers with essential roles in metazoan development, cellular differentiation and cell fate maintenance. How Polycomb proteins access active chromatin in order to confer transcriptional silencing during lineage transitions remains unclear. Here we show that the Polycomb Repressive Complex 2 (PRC2) component PHF19 binds the active chromatin mark H3K36me3 via its tudor domain. PHF19 associates with the H3K36me3 demethylase NO66, and is required to recruit the PRC2 complex and NO66 to stem cells genes during differentiation, leading to PRC2 mediated H3K27 tri-methylation, loss of H3K36me3 and transcriptional silencing. We propose a model whereby PHF19 functions during ES cell differentiation to transiently bind the H3K36me3 mark via its tudor domain, forming essential contact points that allow recruitment of PRC2 and H3K36me3 demethylase activity to active gene loci during their transition to a Polycomb-repressed state. Examination of PHF19 genome-wide binding in mouse embryonic stem cells
Project description:The Polycomb group proteins are repressive chromatin modifiers with essential roles in metazoan development, cellular differentiation and cell fate maintenance. How Polycomb proteins access active chromatin in order to confer transcriptional silencing during lineage transitions remains unclear. Here we show that the Polycomb Repressive Complex 2 (PRC2) component PHF19 binds the active chromatin mark H3K36me3 via its tudor domain. PHF19 associates with the H3K36me3 demethylase NO66, and is required to recruit the PRC2 complex and NO66 to stem cells genes during differentiation, leading to PRC2 mediated H3K27 tri-methylation, loss of H3K36me3 and transcriptional silencing. We propose a model whereby PHF19 functions during ES cell differentiation to transiently bind the H3K36me3 mark via its tudor domain, forming essential contact points that allow recruitment of PRC2 and H3K36me3 demethylase activity to active gene loci during their transition to a Polycomb-repressed state.
Project description:Polycomb repressive complexes (PRCs) play key roles in developmental epigenetic regulation. Yet the mechanisms that target PRCs to specific loci in mammalian cells remain incompletely understood. In this study, we show that Bmi1, a core component of Polycomb Repressive Complex 1 (PRC1), binds directly to the Runx1/CBFbeta transcription factor complex. Genome-wide studies in megakaryocytic cells demonstrate considerable chromatin occupancy overlap between the PRC1 core component Ring1b and Runx1/CBFbeta and functional regulation of a significant fraction of commonly bound genes. Bmi1/Ring1b and Runx1/CBFbeta deficiency generate partial phenocopies of one another in vivo. We also show that Ring1b occupies key Runx1 binding sites in primary murine thymocytes and that this occurs via Polycomb Repressive Complex 2 (PRC2) independent mechanisms. Genetic depletion of Runx1 results in reduced Ring1b binding at these sites in vivo. These findings provide evidence for site-specific PRC1 chromatin recruitment by core binding transcription factors in mammalian cells. ChIP-seq against Runx1, CBFb and Ring1b in L8057 cells (induced & uninduced with biological replicates) and thymocytes from control and Runx1 KO mice
Project description:Whether RNA G-quadruplexes (rG4) form extensively in vivo and what roles they play remain actively debated. Among their proposed functions is recognition of Polycomb repressive complex 2 (PRC2), but how the interaction results in epigenetic regulation is not understood. Here we demonstrate that rG4s form dynamically during ES cell differentiation and require ATRX’s helicase function to unwind competing secondary structures. Mutating ATRX causes rG4 depletion on a transcriptome-wide basis and dramatically increases gene expression. We identify and mutate rG4s within Xist RNA and mechanistically separate PRC2’s recruitment versus catalysis. Surprisingly, although rG4s recruit PRC2, unfolding the rG4 structure causes PRC2 hyperactivation, entrapment of PRC2 in the S1 chromosomal compartment, and loss of gene silencing. Thus, we link dynamic rG4 folding and unfolding to PRC2 recruitment, trans-compartmental Xist migration, regulated activation of PRC2, and whole-chromosome gene silencing.
Project description:Polycomb proteins assemble to form complexes with important roles in epigenetic regulation. The Polycomb Repressive Complex 2 (PRC2) modulates the di- and tri-methylation of lysine 27 on histone H3, each of which are associated with gene repression. Although three subunits, EZH1/2, SUZ12 and EED, form the catalytic core of PRC2, a wider group of proteins associate with low stoichiometry. This raises the question of whether dynamic variation of the PRC2 interactome results in alternative forms of the complex during differentiation. Here we compared the physical interactions of PRC2 in undifferentiated and differentiated states of NTERA2 pluripotent embryonic carcinoma cells. Label-free quantitative proteomics was used to assess endogenous immunoprecipitation of the EZH2 and SUZ12 subunits of PRC2. A high stringency dataset reflecting the endogenous state of PRC2 was produced that included all previously reported ‘core’ and ‘associated’ PRC2 components, and several novel interacting proteins. Comparison of the interactomes obtained in undifferentiated and differentiated cells revealed candidate proteins that favoured either one or other state. For example, SALL4 and ZNF281 associate with PRC2 in pluripotent cells, while PCL1 and SMAD3 more associate with PRC2 in differentiating cells. Analysis of the mRNA and protein levels of these factors found that their association with PRC2 correlated with their cell state-specific expression. Taken together, we propose that dynamic changes to the PRC2 interactome during differentiation may contribute to directing its activity during cell fate transitions.
Project description:Epithelial-to-mesenchymal transitions (EMT) underlie a loss of epithelial traits by normal cells during development and neoplastic cells during cancer metastasis. The long noncoding RNA HOTAIR triggers EMT, in part by serving as a scaffold for Polycomb Repressive Complex 2 (PRC2) and thus promoting repressive histone H3 Lys27 methylation. In addition to PRC2, HOTAIR interacts with the Lsd1 lysine demethylase, an epigenetic regulator of cell fate during development and differentiation. Here, we showed that HOTAIR requires the Lsd1-interacting domain, but not the PRC2-interacting domain, to promote migration of epithelial cells. Our results suggest that the HOTAIR-Lsd1 asociation redistributes Lsd1 on chromatin and hence reprograms the epithelial transcriptome.
Project description:An experiment was performed to map the global binding profile of EZH2 in human embryonic stem cells (hESCs). How the Polycomb Repressive Complex 2 (PRC2) is recruited to the DNA in hESC remains largely unknown. Previous studies on the transcription factor PRDM14 suggested that PRDM14 plays a repressive role in hESCs. Here, we mapped the global binding profile of EZH2 in hESC to investigate the association of PRDM14 binding with the PRC2 in hESCs. EZH2 binding is found to be enriched in PRDM14 binding sites. The PRC2 dependent repressive role of PRDM14 is further supported by the strong correlation of PRDM14 binding with the repressive histone modification H3K27me3.
Project description:The chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development. However, the mechanisms by which these complexes recognize their target sites and function together to form repressive chromatin domains remain poorly understood. Recruitment of PRC1 to target sites has been proposed to occur through a hierarchical process, dependent on the prior nucleation of PRC2 and placement of H3K27me3. Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to the recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain. Genetic ablation of catalytic subunit of the PRC1 complex (RINGA/B) and ChIP-seq analysis of PRC1 and PRC2 components confirmed genome-wide decreases in PRC2 occupancy and H3K27me3 levels at PRC target sites. This activity is restricted to variant PRC1 complexes and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for polycomb domain formation and normal development. Together these observations provide a surprising new PRC1-dependent logic for PRC2 occupancy and polycomb domain formation. RING1A-/-;RING1Bfl/fl ES cells were treated with 800M-BM-5M tamoxifen for 48hours and compared to untreated control cells by ChIP-seq for RING1B, SUZ12, EZH2 and H3K27me3.