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:Polycomb Repressive Complex 2 (PRC2) plays an essential role in development by catalysing trimethylation of histone H3 lysine 27 (H3K27me3), resulting in gene repression. PRC2 consists of two sub-complexes, PRC2.1 and PRC2.2, in which the PRC2 core associates with distinct ancillary subunits such as MTF2 and JARID2, respectively. Both MTF2, present in PRC2.1, and JARID2, present in PRC2.2, play a role in core PRC2 recruitment to target genes in mouse embryonic stem cells (mESCs). However, it remains unclear how these distinct sub-complexes cooperate to establish H3K27me3 domains. Here, we combine a range of Polycomb mutant mESCs with chemical inhibition of PRC2 catalytic activity, to systematically dissect their relative contributions to PRC2 binding to target loci. We find that PRC2.1 and PRC2.2 mediate two distinct paths for recruitment, with mutually reinforced binding. Part of the cross-talk between PRC2.1 and PRC2.2 occurs via their catalytic product H3K27me3, which is bound by the PRC2 core-subunit EED, thereby mediating a positive feedback. Strikingly, removal of either JARID2 or H3K27me3 only has a minor effect on PRC2 recruitment, whereas their combined ablation largely attenuates PRC2 recruitment. This strongly suggests an unexpected redundancy between JARID2 and EED-H3K27me3-mediated recruitment of PRC2. Furthermore, we demonstrate that all core PRC2 recruitment occurs through the combined action of MTF2-mediated recruitment of PRC2.1 to DNA and PRC1-mediated recruitment of JARID2-containing PRC2.2. Both axes of binding are supported by EED-H3K27me3 positive feedback, but to a different degree. Finally, we provide evidence that PRC1 and PRC2 mutually reinforce reciprocal binding. Together, these data disentangle the interdependent and cooperative interactions between Polycomb complexes that are important to establish Polycomb repression at target sites.
Project description:Polycomb Repressive Complex 2 (PRC2) plays an essential role in development by catalysing trimethylation of histone H3 lysine 27 (H3K27me3), resulting in gene repression. PRC2 consists of two sub-complexes, PRC2.1 and PRC2.2, in which the PRC2 core associates with distinct ancillary subunits such as MTF2 and JARID2, respectively. Both MTF2, present in PRC2.1, and JARID2, present in PRC2.2, play a role in core PRC2 recruitment to target genes in mouse embryonic stem cells (mESCs). However, it remains unclear how these distinct sub-complexes cooperate to establish H3K27me3 domains. Here, we combine a range of Polycomb mutant mESCs with chemical inhibition of PRC2 catalytic activity, to systematically dissect their relative contributions to PRC2 binding to target loci. We find that PRC2.1 and PRC2.2 mediate two distinct paths for recruitment, with mutually reinforced binding. Part of the cross-talk between PRC2.1 and PRC2.2 occurs via their catalytic product H3K27me3, which is bound by the PRC2 core-subunit EED, thereby mediating a positive feedback. Strikingly, removal of either JARID2 or H3K27me3 only has a minor effect on PRC2 recruitment, whereas their combined ablation largely attenuates PRC2 recruitment. This strongly suggests an unexpected redundancy between JARID2 and EED-H3K27me3-mediated recruitment of PRC2. Furthermore, we demonstrate that all core PRC2 recruitment occurs through the combined action of MTF2-mediated recruitment of PRC2.1 to DNA and PRC1-mediated recruitment of JARID2-containing PRC2.2. Both axes of binding are supported by EED-H3K27me3 positive feedback, but to a different degree. Finally, we provide evidence that PRC1 and PRC2 mutually reinforce reciprocal binding. Together, these data disentangle the interdependent and cooperative interactions between Polycomb complexes that are important to establish Polycomb repression at target sites.
Project description:While the core subunits of Polycomb group (PcG) complexes are well characterized, little is known about the dynamics of these protein complexes during cellular differentiation. We used quantitative interaction proteomics to study PcG proteins in mouse embryonic stem cells (mESCs) and neural progenitor cells (NPCs). We found the stoichiometry of PRC1 and PRC2 to be highly dynamic during neural differentiation.
Project description:Polycomb repression of gene expression is critical for development, with a pivotal role for trimethylation of lysine 27 of histone H3 (H3K27me3) deposited by Polycomb Repressive Complex 2 (PRC2). While the function and regulation of PRC2 have been extensively studied, the mechanism(s) by which it is recruited to specific genomic targets has remained largely elusive, in particular in vertebrates. Here we identify the PRC2-associated protein Mtf2 as a novel DNA methylation-sensitive PRC2 recruiter in mouse embryonic stem cells (mESCs). Mtf2 directly binds to DNA and is essential for recruitment of PRC2 both in vitro and in vivo. Genome-wide recruitment of the PRC2 catalytic subunit Ezh2 to genomic targets is drastically impaired in Mtf2 knock-out mESCs, resulting in largely reduced H3K27me3 deposition. Mtf2 selectively binds regions with high density of closely spaced unmethylated CpG-containing motifs with a locally unwound helical structure. This binding is dependent on one of the Mtf2 PHD domains, a protein domain shared among Pcl homologs, and an Mtf2-specific domain. The sequences bound by Mtf2 are enriched in PRC2-repressed CpG island-containing targets in zebrafish, Xenopus, mouse and human, suggesting that Mtf2-mediated PRC2 recruitment to unmethylated genomic regions is conserved among vertebrates.
Project description:The Polycomb repressive complexes PRC1 and PRC2 are key mediators of heritable gene silencing in multicellular organisms. Here we characterize AEBP2, a known PRC2 cofactor which, in vitro, has been shown to stimulate PRC2 activity. We show that AEBP2 localises specifically to PRC2 target loci, including the inactive X chromosome. Proteomic analysis confirms that AEBP2 associates exclusively with PRC2 complexes. However, analysis of embryos homozygous for a targeted mutation of Aebp2 unexpectedly revealed a Trithorax phenotype, normally linked to antagonism of Polycomb function. Consistent with this we observe elevated levels of PRC2 mediated histone H3K27 methylation at target loci in Aebp2 mutant embryonic stem cells. We further demonstrate that mutant ES cells assemble atypical hybrid PRC2 sub-complexes, potentially accounting for enhancement of Polycomb activity, and suggesting that AEBP2 normally plays a role in defining the mutually exclusive composition of PRC2 sub-complexes. H3K27me3, SUZ12, and AEBP2 ChIP-Seq in wild-type and AEBP2 KO mouse ESCs, biological replicates, pre-cleared chromatin as input, additionally FS2 ChIP-Seq in cells with FS2 tagged AEBP2, HiSeq2000