Project description:Polycomb proteins are epigenetic regulators that localize to developmental loci in the early embryo where they mediate lineage-specific gene repression. In Drosophila, these repressors are recruited to sequence elements by DNA binding proteins associated with Polycomb repressive complex 2 (PRC2). However, the sequences that recruit PRC2 in mammalian cells have remained obscure. To address this, we integrated a series of engineered bacterial artificial chromosomes into embryonic stem (ES) cells and examined their chromatin. We found that a 44 kb region corresponding to the Zfpm2 locus initiates de novo recruitment of PRC2. We then pinpointed a CpG island within this locus as both necessary and sufficient for PRC2 recruitment. Based on this causal demonstration and prior genomic analyses, we hypothesized that large GC-rich elements depleted of activating transcription factor motifs mediate PRC2 recruitment in mammals. We validated this model in two ways. First, we showed that a constitutively active CpG island is able to recruit PRC2 after excision of a cluster of activating motifs. Second, we showed that two 1 kb sequence intervals from the E. coli genome with GC-contents comparable to a mammalian CpG island are both capable of recruiting PRC2 when integrated into the ES cell genome. Our findings demonstrate a causal role for GC-rich sequences in PRC2 recruitment and implicate a specific subset of CpG islands depleted of activating motifs as instrumental for the initial localization of this key regulator in mammalian genomes. Analysis of YY1 binding in two cell types
Project description:Polycomb proteins are epigenetic regulators that localize to developmental loci in the early embryo where they mediate lineage-specific gene repression. In Drosophila, these repressors are recruited to sequence elements by DNA binding proteins associated with Polycomb repressive complex 2 (PRC2). However, the sequences that recruit PRC2 in mammalian cells have remained obscure. To address this, we integrated a series of engineered bacterial artificial chromosomes into embryonic stem (ES) cells and examined their chromatin. We found that a 44 kb region corresponding to the Zfpm2 locus initiates de novo recruitment of PRC2. We then pinpointed a CpG island within this locus as both necessary and sufficient for PRC2 recruitment. Based on this causal demonstration and prior genomic analyses, we hypothesized that large GC-rich elements depleted of activating transcription factor motifs mediate PRC2 recruitment in mammals. We validated this model in two ways. First, we showed that a constitutively active CpG island is able to recruit PRC2 after excision of a cluster of activating motifs. Second, we showed that two 1 kb sequence intervals from the E. coli genome with GC-contents comparable to a mammalian CpG island are both capable of recruiting PRC2 when integrated into the ES cell genome. Our findings demonstrate a causal role for GC-rich sequences in PRC2 recruitment and implicate a specific subset of CpG islands depleted of activating motifs as instrumental for the initial localization of this key regulator in mammalian genomes.
Project description:ABSTRACT Polycomb group (PcG) proteins are essential for the repression of key developmental regulators during development. In Drosophila, the polycomb repressive complexes (PRC) associate with defined DNA sequences termed polycomb response elements (PREs). In mammals, however, the mechanisms underlying polycomb recruitment at targeted loci are poorly understood. We have used an in vivo approach to try and map DNA sequences of importance for the proper recruitment of polycomb proteins within the genetically well-characterized HoxD genomic locus. Here, we report that relatively small polycomb interacting sequences appear necessary and sufficient to confer polycomb recognition and targeting to ectopic loci. These elements synergize, when clustered together, to form a fully functional repressive domain. In addition, a high GC content, while not sufficient to recruit PRC2, may help its local spreading. We discuss the importance of PRC2 recruitment over Hox gene clusters, in embryonic stem cells, for their subsequent coordinated transcriptional activation during development. ChIP-chip using K27 antibodies
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:CpG islands (CGIs) are key DNA regulatory elements in the vertebrate genome and are often found at gene promoters. In mammalian embryonic stem (ES) cells, CGIs are decorated by either the active or repressive histone marks, H3K4me3 and H3K27me3, respectively, or by both modifications (‘bivalent domains’), but their precise regulation is incompletely understood. Remarkably, we find that the polycomb repressive complex 2 (PRC2)-associated protein C17orf96 (a.k.a. esPRC2p48 and E130012A19Rik) is present at most CGIs in mouse ES cells. At PRC2-rich CGIs, loss of C17orf96 results in an increased chromatin binding of Suz12 and elevated H3K27me3 levels concomitant with gene repression. In contrast, at PRC2-poor CGIs, located at actively transcribed genes, C17orf96 colocalizes with RNA polymerase II and its depletion leads to a focusing of H3K4me3 in the core of CGIs. Our findings thus identify C17orf96 as a novel context-dependent CGI regulator. ChIP-seq of C17orf96, H3K4me3 and H3K27me3 in mouse ES cells (E14).
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:ABSTRACT Polycomb group (PcG) proteins are essential for the repression of key developmental regulators during development. In Drosophila, the polycomb repressive complexes (PRC) associate with defined DNA sequences termed polycomb response elements (PREs). In mammals, however, the mechanisms underlying polycomb recruitment at targeted loci are poorly understood. We have used an in vivo approach to try and map DNA sequences of importance for the proper recruitment of polycomb proteins within the genetically well-characterized HoxD genomic locus. Here, we report that relatively small polycomb interacting sequences appear necessary and sufficient to confer polycomb recognition and targeting to ectopic loci. These elements synergize, when clustered together, to form a fully functional repressive domain. In addition, a high GC content, while not sufficient to recruit PRC2, may help its local spreading. We discuss the importance of PRC2 recruitment over Hox gene clusters, in embryonic stem cells, for their subsequent coordinated transcriptional activation during development.
Project description:Polycomb complexes establish chromatin modifications for maintaining gene repression and are essential for embryonic development in mice. Here we use pluripotent embryonic stem (ES) cells to demonstrate an unexpected redundancy between Polycomb repressive complex 1 (PRC1) and PRC2 during the formation of differentiated cells. ES cells lacking the function of either PRC1 or PRC2 can differentiate into cells of the three germ layers, whereas simultaneous loss of PRC1 and PRC2 abrogates differentiation. On the molecular level the differentiation defect is caused by the derepression of a set of genes that is redundantly repressed by PRC1 and PRC2 in ES cells. Furthermore, we find that genomic repeats are Polycomb targets and show that in the absence of Polycomb complexes endogenous MLV elements can mobilize. This indicates a contribution of the PcG system to the defense against parasitic DNA and a potential role of genomic repeats in Polycomb mediated gene regulation. RNA from wt and PcG mutant ES cells was extracted using Trizol and hybridized to an Affymetrix Mouse 430_2.0 chip. Labeling, hybridization and primary data analysis were performed by a commercial provider (Atlas Biolabs, Berlin). Before RNA extraction, the undifferentiated ES cell state was confirmed by colony morphology. All genotypes were hybridized in biological triplicates.
Project description:Polycomb complexes establish chromatin modifications for maintaining gene repression and are essential for embryonic development in mice. Here we use pluripotent embryonic stem (ES) cells to demonstrate an unexpected redundancy between Polycomb repressive complex 1 (PRC1) and PRC2 during the formation of differentiated cells. ES cells lacking the function of either PRC1 or PRC2 can differentiate into cells of the three germ layers, whereas simultaneous loss of PRC1 and PRC2 abrogates differentiation. On the molecular level the differentiation defect is caused by the derepression of a set of genes that is redundantly repressed by PRC1 and PRC2 in ES cells. Furthermore, we find that genomic repeats are Polycomb targets and show that in the absence of Polycomb complexes endogenous MLV elements can mobilize. This indicates a contribution of the PcG system to the defense against parasitic DNA and a potential role of genomic repeats in Polycomb mediated gene regulation.
Project description:CpG islands (CGIs) are key DNA regulatory elements in the vertebrate genome and are often found at gene promoters. In mammalian embryonic stem (ES) cells, CGIs are decorated by either the active or repressive histone marks, H3K4me3 and H3K27me3, respectively, or by both modifications (‘bivalent domains’), but their precise regulation is incompletely understood. Remarkably, we find that the polycomb repressive complex 2 (PRC2)-associated protein C17orf96 (a.k.a. esPRC2p48 and E130012A19Rik) is present at most CGIs in mouse ES cells. At PRC2-rich CGIs, loss of C17orf96 results in an increased chromatin binding of Suz12 and elevated H3K27me3 levels concomitant with gene repression. In contrast, at PRC2-poor CGIs, located at actively transcribed genes, C17orf96 colocalizes with RNA polymerase II and its depletion leads to a focusing of H3K4me3 in the core of CGIs. Our findings thus identify C17orf96 as a novel context-dependent CGI regulator.