Polycomb complexes in skin epithelium development II
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ABSTRACT: Polycomb group (PcG) proteins are essential epigenetic transcriptional regulators. Traditionally, PcG proteins function as two multi-subunit complexes, Polycomb repressive complex 1 (PRC1) and PRC2, which largely overlap in their genomic binding and cooperate to establish repressive chromatin domains demarcated by H2AK119ub and H3K27me3. Here, using the developing skin epidermis as a paradigm, we uncovered a functional redundancy between Polycomb complexes in the repression of unwanted non-lineage genes.
Project description:Polycomb group (PcG) proteins are essential epigenetic transcriptional regulators. Traditionally, PcG proteins function as two multi-subunit complexes, Polycomb repressive complex 1 (PRC1) and PRC2, which largely overlap in their genomic binding and cooperate to establish repressive chromatin domains demarcated by H2AK119ub and H3K27me3. Here, using the developing skin epidermis as a paradigm, we uncovered a functional redundancy between Polycomb complexes in the repression of unwanted non-lineage genes.
Project description:Polycomb group (PcG) proteins are essential epigenetic transcriptional regulators. Traditionally, PcG proteins function as two multi-subunit complexes, Polycomb repressive complex 1 (PRC1) and PRC2, which largely overlap in their genomic binding and cooperate to establish repressive chromatin domains demarcated by H2AK119ub and H3K27me3. Here, using the developing skin epidermis as a paradigm, we uncovered a functional redundancy between Polycomb complexes in the repression of unwanted non-lineage genes.
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.
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:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
Project description:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
Project description:Polycomb repressive complexes-1 and -2 (PRC1 and 2), silence developmental genes in spatiotemporally regulated manner during metazoan embryogenesis. How PcG proteins contribute to down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role of a PCGF1 (Polycomb group RING finger protein 1)-containing variant PRC1 complex (PCGF1-PRC1) to facilitate induced down-regulation of a group of genes. Binding of PCGF1-PRC1 results in down-regulation of transcriptional activity, followed by Histone H2AK119 mono-ubiquitination (H2AK119ub1) and subsequent recruitment of PRC2, to initiate PcG-repressive domain formation. Based on these findings, we propose that PCGF1-PRC1 mediates establishment of PcG-repressive domains at target genes during differentiation.
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.
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.