Genome-wide profiling of PRC1 and PRC2 Polycomb chromatin binding in Drosophila
Ontology highlight
ABSTRACT: Polycomb group (PcG) proteins maintain transcriptional repression of developmentally important genes and have been implicated in cell proliferation and stem-cell self-renewal. We used a genome-wide approach to map binding patterns of PcG proteins (Pc, esc and Sce) in Drosophila Kc cells. We found that Pc associates with large genomic regions of up to ~150kb in size, hereafter referred to as “Pc-domains”. Sce and esc accompany Pc in most of these domains. PcG-bound chromatin is trimethylated at histone H3 lysine 27 and in general transcriptionally silent. Furthermore, PcG proteins preferentially bind to developmental genes. Many of these encode transcriptional regulators and key components of signal transduction pathways, including Wingless, Hedgehog, Notch and Delta. We also identify several new putative functions of PcG proteins, such as in steroid hormone biosynthesis. These results highlight the extensive involvement of PcG proteins in the coordination of development through the formation of large repressive chromatin domains. Keywords: DamID, Chromatin immunoprecipitation, ChIP-chip
Project description:Polycomb group (PcG) proteins maintain transcriptional repression of developmentally important genes and have been implicated in cell proliferation and stem-cell self-renewal. We used a genome-wide approach to map binding patterns of PcG proteins (Pc, esc and Sce) in Drosophila Kc cells. We found that Pc associates with large genomic regions of up to ~150kb in size, hereafter referred to as âPc-domainsâ. Sce and esc accompany Pc in most of these domains. PcG-bound chromatin is trimethylated at histone H3 lysine 27 and in general transcriptionally silent. Furthermore, PcG proteins preferentially bind to developmental genes. Many of these encode transcriptional regulators and key components of signal transduction pathways, including Wingless, Hedgehog, Notch and Delta. We also identify several new putative functions of PcG proteins, such as in steroid hormone biosynthesis. These results highlight the extensive involvement of PcG proteins in the coordination of development through the formation of large repressive chromatin domains. Keywords: DamID, Chromatin immunoprecipitation, ChIP-chip To study PcG binding profiles we used DamID, which is based on the ability of a chromatin protein fused to E.coli DNA adenine methyltransferase (Dam) to methylate the native binding site of the chromatin protein. Dam-fusion proteins are expressed at very low levels to avoid mistargeting. Subsequently, methylated DNA fragments are isolated, labeled and hybridized to a microarray. Methylated DNA fragments from cells transfected with Dam alone served as reference. Genomic binding sites of the protein can then be identified based on the targeted methylation pattern. For detailed background information on DamID, see: van Steensel, B., Delrow, J. & Henikoff, S. Chromatin profiling using targeted DNA adenine methyltransferase. Nat Genet 27, 304-8 (2001); van Steensel, B. & Henikoff, S. Identification of in vivo DNA targets of chromatin proteins using tethered dam methyltransferase. Nat Biotechnol 18, 424-8 (2000).
Project description:We determined the distribution of three PcG proteins: PC, PSC and E(Z), and of histone H3 trimethylated at Lys 27 by chromatin immunoprecipitation (ChIP) coupled with analysis of immunoprecipitated DNA with a high density genomic tiling microarray (Affymetrix).
Project description:Epigenetic silencing by Polycomb group (PcG) complexes can promote epithelial-mesenchymal transition (EMT) and stemness and is associated with malignancy of solid cancers. Here we report a role for Drosophila PcG repression in a partial EMT event that occurs during wing disc eversion, an early event during metamorphosis. In a screen for EMT genes required for eversion we identified the PcG genes Sex combs extra (Sce) and Sex combs midleg (Scm). Depletion of Sce or Scm resulted in internalised wings and thoracic clefts, and loss of Sce inhibited the EMT of the peripodial epithelium and basement membrane breakdown, ex vivo. Targeted DamID (TaDa) using Dam-Pol II showed that Sce knockdown caused a genomic transcriptional response consistent with maintenance of an epithelial fate. Surprisingly only 17 genes were significantly upregulated in Sce-depleted cells, including Abd-B, abd-A, caudal, and nubbin. Each of these loci were enriched for Dam-Pc binding. Of the four genes, only Abd-B was robustly upregulated in cells lacking Sce expression. RNAi knockdown of all four genes could partly suppress the Sce RNAi eversion phenotype, though Abd-B had the strongest effect. Our results suggest that in the absence of continued PcG repression peripodial cells express genes such as Abd-B which regulate epithelial state and thereby disrupt eversion. Our results emphasise the important role that PcG suppression can play in maintaining cell states required for morphogenetic events throughout development and suggest that PcG repression of Hox genes may affect epithelial traits that could contribute to metastasis.
Project description:Epigenetic silencing by Polycomb group (PcG) complexes can promote epithelial-mesenchymal transition (EMT) and stemness and is associated with malignancy of solid cancers. Here we report a role for Drosophila PcG repression in a partial EMT event that occurs during wing disc eversion, an early event during metamorphosis. In a screen for EMT genes required for eversion we identified the PcG genes Sex combs extra (Sce) and Sex combs midleg (Scm). Depletion of Sce or Scm resulted in internalised wings and thoracic clefts, and loss of Sce inhibited the EMT of the peripodial epithelium and basement membrane breakdown, ex vivo. Targeted DamID (TaDa) using Dam-Pol II showed that Sce knockdown caused a genomic transcriptional response consistent with maintenance of an epithelial fate. Surprisingly only 17 genes were significantly upregulated in Sce-depleted cells, including Abd-B, abd-A, caudal, and nubbin. Each of these loci were enriched for Dam-Pc binding. Of the four genes, only Abd-B was robustly upregulated in cells lacking Sce expression. RNAi knockdown of all four genes could partly suppress the Sce RNAi eversion phenotype, though Abd-B had the strongest effect. Our results suggest that in the absence of continued PcG repression peripodial cells express genes such as Abd-B which regulate epithelial state and thereby disrupt eversion. Our results emphasise the important role that PcG suppression can play in maintaining cell states required for morphogenetic events throughout development and suggest that PcG repression of Hox genes may affect epithelial traits that could contribute to metastasis.
Project description:Polycomb group (PcG) proteins dynamically define cellular identities through epigenetic repression of key developmental genes. PcG target gene repression can be stabilized through the interaction in the nucleus at PcG foci. Here, we report the results of a high-resolution microscopy genome-wide RNAi screen that identifies 129 genes that regulate the nuclear organization of Pc foci. Candidate genes include PcG components and chromatin factors, as well as many novel protein-modifying enzymes, including components of the SUMOylation pathway. In the absence of SUMO Pc foci coagulate into larger aggregates. Conversely, loss of function of the SUMO peptidase velo disperses Pc foci. Moreover, SUMO and velo colocalize with PcG proteins at PREs and Pc SUMOylation affects its chromatin targeting, suggesting that the dynamic regulation of Pc SUMOylation regulates PcG-mediated silencing by modulating the kinetics of Pc binding to chromatin as well as its ability to form Polycomb foci. ChIP-Seq mapping of Polycomb (PC), SUMO and Velo on Drosophila Melanogaster
Project description:Polycomb group (PcG) proteins dynamically define cellular identities through epigenetic repression of key developmental genes. PcG target gene repression can be stabilized through the interaction in the nucleus at PcG foci. Here, we report the results of a high-resolution microscopy genome-wide RNAi screen that identifies 129 genes that regulate the nuclear organization of Pc foci. Candidate genes include PcG components and chromatin factors, as well as many novel protein-modifying enzymes, including components of the SUMOylation pathway. In the absence of SUMO Pc foci coagulate into larger aggregates. Conversely, loss of function of the SUMO peptidase velo disperses Pc foci. Moreover, SUMO and velo colocalize with PcG proteins at PREs and Pc SUMOylation affects its chromatin targeting, suggesting that the dynamic regulation of Pc SUMOylation regulates PcG-mediated silencing by modulating the kinetics of Pc binding to chromatin as well as its ability to form Polycomb foci.
Project description:Drosophila Polycomb group (PcG) and Trithorax group (TrxG) proteins are responsible for the maintenance of stable transcription patterns of many developmental regulators, such as the homeotic genes. We have used a ChIP-on- Chip approach to map the distribution of several PcG/TrxG proteins as well as histone modifications across the two homeotic complexes ANT-C and BX-C. Our data indicate the colocalization of the Polycomb repressive complex 1 (PRC1) with Trx and the DNA binding protein Pleiohomeotic (Pho) at discrete sequence elements as well as significant chromatin assembly differences in active and inactive regions. Trx binds to the promoters of active genes and noncoding transcripts. Most strikingly, in the active state Pho covers extended chromatin domains over many kilobases. The histone modifications investigated, seem to be mutually exclusive, with histone H3 trimethylated at lysine 27 covering inactive chromatin domains whereas hyperacetylated histone H4 is present only at active genes. Keywords: ChIP-chip, cell line comparison
Project description:To understand how actions of the chromatin-remodeler BRAHMA (BRM) and Polycomb Group (PcG) proteins are coordinated during plant development, we performed a genome-wide profiling of trimethylated histone H3 lysine 27 (H3K27me3) in brm mutant seedlings by chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq). Increased H3K27me3 deposition at several hundred genes was observed in brm mutants and this increase was partially supressed upon removal of the CURLING LEAF (CLF) H3K27me3 methyltransferase. ChIP experiments demonstrated that BRM directly binds to a subset of genes and prevents the inappropriate association of PcG proteins at some of the loci. Together, these results indicate a crucial role of BRM in restricting the inappropriate activity of PcG protein complexes during plant development.
Project description:We made Polycomb (PC) and histone H3 lysine 27 trimethylation (H3K27me3) chromatin binding maps in central brain tissue from 3rd instar larvae, allowing us to make a direct comparison to our 4C data (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE23166). Our results demonstrate that our PC and H3K27me3 maps are highly similar, and fit with previously identified hallmarks of PcG-bound chromatin, namely: PC and H3K27me3 co-occur in the genome as large contiguous domains that largely repress transcription of the underlying genes, which encode important regulators of development. Keywords: Genome binding/occupancy profiling by genome tiling array DamID experiments for Polycomb were performed in Drosophila larval brain tissue. Samples were hybridized to 380k NimbleGen arrays with 300 bp probe spacing.
Project description:We made Polycomb (PC) and histone H3 lysine 27 trimethylation (H3K27me3) chromatin binding maps in central brain tissue from 3rd instar larvae, allowing us to make a direct comparison to our 4C data (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE23166). Our results demonstrate that our PC and H3K27me3 maps are highly similar, and fit with previously identified hallmarks of PcG-bound chromatin, namely: PC and H3K27me3 co-occur in the genome as large contiguous domains that largely repress transcription of the underlying genes, which encode important regulators of development. Keywords: Genome binding/occupancy profiling by genome tiling array ChIP-chip experiments for H3K27me3 were performed in Drosophila larval brain tissue. Samples were hybridized to 380k NimbleGen arrays with 300 bp probe spacing.