title: Genome-wide mapping of Polycomb target genes unravels their roles in cell fate transitions.
abstract: The Polycomb group (PcG) proteins form chromatin-modifying complexes that are essential for embryonic development and stem cell renewal and are commonly deregulated in cancer. Here, we identify their target genes using genome-wide location analysis in human embryonic fibroblasts. We find that Polycomb-Repressive Complex 1 (PRC1), PRC2, and tri-methylated histone H3K27 co-occupy >1000 silenced genes with a strong functional bias for embryonic development and cell fate decisions. We functionally identify 40 genes derepressed in human embryonic fibroblasts depleted of the PRC2 components (EZH2, EED, SUZ12) and the PRC1 component, BMI-1. Interestingly, several markers of osteogenesis, adipogenesis, and chrondrogenesis are among these genes, consistent with the mesenchymal origin of fibroblasts. Using a neuronal model of differentiation, we delineate two different mechanisms for regulating PcG target genes. For genes activated during differentiation, PcGs are displaced. However, for genes repressed during differentiation, we paradoxically find that they are already bound by the PcGs in nondifferentiated cells despite being actively transcribed. Our results are consistent with the hypothesis that PcGs are part of a preprogrammed memory system established during embryogenesis marking certain key genes for repressive signals during subsequent developmental and differentiation processes.
authors.affiliation: Biotech Research and Innovation Centre (BRIC), 2100 Copenhagen Ø, Denmark.
authors.forename: Adrian P
authors.initials: AP
authors.lastname: Bracken
authors.forename: Nikolaj
authors.initials: N
authors.lastname: Dietrich
authors.forename: Diego
authors.initials: D
authors.lastname: Pasini
authors.forename: Klaus H
authors.initials: KH
authors.lastname: Hansen
authors.forename: Kristian
authors.initials: K
authors.lastname: Helin
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology; D000071221:Enhancer of Zeste Homolog 2 Protein; D005347:Fibroblasts / Q000378:metabolism*; D020869:Gene Expression Profiling; D020868:Gene Silencing; D015894:Genome, Human; D006801:Humans; D008745:Methylation; D009363:Neoplasm Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D063150:Polycomb Repressive Complex 1; D063151:Polycomb Repressive Complex 2; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013234:Stem Cells / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: C069077:BMI1 protein, human; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C491488:EED protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C430461:SUZ12 protein, human; D014157:Transcription Factors; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2; D063150:Polycomb Repressive Complex 1