title: GC-rich sequence elements recruit PRC2 in mammalian ES cells.
abstract: 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 Escherichia 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.
authors.affiliation: Howard Hughes Medical Institute and Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Mendenhall
authors.forename: Richard P
authors.initials: RP
authors.lastname: Koche
authors.forename: Thanh
authors.initials: T
authors.lastname: Truong
authors.forename: Vicky W
authors.initials: VW
authors.lastname: Zhou
authors.forename: Biju
authors.initials: B
authors.lastname: Issac
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Chi
authors.forename: Manching
authors.initials: M
authors.lastname: Ku
authors.forename: Bradley E
authors.initials: BE
authors.lastname: Bernstein
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D020862:GC Rich Sequence; D006801:Humans; D008322:Mammals / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D063146:Polycomb-Group Proteins; D012097:Repressor Proteins