Article

GC-rich sequence elements recruit PRC2 in mammalian ES cells. PLoS Genet 6:e1001244

Howard Hughes Medical Institute and Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS Genetics (Impact Factor: 7.53). 12/2010; 6(12):e1001244. DOI: 10.1371/journal.pgen.1001244
Source: PubMed

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.

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    • "This indicates that TFs might form a link between specific DNA sequences and the histone modifiers (Benveniste et al. 2014). Conversely, deletion of motifs for transcription activators from NMIs was found to be sufficient for PRC2 recruitment and H3K27me3 deposition in ESCs (Mendenhall et al. 2010). Minimal DNA sequence elements capable of autonomously recruiting PRC2 were recently defined by using iterative genome editing in mouse ESCs. "
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    ABSTRACT: Polycomb group (PcG) proteins are key regulators in establishing a transcriptional repressive state. Polycomb Repressive Complex 2 (PRC2), one of the two major PcG protein complexes, is essential for proper differentiation and maintenance of cellular identity. Multiple factors are involved in recruiting PRC2 to its genomic targets. In this review we will discuss the role of DNA sequence, transcription factors, pre-existing histone modifications, and RNA in guiding PRC2 towards specific genomic loci. The DNA sequence itself influences the DNA methylation state, which is an important determinant of PRC2 recruitment. Other histone modifications are also important for PRC2 binding as PRC2 can respond to different cellular states via crosstalk between histone modifications. Additionally, PRC2 might be able to sense the transcriptional status of genes by binding to nascent RNA, which could also guide the complex to chromatin. In this review we will discuss how all these molecular aspects define a local chromatin state which controls accurate, cell-type specific epigenetic silencing by PRC2. Copyright © 2015. Published by Elsevier Ltd.
    Full-text · Article · May 2015 · The international journal of biochemistry & cell biology
    • "This has been further refined by the finding that sequences with a high content of CpG dinucleotides (CpG islands—CGIs) seem to play an important role in recruiting PcG complexes in mammals. Mammalian CGIs are often enriched for PRC2 binding and H3K27me3 (Tanay et al. 2007; Ku et al. 2008), and artificial chromosome constructs containing CpG islands introduced into the mouse genome can recruit PRC2 components (Mendenhall et al. 2010). These interactions seem to depend on the DNA methylation state of the CpG-rich region (methylated CGIs do not recruit PRC2) and are inhibited by bound transcriptional activators (Simon and Kingston 2013). "
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    ABSTRACT: Lineage-specific phenotypes are the result of characteristic cellular gene expression patterns. Several epigenetic mechanisms have evolved that control the generation of these different phenotypes from the same genotype. Stem cells, in order to prevent differentiation, need to repress lineage-specific transcription factors and maintain the activity of stemness genes that promote self-renewal and pluripotency. In this context differentiation is basically a process governed by changes in gene activity during development that alter the stemness-specific epigenome towards lineage-specific patterns, often in response to transient factors or environmental stimuli. Sophisticated networks of protein complexes maintain epigenomic states in stem cells and determined cells after lineage decision and ensure their transmission through cell division. In addition, they are also essential for the epigenetic changes happening during differentiation induction that are crucial for lineage specification. The Polycomb group of genes codes for a variety of proteins that maintain repressive chromatin states. They are part of a complex cellular memory system that creates a layer of epigenetic information on top of the DNA sequence that ensures the maintenance and transmission of cell-specific expression patterns.
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    • "However, a number of lines of evidence – most notably (i) the acquisition of H3K27me3 by bacterial non-methylated GC-rich sequences integrated into mouse genomes [156], (ii) the acquisition of H3K27me3 by CpG islands that have activating sequences removed [156], and (iii) the anticorrelation of H3K27me3 with DNA methylation [74] [146] – point to the requirement for CpG islands in establishing H3K27me3/polycomb repressed domains in mammals. In the absence of an obvious DNAbinding candidate for this role, indirect effects have been suggested, including the ability of H3K36me2 (which is removed from CpG islands through interactions with the ZF-CxxC-domain containing proteins Kdm2a/b, among other mechanisms) to inhibit PRC2 activity [157] [158]. "
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