Mll2 branch of the COMPASS family regulates bivalent promoters in mouse embryonic stem cells
ABSTRACT: Promoters of many developmentally regulated genes, in the embryonic stem cell state, have a bivalent mark of H3K27me3 and H3K4me3, proposed to confer precise temporal activation upon differentiation. Although Polycomb repressive complex 2 is known to implement H3K27 trimethylation, the COMPASS family member responsible for H3K4me3 at bivalently marked promoters was previously unknown. Here, we identify Mll2 (KMT2b) as the enzyme catalyzing H3K4 trimethylation at bivalently marked promoters in embryonic stem cells. Although H3K4me3 at bivalent genes is proposed to prime future activation, we detected no substantial defect in rapid transcriptional induction after retinoic acid treatment in Mll2-depleted cells. Our identification of the Mll2 complex as the COMPASS family member responsible for H3K4me3 marking at bivalent promoters provides an opportunity to reevaluate and experimentally test models for the function of bivalency in the embryonic stem cell state and in differentiation. ChIP-Seq in mouse embryonic stem (mES) cells for MLL2. ChIP-seq of H3K4me1, H3K4me3 and H3K27me3 for mES cells with RNAi against MLL2(shMLL2) and control (shGFP). ChIP-seq of H3K4me3 in mES cells with RNAi against MLL3 (shMLL3). RNA-seq of mES cells with RNAi against MLL2 and control (shGFP). RNA-seq of control mES cells (shGFP) or MLL2 RNAi mES cells (shMLL2) induced with RA for 6h and 12h.
Project description:Trimethylation of histone 3 lysine 4 (H3K4me3) at promoters of actively transcribed genes is a universal epigenetic mark and a key product of Trithorax-Group action. Here we show that Mll2, one of the six Set1/Trithorax-type H3K4 methyltransferases in mammals, is required for trimethylation of bivalent promoters in mouse embryonic stem cells. Mll2 is bound to bivalent promoters but also to most active promoters, which do not require Mll2 for H3K4me3 or mRNA expression. In contrast, the Set1 complex (Set1C) subunit Cxxc1 is primarily bound to active but not bivalent promoters. This indicates that bivalent promoters rely on Mll2 for H3K4me3 whereas active promoters have more than one bound H3K4 methyltransferase including Set1C. Removal of Mll1, sister to Mll2, had almost no effect on any promoter unless Mll2 was also removed indicating functional back-up between these enzymes. Except for a subset, loss of H3K4me3 on bivalent promoters did not prevent responsiveness to retinoic acid thereby arguing against a priming model for bivalency. In contrast, we propose that Mll2 is the pioneer trimethyltransferase for promoter definition in the naïve epigenome and Polycomb-Group action on bivalent promoters blocks premature establishment of active, Set1C bound, promoters. ChIP-Seq to study MLL2 function using H3K4me3 (12 samples), H3K27me3 (4 samples), Pol2 (1 sample) or GFP (7 samples) antibody, and 6 RNA-Seq profiles
Project description:An immortalized multipotent otic progenitor (iMOP) cell was used to determine H3K4me3 and H3K27me3 histone marks. Promoters containing enriched with both histone marks were considered bivalent promoters. Neurog1 dependent transription was determined in genes with bivalently marked promoters. Overall design: ChIP-Seq was accomplished by immunoprecipitating endogenous H3K4me3 and H3K27me3
Project description:TET protein-catalyzed 5mC oxidation not only creates novel DNA modifications such as 5hmC, but also initiates active or passive DNA demethylation. However, the TETs’ function in crosstalk with specific histone modifications is largely elusive. Here, we show that TET2-mediated DNA demethylation plays a primary role in the de novo establishment and maintenance of H3K4me3/H3K27me3 bivalent domain underlying the methylated DNA CpG islands (CGIs). Overexpression of wild type (WT) but not catalytic inactive mutant (Mut) TET2 in TET-low-expressing cells results in increase of 5hmC level and accompanying DNA demethylation at a subset of CGIs. Importantly, this is sufficient to create de novo bivalent domains at these loci. Genome-wide analysis reveals that these de novo synthesized bivalent domains are largely associated with a subset of key developmental gene promoters, which are often located within CpG islands that are previously hyper-methylated and silenced. On the other hand, depletion of Tet1 and Tet2 in mouse ES cells results in an apparent loss of H3K27me3 at bivalent domains, which are located within CGIs and associated with a particular set of key developmental gene promoters. Collectively, these data suggest that TET proteins have a primary role in charge of regulating the crosstalk between two key epigenetic mechanisms, DNA methylation and histone methylation (H3K4me3 and H3K27me3), particularly at a subset of CpG islands associated with developmental genes. We examined H3K4me3,H3K27me3,5mC and 5hmC in 293T and mES cell types,using Illumina Hiseq2500.
Project description:The spatiotemporal regulation of gene expression is central for cell-lineage specification during embryonic development and is achieved through the combinatorial action of transcription factors/co-factors and the epigenetic states at cis-regulatory elements. Previously, we reported that Mll2 (KMT2B)/COMPASS is responsible for the implementation of H3K4me3 at promoters of bivalent genes. Here, we show that Mll2/COMPASS can also implements H3K4me3 at some of the non-TSS regulatory elements, a subset of which share epigenetic signatures of active enhancers. Our mechanistic studies reveal that the association of Mll2’s CXXC domain with CpG-rich regions plays an instrumental role for chromatin targeting and subsequent implementation of H3K4me3. Although Mll2/COMPASS is required for H3K4me3 implementation on thousands of sites, it appears to be essential for the expression of a subset of genes, including those functioning in the control of transcriptional programs during embryonic development, indicating that not all H3K4 trimethylations implemented by MLL2/COMPASS are functionally equivalent. Overall design: Characterization of H3K4me3 and Mll2 occupancy by ChIP-seq in mouse embryonic stem cells and identifying their role in gene expression and during differentiation by RNA-seq studies. A high resolution 4C-seq experiments involving two restriction digests (HindIII and NlaIII) were performed to investigate the interaction bewteen promoters of Prdm1 and Prdm14 (viewponts) and cis-regulatory elements whose H3K4me3 is catalyzed by Mll2 in mouse embryonic stem cells.
Project description:Trimethylation of histone 3 lysine 4 (H3K4me3) is classically thought of as a mark of active promoters and yet it occurs at untranscribed domains. Partial redundancy of H3K4 methyltransferases has made it difficult to delineate the mechanisms underlying genomic targeting of H3K4me3. The oocyte provides an attractive system to investigate this, because extensive acquisition of H3K4me3 occurs in a non-dividing cell and ablation of a single H3K4 methyltransferase, Mll2, prevents most H3K4me3. We developed low-input chromatin immunoprecipitation to interrogate promoter associated histone modifications H3K4me3, H3K27ac and H3K27me3 throughout oogenesis. In non-growing oocytes, H3K4me3 was restricted to transcriptionally active promoters, but as oogenesis progresses, H3K4me3 accumulates in a transcription-independent manner: targeted to broad inter-genic regions, putative enhancers, and transcriptionally silent H3K27me3-marked promoters. Consequently, thousands of bivalent domains are established during oogenesis. Ablation of Mll2 resulted in loss of transcription-independent H3K4me3, with limited effects on transcription-coupled H3K4me3 or gene expression. Deletion of Dnmt3a/b showed that DNA methylation protects regions from acquiring H3K4me3. Our findings show that there are two independent mechanisms of targeting H3K4me3 to genomic elements, with MLL2 recruited to unmethylated CpG-rich regions independently of transcription. Overall design: We first characterised histone modifications associated with transcriptional regulation (H3K4me3, H3K27ac, and H3K27me3) in oocytes by adapting an ultra-low input native ChIP (ULI-nChIP) sequencing method. This allowed us to obtain high-resolution chromatin maps throughout oogenesis, from non-growing oocytes (NGOs) to fully-grown germinal vesicle (GV) oocytes, and to compare these profiles to gene expression and DNA methylation. Furthermore, this has enabled the first molecular interrogation of H3K4me3 in the conditional Dnmt3a/b and Mll2 KO oocytes.
Project description:Bivalent H3K4me3 and H3K27me3 chromatin domains in embryonic stem cells keep active developmental regulatory genes expressed at very low levels and poised for activation. Here, we show an alternative and previously unknown bivalent modified histone signature in lineage-committed mesenchymal stem cells and preadipocytes that pairs H3K4me3 with H3K9me3 to maintain adipogenic master regulatory genes (Cebpa and Pparg) expressed at low levels yet poised for activation when differentiation is required. We show lineage-specific gene-body DNA methylation recruits H3K9 methyltransferase SETDB1 which methylates H3K9 immediately downstream of transcription start sites marked with H3K4me3 to establish the bivalent domain. At the Cebpa locus, this prevents transcription factor C/EBPβ binding, histone acetylation, and further H3K4me3 deposition and is associated with pausing of RNA polymerase II, which limits Cebpa gene expression and adipogenesis. H3K4me3, H3K27me3, H3K9me3, SETDB1, MBD1, and Pol II ChIP-seq. m5CpG pull-down using recombinant MBD domain of MBD1 followed by next-generation sequencing.
Project description:In embryonic stem (ES) cells, bivalent chromatin domains with overlapping repressive (H3 lysine 27 tri-methylation) and activating (H3 lysine 4 tri-methylation) histone modifications mark the promoters of more than 2000 genes. To gain insight into the structure and function of bivalent domains, we mapped key histone modifications and subunits of Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) genomewide in human and mouse ES cells by chromatin immunoprecipitation followed by ultra high-throughput sequencing. We find that bivalent domains can be segregated into two classes: the first occupied by both PRC2 and PRC1 (PRC1-positive) and the second specifically bound by PRC2 (PRC2-only). PRC1-positive bivalent domains appear functionally distinct as they more efficiently retain lysine 27 tri-methylation upon differentiation, show stringent conservation of chromatin state, and associate with an overwhelming number of developmental regulator gene promoters. We also used computational genomics to search for sequence determinants of Polycomb binding. This analysis revealed that the genomewide locations of PRC2 and PRC1 can be largely predicted from the locations, sizes and underlying motif contents of CpG islands. We propose that large CpG islands depleted of activating motifs confer epigenetic memory by recruiting the full repertoire of Polycomb complexes. Keywords: cell type comparison Suz12, Ezh2, Ring1b ChIP-Seq in singlicate from mouse embryonic stem (mES) cells. H3K4me3, H3K27me3, H3K36me3, Ezh2 and Ring1b ChIP-Seq in singlicate from human embyonic stem cells (hES; H9).
Project description:Chromatin modifications have been implicated in the self-renewal and differentiation of embryonic stem cells (ESCs). However, the function of histone variant H2A.Z in ESCs remains unclear. We show that H2A.Z is highly enriched at promoters and enhancers and is required for both efficient self-renewal and differentiation of murine ESCs. H2A.Z deposition leads to an abnormal nucleosome structure, decreased nucleosome occupancy and increased chromatin accessibility. In self-renewing ESCs, knockdown of H2A.Z compromises OCT4 binding to its target genes and leads to decreased binding of MLL complexes to active genes and of PRC2 complex to repressed genes in self-renewal of ESCs. During differentiation of ESCs, inhibition of H2A.Z also compromises RA-induced RARα binding, activation of differentiation markers and the repression of pluripotency genes. We propose that H2A.Z mediates such contrasting activities by acting as a 'general facilitator' that generates access for a variety of complexes both activating and repressive. ChIP-Seq in murine embryonic stem (mES) cells for H2A.Z and acetylated H2A.Z. ChIP-Seq of H3K4me3, H3K27me3, RbBP5, SUZ12 and OCT4 for mES cells of both H2A.Z RNAi knockdown and shLuc control. ChIP-Seq of RARalpha in H2A.Z knockdown (withdraw of LIF and exposure to RA for 3h) and control cells. MNase-Seq and chromatin accessibility assay using Benzonase digestion followed by next-generation sequencing for mES cells of both H2A.Z RNAi knockdown and shLuc control. ChIP-Seq of H2A.Z and H3K4me3 for mES cells of both MLL4 RNAi knockdown and shLuc control. RNA-Seq for mES cells of H2A.Z knockdown and shluc control. RNA-Seq for embryonic bodies derived from mES cells (H2A.Z knockdown and shLuc control) at day 3 and day 7.
Project description:Bivalent H3K4me3 and H3K27me3 chromatin domains in embryonic stem cells keep active developmental regulatory genes expressed at very low levels and poised for activation. Here, we show an alternative and previously unknown bivalent modified histone signature in lineage-committed mesenchymal stem cells and preadipocytes that pairs H3K4me3 with H3K9me3 to maintain adipogenic master regulatory genes (Cebpa and Pparg) expressed at low levels yet poised for activation when differentiation is required. We show lineage-specific gene-body DNA methylation recruits H3K9 methyltransferase SETDB1 which methylates H3K9 immediately downstream of transcription start sites marked with H3K4me3 to establish the bivalent domain. At the Cebpa locus, this prevents transcription factor C/EBPβ binding, histone acetylation, and further H3K4me3 deposition and is associated with pausing of RNA polymerase II, which limits Cebpa gene expression and adipogenesis. We used microarrays to detail the global programme of gene expression in 3T3-L1 preadipocytes and 10Th1lf mesenchymal stem cells and identified up-regulated genes upon knockdown of SETDB1, MBD1, and MCAF1. SETDB1, MBD1, or MCAF1 was knocked-down in 3T3-L1 preadipocytes and 10Thalf mesenchymal stem cells for RNA extraction and hybridization on Affymetrix microarrays. Small interfering RNAs (siRNA) targeting to Setdb1, Mbd1, or Mcaf1 was transfected to 3T3-L1 preadipocytes or 10Thalf mesenchymal stem cells.
Project description:By mapping the genomic enrichments of H3K4me3 and H3K27me3 modifications in pure populations of hESCs during the G2, mitotic and G1 phases of the cell cycle, we characterize cell cycle-dependent variations in the epigenetic landscape of bivalent genes, altering the current view of mitotic inheritance in pluripotent cells. We identified novel classes of bivalent domains that are highly enriched with H3K4me3 during mitosis, depleted during G1 only, and ubiquitously bivalent. These bivalent domains are associated with specific genes and expression patterns during differentiation. These cell cycle-dependent epigenetic profiles are unique to hESCs and are not observed following initiation of phenotype commitment. Our results establish a new dimension in cell cycle-dependent chromatin regulation that advances understanding of contributions the pluripotent epigenetic landscape to hESC identity. Study of two histone modifications, H3K4me3 and H3K27me3, during three cell cycle phases in two cell types. Study of gene expression from these two cell types in asynchronous cells.