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.
Project description:Methylation of histone H3 lysine 4 (H3K4) by the Set1/COMPASS complex is coupled with active transcription, and this modification is important for regulating gene expression. Set1/COMPASS associates with the RNA polymerase II (RNApII) C-terminal domain (CTD) to establish proper levels and distribution of H3K4 methylations.To ask how the Set1-RNApII CTD binding affects the occupancy and overall level of H3K4 methylations, ChIP-Seq was pefromed in cells transformed with full length or N-terminal truncated Set1. Our results indicate that Set1-RNApII CTD interaction is necessary for maintaining H3K4 methylations throughout the genes.
Project description:The COMPASS family catalyzes histone H3 lysine 4 (H3K4) methylation and its members are essential for regulating developmental gene expression. MLL2/COMPASS methylates H3K4 on many genes but only a subset lose expression upon MLL2 loss. To understand MLL2 -dependent transcriptional regulation, we performed a CRISPR screen in mouse embryonic stem cells (mESCs) and found that MLL2 protects developmental genes from repression by repelling PRC2 and DNA methylation machineries from these loci. Repression in the absence of MLL2 is relieved by inhibition of PRC2 and DNA methyltransferases, demonstrating that prevention of active repression and not H3K4me3 underlies their transcriptional state. DNA demethylation on such loci leads to reactivation of MLL2-dependent genes not only by removing DNA methylation but also by opening up previously CpG methylated regions for PRC2 recruitment, diluting PRC2 at Polycomb-repressed genes. These findings reveal how the context and function of these three epigenetic modifiers can orchestrate transcriptional decisions.
Project description:Here, we showed that acute lost H3K4me3 induces rapid reduction in global transcription with progressively increase in magnitude over the time-course cooccurrence with lost all H3K4 methylations. To further determine the effects of COMPASS subunits degradation on H3K4 methylations occupancies genome-wide, we performed time-course spike-in chromatin immunoprecipitation and sequencing (ChIP-seq, also known as ChIP-Rx) analysis in both degron systems.
Project description:Here, we showed that acute lost H3K4me3 induces rapid reduction in global transcription with progressively increase in magnitude over the time-course cooccurrence with lost all H3K4 methylations. To further determine the effects of COMPASS subunits degradation on H3K4 methylations occupancies genome-wide, we performed time-course spike-in chromatin immunoprecipitation and sequencing (ChIP-seq, also known as ChIP-Rx) analysis in both degron systems.
Project description: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:A hallmark of genes transcribed by RNA polymerase II (RNApII) is a "gradient" of histone H3 lysine 4 (H3K4) methylation. Various factors differentially bind to H3K4me3 near promoters, H3K4me2 just downstream, and H3K4me1 further downstream to modulate gene expression. Set1/COMPASS, the single S. cerevisiae H3K4 methyltransferase, binds transcribing RNApII, but COMPASS may also be allosterically regulated by specific subunits and histone H2B ubiquitylation. To ask whether differential H3K4 methylation is determined by regulated activity at specific gene locations or by the amount of time COMPASS spends near the nucleosome, ChIP-Seq analyses was performed in cells with altered transcription elongation rates or with Set1 fused to RNApII. Our results support a simple model where higher H3K4 methylations result from both increased duration and frequency of COMPASS proximity to the nucleosome.
Project description:Global analysis of H3K4 methylation defines MLL family member targets and points to a role for MLL1-mediated H3K4 methylation in the regulation of transcriptional initiation by RNA polymerase II A common landmark of activated genes is the presence of trimethylation on lysine 4 of histone H3 (H3K4) at promoter regions. The Set1/COMPASS was the founding member and the only H3K4 methylases in S. cerevisiae, however, in mammals at least six H3K4 methylases Set1A/B and MLL1-4 are found in COMPASS-like complexes capable of methylating H3K4. To gain further insight into the different roles and functional targets for the H3K4 methylases, we have undertaken a genome-wide analysis of H3K4 methylation pattern in wild-type Mll1+/+ and Mll1-/- mouse fibroblasts (MEFs). We found that Mll1 is required for the H3K4 trimethylation of less than 5% of promoters carrying this modification. Many of these genes, which include developmental regulators such as Hox genes show decreased levels of RNA polymerase II recruitment and expression concomitant with the loss of H3K4 methylation. Although Mll1 is only required for the methylation of a subset of Hox genes, Menin, a component of the Mll1 and Mll2 complexes, is required for the overwhelming majority of H3K4 methylation at Hox loci. However, the loss of MLL3/4 and/or the Set1 complexes have little to no effect on the Hox loci H3K4 methylation or expression levels in these MEFs. Together these data provide insight into redundancy and specialization of COMPASS-like complexes in mammals and provide evidence on a possible role for Mll1-mediated H3K4 methylation in the regulation of transcriptional initiation. Expression arrays were done with Mll1+/+ and Mll1-/- mouse embryonic fibroblasts. Four replicates were done (dyes were swapped). DNA was hybridized to Agilent Mouse Whole Genome Expression Arrays (4x44k).
Project description: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.
Project description:Histone H3 lysine 4 trimethylation (H3K4me3) facilitates recruitment of transcription factors and epigenetic effectors to promote transcriptional activation and ensure cellular identity. This conserved histone mark is implemented by the COMPASS (COMplex of Proteins ASsociated with Set1) family of H3K4 methyltransferases. COMPASS members Set1A and Set1B have been accredited as primary depositors of global H3K4me3 in mammalian cells. Our previous studies in mouse embryonic stem cells (ESCs) demonstrated that deleting the enzymatic SET domain of Set1A does not perturb bulk H3K4me3, indicating possible compensatory roles played by other COMPASS methyltransferases. Here, we generated a series of ESC lines harboring compounding mutations of the COMPASS enzymes. We find that Set1B is functionally redundant to Set1A in implementing H3K4me3 at highly expressed genes, while Mll2 deposits H3K4me3 at less transcriptionally active promoters. Furthermore, Set1A and Set1B are responsible for broad H3K4me3 peaks, whereas Mll2 establishes H3K4me3 with narrow breadth. Most importantly, Mll2 helps preserve global H3K4me3 levels and peak breadth. Our results illustrate the biological flexibility of such enzymes in regulating transcription in a context-dependent manner to maintain stem cell identity, which could assist our understanding of their disease liability.