Mll2 branch of the COMPASS family regulates bivalent promoters in mouse embryonic stem cells
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. Overall design: 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.