GSE98063
Mll3 and Mll4 facilitate enhancer RNA synthesis and transcriptional elongation from promoters independently of H3K4 monomethylation
Monomethylation of histone H3 at lysine 4 (H3K4me1) and acetylation of histone H3 at lysine 27 (H3K27ac) are correlated with transcriptionally engaged enhancer elements, but the functional impact of these modifications on enhancer activity is not well understood. Here we used CRISPR/Cas9 genome editing to separate catalytic activity-dependent and independent functions of Mll3 (Kmt2c) and Mll4 (Kmt2d, Mll2), the major enhancer H3K4 monomethyltransferases. Loss of Mll3/4 catalytic activity and H3K4me1 from enhancers causes partial depletion of H3K27ac, but surprisingly minor effects on enhancer Pol II binding, enhancer RNA (eRNA) transcription and gene expression. In contrast, loss of Mll3/4 proteins results in dramatic reduction of eRNA production, concomitant with impaired transcriptional elongation at adjacent promoters. Altogether our results suggest the major coactivator function of Mll3/4 is largely independent of H3K4me1 and instead linked to enhancer Pol II occupancy, eRNA transcription and long-range influence on elongation at target promoters. Overall design: ChIP-seq (Mll3/4, H3K4me1, H3K27ac and Pol II), RNA-seq, Start-seq and ATAC-seq, data from WT, knockout and catalytically-deficient Mll3/4 cell lines.