MLL3/MLL4 Histone Methyltranferase Activity Dependent Chromatin Organization at Enhancers during Embryonic Stem Cell Differentiation

MLL3 (KMT2C) and MLL4 (KMT2D), the major mono-methyltransferases of histone H3 lysine 4 (H3K4), are required for cellular differentiation and embryonic development in mammals. We previously observed that MLL3/4 promote long-range chromatin interactions at enhancers, however, it is still unclear how their catalytic activities contribute to enhancer-dependent gene activation in mammalian cell differentiation. To address this question, we mapped histone modifications, long-range chromatin contacts as well as gene expression in MLL3/4 catalytically deficient mouse embryonic stem (ES) cells undergoing differentiation toward neural precursor cells. We showed that MLL3/4 activities are responsible for deposition of H3K4me1 modification and formation of long-range enhancer-promoter contacts at a majority of putative enhancers gained during cell differentiation, but are dispensable for most candidate enhancers found in undifferentiated ES cells that persist through differentiation. While transcriptional induction at most genes is unaltered in the MLL3/4 catalytically deficient cells, genes making more contacts with MLL3/4-dependent putative enhancers are disproportionately affected. These results support that MLL3/4 contributes to cellular differentiation through histone-methyltransferase-activity dependent induction of enhancer-promoter contacts and transcriptional activation at a subset of lineage-specific genes.