Dev109496 1418..1430

The interplay between different levels of gene regulation in modulating developmental transcriptional programs, such as histonemodifications and chromatin remodeling, is not well understood. Here, we show that the chromatin remodeling factor Brg1 is required for enhancer activation in mesoderm induction. In an embryonic stem cell-based directed differentiation assay, the absence of Brg1 results in a failure of cardiomyocyte differentiation and broad deregulation of lineagespecific geneexpressionduringmesoderm induction.We find thatBrg1 co-localizeswithH3K27acat distal enhancers and is required for robust H3K27 acetylation at distal enhancers that are activated during mesoderm induction. Brg1 is also required to maintain Polycombmediated repression of non-mesodermal developmental regulators, suggesting cooperativity between Brg1 and Polycomb complexes. Thus, Brg1 is essential for modulating active and repressive chromatin states during mesoderm lineage commitment, in particular the activation of developmentally important enhancers. These findings demonstrate interplay between chromatin remodeling complexes and histone modifications that, together, ensure robust and broad gene regulation during crucial lineage commitment decisions.