H3.3K4M destabilizes enhancer epigenomic writers MLL3/4 and impairs adipose tissue development

Histone H3K4 mono-methyltransferases MLL3 and MLL4 (MLL3/4) are required for enhancer activation during cell differentiation, though the mechanism is incompletely understood. To address MLL3/4 enzymatic activity in enhancer regulation, we have generated two mouse lines: one expressing H3.3K4M, a lysine-4-to-methionine (K4M) mutation of histone H3.3 that inhibits H3K4 methylation, and the other carrying conditional double knockout of MLL3/4 enzymatic SET domains. Expression of H3.3K4M in lineage-specific precursor cells depletes H3K4 methylation and prevents adipogenesis and adipose tissue development. Mechanistically, H3.3K4M prevents enhancer activation in adipogenesis by destabilizing MLL3/4 proteins but not other Set1-like H3K4 methyltransferases. Notably, deletion of the enzymatic SET domain of MLL3/4 in lineage-specific precursor cells mimics H3.3K4M expression and prevents adipose tissue development. Interestingly, destabilization of MLL3/4 by H3.3K4M in adipocytes does not affect adipose tissue maintenance and function. Together, our findings indicate that H3.3K4M destabilizes enhancer epigenomic writers MLL3/4 and impairs adipose tissue development.