Induction of senescence upon loss of the Ash2l subunit of histone H3K4 methyltransferase complexes (ChIP-Seq)

Post-translational modifications of core histones participate in controlling the expression of genes. Methylation of lysine 4 of histone H3 (H3K4) is associated with open chromatin and gene transcription. This histone mark is catalyzed by type 2 lysine methyltransferase (KMT2) complexes. In mammals, these consist of one of 6 different KMT2 enzymes, each associated with 4 core subunits, WDR5, RBBP5, ASH2L and DPY30, which are necessary for catalytic activity. The knockout of Ash2l is embryonically lethal in mice as well as in adult animals when hepatocytes or hematopoietic cells are targeted. To expand on the mechanistic understanding of Ash2l, we have used mouse embryo fibroblasts (MEFs). The knockout of Ash2l resulted in the downregulation of H3K4me3 at a large number of promoters, preferentially those associated with CpG islands, accompanied with broad repression of gene expression. The consequence in MEFs was induction of senescence concomitant with a set of down-regulated signature genes. Thus, although the loss of Ash2l in MEFs has broad and complex consequences on the transcriptional program, the biological consequences were distinct, culminating in senescence.