Studies on the Role of H3K36 Methylation using Histone Mutants

Abstract

Chromatin is coated in a multitude of epigenetic marks of stereotyped distribution and unclear function. Among them, H3 lysine 36 trimethylation (H3K36me3) is enriched around actively transcribed gene bodies from yeast to humans, but its precise role remains disputed. Here, we interrogate the in vivo function of H3K36me3 using an innovative transgenic mouse model that expresses an inducible, dominant negative histone mutation leading to the genome-wide depletion of H3K36me3. Following induction of the mutation, mice became lethally anemic due to a profound differentiation block in terminal erythropoiesis. While H3K36me3 is typically associated with active chromatin, we found that loss of H3K36me3 does not reduce transcription levels, but rather increases transcription from the antisense strand of actively expressed genes. Importantly, these gains in antisense transcripts occurred specifically at genes with basal antisense transcription and robust levels of H3K36me3. Upregulated antisense transcripts triggered an interferon response that resulted in cell cycle arrest and blocked erythroid maturation. We further show that erythroblasts susceptible to elevated antisense transcription have markedly lower levels of DNA methylation and that other tissues are sensitive to antisense transcription when DNA methylation is inhibited. Based on these data, we propose that H3K36me3 and DNA methylation collaborate to repress antisense transcription at active gene bodies in mammals.