H3K9 dimethyltransferase G9a is an important epigenetic modulator of B cell differentiation

Abstract B cell differentiation is a tightly regulated process coordinated by the timed expression of various transcription factors and chromatin accessibility changes mediated by histone modifying enzymes. The histone methyltransferase (HMT) G9a, dimethylates histone H3 lysine 9 (H3K9) at promoters and inhibits gene expression via recruitment of proteins that impair chromatin accessibility. HMTs are expressed ubiquitously but display distinct enzymatic activities and patterns of chromosomal localization. During B cell differentiation, G9a was found to co-localize with Blimp-1 which is required to silence genes associated with a B cell phenotype and cellular proliferation. However, the B cell processes that are modulated by G9a mediated dimethylation remain to be elucidated. To assess the role of G9a in B-cell differentiation, we crossed G9afl/fl mice onto the CD19Cre/+ background (G9aKO mice). Stimulation of CD19Cre/+ (CreCtrl) and G9aKO mice with the T cell independent antigen LPS resulted in a significant increase of activated B cells and plasmablast in G9aKO mice. Further characterization of this phenotype, identified a skewing within the mature B cell population towards marginal zone (MZ) B cells in G9aKO mice. Regions with chromatin accessibility and expression changes identified by ATAC-Seq and RNA-Seq elucidated the B cell processes that are modulated in G9a deficient mice. B cell processes that are subject to direct modulation by G9a will be determined using CUT&RUN. Together, our data shows the importance of G9a in epigenetic modulation required for B cell function.