H3K27me3-specific demethylases modulate B cell development and differentiation

Abstract B cell terminal differentiation into antibody secreting plasma cells (ASC) must be properly regulated to ensure robust humoral immune responses against foreign but not self-antigens. While the role of transcription factors in this process is well-established, there is also a growing appreciation of the epigenetic regulation of B cell differentiation. The histone modification H3 lysine 27 trimethylation (H3K27me3) is associated with a repressive chromatin state and gene silencing and is highly dynamic during B cell differentiation. EZH2, the enzyme that deposits H3K27me3, is required for proper B cell development, as well as germinal center and ASC formation. However, the role of active demethylation of H3K27me3 by the two demethylases UTX and JMJD3 in B cells is still to be elucidated. To determine the requirements for these enzymes in B lymphocytes, we crossed Utxfl/flJmjd3fl/flmice onto Cd19Cre/+background (dKO mice). In dKO mice, we observed a significant increase in T2 transitional and marginal zone B cells in the spleen and a reduction in circulating mature B cells in the bone marrow. To determine the role of UTX and JMJD3 in T cell dependent B cell responses, we infected CreCtrl and dKO mice with PR8 influenza virus. Fourteen days post infection, we observed a modest increase in GC B cells and skewing in the GC polarity in dKO mice. RNA-seq of CreCtrl and dKO GC B cells revealed that majority of differentially expressed genes (DEGs) were downregulated in the absence of UTX and JMJD3. Furthermore, a subset of down-DEGs were enriched for H3K27me3 in dKO supporting the role of UTX and JMJD3 in promoting gene. expression. Taken together, these data place H3K27me3 demethylases as critical enzymes that regulate the epigenetic dynamics of B cell fate.