B cell differentiation is limited by de novo DNA methylation [RNA-seq]

B cells provide humoral immunity by differentiating into antibody-secreting plasma cells, a process that requires cell division and is linked to DNA hypomethylation and gene regulation. Conversely, accumulation of DNA methylation in B cell differentiation is less apparent. To determine the role of de novo DNA methylation in B cell differentiation, the de novo DNA methyltransferases, Dnmt3a and Dnmt3b, were deleted in B cells resulting in phenotypically normal B cell development in the bone marrow, spleen and lymph nodes. However, upon immunologic challenge, mice deficient for Dnmt3a and Dnmt3b (Dnmt3-deficient) accumulated more antigen-specific B cells and bone marrow chimeras showed this was cell-autonomous. Additionally, a five-fold increase in splenic and bone marrow plasma cells was observed. Molecular analysis revealed that Dnmt3-deficient bone marrow plasma cells failed to repress gene expression to the same level as their Dnmt3ab-sufficient counterparts. This was coupled with a failure of Dnmt3-deficient germinal center B cells and plasma cells to gain and/or maintain DNA methylation at several thousand loci that were clustered in enhancers of genes that function in B cell activation and homing. Analysis of chromatin accessibility showed Dnmt3-deficient plasma cells had increased accessibility at several genes involved in hematopoiesis and B cell differentiation. These data show that de novo DNA methylation limits B cell activation, proliferation and differentiation, and support a model whereby DNA methylation represses the aberrant transcription of genes silenced in B cell differentiation to maintain plasma cell homeostasis. Overall design: Naïve lymph node B cells (B220+ GL7- Fas-), Phycoerythrin-specific germinal center B cells (B220+ GL7+ Fas+ PE+), and bone marrow plasma cells (CD138+) were compared between Cd19cre/wtDnmt3afl/flDnmt3bfl/fl (Dnmt3-deficient) and littermate control Cd19wt/wtDnmt3afl/flDnmt3bfl/fl (Dnmt3-sufficient) mice using RRBS, RNA-seq, and ATAC-seq. Naïve lymph node B cells were taken from naïve mice, whereas PE-specific germinal center B cells and bone marrow plasma cells were isolated from mice that had been immunized with phycoerythrin 30 days prior. This Series includes the RNA-seq component of the study.

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Barwick BG, Scharer CD, Martinez RJ, Price MJ, Wein AN, Haines RR, Bally APR, Kohlmeier JE, Boss JM