PRMT1 is required for antibody affinity maturation by preventing premature B cell differentiation

Germinal center (GC) B cells undergo cycles of somatic hypermutation and selection, thus increasing their antibody affinity before differentiating into plasma or memory cells. The mechanisms dictating the dynamics of GC B cells are incompletely understood. We show that ablating the Protein arginine methyltransferase 1 (PRMT1) in GC B cells reduces antibody affinity maturation by impairing GC dynamics, as shown by compromised GC expansion, accumulation of CXCR4- B cells, and increased memory B cell differentiation, partly, at the expense of plasma cell production. Furthermore, PRMT1 distinguishes the subset of GC B cells that reenter the GC dark zone after positive selection, in which it is upregulated by Myc in conjunction with mTORC signaling. PRMT1 opposes mature B cell differentiation, as shown by higher plasma cell differentiation of PRMT1-deficient B cells activated ex vivo, a function co-opted by B cell lymphoma cells, in which PRMT1 expression also correlates with Myc expression and outcome. 6 RNA-seq mouse samples (2 conditions, 3 biological replicates per condition).