B Cell Division Capacity in Germinal Centers Depends on Myc Transcript Stabilization Through m6A mRNA Methylation and IGF2BP3 Functions

Long-lasting immunity from pathogens depends on the generation of protective antibodies through the germinal center (GC) reaction. The Myc gene produces highly short-lived transcripts which are essential for generation of high-affinity antibodies. mRNA lifetime is regulated by N6-methyladenosine (m 6 A)-modification of mRNAs through METTL3 activity; however, the role of this machinery in the GC remains unclear. Here, we find that m 6 A-modification of mRNAs is required for GC maintenance through Myc mRNA stabilization by the atypical m 6 A-interactor, IGF2BP3. MYC expression, activation of MYC transcriptional programs and cell-cycle progression were diminished in METTL3-deficient GC B cells. METTL3 attenuated Myc -transcript decay and overexpression of MYC in METTL3-deficient GC B cells restored the GC reaction. IGF2BP3 which was induced by CD40-signaling, reinforced MYC expression and MYC-related gene programs in GC B cells. Our findings explain how GC responses are maintained through regulation of Myc -transcript lifetime and expose new targets for manipulation in MYC-driven lymphoma. One Sentence Summary Germinal centers depend on the m 6 A-machinery