The RNA m6A binding protein YTHDF2 promotes the B cell to plasma cell transition

The B cell to plasma cell transition relies on the coordinated remodelling of the gene expression program. We performed a CRISPR/Cas9 knockout screen of RNA binding proteins to identify post-transcriptional regulation of gene expression during the B cell terminal differentiation. The m6A binding protein YTHDF2 was identified as promoting B cell terminal differentiation. In the absence of YTHDF2 the germinal centre reaction is broadly intact, however, plasma cells fail to accumulate. YTHDF2 has previously been shown to mediate RNA decay through the recruitment of the CCR4-NOT deadenylase machinery. Furthermore, our genetic screen in B cells identified that other CCR4-NOT recruitment factors inhibit rather than promote differentiation. Thus, the CCR4-NOT complex coordinates competing regulatory pathways of B cell differentiation at the post-transcriptional level. Overall design: m6A-eCLIP libraries were generated from two biological replicates in B cells after 8 days of iGB culture. Libraries from the input RNA were also generated for each of the replicates. For CRISPR screens, an sgRNA library targeting RNA binding proteins was transduced at day 3 in iGB culture. Screens were performed to assess proliferation/survival (guide representation at day 8 compared with day 4 in bulk B cells, 1 biological replicate each), and differentiation (guide representation in CD138+ compared with CD138- cells at day 8, 2 biological replicates each).