BCLAF1 and responses to RAG-induced DNA breaks enforce pre-B cell checkpoint

During early B cell development, pre-B cells encounter signaling from pre-B cell receptor (pre-BCR) and DNA damage responses (DDR) triggered by RAG-induced DNA double-stranded breaks (DSBs) generated during immunoglobulin light chain (Igl) recombination. These signals drive cooperative and antagonistic programs to promote pre-B cell checkpoint. Here, we show in vivo that pre-B cells transition between distinct subpopulations predominated by either pre-BCR or RAG DSB-induced DDR signals. DDR initiates early in pre-B cells undergoing Igl recombination then drives cellular programming during terminal pre-B stages. We find that RAG DSB-induced DDR regulates coordinated pre-B cell differentiation, in part, by activation of the transcriptional repressor complex SPIC/BCLAF1. Loss of BCLAF1 disrupts pre-B cell developmental progression resulting in concomitant expression of pre-BCR and DDR programs with breakdown in segregation of clonal expansion and Igl recombination. These studies show that RAG DSB-induced DDR and BCLAF1 preserve pre-B cell checkpoint integrity in vivo during Igl recombination.