BioProject

Immunoglobulin heavy chain locus (Igh) VH, D, and JH gene segments are developmentally assembled into V(D)J exons. More...

Immunoglobulin heavy chain locus (Igh) VH, D, and JH gene segments are developmentally assembled into V(D)J exons. RAG endonuclease initiates V(D)J recombination by binding a JH-recombination signal sequence (RSS) within a chromatin-based recombination center (RC) and then, in an orientation-dependent process, scans upstream D-containing chromatin presented by cohesin-mediated loop extrusion for convergent D-RSSs to initiate DJH-RC formation. In primary pro-B cells, 100s of upstream VH-associated RSSs, embedded in convergent orientation to the DJH-RC-RSS, gain proximity to the DJH-RC for VH-to-DJH joining via a mechanistically-undefined VH-locus contraction process. Here, we report that a 2.4 mega-base VH locus inversion in primary pro-B cells nearly abrogates rearrangements of normally convergent VH-RSSs and cryptic RSSs, even though locus contraction per se is maintained. Moreover, this inversion activated rearrangement of both cryptic VH-locus RSSs normally in the opposite orientation and, unexpectedly, of normally-oriented cryptic RSSs within multiple, sequential upstream convergent-CBE domains. Primary pro-B cells had significantly reduced transcription of Wapl, a cohesin-unloading factor, versus levels in v-Abl pro-B lines that lack marked locus contraction or distal VH rearrangements. Correspondingly, Wapl depletion in v-Abl lines activated VH-locus contraction and orientation-specific RAG-scanning across the VH-locus. Our findings indicate that locus contraction and physiological VH-to-DJH joining both are regulated via circumvention of CBE scanning impediments. Overall design: We performed GRO-Seq in BM pro-B cells and v- Abl transformed pro-B cells and its various mutant derivatives to study orientation-dependent linear RAG scanning and locus contraction in long-range cohesin-driven V(D)J recombination. Less...