The fundamental role of chromatin loop extrusion in physiological V(D)J recombination

The RAG endonuclease initiates Igh V(D)J assembly in B cell progenitors by joining D segments to JH segments, before joining upstream VH segments to DJH intermediates1. In mouse progenitor B cells, the CTCF-binding element (CBE)-anchored chromatin loop domain2 at the 3' end of Igh contains an internal subdomain that spans the 5' CBE anchor (IGCR1)3, the DH segments, and a RAG-bound recombination centre (RC)4. The RC comprises the JH-proximal D...