Fundamental roles of chromatin loop extrusion in antibody class switching

Antibody class switch recombination (CSR) in B lymphocytes replaces immunoglobulin heavy chain locus (Igh) Cμ constant region exons (CHs) with one of six CHs lying 100-200 kb downstream1. Each CH is flanked upstream by an I promoter and long repetitive switch (S) region1. Cytokines and activators induce activation-induced cytidine deaminase (AID)2 and I-promoter transcription, with 3' IgH regulatory region (3' IgHRR) enhancers controlling the...