Pre-B Cell Receptor Signaling Induces Immunoglobulin κ Locus Accessibility by Functional Redistribution of Enhancer-Mediated Chromatin Interactions

During b cell development,the precursor b cell receptor (pre-bcr) checkpoint is thought to increase immunoglobulin κ light chain (igκ) locus accessibility to the v(d)j recombinase. accordingly,pre-b cells lacking the pre-bcr signaling molecules btk or slp65 showed reduced germline vκ transcription. to investigate whether pre-bcr signaling modulates vκ accessibility through enhancer-mediated igκ locus topology,we performed chromosome conformation capture and sequencing analyses. these revealed that already in pro-b cells the κ enhancers robustly interact with the ∼3.2 mb vκ region and its flanking sequences. analyses in wild-type,btk,and slp65 single- and double-deficient pre-b cells demonstrated that pre-bcr signaling reduces interactions of both enhancers with igκ locus flanking sequences and increases interactions of the 3′κ enhancer with vκ genes. remarkably,pre-bcr signaling does not significantly affect interactions between the intronic enhancer and vκ genes,which are already robust in pro-b cells. both enhancers interact most frequently with highly used vκ genes,which are often marked by transcription factor e2a. we conclude that the κ enhancers interact with the vκ region already in pro-b cells and that pre-bcr signaling induces accessibility through a functional redistribution of long-range chromatin interactions within the vκ region,whereby the two enhancers play distinct roles. © 2014 stadhouders et al.