Pre-BCR Signaling induce IgK 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 k light chain (Igk) locus accessibility to the V(D)J recombinase. Accordingly, pre-B cells lacking the pre-BCR signaling molecules Btk or Slp65 showed reduced germline Vk transcription. To investigate whether pre-BCR signaling modulates Vk accessibility through enhancer-mediated Igk locus topology, we performed chromosome conformation capture and sequencing analyses. These revealed that already in pro-B cells the k enhancers robustly interact with the ~3.2 Mb Vk 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 Igk locus flanking sequences and increases interactions of the 3k enhancer with Vk genes. Remarkably, pre-BCR signaling does not significantly affect interactions between the intronic enhancer and Vk genes, which are already robust in pro-B cells. Both enhancers interact most frequently with highly used Vk genes, which are often marked by transcription factor E2a. We conclude that the k enhancers interact with the Vk region already in pro-B cells and that pre-BCR signaling induces accessibility through a functional redistribution of long-range chromatin interactions within the Vk region, whereby the two enhancers play distinct roles.

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Stadhouders R, de Bruijn MJ, Rother MB, Yuvaraj S, Ribeiro de Almeida C, Kolovos P, Van Zelm MC, van Ijcken W, Grosveld F, Soler E, Hendriks RW