Antibody class switch recombination (CSR) in B lymphocytes joins two DNA double-strand breaks (DSBs) lying 100-200 kb apart within switch (S) regions in the immunoglobulin heavy-chain locus (IgH). CSR-activated B lymphocytes generate multiple S-region DSBs in the donor Sμ and in a downstream acceptor S region, with a DSB in Sμ being joined to a DSB in the acceptor S region at sufficient frequency to drive CSR in a large fraction of activated B cells. Such frequent joining of widely separated CSR DSBs could be promoted by IgH-specific or B-cell-specific processes or by general aspects of chromosome architecture and DSB repair. Previously, we found that B cells with two yeast I-SceI endonuclease targets in place of Sγ1 undergo I-SceI-dependent class switching from IgM to IgG1 at 5-10% of normal levels. Now, we report that B cells in which Sγ1 is replaced with a 28 I-SceI target array, designed to increase I-SceI DSB frequency, undergo I-SceI-dependent class switching at almost normal levels. High-throughput genome-wide translocation sequencing revealed that I-SceI-generated DSBs introduced in cis at Sμ and Sγ1 sites are joined together in T cells at levels similar to those of B cells. Such high joining levels also occurred between I-SceI-generated DSBs within c-myc and I-SceI- or CRISPR/Cas9-generated DSBs 100 kb downstream within Pvt1 in B cells or fibroblasts, respectively. We suggest that CSR exploits a general propensity of intrachromosomal DSBs separated by several hundred kilobases to be frequently joined together and discuss the relevance of this finding for recurrent interstitial deletions in cancer.

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Journal Article | Research Support, N.I.H., Extramural | Research Support, Non-U.S. Gov't

Authors

Gostissa M, Schwer B, Chang A, Dong J, Meyers RM, Marecki GT, Choi VW, Chiarle R, Zarrin AA, Alt FW

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