Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching

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Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching

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Title: Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching
Author: Dong, Junchao; Panchakshari, Rohit A.; Zhang, Tingting; Zhang, Yu; Hu, Jiazhi; Volpi, Sabrina A.; Meyers, Robin M.; Ho, Yu-Jui; Du, Zhou; Robbiani, Davide F.; Meng, Feilong; Gostissa, Monica; Nussenzweig, Michel C.; Manis, John P.; Alt, Frederick W.

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Citation: Dong, J., R. A. Panchakshari, T. Zhang, Y. Zhang, J. Hu, S. A. Volpi, R. M. Meyers, et al. 2015. “Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching.” Nature 525 (7567): 134-139. doi:10.1038/nature14970. http://dx.doi.org/10.1038/nature14970.
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Abstract: During B cell development, RAG endonuclease cleaves immunoglobulin heavy chain (IgH) V, D, and J gene segments and orchestrates their fusion as deletional events that assemble a V(D)J exon in the same transcriptional orientation as adjacent Cμ constant region exons1,2. In mice, six additional sets of constant region exons (CHs) lie 100-200 kb downstream in the same transcriptional orientation as V(D)J and Cμ exons2. Long repetitive switch (S) regions precede Cμ and downstream CHs. In mature B cells, class switch recombination (CSR) generates different antibody classes by replacing Cμ with a downstream CH2. Activation-Induced Cytidine Deaminase (AID) initiates CSR by promoting deamination lesions within Sμ and a downstream acceptor S region2,3; these lesions are converted into DNA double-strand breaks (DSBs) by general DNA repair factors3. Productive CSR must occur in a deletional orientation by joining the upstream end of an Sμ DSB to the downstream end of an acceptor S region DSB (Fig. 1a). However, the relative frequency of deletional to inversional CSR junctions had not been measured. Thus, whether orientation-specific joining is a programmed mechanistic feature of CSR as it is for V(D)J recombination and, if so, how this is achieved was unknown. To address this question, we adapted high-throughput genome-wide translocation sequencing (HTGTS)4 into a highly sensitive DSB end-joining assay and applied it to endogenous AID-initiated S region DSBs. We find that CSR indeed is programmed to occur in a productive deletional orientation and does so via an unprecedented mechanism that involves in cis IgH organizational features in combination with frequent S region DSBs initiated by AID. We further implicate ATM-dependent DSB response (DSBR) factors in enforcing this mechanism and provide a solution to the enigma of why CSR is so reliant on the 53BP1 DSBR factor.
Published Version: doi:10.1038/nature14970
Other Sources: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592165/pdf/
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Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:26318692
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