Activation-induced cytidine deaminase-initiated off-target DNA breaks are detected and resolved during S phase
Department of Microbiology and Physiological Systems; Department of Cell Biology
Medical Subject Headings
Animals; B-Lymphocytes; Cells, Cultured; Cytidine Deaminase; *DNA Breaks, Double-Stranded; DNA Repair; G1 Phase; Immunoglobulin Class Switching; Immunoglobulin Isotypes; Mice; Mice, Inbred C57BL; Mice, Knockout; S Phase
Genetics and Genomics | Immunology and Infectious Disease
Activation-induced cytidine deaminase (AID) initiates DNA double-strand breaks (DSBs) in the IgH gene (Igh) to stimulate isotype class switch recombination (CSR), and widespread breaks in non-Igh (off-target) loci throughout the genome. Because the DSBs that initiate class switching occur during the G(1) phase of the cell cycle, and are repaired via end joining, CSR is considered a predominantly G(1) reaction. By contrast, AID-induced non-Igh DSBs are repaired by homologous recombination. Although little is known about the connection between the cell cycle and either induction or resolution of AID-mediated non-Igh DSBs, their repair by homologous recombination implicates post-G(1) phases. Coordination of DNA breakage and repair during the cell cycle is critical to promote normal class switching and prevent genomic instability. To understand how AID-mediated events are regulated through the cell cycle, we have investigated G(1)-to-S control in AID-dependent genome-wide DSBs. We find that AID-mediated off-target DSBs, like those induced in the Igh locus, are generated during G(1). These data suggest that AID-mediated DSBs can evade G(1)/S checkpoint activation and persist beyond G(1), becoming resolved during S phase. Interestingly, DSB resolution during S phase can promote not only non-Igh break repair, but also Ig CSR. Our results reveal novel cell cycle dynamics in response to AID-initiated DSBs, and suggest that the regulation of the repair of these DSBs through the cell cycle may ensure proper class switching while preventing AID-induced genomic instability.
Hasham, Muneer G.; Snow, Kathy J.; Donghia, Nina M.; Branca, Jane A.; Lessard, Mark D.; Stavnezer, Janet; Shopland, Lindsay S.; and Mills, Kevin D., "Activation-induced cytidine deaminase-initiated off-target DNA breaks are detected and resolved during S phase" (2012). Microbiology and Physiological Systems Publications and Presentations. 2.