title: Activation-induced cytidine deaminase induces DNA break repair events more frequently in the Ig switch region than other sites in the mammalian genome.
abstract: Activation-induced cytidine deaminase (AID) produces DNA breaks in immunoglobulin genes during antibody diversification. Double-stranded breaks (DSB) in the switch region mediate class switch recombination, and contribute to gene conversion and somatic hypermutation in the variable regions. However, the relative extent to which AID induces DSB in these regions or between these and other actively expressed sequences is unknown. Here, we exploited an enhancer-trap plasmid that identifies DSB in actively expressed loci to investigate the frequency and position of AID-induced vector integration events in mouse hybridoma cells. Compared to control cells, wild-type AID stimulates plasmid integration into the genome by as much as 29-fold. Southern and digestion-circularization PCR analysis revealed non-uniformity in the integration sites, with biases of 30- and 116-fold for the immunoglobulin kappa light chain and mu heavy chain genes, respectively. Further, within the immunoglobulin mu gene, 73% of vector integrations map to the mu switch region, an enhancement of five- and 12-fold compared to the adjacent heavy chain variable and mu gene constant regions, respectively. Thus, among potential highly transcribed genes in mouse hybridoma cells, the immunoglobulin heavy and light chain genes are important AID targets, with the immunoglobulin mu switch region being preferred compared to other genomic sites.
authors.affiliation: Department of Molecular and Cellular Biology, College of Biological Science, University of Guelph, Guelph, Canada.
authors.forename: Shauna A
authors.initials: SA
authors.lastname: Lee
authors.forename: Jahan-Yar
authors.initials: JY
authors.lastname: Parsa
authors.forename: Alberto
authors.initials: A
authors.lastname: Martin
authors.forename: Mark D
authors.initials: MD
authors.lastname: Baker
mesh_terms: D000818:Animals; D001483:Base Sequence; D003564:Cytidine Deaminase / Q000235:genetics / Q000502:physiology*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004274:DNA, Recombinant / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D006825:Hybridomas / Q000201:enzymology; D007134:Immunoglobulin Switch Region; D007148:Immunoglobulin mu-Chains / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D027041:Somatic Hypermutation, Immunoglobulin; D013379:Substrate Specificity; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D004274:DNA, Recombinant; D007148:Immunoglobulin mu-Chains; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase