Abstract
Abstract The immunoglobulin genes of germinal center B cells (GCB) undergo somatic hypermutation in order to generate antibody diversity. Additionally, several non-immunoglobulin (non-Ig) genes are known to accumulate mutations in the germinal center. There are two methods by which mutations are introduced at the Ig and non-Ig loci. The first is through the accumulation of pseudorandom point mutations as a result of activation-induced cytidine deaminase (AID)-dependent double stranded breaks (DSB). The second is through the process of gene conversion, which involves the use of a template sequence to repair a DSB resulting in the template being copied at the site of repair. Findings from our lab suggest that some mutations in the non-Ig genes of human GCB arise through a gene conversion-like mechanism, referred to as templated mutagenesis. We sorted 4 B cell populations, including light zone and dark zone GCB from a young human tonsil and sequenced ~500bp sections from non-Ig genes including FAS, RHOH, and BTG1 via Illumina MiSeq. Previously, our lab has developed a computational pipeline called TRACE, that is able to match mutation clusters within an input sequence to partially homologous donor templates elsewhere in the genome. TRACE-identified donor templates are statistically likely to have been used in a templated mutagenesis event which led to the mutation of the gene. Through this analysis, we found that unlike gene conversion observed in chickens, human templated mutagenesis occurs between sequences on different chromosomes. Furthermore, donor template sequences tend to originate in introns and intergenic regions, not exons. These findings have opened an avenue into the study of non-Ig templated mutagenesis in human B cells.
Published Version
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