Comprehensive annotation and evolutionary insights into the canine (Canis lupus familiaris) antigen receptor loci

Dogs are an excellent model for human disease. For example, the treatment of canine lymphoma has been predictive of the human response to that treatment. However, an incomplete picture of canine (Canis lupus familiaris) immunoglobulin (IG) and T cell receptor (TR)—or antigen receptor (AR)—gene loci has restricted their utility. This work advances the annotation of the canine AR loci and looks into breed-specific features of the loci. Bioinformatic analysis of unbiased RNA sequence data was used to complete the annotation of the canine AR genes. This annotation was used to query 107 whole genome sequences from 19 breeds and identified over 5500 alleles across the 550 genes of the seven AR loci: the IG heavy, kappa, and lambda loci; and the TR alpha, beta, gamma, and delta loci. Of note was the discovery that half of the IGK variable (V) genes were located downstream of, and inverted with respect to, the rest of the locus. Analysis of the germline sequences of all the AR V genes identified greater conservation between dog and human than mouse with either. This work brings our understanding of the genetic diversity and expression of AR in dogs to the same completeness as that of mice and men, making it the third species to have all AR loci comprehensively and accurately annotated. The large number of germline sequences serves as a reference for future studies, and has allowed statistically powerful conclusions to be drawn on the pressures that have shaped these loci.