Diversity of the BoLA-DRB3 Gene in Cattle Breeds From Tropical and Subtropical Regions of South America

Abstract

Background Bovine leukocyte antigens (BoLA) are widely used as markers of disease and immunological traits in cattle because of their primary function in the recognition of pathogens by the immune system. To date, however, the characterization of BoLA gene polymorphisms in Latin American Zebu and mixed zebuine breeds is scarce. By a sequence-based typing method, here we sequenced exon 2 of BoLA class II DRB3 gene of 264 animals from the five breeds (Creole, Brahman, Braford, Brangus and Nellore) most commonly used in northern Argentina. Results The taurine and zebuine breeds contained 61 previously reported alleles. Genetic diversity was high at allelic and molecular levels, particularly in the mixed breeds. Neutrality tests revealed that none of the breeds shows the even gene frequency distribution expected under a balanced selection scenario. The FST index shows significant differences across all populations (FST=0.052, P < 0.001), indicating a substantial differentiation between breeds. UPGMA trees and Metric multidimensional scaling (MDS) analysis show that, as expected, Creole is distantlyrelated to the other zebuinebreeds. Among them, Brahman, Braford and Brangus cluster closer together than with Nellore. These data are consistent with the historical and geographical origin of these breeds. A peptide binding region sequence analysis at the aminoacid level revealed that, despite the nucleotide diversity among the breeds, the key aminoacids involved in peptide recognition are greatly conserved. Conclusions This is the first report of BoLA-DRB3 diversity in pure and mixed zebuine cattle breeds from Argentina. Knowledge ofBoLA-DRB3 variability in breeds adapted to tropical and subtropical environments contributes not only to ongoing efforts to catalog bovine MHC allele frequencies by breed and location but also to the design of peptide-based vaccines.