%0 Journal Article
%T Adaptive molecular evolution of the Major Histocompatibility Complex genes, DRA and DQA, in the genus Equus
%A Pauline L Kamath
%A Wayne M Getz
%J BMC Evolutionary Biology
%D 2011
%I BioMed Central
%R 10.1186/1471-2148-11-128
%X We investigated the evolution of two class II MHC genes of the Equine Lymphocyte Antigen (ELA), DRA and DQA, in the genus Equus with the addition of novel alleles identified in plains zebra (E. quagga, formerly E. burchelli). We found that both genes exhibited a high degree of polymorphism and inter-specific sharing of allele lineages. To our knowledge, DRA allelic diversity was discovered to be higher than has ever been observed in vertebrates. Evidence was also found to support a duplication of the DQA locus. Selection analyses, evaluated in terms of relative rates of nonsynonymous to synonymous mutations (dN/dS) averaged over the gene region, indicated that the majority of codon sites were conserved and under purifying selection (dN < dS). However, the most likely evolutionary codon models allowed for variable rates of selection across codon sites at both loci and, at the DQA, supported the hypothesis of positive selection acting on specific sites.Observations of elevated genetic diversity and trans-species polymorphisms supported the conclusion that balancing selection may be acting on these loci. Furthermore, at the DQA, positive selection was occurring at antigen binding sites, suggesting that a few selected residues may play a significant role in equid immune function. Future studies in natural equid populations will be valuable for understanding the functional significance of the uniquely diverse DRA locus and for elucidating the mechanism maintaining diversity at these MHC loci.Genes of the Major Histocompatibility Complex (MHC) are ideal candidates for investigating the influence of selection in promoting patterns of genetic diversity [1,2], due to their ecological significance. This multi-gene family has been widely demonstrated to play a fundamental role in gnathostome (i.e. jawed vertebrate) immune response by modulation of resistance to parasites and pathogens [1,3,4]. More specifically, class I and II MHC genes encode cell-surface glycoproteins that r
%U http://www.biomedcentral.com/1471-2148/11/128