Molecular and evolutionary study of genetic variability in Equids DRA gene

DÍAZ, S.; IT V.; DI LORENZO M.; ECHEVERRÍA M.G.; PERAL GARCÍA P.; GIOVAMBATTISTA G.

Porto Seguro, Brasil

Congreso; 30th International Conference on Animal Genetics; 2006

International Society of Animal Genetics

  The a chain of most classical Class II genes at the Mayor Histocompatibility Complex are essentially monomorphic in mammals. Several reports indicate that the DRA locus is moderately polymorphic in equids, where eleven DRA exón 2 alleles were reported, four have been found widely distributed among horse breeds and others are almost exclusive in a particular Equidae species. To analyze the genetic variation of the ELA-DRA locus, we screened polymorphism in different domestic horse breeds by PCR-SSCP and DNA sequencing in 121 horses of the Argentine Creole, Thoroughbred, Peruvian Paso, Arab, Spanish and Silla Argentino breeds. In addition, to evaluate the evolutionary pattern of this gene, we compared DRA exón 2 nucleotide sequences from several species of different mammalian orders. The obtained sequences and those retrieved from the database were analyzed by using the MEGA program. For the evolutionary purpose, DRA exón 2 sequences from horses and other mammalian species were analyzed for amino acid sequence variability and the pattern of synonymous and non synonymous substitutions was compared and phylogenetic trees were constructed. Three alleles were detected in the analyzed sample which corresponded to DRA*0101, 0201 and 0301 horse alleles. Allele profiles were significantly different among breeds, while estimated heterozigosity ranged from 0.90 to 0.50. Sequence analysis of the exón 2 showed that equid species presented six amino acid residues that are exclusive for this order. In addition, amino acidic variability among orders was concentrated into 6 well defined amino acidic motifs distributed trough all exón 2 sequence. As expected, this region exhibited high ratios of nonsynonymous to synonymous substitutions in the Antigen Binding Sites (ABS), but in equine species the non synonymous substitutions were only present in ABS sites. Phylogenetic analysis showed that DRA sequences were grouped in agreement with their evolutionary origin. The present study could contribute to increased our knowledge of the patterns of molecular evolution that determine the unusual ELA-DRA polymorphism.