Sequences Analysis Of The Second Exon Of MHC Class Ⅱ B Gene And Trans-species Polymorphism Of Two Reptiles

The major histocompatibility complex (MHC) is a chromosomal region consisting of closely linked loci which are highly polymorphic. Genes of the MHC encode molecules responsible for the recognition and presentation of foreign antigens and thus play an important role in immune system in the vertebrates. The polymorphism is the essential characteristic of MHC genes and variability of MHC genes is an indicator for the parasite and pathogen resistance, which in turn may influence the long-term survival probability of populations, so the genetic variation of MHC is widely applied to conservation genetics. At the present time, studies based on MHC genes are mainly focused on Class â…¡gene, especially the second exon of Class â…¡. In order to study MHC genes of reptile, we investigated genetic variation at exon 2 (including part of the putative antigen-binding sites, pABS) of MHC Class â…¡B gene in Chinemys reevesii and Eumeces chinensis. A pair of degenerate primers was used to amplify the fragments, PCR products were cloned and then sequenced. The purpose in this study was mainly to understand the sequence structure and genetic variations of MHC genes in two reptiles, and put foundation for population genetic structure research of two reptiles. Eight and seven 166bp-long different sequences were obtained from Chinemys reevesii and Eumeces chinensis respectively. The sequences showed highly polymorphic, the ratio of nonsynonymous substitutions was higher than that of synonymous substitutions, which may be the result of balancing selection, and substitutions of amino acid tended to be clustered around the pABS. More than two sequences were found in the same individual, suggesting that there would be locus duplication. At the same time, this study was first documented trans-species polymorphism of MHC Class â…¡B gene in reptile, and would redound to researches of trans-species evolution of MHC genes.