Polymorphism And Genetic Evolution Of MHC Class Genes In Rana Dybowskii

Major histocompatibility complex(MHC)gene is a typical multigene family in vertebrates which can encode MHC molecules and closely related with animal disease resistance,sexual selection and genetic evolution.It can recognize and present exogenous antigen or endogenous antigen to T lymphocytes,and then induce immune response.It is one of the optimal candidate genes in studying adaptive evolution of vertebrates and is also one of the target genes in research on amphibian conservation.Northeast Brown Frogs(Rana dybowskii)is a kind of amphibian,which is distributed mainly over Northeast of China and adaptable for cold climate.There were plentiful wild resources of the species in the past,but they are declining rapidly because of the environmental change.It is responsible for Vulnerable species.In order to protect Rana dybowskii,genetic evolution and polymorphism of MHC genes from three populations(Yichun and Shangzhi of Heilongjiang province,Baishan of Jilin province)will be studied in the study.The main results are as follows:(1)Fragments about 500 bps on MHC class I ?1+?2 were obtained(including partial exon2 and exon3)and 12 MHC I class alleles were identified.It displayed that variation sites of MHC class I alleles were 15.2%,5 alleles were found in Shangzhi population,we deduced that there were more than 3 MHC class I alleles at least in Rana dybowskii in the study.(2)Fragments about 250 bps from exon2 of MHC class ?? are amplified.We also identified 7 MHC class ?? alleles,variation sites of the MHC class ?? alleles were 19.6%.There were 2 MHC class ?? alleles at least in Yichun population.(3)Average amino acid distances were higher than average nucleotide distances in MHC class I ?1+?2 and MHC class ?? exon2 of Rana dybowskii,and there were more non-synonymous compared with synonymous mutations,which indicated that the sequences were under positive selection.(4)26 selection sites were obtained in MHC class I ?1+?2,two of which were located at the putative antigen-binding site(ABS);22 sites were detected in MHC class?? genes and four of them were located at the putative ABS.It is speculated that themaintenance of MHC polymorphism of Rana dybowskii is related to pathogen induction.(5)Recombination of MHC genes was not found by detecting the intron of exon3 and exon2 in Rana dybowskii,there were no cross-species polymorphisms in MHC class I genes and MHC class II genes of three populations.In conclusion,MHC class ? and MHC class ?? genes from Rana dybowskii had rich polymorphisms.Gene duplication,gene mutation took effects during evolution.It will provide theoretical foundation for the species conservation.