Polymorphism Analysis Of Major Histocompatibility Complex (MHC) DQB Gene In Asiatic Black Bear (Ursus Thibetanus)

To protect the wild population of Asiatic black bear and to maintain the sustainable development of its captive population,theoretical and technical support is urgently needed in the field of conservation genetics for population management.The major histocompatibility complex(MHC),an adaptive molecular marker,can be used not only to evaluate genetic diversity of the population,but also to reflect the selective pressure and adaptive capacity to the environment during evolution.Therefore,we investigated the polymorphisms of MHC-DQB gene polymorphism and its evolutionary selection pressure and phylogenetic relationships in Asiatic black bear populations using PCR and cloning and sequencing.The main results are as follows:44 DQB alleles(398 bp)were obtained in 144 individuals of Asiatic black bear and were named Urth-DQB*1?Urth-DQB*29?Urth-DQB*33?Urth-DQB*47,DQB genes including intron 1 fragment 95bp,entire exon 2270bp and intron 2 fragment 33bp.A total of 33 DQB exon 2 alleles were obtained.The haplotype diversities of captive populations and wild populations in Asiatic black bears were 0.926±0.006 and 0.925±0.013 respectively,and the nucleotide diversities were 0.0531±0.0044 and 0.0547±0.0054 respectively.The mean nucleotide differences between alleles were 21.146 and 21.749 respectively.No significant difference was found,the genetic diversities of captive and wild populations were similar.The haplotype diversities of geographic populations of Changbai Mountain and Russia were 0.922±0.020 and 0.933±0.022,and the nucleotide diversities were 0.0530±0.0053 and 0.0531±0.0026 respectively.The mean nucleotide differences between alleles were 21.074 and 21.132 respectively.There was no significant difference,the genetic diversity of Changbai Mountain geographical population was similar to the Russia geographical population.The haplotype diversities of Asiatic black bear mainland population and island population(Japanese black bear)were 0.923 ± 0.005 and 0.644±0.028 respectively.The nucleotide diversities were 0.0567± 0.0063 and 0.0355±0.0020,and the mean nucleotide differences between alleles were 15.318 and 9.662 respectively.The genetic diversity of the population in the mainland was significantly higher than that of the Japanese island population.The haplotype diversity of Manchu black bear was 0.910±0.014,and the nucleotide diversity was 0.0580±0.0068,and the mean nucleotide difference between alleles was 15.650.The genetic diversity of Manchu black bear is higher than Japanese black bear.The non-synonymous mutation rates of DQB gene antigen-binding region and exon 2 region were greater than that of synonymous mutation rate(dN/dS>1)in Asiatic black bear,and the balancing selection maintained the MHC gene polymorphism of Asiatic black bear during evolution.The peptide-binding region in the DQB gene of Asiatic black bear in mainland experienced a stronger selection pressure than the Asiatic black bear in Japan and giant pandas during the evolution process.Asiatic black bear and brown bear were under greater selection pressure than giant panda,Namibian cheetah,European mink and other endangered species.The shared genes were found in Asiatic black bear and giant panda,suggesting that DQB genes have trans-species evolution.The phylogenetic tree can be divided into two branches,but it is impossible to determine the distribution of DQBs in Asiatic black bear based on the evolutionary tree topology.Urth-DQB*2017-14 and Urth-DQB*2017-17 as dominant alleles may play an important role in the resistance to pathogens..