Genetic Diversity And Adaptive Evolution Of MHC-DRB Gene In Tarim Red Deer(Cervuselaphus Yarkandensis)

Major Histocompatibility Complex(MHC)is a multi-gene family of vertebrate immune system,which is composed of highly polymorphic loci and closely related to immune response and disease resistance.MHC gene has been considered as the best candidate marker for studying the adaptive evolutionary mechanism of vertebrates,which has been confirmed by a large number of studies.At present,evolutionary genetics and molecular ecology are the hottest topics to study MHC gene polymorphism and its evolutionary mechanism.So far,there is no evidence from Tarim red deer on the evolutionary mechanism of MHC-DRB gene in deer.Tarim red deer is a special subspecies of Xinjiang Tarim red deer,which is highly adapted to desert habitats.It is a national second-class protected animal and an important economic animal.In this study,MHC-DRB gene was used as a molecular marker to study the polymorphism and adaptive evolutionary mechanism of MHC-DRB in Tarim wapiti deer.The main results are as follows:1.In this study,13 DRB alleles were detected from 51 Tarim red deer samples by PCR-SSCP and cloning sequencing techniques.The 13 alleles contained 76nucleotide mutations(24 Singleton Sites and 52 parsim-info Sites),with 30.5%of the total number of variable Sites.The contents of G,C,A and T in the 13 allele sequences obtained in this study were significantly different.The proportion of each base was 36.2%(G),23.3%(C),22.9%(A),17.6%(T),and the content of G+C(59.5%)was significantly higher than that of A+T(40.5%),showing obvious GC preference.The Transitionsal/Transversional rate was R=0.55.No insertion or deletion sites were found in the full-length sequence,and there was Transversional bias in the sequence variation of MHC-DRB gene inTarim red deer.2.Nucleotide diversity based on MHC-DRB gene(pi):0.1125,Haplotype diversity(h):0.9380,average difference of nucleic acid:28.015.The MHC-DRB gene of Tarim red deer has high polymorphism and genetic diversity.3.The MHC diversity of Tarim red deer is influenced by Selective Pressure,and positive selection is the main maintenance mechanism of MHC-DRB gene polymorphism of Tarim red deer.The d_N of exon 2 of 13 alleles Ceel-DRB*01,Ceel-DRB*02 and non-PBR of Tarim red deer obtained in this study were larger than ds,which indicated that these alleles had positive selection.The results showed that the variation of DRB gene mainly existed in PBR region,and Z-test selectivity test showed that these Sites reached statistical significant level(0.01<P<0.05).The data obtained in this study were further analyzed by EasyCodeML software.The results showed that M8 model was more suitable for our data.It was further confirmed that MHC-DRB gene of Tarim red deer had undergone significant positive selection(P<0.001),and a total of 18 amino acid loci were detected to be affected by positive selection.