Polymorphism And Sequence Characteristics In BoLA-DRB1 And DRB2 Genes In Yak

Major Histcompatibility Complex(MHC) plays an important role in antigen recognition and presentation, immune response and regulation. MHC gene family is closely linkage, highly polymorphic and haplotype inheritance. Bovine MHC had been named as Bovine Lymphocyte Antigen(Bo LA), and associated with many diseases and production performance. DRB1 and DRB2 genes belong to the Bo LA II region.The polymorphism and sequence characteristics of intron 1, exon 2, intron 2 in DRB1 gene and intron 1, intron 2, exon 3 in DRB2 gene were analysised using PCR-SSCP in Gannan yak, Qinghai yak, Tianzhu white yak, Datong yak and cattle in this study. The main results were showed as follows:(1) High polymorphisms were found in intron 1 and exon 2 of DRB1 gene in yak populations and cattle. Four SNPs and one insertion/deletion mutation were detected in intron 1 which corresponding to four alleles(A-D) and seven genotypes. Allele B with the frequency from 0.361 to 0.481 was the most common allele. Eighteen SNPs were identified in exon 2 of DRB1 gene which corresponding to nine alleles(A1-I1) and eleven genotypes. Allele A1 with the frequency of 0.188 and 0.279 were the most common allele in Qinghai yak and Tianzhu white yak, but allele B1 with the frequency from 0.251 to 0.285 were the most common allele in Gannan yak, Datong yak and cattle. PIC ranged from 0.575 to 0.860 with high polymorphisms in these two regions of DRB1 gene in yak populations and cattle.(2) Polymorphism of intron 2 in DRB2 gene was different among the yak populations and cattle. Seven SNPs corresponding to five alleles(A2-E2) were detected in intron 2. Allele A2 with the frequency from 0.188 to 0.276 was the most common allele. High polymorphisms in intron 2 were found in Gannan yak, Tianzhu white yak and Qinghai yak with PIC ranged from 0.525 to 0.571, but moderate polymorpisms in Datong yak and cattle with PIC from 0.428 to 0.459. No nucleotide mutation was found in intron 1 and exon 3 of DRB2 gene in all of yak populations and cattle.(3) The analysis results of population genetics indicated that the hypothesis of Hardy-Weinberg equilibrium were rejected in DRB1 and DRB2 genes in Gannan yak(P<0.01), as well as DRB2 gene in Qinghai yak(P<0.01).(4) Haplotypes linkage disequilibriums were found in DRB1 and DRB2 genes in yak populations and cattle. Total 134 kinds of haplotypes were found in all of populations investigated in this study, including 25 kinds of “intron 1-exon 2 in DRB1” haplotypes, 20 kinds of “intron 1 in DRB1-intron 2 in DRB2” haplotypes, 18 kinds of “exon 2 in DRB1-intron 2 in DRB2” haplotypes and 71 kinds of “intron 1 in DRB1-exon 2 in DRB1-intron 2 in DRB2” haploypes. The number of haplotypes was less than theoretical value, and haplotype frequencies ranged from 0.004 to 0.117 in all of populations. Haplotypes linkage disequilibriums were identified in diferent regions of DRB1 and DRB2 genes in yak populations and cattle as D、and r2 value of four types of haplotype were 0.247-0.581 and 0.155-0.195, respectively.(5) The sequence of exon 2 in yak DRB1 gene was the highest homology with cattle, the phylogenetic distance consistent with their genetic relationship.