黄麂Mhc-DRB基因多态性及其维持机制  

Maintenance of polymorphism of Chinese muntjac (Muntiacus reevesi) Mhc-DRB gene

作　　者：虞健[1] 梁文明[1] 朱飞虎[1] 徐思[1] 吴海龙[1] 

机构地区：[1]安徽师范大学生命科学学院,安徽省高校生物环境与生态安全省级重点实验室,芜湖241000

出　　处：《兽类学报》2010年第1期51-57,共7页Acta Theriologica Sinica

基　　金：国家自然科学基金资助项目(30970433);安徽省自然科学基金资助项目(070413135)

摘　　要：利用牛DRB3特异性引物(LA31和LA32),通过聚合酶链式反应(PCR)、单链构象多态性(SSCP)以及克隆测序技术,从12只黄麂个体中共获得20个DRB第二外显子等位基因,其中6个个体具有3～4个等位基因,提示利用该引物从黄麂中至少可以扩增出2个DRB位点。所有序列均无插入、缺失和终止密码子。基于序列比对(与牛DRB3和鹿科DRB基因同源性非常高),以及所检测到的氨基酸变异位点主要位于抗原结合区,推测本文所获得的黄麂序列为表达的、且具有重要功能的DRB位点。抗原结合区氨基酸位点的非同义替换(dN)显著大于同义替换(dS)(P<0.01),说明历史上黄麂DRB基因经历过正选择作用。CODMEL程序中的模型M7和M8似然比检测(Likelihood ratio test,LRT)结果同样支持上述推论。进一步利用经验贝叶斯法准确地检测出6个受正选择作用的氨基酸位点(位点11、37、61、67、71、86),其中的5个位点位于PBR区。因此,正选择作用可能是维持黄麂DRB基因多态性的主要机制之一。基于DRB外显子2序列利用邻接法(NJ)构建了部分偶蹄动物系统发生关系,在NJ树上,黄麂DRB基因与其它鹿科动物DRB基因呈镶嵌式分布,提示跨物种进化是维持黄麂DRB基因多态性的另一重要机制。此外,黄麂两个等位基因(Mure-DRB1和Mure-DRB11)和马鹿的两个等位基因(Ceel-DRB34和Ceel-DRB46)与牛科的等位基因构成一个独立的进化枝,说明黄麂和马鹿的某些DRB基因具有非常古老的谱系。A pair of primers （LA31 and LA32） specific to BoLA-DRB3 were used to amplify genomic DNA of the Chinese muntjac （Muntiacus reevesi）. Twenty distinct DRB exon 2 alleles were obtained from 12 individuals through polymerase chain reaction （PCR）, single strand conformation polymorphism （SSCP）, and sequencing. At least two DRB loci could be discerned taking into account the fact that three to four alleles were identified from six of 12 individuals analyzed in this study. No insertion, deletion or stop codons within the nucleotide sequences were detected. Multiple sequence alignments demonstrated that the Chinese muntjac DRB alleles showed high similarity to that of the expressed BoLA-DRB3 locus. The amino acid mutation sites were mainly present in the putative peptide binding region （PBR）. These results evidenced that the loci isolated in this study were probably expressed and functioning.The frequency of nonsynonymous substitutions（d_N） was significantly greater than that of synonymous substitutions（d_S） （P0.01） in the peptide binding region （PBR） suggesting that the DRB gene of the Chinese muntjac had historically undergone positive selection. This inference was further confirmed through likelihood ratio test （LRT） from model M7 and M8 of program CODEML. Six robust positive selection amino acid sites （position 11, 37, 61, 67, 71 and 86） were detected by a Bayesian method, of which 5 sites located in PBR. These results provide evidence that positive selection is one of the main mechanisms in maintaining DRB gene polymorphism of the Chinese muntjac. A neighbor-join （NJ） tree was constructed based on DRB gene exon 2 sequences of several deer. In the NJ tree, the Chinese muntjac DRB alleles showed a mosaic pattern with that of other deer, implying a trans-species evolution pattern in maintaining DRB allele polymorphism. Moreover, two DRB alleles of Chinese muntjac （Mure-DRB1 and Mure-DRB11） and two DRB alleles of red deer （Ceel-DRB34 and Ceel-DRB46） were closely cl

关 键 词：黄麂 Mhc-DRB 多态性 正选择 鹿科 

分 类 号：Q786[生物学—分子生物学]