草鱼MHCⅠα基因克隆及其多态性特征分析

Grass carp MHCⅠαgene cloning and its polymorphic characteristics

主要组织相容性复合体(MHC)是存在于脊椎动物染色体上、呈高度多态性的基因群,与机体的抗病性密切关系。MHCⅠ类分子由α链和β_(2m)微球蛋白组成,α链呈高度多态性。为探究草鱼MHCⅠα基因的多态性特征,本研究对3个草鱼个体的MHCⅠα基因进行克隆和测序,并使用生物信息学方法分析比较草鱼与小鼠、牛和鸡的MHCⅠα基因多态性特征。结果:共获得了5条草鱼MHCⅠα基因型序列,其基因编码332个氨基酸,包括信号肽、α1、α2、α3和TM/CY区域。草鱼MHCⅠα基因的氨基酸变异位点主要分布在α1和α2区域,与小鼠、牛和鸡MHCⅠα基因肽结合区(PBR)空间结构相似,多态性位点分布在抗原递呈的关键部位α螺旋或β折叠上。草鱼MHCⅠα基因的进化受自然环境的负向选择作用,而其他3个物种的进化方式均为正向选择。此外,草鱼MHCⅠα基因与其他脊椎动物亲缘关系较远,单独构成进化树上一大分支,且个体间继续分化为不同的亚支。本研究从基因层面阐述了草鱼MHCⅠα基因多态性特征和分子进化规律,为进一步探究低等脊椎动物MHCⅠα基因的生物学特征奠定基础。

Major histocompatibility complexes(MHC)are highly polymorphic gene groups on the chromosomes of vertebrates,which are closely related to the differences in disease resistance.MHC class I molecules are composed by theαchain andβ2m microglobulin,and theαchain shows high polymorphism.To explore the polymorphic characteristics of grass carp MHCⅠαgenes,the MHCⅠαgenes from three individuals of grass crap were cloned and sequenced in this study.The polymorphic characteristics of the grass carp MHCⅠαgenes were analyzed with bioinformatics and were compared with the genes of mice,cattle,and chickens.As a result,five grass carp MHCⅠαgenotype sequences were obtained.The sequence analysis showed that the grass carp MHCⅠαgene encoded 332 amino acids,including the signal peptide region,theα1,α2,α3 and TM/CY domains;and the most polymorphic amino acid residues were concentrated in theα1 andα2 domains.The spatial structures of the peptide binding region(PBR)of the four species’MHCⅠαgenes were similar;the polymorphic sites mainly distributed in the key position of antigen-presentationαhelices orβsheets.The evolution process of the grass carp MHCⅠαgene was influenced by negative selection of natural environment,while that of the other vertebrates was positively selected.In addition,the grass carp MHCⅠαgene shared distant genetic relationship with the other vertebrates,and constituted a large branch of its own,and the individuals continue to differentiate into different subclades,with no obvious individual differences.Our results clarified the polymorphic characteristics and gene evolution of the grass carp MHCⅠαgene,which laid a foundation for further exploration of the biological features of MHCⅠgenes in lower vertebrates.