10个半滑舌鳎家系MHC ⅡB基因多态性初步研究

Polymorphisms and balancing selection in the half-smooth tongue sole, Cynoglossus semilaevis

为检测10个半滑舌鳎(Cynoglossus semilaevis)家系MHCⅡB(Cyse-DAB)基因的多态性水平、MHCⅡ类B位点数目以及平衡选择的作用,作者利用多聚酶链式反应(PCR)和直接测序的方法对10个半滑舌鳎家系MHCⅡB基因位点遗传变异和平衡选择进行了研究。用特异性引物和PCR扩增的半滑舌鳎MHCⅡB基因片段大约397 bp,包含一部分第一外显子,全部第一内含子和全部第二外显子。10个半滑舌鳎家系中,每家系选取5个体,每个体5个克隆序列分析发现60个不同序列,代表60个等位基因,其中有28个是新发现的,已提交到Gen Bank。同源分析表明60个等位基因相似性为89.36%。共50个个体中,有6个存在5个不同等位基因,表明在半滑舌鳎至少存在3个座位。有9个家系的MHCⅡB序列多肽结合区(PBR)的非同义替换(dN)显著高于同义替换(dS)。

In order to detect the polymorphism, number of alleles, and equilibrium selection of the MHC II B（Cyse-DAB） gene ofthe half smooth tongue sole, Cynoglossus semilaevis, we measured the genetic variation and balancing selection at MHC IIB loci in 10 half-smooth tongue sole by polymorphism chain reaction and the direct sequence method. We cloned and sequenced a 397 bp fragment of the MHC class IIB exon2. An amplified fragment spanned the partial exon1, complete intron1, and exon2. Five clones and five fry per individual（n = 50, 10 groups） were selected for MHC IIB sequence analysis. A total of 60 sequences were discovered which revealed 60 alleles, 28 of which were first found in this study and have been submitted to Genbank. The homology similarity was 89.36% among the sixty sequences. Five distinct sequences were presented in each of six individuals which denoted that there were at least three loci in half-smooth tongue sole MHC class IIB genes. Non-synonymous（dN） substitution was significantly higher than synonymous（dS） in the peptide-binding region of the MHC IIB gene in nine of the ten half-smooth tongue sole groups.