禽类Mx基因GTP酶效应区(GED)序列适应性进化分析

Adaptive Evolution Analysis of the GTPase Effector Domain of Avian Mx Gene

为进一步了解禽类Mx基因进化历程及结构与功能变异,测定了4种经济类型11个地方鸡品种:肉用型(惠阳胡须鸡、清远麻鸡、文昌鸡)、兼用型(藏鸡、狼山鸡、寿光鸡、北京油鸡、萧山鸡、鹿苑鸡)、蛋用型(白耳鸡)、药用和观赏型(丝羽乌骨鸡)Mx基因GTP酶效应区(GTPase effector domain,GED)序列,并结合已报道的原鸡及部分其他鸡形目和雁形目禽类相关序列,采用mrModeltest和MrBayes筛查最适核苷酸替代模型、构建贝叶斯进化树,并采用Datamonkey和PAML4b检测位点选择压力。结果:获得了中国地方鸡种Mx基因GED区核苷酸序列,全长231 bp,编码77个氨基酸。序列联配结果表明家鸡Mx基因GED区高度保守,仅发现3个突变位点,分别位于2 032 bp、2 075 bp和2 139 bp处。AIC信息量准则表明禽类Mx基因GED区的最优核苷酸替代模型为GTR+G。基于最优模型重建的禽类Mx基因GED区贝叶斯进化树具有较高的后验概率,揭示的系统发育关系和禽类物种进化基本一致。Datamonkey的单一断裂点扫描和遗传算法扫描均未发现禽类Mx基因GED区序列数据集有重组事件,位点选择压力检测结果表明禽类Mx基因GED区在进化过程中并未受到正选择作用。

The objective of this study was to trace the route of avian Mx gene evolution and the variations of its structure and function.Nucleotide sequences of Mx gene GED domain（GTPase effector domain） were amplified by PCR and sequenced for four economical types in a total of eleven Chinese indigenous chicken breeds.The chicken breeds included HY,QY,WC,TB,LS,SG,BY,XI,LU,BA and SK.The reported sequences of Jungle fowls,some galliform and anseriform avians were also used in this study.mrModeltest and MrBayes were used to select the best nucleotide substitution model and construct the evolutional tree.Datamonkey and PAML4b were used to test the selective pressure on amino acid sites of Mx gene GED domain.Mx gene GED sequences of Chinese indigenous chicken breeds were properly obtained,with a length of 231 bp,which encoded 77 amino acids.Multiple sequence alignment results showed that Mx gene GED sequences of domestic jungles were highly conservative;only three polymorphic sites were identified,which located in 203 2 bp,207 5 bp and 213 9 bp,respectively.AIC information criterion showed that the best nucleotide substitution model of avian Mx gene GED was ＂GTR＋G＂.The Bayes evolutional tree based on this best model had higher posterior probability and which revealed the phylogenetic relationships were basically the same as the evolution of avian species.Single breakpoint scanning and genetic algorithm scanning by Datamonkey found no recombination events in avian Mx gene GED sequences.The site selection pressure test showed that avian Mx gene GED sequences had not suffered positive selection pressure.