Llopart Ana, Comeron Josep M
Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA.
Genetics. 2008 Jun;179(2):1009-20. doi: 10.1534/genetics.107.086231. Epub 2008 May 27.
Our understanding of the role of positive selection in the evolution of genes with male-biased expression can be hindered by two observations. First, male-biased genes tend to be overrepresented among lineage-specific genes. Second, novel genes are prone to experience bursts of adaptive evolution shortly after their formation. A thorough study of the forces acting on male-biased genes therefore would benefit from phylogenywide analyses that could distinguish evolutionary trends associated with gene formation and later events, while at the same time tackling the interesting question of whether adaptive evolution is indeed idiosyncratic. Here we investigate the roughex (rux) gene, a dose-dependent regulator of Drosophila spermatogenesis with a C-terminal domain responsible for nuclear localization that shows a distinct amino acid sequence in the melanogaster subgroup. We collected polymorphism and divergence data in eight populations of six Drosophila species, for a total of 99 rux sequences, to study rates and patterns of evolution at this male-biased gene. Our results from two phylogeny-based methods (PAML and HyPhy) as well as from population genetics analyses (McDonald-Kreitman-based tests) indicate that amino acid replacements have contributed disproportionately to divergence, consistent with adaptive evolution at the Rux protein. Analyses based on extant variation show also the signature of recent selective sweeps in several of the populations surveyed. Most important, we detect the significant and consistent signature of positive selection in several independent Drosophila lineages, which evidences recurrent and concurrent events of adaptive evolution after rux formation.
我们对正向选择在雄性偏向表达基因进化中作用的理解可能会受到两个观察结果的阻碍。首先，雄性偏向基因在谱系特异性基因中往往过度代表。其次，新基因在形成后不久容易经历适应性进化的爆发。因此，对作用于雄性偏向基因的力量进行全面研究将受益于全系统发育分析，这种分析可以区分与基因形成及后续事件相关的进化趋势，同时解决适应性进化是否确实具有特异性这个有趣的问题。在这里，我们研究了粗糙基因（rux），它是果蝇精子发生的剂量依赖性调节因子，其C端结构域负责核定位，在黑腹果蝇亚组中显示出独特的氨基酸序列。我们收集了六个果蝇物种的八个种群中的多态性和分化数据，共99个rux序列，以研究这个雄性偏向基因的进化速率和模式。我们基于两种系统发育方法（PAML和HyPhy）以及群体遗传学分析（基于麦克唐纳-克里特曼的检验）的结果表明，氨基酸替换对分化的贡献不成比例，这与Rux蛋白的适应性进化一致。基于现有变异的分析还显示了在几个被调查种群中近期选择性清除的特征。最重要的是，我们在几个独立的果蝇谱系中检测到了正向选择的显著且一致的特征，这证明了rux形成后适应性进化的反复和同时发生的事件。
