Parsch J, Meiklejohn C D, Hauschteck-Jungen E, Hunziker P, Hartl D L
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138-2020, USA.
Mol Biol Evol. 2001 May;18(5):801-11. doi: 10.1093/oxfordjournals.molbev.a003862.
Genes involved in male fertility are potential targets for sexual selection, and their evolution may play a role in reproductive isolation and speciation. Here we describe a new Drosophila melanogaster gene, ocnus (ocn), that encodes a protein abundant in testes nuclear extracts. RT-PCR indicates that ocn transcription is limited to males and is specific to testes. ocn shares homology with another testis-specific gene, janusB (janB), and is located just distal to janB on chromosome 3. The two genes also share homology with the adjacent janusA (janA) gene, suggesting that multiple duplication events have occurred within this region of the genome. We cloned and sequenced these three genes from species of the D. melanogaster species subgroup. Phylogenetic analysis based on protein-encoding sequences predicts a duplication pattern of janA --> janA janB --> janA janB ocn, with the latter event occurring after the divergence of the D. melanogaster and Drosophila obscura species groups. We found significant heterogeneity in the rates of evolution among the three genes within the D. melanogaster species subgroup as measured by the ratio of nonsynonymous to synonymous substitutions, suggesting that diversification of gene function followed each duplication event and that each gene evolved under different selective constraints. All three genes showed faster rates of evolution than genes encoding proteins with metabolic function. These results are consistent with previous studies that have detected an increased rate of evolution in genes with reproductive function.
参与雄性生育力的基因是性选择的潜在目标，其进化可能在生殖隔离和物种形成中发挥作用。在此，我们描述了一个新的黑腹果蝇基因ocnus（ocn），它编码一种在睾丸核提取物中大量存在的蛋白质。逆转录聚合酶链反应表明，ocn转录仅限于雄性，且特异性地存在于睾丸中。ocn与另一个睾丸特异性基因janusB（janB）具有同源性，并且位于3号染色体上janB的远端。这两个基因还与相邻的janusA（janA）基因具有同源性，表明在基因组的这个区域发生了多次复制事件。我们从黑腹果蝇物种亚组的物种中克隆并测序了这三个基因。基于编码蛋白质序列的系统发育分析预测了janA --> janA janB --> janA janB ocn的复制模式，后一个事件发生在黑腹果蝇和果蝇隐种物种组分化之后。我们发现，通过非同义替换与同义替换的比率衡量，黑腹果蝇物种亚组内这三个基因的进化速率存在显著异质性，这表明基因功能的多样化跟随每次复制事件，并且每个基因在不同的选择约束下进化。所有这三个基因的进化速率都比编码具有代谢功能蛋白质的基因快。这些结果与之前检测到具有生殖功能的基因进化速率增加的研究一致。
