作为猫科动物一种新发现的主要泌尿蛋白基因CES7的加速进化

熊荣川 译

摘要：Cauxin蛋白是近来才在家养猫上发现的泌尿蛋白，有调节猫尿氨酸分泌的功能。而猫尿氨酸是一种信息素前体，与家养和野生猫科动物的社会化学通信和领域标记有关。理解Cauxin蛋白的进化历史可能对基于信息素野生动物的通讯、认知及配偶选择的分子适应进化机制进行阐述。经过我们对代表猫科主要支系的22个物种和多个外群Cauxin蛋白编码基因CES7的测序，表明在猫科分化前及其分化过程中，CES7经历了快速进化。比较猫科动物的cauxin和其它哺乳动物的羧酸酯酶旁系同源物后发现，几个猫科动物支系间及内部表现出较强正向达尔文选择的证据，尤其是在蛋白的一些重要功能位点上。小型猫科动物有更高的氨基酸加速替换率，而大型猫科动物（豹属）缺少猫尿氨酸且Cauxin含量极低，和该基因在豹属的功能分化及其在雪豹中功能完全丧失的假设相关。表达研究结果表明，在睾丸和大脑中有几种不同的剪接转录产物，暗示它在雄性繁殖适应和行为中还有其它功能。我们的研究是对作用在非啮齿哺乳动物主要泌尿蛋白上显著正向自然选择的首次报道，报道提供的证据表明不同的哺乳动物支系信息素的调节存在平行选择压力，即使它们使用不同的代谢途径。我们的结果暗示，自然选择可能驱动不同猫科动物尿液中信息素的调节作用发生迅速的变化，反过来这种变化可能影响到它们的社会行为，如领域标记、同种识别进而作为一种实现哺乳动物种群实现适应性辐射的重要内在机制。

关键词：进化 正向选择 主要泌尿蛋白 猫科

原文：

Accelerated Evolution of CES7, a Gene Encoding a Novel Major Urinary Protein in the Cat Family

Abstract

Cauxin is a novel urinary protein recently identified in the domestic cat that regulates the excretion of felinine, a pheromone precursor involved in sociochemical communication and territorial marking of domestic and wild felids. Understanding the evolutionary history of cauxin may therefore illuminate molecular adaptations involved in the evolution of pheromone-based communication, recognition, and mate selection in wild animals. We sequenced the gene encoding cauxin, CES7, in 22 species representing all major felid lineages, and multiple outgroups and showed that it has undergone rapid evolutionary change preceding and during the diversification of the cat family. A comparison between feline cauxin and orthologous carboxylesterases from other mammalian lineages revealed evidence of strong positive Darwinian selection within and between several cat lineages, enriched at functionally important sites of the protein. The higher rate of radical amino acid replacements in small felids, coupled with the lack of felinine and extremely low levels of cauxin in the urine of the great cats (Panthera), correlates with functional divergence of this gene in Panthera, and its putative loss in the snow leopard. Expression studies found evidence for several alternatively spliced transcripts in testis and brain, suggesting additional roles in male reproductive fitness and behavior. Our work presents the first report of strong positive natural selection acting on a major urinary protein of nonrodent mammals, providing evidence for parallel selection pressure on the regulation of pheromones in different mammalian lineages, despite the use of different metabolic pathways. Our results imply that natural selection may drive rapid changes in the regulation of pheromones in urine among the different cat species, which in turn may influence social behavior, such as territorial marking and conspecific recognition, therefore serving as an important mechanism for the radiation of this group of mammals.

Key words: evolution, positive selection, MUP, cat family.

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