Science快讯：今日出版（03年12月12日）Science一篇报道揭示了人与黑猩猩基因组间的比较学研究。
尽管经过了几十年的研究，遗传学家仍然没有破解人类何以为人之谜。人类和我们的近亲黑猩猩，几乎有着完全一样的DNA。但一项新研究揭示了黑猩猩与人类基因组之间的关键差异。
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加州赛莱拉诊断公司的遗传学家Michele Cargill和他的同事检查了7600个小鼠、人类与黑猩猩共有的基因，并根据每个物种的正常突变速率筛选出碱基变异超过预想的基因。他们得出结论，有1547个人类基因和1534个黑猩猩基因经历了相对较快的变化，这些变化可能赋予物种更强的生命力。小鼠的基因数据可以帮助研究小组确定这些基因随着进化时间是如何变化的。
自5百万年前从最后一个共同祖先分化以来，黑猩猩和人类的许多与细胞信号传导和氨基酸代谢有关的基因自都经历了巨变。但基因的演变轨迹与两个物种的信号和代谢演变并不相同，这说明二者遭遇的是不同的自然选择压力。在人类中，有27到48个嗅觉蛋
白以及21个听力蛋白中的3个显示出显著的变异加速，而黑猩猩并非如此。相反，黑猩猩的中胚发育基因和骨骼结构基因发生的变化却更多。
人类嗅觉基因的快速进化令人困惑不解。由于人类不再严重依赖他们的嗅觉来生存，因此有人认为嗅觉基因的变异没有影响甚至有负面影响。但这项新研究表明，一些嗅觉基因的进化有积极意义：它们的改变似乎是人类进化过程中的选择。这些基因促进了某些饮食改变或机理了性选择，研究的作者之一、纽约康奈尔大学的群体遗传学家Andrew Clark解释说。
这项研究发表在12月12日期的《Science》上，是通过基因组学方法识别“人性”的重要起点，加州大学圣地亚哥分校的生物学家Ajit Varki称赞道。他补充说，将人类和黑猩猩的基因与比小鼠亲缘关系更近的物种的基因组进行比较，如另一种类人猿，将会揭示更多定义灵长类进化树分支的基因。
Original report:
Despite decades of study, geneticists don’t know what makes humans human. Humans and our kissing cousins, chimpanzees, share practically all of our DNA. But new research reveals key differences between chimp and human genomes.
Hear no evil. Changes in genes for hearing, olfaction, and speech helped prompt human evolution.
CREDIT: PAT POWERS AND CHERRYL SCHAFER/GETTY IMAGES/DIGITAL VISION
Michele Cargill, a geneticist at Celera Diagnostics in Alameda, California, and her colleagues examined 7600 genes shared by chimps, humans, and mice, identifying those that had more than the expected number of base changes, given the normal mutation rates in each species. They concluded that 1547 human genes and 1534 chimp genes had experienced relatively rapid changes that likely endowed a survival advantage. The mouse data helped the team determine how the genes had changed over evolutionary time.
In both chimps and humans, many genes involved in cell signaling and amino acid metabolism have undergone major changes since the time of the species' last common ancestor 5 million years ago. But the genes didn’t follow the same track in the two species, suggesting that they faced different pressures from natural selection. In humans, 27 of 48 olfactory proteins and three of 21 hearing proteins showed significant accelerated change, whereas that was not true in the chimp. In contrast, the chimp’s genes for mesoderm development and skeletal structure had changed more.
The rapid evolution of olfactory genes in humans is puzzling. Because humans no longer rely strongly on their sense of smell to survive, any changes were assumed to have had no effect or a negative effect. But the new study suggests that some olfaction genes have been evolving in a positive way: Their changes appear to have been selected for during human evolution. The genes may have promoted certain dietary changes or informed sexual selection, says co-author Andrew Clark, a population geneticist at Cornell University in Ithaca, New York.
The work, reported in the 12 December issue of Science, “is a valuable start to the genomic approach to identify ‘humanness,’ ” says Ajit Varki, a glycobiologist at the University of California, San Diego, who adds that comparing human and chimp genes to the genome of a closer relative than mice, such as another great ape, would reveal even more genes that defined the branches of the primate family tree.
--ELIZABETH PENNISI
Original article:
Inferring Nonneutral Evolution from Human-Chimp-Mouse Orthologous Gene Trios
Andrew G. Clark, Stephen Glanowski, Rasmus Nielsen, Paul D. Thomas, Anish Kejariwal, Melissa A. Todd, David M. Tanenbaum, Daniel Civello, Fu Lu, Brian Murphy, Steve Ferriera, Gary Wang, Xianqgun Zheng, Thomas J. White, John J. Sninsky, Mark D. Adams, and Michele Cargill
Science Dec 12 2003: 1960-1963. [Abstract] [Full Text] [PDF] [Supporting Online Material]
Related articles:
R. Sakate et al., Genome Res. 13, 1022 (2003).[Abstract/Free Full Text]
Y. Satta, J. Klein, B. Takahata, Mol. Phylogenet. Evol. 14, 259 (2000).[CrossRef][ISI][Medline]
