美国科学家的一项最新研究，首次在水螅中找到了动物感光性的起源——视蛋白。相关论文发表在最新一期的《公共科学图书馆.综合》（PLoS ONE）上。
领导最新研究的是美国加州大学圣芭芭拉分校的Todd Oakley，他和同事是最早在刺胞动物（cnidarians，包括珊瑚、水母、海葵等）寻找感光基因的科学家。
水螅也是刺胞动物的一种，主要生活在热带和温带，没有眼睛或其它感光器官。不过，新的研究表明，它们体内确实存在着感知光线的遗传路径。
研究发现，水螅的视蛋白遍布全身，但在嘴部区域尤其集中。因此研究人员推测，水螅可能利用感光性来寻找猎物。
论文第一作者David Plachetzki表示，“我们在更早的分支物种比如海绵中没有找到视蛋白，因此我们能够为动物感光进化过程限定一个最早时间。而最新的研究让我们有了确切的时限，最早拥有感光能力的物种大约生活在距今6亿年前。”
最新的研究还确定了水螅中视蛋白基因的进化历史。Oakley表示，“我们清楚地发现，视蛋白同源复制基因所发生的变化使得新基因与不同蛋白以全新的方式发生联系和作用，而这些已经成为今天视觉遗传机制的根基。”
值得一提的是，澳大利亚昆士兰大学的Bernie Degnan为此次研究提供了重要的生物信息学工具。而由Craig Venter研究所实施的水螅基因组计划也正在紧锣密鼓的进行当中。（科学网 任霄鹏/编译）
原始出处:
PLoS ONE
Received: July 12, 2007; Accepted: September 17, 2007; Published: October 17, 2007
The Origins of Novel Protein Interactions during Animal Opsin Evolution
David C. Plachetzki1, Bernard M. Degnan2, Todd H. Oakley1*
1 Ecology, Evolution and Marine Biology, University of California at Santa Barbara, Santa Barbara, California, United States of America, 2 School of Integrative Biology, University of Queensland, Brisbane, Queensland, Australia
Abstract
Background
Biologists are gaining an increased understanding of the genetic bases of phenotypic change during evolution. Nevertheless, the origins of phenotypes mediated by novel protein-protein interactions remain largely undocumented.
Methodology/Principle Findings
Here we analyze the evolution of opsin visual pigment proteins from the genomes of early branching animals, including a new class of opsins from Cnidaria. We combine these data with existing knowledge of the molecular basis of opsin function in a rigorous phylogenetic framework. We identify adaptive amino acid substitutions in duplicated opsin genes that correlate with a diversification of physiological pathways mediated by different protein-protein interactions.
Conclusions/Significance
This study documents how gene duplication events early in the history of animals followed by adaptive structural mutations increased organismal complexity by adding novel protein-protein interactions that underlie different physiological pathways. These pathways are central to vision and other photo-reactive phenotypes in most extant animals. Similar evolutionary processes may have been at work in generating other metazoan sensory systems and other physiological processes mediated by signal transduction.
Figure 1. Sequence motifs and expression of cnidarian opsin in the nerve net of Hydra magnipallata.
(A) Sequence alignment of 4th cytoplasmic loop region of animal opsins used in this study indicating the Lys 296 chromophore binding site (arrowhead) and the G protein-binding tripeptide (asterisks). (B) In situ hybridization with Hm2 cnidops probe. Asterisk denotes the hypostome. Opsin is expressed most strongly in a ring of sensory neurons that surround the mouth. Inset, oral view.
全文链接：http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0001054
