一项研究发现，对于视觉具有关键作用的感光蛋白——视蛋白，其进化出来的时间可能比此前认为的更早且经历了更少的遗传变化。视觉的遗传起源仍然不清楚，这部分是由于对最早拥有视蛋白的后生动物之间的系统发生学关系的报告的不一致。
Davide Pisani及其同事进行了一项计算分析，从而检验了迄今提出的关于视蛋白进化的每一个假说。这项分析使用了来自所有相关动物世系的所有可用的基因组信息，包括一个新近经过测序的海绵群体和刺胞动物群体，这一群体的动物被认为拥有全世界最古老的眼睛。这组科研人员使用这些信息提出了一条时间线，指出所有动物群的一个拥有视蛋白的共同祖先出现在大约7亿年前。
这种视蛋白被认为是“盲”的，然而在1100万年里经历了关键的遗传变化，让它得到了探测光的能力。这组作者说，通过发现视蛋白进化的关键步骤，该研究提供了视蛋白进化方式与进化时间的详细图景。这组作者说，这些发现为理解包括人类在内的动物视觉起源提供了基础。（生物谷Bioon.com）
doi: 10.1073/pnas.1204609109
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Metazoan opsin evolution reveals a simple route to animal vision
Roberto Feuda, Sinead C. Hamilton, James O. McInerney, and Davide Pisani
All known visual pigments in Neuralia (Cnidaria, Ctenophora, and Bilateria) are composed of an opsin (a seven-transmembrane G protein-coupled receptor), and a light-sensitive chromophore, generally retinal. Accordingly, opsins play a key role in vision. There is no agreement on the relationships of the neuralian opsin subfamilies, and clarifying their phylogeny is key to elucidating the origin of this protein family and of vision. We used improved methods and data to resolve the opsin phylogeny and explain the evolution of animal vision. We found that the Placozoa have opsins, and that the opsins share a common ancestor with the melatonin receptors. Further to this, we found that all known neuralian opsins can be classified into the same three subfamilies into which the bilaterian opsins are classified: the ciliary (C), rhabdomeric (R), and go-coupled plus retinochrome, retinal G protein-coupled receptor (Go/RGR) opsins. Our results entail a simple scenario of opsin evolution. The first opsin originated from the duplication of the common ancestor of the melatonin and opsin genes in a eumetazoan (Placozoa plus Neuralia) ancestor, and an inference of its amino acid sequence suggests that this protein might not have been light-sensitive. Two more gene duplications in the ancestral neuralian lineage resulted in the origin of the R, C, and Go/RGR opsins. Accordingly, the first animal with at least a C, an R, and a Go/RGR opsin was a neuralian progenitor.
