一項(xiàng)研究發(fā)現(xiàn),，對(duì)于視覺(jué)具有關(guān)鍵作用的感光蛋白——視蛋白，其進(jìn)化出來(lái)的時(shí)間可能比此前認(rèn)為的更早且經(jīng)歷了更少的遺傳變化。視覺(jué)的遺傳起源仍然不清楚，這部分是由于對(duì)最早擁有視蛋白的后生動(dòng)物之間的系統(tǒng)發(fā)生學(xué)關(guān)系的報(bào)告的不一致。
Davide Pisani及其同事進(jìn)行了一項(xiàng)計(jì)算分析,，從而檢驗(yàn)了迄今提出的關(guān)于視蛋白進(jìn)化的每一個(gè)假說(shuō)。這項(xiàng)分析使用了來(lái)自所有相關(guān)動(dòng)物世系的所有可用的基因組信息,，包括一個(gè)新近經(jīng)過(guò)測(cè)序的海綿群體和刺胞動(dòng)物群體,，這一群體的動(dòng)物被認(rèn)為擁有全世界最古老的眼睛。這組科研人員使用這些信息提出了一條時(shí)間線(xiàn),，指出所有動(dòng)物群的一個(gè)擁有視蛋白的共同祖先出現(xiàn)在大約7億年前,。
這種視蛋白被認(rèn)為是“盲”的，然而在1100萬(wàn)年里經(jīng)歷了關(guān)鍵的遺傳變化,，讓它得到了探測(cè)光的能力,。這組作者說(shuō)，通過(guò)發(fā)現(xiàn)視蛋白進(jìn)化的關(guān)鍵步驟,，該研究提供了視蛋白進(jìn)化方式與進(jìn)化時(shí)間的詳細(xì)圖景,。這組作者說(shuō)，這些發(fā)現(xiàn)為理解包括人類(lèi)在內(nèi)的動(dòng)物視覺(jué)起源提供了基礎(chǔ),。（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.
