大約5000萬年前,，鯨類的祖先用四條腿從陸地走向海洋,，為適應(yīng)海洋生存環(huán)境，其后肢不斷退化并幾乎消失,，而前肢卻進(jìn)化成鰭狀肢,。鯨類鰭狀肢為何會出現(xiàn)？是不是基因變異的結(jié)果,？華東師大發(fā)布信息：由校生命科學(xué)學(xué)院的博士后王及其合作導(dǎo)師,，以及英國合作者的最新研究成果為解答這一難題提供了重要線索。
據(jù)生物學(xué)家研究,，絕大多數(shù)動物的身體器官都受一個名為Hox的基因家族控制,。而動物的前肢發(fā)育特別受到Hoxd12和Hoxd13基因的控制。這兩個基因的突變會導(dǎo)致動物前肢的畸形,。王等研究人員通過對鯨類和其它哺乳動物類群的Hoxd12和Hoxd13基因測序,，發(fā)現(xiàn)了這兩個基因在鯨類鰭狀肢的起源與分化中起到了重要作用。即鯨和現(xiàn)存的河馬,、牛,、豬等偶蹄目動物具有同一祖先，前肢都有4個獨(dú)立的指頭,，但是由于這兩個基因的突變,，鯨類祖先的前肢多長出了1個指頭，并且指間長出了蹼,。在其后鯨類的再次進(jìn)化過程中,，部分須鯨的前肢卻又從5指進(jìn)化成4指，恢復(fù)了進(jìn)化前的指頭數(shù)量,。
研究人員還發(fā)現(xiàn)這兩個Hox基因在鯨類的平均進(jìn)化速率,，均顯著高于其它哺乳動物類群，并最終認(rèn)定,，Hox基因的適應(yīng)性進(jìn)化時間與鯨類鰭狀肢的宏觀進(jìn)化時代完全相符,，是自然選擇的結(jié)果，而非偶然形成的,。華東師大研究人員的相關(guān)研究論文《5’HoxD基因的適應(yīng)性進(jìn)化在鯨類鰭狀肢的起源與分化中的作用》,，于近日發(fā)表在國際權(quán)威雜志《分子生物學(xué)與進(jìn)化》（Molecular Biology and Evolution）上。(生物谷Bioon.com)
生物谷推薦原始出處：
Molecular Biology and Evolution, doi:10.1093/molbev/msn282
Adaptive evolution of 5’HoxD genes in the origin and diversification of the cetacean flipper
Zhe Wang*, Lihong Yuan, Stephen J. Rossiter, Xueguo Zuo*, Binghua Ru*, Hui Zhong*, Naijian Han, Gareth Jones?, Paul D. Jepson and Shuyi Zhang*
* School of Life Science, East China Normal University, Shanghai, China
Guangdong Entomological Institute, Guangzhou, China
School of Biological and Chemical Sciences, Queen Mary, University of London, London, UK
Institute of Zoology, Chinese Academy of Sciences, Beijing, China
School of Biological Sciences, University of Bristol, Bristol, UK
Institute of Zoology, Zoological Society of London, Regent's Park, London, UK
The homeobox genes Hoxd12 and Hoxd13 control digit patterning and limb formation in tetrapods. Both show strong expression in the limb bud during embryonic development, are highly conserved across vertebrates, and show mutations that are associated with carpal, metacarpal and phalangeal deformities. The most dramatic evolutionary reorganization of the mammalian limb has occurred in cetaceans (whales, dolphins and porpoises), in which the hindlimbs have been lost and the forelimbs have evolved into paddle-shaped flippers. We reconstructed the phylogeny of digit patterning in mammals, and inferred that digit number has changed twice in the evolution of the cetacean forelimb. First, the divergence of the early cetaceans from their even-toed relatives coincided with the reacquisition of the pentadactyl forelimb, whereas the ancestors of tetradactyl baleen whales (Mysticeti) later lost a digit again. To test whether the evolution of the cetacean forelimb is associated with positive selection or relaxation of Hoxd12 and Hoxd13, we sequenced these genes in a wide range of mammals. In Hoxd12, we found evidence of Darwinian selection associated with both episodes of cetacean forelimb reorganization. In Hoxd13, we found a novel expansion of a polyalanine tract in cetaceans compared to other mammals (17/18 residues versus 14/15 residues, respectively), lengthening of which has previously been shown to be linked to synpolydactyly in humans and mice. Both genes also show much greater sequence variation among cetaceans than across other mammalian lineages. Our results strongly implicate 5’HoxD genes in the modulation of digit number, web forming, and the high morphological diversity of the cetacean manus.
