著基因組數(shù)據(jù)的迅速增加,，通過比較基因組學(xué)及生物信息學(xué)的方法探討物種適應(yīng)性進化的遺傳基礎(chǔ)是目前分子進化的研究熱點。張亞平院士課題組針對已公布的海豚基因組,，通過與其他近緣物種的基因組進行比較,，系統(tǒng)地鑒定出海豚中經(jīng)歷正選擇的基因及位點，為理解海豚等鯨目動物的水生適應(yīng)奠定了基礎(chǔ),，同時也為進一步研究這些基因的功能提供了線索,。
鯨目動物是哺乳動物中少有的水生物種，它們與現(xiàn)存的偶蹄類大約分化于50個百萬年以前,。鯨目動物的“二次入水”事件是哺乳動物進化史中一次罕見的生活史轉(zhuǎn)變,，它們的生活習(xí)性由陸生轉(zhuǎn)變?yōu)橥耆×业沫h(huán)境轉(zhuǎn)變導(dǎo)致它們在生理上及結(jié)構(gòu)上都發(fā)生了顯著的改變以適應(yīng)水生生活,，例如具有增厚的皮下脂肪層（“鯨油”）,，長時間潛水及回聲定位的能力，同時具有強大的肌肉系統(tǒng)支持水中運動等,。盡管人們已經(jīng)了解到很多生理/形態(tài)上的適應(yīng)性特征,，但是這些特征的分子基礎(chǔ)并沒有得到系統(tǒng)性的解決,。基于此,，孫艷波博士和周偉平博士等對已公布的海豚基因組進行了系統(tǒng)性的分析,。通過構(gòu)建近緣物種間的高質(zhì)量序列比對（包括海豚、牛,、狗,、大熊貓、以及人,，共11,838個直系同源基因）,，在海豚中檢測到了368個經(jīng)歷正選擇的基因（P < 0.01）。功能聚類分析的結(jié)果顯示,，這些正選擇基因顯著富集于諸如肌肉收縮,、ATP酶、脂肪轉(zhuǎn)運和定位,、感知聲音,、以及糖酵解等功能中。該研究為進一步揭示鯨目動物的進化及其水生適應(yīng)的分子機制具有重要的參考價值,。該研究已在線發(fā)表在《Genome Biology and Evolution》雜志,。(生物谷Bioon.com)
doi: 10.1093/gbe/evs123
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Genome-Wide Scans for Candidate Genes Involved to the Aquatic Adaptation of Dolphins
Yan-Bo Sun1,3,#, Wei-Ping Zhou1,2,3,#, He-Qun Liu1,3,6, David M. Irwin1,4,5, Yong-Yi Shen1,7,* and Ya-Ping Zhang1,3,*
Since their divergence from the terrestrial artiodactyls, cetaceans have fully adapted to an aquatic lifestyle, which represents one of the most dramatic transformations in mammalian evolutionary history. Numerous morphological and physiological characters of cetaceans have been acquired in response to this drastic habitat transition, such as thickened blubber, echolocation, and ability to hold their breath for a long period of time. However, knowledge about the molecular basis underlying these adaptations is still limited. The sequence of the genome of Tursiops truncates provides an opportunity for a comparative genomic analyses to examine the molecular adaptation of this species. Here, we constructed 11,838 high-quality orthologous gene alignments culled from the dolphin and four other terrestrial mammalian genomes and screened for positive selection occurring in the dolphin lineage. A total of 3.1% (368) of the genes were identified as having undergone positive selection by the branch-site model. Functional characterization of these genes showed that they are significantly enriched in the categories of lipid transport and localization, ATPase activity, sense perception of sound, and muscle contraction, areas that are potentially related to cetacean adaptations. In contrast, we did not find a similar pattern in the cow, a closely related species. We re-sequenced some of the positively selected sites (PSSs), within the positively selected genes (PSGs), and showed that most of our identified PSSs (50/52) could be replicated. The results from this study should have important implications for our understanding of cetacean evolution and their adaptations to the aquatic environment.
