生物谷援引新浪科技報道：據(jù)澳大利亞廣播公司報道,，新加坡科學(xué)家發(fā)現(xiàn),，大約4.5億年前,，鯊魚和人類擁有共同的祖先,，這也使得鯊魚成為我們的遠方親戚,。
最新研究稱,，這種親屬關(guān)系在人類DNA上找到了證據(jù)，至少一種鯊魚擁有多個幾乎與人類基因完全相同的基因,。象鯊的基因組同人類的非常相似,，從遺傳學(xué)上講，我們同象鯊比其它物種(如多骨魚)擁有更多共同點,。多骨魚在進化樹上距離人類的位置較近,。領(lǐng)導(dǎo)實施此項研究的比拉帕·文卡塔斯(Byrappa Venkatesh)副教授說：“這無疑是令人吃驚的發(fā)現(xiàn),，因為多骨魚和人類的關(guān)系要比象鯊?fù)祟惖年P(guān)系更為緊密。”
文卡塔斯是新加坡分子與細胞生物研究所首席研究員,，他的研究小組發(fā)現(xiàn),，“象鯊和人類基因組上的多套染色體基因和真實的基因序列非常相似。”研究人員不僅分析了象鯊的基因組,，還分析了包括河豚,、小雞、老鼠和狗等動物的基因,。最新研究發(fā)現(xiàn)刊登在最新一期《大眾科學(xué)圖書館(生物卷)》(PLoS Biology)雜志上,。
研究人員在人體上發(fā)現(xiàn)了同老鼠、狗和象鯊基因很相像的154個基因,?？茖W(xué)家早已料到人類同老鼠和狗的基因相似性，因為它們都是哺乳動物,。但鯊魚屬于軟骨魚綱類動物,，這種魚類似乎同哺乳動物在生理上并不存在相似之處。研究人員經(jīng)過更為細致的檢查,，發(fā)現(xiàn)鯊魚和人類確實擁有某些生理和生物化學(xué)共同點,，其中就包括性。
文卡塔斯說：“象鯊,、其它種類的鯊魚及人類的共同特點是,，受精過程均在體內(nèi)完成，而硬骨魚的受精過程則在體外進行,。”象鯊和人類之間許多相似基因都涉及精子生成,。象鯊和人類所產(chǎn)生的精子似乎在末端擁有能夠與雌性卵子結(jié)合的感受器。多骨魚則沒有這樣的感受器,。它們的精子通過一個稱為卵膜孔的小孔進入卵子,，鯊魚和人類沒有卵膜孔。
研究人員同時發(fā)現(xiàn),，由于鯊魚身上具有所有四種存在于哺乳動物身上的白細胞,，二者的免疫系統(tǒng)非常相似。美國加州遠洋鯊魚研究基金會常務(wù)董事肖恩·范·索默蘭表示,，他對鯊魚同人類之間的這種緊密聯(lián)系并不十分吃驚,。范·索默蘭說：“遺傳學(xué)領(lǐng)域就像一個潘朵拉盒子。鯊魚像哺乳動物一般交配,，雌性鯊魚產(chǎn)下活潑可愛的小鯊魚,，所以說，鯊魚確實同哺乳動物具有某些相似之處,。頗具意義的是,，這些特點在基因組上表現(xiàn)了出來,。”
文卡塔斯表示，未來有關(guān)象鯊基因組的研究,，也許能揭示諸如免疫系統(tǒng)如何發(fā)育等涉及人類基因的信息,。象鯊基因組相對而言不大，研究起來也相對容易,。由于鯊魚是現(xiàn)存最古老的有顎脊椎動物,，針對鯊魚的研究甚至可能揭開人類和其它哺乳動物進化之謎。
原始出處:
PLoS Biology,，Received: October 30, 2006; Accepted: February 7, 2007; Published: April 3, 2007
Survey Sequencing and Comparative Analysis of the Elephant Shark (Callorhinchus milii) Genome
Byrappa Venkatesh1*, Ewen F. Kirkness2*, Yong-Hwee Loh1, Aaron L. Halpern3, Alison P. Lee1, Justin Johnson3, Nidhi Dandona1, Lakshmi D. Viswanathan3, Alice Tay1, J. Craig Venter3, Robert L. Strausberg3, Sydney Brenner1
1 Institute of Molecular and Cell Biology, Singapore, 2 The Institute for Genomic Research, Rockville, Maryland, United States of America, 3 J. Craig Venter Institute, Rockville, Maryland, United States of America
Owing to their phylogenetic position, cartilaginous fishes (sharks, rays, skates, and chimaeras) provide a critical reference for our understanding of vertebrate genome evolution. The relatively small genome of the elephant shark, Callorhinchus milii, a chimaera, makes it an attractive model cartilaginous fish genome for whole-genome sequencing and comparative analysis. Here, the authors describe survey sequencing (1.4× coverage) and comparative analysis of the elephant shark genome, one of the first cartilaginous fish genomes to be sequenced to this depth. Repetitive sequences, represented mainly by a novel family of short interspersed element–like and long interspersed element–like sequences, account for about 28% of the elephant shark genome. Fragments of approximately 15,000 elephant shark genes reveal specific examples of genes that have been lost differentially during the evolution of tetrapod and teleost fish lineages. Interestingly, the degree of conserved synteny and conserved sequences between the human and elephant shark genomes are higher than that between human and teleost fish genomes. Elephant shark contains putative four Hox clusters indicating that, unlike teleost fish genomes, the elephant shark genome has not experienced an additional whole-genome duplication. These findings underscore the importance of the elephant shark as a critical reference vertebrate genome for comparative analysis of the human and other vertebrate genomes. This study also demonstrates that a survey-sequencing approach can be applied productively for comparative analysis of distantly related vertebrate genomes.
全文鏈接：
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050101
