生物谷援引新浪科技报道：据澳大利亚广播公司报道，新加坡科学家发现，大约4.5亿年前，鲨鱼和人类拥有共同的祖先，这也使得鲨鱼成为我们的远方亲戚。
最新研究称，这种亲属关系在人类DNA上找到了证据，至少一种鲨鱼拥有多个几乎与人类基因完全相同的基因。象鲨的基因组同人类的非常相似，从遗传学上讲，我们同象鲨比其它物种(如多骨鱼)拥有更多共同点。多骨鱼在进化树上距离人类的位置较近。领导实施此项研究的比拉帕·文卡塔斯(Byrappa Venkatesh)副教授说：“这无疑是令人吃惊的发现，因为多骨鱼和人类的关系要比象鲨同人类的关系更为紧密。”
文卡塔斯是新加坡分子与细胞生物研究所首席研究员，他的研究小组发现，“象鲨和人类基因组上的多套染色体基因和真实的基因序列非常相似。”研究人员不仅分析了象鲨的基因组，还分析了包括河豚、小鸡、老鼠和狗等动物的基因。最新研究发现刊登在最新一期《大众科学图书馆(生物卷)》(PLoS Biology)杂志上。
研究人员在人体上发现了同老鼠、狗和象鲨基因很相像的154个基因。科学家早已料到人类同老鼠和狗的基因相似性，因为它们都是哺乳动物。但鲨鱼属于软骨鱼纲类动物，这种鱼类似乎同哺乳动物在生理上并不存在相似之处。研究人员经过更为细致的检查，发现鲨鱼和人类确实拥有某些生理和生物化学共同点，其中就包括性。
文卡塔斯说：“象鲨、其它种类的鲨鱼及人类的共同特点是，受精过程均在体内完成，而硬骨鱼的受精过程则在体外进行。”象鲨和人类之间许多相似基因都涉及精子生成。象鲨和人类所产生的精子似乎在末端拥有能够与雌性卵子结合的感受器。多骨鱼则没有这样的感受器。它们的精子通过一个称为卵膜孔的小孔进入卵子，鲨鱼和人类没有卵膜孔。
研究人员同时发现，由于鲨鱼身上具有所有四种存在于哺乳动物身上的白细胞，二者的免疫系统非常相似。美国加州远洋鲨鱼研究基金会常务董事肖恩·范·索默兰表示，他对鲨鱼同人类之间的这种紧密联系并不十分吃惊。范·索默兰说：“遗传学领域就像一个潘朵拉盒子。鲨鱼像哺乳动物一般交配，雌性鲨鱼产下活泼可爱的小鲨鱼，所以说，鲨鱼确实同哺乳动物具有某些相似之处。颇具意义的是，这些特点在基因组上表现了出来。”
文卡塔斯表示，未来有关象鲨基因组的研究，也许能揭示诸如免疫系统如何发育等涉及人类基因的信息。象鲨基因组相对而言不大，研究起来也相对容易。由于鲨鱼是现存最古老的有颚脊椎动物，针对鲨鱼的研究甚至可能揭开人类和其它哺乳动物进化之谜。
原始出处:
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.
全文链接：
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050101
