Nature：科學家破譯猛犸象80%基因組

      美國科學家日前通過一團猛犸象的毛發，成功破譯出這個史前龐然大物80%的基因組。盡管這是一團毫無光澤的毛發，卻使科學家在復活猛犸象的道路上又向前邁進了一步。

      科學家通過已在西伯利亞永久凍結帶冷凍數千年的猛犸象尸體提取的毛發樣本，整理出這種史前巨獸的DNA。基因代碼讓科學家對猛犸象的進化過程有了新的了解，同時表明它們遠比之前想象的更接近于現代象。這項發現還可以使研究人員搞清楚大象的遺傳構造，復活滅絕已久的猛犸象。

      科學家利用從西伯利亞永久凍結帶發現的兩具猛犸象殘骸上獲取的DNA，實施了這種類似于科幻大片《侏羅紀公園》劇情的研究。美國科學家在最新一期科學雜志《自然》（Nature）上報告稱，在這兩具猛犸象尸體中，一具已在地下埋了2萬年，另一具則至少埋了6萬年。通過仔細分析它們的DNA，研究小組已經整理出80%的猛犸象基因組或遺傳密碼。

      這項研究表明，兩頭猛犸象關系十分緊密。另外分析還表明，600萬年前，猛犸象和現代象走向了不同的進化路徑，幾乎與此同時，人類和黑猩猩也走上了與它們一樣的進化道路。200萬年前，猛犸象一分為二，一組在距今4.5萬年前滅絕，另一組在距今1萬年前最后一個冰河時期的末期從地球上消失。

      雄性猛犸象高約10英尺(約合3米)，雌性相對矮一些。它們的尖牙長而彎曲，腹部的毛發最長可達3英尺(約合0.9米)。迄今，科學家已在西伯利亞發現了大約40具猛犸象的尸體。實施最新研究的美國科學家之所以使用提取自猛犸象毛發的DNA，是因為相對于猛犸象尸體其他部位的DNA，它們保存得更為完好。

      一些研究人員一直建議使用冰凍猛犸象尸體的皮膚或毛發克隆猛犸象。領導這項研究的賓夕法尼亞州立大學教授史蒂芬·舒斯特(Stephan Schuster)說：“從理論上講，通過破譯這個基因組，我們可以獲取重要的信息，將來有一天，只要將獨特的猛犸象DNA序列融入現代象的基因組中，這些信息或能幫助其他研究人員復活猛犸象。”

      但是，西澳大利亞默多克大學古生物DNA實驗室主任邁克爾·邦斯(Michael Bunce)博士給舒斯特教授潑了一瓢涼水。他說：“掌握某種生物的DNA代碼并不意味著我們可以通過遺傳手段實現重造滅絕生物體的美好愿望。”（生物谷Bioon.com）

生物谷推薦原始出處：

Nature，456, 387-390，Webb Miller，Stephan C. Schuster

Sequencing the nuclear genome of the extinct woolly mammoth

Webb Miller1, Daniela I. Drautz1, Aakrosh Ratan1, Barbara Pusey1, Ji Qi1, Arthur M. Lesk1, Lynn P. Tomsho1, Michael D. Packard1, Fangqing Zhao1, Andrei Sher2,9, Alexei Tikhonov3, Brian Raney4, Nick Patterson5, Kerstin Lindblad-Toh5, Eric S. Lander5, James R. Knight6, Gerard P. Irzyk6, Karin M. Fredrikson7, Timothy T. Harkins7, Sharon Sheridan7, Tom Pringle8 & Stephan C. Schuster1

1 Pennsylvania State University, Center for Comparative Genomics and Bioinformatics, 310 Wartik Building, University Park, Pennsylvania 16802, USA
2 Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 33 Leninsky Prospect, 119071 Moscow, Russia
3 Zoological Institute, Russian Academy of Sciences, Universitetskaya Naberezhnaya 1, 199034 Saint Petersburg, Russia
4 Center for Biomolecular Science and Engineering, University of California, Santa Cruz, California 95064, USA
5 Broad Institute of MIT and Harvard, 7 Cambridge Center, Cambridge, Massachusetts 02142, USA
6 454 Life Sciences, 20 Commercial Street, Branford, Connecticut 06405, USA
7 Roche Diagnostics Corporation, 9115 Hague Road, Indianapolis, Indiana 46250-0414, USA
8 Sperling Foundation, Eugene, Oregon 97405, USA

In 1994, two independent groups extracted DNA from several Pleistocene epoch mammoths and noted differences among individual specimens1, 2. Subsequently, DNA sequences have been published for a number of extinct species. However, such ancient DNA is often fragmented and damaged3, and studies to date have typically focused on short mitochondrial sequences, never yielding more than a fraction of a per cent of any nuclear genome. Here we describe 4.17 billion bases (Gb) of sequence from several mammoth specimens, 3.3 billion (80%) of which are from the woolly mammoth (Mammuthus primigenius) genome and thus comprise an extensive set of genome-wide sequence from an extinct species. Our data support earlier reports4 that elephantid genomes exceed 4 Gb. The estimated divergence rate between mammoth and African elephant is half of that between human and chimpanzee. The observed number of nucleotide differences between two particular mammoths was approximately one-eighth of that between one of them and the African elephant, corresponding to a separation between the mammoths of 1.5–2.0 Myr. The estimated probability that orthologous elephant and mammoth amino acids differ is 0.002, corresponding to about one residue per protein. Differences were discovered between mammoth and African elephant in amino-acid positions that are otherwise invariant over several billion years of combined mammalian evolution. This study shows that nuclear genome sequencing of extinct species can reveal population differences not evident from the fossil record, and perhaps even discover genetic factors that affect extinction.