美國舊金山州立大學生物學助理教授卡倫-克勞表示：“我們的研究發(fā)現(xiàn)匙吻鱘擁有自身基因組的副本,。這種復制形成了額外的基因材料，提高了比較研究的復雜性,。這可能改變我們針對肢體發(fā)育的研究方式。”為了研究人類的肢體如何發(fā)育,，科學家將老鼠的肢體基因與魚類的鰭基因進行比較,。此前有關匙吻鱘的研究顯示，這種魚類在出現(xiàn)四足動物前很久就擁有生長出肢體所需要的“基因包”,。四足動物最后進化成爬行類,、鳥類、兩棲類和哺乳動物,。
研究中,，克勞和同事對美洲匙吻鱘含有19個Hox基因的染色體片段進行了排序。Hox基因決定體形和肢體發(fā)育,，同時也是幫助科學發(fā)現(xiàn)整個基因族副本的主要指示器,。完整基因組副本被研究人員稱之為進化史上“一個顛覆游戲規(guī)則的事件”，讓一種物種出現(xiàn)新種或者奇特種群創(chuàng)造了條件,。
這種復制的出現(xiàn)是一系列看似不可能的條件同時滿足的結果,，讓匙吻鱘的每一個基因都擁有副本。完成復制后,，基因?qū)χ械囊粋€基因保持原有的功能,，另一個要么消失，要么擁有一個新功能,?？藙诒硎荆?ldquo;額外的基因材料為進化提供了畫布，讓進化過程描繪出各種景象,。”克勞一直從事新奇物種和生物多樣性研究,。
科學家認為這種基因組復制在有頜類脊椎動物出現(xiàn)前就已發(fā)生。在進化樹的特定枝杈(譜系)也出現(xiàn)完整基因組復制現(xiàn)象，植物要比動物更為普遍,?？藙谡f：“我們對匙吻鱘進行的研究顯示動物的完整基因組復制現(xiàn)象并沒有此前認為的那么罕見。”（生物谷Bioon.com）
doi: 10.1093/gbe/evs067
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An independent genome duplication inferred from Hox paralogs in the American paddlefish-a representative basal ray-finned fish and important comparative reference
Karen D. Crow, Christopher D. Smith, Jan-Fang Cheng, Günter P. Wagner and Chris T. Amemiya
Vertebrates have experienced two rounds of whole genome duplication in the stem lineages of deep nodes within the group, and a subsequent duplication event in the stem lineage of the teleosts-a highly diverse group of ray-finned fishes. Here we present the first full Hox gene sequences for any member of the Acipenseriformes, the American paddlefish, and confirm that an independent whole genome duplication occurred in the paddlefish lineage, approximately 42 million years ago based on sequences spanning the entire HoxA cluster and eight genes on the HoxD gene cluster. These clusters comprise different HOX loci, and maintain conserved synteny relative to bichir, zebrafish, stickleback and pufferfish, as well as human, mouse, and chick. We also provide a gene genealogy for the duplicated fzd8 gene in paddlefish and present evidence for the first Hox14 gene in any ray-finned fish. Taken together, these data demonstrate that the American paddlefish has an independently duplicated genome. Substitution patterns of the “beta” paralogs on both the HoxA and HoxD gene clusters suggest transcriptional inactivation-consistent with functional diploidization. Further, there are similarities in the pattern of sequence divergence among duplicated Hox genes in paddlefish and teleost lineages, even though they occurred independently approximately 200 million years apart. We highlight implications on comparative analyses in the study of the “fin-limb transition” as well as gene and genome duplication in bony fishes, which includes all ray-finned fishes as well as the lobe-finned fishes and tetrapod vertebrates.
