Robinson-Rechavi Marc, Boussau Bastien, Laudet Vincent
Laboratoire de Biologie Moléculaire de la Cellule, UMR CNRS5161, Ecole Normale Supérieure de Lyon, Lyon, France.
Mol Biol Evol. 2004 Mar;21(3):580-6. doi: 10.1093/molbev/msh046. Epub 2003 Dec 23.
Vertebrates originated in the lower Cambrian. Their diversification and morphological innovations have been attributed to large-scale gene or genome duplications at the origin of the group. These duplications are predicted to have occurred in two rounds, the "2R" hypothesis, or they may have occurred in one genome duplication plus many segmental duplications, although these hypotheses are disputed. Under such models, most genes that are duplicated in all vertebrates should have originated during the same period. Previous work has shown that indeed duplications started after the speciation between vertebrates and the closest invertebrate, amphioxus, but have not set a clear ending. Consideration of chordate phylogeny immediately shows the key position of cartilaginous vertebrates (Chondrichthyes) to answer this question. Did gene duplications occur as frequently during the 45 Myr between the cartilaginous/bony vertebrate split and the fish/tetrapode split as in the previous approximately 100 Myr? Although the time interval is relatively short, it is crucial to understanding the events at the origin of vertebrates. By a systematic appraisal of gene phylogenies, we show that significantly more duplications occurred before than after the cartilaginous/bony vertebrate split. Our results support rounds of gene or genome duplications during a limited period of early vertebrate evolution and allow a better characterization of these events.
脊椎动物起源于寒武纪早期。它们的多样化和形态创新被认为归因于该类群起源时的大规模基因或基因组复制。这些复制被预测发生了两轮，即“2R”假说，或者它们可能发生在一次基因组复制加上许多片段复制的过程中，尽管这些假说存在争议。在这种模型下，所有脊椎动物中被复制的大多数基因应该在同一时期起源。先前的研究表明，复制确实在脊椎动物与最接近的无脊椎动物文昌鱼分化之后开始，但尚未明确结束时间。考虑到脊索动物的系统发育，软骨脊椎动物（软骨鱼纲）在回答这个问题时的关键地位立刻显现出来。在软骨/硬骨脊椎动物分化与鱼类/四足动物分化之间的4500万年里，基因复制的发生频率是否与之前大约1亿年里一样高呢？尽管时间间隔相对较短，但对于理解脊椎动物起源时的事件至关重要。通过对基因系统发育的系统评估，我们表明在软骨/硬骨脊椎动物分化之前发生的复制明显多于之后。我们的结果支持在脊椎动物早期进化的有限时期内发生了多轮基因或基因组复制，并能更好地描述这些事件。
