Cohn Martin J
Division of Zoology, School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading RG6 6AJ, UK.
Nature. 2002 Mar 28;416(6879):386-7. doi: 10.1038/416386a.
The development of jaws was a critical event in vertebrate evolution because it ushered in a transition to a predatory lifestyle, but how this innovation came about has been a mystery. In the embryos of jawed vertebrates (gnathostomes), the jaw cartilage develops from the mandibular arch, where none of the Hox genes is expressed; if these are expressed ectopically, however, jaw development is inhibited. Here I show that in the lamprey, a primitively jawless (agnathan) fish that is a sister group to the gnathostomes, a Hox gene is expressed in the mandibular arch of developing embryos. This finding, together with outgroup comparisons, suggests that loss of Hox expression from the mandibular arch of gnathostomes may have facilitated the evolution of jaws.
颌骨的发育是脊椎动物进化中的一个关键事件，因为它开启了向捕食性生活方式的转变，但这种创新是如何产生的一直是个谜。在有颌脊椎动物（gnathostomes）的胚胎中，颌软骨由下颌弓发育而来，而下颌弓中没有Hox基因表达；然而，如果这些基因异位表达，颌骨发育就会受到抑制。在这里，我表明在七鳃鳗中，一种与gnathostomes是姐妹群的原始无颌（agnathan）鱼类，一个Hox基因在发育胚胎的下颌弓中表达。这一发现，连同外群比较，表明gnathostomes下颌弓中Hox基因表达的缺失可能促进了颌骨的进化。
