大多数的进化生物学家愿意关注物种间同源的基因、结构以及过程是如何出现或者这些性状如何出现分歧的。但是对于一些形态学特征以及发育的过程来说，“同源”的定义是有问题的。脊索动物中的变态发育就是一个典型的例子。
最近，一个由来自法国、波兰、斯洛伐克和美国科学家组成的跨国研究组对文昌鱼的变态发育进行了研究。在脊索动物的胚胎后发育过程中，不同的谱系中从幼体到成体存在广泛的变态发育，这种现象提示我们，这种形态学上的多样性有可能是通过独立发生的过程而产生的。在脊椎动物中，变态发育是由甲状腺激素（THs）和甲状腺激素受体（TRs）的结合而引发的。科学家通过研究发现，甲状腺激素的衍生物，一种叫做TRIAC的物质，在头索动物文昌鱼中诱导了变态。文昌鱼的甲状腺素受体由于与TRIAC紧密结合，从而介导了自然发生的和由TRIAC诱导的变态过程。而NH3作为甲状腺素的拮抗剂，阻止了自然发生的和由TRIAC诱导的变态过程。文昌鱼的甲状腺素受体的表达水平也随着甲状腺素的增加而增加。因此，由甲状腺素诱导的变态过程受到了甲状腺素受体的调节，这种变态过程是所有脊索动物的祖先特征，这种调节网络的保守性也支持变态在脊索动物谱系中是具有同源性的。相关论文发表在《当代生物学》（Current Biology）上。（生物谷Bioon.com）
生物谷推荐原始出处：
Current Biology，Volume 18, Issue 11, 3 June 2008, Pages 825-830，Mathilde Paris，Vincent Laudet
Amphioxus Postembryonic Development Reveals the Homology of Chordate Metamorphosis
Mathilde Paris1, Hector Escriva2, Michael Schubert1, Frédéric Brunet1, Julius Brtko3, Fabrice Ciesielski4, Dominique Roecklin4, Valérie Vivat-Hannah4, Emilien L. Jamin5, Jean-Pierre Cravedi5, Thomas S. Scanlan6, Jean-Paul Renaud4, Nicholas D. Holland7 and Vincent Laudet1, ,
1Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, CNRS, INRA, UCB Lyon 1, IFR128 Lyon Biosciences, Ecole Normale Supérieure de Lyon, 69364 Lyon Cedex 07, France
2Laboratoire Arago, UMR-7628, CNRS, University Pierre and Marie Curie, 66651 Banyuls sur Mer, France
3Institute of Experimental Endocrinology, Slovak Academy of Sciences, 833 06 Bratislava, Slovak Republic
4AliX, Boulevard Sébastien Brant, Parc d'Innovation, 67400 Illkirch, France
5INRA, UMR-1089 Xenobiotiques, 31931 Toulouse Cedex 9, France
6Department of Physiology and Pharmacology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239
7Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0202
Received 29 October 2007; revised 17 April 2008; accepted 25 April 2008. Published online: May 29, 2008. Available online 2 June 2008.
Summary
Most studies in evolution are centered on how homologous genes, structures, and/or processes appeared and diverged. Although historical homology is well defined as a concept, in practice its establishment can be problematic, especially for some morphological traits or developmental processes. Metamorphosis in chordates is such an enigmatic character. Defined as a spectacular postembryonic larva-to-adult transition, it shows a wide morphological diversity between the different chordate lineages, suggesting that it might have appeared several times independently. In vertebrates, metamorphosis is triggered by binding of the thyroid hormones (THs) T4 and T3 to thyroid-hormone receptors (TRs). Here we show that a TH derivative, triiodothyroacetic acid (TRIAC), induces metamorphosis in the cephalochordate amphioxus. The amphioxus TR (amphiTR) mediates spontaneous and TRIAC-induced metamorphosis because it strongly binds to TRIAC, and a specific TR antagonist, NH3, inhibits both spontaneous and TRIAC-induced metamorphosis. Moreover, as in amphibians, amphiTR expression levels increase around metamorphosis and are enhanced by THs. Therefore, TH-regulated metamorphosis, mediated by TR, is an ancestral feature of all chordates. This conservation of a regulatory network supports the homology of metamorphosis in the chordate lineage.
