Coolen Marion, Nicolle Delphine, Plouhinec Jean-Louis, Gombault Aurélie, Sauka-Spengler Tatjana, Menuet Arnaud, Pieau Claude, Mazan Sylvie
Développement et Evolution des vertébrés, UMR 6218, CNRS et Université d'Orléans, Orleans, France.
PLoS One. 2008 Jul 16;3(7):e2676. doi: 10.1371/journal.pone.0002676.
Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance.
由于海龟像两栖动物一样存在胚孔，有人提出海龟可作为从两栖动物型原肠胚形成模式向鸟类型原肠胚形成模式转变的过渡形式的例证。为了验证这一假设并深入了解羊膜动物在原肠胚形成过程中独特特征的出现，我们首次对一种爬行动物——圆斑龟的原肠胚进行了分子特征分析。对短尾蛋白、Lim1、Otx2和Otx5表达模式的研究表明，其表达动态与羊膜动物模式生物高度保守，并且能够确定中胚层内化的位点，这在爬行动物中一直是个长期存在的问题。对短尾蛋白表达的分析还突出了两个不同阶段的存在，这在模式生物中不太容易识别，分别以早期的环形区域和后期的双侧对称区域为特征。与四足动物模式生物的系统比较，为所有爬行动物共有的胚孔/胚孔板系统与两栖动物的胚孔以及鸟类和哺乳动物的原条之间的关系带来了新的见解。短尾蛋白的双相表达模式也与最近的双侧对称出现模型一致，这就引发了其进化意义的问题。
