Spring Jürg, Yanze Nathalie, Jösch Christoph, Middel Arnoud M, Winninger Brigitte, Schmid Volker
Institute of Zoology, Biocenter/Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056, Basel, Switzerland.
Dev Biol. 2002 Apr 15;244(2):372-84. doi: 10.1006/dbio.2002.0616.
One major difference between simple metazoans such as cnidarians and all the bilaterian animals is thought to involve the invention of mesoderm. The terms diploblasts and triploblasts are therefore, often used to group prebilaterian and bilaterian animals, respectively. However, jellyfish contain well developed striated and smooth muscle tissues that derive from the entocodon, a mesoderm-like tissue formed during medusa development. We investigated the hypothesis, that the entocodon could be homologous to the third germ layer of bilaterians by analyzing the structures and expression patterns of the homologues of Brachyury, Mef2, and Snail in the jellyfish Podocoryne carnea. These are regulatory genes from the T-box, MADS-box and zinc finger families known to play important roles in bilaterian mesoderm patterning and muscle differentiation. The sequence and expression data demonstrate that the genes are structurally and functionally conserved and even more similar to humans or other deuterostomes than to protostome model organisms such as Drosophila or Caenorhabditis elegans. Based on these data we conclude that the common ancestor of the cnidarians and bilaterians not only shared genes that play a role in regulating myogenesis but already used them to develop and differentiate muscle systems similar to those of triploblasts.
诸如刺胞动物等简单后生动物与所有两侧对称动物之间的一个主要差异被认为与中胚层的出现有关。因此，双胚层动物和三胚层动物这两个术语常分别用于对前两侧对称动物和两侧对称动物进行分类。然而，水母含有发育良好的横纹肌和平滑肌组织，这些组织源自内胚层，即水母发育过程中形成的一种类似中胚层的组织。我们通过分析海月水母中短尾相关蛋白（Brachyury）、肌细胞增强因子2（Mef2）和蜗牛相关蛋白（Snail）的同源物的结构和表达模式，研究了内胚层可能与两侧对称动物的第三胚层同源的假说。这些是来自T盒、MADS盒和锌指家族的调控基因，已知在两侧对称动物的中胚层模式形成和肌肉分化中发挥重要作用。序列和表达数据表明，这些基因在结构和功能上是保守的，与人类或其他后口动物的相似性甚至高于与果蝇或秀丽隐杆线虫等原口动物模式生物的相似性。基于这些数据，我们得出结论，刺胞动物和两侧对称动物的共同祖先不仅共享在调节肌生成中起作用的基因，而且已经利用这些基因来发育和分化类似于三胚层动物的肌肉系统。
