Prud'homme Benjamin, de Rosa Renaud, Arendt Detlev, Julien Jean-François, Pajaziti Rafael, Dorresteijn Adriaan W C, Adoutte André, Wittbrodt Joachim, Balavoine Guillaume
Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, UPR 2167, 1 avenue de la terrasse, 91190 Gif sur Yvette, France.
Curr Biol. 2003 Oct 28;13(21):1876-81. doi: 10.1016/j.cub.2003.10.006.
The origin of animal segmentation, the periodic repetition of anatomical structures along the anteroposterior axis, is a long-standing issue that has been recently revived by comparative developmental genetics. In particular, a similar extensive morphological segmentation (or metamerism) is commonly recognized in annelids and arthropods. Mostly based on this supposedly homologous segmentation, these phyla have been united for a long time into the clade Articulata. However, recent phylogenetic analysis dismissed the Articulata and thus challenged the segmentation homology hypothesis. Here, we report the expression patterns of genes orthologous to the arthropod segmentation genes engrailed and wingless in the annelid Platynereis dumerilii. In Platynereis, engrailed and wingless are expressed in continuous ectodermal stripes on either side of the segmental boundary before, during, and after its formation; this expression pattern suggests that these genes are involved in segment formation. The striking similarities of engrailed and wingless expressions in Platynereis and arthropods may be due to evolutionary convergence or common heritage. In agreement with similarities in segment ontogeny and morphological organization in arthropods and annelids, we interpret our results as molecular evidence of a segmented ancestor of protostomes.
动物体节化的起源，即解剖结构沿前后轴的周期性重复，是一个长期存在的问题，最近通过比较发育遗传学又重新引发了人们的关注。特别是，在环节动物和节肢动物中通常都能识别出类似的广泛形态体节化（或分节现象）。长期以来，主要基于这种推测的同源体节化，这些门类被归为有铰动物门。然而，最近的系统发育分析否定了有铰动物门，从而对体节同源性假说提出了挑战。在这里，我们报告了环节动物杜氏阔沙蚕中与节肢动物体节化基因engrailed和wingless直系同源的基因的表达模式。在杜氏阔沙蚕中，engrailed和wingless在体节边界形成之前、期间和之后，在其两侧连续的外胚层条带中表达；这种表达模式表明这些基因参与了体节的形成。杜氏阔沙蚕和节肢动物中engrailed和wingless表达的显著相似性可能是由于进化趋同或共同的遗传。与节肢动物和环节动物在体节个体发生和形态组织上的相似性一致，我们将我们的结果解释为原口动物分节祖先的分子证据。
