动物体内，中枢神经系统（central nervous system；CNS）的进化问题困扰了科学家们好几个世纪。脊椎动物、昆虫和环节动物都从同一个祖先那进化而来，但是他们的CNS却是截然不同。科学家们甚至认为CNS是在他们于进化树上分道扬镳之后才各自进化出的产物。现在，来自海德堡的欧洲分子生物学实验室（European Molecular Biology Laboratory；EMBL）的研究者发现，脊椎动物的神经系统的历史可能比预想的要早一些。发表在《Cell》杂志上的这篇文章，暗示着脊椎动物、昆虫和环节动物的最后的共同祖先，已经具有与当今脊椎动物类似的中央集中的神经系统了。
许多动物都进化出复杂的神经系统，但是物种之间的结构却是可以不相同的，例如脊椎动物在背部有脊髓一般的中枢神经系统，昆虫和环节虫（Annelid Worm；如蚯蚓）的神经细胞却集中在腹部中类似于绳索梯子一般的神经节中。其他的一些无脊椎动物，神经细胞会分散在全身各处。但所有这些物种都起源于一个共同的祖先，即对称动物urbilateria。如果这个祖先已经拥有了神经系统，那么它的形状是怎么样的？它是如何进化出今天动物体内如此千变万化的神经系统的？这些都是Detlev Arendt和他的同事迫切想解答的问题。为此，他们深入研究了海生环节动物沙蚕Platynereis dumerilii的神经系统。
原始出处:
Cell, Vol 129, 277-288, 20 April 2007
Article
Molecular Architecture of Annelid Nerve Cord Supports Common Origin of Nervous System Centralization in Bilateria
Alexandru S. Denes,1,6 Gáspár Jékely,1,6 Patrick R.H. Steinmetz,1,4 Florian Raible,1 Heidi Snyman,1 Benjamin Prud'homme,2,5 David E.K. Ferrier,3 Guillaume Balavoine,2 and Detlev Arendt1,
1 Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, 69117, Germany
2 Centre de Génétique Moléculaire, CNRS, Gif-sur-Yvette 91198, France
3 Department of Zoology, University of Oxford, Oxford, OX1 3PS, United Kingdom
Corresponding author
Detlev Arendt
arendt@embl.de
Summary
To elucidate the evolutionary origin of nervous system centralization, we investigated the molecular architecture of the trunk nervous system in the annelid Platynereis dumerilii. Annelids belong to Bilateria, an evolutionary lineage of bilateral animals that also includes vertebrates and insects. Comparing nervous system development in annelids to that of other bilaterians could provide valuable information about the common ancestor of all Bilateria. We find that the Platynereis neuroectoderm is subdivided into longitudinal progenitor domains by partially overlapping expression regions of nk and pax genes. These domains match corresponding domains in the vertebrate neural tube and give rise to conserved neural cell types. As in vertebrates, neural patterning genes are sensitive to Bmp signaling. Our data indicate that this mediolateral architecture was present in the last common bilaterian ancestor and thus support a common origin of nervous system centralization in Bilateria.
