Segmental mode of neural patterning in Sipuncula
Segmental mode of neural patterning in Sipuncula
复制标题
DOI：
10.1016/j.cub.2008.06.066
复制
发表时间：
2008-08-05
期刊：
影响因子：
9.2
通讯作者：
Wanninger, Andreas
中科院分区：
文献类型：
--
作者：
Kristof, Alen;Wollesen, Tim;Wanninger, Andreas
最近的分子系统发育分析表明，两个蠕虫状的门，不分节的星虫（花生虫）和分节的环节动物（例如，蚯蚓和多毛类）[1-5]。它们的身体结构的显著差异体现在环节动物的成对的、梯形的腹神经系统，其中包含节段排列的神经节，以及星虫的单一腹神经索（VNC），其中没有任何节段结构[6，7]。调查中枢神经系统（CNS）的形成与5-羟色胺和FMRFamide标记在一个代表性的星虫，Phasspeioma agassizii，我们发现，神经发生最初遵循一个节段模式类似的环节动物。从成对的FMRFamidergic和多巴胺能轴突开始，四对相关的多巴胺能胞体和相互连接的连合在前后进展中一个接一个形成。在晚期幼虫中，VNC的两个轴突融合，连合消失，并形成一对额外的胞体。这些细胞（总共10个）相互迁移，最终形成两个簇，每个簇有5个细胞。这些神经重塑过程导致星虫的单一非同色异谱中枢神经系统。我们的数据证实了星虫属的节段祖先，并使Phaspercoma成为一个物种进化历史的个体发生重演的Haeckelian假说的教科书例子[8]。
Recent molecular phylogenetic analyses suggest a close relationship between two worm-shaped phyla, the nonsegmented Sipuncula (peanut worms) and the segmented Annelida (e.g., earthworms and polychaetes) [1-5]. The striking differences in their bodyplans are exemplified by the annelids' paired, ladder-like ventral nervous system, which contains segmentally arranged ganglia, and the sipunculans' single ventral nerve cord (VNC), which is devoid of any segmental structures [6, 7]. Investigating central nervous system (CNS) formation with serotonin and FMRFamide labeling in a representative sipunculan, Phascolosoma agassizii, we found that neurogenesis initially follows a segmental pattern similar to that of annelids. Starting out with paired FMRFamidergic and serotonergic axons, four pairs of associated serotonergic perikarya and interconnecting commissures form one after another in an anterior-posterior progression. In late-stage larvae, the two serotonergic axons of the VNCs fuse, the commissures disappear, and one additional pair of perikarya is formed. These cells (ten in total) migrate toward one another, eventually forming two clusters of five cells each. These neural-remodeling processes result in the single nonmetameric CNS of the adult sipunculan. Our data confirm the segmental ancestry of Sipuncula and render Phascolosoma a textbook example for the Haeckelian hypothesis of ontogenetic recapitulation of the evolutionary history of a species [8].