Early development and segment formation in the centipede, Strigamia maritima (Geophilomorpha)
Early development and segment formation in the centipede, Strigamia maritima (Geophilomorpha)
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DOI：
10.1111/j.1525-142x.2004.04016.x
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发表时间：
2004-03-01
影响因子：
2.9
通讯作者：
Akam, M
中科院分区：
文献类型：
--
作者：
Chipman, AD;Arthur, W;Akam, M
地型蜈蚣表现出许多独特的特征，使它们具有特殊的发育和进化意义。亲地蜈蚣的节数比其他任何蜈蚣都要多，从27到191不等。它们可能在一个物种内是恒定的，在发展过程中以极端的形式呈现“计数”问题，或者它们可能会变化——这种情况为我们提供了研究自然发生的片段数量变化的机会。它们的所有节段都是在胚胎发生过程中产生的，这与更基础的蜈蚣目不同，后者在胚胎中只产生15个躯干节中的一小部分，其余部分在胚胎后发育。在此，我们在迄今为止对沿海物种Strigamia maritima进行的一项研究的基础上，为进一步研究地胚目提供了基础。发育开始于细胞核迁移到卵细胞表面，然后卵细胞凝结形成超过20,000个细胞的胚胎雏形，覆盖整个半球。在早期发育过程中，胚胎可分为两个不同的区域：明显未分化组织的大顶盘和具有清晰的前后轴和分化节段的种带。胚带从终末椎间盘前部形成，并随着椎间盘收缩向前延伸。在胚带的后缘形成新的节段。一旦分割过程结束，胚带就会折叠并沉入蛋黄中。我们注意到，海蒙斯在一个多世纪前对蜈蚣发育的经典描述，在确定轴线上有一个根本性的错误，因此在对早期分割的解释上也有一个根本性的错误。
Geophilomorph centipedes exhibit a number of unique characteristics that make them of particular developmental and evolutionary interest. Segment numbers in geophilomorphs are higher than in any other centipedes, ranging from 27 to 191. They may be constant within a species, presenting in extreme form the "counting" problem in development, or they may vary-a situation that provides us with the opportunity to study naturally occurring variation in segment numbers. All their segments are generated during embryogenesis, a situation unlike that in the more basal centipede orders, which generate only a fraction of their 15 trunk segments in the embryo and develop the rest postembryonically. Here we provide a foundation for further developmental studies of the Geophilomorpha, building on the one study that has been conducted to date, on the coastal species Strigamia maritima. Development begins with the migration of nuclei to the surface of the egg, which then condense to form an embryonic rudiment of more than 20,000 cells, covering an entire hemisphere. During early development, the embryo can be divided into two distinct areas: a large terminal disc of apparently undifferentiated tissue and the germ-band, which has a clear anteroposterior axis and differentiated segments. The germ-band forms from the anterior of the terminal disc and extends anteriorly as the disc contracts. New segments are formed at the posterior margin of the germ-band. Once the process of segmentation ends, the germ-band folds and sinks into the yolk. We note that the classic description of centipede development, by Heymons more than a century ago, contains a fundamental error in the identification of the axes and hence in the interpretation of early segmentation.