Arthropod early neurogenesis shows distinct patterns that have been interpreted in an evolutionary framework. For instance, crustaceans and Hexapoda form the taxon Tetraconata and share the differentiation of specific neural precursors, the neuroblasts, a character which sets them apart from Chelicerata and Myriapoda. Neuroblasts are relatively large stem cells that generate ganglion mother cells by asymmetric divisions. Ganglion mother cells typically divide once to give rise to neurons and glia cells. In hexapods, neuroblasts segregate from the neuroectoderm before they begin their characteristic proliferative activity. In the crustaceans studied so far, neuroblasts remain in the neuroectoderm. Yet, detailed studies on early neurogenesis of crustaceans at the cellular level are largely restricted to some malacostracan and branchiopod species. Crustaceans are very diverse and likely paraphyletic with respect to hexapods. Hence, knowledge about neural differentiation in other crustacean taxa might contribute to the understanding of evolution of neurogenesis in Tetraconata. Here, we describe the early neurogenesis during naupliar development of the copepod Tigriopus californicus. We show that neuroblasts are present that generate ganglion mother cells, which in turn divide to give rise to neurons of the ventral nerve cord. These two neural precursor cell types and their specific arrangement correspond to what has been found in other crustaceans. One obvious difference concerns the relative size of the neuroblasts, which are not much larger than their progeny. Our results complement the picture of neural differentiation in crustaceans and suggest that superficially located neuroblasts are likely the ancestral condition in Tetraconata.

中文翻译：

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pe足类Tigriopus californicus（Tetraconata，Multicrustacea）的幼虫神经发生。

节肢动物早期神经发生显示出不同的模式，这些模式已在进化框架中得到解释。例如，甲壳类动物和六足纲动物形成了四面体分类群，并共享特定神经前体神经母细胞的分化，这一特征使它们不同于鳞翅目昆虫和Myriapoda。成神经细胞是相对较大的干细胞，通过不对称分裂产生神经节母细胞。神经节母细胞通常分裂一次以产生神经元和神经胶质细胞。在六足动物中，成神经细胞在开始其特征性增殖活性之前就从神经外胚层中分离出来。在迄今为止研究的甲壳动物中，神经母细胞保留在神经外胚层中。然而，在细胞水平上对甲壳类动物的早期神经发生的详细研究在很大程度上限于某些疟原虫和支脚类动物。甲壳动物种类繁多，就六足动物而言可能是共生的。因此，有关其他甲壳类群中神经分化的知识可能有助于理解四齿龟中神经发生的进化。在这里，我们描述了pe足类的无节幼体发育过程中的早期神经发生。底栖虎。我们表明存在神经母细胞生成神经节母细胞，继而分裂以产生腹神经索的神经元。这两种神经前体细胞类型及其特定排列与在其他甲壳类动物中发现的相对应。一个明显的差异与成神经细胞的相对大小有关，其不比其后代大很多。我们的研究结果补充了甲壳类动物神经分化的图片，并表明表皮定位的成神经细胞可能是Tetraconata的祖先条件。