Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited
Organization of the central nervous system and innervation of cephalic sensory structures in the water bear Echiniscus testudo (Tardigrada: Heterotardigrada) revisited
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DOI：
10.1002/jmor.21386
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发表时间：
2021-06-23
影响因子：
1.5
通讯作者：
Mayer, Georg
中科院分区：
文献类型：
--
作者：
Gross, Vladimir;Epple, Lisa;Mayer, Georg
缓步动物的大脑一直是一些神经解剖学研究的主题，因为它是理解全节肢动物（缓步动物门+有蹄类+节肢动物门）中枢神经系统进化的关键。尽管缓步动物的头部和头部感觉结构常常不同，但它们的大脑的总体形态似乎很好地保存了下来。因此，早期的缓步动物学家已经绘制出了大脑的一般形状及其与中枢神经系统其他部分的主要连接。尽管随后的调查主要是基于透射电子显微镜或免疫组织化学，表征的不同区域的缓步动物的大脑进展相对缓慢，悬而未决的问题。为了提高我们对不同脑区的理解，我们使用抗突触蛋白和抗乙酰化α-微管蛋白免疫组织化学方法重新研究了异缓步动物Echiniscus testudo的中枢神经系统，以便可视化神经束、连合和神经末梢的数量和位置。我们的数据显示，沿着身体的五个主要的突触蛋白免疫反应域：一个大的单一的，马蹄形的neuropelles在头部和四个neuropils在躯干神经节，支持的假设，背侧脑是连续同源的腹侧躯干神经节。同时，抗突触蛋白和抗微管蛋白免疫反应性的模式在神经节之间不同，增加了现有的证据，即四个主干神经节中的每一个在其形态上是独特的。抗微管蛋白标记进一步揭示了两个连合内的中枢脑神经系统，其中之一是分叉，和额外的套脑外脑头连合与stomodeal神经系统和腹侧细胞簇。此外，我们的研究结果还显示了E.陆龟支持这些结构的子集与真缓步动物的感觉领域的同源性。
The tardigrade brain has been the topic of several neuroanatomical studies, as it is key to understanding the evolution of the central nervous systems in Panarthropoda (Tardigrada + Onychophora + Arthropoda). The gross morphology of the brain seems to be well conserved across tardigrades despite often disparate morphologies of their heads and cephalic sensory structures. As such, the general shape of the brain and its major connections to the rest of the central nervous system have been mapped out already by early tardigradologists. Despite subsequent investigations primarily based on transmission electron microscopy or immunohistochemistry, characterization of the different regions of the tardigrade brain has progressed relatively slowly and open questions remain. In an attempt to improve our understanding of different brain regions, we reinvestigated the central nervous system of the heterotardigrade Echiniscus testudo using anti-synapsin and anti-acetylated alpha-tubulin immunohistochemistry in order to visualize the number and position of tracts, commissures, and neuropils. Our data revealed five major synapsin-immunoreactive domains along the body: a large unitary, horseshoe-shaped neuropil in the head and four neuropils in the trunk ganglia, supporting the hypothesis that the dorsal brain is serially homologous with the ventral trunk ganglia. At the same time, the pattern of anti-synapsin and anti-tubulin immunoreactivity differs between the ganglia, adding to the existing evidence that each of the four trunk ganglia is unique in its morphology. Anti-tubulin labeling further revealed two commissures within the central brain neuropil, one of which is forked, and additional sets of extracerebral cephalic commissures associated with the stomodeal nervous system and the ventral cell cluster. Furthermore, our results showing the innervation of each of the cephalic sensilla in E. testudo support the homology of subsets of these structures with the sensory fields of eutardigrades.