Corrêa Clynton Lourenço, da Silva Paula Grazielle Chaves, Pereira Mário José dos Santos, Allodi Silvana, Martinez Ana Maria Blanco
Departamento de Histologia e Embriologia, ICB, CCS, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Microsc Res Tech. 2008 Mar;71(3):214-9. doi: 10.1002/jemt.20541.
Despite several reports on the morphology and functions associated with the morphometry of the vertebrate axoplasm cytoskeleton, the subject has not been thoroughly explored in invertebrates. In vertebrates, among many other functions, microtubules (MTs) serve as scaffolding for axon assembly, and neurofilaments (NFs) as the elements that determine the axon caliber. Intermediate filaments have never been described by electron microscopy in arthropods, although NF proteins have been revealed in the MT side-arms of the axoplasm of certain species, such as the crab Ucides cordatus. Thus, it is not known which elements of the cytoskeleton of invertebrates are responsible for determination of the axon caliber. We studied, by electron microscopy and morphometric analyses, the MT and axon area variability in differently sized axons of the protocerebral tract of the crab Ucides cordatus. Our results revealed differences in the distance between MTs, in MT density and number, and in the areas of differently sized axons. The number of MTs increases with the axon area, but this relationship is not directly proportional. Therefore, MT density is greater in smaller axons than in medium axons, similar to the morphometry of the vertebrate axon MT. The distance between MTs is, however, directly related to the axonal area. On the basis of the results shown here, and on previous reports by us and others, we suggest that MTs may be involved in the determination of the axon caliber, possibly due to the presence of NF proteins found in the side-arms.
尽管有几篇关于脊椎动物轴浆细胞骨架形态计量学相关的形态学和功能的报道，但该主题在无脊椎动物中尚未得到充分探索。在脊椎动物中，微管（MTs）除了许多其他功能外，还作为轴突组装的支架，而神经丝（NFs）则作为决定轴突管径的元件。尽管在某些物种（如蟹Ucides cordatus）的轴浆微管侧臂中发现了NF蛋白，但节肢动物的中间丝从未通过电子显微镜描述过。因此，尚不清楚无脊椎动物细胞骨架的哪些元件负责轴突管径的决定。我们通过电子显微镜和形态计量分析，研究了蟹Ucides cordatus原脑束不同大小轴突中微管和轴突面积的变异性。我们的结果揭示了微管之间的距离、微管密度和数量以及不同大小轴突面积的差异。微管数量随轴突面积增加，但这种关系不是直接成比例的。因此，与脊椎动物轴突微管的形态计量学相似，较小轴突中的微管密度大于中等轴突。然而，微管之间的距离与轴突面积直接相关。基于此处所示结果以及我们和其他人之前的报道，我们认为微管可能参与轴突管径的决定，这可能是由于在侧臂中发现了NF蛋白。
