Matus A, Bernhardt R, Bodmer R, Alaimo D
Neuroscience. 1986 Feb;17(2):371-89. doi: 10.1016/0306-4522(86)90253-8.
We have followed the appearance of two microtubule proteins, tubulin and microtubule-associated protein 2, in rat hippocampal neurons differentiating in cell culture. Double-label immunofluorescence staining showed that from day 1 in vitro onward tubulin appeared as filaments but that microtubule-associated protein 2 remained distributed throughout the cytoplasm. This difference persisted throughout development and was also detectable in cells that had reached morphological maturity. When cells were treated with the microtubule-depolymerizing agent nocodazole, the depolymerized tubulin became spread throughout the cytoplasm so that its distribution was then identical to microtubule associated protein 2. At the same time, multiple side branches began to emerge along the dendrites. When cells which had been exposed to nocodazole were allowed to recover before staining, the tubulin was again present as filaments but the microtubule-associated protein 2 remained distributed throughout the dendritic cytoplasm. Under these conditions the previously extended proximal side branches were resorbed into the main process. These results suggest that cellular microtubule-associated protein 2 is not necessarily exclusively associated with microtubules. Neuronal dendrites in particular appear to contain this protein at levels in excess of the capacity of microtubular microtubule-associated protein 2 binding sites. In view of the known effectiveness of microtubule-associated protein 2 as a promoter of tubulin polymerization, its abundance in dendrites suggests that it acts to ensure total polymerization of dendritic microtubules. In this way it would contribute both to the support of the growing process and the suppression of adventitious sidebranching.
我们追踪了两种微管蛋白，即微管蛋白和微管相关蛋白2，在细胞培养中分化的大鼠海马神经元中的出现情况。双标记免疫荧光染色显示，从体外培养第1天起，微管蛋白就呈现为细丝状，但微管相关蛋白2仍分布于整个细胞质中。这种差异在整个发育过程中持续存在，在形态学上成熟的细胞中也可检测到。当用微管解聚剂诺考达唑处理细胞时，解聚的微管蛋白扩散至整个细胞质，其分布随后与微管相关蛋白2相同。同时，树突上开始出现多个侧支。当将暴露于诺考达唑的细胞在染色前进行恢复培养时，微管蛋白再次呈现为细丝状，但微管相关蛋白2仍分布于树突细胞质中。在这些条件下，先前延伸的近端侧支被重新吸收回主突起中。这些结果表明，细胞微管相关蛋白2不一定仅与微管相关。特别是神经元树突似乎含有这种蛋白，其含量超过微管微管相关蛋白2结合位点的容量。鉴于微管相关蛋白2作为微管蛋白聚合促进剂的已知有效性，其在树突中的丰富含量表明它起到确保树突微管完全聚合的作用。通过这种方式，它将有助于支持生长过程并抑制不定侧支的形成。
