Sharp D J, Yu W, Baas P W
Department of Anatomy, University of Wisconsin Medical School, Madison 53706, USA.
J Cell Biol. 1995 Jul;130(1):93-103. doi: 10.1083/jcb.130.1.93.
The immature processes that give rise to both axons and dendrites contain microtubules (MTs) that are uniformly oriented with their plus-ends distal to the cell body, and this pattern is preserved in the developing axon. In contrast, developing dendrites gradually acquire nonuniform MT polarity orientation due to the addition of a subpopulation of oppositely oriented MTs (Baas, P. W., M. M. Black, and G. A. Banker. 1989. J. Cell Biol. 109:3085-3094). In theory, these minus-end-distal MTs could be locally nucleated and assembled within the dendrite itself, or could be transported into the dendrite after their nucleation within the cell body. To distinguish between these possibilities, we exposed cultured hippocampal neurons to nanomolar levels of vinblastine after one of the immature processes had developed into the axon but before the others had become dendrites. At these levels, vinblastine acts as a kinetic stabilizer of MTs, inhibiting further assembly while not substantially depolymerizing existing MTs. This treatment did not abolish dendritic differentiation, which occurred in timely fashion over the next two to three days. The resulting dendrites were flatter and shorter than controls, but were identifiable by their ultrastructure, chemical composition, and thickened tapering morphology. The growth of these dendrites was accompanied by a diminution of MTs from the cell body, indicating a net transfer of MTs from one compartment into the other. During this time, minus-end-distal microtubules arose in the experimental dendrites, indicating that new MT assembly is not required for the acquisition of nonuniform MT polarity orientation in the dendrite. Minus-end-distal microtubules predominated in the more proximal region of experimental dendrites, indicating that most of the MTs at this stage of development are transported into the dendrite with their minus-ends leading. These observations indicate that transport of MTs from the cell body is an essential feature of dendritic development, and that this transport establishes the nonuniform polarity orientation of MTs in the dendrite.
产生轴突和树突的未成熟突起含有微管（MTs），这些微管的正端远离细胞体，呈均匀排列，且这种模式在发育中的轴突中得以保留。相比之下，由于添加了一组方向相反的微管亚群，发育中的树突逐渐获得不均匀的MT极性方向（巴斯，P.W.，M.M.布莱克，和G.A.班克。1989年。《细胞生物学杂志》109:3085 - 3094）。理论上，这些负端远离的微管可能在树突自身内部局部成核并组装，或者在细胞体内成核后被转运到树突中。为了区分这些可能性，我们在其中一个未成熟突起发育成轴突后但其他突起尚未形成树突之前，将培养的海马神经元暴露于纳摩尔水平的长春花碱中。在这些浓度下，长春花碱作为MTs的动力学稳定剂，抑制进一步组装，同时不会使现有的MTs大量解聚。这种处理并没有消除树突分化，树突分化在接下来的两到三天内适时发生。产生的树突比对照更扁平、更短，但通过其超微结构、化学成分和变细增厚的形态可以识别。这些树突的生长伴随着细胞体中MTs的减少，表明MTs从一个区室净转移到另一个区室。在此期间，实验性树突中出现了负端远离的微管，这表明在树突中获得不均匀的MT极性方向不需要新的MT组装。负端远离的微管在实验性树突的近端区域占主导地位，表明在发育的这个阶段，大多数MTs是以其负端在前的方式被转运到树突中的。这些观察结果表明，MTs从细胞体的转运是树突发育的一个基本特征，并且这种转运建立了树突中MTs的不均匀极性方向。
