Sharp D J, Kuriyama R, Baas P W
Department of Anatomy, University of Wisconsin Medical School, Madison 53706, USA.
J Neurosci. 1996 Jul 15;16(14):4370-5. doi: 10.1523/JNEUROSCI.16-14-04370.1996.
The microtubules (MTs) within neuronal processes are highly organized with regard to their polarity and yet are not attached to any detectable nucleating structure. Axonal MTs are uniformly oriented with their plus ends distal to the cell body, whereas dendritic MTs are of both orientations. Here, we sought to test the capacity of motor-driven MT transport to organize distinct MT patterns during process outgrowth. We focused on CHO1/MKLP1, a kinesin-related protein present in the midzonal region of the mitotic spindle where MTs of opposite orientation overlap. Insect ovarian Sf9 cells induced to express the N-terminal portion of the molecule form MT-rich processes with a morphology similar to that of neuronal dendrites (Kuriyama et al., 1994). Nascent processes contain uniformly plus-end-distal MTs, but these are joined by minus-end-distal MTs as the processes continue to develop. Thus, this CHO1/MKLP1 fragment establishes a nonuniform MT polarity pattern and does so by a similar sequence of events as occurs with the dendrite, the antecedent of which is a short process with a uniform MT polarity orientation. Two lines of evidence suggest that these results are elicited by motor-driven MT transport. First, there is a depletion of MTs from the cell body during process outgrowth. Second, the same polarity pattern is obtained when net MT assembly is suppressed pharmacologically during process formation. Collectively, these findings provide precedent for the idea that motor-driven transport can organize MTs into distinct patterns of polarity orientation during process outgrowth.
神经元突起内的微管（MTs）在极性方面高度有序，但未附着于任何可检测到的成核结构。轴突微管的正端远离细胞体，方向一致，而树突微管则有两种方向。在此，我们试图测试在突起生长过程中，马达驱动的微管运输组织不同微管模式的能力。我们聚焦于CHO1/MKLP1，一种存在于有丝分裂纺锤体中区的驱动蛋白相关蛋白，在该区域方向相反的微管相互重叠。诱导表达该分子N端部分的昆虫卵巢Sf9细胞形成富含微管的突起，其形态与神经元树突相似（栗山等人，1994年）。新生突起含有方向一致的正端远离的微管，但随着突起继续发育，负端远离的微管也会加入。因此，这个CHO1/MKLP1片段建立了一种不均匀的微管极性模式，其形成过程与树突类似，树突的前身是具有一致微管极性方向的短突起。有两条证据表明这些结果是由马达驱动的微管运输引起的。第一，在突起生长过程中，细胞体中的微管会减少。第二，在突起形成过程中，通过药物抑制微管的净组装时，会得到相同的极性模式。总的来说，这些发现为以下观点提供了先例：在突起生长过程中，马达驱动的运输可以将微管组织成不同的极性方向模式。
