Seiler S, Plamann M, Schliwa M
Adolf Butenandt Institut, Zellbiologie, University of Munich, 80336, Munich, Germany.
Curr Biol. 1999;9(15):779-85. doi: 10.1016/s0960-9822(99)80360-1.
Kinesin and cytoplasmic dynein are force-generating molecules that move in opposite directions along microtubules. They have been implicated in the directed transport of a wide variety of cellular organelles, but it is unclear whether they have overlapping or largely independent functions.
We analyzed organelle transport in kinesin and dynein single mutants, and in a kinesin and dynein double mutant of Neurospora crassa. Remarkably, the simultaneous mutation of kinesin and dynein was not lethal and resulted in an additive phenotype that combined the features of the single mutants. The mutation of kinesin and dynein had opposite effects on the apical and retrograde transport, respectively, of vesicular organelles. In the kinesin mutant, apical movement of submicroscopic, secretory vesicles to the Spitzenkörper - an organelle in the hyphal apex - was defective, whereas the predominantly retrograde movement of microscopic organelles was only slightly reduced. In contrast, the dynein mutant still had a prominent Spitzenkörper, demonstrating that apical transport was intact, but retrograde transport was essentially inhibited completely. A major defect in vacuole formation and dynamics was also evident. In agreement with the observations on apical transport, protein secretion into the medium was markedly inhibited in the kinesin mutant but not in the dynein mutant.
Transport of secretory vesicles is necessary but not sufficient for normal apical extension. A component of retrograde transport, presumably precursors of the vacuole system, is also essential. Our findings provide new information on the role microtubule motors play in cell morphogenesis and suggest that kinesin and cytoplasmic dynein have largely independent functions within separate pathways.
驱动蛋白和细胞质动力蛋白是沿微管向相反方向移动的力产生分子。它们与多种细胞器的定向运输有关，但它们是否具有重叠或基本独立的功能尚不清楚。
我们分析了粗糙脉孢菌驱动蛋白和动力蛋白单突变体以及驱动蛋白和动力蛋白双突变体中的细胞器运输。值得注意的是，驱动蛋白和动力蛋白的同时突变并不致命，而是产生了一种将单突变体特征结合起来的累加表型。驱动蛋白和动力蛋白的突变分别对囊泡细胞器的顶端运输和逆向运输产生相反的影响。在驱动蛋白突变体中，亚显微分泌囊泡向菌丝顶端的细胞器——Spitzenkörper的顶端移动存在缺陷，而显微镜下细胞器的主要逆向移动仅略有减少。相比之下，动力蛋白突变体仍有一个明显的Spitzenkörper，表明顶端运输完好无损，但逆向运输基本上被完全抑制。液泡形成和动态变化也存在一个主要缺陷。与顶端运输的观察结果一致，驱动蛋白突变体中向培养基中的蛋白质分泌明显受到抑制，而动力蛋白突变体中则没有。
分泌囊泡的运输对于正常的顶端延伸是必要的，但不是充分的。逆向运输的一个组成部分，可能是液泡系统的前体，也是必不可少的。我们的研究结果提供了关于微管马达在细胞形态发生中作用的新信息，并表明驱动蛋白和细胞质动力蛋白在不同途径中具有基本独立 的功能。
