Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
Department of Molecular Microbiology and Immunology, Brown University, Providence, Rhode Island, USA.
mSphere. 2019 Nov 13;4(6):e00610-19. doi: 10.1128/mSphere.00610-19.
Mitotic spindles assume a bipolar architecture through the concerted actions of microtubules, motors, and cross-linking proteins. In most eukaryotes, kinesin-5 motors are essential to this process, and cells will fail to form a bipolar spindle without kinesin-5 activity. Remarkably, inactivation of kinesin-14 motors can rescue this kinesin-5 deficiency by reestablishing the balance of antagonistic forces needed to drive spindle pole separation and spindle assembly. We show that the yeast form of the opportunistic fungus assembles bipolar spindles in the absence of its sole kinesin-5, Kip1, even though this motor exhibits stereotypical cell-cycle-dependent localization patterns within the mitotic spindle. However, cells lacking Kip1 function have shorter metaphase spindles and longer and more numerous astral microtubules. They also show defective hyphal development. Interestingly, a small population of Kip1-deficient spindles break apart and reform two bipolar spindles in a single nucleus. These spindles then separate, dividing the nucleus, and then elongate simultaneously in the mother and bud or across the bud neck, resulting in multinucleate cells. These data suggest that kinesin-5-independent mechanisms drive assembly and elongation of the mitotic spindle in and that Kip1 is important for bipolar spindle integrity. We also found that simultaneous loss of kinesin-5 and kinesin-14 (Kar3Cik1) activity is lethal. This implies a divergence from the antagonistic force paradigm that has been ascribed to these motors, which could be linked to the high mitotic error rate that experiences and often exploits as a generator of diversity. is one of the most prevalent fungal pathogens of humans and can infect a broad range of niches within its host. This organism frequently acquires resistance to antifungal agents through rapid generation of genetic diversity, with aneuploidy serving as a particularly important adaptive mechanism. This paper describes an investigation of the sole kinesin-5 in , which is a major regulator of chromosome segregation. Contrary to other eukaryotes studied thus far, does not require kinesin-5 function for bipolar spindle assembly or spindle elongation. Rather, this motor protein associates with the spindle throughout mitosis to maintain spindle integrity. Furthermore, kinesin-5 loss is synthetically lethal with loss of kinesin-14-canonically an opposing force producer to kinesin-5 in spindle assembly and anaphase. These results suggest a significant evolutionary rewiring of microtubule motor functions in the mitotic spindle, which may have implications in the genetic instability of this pathogen.
有丝分裂纺锤体通过微管、马达和交联蛋白的协同作用呈现出双极结构。在大多数真核生物中，驱动蛋白-5 马达对于这个过程至关重要，如果没有驱动蛋白-5 的活性，细胞将无法形成双极纺锤体。值得注意的是，失活驱动蛋白-14 马达可以通过重新建立驱动纺锤极分离和纺锤体组装所需的拮抗力平衡来挽救这种驱动蛋白-5 的缺乏。我们表明，在缺乏其唯一的驱动蛋白-5（Kip1）的情况下，机会主义真菌的酵母形式可以组装双极纺锤体，尽管这种马达在有丝分裂纺锤体中表现出典型的细胞周期依赖性定位模式。然而，缺乏 Kip1 功能的细胞中期纺锤体较短，星体微管较长且数量较多。它们还表现出菌丝发育缺陷。有趣的是，一小部分缺乏 Kip1 的纺锤体分裂并在单个核内重新形成两个双极纺锤体。这些纺锤体随后分离，将核分裂，然后在母细胞和芽体或芽体颈部之间同时伸长，导致多核细胞。这些数据表明，驱动蛋白-5 不依赖的机制驱动了纺锤体的组装和伸长，并且 Kip1 对于双极纺锤体的完整性很重要。我们还发现，同时缺失驱动蛋白-5 和驱动蛋白-14（Kar3Cik1）的活性是致命的。这意味着与已经归因于这些马达的拮抗力范式存在分歧，这可能与该真菌经历的高有丝分裂错误率有关，并且经常将其作为多样性的生成因素加以利用。是人类最常见的真菌病原体之一，可以感染宿主内的广泛生态位。该生物体通过快速产生遗传多样性来经常获得对抗真菌药物的抗性，非整倍性是一种特别重要的适应性机制。本文描述了对酵母中唯一的驱动蛋白-5 的研究，该蛋白是染色体分离的主要调节剂。与迄今为止研究的其他真核生物不同，酵母不需要驱动蛋白-5 功能来组装双极纺锤体或伸长纺锤体。相反，这种马达蛋白在整个有丝分裂过程中与纺锤体结合以维持纺锤体的完整性。此外，驱动蛋白-5 的缺失与驱动蛋白-14 的缺失是合成致死的，在纺锤体组装和后期，驱动蛋白-14 通常是驱动蛋白-5 的拮抗力产生者。这些结果表明，在真菌的有丝分裂纺锤体中，微管马达功能发生了重大的进化重排，这可能对该病原体的遗传不稳定性产生影响。
