Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki, 305-8577, Japan.
Genes Cells. 2014 Feb;19(2):161-76. doi: 10.1111/gtc.12120. Epub 2013 Dec 12.
During cytokinesis in many eukaryotic cells, myosin-II concentrates at the equatorial cortex with actin filaments (F-actin) and is supposed to generate forces to divide the cell into two, which is called the contractile ring (CR) hypothesis. Several lines of evidence indicate that the myosin-II is recruited independently of F-actin and interacts specifically with the equatorial F-actin. Molecular details of these mechanisms are still unknown. We used the fission yeast Schizosaccharomyces pombe to investigate the regulation of myosin-II localization. We demonstrate that the CR myosin-II was composed of F-actin-dependent and -independent fractions by simultaneously observing F-actin and myosin. The F-actin-independent fraction was visualized as cortical dots in the absence of F-actin. IQGAP Rng2, an indispensable element of CR, was implicated in maintenance of the F-actin-independent fraction of myosin-II, whereas anillin Mid1 was required for assembly but not for maintenance of the fraction. In the CR of the rng2 mutant, myosin-II was less concentrated, unstable, and nonhomogeneous, which often resulted in cytokinesis failure. These results suggest that Rng2 tethers myosin-II to the cortex along the CR independently of F-actin to provide a sufficient concentration. The robust localization of myosin-II would ensure successful cytokinesis.
在许多真核细胞的胞质分裂过程中，肌球蛋白-II 与肌动蛋白丝（F-肌动蛋白）集中在赤道皮层，据推测其产生的力将细胞分裂成两个，这就是所谓的收缩环（CR）假说。有几条证据表明，肌球蛋白-II 的募集与 F-肌动蛋白无关，并且与赤道 F-肌动蛋白特异性相互作用。这些机制的分子细节仍不清楚。我们使用裂殖酵母 Schizosaccharomyces pombe 来研究肌球蛋白-II 定位的调节。我们通过同时观察 F-肌动蛋白和肌球蛋白证明，CR 肌球蛋白-II 由 F-肌动蛋白依赖性和非依赖性部分组成。在不存在 F-肌动蛋白的情况下，非 F-肌动蛋白依赖性部分被可视化为皮质点。IQGAP Rng2 是 CR 的必需元件，它参与维持肌球蛋白-II 的 F-肌动蛋白非依赖性部分，而 anillin Mid1 则需要组装但不需要维持该部分。在 rng2 突变体的 CR 中，肌球蛋白-II 的浓度降低、不稳定且不均匀，这常常导致胞质分裂失败。这些结果表明，Rng2 独立于 F-肌动蛋白将肌球蛋白-II 固定在 CR 上，以提供足够的浓度。肌球蛋白-II 的稳定定位将确保成功的胞质分裂。
