Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry, West Midlands CV4 7AL, UK.
Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry, West Midlands CV4 7AL, UK.
Curr Biol. 2018 Mar 19;28(6):955-962.e3. doi: 10.1016/j.cub.2018.01.088. Epub 2018 Mar 1.
The position of the division site dictates the size and fate of daughter cells in many organisms. In animal cells, division-site placement involves overlapping mechanisms, including signaling from the central spindle microtubules, astral microtubules, and spindle poles and through polar contractions [1-3]. In fission yeast, division-site positioning requires overlapping mechanisms involving the anillin-related protein Mid1 and the tip complex (comprising the Kelch-repeat protein Tea1, the Dyrk-kinase Pom1, and the SH3-domain protein Tea4) [4-11]. In addition to these factors, cell shape has also been shown to participate in the maintenance of the position of the actomyosin ring [12-14]. The first principles guiding actomyosin ring placement, however, have not been elucidated in any organism. Because actomyosin ring positioning, ring assembly, and cell morphogenesis are genetically separable in fission yeast, we have used it to derive actomyosin ring placement mechanisms from first principles. We report that, during ring assembly in the absence of cytokinetic cues (anillin-related Mid1 and tip-complex proteins), actin bundles follow the path of least curvature and assemble actomyosin rings in an equatorial position in spherical protoplasts and along the long axis in cylindrical cells and compressed protoplasts. The equatorial position of rings is abolished upon treatment of protoplasts with an actin-severing compound or by slowing down actin polymerization. We propose that the physical properties of actin filaments/bundles play key roles in actomyosin ring assembly and positioning, and that key cytokinetic molecules may modulate the length of actin filaments to promote ring assembly along the short axis.
在许多生物体中，分裂位点的位置决定了子细胞的大小和命运。在动物细胞中，分裂位点的定位涉及重叠的机制，包括来自中心纺锤体微管、星体微管和纺锤体极的信号传导，以及通过极性收缩[1-3]。在裂殖酵母中，分裂位点的定位需要重叠的机制，涉及与肌球蛋白相关蛋白 Mid1 和尖端复合物（包括 Kelch 重复蛋白 Tea1、Dyrk 激酶 Pom1 和 SH3 结构域蛋白 Tea4）[4-11]。除了这些因素外，细胞形状也被证明参与肌动球蛋白环位置的维持[12-14]。然而，任何生物体中肌动球蛋白环定位的第一原则都没有阐明。由于裂殖酵母中的肌动球蛋白环定位、环组装和细胞形态发生在遗传上是可分离的，我们利用它从第一原理推导出肌动球蛋白环定位机制。我们报告说，在没有细胞分裂线索（肌球蛋白相关 Mid1 和尖端复合物蛋白）的情况下进行环组装时，肌动蛋白束沿着最小曲率的路径行进，并在球形原生质体的赤道位置以及圆柱形细胞和压缩原生质体的长轴上组装肌动球蛋白环。在用肌动蛋白切割化合物处理原生质体或减缓肌动蛋白聚合时，环的赤道位置被废除。我们提出，肌动蛋白丝/束的物理性质在肌动球蛋白环的组装和定位中起着关键作用，并且关键的细胞分裂分子可能调节肌动蛋白丝的长度，以促进沿短轴的环组装。
