Cytokinesis is the last step of cell division that physically partitions the mother cell into two daughter cells. Cytokinesis requires the assembly and constriction of a contractile ring, a circumferential array of filamentous actin (F-actin), non-muscle myosin II motors (myosin), and actin-binding proteins that forms at the cell equator. Cytokinesis is accompanied by long-range cortical flows from regions of relaxation toward regions of compression. In the C. elegans one-cell embryo, it has been suggested that anterior-directed cortical flows are the main driver of contractile ring assembly. Here, we use embryos co-expressing motor-dead and wild-type myosin to show that cortical flows can be severely reduced without major effects on contractile ring assembly and timely completion of cytokinesis. Fluorescence recovery after photobleaching in the ingressing furrow reveals that myosin recruitment kinetics are also unaffected by the absence of cortical flows. We find that myosin cooperates with the F-actin crosslinker plastin to align and compact F-actin bundles at the cell equator, and that this cross-talk is essential for cytokinesis. Our results thus argue against the idea that cortical flows are a major determinant of contractile ring assembly. Instead, we propose that contractile ring assembly requires localized concerted action of motor-competent myosin and plastin at the cell equator.

细胞分裂是细胞分裂的最后一步，它将母体细胞物理分为两个子细胞。细胞分裂需要一个收缩环的组装和收缩，一个圆周排列的丝状肌动蛋白（F-actin），非肌肉肌球蛋白II马达（myosin）以及在细胞赤道形成的肌动蛋白结合蛋白。胞质分裂伴随着从松弛区域向压缩区域的远距离皮质流动。在里面秀丽隐杆线虫单细胞胚胎，已经表明前向皮质流是收缩环装配的主要驱动力。在这里，我们使用胚共表达运动死者和野生型肌球蛋白的胚胎，表明可以显着减少皮质血流，而对收缩环组装和胞质分裂的及时完成没有重大影响。进入沟中的光漂白后的荧光恢复表明，肌球蛋白募集动力学也不受皮质流的缺乏影响。我们发现，肌球蛋白与F-肌动蛋白交联剂plastin协同作用，在细胞赤道处对齐并压缩F-肌动蛋白束，并且这种串扰对于胞质分裂是必不可少的。因此，我们的结果与认为皮质血流是收缩环装配的主要决定因素这一观点背道而驰。代替，