Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany.
Biotechnology Centre, Technische Universität Dresden, Tatzberg 47/49, Dresden 01307.
Mol Biol Cell. 2022 Jul 1;33(8):ar74. doi: 10.1091/mbc.E21-12-0599. Epub 2022 May 11.
Contractile forces in the actomyosin cortex are required for cellular morphogenesis. This includes the invagination of the cell membrane during division, where filaments of nonmuscle myosin II (NMII) are responsible for generating contractile forces in the cortex. However, how NMII heterohexamers form filaments in vivo is not well understood. To quantify NMII filament assembly dynamics, we imaged the cortex of embryos at high spatial resolution around the time of the first division. We show that during the assembly of the cytokinetic ring, the number of NMII filaments in the cortex increases and more NMII motors are assembled into each filament. These dynamics are influenced by two proteins in the RhoA GTPase pathway, the RhoA-dependent kinase LET-502 and the myosin phosphatase MEL-11. We find that these two proteins differentially regulate NMII activity at the anterior and at the division site. We show that the coordinated action of these regulators generates a gradient of free NMII in the cytoplasm driving a net diffusive flux of NMII motors toward the cytokinetic ring. Our work highlights how NMII filament assembly and disassembly dynamics are orchestrated over space and time to facilitate the up-regulation of cortical contractility during cytokinesis.
肌动球蛋白皮层中的收缩力对于细胞形态发生是必需的。这包括在细胞分裂过程中细胞膜的内陷，在此过程中非肌肉肌球蛋白 II（NMII）的细丝负责在皮层中产生收缩力。然而，NMII 异六聚体如何在体内形成细丝尚不清楚。为了定量 NMII 细丝组装动力学，我们在第一次分裂前后的高空间分辨率下对 胚胎的皮层进行成像。我们表明，在胞质分裂环的组装过程中，皮层中 NMII 细丝的数量增加，并且更多的 NMII 马达组装到每个细丝中。这些动力学受 RhoA GTPase 途径中的两种蛋白质的影响，即 RhoA 依赖性激酶 LET-502 和肌球蛋白磷酸酶 MEL-11。我们发现这两种蛋白质在前端和分裂部位以不同的方式调节 NMII 活性。我们表明，这些调节剂的协调作用在细胞质中产生了游离 NMII 的梯度，从而导致 NMII 马达向胞质分裂环的净扩散通量。我们的工作强调了 NMII 细丝组装和拆卸动力学如何在空间和时间上协调，以促进胞质分裂过程中皮质收缩力的上调。
