Reichl Elizabeth M, Ren Yixin, Morphew Mary K, Delannoy Michael, Effler Janet C, Girard Kristine D, Divi Srikanth, Iglesias Pablo A, Kuo Scot C, Robinson Douglas N
Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Curr Biol. 2008 Apr 8;18(7):471-80. doi: 10.1016/j.cub.2008.02.056. Epub 2008 Mar 27.
Contractile networks are fundamental to many cellular functions, particularly cytokinesis and cell motility. Contractile networks depend on myosin-II mechanochemistry to generate sliding force on the actin polymers. However, to be contractile, the networks must also be crosslinked by crosslinking proteins, and to change the shape of the cell, the network must be linked to the plasma membrane. Discerning how this integrated network operates is essential for understanding cytokinesis contractility and shape control. Here, we analyzed the cytoskeletal network that drives furrow ingression in Dictyostelium.
We establish that the actin polymers are assembled into a meshwork and that myosin-II does not assemble into a discrete ring in the Dictyostelium cleavage furrow of adherent cells. We show that myosin-II generates regional mechanics by increasing cleavage furrow stiffness and slows furrow ingression during late cytokinesis as compared to myoII nulls. Actin crosslinkers dynacortin and fimbrin similarly slow furrow ingression and contribute to cell mechanics in a myosin-II-dependent manner. By using FRAP, we show that the actin crosslinkers have slower kinetics in the cleavage furrow cortex than in the pole, that their kinetics differ between wild-type and myoII null cells, and that the protein dynamics of each crosslinker correlate with its impact on cortical mechanics.
These observations suggest that myosin-II along with actin crosslinkers establish local cortical tension and elasticity, allowing for contractility independent of a circumferential cytoskeletal array. Furthermore, myosin-II and actin crosslinkers may influence each other as they modulate the dynamics and mechanics of cell-shape change.
收缩网络对于许多细胞功能至关重要，尤其是胞质分裂和细胞运动。收缩网络依赖肌球蛋白-II的机械化学作用在肌动蛋白聚合物上产生滑动力。然而，要实现收缩，网络还必须由交联蛋白交联，并且为了改变细胞形状，网络必须与质膜相连。弄清楚这个整合网络如何运作对于理解胞质分裂收缩性和形状控制至关重要。在此，我们分析了驱动盘基网柄菌中沟侵入的细胞骨架网络。
我们确定在贴壁细胞的盘基网柄菌分裂沟中，肌动蛋白聚合物组装成一个网络，而肌球蛋白-II不会组装成一个离散的环。我们表明，与肌球蛋白-II缺失细胞相比，肌球蛋白-II通过增加分裂沟硬度产生局部力学作用，并在胞质分裂后期减缓沟侵入。肌动蛋白交联蛋白动力蛋白和丝束蛋白同样减缓沟侵入，并以肌球蛋白-II依赖的方式对细胞力学产生影响。通过使用荧光恢复后光漂白技术（FRAP），我们表明肌动蛋白交联蛋白在分裂沟皮质中的动力学比在两极慢，它们在野生型和肌球蛋白-II缺失细胞之间的动力学不同，并且每个交联蛋白的蛋白质动力学与其对皮质力学的影响相关。
这些观察结果表明，肌球蛋白-II与肌动蛋白交联蛋白一起建立局部皮质张力和弹性，从而实现独立于周向细胞骨架阵列的收缩性。此外，肌球蛋白-II和肌动蛋白交联蛋白在调节细胞形状变化的动力学和力学时可能相互影响。
