Department of Chemical Engineering, Columbia University, New York, New York, USA.
Biophys J. 2012 Sep 19;103(6):1265-74. doi: 10.1016/j.bpj.2012.08.028.
Cells assemble a variety of bundled actomyosin structures in the cytoskeleton for activities such as cell-shape regulation, force production, and cytokinesis. Although these linear structures exhibit varied architecture, two common organizational themes are a punctate distribution of myosin II and distinct patterns of actin polarity. The mechanisms that cells use to assemble and maintain these organizational features are poorly understood. To study these, we reconstituted actomyosin bundles in vitro that contained only actin filaments and myosin II. Upon addition of ATP, the bundles contracted and the uniformly distributed myosin spontaneously reorganized into discrete clusters. We developed a mathematical model in which the motion of myosin II filaments is governed by the polarities of the actin filaments with which they interact. The model showed that the assembly of myosins into clusters is driven by their tendency to migrate to locations with zero net actin filament polarity. With no fitting parameters, the predicted distribution of myosin cluster separations was in close agreement with our experiments, including a -3/2 power law decay for intermediate length scales. Thus, without an organizing template or accessory proteins, a minimal bundle of actin and myosin has the inherent capacity to self-organize into a heterogeneous banded structure.
细胞在细胞骨架中组装各种成束的肌动球蛋白结构，用于细胞形状调节、力产生和胞质分裂等活动。尽管这些线性结构表现出不同的结构，但有两个常见的组织主题是肌球蛋白 II 的点状分布和肌动蛋白极性的明显模式。细胞用于组装和维持这些组织特征的机制知之甚少。为了研究这些，我们在体外重新组装了仅包含肌动蛋白丝和肌球蛋白 II 的肌球蛋白束。在添加 ATP 后，束收缩，均匀分布的肌球蛋白自发重新组织成离散的簇。我们开发了一个数学模型，其中肌球蛋白 II 丝的运动受与其相互作用的肌动蛋白丝极性的控制。该模型表明，肌球蛋白组装成簇是由它们向净肌动蛋白丝极性为零的位置迁移的趋势驱动的。没有拟合参数，预测的肌球蛋白簇分离的分布与我们的实验非常吻合，包括中间长度尺度的-3/2 幂律衰减。因此，在没有组织模板或辅助蛋白的情况下，最小的肌动球蛋白束具有内在的自组织成异质带状结构的能力。
