Sato M, Schwarz W H, Pollard T D
Nature. 1987;325(6107):828-30. doi: 10.1038/325828a0.
The cortical cytoplasm, including the cleavage furrow, is largely composed of a network of actin filaments that is rigid even as it is extensively deformed during cytokinesis. Here we address the question of how actin-filament networks such as those in the cortex can be simultaneously rigid (solid-like) and fluid-like. Conventional explanations are that actin filaments rearrange by some combination of depolymerization and repolymerization; fragmentation and annealing of filaments; and inactivation and reestablishment of crosslinks between filaments. We describe the mechanical properties of a model system consisting of actin filaments and Acanthamoeba alpha-actinin, one of several actin crosslinking proteins found in amoeba and other cells. The results suggest another molecular mechanism that may account for the paradoxical mechanical properties of the cortex. When deformed rapidly, these mixtures are 40 times more rigid than actin filaments without alpha-actinin, but when deformed slowly these mixtures were indistinguishable from filaments alone. These time-dependent mechanical properties can be explained by multiple, rapidly rearranging alpha-actinin crosslinks between the actin filaments, a mechanism proposed by Frey-Wyssling to account for the behaviour of cytoplasm long before the discovery of cytoplasmic actin or alpha-actinin. If other actin-filament crosslinking proteins behave like Acanthamoeba alpha-actinin, this mechanism may explain how the cortex recoils elastically from small rapid insults but deforms extensively when minute forces are applied over long periods of time.
皮质细胞质，包括分裂沟，主要由肌动蛋白丝网络组成，即使在胞质分裂过程中发生广泛变形时，该网络也保持刚性。在这里，我们探讨了像皮质中的肌动蛋白丝网络如何能同时具有刚性（类似固体）和流动性的问题。传统的解释是，肌动蛋白丝通过解聚和再聚合、丝的断裂和退火以及丝之间交联的失活和重新建立等某种组合方式进行重排。我们描述了一个由肌动蛋白丝和棘阿米巴α - 肌动蛋白组成的模型系统的力学性质，棘阿米巴α - 肌动蛋白是在变形虫和其他细胞中发现的几种肌动蛋白交联蛋白之一。结果表明了另一种分子机制，该机制可能解释皮质矛盾的力学性质。当快速变形时，这些混合物的刚性比没有α - 肌动蛋白的肌动蛋白丝高40倍，但当缓慢变形时，这些混合物与单独的丝没有区别。这些随时间变化的力学性质可以用肌动蛋白丝之间多个快速重排的α - 肌动蛋白交联来解释，这是弗雷 - 维斯林在发现细胞质肌动蛋白或α - 肌动蛋白之前很久就提出的一种机制，用于解释细胞质的行为。如果其他肌动蛋白丝交联蛋白的行为与棘阿米巴α - 肌动蛋白相似，那么这种机制可能解释皮质如何从小的快速损伤中弹性回弹，但在长时间施加微小力时会发生广泛变形。
