Dependence of the mechanical properties of actin/α-actinin gels on deformation rate

Publisher Website
Google Scholar
Abstract
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 cytokinesis1,2. 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 re-establishment of crosslinks between filaments3–5. We describe the mechanical properties of a model system consisting of actin filaments and Acanthamoeba α-actinin6–8, one of several actin crosslinking proteins found in amoeba and other cells4,9. 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 α-actinin, but when deformed slowly these mixtures were indistinguishable from filaments alone. These time-dependent mechanical properties can be explained by multiple, rapidly rearranging a-actinin crosslinks between the actin filaments, a mechanism proposed by Frey-Wyssling10 to account for the behaviour of cytoplasm long before the discovery of cyto-plasmic actin or α-actinin. If other actin-filament crosslinking proteins behave like Acanthamoeba α-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 time1,11,12