Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et Chimie Industrielle de la ville de Paris, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7636, Université Pierre et Marie Curie, Université Paris Diderot, 10 rue Vauquelin, 75005 Paris, France.
Proc Natl Acad Sci U S A. 2012 Jun 26;109(26):10364-9. doi: 10.1073/pnas.1121238109. Epub 2012 Jun 11.
Actin filaments play a fundamental role in cell mechanics: assembled into networks by a large number of partners, they ensure cell integrity, deformability, and migration. Here we focus on the mechanics of the dense branched network found at the leading edge of a crawling cell. We develop a new technique based on the dipolar attraction between magnetic colloids to measure mechanical properties of branched actin gels assembled around the colloids. This technique allows us to probe a large number of gels and, through the study of different networks, to access fundamental relationships between their microscopic structure and their mechanical properties. We show that the architecture does regulate the elasticity of the network: increasing both capping and branching concentrations strongly stiffens the networks. These effects occur at protein concentrations that can be regulated by the cell. In addition, the dependence of the elastic modulus on the filaments' flexibility and on increasing internal stress has been studied. Our overall results point toward an elastic regime dominated by enthalpic rather than entropic deformations. This result strongly differs from the elasticity of diluted cross-linked actin networks and can be explained by the dense dendritic structure of lamellipodium-like networks.
通过大量的伴侣组装成网络，它们确保了细胞的完整性、变形性和迁移能力。在这里，我们关注的是在爬行细胞前缘发现的密集分支网络的力学特性。我们开发了一种基于磁胶体之间偶极吸引力的新技术，用于测量围绕胶体组装的分支肌动蛋白凝胶的力学性能。该技术允许我们探测大量的凝胶，并通过研究不同的网络，获得它们的微观结构与其力学性能之间的基本关系。我们表明，结构确实调节了网络的弹性：增加盖帽和分支浓度会强烈增强网络的弹性。这些效应发生在蛋白质浓度可以被细胞调节的情况下。此外，还研究了弹性模量对纤维柔韧性和内部应力增加的依赖性。我们的整体结果表明，弹性主要由焓变而不是熵变引起。这一结果与稀释交联肌动蛋白网络的弹性有很大的不同，可以用类似于片状伪足的网络的密集树突状结构来解释。
