The actin cytoskeleton in living cells generates forces in conjunction with myosin motor proteins to directly and indirectly drive essential cellular processes. The semiflexible filaments of the cytoskeleton can respond nonlinearly to the collective action of motors. We here investigate mechanics and force generation in a model actin cytoskeleton, reconstituted in vitro, by observing the response and fluctuations of embedded micron-scale probe particles. Myosin mini-filaments can be modeled as force dipoles and give rise to deformations in the surrounding network of cross-linked actin. Anomalously correlated probe fluctuations indicate the presence of rapid local compression or draining of the network that emerges in addition to the ordinary linear shear elastic (incompressible) response to force dipoles. The anomalous propagation of compression can be attributed to the nonlinear response of actin filaments to the microscopic forces, and is quantitatively consistent with motor-generated large-scale stiffening of the gels.

中文翻译：

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活性凝胶中的快速局部压缩是由非线性网络响应引起的。

活细胞中的肌动蛋白细胞骨架与肌球蛋白运动蛋白共同产生作用力，以直接和间接驱动基本的细胞过程。细胞骨架的半柔性细丝可以非线性地响应马达的集体作用。我们在这里研究在体外重建的模型肌动蛋白细胞骨架中的力学和力生成通过观察嵌入的微米级探针颗粒的响应和波动。肌球蛋白微丝可建模为力偶极子，并引起交联肌动蛋白周围网络的变形。异常相关的探针波动表明，除了对力偶极子的普通线性剪切弹性（不可压缩）响应外，还出现了快速局部压缩或网络排水。压缩的异常传播可以归因于肌动蛋白丝对微观力的非线性响应，并且在定量上与马达产生的凝胶的大规模硬化相一致。