Microtubule and actin are the two major cytoskeletal polymers that form organized functional structures in the interior of eukaryotic cells. Although the structural mechanics of the cytoskeleton has been extensively studied by direct manipulations in in vitro reconstitution systems, such unambiguous characterizations inside the living cell are sparse. Here, we report a comprehensive analysis of how the microtubule and actin cytoskeletons structurally respond to direct intracellular load. Ferrofluid-based intracellular magnetic tweezers reveal rheological properties of the microtubule complex primarily determined by filamentous actin. The strain fields of the microtubule complex and actin meshwork follow the same scaling, suggesting that the two cytoskeletal systems behave as an integrated elastic body. The structural responses of single microtubules to contact and remote forces further evidence that the individual microtubules are enclosed by the elastic medium of actin. These results, directly characterizing the microtubule and actin cytoskeletons as an interacting continuum throughout the cytoplasm, serve as a cornerstone for the physical understanding of intracellular organization.

中文翻译：

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微管和肌动蛋白细胞骨架对直接细胞内负荷的结构反应。


微管和肌动蛋白是在真核细胞内部形成有组织功能结构的两种主要细胞骨架聚合物。尽管细胞骨架的结构机制已经通过体外重建系统中的直接操作进行了广泛的研究，但活细胞内部的这种明确表征很少。在这里，我们报告了微管和肌动蛋白细胞骨架在结构上如何响应直接细胞内负荷的全面分析。基于铁磁流体的细胞内磁镊揭示了主要由丝状肌动蛋白决定的微管复合物的流变特性。微管复合物和肌动蛋白网的应变场遵循相同的缩放，表明两个细胞骨架系统表现为一个集成的弹性体。单个微管对接触力和远程力的结构反应进一步证明，单个微管被肌动蛋白的弹性介质包围。这些结果直接将微管和肌动蛋白细胞骨架表征为整个细胞质的相互作用连续体，是物理理解细胞内组织的基石。