Colombelli Julien, Besser Achim, Kress Holger, Reynaud Emmanuel G, Girard Philippe, Caussinus Emmanuel, Haselmann Uta, Small John V, Schwarz Ulrich S, Stelzer Ernst H K
Cell Biology and Biophysics, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
J Cell Sci. 2009 May 15;122(Pt 10):1665-79. doi: 10.1242/jcs.042986. Epub 2009 Apr 28.
The mechanics of the actin cytoskeleton have a central role in the regulation of cells and tissues, but the details of how molecular sensors recognize deformations and forces are elusive. By performing cytoskeleton laser nanosurgery in cultured epithelial cells and fibroblasts, we show that the retraction of stress fibers (SFs) is restricted to the proximity of the cut and that new adhesions form at the retracting end. This suggests that SFs are attached to the substrate. A new computational model for SFs confirms this hypothesis and predicts the distribution and propagation of contractile forces along the SF. We then analyzed the dynamics of zyxin, a focal adhesion protein present in SFs. Fluorescent redistribution after laser nanosurgery and drug treatment shows a high correlation between the experimentally measured localization of zyxin and the computed localization of forces along SFs. Correlative electron microscopy reveals that zyxin is recruited very fast to intermediate substrate anchor points that are highly tensed upon SF release. A similar acute localization response is found if SFs are mechanically perturbed with the cantilever of an atomic force microscope. If actin bundles are cut by nanosurgery in living Drosophila egg chambers, we also find that zyxin redistribution dynamics correlate to force propagation and that zyxin relocates at tensed SF anchor points, demonstrating that these processes also occur in living organisms. In summary, our quantitative analysis shows that force and protein localization are closely correlated in stress fibers, suggesting a very direct force-sensing mechanism along actin bundles.
肌动蛋白细胞骨架的力学机制在细胞和组织的调控中起着核心作用，但分子传感器如何识别变形和力的细节仍不清楚。通过在培养的上皮细胞和成纤维细胞中进行细胞骨架激光纳米手术，我们发现应力纤维（SFs）的回缩仅限于切口附近，并且在回缩端形成新的黏附。这表明SFs附着于底物。一个新的SFs计算模型证实了这一假设，并预测了收缩力沿SF的分布和传播。然后，我们分析了zyxin（一种存在于SFs中的黏着斑蛋白）的动力学。激光纳米手术和药物处理后的荧光重新分布显示，实验测量的zyxin定位与计算得出的沿SFs的力的定位之间存在高度相关性。相关电子显微镜显示，zyxin非常迅速地被招募到中间底物锚定点，这些锚定点在SF释放时高度紧张。如果用原子力显微镜的悬臂对SFs进行机械扰动，也会发现类似的急性定位反应。如果在活的果蝇卵室中通过纳米手术切割肌动蛋白束，我们还发现zyxin的重新分布动力学与力的传播相关，并且zyxin在紧张的SF锚定点重新定位，这表明这些过程也发生在活生物体中。总之，我们的定量分析表明，在应力纤维中力和蛋白质定位密切相关，这表明沿着肌动蛋白束存在一种非常直接的力传感机制。
