The actin cytoskeleton plays a fundamental role in numerous cellular processes, such as cell motility, cytokinesis, and adhesion to the extracellular matrix. Revealing the polarity of individual actin filaments in intact cells would foster an unprecedented understanding of cytoskeletal processes and their associated mechanical forces. Cryo-electron tomography provides the means for high-resolution structural imaging of cells. However, the low signal-to-noise ratio of cryo-tomograms obscures the high frequencies, and therefore the polarity of actin filaments cannot be directly measured. Here, we developed a method that enables us to determine the polarity of actin filaments in cellular cryo-tomograms. We applied it to reveal the actin polarity distribution in focal adhesions, and show a linear relation between actin polarity and distance from the apical boundary of the adhesion site.

肌动蛋白细胞骨架在许多细胞过程中发挥着重要作用，例如细胞运动、胞质分裂和与细胞外基质的粘附。揭示完整细胞中单个肌动蛋白丝的极性将促进对细胞骨架过程及其相关机械力的前所未有的理解。冷冻电子断层扫描为细胞的高分辨率结构成像提供了手段。然而，cryo-tomograms 的低信噪比掩盖了高频，因此不能直接测量肌动蛋白丝的极性。在这里，我们开发了一种方法，使我们能够确定细胞冷冻断层扫描中肌动蛋白丝的极性。我们应用它来揭示粘着斑中肌动蛋白的极性分布，