Filopodia are actin-rich structures, present on the surface of practically every known eukaryotic cell. These structures play a pivotal role in specific cell-cell and cell-matrix interactions by allowing cells to explore their environment, generate mechanical forces, perform chemical signaling, or convey signals via intercellular tunneling nano-bridges. The dynamics of filopodia appear quite complex as they exhibit a rich behavior of buckling, pulling, length and shape changes. Here, we find that filopodia additionally explore their 3D extracellular space by combining growth and shrinking with axial twisting and buckling of their actin rich core. Importantly, we show the rotational dynamics of the filamentous actin inside filopodia for a range of highly distinct and cognate cell types spanning from earliest development to highly differentiated tissue cells. Non-equilibrium physical modeling of actin and myosin confirm that twist, and hence rotation, is an emergent phenomenon of active filaments confined in a narrow channel which points to a generic mechanism present in all cells. Our measurements confirm that filopodia exert traction forces and form helical buckles in a range of different cell types that can be ascribed to accumulation of sufficient twist. These results lead us to conclude that activity induced twisting of the actin shaft is a general mechanism underlying fundamental functions of filopodia.

中文翻译：

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丝足虫通过主动在肌动蛋白轴中产生扭曲来旋转和盘绕

丝足是富含肌动蛋白的结构，几乎存在于每个已知的真核细胞的表面。这些结构通过允许细胞探索其环境，产生机械力，执行化学信号传递或通过细胞间隧道纳米桥传递信号，在特定的细胞-细胞和细胞-基质相互作用中起关键作用。丝状伪足的动力学表现得非常复杂，因为它们表现出丰富的屈曲，牵拉，长度和形状变化行为。在这里，我们发现丝状足病还通过结合生长和收缩以及富含肌动蛋白的核心的轴向扭曲和屈曲来探索其3D细胞外空间。重要的，我们展示了丝状肌动蛋白在丝状伪足内的旋转动力学，从最早的发育到高度分化的组织细胞，这些类型的高度不同和同源的细胞类型。肌动蛋白和肌球蛋白的非平衡物理模型证实，扭曲和旋转是活性细丝在狭窄通道内的出现现象，这表明存在于所有细胞中的通用机制。我们的测量结果证实，丝状伪足在一系列不同的细胞类型中施加牵引力并形成螺旋形弯曲，这可归因于足够的扭转积累。这些结果使我们得出结论，活性诱导的肌动蛋白轴扭转是丝状伪足基本功能的基本机制。因此，旋转是限制在狭窄通道中的活性细丝的出现现象，这表明存在于所有细胞中的一般机制。我们的测量结果证实，丝状伪足在一系列不同的细胞类型中施加牵引力并形成螺旋形弯曲，这可归因于足够的扭转积累。这些结果使我们得出结论，活性诱导的肌动蛋白轴扭转是丝状伪足基本功能的基本机制。因此，旋转是限制在狭窄通道中的活性细丝的出现现象，这表明存在于所有细胞中的一般机制。我们的测量结果证实，丝状伪足在一系列不同的细胞类型中施加牵引力并形成螺旋形弯曲，这可归因于足够的扭转积累。这些结果使我们得出结论，活性诱导的肌动蛋白轴扭转是丝状伪足基本功能的基本机制。