Rigidity sensing is a critical determinant of cell fate and behavior but its molecular mechanisms are poorly understood. Focal adhesions (FAs) are complexes that anchor cells to the matrix. Among their components, vinculin undergoes an auto-inhibitory head-tail interaction that regulates the recruitment of, and interactions with its partners in a force-dependent manner. It is unknown, however, whether this mechanism is involved in substrate rigidity sensing. Here, we use a range of quantitative fluorescence microscopies on live human Mesenchymal Stem Cells to address this question. We identify two distinct rigidity-sensing molecular modules in FAs, one of which involves vinculin and talin, is regulated by vinculin head-tail interaction, and targets cell morphology. Vinculin and talin are recruited independently in a rigidity-dependent manner to FAs where they directly interact in a rigidity-independent stoichiometry at a site proximal to talin head. Vinculin head-tail interaction is required on soft substrates to destabilize vinculin and talin in FAs, and to allow hMSCs branching. Another module involves paxillin and FAK, which soft substrates also destabilize, but independently of vinculin head-tail interaction. This multi-modularity may be key to allow a versatile response to complex biomechanical cues.

中文翻译：

---

Vinculin头尾相互作用定义了多种用于细胞基质刚性感测的早期机制。

刚性感测是决定细胞命运和行为的关键因素，但对其分子机制了解甚少。粘着斑（FAs）是将细胞锚定在基质上的复合物。在它们的组成部分中，长春菊素经历了自抑制性的头尾相互作用，该相互作用以力依赖的方式调节其伙伴的募集和与其相互作用。然而，尚不清楚该机制是否涉及基板刚度感测。在这里，我们对活的人类间充质干细胞使用一系列定量荧光显微镜检查法来解决这个问题。我们确定FAs中的两个不同的刚性传感分子模块，其中之一涉及vincinin和talin，由vincinin头尾相互作用调节，并靶向细胞形态。Vinculin和talin以刚度依赖性方式独立地招募到FA，在FAs中，它们直接在不依赖于刚度的化学计量中在距talin头近端的位置相互作用。在柔软的底物上需要Vinculin头尾相互作用，以破坏FA中的纽蛋白和塔林的稳定性，并允许hMSC分支。另一个模块涉及paxillin和FAK，它们的软质底物也不稳定，但独立于新蛋白头尾相互作用。这种多模块性可能是允许对复杂的生物力学线索做出通用响应的关键。柔软的底物也会破坏稳定性，但不依赖于纽蛋白头尾相互作用。这种多模块性可能是允许对复杂的生物力学线索做出通用响应的关键。柔软的底物也会破坏稳定性，但不依赖于纽蛋白头尾相互作用。这种多模块性可能是允许对复杂的生物力学线索做出通用响应的关键。