Multi-Scale Linkages between Single-Molecule Integrin Dynamics and Cell Protrusion

Recent advances in light microscopy permit the development of cyto-architectural blueprints with single-molecule resolution. It is now conceptually possible to relate the organization of the molecular machinery to cellular function. However, the disparity between the spatial and temporal scales of molecular and cellular behaviors poses substantial challenges in deriving these relationships. New approaches are required to integrate discrete single-molecule behavior with continuous cellular-level processes. Here, we combined intercalated molecular and cellular imaging with an analytical framework to reveal the roles that individual integrin molecules play in the process of initiating cell adhesion and migration. Despite the stochasticity of molecular and cellular behaviors, our data uncovered ‘rules’ of molecular organization for the components of a functional nascent adhesion, namely αvβ3-integrin, talin and actin, as well as the relationship between the local molecular organization of integrins and cell edge movement. We found that integrins exhibit a basal spatial gradient, with highest density and slowest mobility at the cell edge. In preparation for protrusion, this gradient transiently and locally increases, indicative of the initiation of nascent adhesions prior to cell edge protrusion. Moreover, the molecular behavior of talin, actin and β3 integrin mutants revealed that talin binding regulates integrin mobility, while integrin density modulation is primarily dependent on actin. These data establish a multi-scale linkage between characteristic variations in discrete stochastic molecular behaviors and continuum cellular behaviors.