Abstract
The surface of mammalian cells, i.e. the plasma membrane and the underlying cytoskeletal cortex, constitutes an active platform for many cellular processes including cargo uptake, signaling and formation of cell adhesions. Experimental and theoretical work has recently shown that acto-myosin dynamics can modify the local membrane organization, but the molecular details are not well understood. Here, we use interferometric scattering (iSCAT) microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer. We demonstrate that we are able to detect and distinguish actin and myosin filaments label-free based on their interferometric scattering contrast. The scattering-based approach allows us to follow diffusion of single actin filaments attached to the bilayer at high frame rates revealing different types of diffusion depending on filament length. We investigate the directed motion of myosin II filaments on the actin network quantifying binding kinetics and processivity at varying ATP concentrations. Finally, we follow long-term network flow and organization enabling us to compare our observations with theoretical models of network dynamics. Our results demonstrate that iSCAT microscopy is an ideal tool to investigate multi-component systems on a broad range of length scales, resolving molecular scale mechanisms such as single myosin filament dynamics as well as acto-myosin network contraction on the mesoscopic scale.
