Regulation of actin turnover by myosin activity and network architecture

Actin remodeling through turnover, in which filaments continuously depolymerize from one end while repolymerizing on the other, is essential for the survival of most cells. However, the regulation of this process through actin architecture and myosin activity is poorly studied. Here, we investigate the ability of myosin activity and actin architecture to control turnover. Using a minimal system to recreate turnover in vitro, we observe that severing by the protein cofilin increases the turnover rate in our networks. We additionally find that myosin mediated severing is sufficient to increase the rate of actin turnover, even in systems without cofilin. Preventing filament depolymerization or reducing myosin-mediated buckling filaments reduces this effect, suggesting that the increased rate relies on actin severing and disassembly. This increase in turnover, however, is dependent on actin structure. When actin is bundled, cofilin mediated turnover vanishes. Remarkably, bundling does not impact myosin mediated severing, and myosin is able to increase turnover even in these networks. These results suggest that not only can myosin regulate turnover of actin filaments, but also that different methods of disassembly might be needed to remodel actin depending on its local structure.