Differential Dynamic Microscopy of Active Actin-Microtubule Networks*

The cytoskeleton is a non-equilibrium network of protein filaments, including semiflexible actin and rigid microtubules, as well as associated motor proteins that can dynamically rearrange the filaments. Here, we create co-entangled networks of microtubules and actin that exhibit active contractile dynamics driven by myosin II motors. We use multi-spectral confocal fluorescence microscopy and differential dynamic microscopy to determine the time-varying fluctuation decay times and contraction rates of the networks. We vary the concentrations of actin, microtubules and myosin to tune the dynamics from slow, organized contraction to disordered vortical flow. We also examine the impact of sample age on the non-equilibrium dynamics. Our findings shed light onto how the active composite cytoskeleton can finely tune its dynamics by varying the interactions between its constituents.