Microrheology of active actin-microtubule networks*

The cytoskeleton, composed of actin, microtubules, and associated motor and binding proteins, self-organizes into different structures and morphologies to drive diverse mechanical processes in eukaryotic cells. While in vitro actomyosin networks are well-characterized, few studies have examined how the structure and activity of these networks are altered by the presence of microtubules. We previously synthesized steady-state actin-microtubule networks, finding that mechanical properties, such as network elasticity, depend on molecular interactions between actin and microtubules, such as the degree of crosslinking and bundling. Here, we create active actin-microtubule networks by adding the motor protein myosin. Using confocal microscopy and microrheology, we characterize how the network structure evolves during motor activity, and connect how microscopic changes in network structure affect the mechanical properties of the network. Our results shed important new light on how actin-microtubule interactions influence the structure, mechanics and activity that motor-driven cytoskeleton networks exhibit.