Time-Dependent Microscale Mechanics of Actomyosin Networks During Triggered Activity

Networks of semiflexible actin filaments with their associated motor protein, myosin, are critical elements of the cytoskeleton that enable cellular motility and other key mechanical processes. By varying environmental conditions, such as ATP and salt concentrations, cells can dynamically alter the activity and mechanics of actomyosin networks. However, how changing chemical conditions map to time-varying mechanical properties of actomyosin networks remains to be understood. Here, we couple optical tweezers microrheology with microfluidics to measure the time-dependent viscoelastic response of in vitro crosslinked actomyosin networks while modulating ATP and salt concentrations. In particular, we use optical tweezers to sinusoidally oscillate microspheres embedded in networks and measure the resulting force at set time-intervals as we change buffer conditions via passive exchange of small molecules.We also image labeled actin filaments to characterize corresponding network mobility and structure. Our measurements shed important new light onto how actomyosin networks tune their mechanical activity in response to varying environmental conditions, and how their mechanical properties evolve as they transition from one state to the next.