In vitro light-controlled patterns and force generation for synthetic cytoskeletal networks

The cytoskeleton of a cell enables its shape and motility. To understand how patterns and associated forces may emerge in a simple cytoskeletal protein system, we synthesize, express, and purify a cortical protein (Tcb2) from the ciliated protozoan Tetrahymena. Tcb2 is a 25 kDa calcium-binding protein containing four EF-hand loops. By using caged calcium, we use light as a trigger to control the spatio-temporal assembly and dis-assembly of these in-vitro Tcb2 networks, both in confined microscopic geometries as well as in liquid droplets. We discuss the emergent patterns (reversible and irreversible) and the resultant complex fluid flow fields generated by the contractile network in response to different optical field structures. Through simple reaction-diffusion models, we discuss the associated physical mechanisms controlling the assembly and dis-assembly of these networks. By understanding simple contractile force-generating protein networks, our work offers insight into design and control of artificial cytoskeletons in synthetic and living cells.