Local intracellular flow fields driven by active stresses of molecular motors

Cells actively render both fluid-like and solid-like behaviors. While cells need to be solid enough to maintain mechanical integrity and tissue shape, they also need to be fluid enough to allow necessary remodeling. The rheological properties can be controlled by both mechanical and biochemical processes in the cell. Hence, measuring intracellular flow is a crucial step in understanding subcellular mechanochemical feedback systems. Here, we study flow fields in transient actomyosin networks driven by polymerization and depolymerization of actin filaments, as well as contractile stresses of non-muscle myosin molecular motors. We first start by showing how active stresses propagate in 2d liquid crystalline structure and in disordered networks that are formed by actin filaments. In particular, the response functions of contractile and stable gels are characterized. We then measure the retrograde flow fields of stress fibers in single cells. To understand the convoluted feedback loops in the actomyosin cytoskeleton, we perturb multiple controlling pathways including those that alter viscoelasticity of the network, effective active stresses, and the dynamics of actin filaments.