The Cytoskeleton as an Active Gel: Modelling Cell Polarization, Shape Change, and Migration
Andrew Callan-Jones (Université Paris-Diderot)
Cell polarization and shape change are required for large-scale movements during embryo development and cancer metastasis. I will present recent work to understand these phenomena by studying two model systems: zebrafish embryos during gastrulation and confined HeLa cells. In both cases, individual cells are observed to undergo a novel type of polarization and transformation to a motile state that is crucially dependent on elevated levels of contractility in the actomyosin cortex. Polarization of zebrafish cells in vitro can be triggered by stimulating myosin activity: initially quasi-spherical, immobile cells switch to a polarized state characterized by a high cortical density at the cell rear, persistent cortical actin flows, and a distinctive pear-like morphology. Compressing HeLa cells between two plates results in a transition from a well-spread, mesenchymal-type migration mode to a rounded-up one sustained by cortical flow, and displaying an actin rich uropod at the rear, reminiscent of zebrafish.
We have modeled these cell mechanical responses using active gel theory, a continuum-level description of out-of-equilibrium behavior of the cytoskeleton. In this talk, I will first provide a summary of this theory, and will then show how it accounts for the principal features of contractility-based polarization: cortical flow and density changes, cell shape change, and migration.