Membrane composition-dependent patterning of Rho and F-actin in an artificial cell cortex.

Cortical excitability, a phenomenon in which the cell cortex is dynamically patterned with waves of F-actin assembly, has been described in a variety of animal model systems, including embryos of mammals, flies, frogs and echinoderms, as well as a variety of cultured cells. While the cortical F-actin network is closely linked with the plasma membrane, it is not known if membrane composition or fluidity regulates dynamic cytokinetic patterning. Phospholipids partition within the plasma membrane during cytokinesis, and phosphoinositides play a key regulatory role in other excitable systems, suggesting a role for membrane-dependent regulation of cytokinetic patterning. Here we use an artificial reconstituted cell cortex comprised of Xenopus egg extract and supported lipid bilayers (SLBs) to show that membrane composition regulates self-organized cortical patterning. We find that manipulating levels of candidate lipids, including phosphatidylinositol 4,5-bisphosphate, phosphatidylethanolamine, sphingomyelin and cholesterol, results in both quantitative and qualitative changes in the dynamics of traveling waves and standing oscillatory patterns of active Rho and F-actin, as well as the kinetics of Rho activation and F-actin assembly on supported lipid bilayers. Our findings demonstrate that membrane composition directly regulates the assembly of cortical F-actin, as well as emergent active Rho and F-actin patterning.