The coupling between reactions in the PIP lipid network and Rho pattern formation

The negatively charged class of PIP lipids on the plasma membrane regulate processes such as actin cytoskeletal dynamics in cooperation with the Rho GTPases. How PIP reaction kinetics impact the spatiotemporal patterning of Rho GTPases on the cell cortex remains poorly understood. Using the mast cell as an experimental system, we elucidate how enzymatic reactions modulating the conversion of PI(4)P and PI(4,5)P2 can tune cortical pattern formation of the Rho GTPase Cdc42. By utilizing fluorescent lipid sensors capable of detecting rapid concentration changes, we discovered that PI(4)P, the precursor to PI(4,5)P2, in fact exhibits self-sustained traveling waves after antigen stimulation. We then showed that both PI(4)P and PI(4,5)P2 oscillations are coupled to active GTP-bound Cdc42 oscillations. By applying a specific chemical inhibitor to the rate of PI(4)P synthesis, we found that downstream PI(4,5)P2-mediated Cdc42 oscillations return to a fixed point. Our results demonstrate how cells can use changes in reaction rates in the PIP network to tune Cdc42 pattern formation on the cortex.