Dissecting the molecular mechanisms of electric field-induced cell polarization.

CAMPETELLI A N; PIEL M; CHANG F; MINC N

Barga

Seminario; Gordon Research Seminar; 2012

Gordon Research Seminar

Endogenous electrical signals surround tissues and cells and are thought to participate in the spatial regulation of polarization events such as wound healing, metastasis and development. The application of exogenous electric fields (EFs) can orient polarity in most cell types. Different cell types polarize to different directions. EFs are thought to signal through the membrane by locally altering membrane potential or ion fluxes distribution around the cell; however the mechanisms for how cells sense and transduce EF to orient polarity remain poorly understood. Here, we introduce the budding yeast S. cerevisiae as a genetically tractable model for cell polarity to dissect molecular mechanisms underlying these effects. This cell polarizes by locally selecting sites of bud emergence during vegetative growth or by growing shmoo projection for mating. We apply EFs by immobilizing yeast cells in microfluidic chambers, which allow for heat control, straight EF lines and medium-throughput parallelization of the assay. While the WT haploid budding pattern was generally resistant to the EF, mutants in the bud site selection pathway that normally bud in random direction, such as rsr1 (Bud1, a Ras-like GTPase), were polarized by the EF towards the cathode. In the presence of pheromones (α-factor), the EF directed polarized growth of the shmoo, in the opposite direction, towards the anode in a process dependent on the activation of the small GTPase cdc42p by its GEF cdc24p. To understand the effect of EFs at the cell surface, we screened a set of characterized mutants in ion transporters and drugs that affect ion transport. This screen put forward two conserved membrane potential regulator:the K+ transporter Trk1p and the Na+-K+/H+ antiporter Nha1p.These data coupled with computational model of EF effects on membrane potential, suggest that membrane potential values may influence the local recruitment or stabilization of the polarisome. This work begins to identify conserved factors and processes involved in EF response and brings novel insight into general mechanisms of cell polarity.