Polarizing yeast cells with electric fields.

CAMPETELLI AN; PIEL M; CHANG F; MINC N

Denver, CO

Congreso; The American Society for Cell Biology; 2011

The American Society for Cell Biology

Endogenous electrical signals surround tissues and cells and are thought to participate in the regulation of many polarization events such as wound healing, metastasis and development. Application of exogenous electric fields (EFs) can orient polarity in many cell types ranging from bacteria, to neutrophils and neurons. Different cell types polarize to different directions, some orienting to the anode and other to the cathode or even perpendicular to the EF. 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 orient to EFs remain poorly characterized. Here, we introduce the Budding yeast Saccharomyces cerevisiae as a rigorous model for cell polarity to dissect mechanisms underlying these effects. These cells polarize by locally selecting sites of bud emergence 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 parallelization of the assay. While, the budding pattern was generally resistant to the EF in haploid WT cells, 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 (a-factor), the EF directed polarized growth of the shmoo, but interestingly in the opposite direction, towards the anode. This shmoo orientation in the EFs depended on the formin Bni1. To understand the effect of EFs at the cell surface, we screened a set of characterized mutants in ion transporters and drugs that perturb ion transport. These experiments suggested that proper membrane potential regulation was key to mediate these effects. For instance, mutants lacking the Na+ releasing systems that display depolarized membrane potential or hyperpolarized mutants lacking K+ import directed shmoo polarization to the cathode in the EF, reverting the WT phenotype. This work begins to identify conserved factors and a proce