Polarization and cell-fate decision facilitated by the adaptor Ste50 in Saccharomyces cerevisiae
Polarization or directional growth is a major morphological change that occurs in yeast cells during pheromone response to mate with the opposite partner. In the pheromone signaling pathway, the adaptor Ste50 is required to bind MAP3K Ste11 for proper polarization; cells lacking Ste50 are impaired in polarization. Direct involvement of Ste50 in the polarization process has not been explored systematically. Here, we used single-cell fluorescent time-lapse microscopy to characterize Ste50 involvement in the establishment of cell polarity. We found early localization of Ste50 patches on the cell cortex that mark the point of shmoo initiation, these polarity sites move, and patches remain associated with the growing shmoo tip in a pheromone concentration-dependent manner until shmoo maturation. By quantitative analysis we show that polarization corelates with the rising levels of Ste50 enabling rapid individual cell responses to pheromone that corresponds to a critical level of Ste50 at the initial G1 phase. Suggesting Ste50 to be a pheromone responsive gene. We exploited the quantitative differences in the pattern of Ste50 expression to corelate with the cell-cell phenotypic heterogeneity showing Ste50 involvement in the cellular differentiation choices. Taken together, these findings present spatiotemporal localization of Ste50 during yeast polarization, suggesting that Ste50 is a component of the polarisome, and plays a critical role in regulating the polarized growth of shmoo during pheromone response.