A Predictive Model for Yeast Cell Polarization in Pheromone Gradients

MAP5

Universite Paris Descartes, France

Budding yeast cells exist in two mating types, a and α, which use peptide pheromones to communicate with each other during mating. Mating depends on the ability of cells to polar- ize up pheromone gradients, but cells also respond to spatially uniform fields of pheromone by polarizing along a single axis. We used quantitative measurements of the response of MATa cells response to α-factor to advance a predictive model of yeast polarization towards a pheromone gradient. We found that cells make a sharp transition between polarization and budding despite substantial noise in the strength of signaling and detect pheromone gradients accurately only over a narrow range of pheromone concentrations. We propose a fully predictive mathematical model of the response of yeast cells to pheromone gradients. We take advantage of the yeasts capacity to polarize in a homogeneous field of pheromone to fit all the parameters of the mathematical model by using quantitative data on spontaneous polarization in uniform pheromone concentration. Once these parameters have been computed, and without any further fit, we compare the results with experimental data for yeast cells responding to pheromone gradients. Our model quantitatively predicts the yeast cell response to pheromone gradient providing a step toward a detailled understanding of how cells communicate with each other.