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Icon for: Michael Lawson


University of California at Santa Barbara


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The Truth about A's and Alpha's: How Yeast Cells Find Each Other in a Noisy World

During the mating process, yeast cells emit pheromone molecules that are detected by the opposite mating type. The cells then form a mating projection (the “Shmoo”) in the direction of their mating partner. How do cells accurately determine the correct direction of projection growth? When submitted to pheromone with no directionality (that is, in equal concentrations in all directions), cells still manage to choose a direction. How do they accomplish this? Once a projection is formed, the direction of the pheromone input can be changed, and the cell will accurately and efficiently create a new projection in the new direction. How is it possible that cells can perform these precise tasks in the face of random (stochastic) noise that is the hallmark of molecular interactions on the cellular level?

Our multidisciplinary and inter-university research project seeks to answer these questions by combining numerical simulation, control theory and experimental biology. We have developed a mathematical model that is based on literature in the field of yeast mating. Our model of polarisome formation highlights a mechanism by which eukaryotic cells can harness noise and spatial inhomogeneity to produce robust tight localization of proteins on the cell membrane that is responsive to changes in input. The model was originally motivated by the biology, but its development has been a cycle of modeling driving experiment and the results of those experiments guiding further modeling. Our research indicates that stochastic noise is essential to the cells ability to match the phenotypical behaviors listed above.