Modeling Polarity Site Movement in Yeast Via Calcium-Mediated Regulation of Gap Activity

Symmetry-breaking polarization is a process that occurs in many cells. In budding yeast cells specifically, this polarization is possible due to the presence of a positive feedback loop, which allows for one and only one front to develop. Furthermore, in mating yeast cells the detection of pheromones plays a crucial role in the cell’s development of a polarity site; however, due to the microscopic size of yeast cells, there is often error in the initial polarity site’s accuracy. As a result, yeast cells can correct their polarity site by allowing the GTP-Cdc42 cluster to “wander”. This is typically considered as the indecisive phase of a cell. Recent studies have identified that cytosolic Ca2+ bursts, caused by sexual pheromones, increase the activity of GTPase-activating protein (GAP). This project tests this from a modeling perspective by adding a module of code to an already established positive feedback model that allows periodic spikes of GAP activity to occur. The model was successfully able to simulate the effects of calcium-mediated GAP spikes by portraying oscillating polarity sites and “wandering” polarity sites, using specific parameters based on biochemical data.