Regulation of cell polarity by the cell cycle in Saccharomyces cerevisiae

Abstract

Cell polarity in Saccharomyces cerevisiae is essential for bud formation, which is regulated by the cell cycle. How this regulation occurs is poorly understood. The master regulator of polarity is a Rho-GTPase called Cdc42, which accumulates at a region on the plasma membrane and recruits its downstream effectors and the cell’s cytoskeleton, leading to bud emergence. Previous work suggested that at a time in G1 called Start, the G1 CDK kinase promotes Cdc42 polarization. Recent findings have shown the opposite: Cdc42 is able to polarize prior to Start in daughter cells. Nevertheless, bud growth does not begin until after Start, which lead to the question: what exactly is this kinase regulating? One possibility is that G1 CDK regulates effectors of Cdc42. A partial survey of effectors showed that some were only able to polarize after the kinase activity increased. The aim of this study was to continue surveying effectors of Cdc42, focusing on Gic1 and Gic2. Confocal microscopy was used to obtain movies of yeast cells, which were analyzed using a customized MATLAB program. Gic1 polarization did not occur prior to Start, but Gic2 could polarize pre-Start in daughter cells. Future investigation into the structural difference between Gic1 and Gic2 in combination with that of other effectors may suggest potential ways that G1 CDK regulates effector localization.