Mating Saccharomyces cerevisiae: Detecting Your Partner Through Chemical and Mechanical Cues

Abstract

All cells must be able to sense information about their surroundings to adapt and respond to environmental conditions. Environmental information is conveyed to the cell in the form of chemical and mechanical cues, which the cell translates to coordinate appropriate cellular responses. The budding yeast Saccharomyces cerevisiae utilizes both chemosensing and mechanosensing during the mating process, providing a tractable model to understand how cells receive and integrate information about their environment. To mate, S. cerevisiae identifies the location of a mating partner by orienting sites of polarity. This process requires decoding external chemical gradients created by the secretion of pheromones by potential mating partners. Once polarity sites are oriented, cells remodel their cell wall until contact is made with the mating partner. Only when contact is made with a mating partner of the correct mating type does cell wall removal occur. What contact specific mechanisms exist that allow cells to sense that a mating partner is present, and subsequently coordinate safe cell wall removal? Using live-cell fluorescence microscopy, I address how the chemosensitive pheromone GPCR receptor coordinates downstream signaling to bias polarity site movement in mating S. cerevisiae. I show that while Gα-MAPK interactions can increase the efficiency of polarity site alignment, this phenomenon is not conferred by phosphorylation of a primary substrate Bni1. Furthermore, I address how the mechanosensitive Cell Wall Integrity Pathway (CWI) is regulated such that removal of the cell wall is permitted before fusion. I show that downregulation of the CWI is a contact-dependent phenomenon that requires the presence of the cell wall protein Fig2.