Signal transduction and cellular polarization in yeast
Collecting information about the environment, integrating it and responding in accordance with changing conditions are essential abilities required of all cells. In eukaryotes, one of the most common strategies for detecting and transmitting information across the plasma membrane utilizes surface receptors coupled to heterotrimeric G proteins. Animal cells depend on membrane bound receptors and their associated G proteins to sense hormones, cytokines, neurotransmitters, odorants and light; unicellular eukaryotes use similar molecular switches to communicate with one another and to coordinate developmental fates.
The mating response of Saccharomyces cerevisiae
provides an opportunity to study a model G protein-coupled receptor signaling system in a genetically tractable organism. The consequences of the mating signal run the gamut of cellular responses: cell cycle control, regulation of gene expression, cytoskeletal reorganization, chemotropic growth, cell-cell interaction, and membrane fusion. In essence, pheromone blocks proliferation and induces the differentiation of vegetatively growing cells into gametes.
It has been estimated that a 1% difference in receptor occupancy across the 4 - 5 microns length of a yeast cell in a pheromone gradient is sufficient to elicit robust orientation toward the pheromone source. We are interested in how such a shallow pheromone gradient is accurately interpreted by yeast cells to promote directional growth toward a mating partner. How do cells navigate using such subtle cues? Models of this and analogous processes invoke positive feedback loops that amplify small differences in receptor activation across the cell surface into a substantially steeper intracellular signaling gradient. Our data suggest that the pheromone responsive heterotrimeric G protein functions in a network of interacting positive feedback loops that establish and amplify receptor polarity, link the position of the receptor to the actin and microtubule cytoskeletons, and underlie the tracking of dynamic gradients. The goal of our ongoing investigation is to elucidate these mechanisms.
DeFlorio, R., M. E. Brett, N. Waszczak, E. Apollinari, M. Metodiev, O. Dubrovskyi, D. Eddington, R. A. Arkowitz, and D. E. Stone. 2013. Phosphorylation of G-beta is crucial for efficient chemotropism in yeast. J. Cell Sci 126, 2997-3009.
Dmitry V. Suchkov, Reagan DeFlorio, Edward Draper, Amber Ismael, Madhushalini Sukumar, Robert Arkowitz, and David E. Stone. 2010. Polarization of the Yeast Pheromone Receptor Requires Its Internalization but Not Actin-dependent Secretion. Mol. Biol. Cell., 21: 1737-1752.
Zaichick, S. V., M. V. Metodiev, S. A. Nelson, O. Dubrovskyi, E. Draper, J. A. Cooper, and D. E. Stone. 2009. The mating-specific G-alpha interacts with a kinesin-14 and regulates pheromone-induced nuclear migration in budding yeast. Mol. Biol. Cell., 20. 2820-2830.
Blackwell, E., HJ Kim, and D. Stone. 2007. The pheromone-induced nuclear accumulation of the Fus3 MAPK in yeast depends on its phosphorylation state and on Dig1 and Dig2. BMC Cell Biol. 8, 1-15.
Matheos, D., M. Metodiev, E. Muller, D. Stone, and M. D. Rose. 2004. Pheromone-induced polarization is dependent on the Fus3p MAPK acting through the formin Bni1p. J. Cell Biol. 165, 99-109.
Metodiev, M. V., A. Timanova, and D. E. Stone.  Differential phosphoproteome profiling by affinity capture and tandem MALDI mass spectrometry. Proteomics 4, 1433-1438.
Bar E, Ellicott AT, Stone DE (2003) G-beta/gamma recruits Rho1 to the site of polarized growth during mating in budding yeast. J Biol Chem 278: 21798-804.
Blackwell, E, Halatek IM, Kim HJ, Ellicott AT, Obukhov AA, Stone DE (2003) Effect of the pheromone-responsive G-alpha and phosphatase proteins of Saccharomyces cerevisiae on the subcellular localization of the Fus3 mitogen-activated protein kinase. Mol Cell Biol 23: 1135-50.
Metodiev MV, Matheos D, Rose MD, Stone DE (2002) Regulation of MAPK function by direct interaction with the mating-specific G-alpha in yeast. Science 296: 1483-1486. [Abstract