David Stone, PhD

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.

1. Sukumar M, DeFlorio R, Pai CY, Stone DE. 2023. A member of the claudin superfamily influences formation of the front domain in pheromone-responding yeast cells. Journal of Cell Science. 136 (2): jcs260048. Link
2. Wang X, Pai CY, Stone DE. 2022. Gradient tracking in mating yeast depends on Bud1 inactivation and actin-independent vesicle delivery. Journal of Cell Biology. 221 (12): e202203004. Link
3. Abdul-Ganiyu R, Venegas LA, Wang X, Puerner C, Arkowitz RA, Kay BK, Stone DE. 2021. Phosphorylated Gβ is a directional cue during yeast gradient tracking.  Science Signaling. 14, eabf4710. Link
4. Wang X, Tian W, Banh B, Statler B, Liang J, Stone DE. 2019. Mating yeast cells use an intrinsic polarity site to assemble a pheromone-gradient tracking machine.  Journal of Cell Biology. Link
5. Waszczak N, DeFlorio R, Ismael A, Cheng N, Stone DE. 2019. Quantitative proteomics reveals a Gα/MAPK signaling hub that controls pheromone-induced cellular polarization in yeast. Journal of Proteomics. 207: 103467 Link
6. Ismael A, Tian W, Waszczak N, Wang X, Cao Y, Suchkov D, Bar E,  Metodiev MV, Liang J, Arkowitz RA, Stone DE. 2016. Gβ promotes pheromone receptor polarization and yeast chemotropism by inhibiting receptor phosphorylation. Science Signaling. 9, ra38. Link
7. DeFlorio R, Brett ME, Waszczak N, Apollinari E, Metodiev M,  Dubrovskyi O, Eddington D, Arkowitz RA, Stone DE. 2013. Phosphorylation of Gβ is crucial for efficient chemotropism in yeast. Journal of Cell Science. 126, 2997-3009. Link
8. Suchkov DV, DeFlorio R, Draper E, Ismael A, Sukumar M, Arkowitz R, Stone DE. 2010. Polarization of the Yeast Pheromone Receptor Requires Its Internalization but Not Actin-dependent Secretion. Molecular Biology of the Cell, 21: 1737-1752. Link
9. Zaichick SV, Metodiev MV, Nelson SA, Dubrovskyi O, Draper E,  Cooper JA, Stone DE. 2009. The mating-specific G-alpha interacts with a kinesin-14 and regulates pheromone-induced nuclear migration in budding yeast. Molecular Biology of the Cell, 20. 2820-2830. Link
10. Blackwell E, Kim HJ, Stone DE. 2007. The pheromone-induced nuclear accumulation of the Fus3 MAPK in yeast depends on its phosphorylation state and on Dig1 and Dig2. BMC Molecular and Cell Biology. 8, 1-15. Link
11. Matheos D, Metodiev M, Muller E, Stone DE, Rose MD. 2004. Pheromone-induced polarization is dependent on the Fus3p MAPK acting through the formin Bni1p. Journal of Cell Biology. 165, 99-109. Link
12. Metodiev MV, Timanova A, Stone DE. 2003. Differential phosphoproteome profiling by affinity capture and tandem MALDI mass spectrometry. Proteomics 4, 1433-1438. Link
13. Bar E, Ellicott AT, Stone DE. 2003. Gβγ recruits Rho1 to the site of polarized growth during mating in budding yeast. Journal of Biological Chemistry 278: 21798-804. Link
14. 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. Molecular and Cellular Biology 23: 1135-50. Link
15. 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. Link

PhD, University of Wisconsin–Madison

BA, Wesleyan University