Spatiotemporal Control of Pathway Sensors and Cross-Pathway Feedback Regulate a Cell Differentiation MAPK Pathway in Yeast

Mitogen-Activated Protein Kinase (MAPK) pathways control cell differentiation and the response to stress. MAPK pathways can share components with other pathways yet induce specific responses through mechanisms that remain unclear. In Saccharomyces cerevisiae, the MAPK pathway that controls filamentous growth (fMAPK) shares components with the MAPK pathway that regulates the response to osmotic stress (HOG). By exploring temporal regulation of MAPK signaling, we show here that the two pathways exhibited different patterns of activity throughout the cell cycle. The different patterns resulted from different expression profiles of genes encoding the mucin sensors (MSB2 for fMAPK and HKR1 for HOG). We also show that positive feedback through the fMAPK pathway stimulated the HOG pathway, presumably to modulate fMAPK pathway activity. By exploring spatial regulation of MAPK signaling, we found that the shared tetraspan protein, Sho1p, which has a dynamic localization pattern, induced the fMAPK pathway at the mother-bud neck. A Sho1p-interacting protein, Hof1p, which also localizes to the mother-bud neck and regulates cytokinesis, also regulated the fMAPK pathway. Therefore, spatial and temporal regulation of pathway sensors, and cross-pathway feedback, regulate a MAPK pathway that controls a cell differentiation response in yeast.