UC Davis

Background: The fission yeast Schizosaccharomyces pombe has a cylindrical cell shape, for which growth is strictly limited to both ends, and serves as an excellent model system for genetic analysis of cell-polarity determination. Previous studies identified a cell-end marker protein, Teal, that is transported by cytoplasmic microtubules to cell tips and recruits other cell-end factors, including the Dyrk-family Pom1 kinase. The Delta tea1 mutant cells cannot grow in a bipolar fashion and show T-shaped morphology after heat shock. Results: We identified Wsh3/Tea4 as a novel protein that interacts with Win1 MAP kinase kinase kinase (MAPKKK) of the stress-activated MAP kinase cascade. Wsh3 forms a complex with Teal and is transported to cell tips by growing microtubules. The Delta wsh3 mutant shows monopolar growth with abnormal Teal aggregate at the non-growing cell end; this abnormal aggregate fails to recruit Pom1 kinase. Consistent with the observed interaction between Win and Wsh3, cells lacking Wsh3 or Teal show more severe cell-polarity defects under osmolarity and heat-stress stimuli that are known to activate the stress MAPK cascade. Furthermore, mutants of the stress MAPK also exhibit cell-polarity defects when exposed to the same stress. Conclusions: Wsh3/Tea4 is an essential component of the Teal cell-end complex. In addition to its role in bipolar growth during the normal cell cycle, the Wsh3-Tea1 complex, together with the stress-signaling MAPK cascade, contributes to cell-polarity maintenance under stress conditions.