Interaction between bud-site selection and polarity-establishment machineries in budding yeast.
Saccharomyces cerevisiae yeast cells polarize in order to form a single bud in each cell cycle. Distinct patterns of bud-site selection are observed in haploid and diploid cells. Genetic approaches have identified the molecular machinery responsible for positioning the bud site: during bud formation, specific locations are marked with immobile landmark proteins. In the next cell cycle, landmarks act through the Ras-family GTPase Rsr1 to promote local activation of the conserved Rho-family GTPase, Cdc42. Additional Cdc42 accumulates by positive feedback, creating a concentrated patch of GTP-Cdc42, which polarizes the cytoskeleton to promote bud emergence. Using time-lapse imaging and mathematical modelling, we examined the process of bud-site establishment. Imaging reveals unexpected effects of the bud-site-selection system on the dynamics of polarity establishment, raising new questions about how that system may operate. We found that polarity factors sometimes accumulate at more than one site among the landmark-specified locations, and we suggest that competition between clusters of polarity factors determines the final location of the Cdc42 cluster. Modelling indicated that temporally constant landmark-localized Rsr1 would weaken or block competition, yielding more than one polarity site. Instead, we suggest that polarity factors recruit Rsr1, effectively sequestering it from other locations and thereby terminating landmark activity.
Department of Pharmacology and Cancer Biology, Duke University Medical Center, , Durham, NC 27710, USA.
Chi-Fang
CF
Wu
Natasha S
NS
Savage
Daniel J
DJ
Lew
D016764:Cell Polarity / Q000502:physiology*; D022081:Cell Surface Extensions / Q000502:physiology*; D003599:Cytoskeleton / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000378:metabolism*; D018613:Microscopy, Confocal; D008954:Models, Biological; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D004718:Saccharomycetales / Q000254:growth & development*; D059008:Time-Lapse Imaging; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism
D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; C084013:RSR1 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020691:rab GTP-Binding Proteins
Cdc42; Rsr1; bud; polarity; yeast