title: Exo-endocytic trafficking and the septin-based diffusion barrier are required for the maintenance of Cdc42p polarization during budding yeast asymmetric growth.
abstract: Cdc42p plays a central role in asymmetric cell growth in yeast by controlling actin organization and vesicular trafficking. However, how Cdc42p is maintained specifically at the daughter cell plasma membrane during asymmetric cell growth is unclear. We have analyzed Cdc42p localization in yeast mutants defective in various stages of membrane trafficking by fluorescence microscopy and biochemical fractionation. We found that two separate exocytic pathways mediate Cdc42p delivery to the daughter cell. Defects in one of these pathways result in Cdc42p being rerouted through the other. In particular, the pathway involving trafficking through endosomes may couple Cdc42p endocytosis from, and subsequent redelivery to, the plasma membrane to maintain Cdc42p polarization at the daughter cell. Although the endo-exocytotic coupling is necessary for Cdc42p polarization, it is not sufficient to prevent the lateral diffusion of Cdc42p along the cell cortex. A barrier function conferred by septins is required to counteract the dispersal of Cdc42p and maintain its localization in the daughter cell but has no effect on the initial polarization of Cdc42p at the presumptive budding site before symmetry breaking. Collectively, membrane trafficking and septins function synergistically to maintain the dynamic polarization of Cdc42p during asymmetric growth in yeast.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19096 College of Life Sciences, Nankai University, Tianjin, 300071, China.
authors.forename: Kelly
authors.initials: K
authors.lastname: Orlando
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Sun
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Tu
authors.initials: T
authors.lastname: Lu
authors.forename: Lauren
authors.initials: L
authors.lastname: Yokomizo
authors.forename: Puyue
authors.initials: P
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D004058:Diffusion; D004705:Endocytosis; D005089:Exocytosis; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000254:growth & development* / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D058112:Septins / Q000378:metabolism*; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism*
chemical_list: D058112:Septins; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae