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Yeast Cdc42 functions at a late step in exocytosis, specifically during polarized growth of the emerging bud.

Adamo JE, Moskow JJ, Gladfelter AS, Viterbo D, Lew DJ, Brennwald PJ - J. Cell Biol. (2001)

Bottom Line: The Rho family GTPase Cdc42 is a key regulator of cell polarity and cytoskeletal organization in eukaryotic cells.Extensive genetic interactions between cdc42-6 and mutations in exocytic components support this hypothesis, and indicate a functional overlap with Rho3, which also regulates both actin organization and exocytosis.Localization data suggest that the defect in cdc42-6 cells is not at the level of the localization of the exocytic apparatus.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
The Rho family GTPase Cdc42 is a key regulator of cell polarity and cytoskeletal organization in eukaryotic cells. In yeast, the role of Cdc42 in polarization of cell growth includes polarization of the actin cytoskeleton, which delivers secretory vesicles to growth sites at the plasma membrane. We now describe a novel temperature-sensitive mutant, cdc42-6, that reveals a role for Cdc42 in docking and fusion of secretory vesicles that is independent of its role in actin polarization. cdc42-6 mutants can polarize actin and deliver secretory vesicles to the bud, but fail to fuse those vesicles with the plasma membrane. This defect is manifested only during the early stages of bud formation when growth is most highly polarized, and appears to reflect a requirement for Cdc42 to maintain maximally active exocytic machinery at sites of high vesicle throughput. Extensive genetic interactions between cdc42-6 and mutations in exocytic components support this hypothesis, and indicate a functional overlap with Rho3, which also regulates both actin organization and exocytosis. Localization data suggest that the defect in cdc42-6 cells is not at the level of the localization of the exocytic apparatus. Rather, we suggest that Cdc42 acts as an allosteric regulator of the vesicle docking and fusion apparatus to provide maximal function at sites of polarized growth.

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Vesicle accumulation in rho3-V51 mutants affects both large- and small-budded cells similarly. The rho3-V51 micrographs were reevaluated and vesicle accumulation was now counted with respect to bud size, using the same criteria as in Fig. 4.
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fig6: Vesicle accumulation in rho3-V51 mutants affects both large- and small-budded cells similarly. The rho3-V51 micrographs were reevaluated and vesicle accumulation was now counted with respect to bud size, using the same criteria as in Fig. 4.

Mentions: Because our genetic analyses suggested that the role of Cdc42 in exocytosis overlaps with that of Rho3, we decided to reexamine our previous electron micrographs of the rho3-V51 mutant to determine if there was any detectable cell cycle dependence to the vesicle accumulation in this mutant that had been missed (Adamo et al., 1999). However, using precisely the same criteria as for the analysis cdc42-6, we found no difference in the vesicle accumulation phenotype of rho3-V51 cells as a function of bud size (Fig. 6). This suggests that whereas Cdc42 is especially important for exocytosis early during bud formation, Rho3 is required throughout the cell cycle.


Yeast Cdc42 functions at a late step in exocytosis, specifically during polarized growth of the emerging bud.

Adamo JE, Moskow JJ, Gladfelter AS, Viterbo D, Lew DJ, Brennwald PJ - J. Cell Biol. (2001)

Vesicle accumulation in rho3-V51 mutants affects both large- and small-budded cells similarly. The rho3-V51 micrographs were reevaluated and vesicle accumulation was now counted with respect to bud size, using the same criteria as in Fig. 4.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2198861&req=5

fig6: Vesicle accumulation in rho3-V51 mutants affects both large- and small-budded cells similarly. The rho3-V51 micrographs were reevaluated and vesicle accumulation was now counted with respect to bud size, using the same criteria as in Fig. 4.
Mentions: Because our genetic analyses suggested that the role of Cdc42 in exocytosis overlaps with that of Rho3, we decided to reexamine our previous electron micrographs of the rho3-V51 mutant to determine if there was any detectable cell cycle dependence to the vesicle accumulation in this mutant that had been missed (Adamo et al., 1999). However, using precisely the same criteria as for the analysis cdc42-6, we found no difference in the vesicle accumulation phenotype of rho3-V51 cells as a function of bud size (Fig. 6). This suggests that whereas Cdc42 is especially important for exocytosis early during bud formation, Rho3 is required throughout the cell cycle.

Bottom Line: The Rho family GTPase Cdc42 is a key regulator of cell polarity and cytoskeletal organization in eukaryotic cells.Extensive genetic interactions between cdc42-6 and mutations in exocytic components support this hypothesis, and indicate a functional overlap with Rho3, which also regulates both actin organization and exocytosis.Localization data suggest that the defect in cdc42-6 cells is not at the level of the localization of the exocytic apparatus.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
The Rho family GTPase Cdc42 is a key regulator of cell polarity and cytoskeletal organization in eukaryotic cells. In yeast, the role of Cdc42 in polarization of cell growth includes polarization of the actin cytoskeleton, which delivers secretory vesicles to growth sites at the plasma membrane. We now describe a novel temperature-sensitive mutant, cdc42-6, that reveals a role for Cdc42 in docking and fusion of secretory vesicles that is independent of its role in actin polarization. cdc42-6 mutants can polarize actin and deliver secretory vesicles to the bud, but fail to fuse those vesicles with the plasma membrane. This defect is manifested only during the early stages of bud formation when growth is most highly polarized, and appears to reflect a requirement for Cdc42 to maintain maximally active exocytic machinery at sites of high vesicle throughput. Extensive genetic interactions between cdc42-6 and mutations in exocytic components support this hypothesis, and indicate a functional overlap with Rho3, which also regulates both actin organization and exocytosis. Localization data suggest that the defect in cdc42-6 cells is not at the level of the localization of the exocytic apparatus. Rather, we suggest that Cdc42 acts as an allosteric regulator of the vesicle docking and fusion apparatus to provide maximal function at sites of polarized growth.

Show MeSH
Related in: MedlinePlus