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Characterization of Mug33 reveals complementary roles for actin cable-dependent transport and exocyst regulators in fission yeast exocytosis.

Snaith HA, Thompson J, Yates JR, Sawin KE - J. Cell. Sci. (2011)

Bottom Line: Although mug33Δ mutants are viable, with only a mild cell-polarity phenotype, mug33Δ myo52Δ double mutants are synthetically lethal.Combining mug33 Δ with deletion of the formin For3 (for3Δ) leads to synthetic temperature-sensitive growth and strongly reduced levels of exocytosis.Interestingly, mutants in non-essential genes involved in exocyst function behave in a manner similar to mug33Δ when combined with myo52Δ and for3Δ.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Cell Biology, School of Biological Sciences, University of Edinburgh, Swann Building, Mayfield Road, Edinburgh EH93JR, UK.

ABSTRACT
Although endocytosis and exocytosis have been extensively studied in budding yeast, there have been relatively few investigations of these complex processes in the fission yeast Schizosaccharomyces pombe. Here we identify and characterize fission yeast Mug33, a novel Tea1-interacting protein, and show that Mug33 is involved in exocytosis. Mug33 is a Sur7/PalI-family transmembrane protein that localizes to the plasma membrane at the cell tips and to cytoplasmic tubulovesicular elements (TVEs). A subset of Mug33 TVEs make long-range movements along actin cables, co-translocating with subunits of the exocyst complex. TVE movement depends on the type V myosin Myo52. Although mug33Δ mutants are viable, with only a mild cell-polarity phenotype, mug33Δ myo52Δ double mutants are synthetically lethal. Combining mug33 Δ with deletion of the formin For3 (for3Δ) leads to synthetic temperature-sensitive growth and strongly reduced levels of exocytosis. Interestingly, mutants in non-essential genes involved in exocyst function behave in a manner similar to mug33Δ when combined with myo52Δ and for3Δ. By contrast, combining mug33Δ with mutants in non-essential exocyst genes has only minor effects on growth. We propose that Mug33 contributes to exocyst function and that actin cable-dependent vesicle transport and exocyst function have complementary roles in promoting efficient exocytosis in fission yeast.

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Two pathways to achieve efficient exocytosis. (A) Schematic model of efficient exocytosis involving a combination of frequent delivery of exocytic vesicles (ves, blue) to cell tips, requiring actin cables (green) and type V myosin (yellow), together with tethering of vesicles through an efficiently functioning exocyst complex (e, red). (B) Genetic interactions indicate that Mug33, together with Exo70 and Rho3, acts to improve efficiency of exocyst function. See the text for further discussion.
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Figure 8: Two pathways to achieve efficient exocytosis. (A) Schematic model of efficient exocytosis involving a combination of frequent delivery of exocytic vesicles (ves, blue) to cell tips, requiring actin cables (green) and type V myosin (yellow), together with tethering of vesicles through an efficiently functioning exocyst complex (e, red). (B) Genetic interactions indicate that Mug33, together with Exo70 and Rho3, acts to improve efficiency of exocyst function. See the text for further discussion.

Mentions: More broadly, our data also suggest a model in which two complementary pathways converge to promote efficient exocytosis in fission yeast (Fig. 8). In this model, the first pathway involves formin-driven nucleation of actin cables and type V myosin-based delivery of exocytic vesicles, whereas the second pathway involves robust exocyst-mediated vesicle tethering, which is dependent on exocyst regulators, including Mug33. In the absence of either individual pathway exocytosis is relatively unaffected, but in the absence of both pathways exocytosis is severely compromised. The main experimental evidence for this model is derived from genetic interactions affecting cell viability or acid phosphatase secretion. Our results place for3+ and myo52+ in one genetic-interaction group and mug33+, exo70+ and rho3+ in a second group. Double mutants within a group are relatively non-additive and non-perturbing, whereas double mutants across the two groups are synthetically deleterious.


Characterization of Mug33 reveals complementary roles for actin cable-dependent transport and exocyst regulators in fission yeast exocytosis.

Snaith HA, Thompson J, Yates JR, Sawin KE - J. Cell. Sci. (2011)

Two pathways to achieve efficient exocytosis. (A) Schematic model of efficient exocytosis involving a combination of frequent delivery of exocytic vesicles (ves, blue) to cell tips, requiring actin cables (green) and type V myosin (yellow), together with tethering of vesicles through an efficiently functioning exocyst complex (e, red). (B) Genetic interactions indicate that Mug33, together with Exo70 and Rho3, acts to improve efficiency of exocyst function. See the text for further discussion.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3113670&req=5

Figure 8: Two pathways to achieve efficient exocytosis. (A) Schematic model of efficient exocytosis involving a combination of frequent delivery of exocytic vesicles (ves, blue) to cell tips, requiring actin cables (green) and type V myosin (yellow), together with tethering of vesicles through an efficiently functioning exocyst complex (e, red). (B) Genetic interactions indicate that Mug33, together with Exo70 and Rho3, acts to improve efficiency of exocyst function. See the text for further discussion.
Mentions: More broadly, our data also suggest a model in which two complementary pathways converge to promote efficient exocytosis in fission yeast (Fig. 8). In this model, the first pathway involves formin-driven nucleation of actin cables and type V myosin-based delivery of exocytic vesicles, whereas the second pathway involves robust exocyst-mediated vesicle tethering, which is dependent on exocyst regulators, including Mug33. In the absence of either individual pathway exocytosis is relatively unaffected, but in the absence of both pathways exocytosis is severely compromised. The main experimental evidence for this model is derived from genetic interactions affecting cell viability or acid phosphatase secretion. Our results place for3+ and myo52+ in one genetic-interaction group and mug33+, exo70+ and rho3+ in a second group. Double mutants within a group are relatively non-additive and non-perturbing, whereas double mutants across the two groups are synthetically deleterious.

Bottom Line: Although mug33Δ mutants are viable, with only a mild cell-polarity phenotype, mug33Δ myo52Δ double mutants are synthetically lethal.Combining mug33 Δ with deletion of the formin For3 (for3Δ) leads to synthetic temperature-sensitive growth and strongly reduced levels of exocytosis.Interestingly, mutants in non-essential genes involved in exocyst function behave in a manner similar to mug33Δ when combined with myo52Δ and for3Δ.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Cell Biology, School of Biological Sciences, University of Edinburgh, Swann Building, Mayfield Road, Edinburgh EH93JR, UK.

ABSTRACT
Although endocytosis and exocytosis have been extensively studied in budding yeast, there have been relatively few investigations of these complex processes in the fission yeast Schizosaccharomyces pombe. Here we identify and characterize fission yeast Mug33, a novel Tea1-interacting protein, and show that Mug33 is involved in exocytosis. Mug33 is a Sur7/PalI-family transmembrane protein that localizes to the plasma membrane at the cell tips and to cytoplasmic tubulovesicular elements (TVEs). A subset of Mug33 TVEs make long-range movements along actin cables, co-translocating with subunits of the exocyst complex. TVE movement depends on the type V myosin Myo52. Although mug33Δ mutants are viable, with only a mild cell-polarity phenotype, mug33Δ myo52Δ double mutants are synthetically lethal. Combining mug33 Δ with deletion of the formin For3 (for3Δ) leads to synthetic temperature-sensitive growth and strongly reduced levels of exocytosis. Interestingly, mutants in non-essential genes involved in exocyst function behave in a manner similar to mug33Δ when combined with myo52Δ and for3Δ. By contrast, combining mug33Δ with mutants in non-essential exocyst genes has only minor effects on growth. We propose that Mug33 contributes to exocyst function and that actin cable-dependent vesicle transport and exocyst function have complementary roles in promoting efficient exocytosis in fission yeast.

Show MeSH
Related in: MedlinePlus