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Yeast Miro GTPase, Gem1p, regulates mitochondrial morphology via a novel pathway.

Frederick RL, McCaffery JM, Cunningham KW, Okamoto K, Shaw JM - J. Cell Biol. (2004)

Bottom Line: Biol.Chem. 278:6495-6502), Gem1p is not required for pheromone-induced yeast cell death.Thus, Gem1p defines a novel mitochondrial morphology pathway which may integrate cell signaling events with mitochondrial dynamics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.

ABSTRACT
Cell signaling events elicit changes in mitochondrial shape and activity. However, few mitochondrial proteins that interact with signaling pathways have been identified. Candidates include the conserved mitochondrial Rho (Miro) family of proteins, which contain two GTPase domains flanking a pair of calcium-binding EF-hand motifs. We show that Gem1p (yeast Miro; encoded by YAL048C) is a tail-anchored outer mitochondrial membrane protein. Cells lacking Gem1p contain collapsed, globular, or grape-like mitochondria. We demonstrate that Gem1p is not an essential component of characterized pathways that regulate mitochondrial dynamics. Genetic studies indicate both GTPase domains and EF-hand motifs, which are exposed to the cytoplasm, are required for Gem1p function. Although overexpression of a mutant human Miro protein caused increased apoptotic activity in cultured cells (Fransson et al., 2003. J. Biol. Chem. 278:6495-6502), Gem1p is not required for pheromone-induced yeast cell death. Thus, Gem1p defines a novel mitochondrial morphology pathway which may integrate cell signaling events with mitochondrial dynamics.

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Mitochondrial inheritance is not blocked in the absence of Gem1p. mito-GFP-labeled mitochondria were observed in strains grown to mid-log phase. Large- or small-budded cells containing mitochondria in the bud were scored. n > 250.
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fig5: Mitochondrial inheritance is not blocked in the absence of Gem1p. mito-GFP-labeled mitochondria were observed in strains grown to mid-log phase. Large- or small-budded cells containing mitochondria in the bud were scored. n > 250.

Mentions: Disruption of actin cytoskeleton or ER organization can cause secondary defects in mitochondrial morphology and inheritance (Drubin et al., 1993; Hermann et al., 1997; Prinz et al., 2000; Singer et al., 2000). However, mitochondrial morphology defects in gem1Δ cells are not due to disruption of these structures. Alexa-Phalloidin staining studies showed actin cytoskeletal organization was normal in 99.5% of GEM1 and gem1Δ cells (n = 200). Moreover, actin-based transport of mitochondria remained intact as medium and large-budded gem1Δ cells always inherit mitochondria (Fig. 5). The lack of mitochondria observed in some small-budded gem1Δ cells is likely a delay in movement of large globular organelles to the bud. Vacuole inheritance, another actin-based process in yeast (Hill et al., 1996), was not disrupted in gem1Δ strains. In pulse-chase experiments, FM 4-64–labeled vacuoles were inherited by 98.3 and 95.8% of wild-type and gem1Δ buds, respectively (n = 120). In addition, yeast nuclei (visualized by DAPI staining) and ER morphology (visualized by expression of Sec63-GFP) were normal in the absence of Gem1p (unpublished data). Vacuolar morphology and endocytic function also appeared wild type when tested by monitoring internalization of the vital dye FM 4-64 (unpublished data). Together, these data suggest that disruption of GEM1 causes primary defects in mitochondrial morphology and function but does not disturb organization of other cellular structures.


Yeast Miro GTPase, Gem1p, regulates mitochondrial morphology via a novel pathway.

Frederick RL, McCaffery JM, Cunningham KW, Okamoto K, Shaw JM - J. Cell Biol. (2004)

Mitochondrial inheritance is not blocked in the absence of Gem1p. mito-GFP-labeled mitochondria were observed in strains grown to mid-log phase. Large- or small-budded cells containing mitochondria in the bud were scored. n > 250.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172521&req=5

fig5: Mitochondrial inheritance is not blocked in the absence of Gem1p. mito-GFP-labeled mitochondria were observed in strains grown to mid-log phase. Large- or small-budded cells containing mitochondria in the bud were scored. n > 250.
Mentions: Disruption of actin cytoskeleton or ER organization can cause secondary defects in mitochondrial morphology and inheritance (Drubin et al., 1993; Hermann et al., 1997; Prinz et al., 2000; Singer et al., 2000). However, mitochondrial morphology defects in gem1Δ cells are not due to disruption of these structures. Alexa-Phalloidin staining studies showed actin cytoskeletal organization was normal in 99.5% of GEM1 and gem1Δ cells (n = 200). Moreover, actin-based transport of mitochondria remained intact as medium and large-budded gem1Δ cells always inherit mitochondria (Fig. 5). The lack of mitochondria observed in some small-budded gem1Δ cells is likely a delay in movement of large globular organelles to the bud. Vacuole inheritance, another actin-based process in yeast (Hill et al., 1996), was not disrupted in gem1Δ strains. In pulse-chase experiments, FM 4-64–labeled vacuoles were inherited by 98.3 and 95.8% of wild-type and gem1Δ buds, respectively (n = 120). In addition, yeast nuclei (visualized by DAPI staining) and ER morphology (visualized by expression of Sec63-GFP) were normal in the absence of Gem1p (unpublished data). Vacuolar morphology and endocytic function also appeared wild type when tested by monitoring internalization of the vital dye FM 4-64 (unpublished data). Together, these data suggest that disruption of GEM1 causes primary defects in mitochondrial morphology and function but does not disturb organization of other cellular structures.

Bottom Line: Biol.Chem. 278:6495-6502), Gem1p is not required for pheromone-induced yeast cell death.Thus, Gem1p defines a novel mitochondrial morphology pathway which may integrate cell signaling events with mitochondrial dynamics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.

ABSTRACT
Cell signaling events elicit changes in mitochondrial shape and activity. However, few mitochondrial proteins that interact with signaling pathways have been identified. Candidates include the conserved mitochondrial Rho (Miro) family of proteins, which contain two GTPase domains flanking a pair of calcium-binding EF-hand motifs. We show that Gem1p (yeast Miro; encoded by YAL048C) is a tail-anchored outer mitochondrial membrane protein. Cells lacking Gem1p contain collapsed, globular, or grape-like mitochondria. We demonstrate that Gem1p is not an essential component of characterized pathways that regulate mitochondrial dynamics. Genetic studies indicate both GTPase domains and EF-hand motifs, which are exposed to the cytoplasm, are required for Gem1p function. Although overexpression of a mutant human Miro protein caused increased apoptotic activity in cultured cells (Fransson et al., 2003. J. Biol. Chem. 278:6495-6502), Gem1p is not required for pheromone-induced yeast cell death. Thus, Gem1p defines a novel mitochondrial morphology pathway which may integrate cell signaling events with mitochondrial dynamics.

Show MeSH
Related in: MedlinePlus