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The dynamin-related GTPase, Mgm1p, is an intermembrane space protein required for maintenance of fusion competent mitochondria.

Wong ED, Wagner JA, Gorsich SW, McCaffery JM, Shaw JM, Nunnari J - J. Cell Biol. (2000)

Bottom Line: To study the primary function of MGM1, we characterized new temperature sensitive MGM1 alleles.Although Mgm1p was recently reported to localize to the mitochondrial outer membrane, our studies indicate that Mgm1p is localized to the mitochondrial intermembrane space.Based on our localization data and Mgm1p's structural homology to dynamin, we postulate that it functions in inner membrane remodeling events.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular and Cellular Biology, University of California Davis, Davis, California 95616, USA.

ABSTRACT
Mutations in the dynamin-related GTPase, Mgm1p, have been shown to cause mitochondrial aggregation and mitochondrial DNA loss in Saccharomyces cerevisiae cells, but Mgm1p's exact role in mitochondrial maintenance is unclear. To study the primary function of MGM1, we characterized new temperature sensitive MGM1 alleles. Examination of mitochondrial morphology in mgm1 cells indicates that fragmentation of mitochondrial reticuli is the primary phenotype associated with loss of MGM1 function, with secondary aggregation of mitochondrial fragments. This mgm1 phenotype is identical to that observed in cells with a conditional mutation in FZO1, which encodes a transmembrane GTPase required for mitochondrial fusion, raising the possibility that Mgm1p is also required for fusion. Consistent with this idea, mitochondrial fusion is blocked in mgm1 cells during mating, and deletion of DNM1, which encodes a dynamin-related GTPase required for mitochondrial fission, blocks mitochondrial fragmentation in mgm1 cells. However, in contrast to fzo1 cells, deletion of DNM1 in mgm1 cells restores mitochondrial fusion during mating. This last observation indicates that despite the phenotypic similarities observed between mgm1 and fzo1 cells, MGM1 does not play a direct role in mitochondrial fusion. Although Mgm1p was recently reported to localize to the mitochondrial outer membrane, our studies indicate that Mgm1p is localized to the mitochondrial intermembrane space. Based on our localization data and Mgm1p's structural homology to dynamin, we postulate that it functions in inner membrane remodeling events. In this context, the observed mgm1 phenotypes suggest that inner and outer membrane fission is coupled and that loss of MGM1 function may stimulate Dnm1p-dependent outer membrane fission, resulting in the formation of mitochondrial fragments that are structurally incompetent for fusion.

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Mgm1p is associated with the inner membrane. JSY2519 cells were grown in YPD to log phase and processed for cryoimmunoelectron microscopy using anti-HA. Mitochondrial profiles (m) from JSY2519 cells are shown (A–F). Arrows indicate gold particle labeling and critae decorated by gold particles are indicated (cr). Bars, 0.1 μM.
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Figure 7: Mgm1p is associated with the inner membrane. JSY2519 cells were grown in YPD to log phase and processed for cryoimmunoelectron microscopy using anti-HA. Mitochondrial profiles (m) from JSY2519 cells are shown (A–F). Arrows indicate gold particle labeling and critae decorated by gold particles are indicated (cr). Bars, 0.1 μM.

Mentions: To determine whether Mgm1p is associated with the outer or inner mitochondrial membrane, we examined Mgm1:3XHAp's localization by immunoelectron microscopy using anti-HA antibodies. Immunogold-labeling was performed as described on cryosections of JSY2519 cells (Bleazard et al. 1999). Consistent with data from both indirect immunofluorescence and biochemical analyses, the majority of gold particles were found associated with mitochondrial structures (90%, n = 71; Fig. 7, see m). Further analysis of mitochondrial-associated gold particles indicates that the vast majority were found within the interior of the organelle and, in most cases, clearly associated with the inner membrane (95%, n = 64; Fig. 7, see arrows). This inner membrane association is especially apparent in sections where gold particles are associated with inner membrane folds or cistae (Fig. 7, see cr and arrow). In addition, we did not observe gold particles dispersed throughout mitochondria, unlike the distribution reported for Msp1p, the S. pombe Mgm1p homologue (Pelloquin et al. 1999).


The dynamin-related GTPase, Mgm1p, is an intermembrane space protein required for maintenance of fusion competent mitochondria.

Wong ED, Wagner JA, Gorsich SW, McCaffery JM, Shaw JM, Nunnari J - J. Cell Biol. (2000)

Mgm1p is associated with the inner membrane. JSY2519 cells were grown in YPD to log phase and processed for cryoimmunoelectron microscopy using anti-HA. Mitochondrial profiles (m) from JSY2519 cells are shown (A–F). Arrows indicate gold particle labeling and critae decorated by gold particles are indicated (cr). Bars, 0.1 μM.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2192650&req=5

Figure 7: Mgm1p is associated with the inner membrane. JSY2519 cells were grown in YPD to log phase and processed for cryoimmunoelectron microscopy using anti-HA. Mitochondrial profiles (m) from JSY2519 cells are shown (A–F). Arrows indicate gold particle labeling and critae decorated by gold particles are indicated (cr). Bars, 0.1 μM.
Mentions: To determine whether Mgm1p is associated with the outer or inner mitochondrial membrane, we examined Mgm1:3XHAp's localization by immunoelectron microscopy using anti-HA antibodies. Immunogold-labeling was performed as described on cryosections of JSY2519 cells (Bleazard et al. 1999). Consistent with data from both indirect immunofluorescence and biochemical analyses, the majority of gold particles were found associated with mitochondrial structures (90%, n = 71; Fig. 7, see m). Further analysis of mitochondrial-associated gold particles indicates that the vast majority were found within the interior of the organelle and, in most cases, clearly associated with the inner membrane (95%, n = 64; Fig. 7, see arrows). This inner membrane association is especially apparent in sections where gold particles are associated with inner membrane folds or cistae (Fig. 7, see cr and arrow). In addition, we did not observe gold particles dispersed throughout mitochondria, unlike the distribution reported for Msp1p, the S. pombe Mgm1p homologue (Pelloquin et al. 1999).

Bottom Line: To study the primary function of MGM1, we characterized new temperature sensitive MGM1 alleles.Although Mgm1p was recently reported to localize to the mitochondrial outer membrane, our studies indicate that Mgm1p is localized to the mitochondrial intermembrane space.Based on our localization data and Mgm1p's structural homology to dynamin, we postulate that it functions in inner membrane remodeling events.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular and Cellular Biology, University of California Davis, Davis, California 95616, USA.

ABSTRACT
Mutations in the dynamin-related GTPase, Mgm1p, have been shown to cause mitochondrial aggregation and mitochondrial DNA loss in Saccharomyces cerevisiae cells, but Mgm1p's exact role in mitochondrial maintenance is unclear. To study the primary function of MGM1, we characterized new temperature sensitive MGM1 alleles. Examination of mitochondrial morphology in mgm1 cells indicates that fragmentation of mitochondrial reticuli is the primary phenotype associated with loss of MGM1 function, with secondary aggregation of mitochondrial fragments. This mgm1 phenotype is identical to that observed in cells with a conditional mutation in FZO1, which encodes a transmembrane GTPase required for mitochondrial fusion, raising the possibility that Mgm1p is also required for fusion. Consistent with this idea, mitochondrial fusion is blocked in mgm1 cells during mating, and deletion of DNM1, which encodes a dynamin-related GTPase required for mitochondrial fission, blocks mitochondrial fragmentation in mgm1 cells. However, in contrast to fzo1 cells, deletion of DNM1 in mgm1 cells restores mitochondrial fusion during mating. This last observation indicates that despite the phenotypic similarities observed between mgm1 and fzo1 cells, MGM1 does not play a direct role in mitochondrial fusion. Although Mgm1p was recently reported to localize to the mitochondrial outer membrane, our studies indicate that Mgm1p is localized to the mitochondrial intermembrane space. Based on our localization data and Mgm1p's structural homology to dynamin, we postulate that it functions in inner membrane remodeling events. In this context, the observed mgm1 phenotypes suggest that inner and outer membrane fission is coupled and that loss of MGM1 function may stimulate Dnm1p-dependent outer membrane fission, resulting in the formation of mitochondrial fragments that are structurally incompetent for fusion.

Show MeSH
Related in: MedlinePlus