Limits...
Mmm1p, a mitochondrial outer membrane protein, is connected to mitochondrial DNA (mtDNA) nucleoids and required for mtDNA stability.

Hobbs AE, Srinivasan M, McCaffery JM, Jensen RE - J. Cell Biol. (2001)

Bottom Line: We found that Mmm1p-GFP is located in small, punctate structures on the mitochondrial outer membrane, adjacent to a subset of matrix-localized mitochondrial DNA nucleoids.We also found that the temperature-sensitive mmm1-1 mutant was defective in transmission of mitochondrial DNA to daughter cells immediately after the shift to restrictive temperature.Moreover, we found that mitochondrial inner membrane structure is dramatically disorganized in mmm1 disruption strains.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.

ABSTRACT
In the yeast Saccharomyces cerevisiae, mitochondria form a branched, tubular reticulum in the periphery of the cell. Mmm1p is required to maintain normal mitochondrial shape and in mmm1 mutants mitochondria form large, spherical organelles. To further explore Mmm1p function, we examined the localization of a Mmm1p-green fluorescent protein (GFP) fusion in living cells. We found that Mmm1p-GFP is located in small, punctate structures on the mitochondrial outer membrane, adjacent to a subset of matrix-localized mitochondrial DNA nucleoids. We also found that the temperature-sensitive mmm1-1 mutant was defective in transmission of mitochondrial DNA to daughter cells immediately after the shift to restrictive temperature. Normal mitochondrial nucleoid structure also collapsed at the nonpermissive temperature with similar kinetics. Moreover, we found that mitochondrial inner membrane structure is dramatically disorganized in mmm1 disruption strains. We propose that Mmm1p is part of a connection between the mitochondrial outer and inner membranes, anchoring mitochondrial DNA nucleoids in the matrix.

Show MeSH

Related in: MedlinePlus

mtDNA nucleoids aggregate in mmm1-1 cells at the restrictive temperature. Wild-type and mmm1-1 cells were grown at 24°C, shifted to 37°C for the indicated times, and stained with DAPI. Cells were examined by fluorescence microscopy and representative fluorescent (left) and DIC (right) images are shown.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2199622&req=5

Figure 6: mtDNA nucleoids aggregate in mmm1-1 cells at the restrictive temperature. Wild-type and mmm1-1 cells were grown at 24°C, shifted to 37°C for the indicated times, and stained with DAPI. Cells were examined by fluorescence microscopy and representative fluorescent (left) and DIC (right) images are shown.

Mentions: Since Mmm1p-GFP colocalizes with mtDNA nucleoids, we asked whether Mmm1p function is required for the normal distribution of nucleoids. We used fluorescence imaging to compare wild-type and mmm1-1 cells after the shift to 37°C. DAPI staining of 50 total cells revealed that, before the temperature shift, both wild-type and mmm1-1 cells contained similar numbers (Fig. 5) and sizes (Fig. 6) of mtDNA nucleoids. Most wild-type and mmm1-1 cells contained ∼6–10 separate, mtDNA-containing dots. In wild-type cells, the number of separate nucleoids immediately increased after the shift to the nonpermissive temperature, and then remained constant (Fig. 5). Although the reason that nucleoids rapidly increased in wild-type cells at 37°C is not clear, it is known that number of nucleoids is affected by the growth media and other nutritional factors (MacAlpine et al. 2000). Regardless, the number and size of individual mtDNA nucleoids did not change in wild-type cells at later times at 37°C (Fig. 5 and Fig. 6). In mmm1-1 cells, however, both the number and size of separate nucleoids changed at 37°C. Within 60 min, mmm1-1 cells contained fewer nucleoids that stained more brightly with DAPI, and nucleoids continued to aggregate at later time points (Fig. 5). The number of separate nucleoids steadily decreased at 37°C. After 6 h, some cells contained a single mtDNA-containing structure, while other cells did not contain any mtDNA. At later times, most cells had lost all mtDNA.


Mmm1p, a mitochondrial outer membrane protein, is connected to mitochondrial DNA (mtDNA) nucleoids and required for mtDNA stability.

Hobbs AE, Srinivasan M, McCaffery JM, Jensen RE - J. Cell Biol. (2001)

mtDNA nucleoids aggregate in mmm1-1 cells at the restrictive temperature. Wild-type and mmm1-1 cells were grown at 24°C, shifted to 37°C for the indicated times, and stained with DAPI. Cells were examined by fluorescence microscopy and representative fluorescent (left) and DIC (right) images are shown.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199622&req=5

Figure 6: mtDNA nucleoids aggregate in mmm1-1 cells at the restrictive temperature. Wild-type and mmm1-1 cells were grown at 24°C, shifted to 37°C for the indicated times, and stained with DAPI. Cells were examined by fluorescence microscopy and representative fluorescent (left) and DIC (right) images are shown.
Mentions: Since Mmm1p-GFP colocalizes with mtDNA nucleoids, we asked whether Mmm1p function is required for the normal distribution of nucleoids. We used fluorescence imaging to compare wild-type and mmm1-1 cells after the shift to 37°C. DAPI staining of 50 total cells revealed that, before the temperature shift, both wild-type and mmm1-1 cells contained similar numbers (Fig. 5) and sizes (Fig. 6) of mtDNA nucleoids. Most wild-type and mmm1-1 cells contained ∼6–10 separate, mtDNA-containing dots. In wild-type cells, the number of separate nucleoids immediately increased after the shift to the nonpermissive temperature, and then remained constant (Fig. 5). Although the reason that nucleoids rapidly increased in wild-type cells at 37°C is not clear, it is known that number of nucleoids is affected by the growth media and other nutritional factors (MacAlpine et al. 2000). Regardless, the number and size of individual mtDNA nucleoids did not change in wild-type cells at later times at 37°C (Fig. 5 and Fig. 6). In mmm1-1 cells, however, both the number and size of separate nucleoids changed at 37°C. Within 60 min, mmm1-1 cells contained fewer nucleoids that stained more brightly with DAPI, and nucleoids continued to aggregate at later time points (Fig. 5). The number of separate nucleoids steadily decreased at 37°C. After 6 h, some cells contained a single mtDNA-containing structure, while other cells did not contain any mtDNA. At later times, most cells had lost all mtDNA.

Bottom Line: We found that Mmm1p-GFP is located in small, punctate structures on the mitochondrial outer membrane, adjacent to a subset of matrix-localized mitochondrial DNA nucleoids.We also found that the temperature-sensitive mmm1-1 mutant was defective in transmission of mitochondrial DNA to daughter cells immediately after the shift to restrictive temperature.Moreover, we found that mitochondrial inner membrane structure is dramatically disorganized in mmm1 disruption strains.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.

ABSTRACT
In the yeast Saccharomyces cerevisiae, mitochondria form a branched, tubular reticulum in the periphery of the cell. Mmm1p is required to maintain normal mitochondrial shape and in mmm1 mutants mitochondria form large, spherical organelles. To further explore Mmm1p function, we examined the localization of a Mmm1p-green fluorescent protein (GFP) fusion in living cells. We found that Mmm1p-GFP is located in small, punctate structures on the mitochondrial outer membrane, adjacent to a subset of matrix-localized mitochondrial DNA nucleoids. We also found that the temperature-sensitive mmm1-1 mutant was defective in transmission of mitochondrial DNA to daughter cells immediately after the shift to restrictive temperature. Normal mitochondrial nucleoid structure also collapsed at the nonpermissive temperature with similar kinetics. Moreover, we found that mitochondrial inner membrane structure is dramatically disorganized in mmm1 disruption strains. We propose that Mmm1p is part of a connection between the mitochondrial outer and inner membranes, anchoring mitochondrial DNA nucleoids in the matrix.

Show MeSH
Related in: MedlinePlus