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Mitofusins Mfn1 and Mfn2 coordinately regulate mitochondrial fusion and are essential for embryonic development.

Chen H, Detmer SA, Ewald AJ, Griffin EE, Fraser SE, Chan DC - J. Cell Biol. (2003)

Bottom Line: We find that mice deficient in either Mfn1 or Mfn2 die in midgestation.However, whereas Mfn2 mutant embryos have a specific and severe disruption of the placental trophoblast giant cell layer, Mfn1-deficient giant cells are normal.Strikingly, a subset of mitochondria in mutant cells lose membrane potential.

View Article: PubMed Central - PubMed

Affiliation: Division of Biology, Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.

ABSTRACT
Mitochondrial morphology is determined by a dynamic equilibrium between organelle fusion and fission, but the significance of these processes in vertebrates is unknown. The mitofusins, Mfn1 and Mfn2, have been shown to affect mitochondrial morphology when overexpressed. We find that mice deficient in either Mfn1 or Mfn2 die in midgestation. However, whereas Mfn2 mutant embryos have a specific and severe disruption of the placental trophoblast giant cell layer, Mfn1-deficient giant cells are normal. Embryonic fibroblasts lacking Mfn1 or Mfn2 display distinct types of fragmented mitochondria, a phenotype we determine to be due to a severe reduction in mitochondrial fusion. Moreover, we find that Mfn1 and Mfn2 form homotypic and heterotypic complexes and show, by rescue of mutant cells, that the homotypic complexes are functional for fusion. We conclude that Mfn1 and Mfn2 have both redundant and distinct functions and act in three separate molecular complexes to promote mitochondrial fusion. Strikingly, a subset of mitochondria in mutant cells lose membrane potential. Therefore, mitochondrial fusion is essential for embryonic development, and by enabling cooperation between mitochondria, has protective effects on the mitochondrial population.

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Immunoprecipitation of Mfn complexes. (A) Wild-type cells were infected with retroviruses expressing Myc- or HA-tagged Mfn1 (labeled 1), Mfn2 (labeled 2), or Drp1 (labeled D) as indicated on top. Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) were analyzed by Western blotting against the HA epitope. The total cell lysate samples contain one sixth cell equivalents compared with the immunoprecipitates. (B) Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) from Mfn1 or Mfn2 mutant cells (indicated on top) were used in an analysis similar to A.
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fig9: Immunoprecipitation of Mfn complexes. (A) Wild-type cells were infected with retroviruses expressing Myc- or HA-tagged Mfn1 (labeled 1), Mfn2 (labeled 2), or Drp1 (labeled D) as indicated on top. Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) were analyzed by Western blotting against the HA epitope. The total cell lysate samples contain one sixth cell equivalents compared with the immunoprecipitates. (B) Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) from Mfn1 or Mfn2 mutant cells (indicated on top) were used in an analysis similar to A.

Mentions: Because both Mfn1 and Mfn2 are essential for normal mitochondrial morphology, it is possible that they act in concert to promote mitochondrial fusion. To explore this idea, we tested whether these two proteins form a complex when expressed in wild-type MEF cells (Fig. 9 A). Our results revealed three types of intermolecular interactions. First, both Mfn1 and Mfn2 can form homotypic complexes. Mfn1-HA is coimmunoprecipitated with Mfn1-Myc; analogously, Mfn2-HA is coimmunoprecipitated with Mfn2-Myc. Second, Mfn1 and Mfn2 form heterotypic complexes. Mfn2-HA is coimmunoprecipitated with Mfn1-Myc; conversely, Mfn1-HA is coimmunoprecipitated with Mfn2-Myc. All of these interactions are specific because no HA-tagged protein is found in the anti-Myc immunoprecipitate when the Myc-tagged protein is omitted (unpublished data) or when a control Drp1-Myc is used.


Mitofusins Mfn1 and Mfn2 coordinately regulate mitochondrial fusion and are essential for embryonic development.

Chen H, Detmer SA, Ewald AJ, Griffin EE, Fraser SE, Chan DC - J. Cell Biol. (2003)

Immunoprecipitation of Mfn complexes. (A) Wild-type cells were infected with retroviruses expressing Myc- or HA-tagged Mfn1 (labeled 1), Mfn2 (labeled 2), or Drp1 (labeled D) as indicated on top. Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) were analyzed by Western blotting against the HA epitope. The total cell lysate samples contain one sixth cell equivalents compared with the immunoprecipitates. (B) Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) from Mfn1 or Mfn2 mutant cells (indicated on top) were used in an analysis similar to A.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172648&req=5

fig9: Immunoprecipitation of Mfn complexes. (A) Wild-type cells were infected with retroviruses expressing Myc- or HA-tagged Mfn1 (labeled 1), Mfn2 (labeled 2), or Drp1 (labeled D) as indicated on top. Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) were analyzed by Western blotting against the HA epitope. The total cell lysate samples contain one sixth cell equivalents compared with the immunoprecipitates. (B) Anti-Myc immunoprecipitates (top) and total cell lysates (bottom) from Mfn1 or Mfn2 mutant cells (indicated on top) were used in an analysis similar to A.
Mentions: Because both Mfn1 and Mfn2 are essential for normal mitochondrial morphology, it is possible that they act in concert to promote mitochondrial fusion. To explore this idea, we tested whether these two proteins form a complex when expressed in wild-type MEF cells (Fig. 9 A). Our results revealed three types of intermolecular interactions. First, both Mfn1 and Mfn2 can form homotypic complexes. Mfn1-HA is coimmunoprecipitated with Mfn1-Myc; analogously, Mfn2-HA is coimmunoprecipitated with Mfn2-Myc. Second, Mfn1 and Mfn2 form heterotypic complexes. Mfn2-HA is coimmunoprecipitated with Mfn1-Myc; conversely, Mfn1-HA is coimmunoprecipitated with Mfn2-Myc. All of these interactions are specific because no HA-tagged protein is found in the anti-Myc immunoprecipitate when the Myc-tagged protein is omitted (unpublished data) or when a control Drp1-Myc is used.

Bottom Line: We find that mice deficient in either Mfn1 or Mfn2 die in midgestation.However, whereas Mfn2 mutant embryos have a specific and severe disruption of the placental trophoblast giant cell layer, Mfn1-deficient giant cells are normal.Strikingly, a subset of mitochondria in mutant cells lose membrane potential.

View Article: PubMed Central - PubMed

Affiliation: Division of Biology, Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.

ABSTRACT
Mitochondrial morphology is determined by a dynamic equilibrium between organelle fusion and fission, but the significance of these processes in vertebrates is unknown. The mitofusins, Mfn1 and Mfn2, have been shown to affect mitochondrial morphology when overexpressed. We find that mice deficient in either Mfn1 or Mfn2 die in midgestation. However, whereas Mfn2 mutant embryos have a specific and severe disruption of the placental trophoblast giant cell layer, Mfn1-deficient giant cells are normal. Embryonic fibroblasts lacking Mfn1 or Mfn2 display distinct types of fragmented mitochondria, a phenotype we determine to be due to a severe reduction in mitochondrial fusion. Moreover, we find that Mfn1 and Mfn2 form homotypic and heterotypic complexes and show, by rescue of mutant cells, that the homotypic complexes are functional for fusion. We conclude that Mfn1 and Mfn2 have both redundant and distinct functions and act in three separate molecular complexes to promote mitochondrial fusion. Strikingly, a subset of mitochondria in mutant cells lose membrane potential. Therefore, mitochondrial fusion is essential for embryonic development, and by enabling cooperation between mitochondria, has protective effects on the mitochondrial population.

Show MeSH