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Role of Bax and Bak in mitochondrial morphogenesis

Nature volume 443, pages 658662 (12 October 2006) | Download Citation



Bcl-2 family proteins are potent regulators of programmed cell death. Although their intracellular localization to mitochondria and the endoplasmic reticulum has focused research on these organelles, how they function remains unknown. Two members of the Bcl-2 family, Bax and Bak, change intracellular location early in the promotion of apoptosis to concentrate in focal clusters at sites of mitochondrial division. Here we report that in healthy cells Bax or Bak is required for normal fusion of mitochondria into elongated tubules. Bax seems to induce mitochondrial fusion by activating assembly of the large GTPase Mfn2 and changing its submitochondrial distribution and membrane mobility—properties that correlate with different GTP-bound states of Mfn2. Our results show that Bax and Bak regulate mitochondrial dynamics in healthy cells and indicate that Bcl-2 family members may also regulate apoptosis through organelle morphogenesis machineries.

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We thank N. Swarup for help in the early stages of this work; C. Thompson, J. Lum and T. Lindsten for Bax/Bak DKO bone marrow cells, Bak-transfected DKO cells and DKO primary MEFs; E. White, S. Korsmeyer and D. Chan for Bax/Bak DKO BMK cells, Bax/Bak DKO MEFs and Mfn KO MEFs, respectively; B. Vogelstein for HCT116 Bax-/- cells, J. Norris for DU145 cells, V. Goldmacher for vMIA HeLa cells, H. McBride for antibodies to Mfn2 and mutant Mfn2 constructs; P. Hajek and G. Attardi for antibodies to Mfn2; A. Antignani, A. Neutzner, B. Fell, S.-W. Ryu and S. Smith for technical assistance; and C. Smith for assistance with confocal microscopy and data analysis and for reading the manuscript. This work was supported by the Intramural Research Program of the NIH, National Institute of Neurological Disorders and Stroke. Author Contributions M.K., K.N. and R.Y. contributed to the conception, interpretation, execution and presentation of the experiments; S-Y.J. contributed to the RNAi experiments; M.C. participated in FRAP experiments and data analysis.

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Author notes

    • Mariusz Karbowski
    •  & Seon-Yong Jeong

    †Present addresses: University of Maryland Biotechnology Institute, Medical Biotechnology Center, UMBI Building, 725 West Lombard Street, Baltimore, Maryland 21201, USA (M.K.); Department of Medical Genetics, School of Medicine, Ajou University, Suwon 443-721, Korea (S.-Y.J.)

    • Mariusz Karbowski
    •  & Kristi L. Norris

    *These authors contributed equally to this work


  1. Biochemistry Section, SNB, NINDS, NIH, Bethesda, Maryland 20892, USA

    • Mariusz Karbowski
    • , Kristi L. Norris
    • , Megan M. Cleland
    • , Seon-Yong Jeong
    •  & Richard J. Youle


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Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Corresponding authors

Correspondence to Mariusz Karbowski or Richard J. Youle.

Supplementary information

Word documents

  1. 1.

    Supplementary Notes

    This file contains Supplementary Methods and Supplementary Figure Legends

Image files

  1. 1.

    Supplementary Figure 1

    Quantification of mitochondrial morphology with and without Bax/Bak expression in baby mouse kidney cells (BMK) and primary mouse embryonic fibroblasts (MEFs).

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    Supplementary Figure 2

    Development and mitochondrial phenotype of Bax and Bak double RNAi cells

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    Supplementary Figure 3

    Viral mitochondria-associated inhibitor of apoptosis (vMIA) interacts with both Bax and Bak and inhibits apoptosis induced by Bak-overexpression

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    Supplementary Figure 4

    Certain Bcl-2 family members other than Bax do not reverse vMIA-induced mitochondrial fragmentation

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    Supplementary Figure 5

    Blocking fission does not reverse fragmentation induced by vMIA expression or loss of Bax/Bak

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    Supplementary Figure 6

    vMIA blocks mitochondrial fusion

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    Supplementary Figure 7

    Drp1 RNAi effect on mitochondria in Bax/Bak DKO MEFs

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    Supplementary Figure 8

    Expression and sub-cellular distribution of mitochondrial fusion and fission proteins in 129/CD1 WT and 129/CD1 Bax/Bak DKO MEFs

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    Supplementary Figure 9

    Quantification of Mfn2-YFP sub-mitochondrial localization in WT and Bax/Bak DKO MEFs

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    Supplementary Figure 10

    FRAP of mitochondrial outer membrane-associated proteins in Bax/Bak DKO MEFs

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    Supplementary Figure 11a-d

    Sub-mitochondrial distribution of YFP chimeras of several Mfn2 mutants.

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    Supplementary Figure 11e-h

    Sub-mitochondrial distribution of YFP chimeras of several Mfn2 mutants.

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    Supplementary Figure 12

    Opa1 complex formation is not altered in WT and Bax/Bak DKO MEFs

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    Supplementary Figure 13

    Gel Filtration analysis of Mfn2 complex formation

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    Supplementary Figure 14

    Mitochondrial membrane potential (m) and ATP levels in WT and Bax/Bak DKO MEFs

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