Letter | Published:

GGGGCC repeat expansion in C9orf72 compromises nucleocytoplasmic transport

Nature volume 525, pages 129133 (03 September 2015) | Download Citation

Abstract

The GGGGCC (G4C2) repeat expansion in a noncoding region of C9orf72 is the most common cause of sporadic and familial forms of amyotrophic lateral sclerosis and frontotemporal dementia1,2. The basis for pathogenesis is unknown. To elucidate the consequences of G4C2 repeat expansion in a tractable genetic system, we generated transgenic fly lines expressing 8, 28 or 58 G4C2-repeat-containing transcripts that do not have a translation start site (AUG) but contain an open-reading frame for green fluorescent protein to detect repeat-associated non-AUG (RAN) translation. We show that these transgenic animals display dosage-dependent, repeat-length-dependent degeneration in neuronal tissues and RAN translation of dipeptide repeat (DPR) proteins, as observed in patients with C9orf72-related disease. This model was used in a large-scale, unbiased genetic screen, ultimately leading to the identification of 18 genetic modifiers that encode components of the nuclear pore complex (NPC), as well as the machinery that coordinates the export of nuclear RNA and the import of nuclear proteins. Consistent with these results, we found morphological abnormalities in the architecture of the nuclear envelope in cells expressing expanded G4C2 repeats in vitro and in vivo. Moreover, we identified a substantial defect in RNA export resulting in retention of RNA in the nuclei of Drosophila cells expressing expanded G4C2 repeats and also in mammalian cells, including aged induced pluripotent stem-cell-derived neurons from patients with C9orf72-related disease. These studies show that a primary consequence of G4C2 repeat expansion is the compromise of nucleocytoplasmic transport through the nuclear pore, revealing a novel mechanism of neurodegeneration.

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Acknowledgements

We thank the Bloomington Drosophila Stock Center, the VDRC Stock Center, K. McKim and E. Baehrecke for fly lines, V. Budnik for Lamin C antibody, as well as the Cell and Tissue Imaging Center at St Jude Children’s Research Hospital and the University of Massachusetts Medical School Confocal Core for assistance. This work was supported by grants from Target ALS, The Packard Center for ALS Research at the Johns Hopkins University, and the ALS Association to F.-B.G., and J.P.T., and ALS Therapy Alliance, NIH (N079725) to F.-B.G., NIH (NS079725 and AG019724) to B.L.M., and the American-Lebanese-Syrian Associated Charities to J.P.T.

Author information

Author notes

    • Brian D. Freibaum
    •  & Yubing Lu

    These authors contributed equally to this work.

Affiliations

  1. Department of Cell and Molecular Biology, St Jude Children’s Research Hospital, Memphis, Tennessee 38105, USA

    • Brian D. Freibaum
    • , Nam Chul Kim
    • , Kyung-Ha Lee
    • , Nisha Badders
    • , Marc Valentine
    •  & Hong Joo Kim
  2. Department of Neurology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA

    • Yubing Lu
    • , Rodrigo Lopez-Gonzalez
    • , Sandra Almeida
    •  & Fen-Biao Gao
  3. Memory and Aging Center, Department of Neurology, University of California San Francisco, San Francisco, California 94158, USA

    • Bruce L. Miller
  4. Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA

    • Philip C. Wong
  5. Department of Neuroscience, Mayo Clinic Florida, Jacksonville, Florida 32224, USA

    • Leonard Petrucelli
  6. Howard Hughes Medical Institute, Department of Cell and Molecular Biology, St Jude Children’s Research Hospital, Memphis, Tennessee 38105, USA

    • J. Paul Taylor

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Contributions

F.-B.G. and J.P.T. conceived and supervised the project. B.D.F., Y.L., H.J.K., F.-B.G. and J.P.T. wrote the manuscript. B.D.F. and Y.L. performed the genetic screen and validation. B.D.F., Y.L., N.C.K., N.B. and K.-H.L. characterized Drosophila phenotypes and performed the assays characterizing RNA export in human cells. S.A. established human fibroblast cell lines, R.L.-G. generated some iPSC lines; S.A. and R.L.-G. performed cortical neuron differentiation. M.V. and B.D.F. conducted FISH experiments. L.P., B.L.M. and P.C.W. provided key reagents.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Fen-Biao Gao or J. Paul Taylor.

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DOI

https://doi.org/10.1038/nature14974

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