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ER network formation requires a balance of the dynamin-like GTPase Sey1p and the Lunapark family member Lnp1p

Nature Cell Biology volume 14, pages 707–716 (2012)Cite this article

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Abstract

Although studies on endoplasmic reticulum (ER) structure and dynamics have focused on the ER tubule-forming proteins (reticulons and DP1/Yop1p) and the tubule fusion protein atlastin, nothing is known about the proteins and processes that act to counterbalance this machinery. Here we show that Lnp1p, a member of the conserved Lunapark family, plays a role in ER network formation. Lnp1p binds to the reticulons and Yop1p and resides at ER tubule junctions in both yeast and mammalian cells. In the yeast Saccharomyces cerevisiae, the interaction of Lnp1p with the reticulon protein, Rtn1p, and the localization of Lnp1p to ER junctions are regulated by Sey1p, the yeast orthologue of atlastin. We propose that Lnp1p and Sey1p act antagonistically to balance polygonal network formation. In support of this proposal, we show that the collapsed, densely reticulated ER network in lnp1 Δ cells is partially restored when the GTPase activity of Sey1p is abrogated.

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Figure 1: Cortical ER morphology is abnormal in the lnp1 mutant.
Figure 2: Lnp1p resides at three-way junctions.
Figure 3: The cortical ER is highly reticulated in the lnp1 Δ mutant.
Figure 4: Lnp1p acts synergistically with the reticulons and Yop1p, but antagonistically with Sey1p.
Figure 5: The GTPase activity of Sey1p retains Lnp1p at three-way junctions.
Figure 6: Sey1p regulates the interaction of Lnp1p with Rtn1p.
Figure 7: The sey1 Δ mutant exhibits a delay in cortical ER fusion that is not suppressed by the loss of Lnp1p.
Figure 8: The sey1 Δ mutant exhibits a defect in nuclear fusion that is not suppressed by the loss of Lnp1p.

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Acknowledgements

We thank G. Voeltz (Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, USA) for plasmids. We also thank Y. Jones in the Electron Microscopy Facility in the Department of Cellular and Molecular Medicine at the University of California at San Diego, USA, headed by M. Farquhar, for the preparation of electron microscopy samples, and we acknowledge use of the UCSD Neuroscience Microscopy Facility funded by grant P30 NS047101. This work was supported by a grant from the National Institutes of Health (GM073892) and the Howard Hughes Medical Institute. Salary support for S.C. and S.F-N. was provided by the Howard Hughes Medical Institute.

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Authors and Affiliations

  1. Department of Cellular and Molecular Medicine, George Palade Labs, University of California at San Diego, La Jolla, California 92093-0668, USA

    Shuliang Chen, Peter Novick & Susan Ferro-Novick

  2. Howard Hughes Medical Institute, George Palade Labs, University of California at San Diego, La Jolla, California 92093-0668, USA

    Shuliang Chen & Susan Ferro-Novick

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  1. Shuliang Chen
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S.F-N. and P.N. conceived the idea for the screen. S.F-N., P.N. and S.C. designed the experiments, analysed the data and wrote the manuscript. S.C. performed the research.

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Correspondence to Peter Novick or Susan Ferro-Novick.

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The authors declare no competing financial interests.

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Chen, S., Novick, P. & Ferro-Novick, S. ER network formation requires a balance of the dynamin-like GTPase Sey1p and the Lunapark family member Lnp1p. Nat Cell Biol 14, 707–716 (2012). https://doi.org/10.1038/ncb2523

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