Abstract
The actin cytoskeleton is best known for its role during cellular morphogenesis. However, other evidence suggests that actin is also crucial for the organization and dynamics of membrane organelles such as endosomes and the Golgi complex1,2,3. As in morphogenesis, the Rho family of small GTPases are key mediators of organelle actin-driven events4,5, although it is unclear how these ubiquitously distributed proteins are activated to regulate actin dynamics in an organelle-specific manner. Here we show that the brain-specific Rho-binding protein Citron-N6 is enriched at, and associates with, the Golgi apparatus of hippocampal neurons in culture. Suppression of the whole protein or expression of a mutant form lacking the Rho-binding activity results in dispersion of the Golgi apparatus. In contrast, high intracellular levels induce localized accumulation of RhoA and filamentous actin, protecting the Golgi from the rupture normally produced by actin depolymerization. Biochemical and functional analyses indicate that Citron-N controls actin locally by assembling together the Rho effector ROCK-II and the actin-binding, neuron-specific, protein Profilin-IIa (PIIa). Together with recent data on endosomal dynamics5, our results highlight the importance of organelle-specific Rho modulators for actin-dependent organelle organization and dynamics.
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Acknowledgements
We are grateful to B. Hellias and E. Cassin for the excellent preparation of the primary cultures, to L. Doglio for help with the microinjections and to C. Galvan for help with the cell fractionation experiments. We are also grateful to A. Habermann for excellent technical assistance with the immuno-electron microscopy and to W. Witke for the generous gift of anti-PIIa antibodies. J.S.S. is supported by an FCT/PRAXIS XXI scholarship (Portuguese Ministry of Science and Technology). The financial support of Telethon-Italy to C.G.D. (GP0245Y02) and F.D.C. (GGP02075) is gratefully acknowledged. In addition, C.G.D. and F.D.C. are supported by the EU DIADEM project (QLRT-2000-02392) and by the Jerome Lejeune foundation, respectively.
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Camera, P., Da Silva, J., Griffiths, G. et al. Citron-N is a neuronal Rho-associated protein involved in Golgi organization through actin cytoskeleton regulation. Nat Cell Biol 5, 1071–1078 (2003). https://doi.org/10.1038/ncb1064
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DOI: https://doi.org/10.1038/ncb1064
