Vertebrate Smoothened functions at the primary cilium

The unanticipated involvement of several intraflagellar transport proteins in the mammalian Hedgehog (Hh) pathway has hinted at a functional connection between cilia and Hh signal transduction. Here we show that mammalian Smoothened (Smo), a seven-transmembrane protein essential for Hh signalling, is expressed on the primary cilium. This ciliary expression is regulated by Hh pathway activity; Sonic hedgehog or activating mutations in Smo promote ciliary localization, whereas the Smo antagonist cyclopamine inhibits ciliary localization. The translocation of Smo to primary cilia depends upon a conserved hydrophobic and basic residue sequence homologous to a domain previously shown to be required for the ciliary localization of seven-transmembrane proteins in Caenorhabditis elegans. Mutation of this domain not only prevents ciliary localization but also eliminates Smo activity both in cultured cells and in zebrafish embryos. Thus, Hh-dependent translocation to cilia is essential for Smo activity, suggesting that Smo acts at the primary cilium.

[1]  M. Scott,et al.  Altered localization of Drosophila Smoothened protein activates Hedgehog signal transduction. , 2003, Genes & development.

[2]  Andrew P. McMahon,et al.  Smoothened Mutants Reveal Redundant Roles for Shh and Ihh Signaling Including Regulation of L/R Asymmetry by the Mouse Node , 2001, Cell.

[3]  M. Scott,et al.  Communicating with Hedgehogs , 2005, Nature Reviews Molecular Cell Biology.

[4]  M. Caron,et al.  ß-Arrestin 2 Regulates Zebrafish Development Through the Hedgehog Signaling Pathway , 2004, Science.

[5]  M. Hamon,et al.  Localization of 5-HT6 receptors at the plasma membrane of neuronal cilia in the rat brain , 2000, Brain Research.

[6]  H. L. Stickney,et al.  The zebrafish slow-muscle-omitted gene product is required for Hedgehog signal transduction and the development of slow muscle identity. , 2000, Development.

[7]  P. Beachy,et al.  Teratogen-mediated inhibition of target tissue response to Shh signaling. , 1998, Science.

[8]  D. Wheatley.  Primary cilia in normal and pathological tissues. , 1995, Pathobiology : journal of immunopathology, molecular and cellular biology.

[9]  P. Ingham,et al.  iguana encodes a novel zinc-finger protein with coiled-coil domains essential for Hedgehog signal transduction in the zebrafish embryo. , 2004, Genes & development.

[10]  Jussi Taipale,et al.  Inhibition of Hedgehog signaling by direct binding of cyclopamine to Smoothened. , 2002, Genes & development.

[11]  S. Cohen,et al.  Hedgehog Induces Opposite Changes in Turnover and Subcellular Localization of Patched and Smoothened , 2000, Cell.

[12]  R. Lefkowitz,et al.  Activity-Dependent Internalization of Smoothened Mediated by ß-Arrestin 2 and GRK2 , 2004, Science.

[13]  Maurice J. Kernan,et al.  Intraflagellar Transport Is Required in Drosophila to Differentiate Sensory Cilia but Not Sperm , 2003, Current Biology.

[14]  Aimin Liu,et al.  Mouse intraflagellar transport proteins regulate both the activator and repressor functions of Gli transcription factors , 2005, Development.

[15]  H. Strutt,et al.  Functional domains and sub-cellular distribution of the Hedgehog transducing protein Smoothened in Drosophila , 2004, Mechanisms of Development.

[16]  M. Scott,et al.  Effects of oncogenic mutations in Smoothened and Patched can be reversed by cyclopamine , 2000, Nature.

[17]  Cori Bargmann,et al.  Polarized Dendritic Transport and the AP-1 μ1 Clathrin Adaptor UNC-101 Localize Odorant Receptors to Olfactory Cilia , 2001, Neuron.

[18]  S. Schulz,et al.  Selective targeting of somatostatin receptor 3 to neuronal cilia , 1999, Neuroscience.

[19]  J. Cunnick,et al.  Visual transduction in rod outer segments. , 1990, Cellular signalling.

[20]  R. Lefkowitz,et al.  Beta-adrenergic receptor kinase-2 and beta-arrestin-2 as mediators of odorant-induced desensitization. , 1993, Science.

[21]  Cornelia I Bargmann,et al.  Odorant Receptor Localization to Olfactory Cilia Is Mediated by ODR-4, a Novel Membrane-Associated Protein , 1998, Cell.

[22]  J. Gruenberg,et al.  Sonic Hedgehog Induces the Segregation of Patched and Smoothened in Endosomes , 2002, Current Biology.

[23]  L. Goldstein,et al.  Kinesin-II Is Required for Axonal Transport of Choline Acetyltransferase in Drosophila , 1999, The Journal of cell biology.

[24]  S. Burgess,et al.  Analysis of the zebrafish smoothened mutant reveals conserved and divergent functions of hedgehog activity. , 2001, Development.

[25]  A. Amores,et al.  Zebrafish smoothened functions in ventral neural tube specification and axon tract formation. , 2001, Development.

[26]  J. Salisbury.  Primary Cilia: Putting Sensors Together , 2004, Current Biology.

[27]  T. Jessell,et al.  Floor plate and motor neuron induction by vhh-1, a vertebrate homolog of hedgehog expressed by the notochord , 1994, Cell.

[28]  Lee Niswander,et al.  Hedgehog signalling in the mouse requires intraflagellar transport proteins , 2003, Nature.

[29]  J. Carson,et al.  Morphogenesis of the murine node and notochordal plate , 1994, Developmental dynamics : an official publication of the American Association of Anatomists.