Abstract
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.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Motifs
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Amino Acid Sequence
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Animals
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Caenorhabditis elegans / chemistry
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Cell Line
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Cilia / drug effects
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Cilia / metabolism*
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Dogs
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Drosophila Proteins / chemistry
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Embryo, Mammalian / metabolism
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Embryo, Nonmammalian
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Genes, Reporter / genetics
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Mice
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Mutation / genetics
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Protein Sorting Signals / genetics
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Protein Sorting Signals / physiology
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Receptors, G-Protein-Coupled / antagonists & inhibitors
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Receptors, G-Protein-Coupled / chemistry
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Receptors, G-Protein-Coupled / genetics
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Receptors, G-Protein-Coupled / metabolism*
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Signal Transduction
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Smoothened Receptor
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Veratrum Alkaloids / pharmacology
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Vertebrates / embryology
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Vertebrates / genetics
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Vertebrates / metabolism*
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Zebrafish / embryology
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Zebrafish / genetics
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Zebrafish / metabolism
Substances
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Drosophila Proteins
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Protein Sorting Signals
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RNA, Messenger
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Receptors, G-Protein-Coupled
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Smo protein, mouse
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Smoothened Receptor
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Veratrum Alkaloids
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smo protein, Drosophila
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cyclopamine