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.
Corbit
Kevin C
KC
Developmental and Stem Cell Biology Program, University of California, San Francisco, California 94143, USA.
Aanstad
Pia
P
Singla
Veena
V
Norman
Andrew R
AR
Stainier
Didier Y R
DY
Reiter
Jeremy F
JF
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000737:chemistry; D002460:Cell Line; D002923:Cilia / Q000187:drug effects / Q000378:metabolism*; D004285:Dogs; D029721:Drosophila Proteins / Q000737:chemistry; D004622:Embryo, Mammalian / Q000378:metabolism; D004625:Embryo, Nonmammalian; D017930:Genes, Reporter / Q000235:genetics; D051379:Mice; D009154:Mutation / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000072086:Smoothened Receptor; D014704:Veratrum Alkaloids / Q000494:pharmacology; D014714:Vertebrates / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology / Q000235:genetics / Q000378:metabolism
D029721:Drosophila Proteins; D021382:Protein Sorting Signals; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; C491022:Smo protein, mouse; D000072086:Smoothened Receptor; D014704:Veratrum Alkaloids; C100664:smo protein, Drosophila; C000541:cyclopamine