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First published online 6 February 2007
doi: 10.1242/jcs.03382

Journal of Cell Science 120, 826-837 (2007)
Published by The Company of Biologists 2007
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Research Article

A large complex containing Patched and Smoothened initiates Hedgehog signaling in Drosophila

Sabrina L. Walthall1, Michelle Moses1 and Jamila I. Horabin2,*

1 Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
2 Department of Biomedical Sciences, Florida State University, Tallahassee, FL 32306, USA

* Author for correspondence (e-mail: jamila.horabin{at}med.fsu.edu)

Accepted 21 December 2006

Hedgehog acts as an organizer during development. Its signaling involves the receptor Patched, signal transducer Smoothened and a cytoplasmic complex containing the transcription factor Cubitus interruptus tethered to the Smoothened carboxyl tail. Without Hedgehog, Patched represses Smoothened resulting in proteolysis of Cubitus interruptus to its repressor form. With Hedgehog, Patched repression of Smoothened is relieved and Cubitus interruptus is activated. Sex-lethal, the master switch for sex determination in Drosophila, has been shown to associate with Cubitus interruptus and the cytoplasmic components of the Hedgehog signaling pathway. Additionally, Sex-lethal responds to the presence of Hedgehog in a Patched-dependent manner. The latter prompted us to examine the role of Patched in signaling. We find that Cubitus interruptus, Sex-lethal, Patched and Smoothened co-immunoprecipitate and co-fractionate, suggesting a large complex of both membrane and cytoplasmic components of the Hedgehog pathway. The entire complex is present at the plasma membrane and the association of Patched changes depending on the activation state of the pathway; it also is not female specific. Colocalization analyses suggest that Sex-lethal alters the endocytic cycling of the Hedgehog components and may augment the Hedgehog signal in females by decreasing the proteolytic cleavage of Cubitus interruptus, availing more of it for activation.

Key words: Hedgehog, Sex-lethal, Endocycling, Patched, Drosophila






© The Company of Biologists Ltd 2007