Identification of a novel hedgehog receptor from a systematic survey of the Drosophila genome.
- Resource Type
- Theses
- Authors
- Yao, Shenqin
- Source
- Dissertation Abstracts International; Dissertation Abstract International; 67-04B.
- Subject
- Biology, Molecular
Biology, Genetics
- Language
- English
Summary: Despite the importance of Hedgehog (Hh) signaling in normal development and tumorigenesis, the molecular mechanism of Hh signal reception is not well understood. Here we characterize a conserved Hh receptor component ihog (i&barbelow;nterference hedgehog) identified by RNAi in Drosophila cultured cells. ihog mutations lead to defects characteristic of loss of Hh signaling in embryos and imaginal discs. Epistasis studies in cultured cells and Drosophila embryos further map Ihog functions upstream of or at the level of Patched (Ptc), a negative receptor component. We also demonstrate that Ihog interacts directly with Hh in vitro via the first of two fibronectin type III (FNIII) domains in the extracellular region. The second FNIII domain is also required for in vivo signaling activity of the Ihog protein and for Ihog-enhanced binding of Hh protein to cells co-expressing Ptc. We also show that Hh can form an in vitro complex with the Ihog FNIII domains (FN1-2) in the presence of heparin. The crystal structure of the Hh:Ihog FN1-2 complex reveals that two Hh proteins interact with an Ihog FN 1-2 dimer via the first FNIII domains (FN1) to form a 2:2 complex. Heparin facilitates both Ihog dimerization and interactions between Ihog and Hh. Site-directed mutagenesis combined with cell-based signaling and Hh binding assays provide evidence that the predicted Ihog/Hh interface and a heparin binding site in FN1 are important for Ihog function. Other members of the Ihog family, including one Drosophila and two mammalian proteins, also interact with Hh ligands via a specific FNIII domain. We thus identify an evolutionarily conserved family of Hh receptors.