title: Ihog and Boi elicit Hh signaling via Ptc but do not aid Ptc in sequestering the Hh ligand.
abstract: Hedgehog (Hh) proteins are secreted molecules essential for tissue development in vertebrates and invertebrates. Hh reception via the 12-pass transmembrane protein Patched (Ptc) elicits intracellular signaling through Smoothened (Smo). Hh binding to Ptc is also proposed to sequester the ligand, limiting its spatial range of activity. In Drosophila, Interference hedgehog (Ihog) and Brother of ihog (Boi) are two conserved and redundant transmembrane proteins that are essential for Hh pathway activation. How Ihog and Boi activate signaling in response to Hh remains unknown; each can bind both Hh and Ptc and so it has been proposed that they are essential for both Hh reception and sequestration. Using genetic epistasis we established here that Ihog and Boi, and their orthologs in mice, act upstream or at the level of Ptc to allow Hh signal transduction. In the Drosophila developing wing model we found that it is through Hh pathway activation that Ihog and Boi maintain the boundary between the anterior and posterior compartments. We dissociated the contributions of Ptc from those of Ihog/Boi and, surprisingly, found that cells expressing Ptc can retain and sequester the Hh ligand without Ihog and Boi, but that Ihog and Boi cannot do so without Ptc. Together, these results reinforce the central role for Ptc in Hh binding in vivo and demonstrate that, although Ihog and Boi are dispensable for Hh sequestration, they are essential for pathway activation because they allow Hh to inhibit Ptc and thereby relieve its repression of Smo.
authors.affiliation: McGill Centre for Research in Neuroscience and the McGill University Health Centre Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4 Molecular Biology of Neural Development, Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada H2W 1R7 Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada H3A 1A3.
authors.forename: Darius
authors.initials: D
authors.lastname: Camp
authors.affiliation: McGill Centre for Research in Neuroscience and the McGill University Health Centre Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4.
authors.forename: Billy
authors.initials: B
authors.lastname: Haitian He
authors.affiliation: McGill Centre for Research in Neuroscience and the McGill University Health Centre Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4.
authors.forename: Sally
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Irene W
authors.initials: IW
authors.lastname: Althaus
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, MI 48109, USA Medical Scientist Training Program, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Holtz
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA benallen@umich.edu Frederic.Charron@ircm.qc.ca don.vanmeyel@mcgill.ca.
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Allen
authors.affiliation: Molecular Biology of Neural Development, Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada H2W 1R7 Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada H3A 1A3 Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada H3A 2B4 Program in Neuroengineering, McGill University, Montreal, Quebec, Canada H3A 2K6 Department of Medicine, University of Montreal, Montreal, Quebec, Canada H3T 1J4 Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada H3A 0C7 Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1 benallen@umich.edu Frederic.Charron@ircm.qc.ca don.vanmeyel@mcgill.ca.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Charron
authors.affiliation: McGill Centre for Research in Neuroscience and the McGill University Health Centre Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4 Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada H3A 1A3 Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada H3A 2B4 Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1 benallen@umich.edu Frederic.Charron@ircm.qc.ca don.vanmeyel@mcgill.ca.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: van Meyel
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D029721:Drosophila Proteins / Q000502:physiology*; D004331:Drosophila melanogaster / Q000196:embryology; D004843:Epistasis, Genetic; D008024:Ligands; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000502:physiology*; D011995:Recombination, Genetic; D015398:Signal Transduction; D013116:Spinal Cord / Q000196:embryology; D014921:Wings, Animal / Q000196:embryology
chemical_list: C555140:Boi protein, Drosophila; D002352:Carrier Proteins; D029721:Drosophila Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; C000606240:Ptch1 protein, mouse; D011956:Receptors, Cell Surface; C510880:iHog protein, Drosophila; C070844:ptc protein, Drosophila
keywords: Drosophila; Morphogenesis; Pattern formation; Signaling