title: Shh signaling within the dental epithelium is necessary for cell proliferation, growth and polarization.
abstract: Sonic hedgehog (Shh), a member of the mammalian Hedgehog (Hh) family, plays a key role during embryogenesis and organogenesis. Tooth development, odontogenesis, is governed by sequential and reciprocal epithelial-mesenchymal interactions. Genetic removal of Shh activity from the dental epithelium, the sole source of Shh during tooth development, alters tooth growth and cytological organization within both the dental epithelium and mesenchyme of the tooth. In this model it is not clear which aspects of the phenotype are the result of the direct action of Shh on a target tissue and which are indirect effects due to deficiencies in reciprocal signalings between the epithelial and mesenchymal components. To distinguish between these two alternatives and extend our understanding of Shh's actions in odontogenesis, we have used the Cre-loxP system to remove Smoothened (Smo) activity in the dental epithelium. Smo, a seven-pass membrane protein is essential for the transduction of all Hh signals. Hence, removal of Smo activity from the dental epithelium should block Shh signaling within dental epithelial derivatives while preserving normal mesenchymal signaling. Here we show that Shh-dependent interactions occur within the dental epithelium itself. The dental mesenchyme develops normally up until birth. In contrast, dental epithelial derivatives show altered proliferation, growth, differentiation and polarization. Our approach uncovers roles for Shh in controlling epithelial cell size, organelle development and polarization. Furthermore, we provide evidence that Shh signaling between ameloblasts and the overlying stratum intermedium may involve subcellular localization of Patched 2 and Gli1 mRNAs, both of which are targets of Shh signaling in these cells.
authors.affiliation: Department of Oral Biochemistry, Sahlgrenska Academy at Göteborg University, Sweden.
authors.forename: Amel
authors.initials: A
authors.lastname: Gritli-Linde
authors.forename: Marianna
authors.initials: M
authors.lastname: Bei
authors.forename: Richard
authors.initials: R
authors.lastname: Maas
authors.forename: Xiaoyan M
authors.initials: XM
authors.lastname: Zhang
authors.forename: Anders
authors.initials: A
authors.lastname: Linde
authors.forename: Andrew P
authors.initials: AP
authors.lastname: McMahon
mesh_terms: D000565:Ameloblasts / Q000166:cytology / Q000378:metabolism; D000818:Animals; D015820:Cadherins / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology*; D016764:Cell Polarity; D003599:Cytoskeleton / Q000378:metabolism; D004658:Enamel Organ / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism*; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009804:Odontoblasts / Q000378:metabolism; D009805:Odontogenesis / Q000502:physiology; D015513:Oncogene Proteins / Q000378:metabolism; D000072079:Patched Receptors; D000072082:Patched-2 Receptor; D010750:Phosphoproteins / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction / Q000502:physiology*; D000072086:Smoothened Receptor; D014070:Tooth / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D000071676:Zinc Finger Protein GLI1; D062826:Zonula Occludens-1 Protein
chemical_list: D015820:Cadherins; C104149:Dlx4 protein, mouse; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D008565:Membrane Proteins; D015513:Oncogene Proteins; D000072079:Patched Receptors; D000072082:Patched-2 Receptor; D010750:Phosphoproteins; C000606241:Ptch2 protein, mouse; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C465570:Shh protein, mouse; C491022:Smo protein, mouse; D000072086:Smoothened Receptor; C569043:Tjp1 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D062826:Zonula Occludens-1 Protein