title: Making teeth to order: conserved genes reveal an ancient molecular pattern in paddlefish (Actinopterygii).
abstract: Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of Polyodon spathula (American paddlefish), assigned to the basal group Acipenseriformes. Although teeth are present and functional in young individuals of Polyodon, they are completely absent in adults. Our current understanding of developmental genes operating in the dentition is primarily restricted to teleosts; we show that shh and bmp4, as highly conserved epithelial and mesenchymal genes for gnathostome tooth development, are similarly expressed at Polyodon tooth loci, thus extending this conserved developmental pattern within the Actinopterygii. These genes map spatio-temporal tooth initiation in Polyodon larvae and provide new data in both oral and pharyngeal tooth sites. Variation in cellular intensity of shh maps timing of tooth morphogenesis, revealing a second odontogenic wave as alternate sites within tooth rows, a dental pattern also present in more derived actinopterygians. Developmental timing for each tooth field in Polyodon follows a gradient, from rostral to caudal and ventral to dorsal, repeated during subsequent loss of teeth. The transitory Polyodon dentition is modified by cessation of tooth addition and loss. As such, Polyodon represents a basal actinopterygian model for the evolution of developmental novelty: initial conservation, followed by tooth loss, accommodating the adult trophic modification to filter-feeding.
authors: Craniofacial Development and Stem Cell Biology, King's College London Dental Institute, London, UK Department of Earth Sciences, Natural History Museum, London, UK moya.smith@kcl.ac.uk.
authors: Moya M
authors: MM
authors: Smith
authors: Department of Earth Sciences, Natural History Museum, London, UK.
authors: Zerina
authors: Z
authors: Johanson
authors: MRC Centre for Developmental Neurobiology, King's College London, London, UK.
authors: Thomas
authors: T
authors: Butts
authors: Department of Earth Sciences, Natural History Museum, London, UK.
authors: Rolf
authors: R
authors: Ericsson
authors: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK.
authors: Melinda
authors: M
authors: Modrell
authors: Department of Biology and Physics, College of Science and Mathematics, Kennesaw State University, Kennesaw, GA, USA.
authors: Frank J
authors: FJ
authors: Tulenko
authors: Department of Biology and Physics, College of Science and Mathematics, Kennesaw State University, Kennesaw, GA, USA.
authors: Marcus C
authors: MC
authors: Davis
authors: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK.
authors: Gareth J
authors: GJ
authors: Fraser
mesh_terms: D000818:Animals; D005075:Biological Evolution; D017124:Conserved Sequence / Q000235:genetics*; D003817:Dentition; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism; D005399:Fishes / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development*; D018507:Gene Expression Regulation, Developmental; D008969:Molecular Sequence Data; D009805:Odontogenesis; D017422:Sequence Analysis, DNA
chemical_list: D029941:Fish Proteins
keywords: Polyodon; bmp4; dentition; evolution; paddlefish; shh