title: New genomic and fossil data illuminate the origin of enamel.
abstract: Enamel, the hardest vertebrate tissue, covers the teeth of almost all sarcopterygians (lobe-finned bony fishes and tetrapods) as well as the scales and dermal bones of many fossil lobe-fins. Enamel deposition requires an organic matrix containing the unique enamel matrix proteins (EMPs) amelogenin (AMEL), enamelin (ENAM) and ameloblastin (AMBN). Chondrichthyans (cartilaginous fishes) lack both enamel and EMP genes. Many fossil and a few living non-teleost actinopterygians (ray-finned bony fishes) such as the gar, Lepisosteus, have scales and dermal bones covered with a proposed enamel homologue called ganoine. However, no gene or transcript data for EMPs have been described from actinopterygians. Here we show that Psarolepis romeri, a bony fish from the the Early Devonian period, combines enamel-covered dermal odontodes on scales and skull bones with teeth of naked dentine, and that Lepisosteus oculatus (the spotted gar) has enam and ambn genes that are expressed in the skin, probably associated with ganoine formation. The genetic evidence strengthens the hypothesis that ganoine is homologous with enamel. The fossil evidence, further supported by the Silurian bony fish Andreolepis, which has enamel-covered scales but teeth and odontodes on its dermal bones made of naked dentine, indicates that this tissue originated on the dermal skeleton, probably on the scales. It subsequently underwent heterotopic expansion across two highly conserved patterning boundaries (scales/head-shoulder and dermal/oral) within the odontode skeleton.
authors.affiliation: Subdepartment of Evolution and Development, Department of Organismal Biology, Uppsala University, Norbyvägen 18A, SE 75236 Uppsala, Sweden.
authors.forename: Qingming
authors.initials: Q
authors.lastname: Qu
authors.affiliation: Subdepartment of Evolution and Development, Department of Organismal Biology, Uppsala University, Norbyvägen 18A, SE 75236 Uppsala, Sweden.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Haitina
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
authors.forename: Min
authors.initials: M
authors.lastname: Zhu
authors.affiliation: Subdepartment of Evolution and Development, Department of Organismal Biology, Uppsala University, Norbyvägen 18A, SE 75236 Uppsala, Sweden.
authors.forename: Per Erik
authors.initials: PE
authors.lastname: Ahlberg
mesh_terms: D000470:Alkaloids; D053523:Amelogenin / Q000235:genetics; D000818:Animals; D005075:Biological Evolution; D002681:China; D003743:Dental Enamel; D003746:Dental Enamel Proteins / Q000235:genetics; D003804:Dentin; D019143:Evolution, Molecular; D029941:Fish Proteins / Q000235:genetics; D005399:Fishes / Q000235:genetics*; D005580:Fossils; D016678:Genome / Q000235:genetics*; D023281:Genomics; D005810:Multigene Family / Q000235:genetics; D011758:Pyrroles; D012867:Skin / Q000033:anatomy & histology / Q000737:chemistry; D012886:Skull / Q000737:chemistry; D014070:Tooth / Q000033:anatomy & histology / Q000737:chemistry
chemical_list: D000470:Alkaloids; D053523:Amelogenin; D003746:Dental Enamel Proteins; D029941:Fish Proteins; D011758:Pyrroles; C109069:enamel matrix proteins; C038456:tuftelin; C067951:ganoine