title: Identification and characterization of a squamate reptilian amelogenin gene: Iguana iguana.
abstract: As the principal components of the developing tooth enamel matrix, amelogenins play a significant role in tooth enamel formation and organization. In order to elucidate the structure and function of amelogenins in the evolution of enamel, we have selected the Iguana iguana as a squamate model organism. Here we report the first complete squamate amelogenin sequence available as of yet and document unique features of Iguana amelogenins and enamel. Transmission electron microscopy documented randomly oriented Iguana enamel crystals during the elongation phase compared with organized enamel crystal patterns at comparable stages in mammals. Sequencing of PCR amplified products revealed a full-length I. iguana amelogenin cDNA containing 877 nucleotides with a 564 nucleotide coding sequence encoding 187 amino acids. The homologies of the newly discovered I. iguana amelogenin amino acid sequence with the published mouse, caiman (Palaeosuchus), and snake (Elaphe) amelogenin were 41.3%, 53.5%, and 55.5%, respectively. On Western blots one major protein with a molecular weight of 24 kDa, and two minor proteins with molecular weights of 28 and 13.5 kDa, respectively, were detected based on the cross-reactivity of antisera against recombinant Rana pipiens amelogenin proteins. Sequence analysis revealed a moderate sequence homology between mammalian and reptilian amelogenin genes. A significant alteration was the deletion of the hydrophilic GSP sequence from exon 3 in the mouse sequence resulting in a conversion to a hydrophobic region in Iguana. Together, these findings identified a novel amelogenin cDNA sequence in the squamate reptilian I. iguana and functional implications for the evolution of amelogenins and enamel in squamates.
authors.affiliation: Department of Oral Biology and Allan G. Brodie Laboratory for Craniofacial Genetics, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
authors.forename: Xinping
authors.initials: X
authors.lastname: Wang
authors.forename: Ji-Lao
authors.initials: JL
authors.lastname: Fan
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ito
authors.forename: Xianghong
authors.initials: X
authors.lastname: Luan
authors.forename: Thomas G H
authors.initials: TG
authors.lastname: Diekwisch
mesh_terms: D053523:Amelogenin; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D003429:Cross Reactions; D003743:Dental Enamel / Q000254:growth & development / Q000276:immunology; D003746:Dental Enamel Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics; D020869:Gene Expression Profiling; D057927:Hydrophobic and Hydrophilic Interactions; D007076:Iguanas / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008322:Mammals; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D014070:Tooth / Q000254:growth & development / Q000378:metabolism
chemical_list: D053523:Amelogenin; C507200:Amelx protein, mouse; D003746:Dental Enamel Proteins