title: Overexpression of TRAP in the enamel matrix does not alter the enamel structural hierarchy.
abstract: The secreted, full-length amelogenin is the dominant protein of the forming enamel organ. As enamel mineralization progresses, amelogenin is quickly subjected to proteolytic activity, and eliminated from the enamel environment. Mature enamel contains only traces of structural proteins, including enamelin and the sheath protein ameloblastin. In addition, a proteolytic fragment of amelogenin, known as the tyrosine-rich amelogenin peptide or TRAP, is present in low but isolatable quantities. By overexpressing TRAP during enamel development we sought to determine if such overexpression would result in structural alterations to the mature enamel. We reasoned that overexpressing a protein associated with enamel maturation, at an inappropriate developmental stage, would result in alterations to the enamel protein assembly and hence, alterations in enamel structure and morphology. As judged by transmission and scanning electron microscopy, the enamel formed by overexpressing TRAP showed little morphological differences when compared to the enamel of normal nontransgenic animals. Based on scanning electron-microscopic images, there was modest hypomineralization evident in the interrod enamel of the TRAP-overexpressing animals. However, this finding was inconsistent and inconsequential from a structural and functional perspective. From these results it appears that additional amounts of TRAP protein in the immature enamel matrix are not sufficient to alter the properties of the enamel extracellular matrix to an extent that the hierarchical structure of mature enamel is altered.
authors.affiliation: Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, Los Angeles, Calif., USA. paine@usc.edu
authors.forename: Michael L
authors.initials: ML
authors.lastname: Paine
authors.forename: Dan-Hong
authors.initials: DH
authors.lastname: Zhu
authors.forename: Wen
authors.initials: W
authors.lastname: Luo
authors.forename: Malcolm L
authors.initials: ML
authors.lastname: Snead
mesh_terms: D000565:Ameloblasts / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D000566:Amelogenesis / Q000235:genetics / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D003743:Dental Enamel / Q000033:anatomy & histology / Q000378:metabolism* / Q000648:ultrastructure; D003746:Dental Enamel Proteins / Q000032:analysis / Q000235:genetics*; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D007150:Immunohistochemistry; D007180:Incisor / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D008334:Mandible / Q000033:anatomy & histology / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009842:Oligopeptides; D010455:Peptides / Q000235:genetics / Q000276:immunology; D010957:Plasmids / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D003746:Dental Enamel Proteins; D009842:Oligopeptides; D010455:Peptides; C084495:tyrosine-rich amelogenin polypeptide; C085706:FLAG peptide