title: A mutation in the mouse Amelx tri-tyrosyl domain results in impaired secretion of amelogenin and phenocopies human X-linked amelogenesis imperfecta.
abstract: Amelogenesis imperfecta (AI) describes a broad group of clinically and genetically heterogeneous inherited defects of dental enamel bio-mineralization. Despite identification of a number of genetic mutations underlying AI, the precise causal mechanisms have yet to be determined. Using a multi-disciplinary approach, we describe here a mis-sense mutation in the mouse Amelx gene resulting in a Y --> H substitution in the tri-tyrosyl domain of the enamel extracellular matrix protein amelogenin. The enamel in affected animals phenocopies human X-linked AI where similar mutations have been reported. Animals affected by the mutation have severe defects of enamel bio-mineralization associated with absence of full-length amelogenin protein in the developing enamel matrix, loss of ameloblast phenotype, increased ameloblast apoptosis and formation of multi-cellular masses. We present evidence to demonstrate that affected ameloblasts express but fail to secrete full-length amelogenin leading to engorgement of the endoplasmic reticulum/Golgi apparatus. Immunohistochemical analysis revealed accumulations of both amelogenin and ameloblastin in affected cells. Co-transfection of Ambn and mutant Amelx in a eukaryotic cell line also revealed intracellular abnormalities and increased cytotoxicity compared with cells singly transfected with wild-type Amelx, mutant Amelx or Ambn or co-transfected with both wild-type Amelx and Ambn. We hypothesize that intracellular protein-protein interactions mediated via the amelogenin tri-tyrosyl motif are a key mechanistic factor underpinning the molecular pathogenesis in this example of AI. This study therefore successfully links phenotype with underlying genetic lesion in a relevant murine model for human AI.
authors.affiliation: Faculty of Life Sciences and School of Dentistry, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Barron
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Brookes
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kirkham
authors.forename: Roger C
authors.initials: RC
authors.lastname: Shore
authors.forename: Charlotte
authors.initials: C
authors.lastname: Hunt
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Mironov
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Kingswell
authors.forename: Joanne
authors.initials: J
authors.lastname: Maycock
authors.forename: C Adrian
authors.initials: CA
authors.lastname: Shuttleworth
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dixon
mesh_terms: D000567:Amelogenesis Imperfecta / Q000235:genetics*; D053523:Amelogenin / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D002470:Cell Survival; D003743:Dental Enamel / Q000473:pathology; D003746:Dental Enamel Proteins / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000502:physiology; D005260:Female; D040181:Genetic Diseases, X-Linked / Q000235:genetics*; D007180:Incisor / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D020125:Mutation, Missense; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection
chemical_list: C490890:Ambn protein, mouse; D053523:Amelogenin; C507200:Amelx protein, mouse; D003746:Dental Enamel Proteins; D012333:RNA, Messenger