title: The Importance of Serine Phosphorylation of Ameloblastin on Enamel Formation.
abstract: FAM20C is a newly identified kinase on the secretory pathway responsible for the phosphorylation of serine residues in the Ser-x-Glu/pSer motifs in several enamel matrix proteins. Fam20C-knockout mice showed severe enamel defects very similar to those in the ameloblastin ( Ambn)-knockout mice, implying that phosphoserines may have a critical role in AMBN function. To test this hypothesis, we generated amelogenin ( Amel) promoter-driven Ambn-transgenic mice, in which Ser48, Ser226, and Ser227were replaced by aspartic acid (designated as D-Tg) or alanines (designated as A-Tg). The negative charge of aspartic acid is believed to be able to mimic the phosphorylation state of serine, while alanine is a commonly used residue to substitute serine due to their similar structure. Using Western immunoblotting and quantitative polymerase chain reaction, the authors identified transgenic lines expressing transgenes somewhat higher (Tg+) or much higher (Tg++) than endogenous Ambn. The lower incisors collected from 7-d-old and 7-wk-old mice were analyzed by histology, scanning electron microscopy, immunohistochemistry, and Western immunoblotting to examine the morphology and microstructure changes in enamel, as well as the expression pattern of enamel matrix proteins. The A-Tg+ and A-Tg++ mice displayed severe enamel defects in spite of the expression level of transgenes, while the D-Tg+ and D-Tg++ mice showed minor to mild enamel defects, indicating that the D-Tg transgenes disturbed enamel formation less than the A-Tg transgenes did. Our results suggest that the phosphorylation state of serines is likely an essential component for the integrity of AMBN function.
authors.affiliation: 1 Department of Oral Implantology, Beijing Stomatological Hospital, Capital Medical University, Beijing, China.|2 Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.
authors.forename: P
authors.initials: P
authors.lastname: Ma
authors.affiliation: 2 Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.
authors.forename: W
authors.initials: W
authors.lastname: Yan
authors.affiliation: 2 Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Tian
authors.affiliation: 2 Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.
authors.forename: J
authors.initials: J
authors.lastname: He
authors.affiliation: 3 Department of Oral Biology, University of Leeds, St. James's University Hospital, Leeds, UK.
authors.forename: S J
authors.initials: SJ
authors.lastname: Brookes
authors.affiliation: 2 Department of Biomedical Sciences and Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.
authors.forename: X
authors.initials: X
authors.lastname: Wang
mesh_terms: D000566:Amelogenesis / Q000235:genetics / Q000502:physiology*; D053523:Amelogenin / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000502:physiology*; D003746:Dental Enamel Proteins / Q000235:genetics / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D012694:Serine / Q000378:metabolism*
chemical_list: C490890:Ambn protein, mouse; D053523:Amelogenin; D002135:Calcium-Binding Proteins; D003746:Dental Enamel Proteins; D016326:Extracellular Matrix Proteins; C509696:FAM20C protein, mouse; C109069:enamel matrix proteins; D012694:Serine
keywords: FAM20C; amelogenesis; extracellular matrix; kinase; phosphoserine; transgene