175 Ameloblastin and Ameloblast Differentiation in Enamel Formation

Thursday, March 22, 2012: 10:45 a.m. - 12:15 p.m.
Presentation Type: Oral Session
Y.P. CHUN, Periodontics, University of Texas at San Antonio, San Antonio, TX, J. TEEPE, Periodontics, U.S. Air Force Dental Service, San Antonio, TX, Y. YAMADA, National Institute for Dental and Craniofacial Research, Bethesda, MD, C. SMITH, McGill University, Montreal, QC, Canada, S. ABBOUD WERNER, Pathology, University of Texas - San Antonio / Health Science Ctr, San Antonio, TX, R.J. FAJARDO, Orthopaedics, University of Texas - San Antonio / Health Science Ctr, San Antonio, TX, and S. HARRIS, Periodontics, University of Texas Health Science Center at San Antonio, San Antonio, TX
Ameloblastin (Ambn), one of the non-amelogenin enamel matrix proteins, is expressed and secreted by ameloblasts during both secretory and maturation stages. In Ambn mutant mice, lacking exons 5 and 6 (Ambnmutant), ameloblasts are dysplastic and fail to form enamel. Objectives: The goal was to define the role of Ambn for ameloblasts and enamel formation by expressing Ambn from a transgene in Ambnmutant mice. Methods: By reconstituting the enamel layer with Ambn from a transgene, enamel formation was analyzed in mice using mandibular incisors with all stages of enamel formation. Ambnmutant mice were mated with mice from two different mouse lines expressing Ambn in a dose lower or similar to normal from a transgene driven by the amelogenin promoter. The transgenic Ambn level was determined by Western Blot analysis of molars at 5 days age. Ameloblasts and enamel mineralization were analyzed by histology and micro-computed tomography (microCT). Both analyses were performed for each stage of enamel formation (secretory, early, mid and late maturation) on cross-sections of mandibular incisors at 7 weeks age. Results: In Ambnmutant animals, microCT and histological analyses displayed that an enamel layer failed to be deposited and that the ameloblasts were dysplastic. In Ambnmutant/Tg, low animals, the deposition and mineralization of enamel were delayed compared to wildtype controls. In Ambnmutant/Tg, high animals, enamel deposition and mineralization started earlier than wildtype controls. The histological analysis of ameloblasts revealed that at low dose of transgenic Ambn, a few ameloblasts displayed polarization. The enamel organ was lacking stage-specific layers, instead extensive cyst formation was observed. Ambnmutant/Tg, high animals displayed ameloblasts with polarization and the enamel organ consisted of layers similar to wildtype controls. Conclusions: Ambn is required for enamel mineralization, for ameloblasts differentiation, and for stage-specific morphology in the enamel organ. This study was funded by the University Research Council, UTHSCSA.

Keywords: Ameloblasts, Enamel, Extracellular matrix molecules, Mineralization and Molecular biology