756 Osterix is Obligatory for Odontoblast-Ameloblast Maturation but Not Tooth-Morphogenesis

Friday, March 23, 2012: 10:45 a.m. - 12:15 p.m.
Presentation Type: Oral Session
M.D. ADHAMI1, J. BAE2, H. RASHID1, H. CHEN1, D. SUMMERFORD1, D. NAPIERALA1, K. SINHA3, S. GUTIERREZ4, B. DE CROMBRUGGHE3, and A. JAVED1, 1Oral and Maxillofacial Surgery, University of Alabama, Birmingham, AL, 2Dental Biomaterials, Wonkwang University College of Dentistry, Iksan, Jeonbuk, Republic Of Korea, 3Department of Genetics, University of Texas M. D. Anderson Cancer Center, Houston, TX, 4University of Concepcion, Concepcion, Chile
Runx2 and its downstream target Osterix are essential for skeletogenesis, and mutations of these genes in humans are associated with CCD and osteogenesis imperfecta. Tooth formation in Runx2-null mice arrests at the cap stage.  However, these mice completely lack alveolar bone, whose presence is considered a pre-requisite for tooth development. Osx-null model provide unique opportunity to reveal Osterix role in odontogenesis, and distinguish between contribution of alveolar bone and Runx2 in tooth-formation.  Objective:   Investigate function of Osterix during tooth development.  Methods: Odontogenesis in Osterix-null mice was evaluated by histological, biochemical, and molecular approaches.  Results: Osterix-null mice exhibited failed skeletogenesis and absence of alveolar bone.  Newborn heads were sectioned sagitally to evaluate tooth development.  Surprisingly, homozygous mutants showed normal tooth morphogenesis.  Incisors and multi-cusped 1st and 2nd molar were noted in WT and homozygous littermates.  These data demonstrate that alveolar bone is not a prerequisite for tooth morphogenesis.  Despite normal shape and number, Osx-null tooth-organs were significantly smaller in size.  BrdU-labeling assays at E18 revealed Osterix role in regulating cell proliferation.  We next followed differentiation of epithelial-ameloblasts and mesenchymal-odontoblasts.  Impaired matrix synthesis and collagen production was noted in Osx-null incisors.  WT incisors exhibited well-polarized, and fully mature odontoblasts/ameloblasts. However, Osx-null showed only cuboidal and aggregated cells in epithelial and mesenchymal portions of teeth. To better understand if this finding reflects a developmental arrest or a delayed differentiation, we compared expression of stage/cell-specific markers.   DSPP/DMP1 were undetectable in Osx-null odontoblast, and only a weak Amelogenin signal was noted in ameloblasts.  Analysis of WT and Osx-null incisor mRNA further confirmed lack of maturation, with reduced expression of key odontoblast/ameloblast markers by 4-8 fold.  Conclusions: We report for the first time that alveolar bone is not essential for tooth morphogenesis, and show Osterix is obligatory for odontoblast and ameloblast maturation, but not their commitment.
This abstract is based on research that was funded entirely or partially by an outside source: R01AG030228 T32DE017607

Keywords: Ameloblasts, Gene expression, Genetics, Odontoblasts and Teeth