DMP1 Controls Odontogenesis partly through Osterix

OBJECTIVES: Dentin matrix protein 1 (DMP1) is expressed in both pulp and odontoblast cells and deletion of the Dmp1 gene leads to defects in odontogenesis and mineralization. The goals of this study were to examine how DMP1 controls dentin mineralization and odontogenesis both in vivo and in vitro. METHODS: 1) Dmp1 transgenic mice driven by the 3.6 kb type-1A1 collagen promoter (active in both early and late odontoblasts and pulp cells) or the 6 kb Dspp promoter (active only in mature odontoblasts) were crossed with the Dmp1-null mice for re-expression of DMP1 at different stages during odontogenesis. 2) Combinations of histology, radiography, fluorochrome labeling (measuring dentin apposition rate), SEM, and in situ hybridization were used to phenotype dentin changes. 3) Generation of transgenic mice harboring the DMP1 C-terminal transgene driven by the 3.6 kb Col1 promoter for rescue of Dmp1-null mice. 4) Transient transfection DMP1 into odontoblast cell line for gene expression changes. RESULTS: Re-expression of Dmp1 under control of the Col1a1 promoter completely rescued the defects mineralization as well as the defects in the dentinal tubules and third molar development. In contrast, re-expression, using the Dspp promoter, produced only a partial rescue of the mineralization defects. Further, osterix, a transcription factor expressed in both pulp and odontoblast cells, is sharply reduced in Dmp1-null newborns and 10 day-old pulps. Re-expression of DMP1 restores osterix in both pulp and odontoblasts. In vitro overexpression of DMP1 shows induction of osterix in odontoblast cell line. Finally, 5 lines of DMP1 C-terminal transgene are produced, which show no apparent phenotype. CONCLUSION: DMP1 is a key regulator of odontoblast differentiation, formation of the dentin tubular system and mineralization and restoration of osterix by transgenic DMP1 may explain in part for its role in controlling early odontogenesis. (Work supported by NIH grants: DE00455 and AR51587)