The fate of Osterix-expressing mesenchymal cells in dental root formation and maintenance.

OBJECTIVES: Osterix (Osx)-expressing mesenchymal cells are progenitors for tooth root forming cells. The aim of this study was to reveal the fates of Osx-expressing cells during and after root formation using a lineage tracing experiment. MATERIAL AND METHODS: To reveal the fates of Osx-expressing dental mesenchymal progenitors, we took advantage of tamoxifen-inducible Cre reporter system. Osx-creER; R26R-tdTomato mice received tamoxifen (0.1 mg/body) at postnatal day 3 (P3). In this system, Osx-expressing at P3 (Osx-P3) cells undergo recombination, and they and their descendants continue to express Tomato red fluorescence protein permanently. Mandibles were dissected at serial time points ranging from P4 to P116 to investigate how Osx-P3 cells participated in root formation. Tomato(+) cells on frozen sections were imaged under fluorescence microscopy. RESULTS: Osx-P3 cells and their descendants differentiated into all kinds of cells that contributed to the root and periodontal tissues, such as odontoblasts, cementoblasts, alveolar bone osteoblasts and periodontal ligament (PDL) cells during root formation. Even after root formation was completed, they persisted in dental pulp and PDL to provide progenitor cells for odontoblasts and cementoblasts. CONCLUSION: Osx-expressing cells play important roles in the entire processes of tooth root formation; their progeny continue to contribute to maintenance of tooth root even after root formation is complete.