Reduced enamel epithelium‐derived cell niche in the junctional epithelium is maintained for a long time in mice

Background Although numerous reports have demonstrated that the junctional epithelium (JE) is derived from the reduced enamel epithelium (REE), the fate of the REE‐derived JE remains controversial. The present study elucidated the fate of the REE‐derived JE and the cell dynamics of stem/progenitor cells in the JE following tooth eruption. Methods Mandibular first molar germs (embryonic days 15 to postnatal 1‐day‐old) were transplanted into the socket of 2‐week‐old mice after extraction of the upper first molars of B6 wild‐type (WT) and green fluorescent protein (GFP) transgenic mice. After analysis by µ‐CT, paraffin sections were processed for immunohistochemistry for Nestin, Ki67 and GFP. We also performed chasing analysis using BrdU‐administered TetOP‐H2B‐GFP mice. Results Amelogenesis progressed normally in the cervical areas, and the structure of the JE was like that in normal tooth development. The JE was GFP‐negative in transplantations using GFP transgenic mice as the host, and the oral epithelium (OE) showed a positive reaction. By contrast, the JE remained GFP‐positive throughout the experimental period in transplantations using GFP transgenic mice as the donor. Chasing analysis revealed that H2B‐GFP‐ and 5‐Bromo‐2′‐deoxyuridine (BrdU)‐labeled cells in the basal side of the JE translocated to oral side of the JE as the chasing time increased. Some label‐retaining cells remained at the supra‐basal cell layer in the JE. Conclusion These results suggest that REE‐derived cell niche in the JE is maintained for a long time following tooth eruption. Therefore, the JE may be available as the source of the odontogenic epithelium.