Induction of New Tooth Formation in Adult Oral Ectoderm

Induction of teeth is determined by the balance between tooth-stimulators and inhibitors. Wnt signaling stimulates tooth formation. Expressing stabilized ß-catenin in mouse embryonic oral epithelium results in supernumerary tooth formation. Adenomatous polyposis coli (APC) inhibits Wnt signaling by targeting ß-catenin for degradation. Loss of APC is associated with stabilization of cytosolic ß-catenin leading to its migration to the nucleus and activating Wnt target genes. We showed previously that K14-Cre mediated Apc inactivation in embryonic oral ectoderm (K14Cre;Apc^CKO/CKO) generated multiple supernumerary teeth. Objectives: We noticed that although all K14Cre;Apc^CKO/CKO pups die before P18, the number of supernumerary teeth dramatically increase with age. The purpose of this study was to determine whether adult oral epthelium remains responsive to APC loss of function or ß-catenin gain-of-function, and retains tooth-forming potential. Methods: We have used a combination of in situ hybridisation, immunohistochemstry, and mouse transgenic analysis. We inactivated Apc gene in adult mice expressing the floxed Apc allele in conjection with a K14CreER^TM allele. We also activated Wnt signaling in adult tissues by using K14CreER^TM;ß-catenin^Δex3fl/+ mice. These transgenic mice have a tamoxifen inducible Cre-mediated recombination system driven by K14 promoter. We injected 4-hybroxitamoxifen (4-OHT) intraperitoneally for 5 consecutive days to activate CreER^TM, then sacrificed the mice 2-3 weeks later after the last injection. Results: Administration of 4-OHT can induce extra teeth at the molar region in postnatal 5-day-old mice. Large numbers of supernumerary teeth can still be induced at the incisor region at 6-month-old age. Conclusions: These results indicate that Wnt stimulates while APC inhibits odontogenic potential throughout the adult oral ectoderm. Adult oral ectoderm is still able to form new teeth, with tamoxifen-induced Wnt activation or Apc inactivation allowing expression of the “latent” odontogenic potential. These data may be used for developing new teeth in humans and regenerative therapies. (NIH/NIDCR 5R37DE011697-10).