Temporospatial tissue interactions regulating the regeneration of the enamel knot in the developing mouse tooth.

The enamel knot (EK), which is a transient signaling center in the tooth germ, regulates both the differential growth of the dental epithelium and the tooth shape. In this study, the regeneration of the EK was evaluated. The EK regions were removed from the E14 and E16 dental epithelia, and the remaining epithelia were recombined with their original dental mesenchymes. All these tooth germs could develop into calcified teeth after being transplanted into the kidney capsule for 3 weeks. One primary EK was regenerated earlier, and two or three secondary EKs were regenerated later in culture. When simply recombined without removing the EK, the tooth germ, which had four secondary EKs and four cuspal areas of the dental papilla, generated one primary EK first and subsequent secondary EKs. These results indicate that the patterning of the EK in all tooth germs always starts from a primary EK independent of the direct epithelial or mesenchymal control. This suggests that neither the dental epithelium nor the dental mesenchyme can dictate the pattern or number of the EK formation, but the interaction between the dental epithelium and the dental mesenchyme is essential for the regeneration and patterning of the EKs.