Partial epithelial–mesenchymal transition during enamel development

Objectives: We set out to investigate whether a hybrid stem-like p-EMT phenotype develops during murine molar enamel development in vivo. Setting and Sample Population: Histology specimens incorporating molar tooth buds harvested from mice at post-natal day 4 (P4) were included in our studies. Materials and Methods: We employed double immunofluorescence staining to analyze the simultaneous expression of the epithelial marker E-cadherin and the mesenchymal marker N-cadherin in histology specimens with tooth buds harvested from P4 mice. Moreover, we evaluated the expression of the core master stem cell markers Oct4 and Sox2, as well as the mature ameloblast marker amelogenin. Results: Here we document the co-expression of E-cadherin and N-cadherin in a sub-population of pre-ameloblasts in the inner enamel epithelium suggestive of the presence of a hybrid epithelial/mesenchymal phenotype resulting from p-EMT. Moreover, the core stem cell factors Oct4 and Sox2 colocalized with E-cadherin expressing pre-ameloblasts, whereas the mesenchymal marker N-cadherin was expressed specifically by amelogenin–positive mature secretory ameloblasts. Conclusions: The differentiation of E-cadherin–positive pre-ameloblasts towards N-cadherin–positive mature secretory ameloblasts transition through a previously unidentified epithelial/mesenchymal stage derived through p-EMT, co-expressing the master transcription factors Oct4 and Sox2.