Epithelial-mesenchymal signaling during tooth development.

Classic studies on experimental embryology have shown that organ development in an embryo is largely regulated by so called inductive tissue interactions which mostly take place between epithelial and mesenchymal tissues. Also in the developing tooth, both morphogenesis and cell differentiation are governed by such interactions. Characteristic features of epithelial-mesenchymal interactions are that they are sequential and reciprocal, i.e. “induction” appears to consist of a chain of signaling events between the tissues.During the last decade, the expression patterns of numerous molecules have been studied in developing organs by in situ hybridization and immunohistology. Many of them have been associated with epithelial-mesenchymal interactions, and it is apparent that same molecules participate in regulation of morphogenesis in a number of different organs. Transcription factors such as Msx-1, Msx-2 and Egr-1, growth factors, including TGFB's, BMPs, and FGFs, and structural proteins such as syndecan and...