Signalling networks regulating dental development.

There has been rapid progress recently in the identification of signalling pathways regulating tooth development. It has become apparent that signalling networks involved in Drosophila development and development of mammalian organs such as the limb are also used in tooth development. Teeth are epithelial appendages formed in the oral region of vertebrates and their early developmental anatomy resembles that of other appendages, such as hairs and glands. The neural crest origin of tooth mesenchyme has been confirmed and recent evidence suggests that specific combinations of homeobox genes expressed in the neural crest cells may regulate the types of teeth and their patterning. Signalling molecules in the Shh, FGF, BMP and Wnt families appear to regulate the early steps of tooth morphogenesis and some transcription factors associated with these pathways have been shown to be necessary for tooth development. Several of the conserved signals are also transiently expressed in the enamel knots in the dental epithelium. The enamel knots are associated with the characteristic epithelial folding morphogenesis which is responsible for the development of tooth shape and it is currently believed that the enamel knots function as signalling centres regulating tooth shape development. The developing tooth has proven to be an excellent model in studies of the molecular basis of patterning and morphogenesis of organs and it can be expected that continuing studies will rapidly increase the understanding of these mechanisms.