SIGNALING NETWORKS REGULATING DENTAL DEVELOPMENT

There has been rapid progress recently in the identification of signal ling pathways regulating tooth development. It has become apparent tha t signalling networks involved in Drosophila development and developme nt of mammalian organs such as the limb are also used in tooth develop ment Teeth are epithelial appendages formed in the oral region of vert ebrates 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 speci fic combinations of homeobox genes expressed in the neural crest cells may regulate the types of teeth and their patterning. Signalling mole cules in the Shh, FGF, BMP and Wnt families appear to regulate the ear ly steps of tooth morphogenesis and some transcription factors associa ted with these pathways have been shown to be necessary for tooth deve lopment. Several of the conserved signals are also transiently express ed in the enamel knots in the dental epithelium. The enamel knots are associated with the characteristic epithelial folding morphogenesis wh ich is responsible for the development of tooth shape and it is curren tly believed that the enamel knots function as signalling centres regu lating 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 studie s will rapidly increase the understanding of these mechanisms. (C) 199 7 Elsevier Science Ireland Ltd.