Genetic basis of tooth development and dental defects.

Tooth development is under strict genetic control, and during recent years an increasing number of genes have been identified that are involved in the regulation of tooth morphogenesis. One of the organs in which development is now beginning to be understood at the gene level, the tooth is an example of a typical vertebrate organ starting as an epithelial bud and undergoing complex morphogenesis, regulated by interactions between epithelial and mesenchymal tissue layers. It has become evident that developmental regulatory genes have been conserved to a high degree during evolution and that similar gene networks regulate the development of teeth as of other vertebrate organs. So far, all genes that have been linked with early tooth morphogenesis have developmental regulatory functions in other organs, too. The majority of these genes are associated with the signaling pathways transmitting interactions between cells and tissues. They include genes encoding the actual signals as well as their receptors, mediators of signaling in the cytoplasm and transcription factors regulating gene expression in the nucleus. Deletion of the function of many of these genes in transgenic mice results in arrested tooth development, but all these mutants also show defects in many other tissues. Mutations in several of these genes in humans have been identified as causes of dental defects, mainly hypodontia.