CONTRIBUTION OF FOREGUT ENDODERM TO TOOTH INITIATION OF MANDIBULAR INCISOR IN RAT EMBRYOS

Classical transplantation experiments with various amphibian tissues h ave shown that tooth development requires not only oral ectoderm and n eural crest but also foregut endoderm. In addition, histological obser vation of oral membrane showed that the tooth germs are initiated in s ome ectodermal cells and neural crest cells adjacent to foregut endode rm, These studies suggest that tooth initiation requires the presence and cooperation of these three components. In mammals, however, there is no direct evidence that tooth formation is involved in the region o f oral ectoderm adjacent io foregut endoderm. In order to elucidate th e contribution of foregut endoderm to tooth formation, we established a new type of endodermal cell tracing system with a recombinant adenov irus called Adex-lacZ, and performed endodermal cell tracing in a long -term culture system. Cells labelled with Adex-lacZ were seen next to non-labelled thickening epithelium, presumptive incisor epithelium. Th ese findings show the first direct evidence in mammals that tooth form ation takes place in the specified part of oral ectoderm adjacent to f oregut endoderm,suggesting that foregut endoderm plays a role in tooth initiation.