Neural crest potential for tooth development in a urodele amphibian: developmental and evolutionary significance.

Tooth development in urodele amphibians occurs from a restricted region of anterior cranial neural crest. An in vitro culture system was used to test the odontogenic potential of more caudal regions of neural crest, including an "intermediate region" of neural folds which has never previously been tested for either fate or potential. Explants of different axial levels of neural crest with stomodaeal ectoderm and endoderm demonstrated that odontogenic potential extends not only further caudally than the axial level fated to produce teeth, but also beyond that with potential to produce cartilage. Our results show that chondrogenic potential is found only within the most rostral portion of the intermediate region, but that odontogenic potential extends to its most caudal limit. This separation of skeletogenic cell lineages in the neural crest necessitates a reevaluation of the designations of "cranial" and "trunk" and a reconsideration of the evolutionary implications of developmentally distinct crest-derived mesenchyme populations. The proposal that odontogenic potential extends into the trunk neural crest may be explained as conserved from a phylogenetically older, more extensive skeletogenic ability which produced the exoskeleton of more basal vertebrates.