Dental Lamina as Source of Odontogenic Stem Cells: Evolutionary Origins and Developmental Control of Tooth Generation in Gnathostomes

This study considers stem cells for odontogenic capability in biological tooth renewal in the broad context of gnathostome dentitions and the derivation of them from oral epithelium. The location of the developmental site and cell dynamics of the dental lamina are parameters of a possible source for odontogenic epithelial stem cells, but the phylogenetic history is not known. Understanding the phylogenetic basis for stem cell origins throughout continuous tooth renewal in basal jawed vertebrates is the ultimate objective of this study. The key to understanding the origin and location of stem cells in the development of the dentition is sequestration of stem cells locally for programmed tooth renewal. We suggest not only the initial pattern differences in each dentate field but local control subsequently for tooth renewal within each family. The role of the specialized odontogenic epithelium (odontogenic band) is considered as that in which the stem cells reside and become partitioned. These regulate time, position and shape in sequential tooth production. New histological data for chondrichthyan fish show first a thickening of the oral epithelium (odontogenic band). After this, all primary and successive teeth are only generated deep to the oral epithelium from a dental lamina. In contrast, in osteichthyan fish the first teeth develop directly within the odontogenic band. In addition, successors are initiated at each tooth site in the predecessor tooth germ (without a dental lamina). We suggest that stem cells specified for each tooth family are set up and located in intermediate cells between the outer and inner dental epithelia. J. Exp. Zool. (Mol. Dev. Evol.) 312B:260-280, 2009. (c) 2009 Wiley-Liss, Inc.