Although many organs renew throughout life, the regenerative capacity of some organs varies between species. For example, reptiles replace their teeth continuously, whereas mammals have only a single round of tooth replacement. The development of new teeth involves dental epithelial cells that are competent for tooth formation. Now, Irma Thesleff and colleagues () identify the transcription factor Sox2 as a marker for these cells. The researchers report that Sox2 is expressed in the dental lamina that gives rise to successional teeth in ferrets and humans, which have a single round of tooth replacement, and in five reptiles with continuous tooth replacement. Sox2 is also expressed in the dental lamina during the serial addition of mammalian molars and, in mice, Sox2+ cells in the first molar give rise to the sequentially developing second and third molars. These data suggest that Sox2 function has been conserved during evolution, and identify tooth replacement and the serial addition of primary teeth as variations of the same developmental process.
