The dentition of vertebrates evolved from a condition with simple conical teeth, showing continuous replacement, to a condition with teeth of a highly complex shape, and - in mammals - replaced only once, at the most. The zebrafish (Danio rerio) has become a model organism for genetic, molecular and developmental studies and is used in our laboratories to analyse the mechanism responsible for such continuous tooth replacement. This review addresses three issues. Firstly, we show that understanding the tooth replacement pattern is vital for a correct interpretation of experimental and molecular data regarding odontogenesis in this zebrafish model. Secondly, recent morphological evidence suggests that tooth replacement in the zebrafish is a biphasic process, possibly regulated by independent mechanisms: the formation of an epithelial down growth (called successional dental lamina), and the development of a tooth germ from this lamina. Thirdly, within the frame of testing the hypothesis where adult epithelial stem cells underlie the process of continuous tooth renewal in the zebrafish (and other polyphyodont vertebrates); we focus on the Wnt signaling pathway as a possible molecular control mechanism.
Conclusion: Future studies can take advantage from the wide array of tools available for zebrafish research to test the hypothesis of stem cell involvement and to examine the potential role of Wnt signaling in the process of tooth renewal. Eventually, answering the question of why zebrafish (and most other vertebrates) are capable of renewing their teeth throughout life can help to solve the riddle why this process is arrested in mammals.
Keywords: tooth replacement, stem cells, zebrafish, Wnt