Most reptiles and fish have multiple sets of teeth during their lifetime. But most mammals such as humans only have one set of replacement teeth. Some mammals like mice only have a single set with no replacement. This diversity raises questions about how different tooth replacement strategies evolved and which mechanisms prevent replacement teeth in animals that have lost them.
Researchers at King’s College London have tackled these questions with a molecular analysis of mouse tooth development. They have pinpointed why mice don’t have replacement teeth by comparing gene expression in the dental lamina, the area that forms the teeth, of the mouse and of the minipig, which has two sets of teeth.
Wnt signaling is required for tooth replacement in other vertebrates. The researchers now have found that Wnt activity is absent in a rudimentary form of the dental lamina (RSDL) in mice. This structure forms in the mouse but then disappears, stopping the generation of another set of teeth.
Using sophisticated genetic techniques, the researchers activated Wnt signaling in the mouse RSDL at E.15.5 and E16 stages of development, revitalizing the structure, and additional teeth formed as a result. The researchers say these results demonstrate the RSDL’s potential as a source for replacement teeth in mice and provide an experimental system suitable for studying the mechanisms behind replacement.
“Why the potential for tooth replacement varies so much across vertebrates is an intriguing question,” said PhD student Elena Popa. “Our results show that, although the mouse normally does not form a second replacement set of teeth, it still has the potential to do so given the right signals.”
Finally, the researchers report that culturing the RSDL in isolation stimulated its tooth-forming potential, suggesting that the first generation of teeth might prevent replacement teeth from developing and that the previous set of teeth also influence the development of a next set.
“This is relevant to human tooth replacement, as structures similar to the RSDL have been identified next to the permanent teeth during development. In normal development of our teeth, therefore, the second set or permanent tooth may inhibit the generation of a third set of teeth,” said Abigail S. Tucker, PhD, dean for research at the King’s College Faculty of Dentistry, Oral & Craniofacial Sciences.
The researchers conclude that their results provide a conceptual advance in the tooth-replacement field as well as new insights into how traits are lost during mammalian evolution and how they might be restored.
The study, “Revitalising the Rudimentary Replacement Dentition in the Mouse,” was published by Development.
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