Baring the genetic secrets of mice teeth
The gene responsible for the formation of tooth enamel has been identified by a team from the University of Helsinki. They believe they now have the key to understanding how the teeth of rodents stay so sharp. In a second study, Helsinki researchers have also discovered a method to explore the evolution of species through fossilised teeth.
Rodents’ incisors are characterised by their sharp cutting edge, which retains its sharpness although the rest of the tooth is worn down gradually by gnawing. The Helsinki team, together with partners from the USA and Switzerland, have identified a gene which codes a signalling module – bone morphogenetic protein (BMP) – which is critical to the formation of enamel.
|The teeth of mice tell us a lot about their evolutionary history|
The research, published in the journal Developmental Cell, shows that BMP, together with its specific inhibitor follistatin, initiates the development of enamel. The inhibition of the BMP signalling molecule on the inner surface of the tooth means that enamel is only built on the outer side. Therefore, the outer surface is harder, wearing down more slowly, and a sharp edge forms at the point where the two surfaces meet.
Fine-tuning of signalling molecules is the most important mechanism in regulating the shape of tissues and organs, the research suggests. The example of rodents’ teeth (mice in this case) shows how local differences in the activities of the signalling molecules determine the creation of complex structures.
Chewing over the past
Many mammal species are now extinct and the only remains available for study are fossilised teeth. Exploring the genetic make-up of these teeth helps researchers to understand the links between different species. A second team also from the University of Helsinki, in a study published in Nature, have demonstrated that one signalling molecule can change the characteristics of teeth.
This team focused on the signalling molecule ectodysplasin. By increasing the secretion of this molecule in a mouse, the teeth developed structures found in a kangaroo’s teeth. Furthermore, it caused the mouse to have an additional tooth, in a place where ancestral species of rodents – 45 million years ago – had a tooth. On the other hand, by decreasing the secretion of ectodysplasin, the mouse’s teeth lost several structures.
These results will help evolutionary biologists to determine the relationships between species. They will also help in studying why closely related species, such as the chimpanzee and human, have so many structural differences.
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Developmental Cell, 7(5), November 2004
Nature 432: 211-214, 11 November 2004