A system of opposing genetic forces determines why mammals develop a single row of teeth, while sharks sport several, according to a study.
When completely understood, the genetic programme described in the study may help guide efforts to re-grow missing teeth and prevent cleft palate, one of the most common birth defects.
Gene expression is the process by which information stored in genes is converted into proteins that make up the body's structures and carry its messages.
As the baby's face takes shape in the womb, the development of teeth and palate are tightly controlled in space and time by gene expression.
Related abnormalities result in the development of teeth outside of the normal row, missing teeth and cleft palate, and the new insights suggest ways to combat these malformations.
The current study adds an important detail to the understanding of the interplay between biochemicals that induce teeth formation, and others that restrict it, to result in the correct pattern.
Specifically, researchers discovered that turning off a single gene in mice resulted in development of extra teeth, next to and inside of their first molars. While the study was in mice, past studies have shown that the involved biochemical players are active in humans as well.
"This finding was exciting because extra teeth developed from tissue that normally does not give rise to teeth," said Rulang Jiang, associate professor of biomedical genetics at the University of Rochester Medical Centre, and co-author of the paper.
"It takes the concerted actions of hundreds of genes to build a tooth, so it was amazing to find that deleting one gene caused the activation of a complete tooth developmental programme outside of the normal tooth row in those mice."
"Finding out how the extra teeth developed will reveal how nature makes a tooth from scratch, which will guide tooth regeneration research," said Jiang, according to a Rochester release.
These findings were published in Science.