Scientists have discovered a network of genes that gave humans their first tooth.
Gareth Fraser, postdoctoral fellow at Georgia Tech's School of Biology, describes it as a common gene regulatory circuit that controls the development of all dentitions, from the first teeth in the throats of jawless fishes that lived half a billion years ago, to the incisors and molars of modern vertebrates.
"It's likely that every tooth made throughout the evolution of vertebrates has used this core set of genes," Fraser says.
Writing about their study in the journal 'PLoS Biology', the researchers said that the first vertebrates to have teeth were a group of eel-like jawless fish, known as the conodonts, which had teeth not in their mouth, but lining the throat.
According to them, this particular group is long since extinct, but some modern fish retain teeth in the throat (pharynx).
Fraser's team studied tooth formation in a group of fish known for their rapid rate of evolution, the cichlids of Africa's Lake Malawi.
The researchers highlight the fact that the cichlids have teeth both in their oral jaws, like humans, and deep in their throats on a pharyngeal jaw.
They first identified a surprising positive correlation between the number of teeth in the oral jaw and in the throat in the fish.
"Originally, I thought there wouldn't be a correlation due to the developmental differences and the evolutionary distinction between the two jaw regions, but it turns out, there is. So fish that have fewer oral teeth also have fewer pharyngeal teeth. This shows that on some level there's a genetic control that governs the number of teeth in both regions," said Fraser.
The team used a technique called in situ hybridization to probe what this control might be, and found that a common genetic network governs teeth in the two locations.
"So seemingly, regardless of where you grow a tooth, whether it's in the jaw or the pharynx, you use the same core set of genes to do it. We also think it's probable that this network is not just acting in teeth, but also in other similarly patterned structures like hair and feathers," said study co-author J. Todd Streelman.