Teething trouble resolved

Where do teeth come from? Not just in terms of popping through the gums of a dribbling baby, but in an evolutionary context. Now research published in the journal PloS Biology shows that a common genetic control system is in charge of the development of all known teeth, from the first ever teeth in fish living half a billion years ago, to our own pearly whites.

This is research by Gareth Fraser and his colleagues from the US. They studied tooth formation in a group of fish that undergo rapid evolution - fish known as cichlids that are found in Lake Malawi in Africa. These fish have two sets of teeth - one set in their jaws in their mouths, and another set back in their throat. 

These two sets of teeth re very different in evolutionary and developmental terms - teeth set back in the throat are a much older invention that teeth in the mouth. But the researchers were surprised to find that there was a link between the number of teeth in the mouth and in the throat, suggesting that they were genetically linked in some way.

The researchers used a technique called in situ hybridisation, which allows scientists to precisely reveal the gene activity patterns of specific genes. Using this, they found that a common set of genes controls the teeth in the cichlids' mouths and also in their throats. These genes are Hox genes - which are involved in patterning many of the body's structures.  For example, some of our Hox genes give us a regular pattern of vertebrae in our spine, and five fingers and toes.

The scientists found that a precise pattern of Hox gene activity, along with other related genes controlled by Hox genes, was needed for developing both teeth in the throat and in the mouth.  So it's likely that the earliest fishes used Hox genes to create teeth in their throats, and later on in evolution, the same genetic pathway was co-opted, with a few tweaks, to create mouth teeth.

So the researchers think that every tooth made throughout evolution probably uses this core set of genes. And similar pathways could be at work in other patterned structures like hair and feathers.