The small teeth lining cichlid fishes’ throats won’t make it into any baby scrapbooks, but the nubs have helped researchers figure out how vertebrates got their chompers. Research has uncovered what may be a shared toolkit of genes “common to the first tooth and all of its descendents,” a team reports online February 10 in PLoS Biology. Tooth formation is likely controlled similarly in cichlids and in humans, the study suggests.
“The genes in fish are the genes that make teeth in humans,” says coauthor Gareth Fraser of Georgia Institute of Technology in Atlanta.
Vertebrates cut their teeth about half a billion years ago in the seas. Pearly whites first showed up in ancient eel-like fish called conodonts, described by Fraser as “jawless beasts that roamed the seas with rows and rows of teeth in their throats.”
The great diversity of modern-day cichlids in Africa’s Lake Malawi extends to their teeth. Like the conodonts, cichlids have teeth in their pharynx. But they also have them in their mouths — the teeth can form in many different patterns and can number from very few into the thousands. And some cichlids lose and regrow their teeth every two weeks, Fraser says.
“We sat down and counted all the teeth, a laborious task,” Fraser says. From this counting, the researchers found that fish with fewer teeth in the mouth also had fewer teeth in the throat, suggesting that similar genetic factors control the two types of teeth.
The researchers went on to find that many of the same genes were active in regions surrounding teeth in the throat as in the mouth. Not only were the same genes controlling tooth formation in different parts of the fish, but these same genes have also been shown to control tooth formation in mammals, including humans.
In zebra fish, earlier studies have found that these genes are directly involved in tooth formation. “Little tweaks in these networks can lead to strange little teeth poking out in weird places,” Fraser says of the genes in zebra fish.
Thimios Mitsiadis, a researcher at the University of Zurich in Switzerland, says people born with tooth abnormalities or people who lose teeth later in life benefit if researchers understand the signals that create teeth. “If you know what genes to activate, then you can make cells form teeth,” says Mitsiadis.
The new research doesn’t directly test the role of these genes on tooth formation in cichlids, as the zebrafish study did, Mitsiadis points out. In the future, he says, it would be nice to see whether cichlid fish have abnormal teeth if these genes are missing or overactive.