In A Nutshell
Everyone knows that birds in general have no teeth. But did you know that birds used to have teeth, long ago when dinosaurs still roamed the earth? They have long since lost their teeth, but new research on the talpid2 gene mutation in chickens has shown that they still have the genes for growing chompers. With some gene tweaking experiments, scientists succeeded in inducing teeth growth in healthy chickens, proving that the gene can work in mutated and non-mutated chickens alike.
The Whole Bushel
Developmental biologist Matthew Harris of the Max Planck Institute in Tubingen, Germany, was investigating a gene mutation known as talpid2 that affects organ development in chicken embryos when he made an accidental discovery that revealed that chickens retain the ability to grow teeth. He was examining the head of a 16-day-old mutant chicken embryo while working late in the lab one night, when he noticed the tiny protuberances on the edge of the beak. Scientists have known about the lethal and recessive talpid2 gene for years, but have never made the link between the gene and teeth formation because the mutant embryos never survive to the hatching stage, which usually takes 21 days. However, scientists have managed to incubate them for up to 18 days, and during the last few of those 18 days, they began to grow nascent teeth that haven’t been seen in avians for millions of years, until now.
Though small, the teeth were definitely conical and saber-shaped, like those found in the mouths of crocodiles and ancient bird fossils. The earliest known bird ancestors were called archosaurs and they had teeth and mouths that were shaped very much like a crocodiles’. The similarity is no surprise to the scientists at all, since birds are much more closely related to reptiles than they are to mammals. Over time, the development of beaks eventually caused birds to lose their teeth, giving birth to the modern birds that we know today.
Scientists are surprised that these mutant chicks still retained the genes responsible for teeth formation because the birds lost their toothy features about 70–80 million years ago. In an experiment conducted in 1980, scientists relied on introducing genetic information from mice to produce teeth in chickens, resulting in chickens that grew mammalian molars. But since birds and mammals are not as closely related, scientists doubted whether the experiment proved that the birds truly retain the teeth forming genetic vestige of their ancestors.
Harris and colleague John Fallon at the University of Wisconsin (Madison) decided to further their investigations and find out if healthy chickens really still retained the genetic pathway for teeth formation. By “activating” the talpid2 gene in the mouths of normal healthy chicken embryos, they were able to induce teeth formation in chicks. The chicks developed the same reptilian teeth and share many similar genetic traits. The success of their experiments not only confirms their hypothesis but it also proves that the teeth formation was not a one-off freak occurrence only found in mutant chicks.