| THE first birds with teeth since the age of the dinosaurs have been created by an Anglo-French team of scientists, raising the prospect of new dental treatments for people — and even a cure for baldness. A batch of chicken embryos raised at a French laboratory have been coaxed into growing rudimentary teeth, after researchers managed to re-awaken a gene that has lain dormant in birds for at least 70 million years. The results of the experiments, which are published in the journal Proceedings of the National Academy of Sciences, have caused jaws to drop all over France: the French expression “quand les poules auront des dents”, meaning “when hens have teeth”, is the equivalent of the English “pigs might fly”. The experiment suggests that one day it may be possible to switch on similar human genes, governing tooth or hair growth, that have become inactive. Such a technique could be used to cultivate replacement teeth and hair for those who have lost their originals to age or disease. Although no modern birds have teeth, their ancestors once boasted beaks bristling with incisors. The teeth sported 147 million years ago by the Archaeopteryx, the first bird known to science, disappeared from its descendants between 70 and 80 million years ago. The DNA that triggers tooth growth did not disappear completely, but instead lingered uselessly in the avian genetic blueprint. A team led by Josiane Fontaine-Perus, of the University of Nantes, has managed to switch this genetic signal back on. In the experiment, which also involved Paul Sharpe, Professor of Craniofacial Development at King’s College London, and other French researchers, a few mouse cells were transplanted into chicken embryos to create hybrids known as chimeras. Whereas chicken cells are incapable of deciphering genetic messages telling them to turn into teeth, mouse cells are receptive to them. They migrated to the correct place in the jaw, and the chicken embryos, which were otherwise normal, began to develop teeth. “The tissue transplant produces cells that contribute to tooth formation,” Professor Sharpe said. “Basically, this tells you that the bird still has the genetic information required to initiate tooth development, if there are cells capable of responding to it.” The implications for people remain a long way in the future: no one is proposing the insertion of mouse cells into human embryos. Insights into tooth and hair formation, however, which share very similar mechanisms, could have valuable dental and trichological benefits. Scientists are particularly hopeful that it might prove possible to identify the genetic cues that prompt hair follicle and tooth growth, both of which occur readily in the embryo but cease in adulthood. If such signals can be traced, drugs could be developed to tell stem cells to form hair follicles rather than skin, and thus reverse baldness. In March an American team announced the discovery of two proteins, named Wnt and noggin, which appear to do exactly that. Dr Fontaine-Perus said that discovering the genetic key to tooth and hair growth in the embryo, which the chicken research is assisting, would help efforts to revive both in older age. “We need to find the spark that would set it off,” she said. “But I am a little sceptical as far as teeth are concerned, since there are perfectly good dentistry techniques as it is. It might be more interesting for those who have lost their hair.” Professor Sharpe agreed that research into baldness could benefit. “It’s possible it will help, but it’s a small part in a bigger ongoing story,” he said. “The idea is that you could somehow awaken dormant processes that happen in the embryo but not in the adult.” His research team has also managed to grow mouse teeth from stem cells in the laboratory, and he hopes to begin human trials of replacement teeth within five years. Most palaeontologists believe that modern birds are descended from the family of predatory dinosaurs known as theropods, which includes Velociraptor and Tyrannosaurus rex — a view that was first advanced by Thomas Henry Huxley in 1868. The discovery of winged and feathered dinosaur fossils in China, particularly of Microraptor gui, from 128 million years ago, suggests strongly that tree-dwelling dinosaurs used feathered limbs to glide from tree to tree, like flying squirrels. This behaviour eventually evolved into powered flight. Microraptor, its relatives and Archaeopteryx all had teeth, but the last bird-like fossils with toothed beaks have been dated to between 70 and 80 million years ago. Though Archaeopteryx is almost 20 million years older than Microraptor, both species are thought to have evolved from similar feathered dinosaurs. It is not known which evolutionary line went on to develop into modern birds. | 
