Birds share 'language' gene with humans 30/3/04. By Duke University Medical Center A nearly identical version of a gene whose mutation produces an inherited language deficit in humans is a key component of the song-learning machinery in birds.

The researchers, who published their findings in the 31 March 2004 issue of the Journal of Neuroscience, said that their finding will aid research on how genes contribute to the architecture and function of brain circuitry for singing in birds.

Lead researchers included neurobiologist Erich Jarvis, of Duke University Medical Center and Constance Scharff of the Max Planck Institute for Molecular Genetics in Germany.

According to Jarvis, the search for the gene, called FOXP2, began when other researchers reported that the human version of the gene was responsible for a deficit in language production in humans.

"In affected humans, the mutation causes a very specific dysfunction," said Jarvis. "These people have largely normal motor coordination, but an inability to correctly pronounce words or form them into grammatically correct sentences. What's more, they have trouble understanding complex language."

Feature: The FOXP2 story

When evolutionary geneticists compared the DNA sequence of the normal human FOXP2 gene with nonhuman primates and other species, they found that humans have a specific sequence variation not found in any other mammal, said Jarvis. "Since birdsong is a learned vocal behaviour like speech, we decided to find out if a version with this same variation was present in vocal-learning birds," said Jarvis.

Particularly significant, he said, is that the human version of FOXP2 is a type of gene that regulates many other genes – thus making it an ideal candidate for a gene in which a single change during evolution could create a cascade of changes that would influence an advance such as speech or birdsong.

"One advantage of using vocal learning birds," said Wada, also at Duke, "is that there are thousands of songbird species and several hundred parrot and hummingbird species that have vocal learning, but only one primate species that has vocal learning, us humans. Thus, vocal-learning birds provide a rich source of material for evolutionary comparisons."

In their studies, Jarvis and Kazuhiro Wada at Duke, and Scharff and Sebastian Haesler in Germany, compared brain expression of the FOXP2 gene in birds that are vocal learners with those that are nonlearners.

Vocal learners included species of finches, song sparrows, canaries, black-capped chickadees, parakeets and hummingbirds. A vocal nonlearner included ring doves; and the researchers also studied the gene in crocodiles, the closest living relative to birds.

Researchers in another laboratory headed by Stephanie White at UCLA published a paper in the same issue of the Journal of Neuroscience comparing the expression of FOXP2 and its close relative FOXP1 in songbirds and humans.

Scharff, Jarvis and their colleagues confirmed that all the non-mammals they studied, including crocodiles, did have a FOXP2 gene. And although the genes in humans and song-learning birds were almost identical (98 per cent), the song-learning birds did not have the specific variation characteristic of humans.

"Thus, this human-specific mutation is not necessarily required for vocal learning, at least not in birds," said Jarvis. "Or perhaps there's another variation in the songbird gene that also leads to vocal learning."

The researchers did find that the FOXP2 gene was expressed in the same area of the brain – called the basal ganglia – in both humans and song-learning birds. And most importantly, the researchers found the FOXP2 gene to be expressed at higher levels in the "vocal learning nucleus of the basal ganglia of song-learners" at times during the bird's life when it is learning song. This critical learning time might either be during early development in the case of zebra finches, or during seasonal changes in song learning, as in canaries.

Jarvis emphasised that the discovery of FOXP2 represents only the beginning of a major effort to explore the genetic machinery underlying vocal learning and cautions that it has not been proven that FOXP2 is required for vocal learning.

"We definitely don't think that FOXP2 is the single causal gene for vocal learning," he said. "The difference between vocal learners and nonlearners – whether between humans and nonhuman primates; or between learning and nonlearning birds – is most likely to arise in connections of forebrain areas to motor neurons that control the voice. It is intriguing though that an ancient gene like FOXP2 appears to have something to do with learned vocalisations both in humans and in birds.

Adapted from a news release by Duke University Medical Center .

Further reading

Erich Jarvis research pages

Constance Scharff research pages

S Haesler et al. Fox P2 Expression in Avian Vocal Learners and Non-Learners. Journal of Neuroscience 2004 24(13):3164-3175. Abstract