Bird genes help explain speech

The first genome sequence of a songbird, published in Nature this week, has provided scientists with the tools to begin studying the molecular underpinnings of vocal learning -- an ability present in just a few other animals, including whales, bats and humans. The zebra finch gets its name from the black- and-white stripes on the male finch's throat Image: L. Brian Stauffer, U. of Illinois News Bureau "This is a really important step forward for our field," said linkurl:Allison Doupe,;http://keck.ucsf.edu/neurograd/faculty/doupe.html a neuroscientist and psychiatrist at the University of California, San Francisco, who studies bird song and was not involved in the research. "We don't have many models for one of our most amazing capabilities -- humans' ability to learn to speak." Zebra finches, one of more than 4000 species of songbirds, learn their song from their male parents, reproducing it with slight variation and passing it down to their own male offspring. This process is analogous to what happens in humans, who first begin babbling as babies and then learn speech from their parents during development, said linkurl:Wesley Warren,;http://genomeold.wustl.edu/Bio/WarrenBIO.cgi a geneticist at the University of Washington, St Louis, and the lead author on the paper. Many of the genes involved in the process are also conserved. To find them, Warren and an international consortium of scientists compared to songbird genome to another avian genome -- the chicken, which was sequenced in 2004, and cannot learn vocalizations. Structurally, the researchers found, the two avian genomes had many similarities, but one difference stood out: The two species appear to differ in how they regulate their sex chromosomes. That "seemed interesting," said Doupe, "given that sex chromosomes are so important to the development of song" in zebra finches, with song learning being limited to males. A previous study had identified RNAs of genes in the zebra finch auditory cortex that are up- or down-regulated in response to hearing song. The researchers mapped those genes to the zebra finch sequence, determining that more than 40 percent did not code for proteins. Response to novel song is thought to be especially indicative of vocal learning, compared to previously-heard song to which the bird may have habituated; two thirds of the RNA that was suppressed right after experiencing a novel song was noncoding. Some of these were microRNAs, short regulatory elements that function by silencing genes. The researchers also identified one long non-coding region in the gene for a song-regulated transcription factor. This gene has a close homolog in humans. Looking closer, initial experiments identified binding sites within this noncoding region for 11 microRNAs, suggesting that "one thing [the noncoding element] could be doing is mediating interactions with microRNAs," said linkurl:David Clayton;http://www.life.illinois.edu/clayton/Home.html at the University of Illinois at Urbana-Champaign and a coauthor on the study. "This is still hand-waving -- it's not proving anything," stressed Clayton. But these layers of regulation, he said -- a transcription factor that seems to be a target for several microRNAs -- might explain how learning vocalizations, whether song or speech, is modulated by a complex circuit of genes being turned on and off. Finally, the researchers conducted a phylogenomic comparison between chicken, zebra finch and genes from several species of mammals. Measuring the changes in sequence and mapping them to the phylogenetic distance between the organisms allowed them to identify genes in the zebra finch that seemed to be evolving more quickly than others -- suggesting they are under particular selection pressure in the species. Of those, 49 were also on the list of genes that were downregulated specifically after hearing a novel song, as opposed to a familiar song or silence. Six of them, they found, coded for ion channels, which are known to be involved in complex neurological processes. Download Flash player to listen to University of Illinois cell & developmental biology professor David Clayton compare the songs of two zebra finches. Each individual sings a unique song. University of Illinois cell & developmental biology professor David Clayton compares the songs of two zebra finches. Each individual sings a unique song. More than anything, said linkurl:Rebecca Kimball,;http://people.biology.ufl.edu/rkimball/ an evolutionary geneticist at the University of Florida, the study identifies potentially interesting genetic features and "points out areas where we need to do more work." Indeed, Richard Mooney, a neurobiologist who studies birdsong at Duke University, said he isn't convinced that the identified genes are important in vocal learning, rather than responding to vocalizations, which most animals do. It is, however, a start, he said. "What I would like to see is a comparison to another bird that really uses vocalization a lot, that hasn't been domesticated." Comparing the zebra finch genome to other songbird species will allow researchers to tease out genes relating to specific aspects of song, said Doupe. For example, looking at the zebra finch sequence along with that of a species in which both males and females sing may reveal the molecular underpinnings of sex differences. **__Related stories:__*** linkurl:Erich Jarvis;http://www.the-scientist.com/article/display/36472/ [November 2006]*linkurl:Singing in the Bird Brain;http://www.the-scientist.com/article/display/24844/ [October 2006]

Bird genes help explain speech

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