Songbird DNA clue in language puzzle

Scientists believe comparing zebra finch and human genomes may lead to better ways of diagnosing and treating problems such as stuttering and autism.

Like other songbirds, only the male zebra finch sings as it serenades females to attract a mate.

The finch learns to sing as a baby by copying its father. At first the young bird "babbles" nonsensically, much like a human infant, but with practice learns to imitate his father's song.

When the bird grows to an adult he, in turn, passes the family song to the next generation. Although female zebra finches do not sing themselves, they can distinguish between different song types

The zebra finch song melody only lasts a few seconds, but involves an enormously complex array of brain circuits.Far more of the bird's genome is devoted to singing than scientists expected, the study showed.

The researchers identified more than 800 genes involved in song-learning, many of which had undergone accelerated evolution in the finch.

A key surprise discovery was that singing engaged numerous non-coding elements within the birds' brains - genetic networks that would once have been dismissed as purposeless "junk".

This was one of the main differences seen between zebra finches and chickens, which "cluck" but do not sing.

Genes are normally thought of as stretches of DNA bearing the coded "instructions" for making proteins within their chemical make-up. But in songbirds large numbers of small non-coding genetic molecules called micro RNAs seem to exert a powerful influence. By "jamming" hundreds of genes, they help determine which parts of the singing circuitry are switched on and off.

"The system for singing has much more complexity than we imagined," said Professor Erich Jarvis, a US researcher from Duke University Medical Centre in Durham, North Carolina.

"In the part of the brain that controls learning how to sing, about 5% of the genes are regulated by the action of singing. I thought there might be 100 genes, but our laboratory found that there were at least 800 regulated genes turning off and on, and there may be many more."

The findings are published today in the journal Nature.

Scientists expect the work to help them understand the origins of language, uncover the causes of speech disorders such as stuttering, and learn why autistic people have trouble communicating.

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