Gene tells fruit fly how to wing it.

This hapless fruit fly has wings growing out of its large, tomato-red eyes.

The stubby gray wings don't help the insect fly-they can't even move-but biologists are abuzz over the laboratory feat.

"We've turned one kind of tissue into another," says study leader Sean B. Carroll of the Howard Hughes Medical Institute at the University of Wisconsin-Madison.

Carroll says he was surprised that a single gene-not several-was enough to spark the formation of a major structure like wings. He and his colleagues activated the gene, called vestigial, in regions of embryonic flies that don't normally form wings. In the resulting adult flies, wing tissue developed in eyes, heads, antennae, or legs.

The researchers had to limit where they activated vestigial, Carroll notes, to prevent wing tissue from sprouting all over the fly.

The team's goal wasn't to design winged freaks, however. The discovery, reported in the July 11 Nature, is intended to help unravel the genetic tangle behind the development of such complex animal structures as claws, arms, legs, and tails, all of which form out of the seemingly uniform tissue of embryos. The report also shows that although vestigial alone can prompt wing tissue growth, a number of other genes must respond to its initial signal.