Getting a Leg Up on the Birds

Drumsticks, anyone? If you're partial to chicken legs, here's good news for you. Thanks to some clever genetic engineering, scientists at the Salk Institute in La Jolla, Calif., have come up with a way to grow birds with an extra pair of legs.

The work, described in last week's Nature, centers on so-called T-box genes. Common to all vertebrates, including humans, they're important in the development of limbs in the embryo--determining, for example, whether they become hind- or forelimbs (or in chickens, legs or wings). But, says geneticist Juan Carlos Belmonte, the study's senior scientist, "we didn't know if one of these genes by itself was sufficient to send a limb down one pathway or the other."

To unravel the puzzle, the scientists infected the unformed wing region of day-old chicken embryos with a virus carrying a T-box gene known as Tbx-4. A day later, they transferred the tissue to other embryos still in their shells.The transplanted cells quickly grew into recognizable legs. By contrast, when the scientists transferred wing tissue without first infecting it with Tbx-4 genes, the tissue always grew into wings. That shows that Tbx-4 contains a full genetic blueprint for a leg, says Belmonte.

The scientists hope to learn how T-box genes turn on and off. That could give them clues to human birth disorders like Holt-Oram syndrome, which is characterized by stunted arms and hands and is linked to these genes. As for the chicks, the scientists didn't let them hatch, resisting the temptation to grow drumsticks for KFC.