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A Master Key to Insect Diversity?

BOSTON--The startling diversity of insect body plans may have arisen thanks in part to a small stretch of DNA that unleashed the potential of key developmental genes shared by many animals, a researcher said today at the annual meeting of the American Association for the Advancement of Science, the publisher of ScienceNOW.

Genes that guide development are conserved across a diverse range of organisms, from moths to mackerel to monkeys. Principal among these are the homeotic (Hox) genes that influence the location and function of various body regions. Scientists think the great differences among organisms result less from the number or type of such developmental genes than from the way they are regulated. But just how the same or similar genes can create such different organisms has remained elusive.

Now, researchers have pinpointed a regulatory change that appears to have been key in the evolution of Earth's most varied group, the insects. Ron Galant and Sean Carroll of the University of Wisconsin, Madison, studied a Hox gene called Ultrabithorax (Ubx) that controls which limbs are attached to which body segments. After examining the DNA of fruit flies and four other kinds of insects, the duo discovered that a neighboring region of DNA is almost nearly identical in all of them. The region turned out to vary considerably in other arthropods and related wormlike organisms such as onychophorans.

To find out the function of this neighboring region, Galant and Carroll swapped it between flies and onychophorans. The onychophoran's DNA functioned just fine when placed in a fruit fly's genome. But the fruit fly DNA from this region gave the onychophoran new developmental abilities that only insects possess; for instance, it could turn thoracic tissue into abdominal segments and repress certain target genes. The researchers suggest that this region placed insects' legs on their thoraxes and freed up abdominal segments to take on new shapes and functions. Galant and Carroll first published their findings in the 6 February online edition of Nature.

The story shows that if biologists compare the evolutionary history of organisms and ask the right questions, says Ann Burke, an evolutionary developmental biologist at Wesleyan University in Middletown, Connecticut, "we can mine all this incredible data even out of systems that seem so well-known."