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The Logic of the Response
by Karen F. Schmidt
Researching wound response, Mark Krasnow (left) and Michael Galko can watch it at the cellular level, study it in live animals, and analyze it rapidly.
While studying a homely "kissing bug," British insect physiologist Sir Vincent Wigglesworth injured a spot on the creature's epidermis. He observed an inflammatory response and then watched the epidermis grow back under the outermost protective cuticle layer and reseal itself.
Wigglesworth documented his findings about how a wound heals in 1937. But even through today, basic understanding of wound healing hasn't progressed much beyond his work. Researchers, for example, still don't know much about the key genes involved and their specific roles.
Wanting to study wound healing at the molecular level, HHMI investigator Mark A. Krasnow was inspired to repeat Wigglesworth's experiment. Only this time, he and postdoctoral researcher Michael J. Galko were studying the tiny fruit fly (Drosophila)—and they were armed with the latest light and electron microscopes as well as techniques for creating mutants and analyzing gene expression. "Wigglesworth would have killed for these tools," says Krasnow.
Their cutting-edge approach allowed the Stanford University researchers to develop a powerful new model for the study of wound healing. "We've begun to dissect out the logic of the response, which has proved very difficult to sort out in vertebrates," says Krasnow. Because the ability to heal wounds exists in even the simplest animals and must have evolved early, he and Galko believe the core molecular controls in fruit flies will be similar to those in higher animals, including humans.
Galko figured out how to poke a hole in Drosophila's cuticle and epidermis without killing the insect. He identified a larval stage amenable to study—when the then-clear cuticle makes it easy to see fluorescent markers that signal gene expression. He also found a way to turn off a critical gene in the epidermis at this larval stage so that early development would remain normal and undisturbed. "We can now watch the wound response at the cellular level in transgenic larvae; study it in live animals, including mutants; and analyze it rapidly," Galko says.
The Stanford researchers tested their model by knocking out two genes suspected of playing a role in wound healing: the transcription factor lozenge (which controls development of a specific kind of blood cell) and the gene that codes for Jun N-terminal kinase (an enzyme critical for programming development of epidermal sheets). Their experiments showed that the latter is required for epidermal closure, while the former is needed for scab formation. Although the two genes are involved in separate pathways, they clearly engage in some crosstalk. The researchers published their findings in the August 2004 issue of Public Library of Science Biology.
Photo: Timothy Archibald