Rulifson said the same could be true for insulin-producing cells. "If the fly cells are using the same molecules and genes as humans, then there's a good chance that much of the pathway of development is conserved," he said.

To make the diabetic flies, Rulifson first identified a group of cells in the brain that produce insulin. He then specifically destroyed only those insulin-producing cells in the fly larvae. These larvae were significantly smaller than their normal counterparts and took longer to develop into full-fledged flies. What's more, the fly larvae that lacked insulin had high blood-sugar levels, comparable to human diabetes.

When Rulifson looked at where the insulin-producing cells were located in the fly brain, he found that they sent projections to the heart, where the nerves released insulin into the larvae's circulatory system. This is similar to how the pancreatic cells release insulin into the human bloodstream.

The nerves also sent projections to a group of cells that release a protein similar to human glucagon. This substance has the opposite effect of insulin - causing cells to release stored sugar into the blood when blood-sugar levels are low. Together, the two opposing hormones keep human blood-sugar levels steady, and may do the same in flies.

Rulifson called these similarities between fly and human hormonal systems "the tip of the iceberg." He said there is enough similarity to suspect his diabetic flies will be good models for the human disease. "This fly model could help us understand the origin of insulin-producing cells in people," he said.

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Contact: Amy Adams
amyadams@stanford.edu
650-723-3900
Stanford University Medical Center
9-May-2002