Two years ago Rulifson and Kim showed that a group of cells in the brain of the fly make insulin, which parallels the role of beta cells in humans. Now, in the September 16 issue of Nature, the researchers describe cells that produce a glucagon-like hormone, which are akin to alpha cells in mammals. These two cell types within the pancreatic islets are the main cellular sensors of blood-sugar levels. Together the fly's insulin- and glucagon-producing cells could be seen to represent a primitive pancreatic islet.
After eating food, insulin notifies muscles, fat cells, and the liver to take up excess sugar in the blood and store it as glycogen. Conversely, when the sugar level in blood dips between snacks, glucagon notifies the muscles and liver to break down stored energy like glycogen and fat to release as glucose. However, when this finely tuned system goes wrong, all-too-familiar diseases arise: diabetes when there is too much sugar; hypoglycemia when there is too little.
Because of the unexpected similarities between the insect and human pancreas, Rulifson explains that now the fly can serve as a simple model of how sugar is regulated at a very basic level. "At this point investigators would like to understand how this ancient mechanism for cells that sense the nutrient and energy status of an animal can adjust an animal's growth and metabolic state," he says. "Now we have a model for that."
Coaxing stem cells to become pancreatic islet cells for
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Contact: Karen Kreeger
karen.kreeger@uphs.upenn.edu
215-349-5658
University of Pennsylvania School of Medicine
15-Sep-2004