Given the role of the insulin signaling pathway in the control of cellular metabolism in vertebrates and in C. elegans , a test was performed to see whether energy stores are altered in chico mutant flies. The amount of lipid, protein, and glycogen per unit of fresh weight was determined. While there was no significant difference in levels of proteins and glycogen, lipid levels are increased significantly in chico males. In fact, despite their smaller size, chico males have almost twice as much lipids as wild-type males per milligram of fresh weight. Given the fact that in vertebrates, the insulin receptor pathway plays a critical role in regulating cellular metabolism and growth, it is interesting to speculate that the insulin signaling pathway in flies is part of a nutritional sensing system for each individual cell.
Growth is dependent on the availability of nutrients.
The reduced body size of chico flies is similar to that of flies reared under poor nutritional conditions. Poorly fed flies also eclose later and possess fewer and smaller cells. In multicellular organisms a system of overall growth coordination is required, since nutrient conditions are unlikely to be the same for all cells in an organism. As a result, cells grow and divide when a critical cell size has been reached. However, when the level of these growth factors drops because of adverse food conditions, the INR pathway activity is reduced.