Examination of akt and foxo in growth and survival during conditions of nutritional stress in Drosophila melanogaster

The insulin signaling pathway has been implicated as a regulator of cell growth and survival. To better understand the role of this pathway in these processes, two key effectors of insulin signaling, including the central component protein kinase akt, and its downstream target, the transcription factor foxo, were investigated. Novel derivatives of a P-element allele of Drosophila melanogaster akt exhibit lifespans which are comparable to controls. Analysis of somatic clones of the eye of these derivatives reveal that altered akt activity often leads to a reduction in cell number and size. Two FRT/FLP methods were used to generate clones, and the ey-GAL4/UAS-FLP method was shown to be more sensitive than the ey-FLP method. Analysis of foxo as a mediator of insulin signaling effects under various conditions of nutritional stress revealed its necessity during protein starvation, as foxo mutants did not live as long as controls or heterozygotes upon amino-acid starvation. A novel foxo-responsive luciferase assay revealed that as time of protein starvation increases, the expression of foxo is upregulated. Differences in total body mass between foxo mutants and controls after 96 hours of starvation suggest a possible maternal effect. Analysis of foxo protein activity within the akt⁰⁴²²⁶ derivatives showed that both homozygous and heterozygous derivatives experienced a decrease in foxo activity compared to the control, but to varying degrees. Taken together, these findings support a role for insulin signaling in the control of cell growth and survival. In addition, they suggest the ability of insulin signaling to mediate cellular processes in response to nutrient availability