The trillions of cells that make up our bodies are each enclosed in membranes. Surprisingly, the lipid composition of these cellular membranes − that is the nature of the various fats and related substances that make them up − must be precisely regulated to prevent inappropriate cell growth. Indeed, imbalances in the phosphatidylinositol (PI) lipids, a class of regulatory lipids, have been directly implicated in tumor formation in humans. To understand how PI lipids control cell growth, we are studying fruit flies with mutations in key enzymes termed PI 4-kinases (PI4Ks) that control PI lipid production. This allows us to use the powerful genetic tools available in the fly system to teach us about how these enzymes function in complex animals such as humans. Studies outlined in the current application will use fly genetics, molecular biology and specialized microscopy techniques to uncover the roles of PI4Ks in a newly discovered cancer signaling pathway.