One of the most important requirements for healthy cellular growth is the ability to sense and respond to extracellular nutrients. When nutrient supply is plentiful, cells need only to fine tune their anabolic and catabolic rates so that their energy requirements match the available resources. When nutrients become limiting or are completely unavailable, a much stronger course of action is required to allow the cells to survive. During such times of nutrient withdrawal, the cells respond by initiating autophagy, a degradative pathway that allows the breakdown of intracellular proteins into amino acids that can be used subsequently for new protein synthesis or energy generation. An important question in autophagy concerns the mechanisms by which cells sense their extracellular nutrient content. Recent work from many groups has indicated that a small lipid molecule termed phosphatidylinositol 3 phosphate (PI3P) is an important signal for nutrient sensing. Our own work also indicates that autophagy is induced partially as a result of the formation of PI3P in specialised membrane compartments called omegasomes. Therefore, the mechanisms and signals that generate PI3P early during autophagy are likely to provide important information on the control of autophagy by nutrient sensing. The aim of this grant is to identify all human genes that are involved in this pathway. We plan to systematically silence all known human genes and then look at the effect that this will have in formation of PI3P during autophagy. By identifying all such genes we will be able to construct a wiring diagram of the cellular pathways that are implicated in nutrient sensing and respond during nutrient limitation by the induction of autophagy.