A local insulin reservoir ensures developmental progression in condition of nutrient shortage in Drosophila

Insulin/IGF signalling (IIS) controls many aspects of development and physiology. In Drosophila, a conserved family of insulin-like peptides (Ilp) is produced by brain neurosecretory cells and exerts systemic functions. Here, we describe the local uptake and storage of Ilps in the Corpora Cardiaca (CC), a group of alpha cell homolog that produces the glucagon-like hormone AKH. Dilp uptake relies on the expression of Impl2, an IGF-BP that accumulates in the CCs. During nutrient shortage, this specific reserve of Ilps is released and activates IIS in a paracrine manner in the prothoracic gland, securing accelerated entry into pupal development through the production of the steroid hormone ecdysone. We therefore uncover a sparing mechanism whereby local Ilp storage and release activates the production of steroids and ensures early developmental progression in adverse food conditions. Highlights- Dilps are uptaken by CC cells through the IGF-BP Imp-L2 - the CC-Dilp store is released upon nutrient shortage and activates IIS through CC projections on the PG - upon nutrient shortage, IIS activation in the PG ensures an accelerated transition from larval feeding stage to metamorphosis.