Abstract
Secreted ligands of the insulin family promote cell growth and maintain sugar homeostasis. Insulin release is tightly regulated in response to dietary conditions, but how insulin-producing cells (IPCs) coordinate their responses to distinct nutrient signals is unclear. Here we show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches-whereas amino acids promote the secretion of Drosophila insulin-like peptide 2 (Dilp2), circulating sugars promote the selective release of Dilp3. Dilp3 is uniquely required for the sugar-mediated activation of TOR signalling and suppression of autophagy in the larval fat body. Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and we demonstrate that AKH signalling is required in the IPCs for sugar-dependent Dilp3 release. Thus, IPCs integrate multiple cues to regulate the secretion of distinct insulin subtypes under varying nutrient conditions.
