Insulin signalling activates multiple feedback loops to elicit hunger-induced feeding in Drosophila

Insulin, a highly conserved peptide hormone, links nutrient availability to metabolism and growth in animals. Besides this, in fed states insulin levels are high and insulin acts as a satiety hormone. In animals that are food deprived insulin levels remain low which facilitates hunger induced feeding. Contrary to expectations, we present evidence for persistent Drosophila insulin-like peptide gene expression and insulin signalling during initial phases of starvation. Maintenance of insulin signalling is crucial to sustain feeding responses during initial stages of starvation. Insulin signalling acts in a feedback loop involving the abdominal fatbody to maintain dilp gene expression in the early stages of food deprivation. Furthermore, another feedback regulatory loop between insulin-producing cells (IPCs) and neurons that produce the orectic hormone short-neuropeptide-F (sNPF), maintains sNPF levels and triggers feeding behavior. Thus, insulin acts through multiple feedback regulatory loops to elicit orexigenic responses and aid in efficient utilization of energy stores during early starvation.