ppGpp is present in, and functions to regulate sleep of, Drosophila

Sleep is essential for animals, and receives inputs from circadian, homeostasis, and environment, yet the mechanisms of sleep regulation remain elusive. Discovery of molecules in living systems and demonstration of their functional roles are pivotal in furthering our understanding of the molecular basis of biology. Here, we report that guanosine-5'-diphosphate, 3'-diphosphate (ppGpp) is present in Drosophila, and plays an important role in regulation of sleep and starvation-induced sleep loss (SISL). ppGpp is detected in germ-free Drosophila and hydrolyzed by an enzyme encoded by the mesh1 gene in Drosophila. Nighttime sleep and SISL were defected in mesh1 mutant flies, and rescued by expression of wildtype Mesh1, but not the enzymatically defective mutant Mesh1E66A. Ectopic expression of RelA, the Escherichia coli synthetase for ppGpp, phenocopied mesh1 knockout mutants, whereas overexpression of Mesh1 resulted in the opposite phenotypes, supporting that ppGpp is both necessary and sufficient in sleep regulation. A chemo connectomic screen followed by genetic intersection experiments implicates the Dilp2 neurons in the pars intercerebralis (PI) brain region as the site of ppGpp function. Our results have thus validated the presence of ppGpp in Drosophila and revealed a physiological role of ppGpp in sleep regulation for the first time.