ppGpp is Present in and Functions to Regulate Sleep inDrosophila

Abstract

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 ppGpp (guanosine-5-diphosphate, 3-diphosphate), a molecule that has been detected in prokaryotes for more than five decades, is present inDrosophila, and plays an important role in regulation of sleep and SISL (starvation induced sleep loss). ppGpp is detected in germ-freeDrosophilaand hydrolyzed by an enzyme encoded by themesh1gene inDrosophila. Nighttime sleep and SISL were defected inmesh1mutant flies, and rescued by expression of wildtype Mesh1, but not the enzymatically defective mutant Mesh1E66A. Ectopic expression of RelA, theE. colisynthetase for ppGpp, phenocopiedmesh1knockout mutants, whereas overexpression of Mesh1 resulted in the opposite phenotypes, supporting that ppGpp is both necessary and sufficient in sleep regulation. A chemoconnectomic screen followed by genetic intersection experiments implicate the Dilp2 neurons in thepars intercerebralis(PI) brain region as the site of ppGpp function. Our results have thus supported that ppGpp is present in animals after long lag since its discovery in bacteria, and revealed a physiological role of ppGpp in sleep regulation for the first time.