ppGpp Is Present in, and Regulates Sleep of, Drosophila

Discovery of molecules in living systems and demonstration of their functional roles are pivotal in furthering our understanding of the molecular basis of biology. ppGpp (guanosine-5-diphosphate, 3-diphosphate) has been detected in prokaryotes for more than five decades. Here we report that a genetic screen followed by chemical analysis revealed the presence of ppGpp in Drosophila. It can be detected in germ-free Drosophila and its level is controlled by an enzyme encoded by the mesh1 gene in Drosophila. Loss of function mutations in mesh1, which encoded the ppGpp degrading enzyme led to longer sleep latency and less total sleep. These phenotypes could be rescued by wild type mesh1, but not by the enzymatically defective mutant Mesh1E66A, functionally implicating ppGpp. Ectopic expression of RelA, the E. 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. mesh1 is expressed in a specific population of neurons, and a chemoconnectomic screen followed by genetic intersection experiments implicate the pars intercerebralis (PI) as the site of ppGpp function. Our results have thus revealed that ppGpp is present in animals after long lag since its discovery in bacteria. Furthermore, we have demonstrated that ppGpp in a specific subset of neurons plays a physiological role in regulating sleep. We speculate that ppGpp may play function in mammals.