Reverse genetic screening during L1 arrest reveals a role of the diacylglycerol kinase 1 gene dgk-1 and sphingolipid metabolism genes in sleep regulation.

Sleep is a fundamental state of behavioral quiescence and physiological restoration. Sleep is controlled by environmental conditions, indicating a complex regulation of sleep by multiple processes. Our knowledge of the genes and mechanisms that control sleep during various conditions is, however, still incomplete. In Caenorhabditis elegans, sleep is increased when development is arrested upon starvation. Here, we performed a reverse genetic sleep screen in arrested L1 larvae for genes that are associated with metabolism. We found over 100 genes that are associated with a reduced sleep phenotype. Enrichment analysis revealed sphingolipid metabolism as a key pathway that controls sleep. A strong sleep loss was caused by the loss of function of the diacylglycerol kinase 1 gene, dgk-1, a negative regulator of synaptic transmission. Rescue experiments indicated that dgk-1 is required for sleep in cholinergic and tyraminergic neurons. The Ring Interneuron S (RIS) neuron is crucial for sleep in C. elegans and activates to induce sleep. RIS activation transients were abolished in dgk-1 mutant animals. Calcium transients were partially rescued by a reduction-of-function mutation of unc-13, suggesting that dgk-1 might be required for RIS activation by limiting synaptic vesicle release. dgk-1 mutant animals had impaired L1 arrest survival and dampened expression of the protective heat shock factor gene hsp-12.6. These data suggest that dgk-1 impairment causes broad physiological deficits. Microcalorimetry and metabolomic analyses of larvae with impaired RIS showed that RIS is broadly required for energy conservation and metabolic control, including for the presence of sphingolipids. Our data support the notion that metabolism broadly influences sleep and that sleep is associated with profound metabolic changes. We thus provide novel insights into the interplay of lipids and sleep and provide a rich resource of mutants and metabolic pathways for future sleep studies.