Summary Prolonged wakefulness leads to an increased pressure for sleep, but how this homeostatic drive is generated and subsequently persists is unclear. Here, from a neural circuit screen in Drosophila, we identify a subset of ellipsoid body (EB) neurons whose activation generates sleep drive. Patch-clamp analysis indicates these EB neurons are highly sensitive to sleep loss, switching from spiking to burst-firing modes. Functional imaging and translational profiling experiments reveal that elevated sleep need triggers reversible increases in cytosolic Ca2+ levels, NMDA receptor expression, and structural markers of synaptic strength, suggesting these EB neurons undergo “sleep need”-dependent plasticity. Strikingly, the synaptic plasticity of these EB neurons is both necessary and sufficient for generating sleep drive, indicating that sleep pressure is encoded by plastic changes within this circuit. These studies define an integrator circuit for sleep homeostasis and provide a mechanism explaining the generation and persistence of sleep drive.

Signaling through tyrosine kinase receptors (TKRs) is thought to be modulated by receptor-mediated endocytosis and degradation of the receptor in the lysosome. However, factors that regulate endosomal sorting of TKRs are largely unknown. Here, we demonstrate that Hrs (Hepatocyte growth factor-regulated tyrosine kinase substrate) is one such factor. Electron microscopy studies of hrs mutant larvae reveal an impairment in endosome membrane invagination and formation of multivesicular bodies (MVBs). hrs mutant animals fail to degrade active epidermal growth factor (EGF) and Torso TKRs, leading to enhanced signaling and altered embryonic patterning. These data suggest that Hrs and MVB formation function to downregulate TKR signaling.

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Sleep is an essential process conserved from flies to humans. The importance of sleep is underscored by its tight homeostatic control. Here, through a forward-genetic screen, we identify a novel gene, sleepless, required for sleep in Drosophila. sleepless encodes a brain-enriched, glycosylphosphatidylinositol-anchored protein. Loss of SLEEPLESS protein causes an extreme (>80%) reduction in sleep. Furthermore, a moderate reduction in SLEEPLESS protein has minimal effects on baseline sleep, but markedly reduces recovery sleep following sleep deprivation. Genetic and molecular analyses reveal that quiver, a mutation that impairs Shaker-dependent K + current, is an allele of sleepless. Consistent with this finding, Shaker protein level is reduced in sleepless mutants. We propose that SLEEPLESS is a signaling molecule that connects sleep drive to lowered membrane excitability.Insufficient and poor quality sleep is an increasing problem in industrialized nations. Chronic sleep problems diminish quality of life, reduce workplace productivity, and contribute to fatal accidents (1). Although the biological needs fulfilled by sleep are unclear (2), they are likely to be important because sleep is conserved from flies to humans (3-7), and prolonged sleep deprivation can lead to lethality (8-10). Identifying mechanisms that control sleep may lead to novel approaches for improving sleep quality.Sleep is regulated by two main processes: circadian and homeostatic (11,12). The circadian clock regulates the timing of sleep, whereas the homeostatic mechanism controls sleep need. Homeostatic pressure to sleep increases with time spent awake and decreases with time spent asleep. Homeostatic control is thought to influence sleep under normal (baseline) conditions as well as recovery (rebound) sleep following deprivation. However, the molecular mechanisms underlying homeostatic regulation of sleep remain unclear.A powerful approach to unraveling a poorly understood biological process is to conduct unbiased genetic screens to identify novel molecules required for that process. The Drosophila model for sleep is well-suited for such an approach, which proved invaluable for elucidation of the molecular basis of the circadian clock. Although several Drosophila genes have been implicated in sleep regulation (for example, 13-15), only one of these, the gene encoding the Shaker (Sh) K + channel, was isolated as a result of a genetic screen (16). A mutation in this gene causes one of the shortest-sleeping phenotypes known, validating the use of screens and suggesting that control of membrane excitability is a critical requirement for # This manuscript has been accepted for publication in Science. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/. Their manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the