Identification of SLEEPLESS, a Sleep-Promoting Factor

Abstract

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

Day–night cycles and the sleep-promoting factor, Sleepless, affect stem cell activity in the Drosophila testis

“…altered (Fig. 3A), presumably because of their less severe sleep phenotypes (23)(24)(25)(26). Alternatively, SSS may modulate stem cell divisions through mechanisms unrelated to its function in sleep, or the sleep-regulating pathways affected in sss flies may be different from the pathways altered in other sleep mutants (discussed below).…”

“…The apparent loss of rhythms may be caused by the overall increased rate of divisions. The other mutants tested here do not have sleep phenotypes as extreme as the reduction of sleep in sss mutants (23)(24)(25)(26), which may account for the maintenance of normal stem cell activity in these flies. However, it is possible that some sleep-regulating pathways also regulate stem cell activity, whereas others do not.…”

“…We kept flies awake at night through mechanical stimulation, which has been previously described (23), and measured cell divisions after this treatment. GSC activity increased after 24-h stimulation; comparison of 0.09 ± 0.02 (n = 159) with 0.16 ± 0.03 (n = 186) dividing GSCs per testis in nondeprived and sleep-deprived males, respectively, suggests that reduced sleep may affect stem cell activity.…”

Independent Effects of γ-Aminobutyric Acid Transaminase (GABAT) on Metabolic and Sleep Homeostasis

“…) was used as the wild-type strain in this study (9). This strain, as well as cg1640 EPgy2 , got1 wHy , ELAV-GAL4, gabat…”

Sleepless in Drosophila

“…Lack of sleepless protein in D. melanogaster led to a greater than 80% reduction in amount of sleep compared with that for wild-type flies. 2 Although moderate decreases in the level of sleepless protein in D. melanogaster caused a minimal decline in baseline sleep, it led to severe reductions in sleep rebound, which is recovery sleep after sleep deprivation. Only a few genes have been shown to be important for sleep rebound.…”