RPamide neuropeptides NLP-22 and NLP-2 act through GnRH-like receptors to promote sleep and wakefulness in C. elegans

Abstract

Sleep and wakefulness are fundamental behavioral states of which the underlying molecular principles are becoming slowly elucidated. Transitions between these states require the coordination of multiple neurochemical and modulatory systems. In Caenorhabditis elegans sleep occurs during a larval transition stage called lethargus and is induced by somnogenic neuropeptides. Here, we identify two opposing neuropeptide/receptor signaling pathways: NLP-22 promotes behavioral quiescence, whereas NLP-2 promotes movement during lethargus, by signaling through gonadotropin-releasing hormone (GnRH) related receptors. Both NLP-2 and NLP-22 belong to the RPamide neuropeptide family and share sequence similarities with neuropeptides of the bilaterian GnRH, adipokinetic hormone (AKH) and corazonin family. RPamide neuropeptides dose-dependently activate the GnRH/AKH-like receptors GNRR-3 and GNRR-6 in a cellular receptor activation assay. In addition, nlp-22-induced locomotion quiescence requires the receptor gnrr-6. By contrast, wakefulness induced by nlp-2 overexpression is diminished by deletion of either gnrr-3 or gnrr-6. nlp-2 is expressed in a pair of olfactory AWA neurons and cycles with larval periodicity, as reported for nlp-22, which is expressed in RIA. Our data suggest that the somnogenic NLP-22 neuropeptide signals through GNRR-6, and that both GNRR-3 and GNRR-6 are required for the wake-promoting action of NLP-2 neuropeptides. Sleep is an essential quiescent state, conserved at the molecular level across distantly related animals 1-5. Because animals display a remarkable diversity of sleep traits, a consensus definition for sleep-like states has been set based on behavioral changes shared with human sleep. These include behavioral quiescence, reduced sensory responsiveness, reversibility, the assumption of a specific posture, and homeostatic regulation 1,4,6,7. Sleep deprivation is detrimental to diverse biological processes, including metabolism, longevity, and memory formation 8-11. Genetic studies in model organisms such as mice, zebrafish, Drosophila and C. elegans have provided powerful ways to dissect core mechanisms of sleep-like states that are evolutionarily conserved across these species 1-3,6,10. A well-known example is the circadian protein PERIOD that regulates the timing of sleep 12,13. Other conserved sleep pathways include epidermal growth factor (EGF) and notch signaling 14-16. Conserved wake-promoting pathways include dopamine and pigment dispersing factor (PDF) signaling 17-19. How these sleep and wake pathways interact is still unclear (for review, see 3,4,18). Mounting evidence indicates that sleep-wake transitions require the coordination of several brain regions and engage multiple neurochemical systems, including biogenic amines 1,17,20 and neuropeptides 19,21. In mammals, hypothalamic orexin/hypocretin neuropeptides promote

Neuropeptide VF neurons promote sleep via the serotonergic raphe

“…If the EGFR-NPVF-RN sleep-promoting circuit plays a central and important role in regulating sleep, one might expect it to be evolutionarily conserved. Indeed, similar to zebrafish, EGFR signaling promotes sleep in C. elegans and Drosophila ( Donlea et al, 2009 ; Foltenyi et al, 2007 ; Konietzka et al, 2020 ; Van Buskirk and Sternberg, 2007 ), and genetic experiments suggest that it does so in part via RFamide neuropeptides that may be invertebrate homologs of npvf ( He et al, 2013 ; Iannacone et al, 2017 ; Konietzka et al, 2020 ; Lenz et al, 2015 ; Nagy et al, 2014 ; Nath et al, 2016 ; Nelson et al, 2014 ; Shang et al, 2013 ; Turek et al, 2016 ; Van der Auwera et al, 2020 ). Serotonin has also been shown to promote sleep in Drosophila ( Qian et al, 2017 ; Yuan et al, 2006 ), and by analogy to our results, we hypothesize that RFamide neuropeptides such as FMRFamide ( Lenz et al, 2015 ) may act upstream of 5-HT to promote Drosophila sleep.…”

Dopamine receptor DOP-1 engages a sleep pathway to modulate swimming in C. elegans

“…During each larval molt, the worms enter into a prolonged period (∼2 hr) of behavioral quiescence with inactivation of locomotion and feeding behaviors, with properties similar to the sleep-like state in mammals and Drosophila melanogaster ( Hendricks et al., 2000 ; Huber et al., 2004 ; Nelson and Raizen, 2013 ; Raizen et al., 2008 ; Shaw et al., 2000 ). Neuropeptide pathways have been found to regulate this developmentally timed behavior quiescence in C. elegans ( Choi et al., 2013 ; Turek et al., 2016 ; Van der Auwera et al., 2020 ). Among them, a FMRFamide-related neuropeptide FLP-11, stored in the sleep interneuron RIS, strongly inhibits locomotion at the onset of sleep ( Turek et al., 2016 ).…”

Regulation of Satiety Quiescence by Neuropeptide Signaling in Caenorhabditis elegans

“…In zebrafish, the RFamide neuropeptide VF (NPVF) and the npvf -expressing neurons are necessary and sufficient to promote sleep (Lee et al, 2017). In C. elegans, both FLPs and NLPs regulate sleep: FLP-18, NLP-2, NLP-22, and NLP-14 regulate DTS and FLP-13, FLP-24, and NLP-8 do SIS (Nelson et al, 2013;Nagy et al, 2014;Nath et al, 2016;Iannacone et al, 2017;Honer et al, 2020;Van der Auwera et al, 2020).…”