Caenorhabditis elegans sleeps during a life stage called lethargus (Raizen et al., 2008). Lethargus is timed by a transcription factor called LIN-42, homologous to the protein PERIOD, a circadian clock protein which regulates sleep timing in both Drosophila melanogaster and mammals (Jeon et al., 1999; Monsalve et al., 2011). However, the mechanisms by which LIN-42 controls sleep are largely unknown. However, rhythmic secretion of neuropeptides may play a central role (Nelson et al., 2013; Turek et al., 2016). The neuropeptide encoding genes,
nlp-14 and
nlp-15, show higher expression levels during lethargus (George-Raizen et al., 2014). NLP-14 and -15 share sequence similarities (~69%) with a class of neuropeptides in arthropods called orcokinins (Nathoo et al., 2001). Orcokinins appear to be highly conserved within the Ecdysozoa group. Interestingly, in cockroaches, injection of exogenous orcokinin into the accessory medulla, a circadian pacemaker in the brain, results in a circadian phase shift (Hofer and Homberg, 2006). Taken together, this led us to hypothesize that NLP-14 and -15 regulate sleep in C. elegans. Our data show that
nlp-14 but not
nlp-15 over-expression induces behavioral quiescence in active adult animals. Specifically, when
nlp-14 over-expression is induced under the control of a heat shock promoter, animals become quiescent for locomotion and show prolonged defecation cycles. To understand how NLP-14 induces quiescence, we have conducted a forward genetic screen in which
nlp-14 over-expressing worms were randomly mutagenized with EMS, an approach we have taken in the past (Iannacone et al., 2017). The mutated F2 progeny were screened and rare suppressor mutants, that did not become quiescent upon heat-induced over-expression of
nlp-14, were isolated. We are currently isolating genomic DNA, which will be followed by whole genome sequencing to identify the causative alleles.