Exploring the role of redundant RFamide neuropeptide pathways during sleep in Caenorhabditis elegans

Abstract

RFamide neuropeptide signaling is required for sleep in vertebrates and invertebrates, suggesting an ancient evolutionary role during sleep regulation. In fruit flies and zebrafish, a single RFamide gene encodes neuropeptides that signal through one or possibly two receptors to regulate sleep. In contrast, the genetically tractable nematode, Caenorhabditis elegans, possesses >30 FMRFamide‐related peptide genes (flp), multiple of which have been shown to be either required for sleep or capable of inducing sleep when overexpressed. Moreover, their genome codes for >15 FMRFamide peptide receptors (frpr). We sought to explore the function of these pathways during sleep by measuring total sleep in single, double and triple mutants of flp and frpr genes. During these analyses, we found that two neuropeptide genes, flp‐3 and flp‐33, are required for sleep and likely function redundantly. Also, when either the flp‐3 or flp‐33 gene is overexpressed, a strong inhibition of movement, reminiscent of sleep, occurs. Additionally, we identified a redundant sleep role for the related GPCR‐encoding genes frpr‐4, frpr‐6, and frpr‐16 and a unique role for the highly similar frpr‐11 and frpr‐12 genes. We are currently assessing peptide‐receptor interactions using in vitro cell culture systems and testing for genetic interactions of the FLP‐33 pathways in vivo. Our work demonstrates an expansive network of RFamide signaling during sleep in C. elegans. Our work identifies novel mechanisms for sleep regulation in C. elegans. It remains unclear why such a diverse collection of pathways evolved in this simple organism but not in more complex animals like vertebrates.