Background: Ascarosides play central roles regulating C. elegans behavior and development. Results: L1 larvae produce starvation-dependent ascarosides based on succinylated octopamine. Conclusion: Succinylation is an important pathway for metabolism of biogenic amines in C. elegans. Significance: Octopamine ascarosides connect neurotransmitter and ascaroside signaling in C. elegans.

We describe a new type of collective behavior in C. elegans nematodes, aggregation of starved L1 larvae. Shortly after hatching in the absence of food, L1 larvae arrest their development and disperse in search for food. In contrast, after two or more days without food, the worms change their behavior—they start to aggregate. The aggregation requires a small amount of ethanol or acetate in the environment. In the case of ethanol, it has to be metabolized, which requires functional alcohol dehydrogenase sodh-1. The resulting acetate is used in de novo fatty acid synthesis, and some of the newly made fatty acids are then derivatized to glycerophosphoethanolamides and released into the surrounding medium. We examined several other Caenorhabditis species and found an apparent correlation between propensity of starved L1s to aggregate and density dependence of their survival in starvation. Aggregation locally concentrates worms and may help the larvae to survive long starvation. This work demonstrates how presence of ethanol or acetate, relatively abundant small molecules in the environment, induces collective behavior in C. elegans associated with different survival strategies.

Neuropeptides are essential for the regulation of appetite. Here we show that neuropeptides could regulate feeding in mutants that lack neurotransmission from the motor neurons that stimulate feeding muscles. We identified nlp-24 by an RNAi screen of 115 neuropeptide genes, testing whether they affected growth. NLP-24 peptides have a conserved YGGXX sequence, similar to mammalian opioid neuropeptides. In addition, morphine and naloxone respectively stimulated and inhibited feeding in starved worms, but not in worms lacking NPR-17, which encodes a protein with sequence similarity to opioid receptors. Opioid agonists activated heterologously expressed NPR-17, as did at least one NLP-24 peptide. Worms lacking the ASI neurons, which express npr-17, did not response to naloxone. Thus, we suggest that Caenorhabditis elegans has an endogenous opioid system that acts through NPR-17, and that opioids regulate feeding via ASI neurons. Together, these results suggest C. elegans may be the first genetically tractable invertebrate opioid model.DOI: http://dx.doi.org/10.7554/eLife.06683.001

To investigate the biochemical mechanism underlying the effect of sterol deprivation on longevity in Caenorhabditis elegans, we treated parent worms (P0) with 25-azacoprostane (Aza), which inhibits sitosterol-to-cholesterol conversion, and measured mean lifespan (MLS) in F2 worms. At 25 M (ϳEC 50 ), Aza reduced total body sterol by 82.5%, confirming sterol depletion. Aza (25 M) treatment of wild-type (N2) C. elegans grown in sitosterol (5 g/ml) reduced MLS by 35%. Similar results were obtained for the stress-related mutants daf-16(mu86) and gas-1(fc21). Unexpectedly, Aza had essentially no effect on MLS in the stress-resistant daf-2(e1370) or mitochondrial complex II mutant mev-1(kn1) strains, indicating that Aza may target both insulin/IGF-1 signaling (IIS) and mitochondrial complex II. Aza increased reactive oxygen species (ROS) levels 2.7-fold in N2 worms, but did not affect ROS production by mev-1(kn1), suggesting a direct link between Aza treatment and mitochondrial ROS production. Moreover, expression of the stress-response transcription factor SKN-1 was decreased in amphid neurons by Aza and that of DAF-28 was increased when DAF-6 was involved, contributing to lifespan reduction.Sterols are important molecules involved in membrane organization, hormone production, and signal processing. Because Caenorhabditis elegans lacks a de novo sterol biosynthesis pathway, it requires dietary cholesterol or plant sterols (e.g. sitosterol) that can be converted to cholesterol or its most abundant sterol, 7-dehydrocholesterol (1, 2) (Fig. 1A). Sterol depletion experiments have revealed that a restriction in the sterol supply caused by inadequate nutrition produces serious defects in development and reduces the longevity of C. elegans (3-7). For example, sterol starvation leads to an increase in embryonic lethality (7) and a decrease in lifespan (ϳ40%) in wild-type N2 worms (6). Most of the sterol depletion phenotype also occurs when worms are grown in the presence of sitosterol as a sterol nutrient and 25-azacoprostane (Aza), 2 an inhibitor of sterol C24-reductase and dealkylation of desmosterol during its conversion to cholesterol (8). Using proteomic approaches, our laboratory has previously shown that defects in development and growth in C. elegans caused by Aza treatment are associated with changes in the abundance of many proteins (3). The major proteins influenced by Aza treatment were the lipoproteins VIT-2 and VIT-6 and their putative receptors RME-2 and LRP-1, which were previously known to respond to sterols (3). Recently, the endogenous ligands of DAF-12 have been discovered to be 3-keto bile acid-like steroids, called ⌬ 4 -and ⌬ 7 -dafachronic acids (9). Dafachronic acids and related metabolites regulate longevity and stress resistance (9 -11). DAF-36, a Rieske-like oxygenase, and DAF-9, a cytochrome P450 enzyme, produce dafachronic acid ligands that activate the DAF-12 nuclear receptor (9). It was also reported that methyltransferase STRM-1 modifies sterol substrates for the synthesis of dafachronic acid (...