A primer on pheromone signaling in Caenorhabditis elegans for systems biologists

Abstract

Individuals communicate information about their age, sex, social status, and recent life history with other members of their species through the release of pheromones, chemical signals that elicit behavioral or physiological changes in the recipients. Pheromones provide a fascinating example of information exchange: animals have evolved intraspecific languages in the presence of eavesdroppers and cheaters. In this review, we discuss the recent work using the nematode C. elegans to decipher its chemical language through the analysis of ascaroside pheromones. Genetic dissection has started to identify the enzymes that produce pheromones and the neural circuits that process these signals. Ecological experiments have characterized the biotic environment of C. elegans and its relatives, including ecological relationships with a variety of species that sense or release similar blends of ascarosides. Systems biology approaches should be fruitful in understanding the organization and function of communication systems in C. elegans.

Figure 1.

Overview of the chemical structure of the ascaroside pheromones, summarizing the diversity of hundreds of unique molecules identified in nematode secretions. Each ascaroside contains an ascarylose sugar (black) attached to a fatty acid of variable length (blue). Additional moieties (R¹, R², red, and green) could decorate the ascarylose and the fatty acid.

Figure 2.

Schematic representation of a relationship between ascarosides, their cognate receptors, sensory neurons, and the phenotypic effects they elicit. Colored squares underneath ascarosides and receptors correspond to the phenotypes regulated by them. Solid lines between ascarosides and receptors indicate inferences based on heterologous expression or pull-down assays; dotted lines indicate that genetic information was used to assign ascaroside/chemoreceptor pairing. The arrows connecting receptors and sensory neurons represent expression patterns. Estimated numbers of GPCRs expressed by each neuron (extrapolated from [68]) are shown.