Wormfest Pheremones (ascarosides)
You may not think much of wriggling roundworms, but for decades, one species of small see-through soil dwellers has engrossed scientists interested in studying a range of behaviors, from sleep to addiction. These well-studied nematodes (Caenorhabditis elegans) also display highly variable social habits, with some strains preferring to eat alone while others gorge on bacteria as a group.
The foraging styles of this species are thought to be regulated by small molecules called ascarosides, but these chemical signals aren’t one-size-fits-all. They entice males but either repulse or elicit no response in hermaphrodites, which make up the vast majority of the population. Because pheromones that strongly attract hermaphrodites had not been identified, chemical biologist Frank Schroeder of Cornell University and his team suspected the existence of an unknown family of signaling molecules that stimulate nematode aggregation during feeding.
In this month’s issue of PLoS Biology, these researchers have revealed a new set of potent small molecules—indole ascarosides—that promote aggregation in social and solitary hermaphrodites. The findings suggest that these worms possess a highly evolved chemical language for coordinating social behavior.
To search for novel signaling molecules in C. elegans, Schroeder and his team compared metabolites from wild-type organisms with those from mutants lacking the protein DAF-22, which is required for the biosynthesis of all known small-molecule pheromones in this species. They identified several new substances—derived from the amino acid tryptophan in the nematode diet—that are structurally similar to ascarosides, except they contain the compound indole.