The cue, abbreviated as ascr#8, is released into the environment by fertile sexually mature hermaphrodites in the hopes of attracting any nearby males. We have previously shown that male C. elegans sense this cue and enact a search behavior that we quantify through the time the male spends within ascr#8.
In the new study, Reilly showed that this response is regulated by a specific neuropeptide called FLP-3. Neuropeptides are small proteins produced and released by neurons through the regulated secretory route and act on neural substrates or other tissues.
FLP-3 peptide is active only in males to regulate the behavioral response to the mating pheromone. In mutant animals that do not express the gene encoding the FLP-3 peptides, males avoid the pheromone just as hermaphrodites do.
Using CRISPR/Cas technology to generate new mutants for proteins that act as receptors detecting FLP-3 peptides, we determined that two receptors are involved in sensing the FLP-3 signal. Even more interesting, the two receptors are not evolutionarily related.
How did we know to look at those receptors? Reilly initiated a collaboration with Professor Isabel Beets, a faculty member at KU Leuven. Beets is a world leader known for spearheading an initiative to “deorphanize” every receptor in the C. elegans genome. Her laboratory determined that the peptides encoded by the FLP-3 gene are extremely specific in their activation of the two unrelated receptors, termed NPR-4 and FRPR-16.
Our lab went on to find that the gene that expresses FLP-3 produces a protein sequence that is further processed before it is functional, reminiscent of the way human insulin protein is processed before it is able to signal properly. In the worm, the process resulted in 10 unique FLP-3 peptides.