[
WormBook,
2008]
The role of neuropeptides in modulating behavior is slowly being elucidated. With the sequencing of the C. elegans genome, the extent of the neuropeptide genes in C. elegans can be determined. To date, 113 neuropeptide genes encoding over 250 distinct neuropeptides have been identified. Of these, 40 genes encode insulin-like peptides, 31 genes encode FMRFamide-related peptides, and 42 genes encode non-insulin, non-FMRFamide-related neuropeptides. As in other systems, C. elegans neuropeptides are derived from precursor molecules that must be post-translationally processed to yield the active peptides. These precursor molecules contain a single peptide, multiple copies of a single peptide, multiple distinct peptides, or any combination thereof. The neuropeptide genes are expressed extensively throughout the nervous system, including in sensory, motor, and interneurons. In addition, some of the genes are also expressed in non-neuronal tissues, such as the somatic gonad, intestine, and vulval hypodermis. To address the effects of neuropeptides on C. elegans behavior, animals in which the different neuropeptide genes are inactivated or overexpressed are being isolated. In a complementary approach the receptors to which the neuropeptides bind are also being identified and examined. Among the knockout animals analyzed thus far, defects in locomotion, dauer formation, egg laying, ethanol response, and social behavior have been reported. These data suggest that neuropeptides have a modulatory role in many, if not all, behaviors in C. elegans.
[
WormBook,
2005]
Genetic suppression has provided a very powerful tool for analyzing C. elegans. Suppression experiments are facilitated by the ability to handle very large numbers of individuals and to apply powerful selections. Because the animal grows as a self-fertilizing diploid, both dominant and recessive suppressors can be recovered. Many different kinds of suppression have been reported. These are discussed by category, with examples, together with discussion of how suppressors can be used to interpret the underlying biology, and to enable further experimentation. Suppression phenomena can be divided into intragenic and extragenic classes, depending on whether the suppressor lies in the same gene as the starting mutation, or in a different gene. Intragenic types include same-site replacement, compensatory mutation, alteration in splicing, and reversion of dominant mutations by cis- knockout. Extragenic suppression can occur by a variety of informational mechanisms, such as alterations in splicing, translation or nonsense-mediated decay. In addition, extragenic suppression can occur by bypass, dosage effects, product interaction, or removal of toxic products. Within signaling pathways, suppression can occur by modulating the strength of signal transmission, or by epistatic interactions that can reveal the underlying regulatory hierarchies. In C. elegans biology, the processes of muscle development, vulva formation and sex determination have provided remarkably rich arenas for the investigation and exploitation of suppression.