Abstract
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.
Highlights
Neuropeptides are short sequences of amino acids that function either directly or indirectly to modulate synaptic activity
Once the precursor molecules are cleaved by the proprotein convertases, the basic residues themselves are removed from the peptide sequences by the activity of carboxypeptidase E. egl-21 encodes a neural-specific carboxypeptidase E that is expressed in about 60% of the neurons (Jacob and Kaplan, 2003)
Because no neuropeptide Y is present in C. elegans, the assumption was that the NPR-1 ligand was a FLP
Summary
Neuropeptides are short sequences of amino acids that function either directly or indirectly to modulate synaptic activity. The number of predicted neuropeptides in C. elegans is well over one hundred (Li et al, 1999; Pierce et al, 2001); most of the neuropeptides fall into two large families: the insulin-like peptides (Pierce et al, 2001; Li et al, 2003) and the FMRFamide (Phe-Met-Arg-Phe-NH )-related peptides or FaRPs, which are referred to as FLPs in C. elegans (Li et al, 1998; Li, 2005). With a few striking exceptions, the functions of the different neuropeptides remain largely unknown in C. elegans. This overview serves to summarize the current state of the neuropeptide field
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