Neuropeptides are an important class of signaling molecules involved in nervous system function. The C. elegans gene
flp-18 is predicted to encode six distinct neuropeptides of the FMRFamide family. We found that a transgene carrying extra copies of
flp-18 causes multiple behavioral abnormalities, including a characteristically coiled posture, uncoordinated reverse locomotion, increased spontaneous reversal frequency, and a Sho (suppression-of-head oscillation) phenotype. We have isolated a
flp-18 deletion allele,
n4766, in which all the neuropeptide-encoding sequences are absent. In contrast to
flp-18 overexpressors,
flp-18 deletion mutants do not exhibit any obvious defects. We are currently assaying
flp-18 deletion mutants in sensitized backgrounds to detect more subtle behavioral defects. To characterize the neuronal circuitry underlying the abnormalities in
flp-18 overexpressors, we have generated transgenic animals expressing translational fusions of
flp-18 and GFP.
flp-18::gfp is expressed in many parts of the C. elegans neuromusculature, including head neurons, the ventral and dorsal nerve cords, tail neurons, and (weakly) body-wall muscles. We are currently identifying the
flp-18::gfp-expressing cells. To identify other components of the
flp-18 signaling pathway, we screened ~10,000 haploid genomes in
flp-18-overexpressing backgrounds, looking for suppressors of the posture and locomotion defects. Fifteen independent suppressors were isolated, defining at least four complementation groups. We recovered seven alleles of Y58G8A.4, which encodes a G protein-coupled receptor that binds to FLP-18 peptides in vitro (Lowery et al., 2003, U.S. Patent 6,632,621). So far, we have identified molecular lesions in the Y58G8A.4 coding region for five of the seven alleles. Y58G8A.4 overexpression phenocopies
flp-18 overexpression; the Y58G8A.4 overexpression phenotype is suppressed by
flp-18 deletion. Of the remaining suppressors, six cause a twitcher phenotype and are probably alleles of
unc-22, which encodes a structural protein required for proper muscle contraction. Two other suppressors each define one complementation group.