In a screen for suppressors of the
sma-1 defect in embryonic elongation, we isolated a set of 13 Sue ( su ppressor of e longation defects) mutants that alter regulation of muscle contraction as well as increasing elongation of
sma-1 embryos. Sue mutants display multiple phenotypes associated with misregulated muscle contraction: constitutive egg laying and lengthened defecation cycles as well as hyperactive body movement and pharyngeal pumping. Recessive sue mutations that map to different loci fail to complement, suggesting that these genes act in a common pathway. sue mutations also fail to complement
goa-1 mutations. GOA-1 is the alpha subunit of Go, a G protein also involved in the regulation of egg laying, defecation, pharyngeal pumping and movement but that does not affect embryonic elongation. We identified the
sue-1 gene product by rescue of its Egl-c phenotype. Using extrachromosomal arrays generated by microparticle bombardment, we rescued the
sue-1(
ru23) phenotype with a 100bp fragment located within an intron of the predicted gene F07A5.5. This fragment contains a single open reading frame encoding a putative 23 amino acid peptide required for rescue; a truncated peptide generated by a single base pair change does not rescue. The full length peptide contains a short, 9 amino acid signal sequence followed by a di-lysine cleavage site and a potential secreted neuropeptide. Using a
sue-1 promoter GFP construct, we observe expression in the HSN and VC neurons, which regulate vulval muscle contraction. We propose that the
sue-1 Egl-c phenotype is the result of loss of SUE-1 function in these neurons. In addition, we observe expression in head and tail neurons that may identify additional SUE-1-expressing neurons. Based on its sequence, SUE-1 is not a member of the FaRP neuropeptide family. Since the
sue-1 gene encodes only a single copy of the SUE-1 peptide, it would also not have been identified in a genome neuropeptide search that relied on the presence of nearly identical amino acid repeats (1). These data suggest that SUE-1 is a novel C. elegans neuropeptide. We are cloning two additional sue genes that contain the gain-of-function mutations
sue-2(
ru27) and
sue-3(
ru36) . We are able to phenocopy the Egl-c phenotypes of these mutations by overexpression using extrachromosomal arrays. We find that
sue-2(
ru27) can be phenocopied by overexpression of a 2.7 kb fragment of cosmid R05F9; the
sue-3(
ru36) defect in egg laying can be phenocopied by overexpression of a 9 kb fragment of the cosmid H09G03. We are interested in determining whether these genes encode additional neuropeptides or other components of a neuronal signaling pathway or whether they regulate muscle contraction by a different mechanism. (1)Li, C. et al . 1999. Ann. NY Acad. Sci. 897: 239-252.