The mutant
cat-4(
el411)V was first isolated as a dopamine deficient mutant lacking formaldehydeinduced fluorescence (FIF); it was subsequently found to lack serotonin immunoreactivity (Sulston et al., 1975, J. Comp. Neurol. 163: 215; Desai et al., 1988, Nature 336: 638). Although
cat-4 mutant worms were previously described as serotonin hypersensitive, we have found that
cat-4 mutants are also hypersensitive to a variety of other unrelated agents. We first noticed that
cat-4 mutant worms died much more rapidly than wild type worms during routine "cleaning" of worms with bleach. Whereas wild type worms squirm in bleach for several seconds before becoming rigid,
cat-4 mutants stop moving almost instantly (< 1 sec). In addition,
cat-4 mutant carcasses seem to disappear/dissolve during this treatment, unlike those of wild type worms. We confirmed that
cat-4 mutants are hypersensitive to serotonin in an egg laying assay; they are also hypersensitive to SDS, levamisole and imipramine. Weinshenker and others (1995, J. Neurosci. 15: 6975) have also noted hypersensitivity of
cat-4 to some drugs. These observations suggest that mutation of the
cat-4 gene affects not only production of neurotransmitters, but also construction of the cuticle. If
cat4 mutants have a more permeable cuticle than wild type, this could be caused by decreased crosslinking of proteins in the cuticle. Nematode cuticle proteins are highly crosslinked by disulfide and nonreducible cross links (reviewed by Cox, 1992, J. Parasitol. 78: 1). Among the nonreducible crosslinks found in nematode cuticle proteins are those between tyrosine residues (forming dityrosine and isotrityrosine, Fujimoto et al., 1981, Biochem. Biophys. Res. Comm. 99: 637). Since serotonin, dopamine and tyrosine are all derived by hydroxylation of aromatic amino acids (tryptophan, tyrosine, and phenylalanine respectively),
cat-4 mutants could be generally defective in this process. All aromatic amino acid hydroxylase enzymes share a common biopterin cofactor that must be synthesized and recycled;
cat-4 mutations may affect a gene in this pathway, similar to the Punch mutant of Drosophila. To test whether
cat-4 mutants have less crosslinked cuticles, we isolated cuticles of
cat-4 and wild type young adult worms. We first compared them under Nomarski optics, but found no gross differences. We then compared the isolated cuticles by reducing, denaturing PAGE. Our preliminary data suggest that
cat-4 mutants indeed lack some higher molecular weight bands found among wild type cuticle proteins.