We are characterizing genes used by serotonergic neurons in C. elegans to learn how they are regulated; among these is the
cat-4 gene. Worms with mutations in the
cat-4 gene lack serotonin and dopamine, and are hypersensitive to a variety of agents. The
cat-4 gene appears to correspond to the predicted gene F32G8.6, which encodes GTP Cyclohydrolase I (GCH), an enzyme necessary for synthesis of biopterin. Biopterin is a cofactor required by (among others) all aromatic amino acid hydroxylases (AAAHs); these include the enzymes catalyzing synthesis of serotonin, dopamine and tyrosine. We have found that the original
cat-4 mutant allele (
e1141) has a missense mutation in the GCH coding sequence altering a highly conserved amino acid. A new mutant (kindly provided by the C.e. Gene Knockout Consortium) that deletes the F32G8.6/GCH gene is also serotonin-deficient, hypersensitive, and fails to complement
cat-4(
e1141). We hypothesize that hypersensitivity of
cat-4 mutants is caused by tyrosine deficiency during cuticle synthesis, leading to a reduction in tyrosine cross-linking in cuticle proteins, and a 'leaky' cuticle. We are continuing characterization of the new
cat-4 deletion allele, including comparing the presence of dityrosine cross-links in the cuticles of mutant vs. wild type worms.