DOPA DECARBOXYLASE AND GTP CYCLOHYDROLASE I GENES OF THE NEMATODE C. ELEGANS
C. M. Loer*, N. Marsden-Haug and C. Ramirez. Dept. of Biology, University of San Diego, CA 92110.
We are interesting in learning how neurons in C. elegans decide to use the neurotransmitter serotonin. Serotonin is synthesized from tryptophan in two steps: Trp is first hydroxylated by an aromatic amino acid hydroxylase (AAAH), then decarboxylated by an AAA decarboxylase (AAADC) to yield serotonin. We have previously identified genes encoding both enzymes in C. elegans from ORFs first predicted by the C. elegans Genome Sequencing Consortium. We have now rescued the serotonin- and dopamine-deficient mutant bas-1 by injection of a 15.1 kb subclone (courtesy Fred Wolf) of the cosmid C05D2 containing two predicted AAADC genes. We are continuing to characterize these and other terminal differentiation genes used by serotonergic neurons. Learning how these genes are controlled is important to understanding how a neuron chooses a particular neurotransmitter during its development.
All AAAH enzymes, which include Trp hydroxylase (serotonin synthesis), Tyr hydroxylase (dopamine synthesis) and Phe hydroxylase (tyrosine synthesis), require a biopterin cofactor to catalyze their respective hydroxylations. The mutant cat-4 (e1141)V is serotonin- and dopamine-deficient (Sulston et al., 1975, J. Comp. Neurol. 163: 215; Desai et al., 1988, Nature 336: 638) and appears to have a leaky cuticle. Sequencing through the region in which cat-4 maps genetically has identified a likely candidate gene for cat-4: a predicted gene with homology to GTP cyclohydrolase I (GCH), which is required for synthesis of biopterin cofactor, located on cosmid F32G8. Mutation in the Drosophila Punch locus, which encodes a GCH, causes a phenotype similar to that of the cat-4 mutant (O'Donnell et al., 1989, Dev. Genet. 10:273). We are currently injecting the F32G8 cosmid into cat-4 mutants, subcloning the GCH gene, and constructing reporter fusions. This work is supported by NSF (RUI) Grant IBN9796217 to CML.