We are interested in identifying POU-factor
unc-86 downstream genes that mediate neuronal function and animal behaviors. UNC-86 is expressed in the serotonergic neurons NSM, RIH, AIM, and HSN. In
unc-86 null mutants, these neurons are generated, but RIH, AIM, and HSN do not accumulate serotonin. We have used a candidate gene approach and found that a putative tryptophan hydroxylase gene is regulated by
unc-86. The enzyme tryptophan hydroxylase catalyzes the first and rate-limiting step of neurotransmitter serotonin biosynthesis. The complete genome sequence of C. elegans reveals the presence of one sequence homologous to tryptophan hydroxylase,
zk1290.2, which we name
tph-1. Analysis of
tph-1 cDNA indicates that
tph-1 has 41% identity over the entire coding region and 59% identity at the C-terminal 2/3 of the sequence corresponding to the catalytic domain to the human brain tryptophan hydroxylase. The
tph-1::GFP is strongly expressed in the secretory motor neuron NSM, the amphid sensory neuron ADF, and the motor neuron HSN. Vary rarely, it is expressed in the interneurons AIM and RIH. In males, it is in addition expressed very strongly in the male-specific CP neurons and 4-5 cells in the tail.
unc-86 is expressed in the serotonergic neurons NSM, AIM, RIH, and HSN. In
unc-86(
n846) null mutant animals, these neurons are generated, but do not express the
tph-1::GFP, whereas the
tph-1::GFP expression in ADF is not affected. ADF does not express UNC-86.
tph-1 is located in the genetic region to which a male mating mutant
cod-5 has been approximately mapped, a
tph-1 intron mutation in
cod-5(
sy181) that we reported in the 1998 East Coast worm meeting abstract was not detected in subsequent analyses, so we are still unsure about the connection between
cod-5 andtph-1. We generated a
tph-1 deletion mutation by sib-screening mutagenized animals with PCR primers from the
tph-1 gene. The resulting mutant allele,
tph-1(
mg280) is viable, but shows a variety of behavior defects. We are currently screening for other factors that regulate the
tph-1::GFP expression, and mutations that suppresstph-1
(mg280) phenotypes.