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 mutants, these neurons are generated, but RIH, AIM, and HSN do not accumulate serotonin. We have used a candidate gene approach and found that the putative tryptophan hydroxylase gene
cod-5 is regulated by
unc-86. The enzyme tryptophan hydroxylase catalyzes the first and rate-limiting step of neurotransmitter serotonin biosynthesis.
cod-5 was isolated based on abnormal male-mating behaviors, specifically, tail turning, and mapped between
dpy-10 and
let-23 on the chromosome II. We have sequenced the single allele
cod-5(
sy181) and found a point mutation in the second intron. Anti-serotonin antibody staining shows that
cod-5(
sy181) animals have dramatically reduced serotonin levels. A
cod-5::GFP reporter shows that
cod-5 is specifically expressed in the serotonergic neurons previously identified based on anti-serotonin antibody staining. The
cod-5::GFP reporter is strongly expressed in the secretory neuron NSM, the amphid neuron ADF, and the motor neuron HSN. It is weakly expressed in the interneurons AIM and RIH. In males, it is in addition expressed in the male-specific CP neurons, and 4-5 cells in the tails. The expression of
cod-5 in the head neurons is initiated in newly hatched L1 and sustains throughout the animal's life. The
cod-5 expression in the sex-specific neurons is only observed in adults. The
cod-5 expression in NSM, AIM, RIH, and HSN is regulated by the POU-factor
unc-86. Two putative
unc-86 binding sites have been found in the
cod-5 gene, one is upstream of the translation start, and the other one is in the second intron, close to where the
cod-5(
sy181) mutation is located. We speculate that the second intron may contain several transcriptional regulatory elements and that the
cod-5(
sy181) mutation may decrease the expression level. We are testing the hypothesis by Northern and promoter analysis. In addition to the male-mating behavioral defect,
cod-5(
sy181) mutant animals are hyperforaging (identified by S. Nurrish in J. Kaplan's lab) and resistant to the serotonin reuptake inhibitor imipramine.
cod-5 mutant animals also display altered odor attractant adaptation and thermotactic behaviors, similar to those induced by starvation1,2. We are trying to reverse these phenotypes by candidate gene rescue and by exogenous supply of serotonin. Interestingly, we found that the
cod-5(
sy181) promoted odorant adaptation behaviors can be suppressed by the translational inhibitor cyclohexmide. We suggest that a decreased serotonin transmission may stimulate the synthesis of odorsensory signaling components and modify animal sensitivity to environmental cues. 1.Colbert A. C. and Bargmann, C.I.(1997). Learning and Memory 4, 179-191. 2. Hedgecock E.M. and Russell, R.L. (1975). Proc. Acad.Sci. 72, 4061-4065.