Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the conversion of circulating tryptophan to serotonin, a monoamine neurotransmitter in the central nervous system. While tryptophan hydroxylase is known to be regulated through a protein kinase- mediated phosphorylation, this key enzyme may also be regulated at the level of gene expression. Synthesis of an oligonucleotide probe for rat tryptophan hydroxylase mRNA based on the sequence of cloned, pineal cDNAs has been achieved. This probe will detect gene sequences by hybridization and mRNA levels by the sensitive technique of primer extension. Initial results demonstrate the CNS form of tryptophan hydroxylase mRNA is altered at the 5'end when compared with the cloned, pineal cDNAs. Pharmacological agents which alter serotonin levels have an effect on steady-state TPH mRNA levels in the raphe nuclei--a region of high concentration of serotonergic cells in the CNS. Rat genomic clones containing the TPH gene will be used to determine the patterns of expression that lead to tissue-specific mRNAs. These studies will provide necessary information about TPH structures leading to the development of regulatory studies.
