Post-transcriptional control of tryptophan hydroxylase gene expression in rat brain stem and pineal gland.

We have cloned a segment of the rat tryptophan hydroxylase (TPH) gene and used it to investigate differences in mRNA levels in two tissues: brain stem and pineal gland. The cloned, 13-kb genomic region contains five exons corresponding to cloned TPH cDNA sequence. Most intron/axon junctions are homologous to those found in the closely related genes encoding tyrosine and phenylalanine hydroxylase. The gene segment contains a region of low complexity that is repeated in the genome, but the remainder of the segment is single-copy sequence. TPH mRNAs can be detected by RNase protection assays and demonstrate a large difference in steady-state mRNA levels between pineal gland and brain stem dissections, agreeing with the results of Dumas and collaborators (1989, J. Neurosci. Res. 24:537-547). However, nuclear run-on assays of TPH gene transcription rates reveal similar levels of gene expression for pineal and brain stem. Control of TPH mRNA levels, therefore, appears to be post-transcriptional.