CRE AND TRE SEQUENCES OF THE RAT TYROSINE-HYDROXYLASE PROMOTER ARE REQUIRED FOR TH BASAL EXPRESSION IN ADULT MICE BUT NOT IN THE EMBRYO

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesi s of catecholamine neurotransmitters, is expressed in a restricted num ber of areas, and subject to numerous regulations during development a nd in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo th e role of these two sites, we produced transgenic mice bearing a 5,3-k b fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fuse d to two different reporter genes (HSV1-tk and lacZ), we show that thi s promoter fragment is able to specifically direct expression in catec holaminergic tissues both in adult mice and embryos. Interestingly, th e CRE- and TRE-mutated transgenes were not expressed in adult mice, co ntrary to the situation in embryos where they were specifically expres sed in catecholaminergic regions. These results demonstrate that the C RE and TRE play an essential role in basal TH expression in adult tiss ues in vivo. Moreover, they suggest that distinct transcription factor s are involved in TH regulation in developing and adult tissues. In su pport of this, gel mobility shift experiments revealed a complex prese nt only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintena nce of the catecholaminergic phenotype.