Raya Al-Shawi

Expression of a foreign gene in a line of transgenic mice is modulated by a chromosomal position effect.

Unusual aberrant expression of a foreign gene in a particular transgenic mouse line is often attributed to chromosomal position effect, although proof of this is lacking. An alternative explanation is that expression has been modified by the arrangement of multiple copies of the foreign gene at the insertion site or by mutation or gene rearrangement. We have distinguished between these explanations in the case of one particular transgenic line by recovering the aberrantly expressed foreign DNA and reintroducing it into the mouse genome to produce secondary transgenic mice. The expression pattern of the gene in the secondary transgenic mice was normal, showing that this case of aberrant expression is due to a chromosomal position effect.

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 biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and 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 the role of these two sites, we produced transgenic mice bearing a 5.3‐kb 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 fused to two different reporter genes (HSV1‐tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE‐ and TRE‐mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.