Expression of human tyrosine hydroxylase-chloramphenicol acetyltransferase (CAT) fusion gene in the brains of transgenic mice as examined by CAT immunocytochemistry

We have produced transgenic (Tg) mice carrying 5.0-kb fragment from the 5'-flanking region of the human tyrosine hydroxylase (hTH) gene fused to a reporter gene, chloramphenicol acetyltransferase (CAT) [Sasaoka et al. (1992) Mol Brain Res 16: 274-286]. In the brain of the Tg mice, CAT expression has been observed in catecholaminergic (CAnergic) neurons and also in non-CAnergic neurons. The aim of the present study is to examine in detail the cell-type specific expression of the hTH-CAT fusion gene in the brain of the Tg mice, by use of immunohistochemistry for CAT, TH, and aromatic L-amino acid decarboxylase (AADC). CAT-immunoreactive cells were found in CAnergic brain regions which contained TH-positive cells, and also in non-CAnergic brain regions which contained no TH-labeled cells. The non-CAnergic brain regions that represented CAT-stained cells were further divided into two groups: (i) regions containing AADC-labeled cells, for example, bed nucleus of the stria terminalis, nucleus suprachiasmaticus, mammillary body, nucleus raphe dorsalis, inferior colliculus, and nucleus parabrachialis, and (ii) regions containing no AADC-positive cells, for example, main olfactory bulb (except A16), accessory olfactory bulb, nucleus olfactorius anterior, caudoputamen, septum, nucleus accumbens, hippocampus, medial nucleus of the amygdala, entorhinal cortex, nucleus supraopticus, and parasubiculum. The results indicate that the 5.0-kb DNA fragment flanking the 5' end of the hTH gene may contain the element(s) specific for neuron-specific TH expression but which may be insufficient to attenuate ectopic expression.