Identification of cell type-specific promoter elements associated with the rat tyrosine hydroxylase gene using transgenic founder analysis

Transcriptional regulatory elements capable of directing transgene expression to individual cells are powerful tools for manipulating a given CNS circuit. Delineating these elements via traditional transgenic analysis is both costly and labor intensive. Here we have used the rat tyrosine hydroxylase (TH) promoter as a model to describe and validate the use of founder animals for systematic promoter studies. No significant differences were found when data obtained from founder animals expressing a 6.0 kb TH promoter directing LacZ were compared with animals derived from an analogous transgenic line. Subsequent studies with founder animals expressing β-galactosidase directed by various lengths of rat TH promoter revealed different patterns of expression. Specifically, a locus coeruleus regulatory domain was localized between 3.4 and 6.0 kb of the rat TH promoter, a hypothalamic regulatory domain between 2.5 and 3.4 kb and a brainstem regulatory domain between 0.8 and 6.0 kb. At least one element of a midbrain specific regulatory domain was within 2.5 kb of the transcriptional start site. Olfactory bulb specific elements however appeared to reside outside of the sequences tested. Specific patterns of ectopic gene expression were also observed suggesting the presence of negative regulatory elements. Thus, TH appears to be regulated in a complex modular fashion by both positive and negative regulatory elements. Taken together, this study demonstrates the feasibility and reliability of founder analysis for promoter studies of genes expressed in complex spatial and temporal patterns.