Rat tyrosine hydroxylase promoter directs tetracycline-inducible foreign gene expression in dopaminergic cell types

A prerequisite for creating animal models in which gene expression is spatially and temporally controlled is the development of promoters to target genetic switches to specific populations of cells. Here we used the dopaminergic biosynthetic enzyme, tyrosine hydroxylase (TH) to test various combinations of tetracycline (Tet) system elements to determine the optimal configuration for inducible, tissue-specific expression. The present study shows that the degree of expression and level of leakiness associated with the Tet transactivators rtTA, rtTA2^S-M2, tTS/rtTA or tTS/rtTA2^S-M2 was dependent upon both the promoter and cell type utilized. Specifically, CMV-driven tTS/rtTA2^S-M2 exhibited the highest level of inducibility in HEK cells (∼1000-fold) versus the dopaminergic cell line, MN9D (∼70-fold). In contrast, TH-driven rtTA2^S-M2 yielded the highest level of expression with the least background in dopaminergic cell types versus HEK cells. Moreover, the TH promoter could be combined with the bi-directional Tet response system, BiTetO, allowing for the co-expression and regulation of two genes in the same cell. To further test the feasibility of this system we replaced the reporter gene with human Bcl-2. Consistent with previous studies, induction of Bcl-2 expression in dopaminergic cell types attenuated cell death due to the neurotoxin, MPP⁺. Taken together, these data suggest that targeted, inducible gene expression can be achieved in dopaminergic cell types.