AN HSV-1 VECTOR CONTAINING THE RAT TYROSINE-HYDROXYLASE PROMOTER ENHANCES BOTH LONG-TERM AND CELL-TYPE-SPECIFIC EXPRESSION IN THE MIDBRAIN

A defective herpes simplex virus type one (HSV-1) vector that contains a 6.8-kb fragment of the rat tyrosine hydroxylase promoter (pTHlac-7k b) was examined for its capability to target catecholaminergic cell ty pe-specific expression in the CNS, Cell type-specific expression was a ssessed by comparison with a control vector (pHSVlac) that uses the HS V-1 immediate early 4/5 promoter to support expression in multiple cel l types, In initial experiments comparing expression in catecholaminer gic and noncatecholaminergic cell lines, pTHlac-7kb supported a seven- to 20-fold increase in reporter gene expression in catecholaminergic cell lines. Four days after stereotactic injection into the midbrain o f adult rats, pTHlac-7kb supported a IO-fold targeting of beta-galacto sidase expression to tyrosine hydroxylase-expressing neurons in the su bstantia nigra pars compacta compared with pHSVlac. Expression from pT Hlac-7kb was stably maintained for 6 weeks with no significant changes in the pattern of expression. Long-term expression from pTHlac-7kb wa s confirmed by RNA and DNA analysis, In contrast, reporter gene expres sion in the midbrain from pHSVlac decreased similar to 30-fold between 4 days and 6 weeks after gene transfer, Thus, within the context of t his HSV-1 vector system, the tyrosine hydroxylase promoter enhanced ce ll type-specific expression and contributed to stable, long-term expre ssion of a recombinant gene product in neurons. The capability to targ et recombinant gene expression to catecholaminergic neurons in specifi c brain areas may be useful for studies on the roles of these neurons in brain physiology and behavior.