A tyrosine hydroxylase-neurofilament chimeric promoter enhances long-term expression in rat forebrain neurons from helper virus-free HSV-1 vectors

Helper virus-free herpes simplex virus (HSV-I) plasmid vectors are attracti ve for neural gene transfer but a promoter that supports neuronal-specific, long-term expression is required. Although expression from many promoters is unstable, a 6.8-kb, but not a 766-bp, fragment of the tyrosine hydroxyla se (TH) promoter supports long-term expression. Thus, 5' upstream sequences in this promoter may enhance expression. In this study, we evaluated expre ssion from vectors that contain 5' upstream sequences from this promoter (- 0.5 to -6.8 kb inserted at the 5' end of either a neurofilament heavy subun it (NF-H) promoter or the cytomegalovirus (CMV) immediate early promoter. T he TH-NFH promoter supported expression for 6 months in the striatum, 2 mon ths in the hippocampus, and for 1 month in both perirhinal and postrhinal c ortex (the longest lime points examined). Expression was targeted to neuron s. The enhanced expression may require specific sequences in the TH promote r fragment because replacing this fragment with a similar sized fragment of bacteriophage lambda DNA did not enhance expression. The reverse orientati on of the TH promoter fragment also enhanced expression. Insertion of insul ators from the chicken P-globin locus between the TH-NFHlac transcription u nit and the vector backbone may support a modest additional enhancement in expression. Other eucaryotic sequences may also enhance expression; a S. ce revisiae (40-kb fragment)-NFH promoter enhanced expression. In contrast, th e TH-CMV promoter did not enhance expression. Thus, the TH-NFH promoter may support some physiological studies that require long-term expression in fo rebrain neurons. (C) 2000 Elsevier Science B.V. All rights reserved.