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Neurogenetics

Regulated expression of transferred genes is critical for experimental evaluation of gene function as well as for gene therapy applications. Several prokaryotic transcription control systems have the ability to specifically and efficiently regulate gene expression even after adaption to eukaryotic cells. The tetracycline system (tet system) consists of two plasmid based elements, i.e. the "regulator unit" coding for a transactivator hybrid protein (tTA) composed of the tetracycline repressor (tetR) fused to the herpes simplex virus transactivator protein VP16 under control of an SV40 promoter, and the "response unit" composed of E.coli-derived tet operator sequences (tetO) embedded within a minimal CMV promoter driving the gene of interest (PNAS 89, 5547, 1992). We placed the two transcriptional units within the same retroviral vector so that high levels of constitutively produced tTA transcripts function not only for production of tTA protein (and consecutively high induced levels of the gene of interest) in the ON state (absence of tetracycline), but also to decrease basal expression of the response unit by apparent antisense inhibition in the OFF state (presence of tetracycline). Tetracycline-dependent regulation, as examined using a luciferase indicator gene, was 336-fold in infected NIH 3T3 fibroblasts, and ranged from 24 to 127-fold in different epithelial and glial cell types. By replacing the internal SV40 promoter driving the tTA gene by the glial specific JC virus early promoter, induced luciferase expression as well as regulability could be increased in glioma cells but not in other cell types. These retroviral vectors that allow for the regulation of heterologous genes and can infect virtually all dividing cells should be useful for the functional examination of a broad range of genes as well as for gene therapy applications.


Headings
retroviral vector
tetracycline-regulatable expression

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