Conditional cell ablation by stringent tetracycline-dependent regulation of barnase in mammalian cells.

Conditional expression of suicide genes in vivo has a wide range of applications in biological research and requires a minimal basal promoter activity in the uninduced state. To reduce basal activity of tetracycline (tc)-inducible target promoters we combined synthetic tet operators in varying numbers with a core promoter derived from the plant viral 35S promoter. An optimized promoter, P(TF), was found to exert a stringent regulation of luciferase in combination with tTA and rtTA in different mammalian cell lines. We linked P(TF) to the barnase gene, coding for a highly active RNase from Bacillus amyloliquefaciens. Stable cell clones expressing barnase under control of tTA exerted cell death only after tc withdrawal, correlating with a 10-fold induction of barnase mRNA expression. Directing tTA expression through a neuron-specific enolase promoter (P(NSE)) leads to barnase expression and cell death in neuronal cells after tc withdrawal. Taken together, our data demonstrate that a stringent control of barnase expression in the uninduced state improves cell ablation studies, as high frequencies of transgene propagation in both cell lines and in transgenic mice are observed.