Low-cost system for real-time monitoring of luciferase gene expression

In some mammalian cells transfected with luciferase reporter genes, the luciferase/luciferin reaction in a cell monolayer produces a very small light flux. While the low light levels are often measureable with single-photon counting cameras, these devices are expensive and may require long averaging times to acquire an image. We describe an approach for real-time monitoring of light produced by luciferase gene expression in intact, cultured cells using readily available and relatively inexpensive components. The system uses a single-photon counting photomultiplier tube with built-in high voltage supply and photon counting circuitry to rapidly measure average light output from growing cells in a 35-mm culture dish. The fast, accurate and highly sensitive response of the system makes it useful for studying the dynamics of gene expression over time periods ranging from minutes to days.