Use of firefly luciferase activity assays to monitor circadian molecular rhythms in vivo and in vitro.

Circadian rhythms in metabolic, physiological, and behavioral processes are regulated by biological clocks. Many of these rhythmic processes can be measured over many days or weeks using automated recording devices, thus making it possible to precisely calculate period, phase, and amplitude values. With the advent of luciferase reporter genes and machines capable of quantifying luciferase-generated bioluminescence over long time frames, it is now possible to precisely monitor the rhythms in gene expression that underlie circadian clock function. These assays can be used to monitor gene expression in large numbers of individual plants and animals, and/or various cultured tissues and cells. After acquiring bioluminescence data, rhythm analysis programs are used to calculate the period, phase, amplitude, and overall levels of gene expression for individuals or groups, and to measure their statistical significance. Here we will describe how luciferase assays are performed and analyzed to measure gene expression rhythms in Drosophila.