Generation and Validation of an Inducible, Tissue-Specific Reporter of Drosophila Circadian Transcriptional Activity

Circadian rhythms are endogenously controlled within organisms through the function of cell-autonomous molecular clocks. In addition to a central clock located in the brain, molecular clocks are present in most peripheral tissues. Circadian clocks are coordinated within and across tissues, but the manner through which this coordination is achieved is not well understood. We reasoned that the ability to track molecular clock activity in specific tissues of living flies would facilitate an investigation into the relationship between different clock-containing tissues. Previous efforts to monitor clock gene expression in single Drosophila in vivo have used regulatory elements of different clock genes to dictate expression of a luciferase reporter enzyme, the activity of which can be monitored using a luminometer. Although these reporter lines have been instrumental in our understanding of the circadian system, they generally lack cell specificity, making it difficult to compare molecular clock oscillations between different tissues. Here we report the generation of several novel transgenic fly lines that allow for inducible expression of a luciferase reporter in a tissue-specific manner. We find that these lines faithfully report circadian transcriptional activity, as they exhibit rhythmic luciferase activity that is dependent on a functional molecular clock. We have used these lines to track circadian transcriptional activity in the whole body, fat body (a peripheral metabolic tissue), and brain of Drosophila. Our results confirm the efficacy of our reporter lines, which will enable future studies of the function and coordination of circadian clocks in different tissu