Techniques that revealed the network of the circadian clock of Drosophila

The techniques are reviewed that revealed the neuronal network of the circadian clock in the brain of the fruit fly as well as the function and localization of peripheral oscillators. Three principal techniques helped characterize the circadian clock network of Drosophila consisting of pacemaker centers in the brain and oscillators in peripheral tissues: (1) Immunolabeling with antibodies raised against specific clock proteins detected the tissues and cells that express the clock proteins, revealed the subcellular localization of clock molecules, and illuminated their abundance at different time points during the day; (2) reporter genes unraveled the network of clock neurons and reported the circadian cycling of the clock genes in vivo; and (3) genetic manipulations of clock gene expression elucidated the function of specific clock genes and clock cells. These techniques and the results gained by them are reviewed briefly.