Synchronization of the phases by changing the medium. Antiphasic oscillations were induced in Bmal1–GR and Bmal1–RED cells, as shown in the figure. After 3 d of measurement, the medium was replaced with fresh luciferin medium. The independently phased circadian rhythms of the luciferase activities of Bmal1–GR and Bmal1–RED cells were reset by the medium change. Luciferase activities are shown on the Y axis and the time after starting measurement of the bioluminescence is shown on the X axis.