A resetting signal between Drosophila pacemakers synchronizes morning and evening activity

At the end of the day Most animal cells, even in tissue cultures, can develop the molecular oscillations underlying circadian rhythms. To harness this property into the complex time-related behavioural patterns seen in whole organisms requires the intervention of a series of individual brain oscillators. Drosophila is proving to be a good model in which to study this system. The flies manifest characteristic morning and evening locomotor activity, each controlled by a different group of adult brain clock neurons. Now, by generating transgenic animals with different circadian periods in these morning and evening cells, the brain clock cells are shown to be organized into two separate neuronal circuits. One circuit includes the morning and evening cells and drives circadian locomotor activity. The timing of the evening cells is determined by the morning cells as a result of a daily resetting signal from the morning to the evening cells, which then run at their genetically programmed pace between signals.