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Coordinating the Clock
In flies, the mechanosensory chordotonal organs help to coordinate the effects of temperature on circadian cycles. Simoni et al. (p. 525) provide a mechanism by which mechanosensory input is processed to help to synchronize the biological clock in Drosophila melanogaster. The chordotonal organs, which have similarities to the mammalian ear, were also required for sensation of a vibration stimulus and its effects on the endogenous brain clock. The chordotonal organs, present in the joints of the limbs, provide neuronal signals that allow the animal to sense its position or posture—and thus might mediate feedback of a range of behaviors onto the endogenous biological clock.
Circadian clocks attune the physiology of virtually all living organisms to the diurnal cycles of their environments. In metazoan animals, multiple sensory input pathways have been linked to clock synchronization with the environmental cycle (entrainment). Extrinsic entrainment cues include light and temperature. We show that (12-hour:12-hour) cycles of vibration and silence (VS) are sufficient to synchronize the daily locomotor activity of wild-type Drosophila melanogaster. Behavioral synchronization to VS cycles required a functional clock and functional chordotonal organs and was accompanied by phase-shifts of the daily oscillations of PERIOD protein concentrations in brain clock neurons. The feedback from mechanosensory—and particularly, proprioceptive—organs may help an animal to keep its circadian clock in sync with its own, stimulus-induced activities.