A temperature-dependent timing mechanism is involved in the circadian system that drives locomotor rhythms in the fruit fly Drosophila melanogaster

The circadian clock of Drosophila melanogaster is thought to include rhythmic expression of period gene. Recent studies suggested, however, that a per-less oscillation is also involved in the regulation of circadian locomotor rhythms. In the present study, we examined the existence and the property of the possible per-less oscillation using arrhythmic clock mutant flies carrying per⁰¹, tim⁰¹, dClk^Jrk or cyc⁰¹, which lack rhythmic per expression. When temperature cycles consisting of 25°C and 30°C with various periods (T=8∼32 hr) were given, wild-type (Canton-S) flies showed locomotor rhythms entrained to temperature cycles over a wide range of period (T=8∼32 hr) in constant light (LL) while only to T=24 hr in constant darkness (DD). The mutant flies showed rhythms synchronizing with the given cycle both under LL and DD. In per⁰¹ and tim⁰¹ flies, the phase of a major peak slightly changed dependent on Ts in DD, while it did not in dClk^Jrk and cyc⁰¹ flies. When they were transferred from a constant temperature to a temperature cycle under DD, several cycles were necessary to establish a clear temperature entrainment in per⁰¹ and tim⁰¹ flies. These results suggest that per⁰¹ and tim⁰¹ flies have a temperature-entrainable weak oscillatory mechanism and that the per-less oscillatory mechanism may require dClk and cyc. In addition, per⁰¹ and tim⁰¹ flies changed from thermoactive in DD to cryoactive in LL, while dClk^Jrk and cyc⁰¹ flies did not. It is thus suggested that dClk and cyc are also involved in determining the light-associated temperature preference in per⁰¹ and tim⁰¹ flies.