PER-TIM Interactions with the Photoreceptor Cryptochrome Mediate Circadian Temperature Responses in Drosophila

Drosophila cryptochrome (CRY) is a key circadian photoreceptor that interacts with the period and timeless proteins (PER and TIM) in a light-dependent manner. We show here that a heat pulse also mediates this interaction, and heat-induced phase shifts are severely reduced in the cryptochrome loss-of-function mutant cryb. The period mutant perL manifests a comparable CRY dependence and dramatically enhanced temperature sensitivity of biochemical interactions and behavioral phase shifting. Remarkably, CRY is also critical for most of the abnormal temperature compensation of perL flies, because a perL; cryb strain manifests nearly normal temperature compensation. Finally, light and temperature act together to affect rhythms in wild-type flies. The results indicate a role for CRY in circadian temperature as well as light regulation and suggest that these two features of the external 24-h cycle normally act together to dictate circadian phase. : Circadian rhythms profoundly affect the physiology and behavior of most organisms. These rhythms are generated by a self-sustained molecular clock, which is largely conserved between fruit flies and mammals and synchronizes to the day/night cycle. This synchronization is achieved in most organisms by a daily resetting caused by light and/or temperature fluctuations. The molecular mechanisms underlying light synchronization are reasonably well understood, but an understanding of how temperature affects the circadian clock is lacking. This study demonstrates a striking and unanticipated relationship between light and temperature resetting mechanisms in Drosophila. An interaction between the circadian photoreceptor CRYPTOCHROME (CRY) and a complex composed of the key circadian regulators PERIOD (PER) and TIMELESS (TIM) are critical for circadian temperature responses as well a circadian light responses. Moreover, the data not only indicate that light and temperature reset the clock through similar mechanisms but also that these two inputs can act synergistically. An interaction between light and temperature may fine-tune the dawn and dusk response of the clock and even contribute to seasonal adaptation of clock function, an emerging area of research in circadian biology. Temperature-dependent changes in circadian rhythms are mediated by interactions between the photoreceptor cryptochrome (CRY) and the proteins period (PER) and timeless (TIM).