Differential Effects of Light and Heat on the Drosophila Circadian Clock Proteins PER and TIM

Abstract

Circadian (Х24-h) rhythms are governed by endogenous biochemical oscillators (clocks) that in a wide variety of organisms can be phase shifted (i.e., delayed or advanced) by brief exposure to light and changes in temperature. However, how changes in temperature reset circadian timekeeping mechanisms is not known. To begin to address this issue, we measured the effects of short-duration heat pulses on the protein and mRNA products from the Drosophila circadian clock genes period (per) and timeless (tim). Heat pulses at all times in a daily cycle elicited dramatic and rapid decreases in the levels of PER and TIM proteins. PER is sensitive to heat but not light, indicating that individual clock components can markedly differ in sensitivity to environmental stimuli. A similar resetting mechanism involving delays in the per-tim transcriptional-translational feedback loop likely underlies the observation that when heat and light signals are administered in the early night, they both evoke phase delays in behavioral rhythms. However, whereas previous studies showed that the light-induced degradation of TIM in the late night is accompanied by stable phase advances in the temporal regulation of the PER and TIM biochemical rhythms, the heat-induced degradation of PER and TIM at these times in a daily cycle results in little, if any, long-term perturbation in the cycles of these clock proteins. Rather, the initial heat-induced degradation of PER and TIM in the late night is followed by a transient and rapid increase in the speed of the PER-TIM temporal program. The net effect of these heat-induced changes results in an oscillatory mechanism with a steady-state phase similar to that of the unperturbed control situation. These findings can account for the lack of apparent steady-state shifts in Drosophila behavioral rhythms by heat pulses applied in the late night and strongly suggest that stimulus-induced changes in the speed of circadian clocks can contribute to phase-shifting responses.Circadian (Х24-h) rhythms are governed by endogenous biochemical oscillators, or clocks (reviewed in references 18 and 46). Although these rhythms persist under constant environmental conditions, they can be entrained (synchronized) by external time cues (zeitgebers), most notably the daily light/ dark and temperature cycles. The adaptive ability of circadian clocks to be reset by external cues enables organisms to maintain temporal alignment between their endogenously driven rhythms and biologically advantageous times in a daily cycle. A powerful strategy for probing this resetting feature is based on the ability of short pulses of environmental stimuli or other agents to elicit phase shifts in circadian pacemakers. These perturbation experiments revealed that the direction (i.e., delay or advance) and magnitude of a phase shift are functions of the time in a daily cycle that the zeitgeber is administered. Plotting the average phase shift as a function of time that the stimulus was applied yields a phase-response curve (PRC) that describes...

Histamine and Its Receptors Modulate Temperature-Preference Behaviors inDrosophila

“…(3) Finally, hisCl1 is expressed in circadian clock neurons. Recently, several reports showed that changes in environmental temperature could directly control the circadian clock (Sawyer et al, 1997;Sidote et al, 1998;Majercak et al, 1999;Glaser and Stanewsky, 2005). In addition, our previous data suggested that clock neurons can affect temperature preference in Drosophila .…”

Veela defines a molecular link between Cryptochrome and Timeless in the light-input pathway to Drosophila 's circadian clock

“…Preparations of head extracts and protein blots were performed by using anti-PER and -TIM as well as dilutions of these antibodies, as described (5), except that for the blots shown in Fig. 5, a different anti-TIM antibody was applied (31).…”

Thermosensitive Splicing of a Clock Gene and Seasonal Adaptation

“…Subsequently, separate aliquots of cells were incubated for 24 hours at different temperatures in the dark. Total RNA was extracted, and the relative levels of spliced and nonspliced products were determined as previously described using reverse transcriptase-polymerase chain reaction (RT-PCR) whereby values are normalized to an internal RNA standard (Majercak et al 2004). The dmpi8 control RNA exhibited approximately 2.5-3.2-fold increases (n > 10; P <0.001 using Student's t-test for values obtained at 12°C and 24°C) in the proportion of spliced-to-unspliced RNA at 12°C compared to 24°C (Fig.…”

“…Although period length is rather insensitive to temperature fluctuations, the phases and amplitudes of circadian rhythms can exhibit clear temperature-induced changes. Most notably, circadian rhythms can be phase-shifted by changes in temperature (pulses and step-up or -down) and entrained by daily temperature cycles (see, e.g., Sweeney and Hastings 1961;Wheeler et al 1993;Liu et al 1997Liu et al , 1998Sidote et al 1998;and references therein). Other work indicates that the amplitude of a circadian oscillator changes as a function of temperature (usually perceived as increasing with rising temperature), suggested by some as a solution to temperature compensation of period length (LakinThomas et al 1991;Pittendrigh et al 1991).…”