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. 2015 Nov 17;112(46):E6284-92.
doi: 10.1073/pnas.1511215112. Epub 2015 Nov 2.

Temperature compensation and temperature sensation in the circadian clock

Affiliations

Temperature compensation and temperature sensation in the circadian clock

Philip B Kidd et al. Proc Natl Acad Sci U S A. .

Abstract

All known circadian clocks have an endogenous period that is remarkably insensitive to temperature, a property known as temperature compensation, while at the same time being readily entrained by a diurnal temperature oscillation. Although temperature compensation and entrainment are defining features of circadian clocks, their mechanisms remain poorly understood. Most models presume that multiple steps in the circadian cycle are temperature-dependent, thus facilitating temperature entrainment, but then insist that the effect of changes around the cycle sums to zero to enforce temperature compensation. An alternative theory proposes that the circadian oscillator evolved from an adaptive temperature sensor: a gene circuit that responds only to temperature changes. This theory implies that temperature changes should linearly rescale the amplitudes of clock component oscillations but leave phase relationships and shapes unchanged. We show using timeless luciferase reporter measurements and Western blots against TIMELESS protein that this prediction is satisfied by the Drosophila circadian clock. We also review evidence for pathways that couple temperature to the circadian clock, and show previously unidentified evidence for coupling between the Drosophila clock and the heat-shock pathway.

Keywords: circadian clock; mathematical models; temperature compensation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. S1.
Fig. S1.
Comparison of tim mRNA concentrations (relative to gapdh) and tim-luc reporter luminescence on the second day in DD at two different temperatures. Curves are rescaled to have mean 0 and rms deviation 1. Like luminescence, mRNA concentration oscillations show similar shapes at different temperatures, and the delay between peak mRNA concentration and peak luminescence is about 5–6 h independent of temperature.
Fig. 1.
Fig. 1.
(A) Diagram of a simple model for oscillator temperature compensation. mRNA isoforms X/X* are translated into proteins Y/Y*, which are converted into a second form Z/Z*, which represses transcription of X/X*. Each half of an isoform pair can be reversibly converted into and plays the same role as the other but has a different degradation rate. (B) Circadian oscillation of TIM protein, with various phases of the daily circadian cycle marked on corresponding locations on the oscillation. In red, a hypothetical scenario is shown in which a change in temperature causes a shortening of nuclear translocation time and a compensating increase in transcription time, leading to a change in shape of the oscillation.
Fig. 2.
Fig. 2.
TIM protein Western blots at three different temperatures. Representative blot images are shown on the left. In A, bands correspond to time points 2 h apart as shown, covering a full day at the indicated temperature. B shows bands from the first 6 h of the day at both 18° C and 29° C (as labeled) run side-by-side. C shows quantification of TIM protein concentrations relative to CDH, normalized so that the mean of the 18° C time series is 1. D shows that the same curves effectively coincide after rescaling to a mean of 0 and an rms deviation of 1. All error bars are SEM for three biological replicates.
Fig. 3.
Fig. 3.
Luminescence from tim-luc flies at 18°C, 25°C, and 29° C. (A) Sample of raw luminescence data plotted in millions of photon cpm. (B) The same data after detrending and smoothing. (C) Rescaled luminescence curves from tim-luc flies at different temperatures, taken from the second day in constant darkness. Shaded areas indicate SEM across three repetitions of the experiment.
Fig. 4.
Fig. 4.
(A) TIM protein oscillations in perL flies, rescaled to have mean 0 and rms deviation 1. CT corresponds to a 30-h period with hour 0 being subjective morning on the second day in DD. Error bars are SEM for three biological replicates. (B) Rescaled luminescence curves from perL; tim-luc flies at different temperatures, taken from the second day in constant darkness, showing a change in shape. Shaded areas indicate SEM across three different experiments. (C) Peaks of protein (solid lines) and luminescence (dotted lines) oscillations show a change in relative phase in perL. Each wedge is centered on the peak phase, with the width of the wedges giving the error in the location the peak (determined by a sinusoidal fit). Wedges on the inner circle come from perL flies, and wedges on the outer circle come from WT flies. Phase labels around the two concentric circles correspond to fractions of the period for each strain. The wedges corresponding to WT are offset slightly to aid visibility.
Fig. S2.
Fig. S2.
Raw data from circadian oscillation measurements in perL flies. (A) Representative Western blot images at three different temperatures. Time points span a 30-h period starting at CT1 on the second day in DD, at 3-h intervals as indicated. (B) Raw luminescence from perL; tim-luc flies, taken at 25° C. Note that the oscillations are relatively noisy and low in amplitude compared with WT (Fig. 3A), as noted in Western Blot and Luciferase Measurements.
Fig. S3.
Fig. S3.
Phase shift of circadian activity resulting from a 30-min heat pulse at 37° C, applied at CT 15. (Upper) Average activity of WT flies for a heat-shocked population (green) and a control population held at 25° C (blue). (Lower) The same data for cryb flies. The heat shock was applied at hour 0 on the plots, and in all cases, the results are an average of at least 19 flies. The phase shifts, computed by cross-correlation, are 3.1±0.24 for WT and 2.9±0.23 for cryb (SEM) and are thus statistically indistinguishable.
Fig. 5.
Fig. 5.
(A) Results of a PRC experiment applying a temperature step from 18° C to 29° C to three strains of flies. HSF/- indicates a heterozygous knockout of the heat-shock transcription factor, and HSFTS indicates a temperature-sensitive HSF mutant. Phase shifts are plotted against the hour of the subjective day at which the step occurred and are calculated relative to the phase of the group at CT 13. Error bars are SEM. (B and C) Effect of temperature on sleep profile in WT and heat-shock mutant flies. Sleep per 30 min is shown over the course of the circadian day at 18° C and 29° C in WT flies (B) and heterozygous heat-shock transcription factor knockouts (C). Shaded regions indicate SEM across at least 15 individuals.
Fig. S4.
Fig. S4.
Control PRC experiment (Fig. 5A) applying a temperature step from 25° C to 18° C to two strains: WT and a heterozygous knockout of the heat-shock transcription factor (HSF/-). The HSFTS strain is not tested because the HSFTS molecule is expected to have normal activity at both 18° C and 25° C. Phase shifts are plotted against the hour of the subjective day at which the step occurred and are calculated relative to the phase of the group at CT 13. Error bars are SEM.

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