Temperature Regulates Transcription in the Zebrafish Circadian Clock

Abstract

It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation). In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic model, we demonstrate first that in the absence of light, exposure of embryos and primary cell lines to temperature cycles entrains circadian rhythms of clock gene expression. Temperature steps drive changes in the basal expression of certain clock genes in a gene-specific manner, a mechanism potentially contributing to entrainment. In the case of the per4 gene, while E-box promoter elements mediate circadian clock regulation, they do not direct the temperature-driven changes in transcription. Second, by studying E-box-regulated transcription as a reporter of the core clock mechanism, we reveal that the zebrafish clock is temperature-compensated. In addition, temperature strongly influences the amplitude of circadian transcriptional rhythms during and following entrainment by light–dark cycles, a property that could confer temperature compensation. Finally, we show temperature-dependent changes in the expression levels, phosphorylation, and function of the clock protein, CLK. This suggests a mechanism that could account for changes in the amplitude of the E-box-directed rhythm. Together, our results imply that several key transcriptional regulatory elements at the core of the zebrafish clock respond to temperature.

Nonparametric entrainment of the in vitro circadian phosphorylation rhythm of cyanobacterial KaiC by temperature cycle

“…To elucidate how the intracellular oscillators physiologically interact with the external temperature cycles, entrainment kinetics were carefully studied by applying various non-24-hour cycles (T cycles; 9, 10). On the other hand, to study molecular events that linked with external temperature signals, temperature-dependent processes such as transcription, translation, RNA processing, protein stability, and protein-protein interactions were analyzed in several model organisms (11)(12)(13).…”

Synchronization of theDrosophilaCircadian Clock by Temperature Cycles

“…Similar to behavioral rhythms in Drosophila, RNA rhythms in fish were synchronized even if the amplitude of the thermocycle was as low as 2°C (Wheeler et al 1993;Lahiri et al 2005). Moreover, it was shown that the abundance and phosphorylation status of zebra fish Clk1 is different at constant low (20°C) versus high (30°C) temperatures during LD cycles (Lahiri et al 2005). Although this does not directly address the question of whether these differences at the protein level contribute to temperature entrainment, it does suggest that posttranscriptional regulation also contributes to thermal entrainment in vertebrates.…”

“…Transcriptional rhythms of potential core clock genes could also be induced by temperature cycles in zebra fish cells and larvae (Lahiri et al 2005). Similar to behavioral rhythms in Drosophila, RNA rhythms in fish were synchronized even if the amplitude of the thermocycle was as low as 2°C (Wheeler et al 1993;Lahiri et al 2005).…”

“…Therefore, the situation seems to be similar to that for light entrainment, where it has been shown that isolated tissues can be synchronized by LD cycles (see, e.g., Emery et al 1997;Plautz et al 1997;Ivanchenko et al 2001;Levine et al 2002a). Moreover, in zebra fish, it has been demonstrated that temperature entrainment occurs on a cell-autonomous level, suggesting that this may also be the case in flies (Lahiri et al 2005).…”

“…Overall, their experiments In light of the above-mentioned temperature effects on the circadian clock, especially the ability of the clock to actively compensate for different temperatures, it seems remarkable that daily temperature fluctuations can serve as a robust zeitgeber in many organisms (Dunlap et al 2004). Even more astonishing, the amplitude of the temperature cycle necessary to elicit entrainment can be tiny, often only 1-3°C (see, e.g., Wheeler et al 1993;Lahiri et al 2005). In mammals, temperature cycles with a 1.5°C amplitude are able to induce rhythmic per1 and per2 expression in suprachiasmatic nucleus (SCN) glia cells (Prolo et al 2005), and the daily body temperature cycles seem to be capable of synchronizing circadian transcripts in mouse liver and fibroblasts (Brown et al 2002;Kornmann et al 2007).…”