Na ⁺ /Ca ²⁺ exchanger mediates cold Ca ²⁺ signaling conserved for temperature-compensated circadian rhythms

Abstract

Circadian rhythms are based on biochemical oscillations generated by clock genes/proteins, which independently evolved in animals, fungi, plants, and cyanobacteria. Temperature compensation of the oscillation speed is a common feature of the circadian clocks, but the evolutionary-conserved mechanism has been unclear. Here, we show that Na+/Ca2+ exchanger (NCX) mediates cold-responsive Ca2+ signaling important for the temperature-compensated oscillation in mammalian cells. In response to temperature decrease, NCX elevates intracellular Ca2+, which activates Ca2+/calmodulin-dependent protein kinase II and accelerates transcriptional oscillations of clock genes. The cold-responsive Ca2+ signaling is conserved among mice, Drosophila, and Arabidopsis. The mammalian cellular rhythms and Drosophila behavioral rhythms were severely attenuated by NCX inhibition, indicating essential roles of NCX in both temperature compensation and autonomous oscillation. NCX also contributes to the temperature-compensated transcriptional rhythms in cyanobacterial clock. Our results suggest that NCX-mediated Ca2+ signaling is a common mechanism underlying temperature-compensated circadian rhythms both in eukaryotes and prokaryotes.

Real time monitoring of cold Ca2+ dependent transcription and its modulation by NCX inhibitors

“…The previous studies revealed that expression levels of Per1 and Per2 are transiently induced by cytoplasmic Ca 2+ increase both in the SCN and peripheral cells 18 , 19 , 22 . We found that temperature decrease chronically elevates cytoplasmic Ca 2+ levels and Per1 and Per2 transcripts 18 (Fig. 1 ).…”

“…We employed transcriptional reporters that express luciferase under the control of Per1 or Per2 promotor 22 . In addition, luciferase reporter of Bmal1 19 promoter was also analyzed as a negative control reporter, because the mRNA levels of Bmal1 showed no increase under lower temperature 18 . The cells were first synchronized with 1 h-pulse of 0.1 μM dexamethasone, and the medium was replaced with an air culture medium before measuring bioluminescence.…”

“…Recently, we found that cytoplasmic Ca 2+ signaling is activated by lowering temperature for compensation of the transcriptional oscillation 18 . In response to temperature decrease, Na + /Ca 2+ exchanger (NCX) promotes Ca 2+ influx, which activates Ca 2+ /calmodulin-dependent protein kinase II (CaMKII).…”

“…The study clarified that the circadian clock is highly responsive to ambient temperature, and Ca 2+ signaling transduces the temperature information to the TTFLs. Importantly, NCX-dependent cold Ca 2+ signaling is functionally conserved among mammals, Drosophila , Arabidopsis and cyanobacteria, indicating that the cold Ca 2+ signaling is a general temperature response inherited from a common ancestor of the organisms 18 . Based on the study, we thought that development of a real-time monitoring system for the temperature response of the molecular clock is an important technique to study the conserved temperature signaling in living cells.…”

period Translation as a Core Mechanism Controlling Temperature Compensation in an Animal Circadian Clock

“…Previously described genetic perturbations that alter temperature compensation in animals have or may have altered the Q 10 of the encoded protein. Even in the case of pharmacological manipulations that alter temperature compensation, direct measures indicate inhibitors/antagonists can also significantly perturb the Q 10 of their targets(35) or the Q 10 has not been independently measured(31). In other cases, some gene dosage mutants in fungi that perturb temperature compensation actually exhibit phenotypes with better temperature compensation, i.e., Q 10 s closer to 1(5).…”