The circadian clock stops ticking during deep hibernation in the European hamster

Abstract

Hibernation is a fascinating, yet enigmatic, physiological phenomenon during which body temperature and metabolism are reduced to save energy. During the harsh season, this strategy allows substantial energy saving by reducing body temperature and metabolism. Accordingly, biological processes are considerably slowed down and reduced to a minimum. However, the persistence of a temperature-compensated, functional biological clock in hibernating mammals has long been debated. Here, we show that the master circadian clock no longer displays 24-h molecular oscillations in hibernating European hamsters. The clock genes Per1, Per2, and Bmal1 and the clock-controlled gene arginine vasopressin were constantly expressed in the suprachiasmatic nucleus during deep torpor, as assessed by radioactive in situ hybridization. Finally, the melatonin rhythm-generating enzyme, arylalkylamine N-acetyltransferase, whose rhythmic expression in the pineal gland is controlled by the master circadian clock, no longer exhibits day/night changes of expression but constantly elevated mRNA levels over 24 h. Overall, these data provide strong evidence that in the European hamster the molecular circadian clock is arrested during hibernation and stops delivering rhythmic output signals.deep torpor ͉ suprachiasmatic ͉ euthermia

Functional circadian clock genes are essential for the overwintering diapause of the Northern house mosquito,Culex pipiens

“…The role of the circadian clock during mammalian hibernation has not been extensively investigated either, but Revel et al (Revel et al, 2007) reported that circadian clock genes do not cycle in hibernating European hamsters. In contrast, we found that the clock genes per, tim, cyc and cry2 continue to show robust daily oscillations during diapause in the brains of C. pipiens.…”

“…In this study, we first compared the daily expression profiles of several circadian clock genes (per,tim,Clk,cyc,cry1 and cry2) in the brains of non-diapausing and diapausing adult females 1 week after adult eclosion, as well as in females at various times throughout diapause and after diapause was terminated. The circadian clock stops cycling during hibernation in European hamsters (Revel et al, 2007), but whether this is also true for insect diapause remains unclear and was tested here. Next, we used RNAi to knock down expression of several core circadian clock genes (per, tim, cry2, cyc and pdf) to assess the impact of this manipulation on egg follicle length and lipid content, two prominent markers of photoperiodic diapause in C. pipiens (Sim and Denlinger, 2008).…”

Efeitos das variações de temperatura ambiental em ritmos circadianos

“…Em morcegos da espécie Myotis lucifugus, por exemplo, a temperatura corporal pode chegar a 3 o C. Estudos com essa espécie demonstraram que o τ do ritmo circadiano de temperatura corporal é compensado a essas variações (Menaker, 1961). No entanto, em outros mamíferos, como no hamster-comum (Cricetus cricetus), a expressão do oscilador circadiano deixa de ser detectada durante a hibernação ou torpor (Revel, 2007). Outras evidências de compensação de τ a variações da temperatura em mamíferos vieram de experimentos in vitro.…”

“…Os ritmos de disparos neuronais dos NSQs in vitro apresentam Q 10 =0,99 (Ruby e col., 1999). Porém, a temperaturas menores de 15 o C há perda da atividade elé-trica de neurônios dos NSQs (Miller, 1994) e de expressão rítmica de genes do relógio (Revel, 2007). Esses resultados indicam que os NSQs de mamíferos têm compensação à temperatura, mas, ao menos em algumas espécies, deixam de expressar seus ritmos quando a temperatura cai abaixo de determinado limiar.…”

Molecular control of winter dormancy establishment in trees: a review

“…This parallelism between two such evolutionary distinct organisms suggests that the stopping of the circadian clock in response to cold could be part of a general adaptive strategy that enables living organisms that undergo dormancy or hibernation to survive the winter. Recently, the interruption of the molecular circadian clock in the European hamster during hibernation has also been described (Revel et al, 2007).…”