CNRS, UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France.
PLoS One. 2010 Dec 15;5(12):e15316. doi: 10.1371/journal.pone.0015316.
The mammalian circadian system is composed of multiple peripheral clocks that are synchronized by a central pacemaker in the suprachiasmatic nuclei of the hypothalamus. This system keeps track of the external world rhythms through entrainment by various time cues, such as the light-dark cycle and the feeding schedule. Alterations of photoperiod and meal time modulate the phase coupling between central and peripheral oscillators. In this study, we used real-time quantitative PCR to assess circadian clock gene expression in the liver and pituitary gland from mice raised under various photoperiods, or under a temporal restricted feeding protocol. Our results revealed unexpected differences between both organs. Whereas the liver oscillator always tracked meal time, the pituitary circadian clockwork showed an intermediate response, in between entrainment by the light regimen and the feeding-fasting rhythm. The same composite response was also observed in the pituitary gland from adrenalectomized mice under daytime restricted feeding, suggesting that circulating glucocorticoids do not inhibit full entrainment of the pituitary clockwork by meal time. Altogether our results reveal further aspects in the complexity of phase entrainment in the circadian system, and suggest that the pituitary may host oscillators able to integrate multiple time cues.
哺乳动物的生物钟系统由多个外周时钟组成，这些时钟通过下丘脑视交叉上核的中央起搏器同步。这个系统通过各种时间线索（如光暗周期和进食时间表）的驯化来跟踪外部世界的节奏。光周期和用餐时间的改变会调节中枢和外周振荡器之间的相位耦合。在这项研究中，我们使用实时定量 PCR 评估了在不同光周期或限时进食方案下饲养的小鼠肝脏和垂体中的生物钟基因表达。我们的结果揭示了两个器官之间出人意料的差异。虽然肝脏振荡器始终跟踪用餐时间，但垂体生物钟表现出中间反应，介于光方案和进食-禁食节律的驯化之间。在白天限时进食的肾上腺切除小鼠的垂体中也观察到了相同的复合反应，这表明循环糖皮质激素不会抑制垂体时钟完全被用餐时间驯化。总之，我们的研究结果揭示了生物钟系统相位驯化复杂性的进一步方面，并表明垂体可能存在能够整合多种时间线索的振荡器。
