Tournier B B, Birkenstock J, Pévet P, Vuillez P
Institute for Cellular and Integrative Neurosciences, Department Neurobiology of the Rhythms, UPR 3212 CNRS, University of Strasbourg, 5 Rue Blaise Pascal, 67084 Strasbourg, France.
Neuroscience. 2009 Apr 21;160(1):240-7. doi: 10.1016/j.neuroscience.2009.02.002.
In mammals, the 24 h-rhythmicity of many physiological events is driven by the circadian clock contained in the suprachiasmatic nuclei (SCN). In the SCN, clock gene expressions produce the rhythmicity and control the expression of clock-controlled genes which play a role in the distribution of daily messages. The daily expression of all these genes is modulated by the duration of the light phase (i.e. photoperiod). The aim of this study was first to determine if these daily changes of expression reflect a real integration of a new photoperiod by the circadian clock or reflect only a passive effect of the light. In this way, we performed a time course of the modifications of gene expression after a transfer of Syrian hamsters from long to short photoperiod (LP and SP). Our results demonstrate that the core of the SCN (clock genes) integrates quickly a new photoperiod which entrains a slow adaptation of the clock-controlled gene expressions and induces a differential daily functioning of an SCN-target tissue, the pineal gland. We next asked the question whether SCN are involved in the photorefractory phase observed in Syrian hamsters exposed to SP for 26 weeks. All genes analyzed present a similar daily expression in SP-refractory and in SP with the exception of Clock. Its particular expression in SP-refractory is different than ones observed in SP or in LP. Thus, Clock seems to play a role in the development of the photorefractory phase, or this physiological state may modify the expression of Clock in the SCN. As a conclusion, it appears that the photoperiodic time measurement involves daily modifications of the molecular functioning of the SCN and that SCN also play a role in the measurement of the duration of the time passed in a short photoperiod.
在哺乳动物中，许多生理活动的24小时节律是由视交叉上核（SCN）中的生物钟驱动的。在SCN中，生物钟基因的表达产生节律性，并控制生物钟控制基因的表达，这些基因在日常信息的分配中发挥作用。所有这些基因的日常表达都受光照期时长（即光周期）的调节。本研究的目的首先是确定这些表达的日常变化是反映了生物钟对新光周期的真正整合，还是仅仅反映了光照的被动效应。通过这种方式，我们在叙利亚仓鼠从长光周期（LP）转移到短光周期（SP）后，对基因表达的变化进行了时间进程研究。我们的结果表明，SCN的核心（生物钟基因）能快速整合新的光周期，这会引发生物钟控制基因表达的缓慢适应，并诱导SCN靶组织松果体的日常功能差异。接下来，我们提出一个问题，即SCN是否参与了暴露于短光周期26周的叙利亚仓鼠中观察到的光不应期。除了Clock基因外，所有分析的基因在光不应期的短光周期和短光周期中的日常表达都相似。它在光不应期的短光周期中的特殊表达与在短光周期或长光周期中观察到的不同。因此，Clock基因似乎在光不应期的发展中起作用，或者这种生理状态可能会改变SCN中Clock基因的表达。总之，似乎光周期时间测量涉及SCN分子功能的日常变化，并且SCN在短光周期中经过的时间持续测量中也起作用。
