van der Veen Daan R, Mulder Ellis Ga, Oster Henrik, Gerkema Menno P, Hut Roelof A
Department of Chronobiology, University of Groningen, P,O, Box 14, 9750 AA Haren, The Netherlands.
J Circadian Rhythms. 2008 Mar 20;6:5. doi: 10.1186/1740-3391-6-5.
Circadian organisation of behavioural and physiological rhythms in mammals is largely driven by the clock in the suprachiasmatic nuclei (SCN) of the hypothalamus. In this clock, a molecular transcriptional repression and activation mechanism generates near 24 hour rhythms. One of the outputs of the molecular clock in specific SCN neurons is arginine-vasopressin (AVP), which is responsive to transcriptional activation by clock gene products. As negative regulators, the protein products of the period genes are thought to repress transcriptional activity of the positive limb after heterodimerisation with CRYPTOCHROME. When both the Per1 and Per2 genes are dysfunctional by targeted deletion of the PAS heterodimer binding domain, mice lose circadian organization of behaviour upon release into constant environmental conditions. To which degree the period genes are involved in the control of AVP output is unknown.
Using an in vitro slice culture setup, SCN-AVP release of cultures made of 10 wildtype and 9 Per1/2 double-mutant mice was assayed. Mice were sacrificed in either the early light phase of the light-dark cycle, or in the early subjective day on the first day of constant dark.
Here we report that in arrhythmic homozygous Per1/2 double-mutant mice there is still a diurnal peak in in vitro AVP release from the SCN similar to that of wildtypes but distinctively different from the release pattern from the paraventricular nucleus. Such a modulation of AVP release is unexpected in mice where the circadian clockwork is thought to be disrupted.
Our results suggest that the circadian clock in these animals, although deficient in (most) behavioural and molecular rhythms, may still be (partially) functional, possibly as an hourglass mechanism. The level of perturbation of the clock in Per1/2 double mutants may therefore be less than was originally thought.
哺乳动物行为和生理节律的昼夜组织主要由下丘脑视交叉上核（SCN）中的生物钟驱动。在这个生物钟中，一种分子转录抑制和激活机制产生接近24小时的节律。特定SCN神经元中分子生物钟的输出之一是精氨酸加压素（AVP），它对生物钟基因产物的转录激活有反应。作为负调节因子，周期基因的蛋白质产物被认为在与隐花色素异二聚化后抑制正相肢体的转录活性。当通过靶向缺失PAS异二聚体结合域使Per1和Per2基因均功能失调时，小鼠在释放到恒定环境条件下会失去行为的昼夜组织。周期基因在多大程度上参与AVP输出的控制尚不清楚。
使用体外切片培养装置，检测了由10只野生型和9只Per1/2双突变小鼠制成的培养物中SCN-AVP的释放。小鼠在明暗周期的早期光照阶段或在持续黑暗的第一天的早期主观白天被处死。
我们在此报告，在无节律的纯合Per1/2双突变小鼠中，SCN体外AVP释放仍有昼夜峰值，类似于野生型，但与室旁核的释放模式明显不同。在被认为生物钟机制被破坏的小鼠中，这种AVP释放的调节是出乎意料的。
我们的结果表明，这些动物的生物钟虽然在（大多数）行为和分子节律方面存在缺陷，但可能仍然（部分）功能正常，可能作为一种沙漏机制。因此，Per1/2双突变体中生物钟的扰动程度可能比最初认为的要小。
