Network balance via CRY signalling controls the Arabidopsis circadian clock over ambient temperatures

Circadian clocks exhibit ‘temperature compensation’, meaning that they show only small changes in period over a broad temperature range. Several clock genes have been implicated in the temperature‐dependent control of period in Arabidopsis. We show that blue light is essential for this, suggesting that the effects of light and temperature interact or converge upon common targets in the circadian clock. Our data demonstrate that two cryptochrome photoreceptors differentially control circadian period and sustain rhythmicity across the physiological temperature range. In order to test the hypothesis that the targets of light regulation are sufficient to mediate temperature compensation, we constructed a temperature‐compensated clock model by adding passive temperature effects into only the light‐sensitive processes in the model. Remarkably, this model was not only capable of full temperature compensation and consistent with mRNA profiles across a temperature range, but also predicted the temperature‐dependent change in the level of LATE ELONGATED HYPOCOTYL, a key clock protein. Our analysis provides a systems‐level understanding of period control in the plant circadian oscillator.     

生物节律基因period3的研究进展

昼夜节律是所有真核生物和部分原核生物的基本特征,一组节律表达的生物钟基因形成24 h周期振荡的自主调节转录-翻译反馈回路。period（per）基因家族是生物钟反馈回路中重要组成成分,per3基因是period基因家族成员之一。人类的per3基因定位于染色体1p36,其编码区第18外显子中含有一个灵长类特有的串联重复序列（variable number tandem repeat,VNTR）。该VNTR包含一簇理论上的磷酸化位点,能影响PER3蛋白的磷酸化降解,影响PER3蛋白的功能。近年研究发现,per3基因多态性与睡眠结构、睡眠紊乱发病年龄、睡眠剥夺后次日清晨执行能力等密切相关。     

Rhythmic oscillations in KaiC1 phosphorylation and ATP/ADP ratio in nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142

Cyanobacterial circadian clock composed of the Kai oscillator has been unraveled in the model strain Synechococcus elongatus PCC 7942. Recent studies with nitrogen-fixing Cyanothece sp. ATCC 51142 show rhythmic oscillations in the cellular program even in continuous light albeit with a cycle time of ~11 h. In the present study, we investigate correlation between cellular rhythms, KaiC1 phosphorylation cycle, ATP/ADP ratio, and the redox state of plastoquinone pool in Cyanothece. KaiC1 phosphorylation cycle of Cyanothece was similar to that of Synechococcus under diurnal cycles. However, under continuous light, the cycle time was shorter (11 h), in agreement with physiological and gene expression studies. Interestingly, the ATP/ADP ratio also oscillates with an 11 h period, peaking concomitantly with the respiratory burst. We propose a mathematical model with C/N ratio as a probable signal regulating the clock in continuous light and emphasize the existence of a single timing mechanism regardless of the cycle time.     

ELF3 recruitment to the PRR9 promoter requires other Evening Complex members in the Arabidopsis circadian clock

Biological timekeeping is essential for proper growth and development. Organisms such as the model plant Arabidopsis use the circadian clock to coordinate biological processes with the environment so that changes in conditions are anticipated and processes favorably phased. Despite the identification of numerous clock genes, knowledge of their molecular connectivity and influence on output programs remains limited. We recently showed LUX encodes a sequence-specific DNA-binding protein that directly regulates expression of the morning clock gene PRR9. We also showed that LUX interacts with the evening-phased proteins ELF3 and ELF4 to form a complex called the Evening Complex (EC). The EC binds the PIF4 and PIF5 promoters to control hypocotyl growth as a clock output. Here we provide evidence that LUX also recruits ELF3 to the PRR9 promoter. As with the PIF4 and PIF5 promoters, both LUX and its close homolog NOX are required for recruitment. Hence the entire EC likely functions together as part of the core clock oscillator to optimize plant fitness.     

Phase control of circadian activity in the antelope ground squirrel

Abstract

Wheel‐running activity of forty antelope ground squirrels, Ammospermophilus leucurus, was monitored for several months in both an outdoor cage and in the laboratory. The squirrels demonstrated a highly diurnal pattern which persisted in “constant conditions.” After removal from the field the initial free‐running period was close to 24 hrs, but typically lengthened in a nearly linear fashion at least for the first few months. There was no evidence of any difference in this trend for squirrels, in D/D, L/L 100 lx, 250 lx or 1200 lx. Eventually, about 90 percent of the squirrels had periods longer than 24 hrs.

The synchronizing capacity of the natural photoperiod was used to “catch the free‐running rhythm” and thereby demonstrate a response curve. Synchronization occurred by a shortening of the period when the time of sunrise was between 125° and 0° (subjective night) and by a lengthening of the period when the time of sunrise was between 0° and 125° (subjective day).

To more thoroughly examine the underlying mechanisms of phase control, phase‐response curves based on sixty one light‐pulse experiments were constructed. Comparisons of curves based on 6‐hr and 15‐min pulses, showed that the integral action of light is important (i.e., the entire pulse is involved in phase shifting). It was found that light pulses not only affected the phase of the rhythm but also the phase. Large phase shifts were usually associated with decreases in free‐running period. Several hypotheses on the controlling mechanisms were advanced.     

Endogenous control of circadian rhythms of pheromone production in the turnip moth, Agrotis segetum

The circadian variation of pheromone production in the turnip moth, Agrotis segetum, was characterized by quantifying (Z)-7-dodecenyl acetate (Z7-12:OAc), the most abundant pheromone component produced by female turnip moth, at different times of day. Under 17:7 h light-dark cycle (LD), the peak of Z7-12:OAc production occurred around 4 h into the scotophase, while there was very little pheromone production during the photophase. When females were maintained under constant darkness (DD), the periodicity of pheromone production was sustained for 3 consecutive days. Furthermore, the rhythm in pheromone production could be entrained to a shifted LD. These results demonstrate that the pheromone production in the turnip moth is regulated endogenously by a circadian clock. To understand how the circadian rhythm of pheromone production is generated, circadian variation of pheromone- biosynthesis-activating neuropeptide (PBAN)-like activity in the brain-suboesophageal ganglion complexes (Br-SOG), hemolymph, and ventral nerve cord (VNC) was also examined. Under both LD and DD, only the VNC displayed a circadian variation in the PBAN-like activity, which was significantly higher during the late-photophase than that in the scotophase. In addition, the present study showed that removal of VNC in isolated abdomen did not affect PBAN stimulation of pheromone production, while severing the VNC impaired normal pheromone production. The role of Br-SOG, VNC, and hemolymph in the regulation of the periodicity of pheromone production is discussed.     

Effects of bisphenol A and light conditions on the circadian rhythm of the goldfish Carassius auratus

We investigated how exposure to bisphenol A (BPA) under different photoperiodic conditions affected the expression of clock genes in the brain and liver of the goldfish, Carassius auratus. Three photoperiodic conditions were used: control, LD; continuous light, LL; and continuous dark, DD; the fish were exposed to three concentrations of BPA, namely 0, 10, or 100 μg/L. We measured changes in the expression of cryptochrome 1 (Cry1), period 2 (Per2), and melatonin receptor 1 (MT-R1). The levels of Cry1, Per2, and MT-R1 mRNAs decreased with increasing BPA concentration and with increasing exposure time. Expression of Cry1 and Per2 increased more in the LL group than in the LD and DD groups. However, for MT-R1, the DD group showed increased expression compared to the LL and LD groups. Our analysis shows that circadian rhythms in goldfish can be disrupted by exposure to BPA and that the response can be modified by regulating the photoperiod.     

哺乳动物生物钟的遗传和表观遗传研究进展

生物钟对生物机体的生存与环境适应具有着重要意义,其相关研究近年来受到人们的广泛关注。生物钟的重要性质之一是内源节律的周期性,当前的研究认为这种周期性是由生物钟相关基因转录翻译的多反馈环路构成核心机制调控着近似24 h的节律振荡。哺乳动物的生物钟系统存在一个多层次的结构,包括位于视交叉上核的主时钟和外周器官和组织的子时钟。虽然主时钟和子时钟存在的组织不同,但是参与调节生物钟的分子机制是一致的。近年来,通过正向、反向遗传学方法和表观遗传学的研究方法,对生物钟的分子机制的解析和认知愈发深入。本文在简单回顾生物钟基因发现历史的基础上,重点从遗传学和表观遗传学两个方面,从振荡周期的角度,对哺乳动物生物钟分子机制的研究进展进行了综述性介绍,以期为靶向调节生物钟来改善机体的稳态系统的研究提供参考,同时希望能促进时间生物学领域与更多其他领域形成交叉研究。