Life's 24-hour clock: molecular control of circadian rhythms in animal cells

Our sleep–wake cycles and many other 24-hour rhythms of behavior and physiology persist in the absence of environmental cues. Genetic and biochemical studies have shown that such rhythms are controlled by internal molecular clocks. These are assembled from the cycling RNA and protein products of a small group of genes that are conserved throughout the animal kingdom.     

The effects of chronic marijuana use on circadian entrainment

Animal literature suggests a connection between marijuana use and altered circadian rhythms. However, the effect has not yet been demonstrated in humans. The present study examined the effect of chronic marijuana use on human circadian function. Participants consisted of current users who reported smoking marijuana daily for at least a year and non-marijuana user controls. Participants took a neurocognitive assessment, wore actigraphs and maintained sleep diaries for three weeks. While no significant cognitive changes were found between groups, data revealed that chronic marijuana use may act as an additional zeitgeber and lead to increased entrainment in human users.     

Diurnality and nocturnality in nonhuman primates: comparative chronobiological studies in laboratory and nature

Looking for differences in circadian clock characteristics of diurnal and nocturnal nonhuman primates, this article summarizes results of chronobiological studies carried out in various nocturnal, diurnal, and cathemeral prosimian and anthropoid primate species under controlled laboratory conditions, under seminatural conditions, and in the wild. In almost all circadian parameters investigated, no differences were discernible between the two main chrono-ecotypes, either in circadian period length and the influence upon it of after-effects, of light intensity, and ambient temperature, or in the PRC, re-entrainment behavior, rhythm splitting, and internal desynchronization. Diurnal and nocturnal or cathemeral species differed only in the phase of artificial or natural LDs to which their circadian activity phase was adjusted as well as in the characteristics of masking activity upon the rhythms produced by the direct inhibiting or enhancing effects of light. Pronounced lunar periodicity—observed in the activity rhythm of nocturnal neotropical owl monkeys, genus Aotus, in seminatural and natural environments as well as in wild cathemeral Malagasy lemurs, genus Eulemur—is shown to result from masking effects of moonlight. In captive Eulemur fulvus albifrons, a change from dark-active over cathemeral to light-active behavior, without concurrently changing the circadian phase-setting of activity to D, was produced by direct masking effects of a stepwise reduction of darktime luminosity on an LD 12:12 cycle. Long-term activity recordings carried out in wild diurnal Malagasy sifakas (Propithecus verreauxi) and cathemeral redfronted lemurs (Eulemur fulvus rufus), as well as in wild nocturnal owl monkeys (Aotus a. azarai) of the North Argentinean Chaco, yielded in all species distinct bimodal long- and short-day activity patterns with pronounced peaks during dusk and dawn. Applying Pittendrigh's two-oscillator concept to these results, it is hypothesized that the differences in chrono-ecotype behavior may result from variations in internal coupling and external phase-setting of morning and evening oscillators (m, e) to dawn and dusk, interacting with direct masking effects of light.     

Social synchronization of circadian rhythms of metabolism in honeybees (Apis mellifera)

ABSTRACT. Groups of honeybee workers ( Apis mellifera Linn.; Hymenoptera: Apidae) show endogenous circadian rhythms in metabolic activity. Workers entrained to two different photoperiods, when put together in a group, coordinate their individual metabolic activity cycles into a synchronized group oscillation. Either physical interaction among workers, or a low volatility contact pheromone, is implicated in the control of this oscillating system.     

Plasticity of diel and circadian activity rhythms in fishes

In many fish species, some individuals arediurnal while others are nocturnal. Sometimes,the same individual can be diurnal at first andthen switch to nocturnalism, or vice-versa.This review examines the factors that areassociated with such plasticity. It covers thebreakdown of activity rhythms during migration,spawning, and the parental phase; reversals ofactivity patterns during ontogeny or from oneseason to the next; effects of light intensity,temperature, predation risk, shoal size, foodavailability, and intraspecific competition.Case studies featuring goldfish (Carassiusauratus), golden shiner (Notemigonuscrysoleucas), lake chub (Couesiusplumbeus), salmonids, sea bass (Dicentrarchus labrax), and parentalsticklebacks and cichlids illustrate some ofthese influences. It is argued that mostspecies have a circadian system but that havingsuch a system does not necessarily imply strictdiurnalism or nocturnalism. Rigidity ofactivity phase seems more common in species,mostly marine, that display behavioral sleep,and for these animals the circadian clock canhelp maintain the integrity of the sleepperiod and ensure that its occurrence takes place atthat time of day to which the animal's sensoryequipment is not as well adapted. However, inother fishes, mostly from freshwater habitats,the circadian clock seems to be used mainly foranticipation of daily events such as thearrival of day, night, or food, and possiblyfor other abilities such as time-place learningand sun compass orientation, rather than forstrict control of activity phase. In thesespecies, various considerations relating toforaging success and predation risk maydetermine whether the animal is diurnal ornocturnal at any particular time and place.     

草地贪夜蛾生殖行为及其昼夜节律研究

草地贪夜蛾Spodoptera frugiperda是当前跨国迁飞性重大害虫,云南是其重要虫源地及其向内地迁移的重要通道。生殖行为是性选择和物种进化的重要基础,基于生殖行为的害虫监测和防治策略也有重要价值。本研究模拟自然条件下可能出现的择偶情况,采用永久配对和每日更换配偶两种处理,对草地贪夜蛾成虫一生(约10 d)的生殖行为和节律进行了连续观测。结果表明,该蛾在羽化当日(0日龄)即出现召唤和求偶行为但无交配发生,在1日龄开始出现交配行为并在2日龄开始产卵,从2日龄到6日龄期间一直保持了较高的生殖活动,之后开始下降。雄虫求偶与雌虫召唤在节律上有较高的同步性,交配高峰多出现在召唤和求偶高峰之后。每日更换配偶与永久配对相比,雌蛾表现出较高的求偶频率和持续时间,较高交配比率和频率。雌虫在遇到新配偶或与新配偶交配后,会延缓产卵或下调产卵速率。从性选择理论来看,这些行为策略将有助于雌虫获得物质或基因利益,值得进一步探究。交配次数、召唤时长与雌虫寿命之间相关性不显著,但前5 d产卵速率与雌虫寿命间存在显著负相关,即早期产卵量较高的雌虫寿命较短,符合早期繁殖-后期存活基因拮抗假说。     

The effects of feedback lighting on the circadian drinking rhythm in the diurnal new world primate Saimiri sciureus

Feedback lighting provides illumination primarily during the subjective night (i.e., the photosensitive portion of the circadian cycle) in response to a given behavior. This technique has previously been used to test the nonparametric model of entrainment in nocturnal rodents. In three species (Rattus norvegicus, Mesocricetus auratus, and Mus musculus), the free-running period of the locomotor activity rhythm was similar whether the animals were exposed to continuous light or discrete light pulses occurring essentially only during the subjective night (i.e., feedback lighting). In the current experiments, feedback lighting was presented to squirrel monkeys so that light fell predominantly during the subjective night. Feedback lighting was linked to the drinking behavior in this diurnal primate so that when the animal drank, the lights went out. Despite the seemingly adverse predicament, the monkeys maintained regular circadian drinking rhythms. Furthermore, just as the period of the free-running activity rhythms of nocturnal rodents exposed to continuous light or feedback lighting were similar, the period of the drinking rhythms of the squirrel monkeys in continuous light and feedback lighting were comparable (25.6 +/- 0.1 and 25.9 +/- 0.1 hours, respectively), despite a substantial decrease in the total amount of light exposure associated with feedback lighting. The free-running period of monkeys exposed to continuous dark (24.5 +/- 0.1 hours) was significantly shorter than either of the two lighting conditions (P < 0.001). The results presented for the drinking rhythm were confirmed by examination of the temperature and activity rhythms. Therefore, discrete light pulses given predominately during the subjective night are capable of simulating the effects of continuous light on the free-running period of the circadian rhythms of a diurnal primate. The response of squirrel monkeys to feedback lighting thus lends further support for the model and suggests that the major entrainment mechanisms are similar in nocturnal rodents and diurnal primates.     

Clock polymorphisms and circadian rhythms phenotypes in a sample of the Brazilian population

A Clock polymorphism T to C situated in the 3' untranslated region (3'-UTR) has been associated with human diurnal preference. At first, Clock 3111C had been reported as a marker for evening preference. However these data are controversial, and data both corroborating and denying them have been reported. This study hypothesizes that differences in Clock genotypes could be observed if extreme morning-type subjects were compared with extreme evening-type subjects, and the T3111C and T257G polymorphisms were studied. The possible relationship between both polymorphisms and delayed sleep phase syndrome (DSPS) was also investigated. An interesting and almost complete linkage disequilibrium between the polymorphisms T257G in the 5' UTR region and the T3111C in the 3' UTR region of the Clock gene is described. Almost always, a G in position 257 corresponds to a C in position 3111, and a T in position 257 corresponds to a T in position 3111. The possibility of an interaction of these two regions in the Clock messenger RNA structure that could affect gene expression was analyzed using computer software. The analyses did not reveal an interaction between those two regions, and it is unlikely that this full allele correspondence affects Clock gene expression. These results show that there is no association between either polymorphism T3111C or T257G in the Clock gene with diurnal preference or delayed sleep phase syndrome (DSPS). These controversial data could result from the possible effects of latitude and clock genes interaction on circadian phenotypes.     

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。     

A circadian rhythm of thermal preference in the ant Camponotus mus: masking and entrainment by temperature cycles

Abstract. Along a stable temperature gradient and under a LD 12:12 h cycle, nurse workers of the ant Camponotus mus Roger 1863 (Hymenoptera: Formicidae) select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (circadian phase = 210°), this rhythm being of endogenous nature.When a 24 h temperature cycle was superimposed along the thermal gradient, so that the immobile brood experienced a temperature transition as they receive when translocated by nurses (8 h at 30.8°C and 16 h at 27.5°C), no brood translocations occurred.The thermal cycle masked the rhythm of brood translocation when temperature fitted the daily pattern expected by nurses.When the same temperature cycle was presented with a phase-advance, nurses did not tolerate the early thermal increase and removed the brood as temperature rose.However, when workers experienced this new phase relationship between light and temperature cycles for more than 10 days, brood translocations were suppressed.Records under constant conditions of light and temperature indicated that the overt rhythm was locked-on to the expected early increase in temperature, so that the temperature cycle dominated over the LD cycle in resetting brood-carrying activity.     

Freerunning and entrained circadian rhythms in activity,eating and drinking in the cat

Abstract

Because cats with pontile lesions exhibit an abnormal behavior that is under photoperiodic control, and because circadian rhythms are implicated in photoperiodic control mechanisms, an effort was made to detect circadian rhythms in the cat. Cats were isolated from all extraneous stimuli in soundproof chambers for extended periods of time. Photocells were used to monitor activity, eating and drinking in different LD cycles, in constant light at two intensities, and in constant dark. Freerunning circadian rhythms were found in the constant conditions, and entrained nocturnal patterns occurred in most of the LD cycles. The higher intensities of ambient illumination disrupted the freerunning rhythms. The freerunning rhythms were always greater than 24 h, ranging from 24.2 to 25 h. Measurements of food intake of cats living in a large colony room, obtained by weighing the food, revealed that a nocturnal pattern of entrainment was not present in the majority of the cats. Instead, most cats in the colony exhibited a random pattern of eating throughout the light and dark period of the LD cycle. However, the variation among the cats in the colony was considerable, extending from nocturnal to diurnal patterns of eating. A diurnal pattern of human activity was present in the colony and may account for the disruption of a basic nocturnal pattern. The presence of circadian rhythms in the cat leads us to consider the coincidence models for photoperiodic induction as possible explanations of the photoperiodic control of the lesion‐induced abnormal behavior.     

Impacts of high-sucrose diet on circadian rhythms in the small intestine of rats

Excessive sucrose intake, known as fructose toxicity, leads to fatty liver, hyperlipidemia, and metabolic syndrome. Circadian disorders also contribute to metabolic syndrome. Here, we investigated the effect of excessive sucrose intake on circadian rhythms of the small intestine, the main location of sucrose absorption, to elucidate a mechanism of sucrose-induced abnormal lipid metabolism. Male Wistar rats were fed control starch or high-sucrose diets for 4 weeks. High-sucrose diet-induced fatty liver and hypertriglyceridemia in rats. Amplitudes of PER1/2 expression oscillations in the small intestine were reduced by excessive sucrose, while gene expression of GLUT5 and gluconeogenic enzymes was enhanced. These changes would contribute to interfering in lipid homeostasis as well as adaptive responses to control fructose toxicity in rats.     

On-line data acquisition and evaluation of long-term measurements of circadian rhythms in individual cells ofAcetabularia

A multitasking time-sharing computer system was implemented for studies of different circadian rhythms in individual cells of the unicellular green alga,Acetabularia. This fully automatized system allows simultaneous data acquisition and analysis. Graphical presentation of untreated and mathematically treated data is permanently available on three graphic displays and on a digital plotter. The sampling rate for the data acquisition in each of the 60 channels connected to the system is 720/24 h. Provisions have been made to guarantee uninterrupted data uptake for these long-term measurements by including an auto-restart module and by providing extremely reliable software for the experimenter using menu techniques.     

Activity patterns of rodents: the physiological ecology of biological rhythms

To date, most research in the field of biological rhythms has been performed on nocturnal rodents under laboratory conditions. This research has made much progress in recent years. It is now time to investigate the adaptive value of the studied molecular mechanisms under natural conditions. Here we review relevant studies of rodent activity patterns. We also review a case study of temporal partitioning between spiny mice. We conclude that the response to environmental stimuli, using a system composed of a rigid master circadian oscillator and more flexible mechanisms such as peripheral oscillators with weak coupling, masking responses, and downstream switching mechanisms, is adaptive since it enables an animal to reset its activity phase without the cost of shifting the phase of the entire circadian system. We suggest that these mechanisms play a significant role in determining activity patterns under natural conditions, and are important for understanding the ecology and evolution of activity rhythms.     

Synchronization of the mammalian circadian timing system: Light can control peripheral clocks independently of the SCN clock

A vast network of cellular circadian clocks regulates 24‐hour rhythms of behavior and physiology in mammals. Complex environments are characterized by multiple, and often conflicting time signals demanding flexible mechanisms of adaptation of endogenous rhythms to external time. Traditionally this process of circadian entrainment has been conceptualized in a hierarchical scheme with a light‐reset master pacemaker residing in the hypothalamus that subsequently aligns subordinate peripheral clocks with each other and with external time. Here we review new experiments using conditional mouse genetics suggesting that resetting of the circadian system occurs in a more “federated” and tissue‐specific fashion, which allows for increased noise resistance and plasticity of circadian timekeeping under natural conditions.     

Effect of different lighting conditions on circadian developmental rhythms and behaviour in Ephestia kuehniella Zell

Abstract

A study was made on the developmental rhythms of Ephestia kuehniella during different photoperiods: constant lighting (L/L), under conditions of 12 hours light per day (L/D) and in constant darkness (D/D). Observations were made every 2 hrs, for 3 successive 24‐hr periods, of the number of wandering larvae emerging from food, the number of pupations and of imaginai moults. Emergence of wandering larvae is rhythmic only under L/D conditions, and in addition this is also affected by the density of the larvae. Rhythm is least apparent with greatest density of the larvae. Pupation in E. kuehniella is a non‐rhythmic process with each of the photoperiods examined, whereas the imaginai moult is characterized by an endogenous (existing under D/D conditions) rhythm. Emergence of imagines is non‐rhythmic under L/L, and also when pupae under L/D fail to receive the final period of darkness. The rhythm of the imaginai moult is possibly controlled by the biological clock, which stops under conditions of constant light.     

Phytochrome A resets the circadian clock and delays tuber formation under long days in potato

Transgenic potatoes (Solanum tuberosum) with either increased (sense transformants) or reduced (antisense transformants) phytochrome A (phyA) levels were used, in combination with specific light treatments, to investigate the involvement of phyA in the perception of signals that entrain the circadian clock. Far-red or far-red plus red light treatments given during the night reset the circadian rhythm of leaf movements in wild-type plants and phyA over-expressors, but had little effect in phyA under-expressors. Far-red light was also able to reset the rhythm of leaf movement in wild-type Arabidopsis thaliana but was not effective in mutants without phyA. Blue light was necessary to reset the rhythm in phyA-deficient potato plants. Resetting of the rhythm by far-red plus red light was only slightly affected in transgenic plants with reduced levels of phytochrome B. The production of tubers was delayed by day extensions with far-red plus red light, but this effect was reduced in transgenic lines deficient in phyA. We conclude that phyA is involved in resetting the circadian clock controlling leaf movements and in photoperiod sensing in light-grown potato plants.