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.     

Circadian expression of the presynaptic active zone protein bruchpilot in the lamina of Drosophila melanogaster

In the fly's visual system, the morphology of cells and the number of synapses change during the day. In the present study we show that in the first optic neuropil (lamina) of Drosophila melanogaster, a presynaptic active zone protein Bruchpilot (BRP) exhibits a circadian rhythm in abundance. In day/night (or light/dark, LD) conditions the level of BRP increases two times, in the morning and in the evening. The same pattern of changes in the BRP level was detected in whole brain homogenates, thus indicating that the majority of synapses in the brain peaks twice during the day. However, these two peaks in BRP abundance, measured as the fluorescence intensity of immunolabeling, seem to be regulated differently. The peak in the morning is predominantly regulated by light and involves the transduction pathway in the retina photoreceptors. This peak is present neither in wild‐type Canton‐S flies in constant darkness (DD), nor in norpA⁷ phototransduction mutant in LD. However, it also depends on the clock gene per, because it is abolished in the per⁰ arrhythmic mutant. In turn, the peak of BRP in the evening is endogenously regulated by an input from the pacemaker located in the brain. This peak is present in Canton‐S flies in DD, as well as in the norpA⁷ mutant in LD, but is absent in per⁰¹, tim,⁰¹ and cry⁰¹ mutants in LD. In addition both peaks seem to depend on clock gene‐expressing photoreceptors and glial cells of the visual system. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013     

生物钟在卵巢生理和病理中的作用

哺乳动物的昼夜节律是基因编码的分子钟在体内产生的一种以大约24 h为周期的生理现象,使机体的生理过程与外界环境的变化相协调,是对环境适应的一种表现.在哺乳动物中,繁殖生理功能受生物钟系统的调节.在下丘脑-垂体-卵巢(hypothalamic-pituitary-ovarian,HPO)轴的各组织中均已观察到生物钟基因的...     

Circadian rhythm of DNA synthesis and mitotic activity in tongue keratinocytes

Tongue keratinocytes have a high mitotic index (MI) with an evident circadian variation. Our study set out to compare and contrast two phases of the cell cycle: DNA synthesis (S-phase), with inmunocytochemical detection by bromodeoxyuridine (BrdU), and mitosis (M-phase), by the colchicine-arrest of metaphase method, exploring both the dorsal and ventral surfaces of the mouse tongue throughout a circadian period. Adult male mice standardized for light periodicity used for MI experiment were injected intraperitoneally with colchicine. Other animals were injected intraperitoneally with 5-BrdU for S-phase determination. Animals given both treatments were divided into six groups and killed at 4 h intervals until 20:00 h. Tongue samples were processed for histology and immuno-histochemistry. S and M indices were expressed as labelled nuclei or colchicine metaphases, respectively, per 1000 nuclei. Peak MI occurred at 12:00, with the minimum value at 20:00 on dorsal and ventral tongue surfaces. Peak S-phase was at 04:00, whereas the minimum value was at 16:00 for both surfaces. These results show that the proliferative activity of the tongue epithelium is of similar intensity and temporal distribution on both surfaces.     

Circadian rhythms and glial cells of the central nervous system

Glial cells are the most abundant cells in the central nervous system and play crucial roles in neural development, homeostasis, immunity, and conductivity. Over the past few decades, glial cell activity in mammals has been linked to circadian rhythms, the 24-h chronobiological clocks that regulate many physiological processes. Indeed, glial cells rhythmically express clock genes that cell-autonomously regulate glial function. In addition, recent findings in rodents have revealed that disruption of the glial molecular clock could impact the entire organism. In this review, we discuss the impact of circadian rhythms on the function of the three major glial cell types – astrocytes, microglia, and oligodendrocytes – across different locations within the central nervous system. We also review recent evidence uncovering the impact of glial cells on the body's circadian rhythm. Together, this sheds new light on the involvement of glial clock machinery in various diseases.     

Non-canonical Phototransduction Mediates Synchronization of the Drosophila melanogaster Circadian Clock and Retinal Light Responses

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Effect of sleep deprivation on rhythms of clock gene expression and melatonin in humans

This study investigated the impact of sleep deprivation on the human circadian system. Plasma melatonin and cortisol levels and leukocyte expression levels of 12 genes were examined over 48?h (sleep vs. no-sleep nights) in 12 young males (mean?±?SD: 23?±?5 yrs). During one night of total sleep deprivation, BMAL1 expression was suppressed, the heat shock gene HSPA1B expression was induced, and the amplitude of the melatonin rhythm increased, whereas other high-amplitude clock gene rhythms (e.g., PER1-3, REV-ERBα) remained unaffected. These data suggest that the core clock mechanism in peripheral oscillators is compromised during acute sleep deprivation.     

Reconfiguration of a Multi-oscillator Network by Light in the Drosophila Circadian Clock

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Pineal circadian clocks gate arylalkylamine N-acetyltransferase gene expression in the mouse pineal gland

In mammals it has been thought that the circadian clock localizes only in the suprachiasmatic nucleus of the hypothalamus. Recent studies have revealed that certain brain regions and peripheral tissues may also have intrinsic circadian clocks. However, the roles played by 'peripheral circadian clocks' have not been fully elucidated. In this study, we investigated their function using mouse pineal glands, and found that expression of the arylalkylamine N-acetyltransferase (Aa-Nat, EC 2.3.1.87, the rate-limiting enzyme of melatonin synthesis) gene after adrenergic receptor stimulation depended on the time of day even in vitro (gating). Phase-dependent Aa-Nat responses were observed in both melatonin-proficient and melatonin-deficient mouse pineal glands. Phosphodiesterases are unlikely to suppress Aa-Nat induction because a phosphodiesterase inhibitor itself had no effect on the mRNA levels. Puromycin was ineffective in inducing Aa-Nat mRNA levels in either the presence or absence of isoproterenol, suggesting that newly synthesized proteins may not be necessary to gate the Aa-Nat responses. We also discovered circadian dependence of the expression of Period1-luminescence in Period1-luciferase transgenic mouse pineal glands: circadian clocks may be functional in culture. Aa-Nat mRNA levels showed no significant circadian rhythms in the absence of isoproterenol, thus suggesting that Aa-Nat mRNA levels are induced by adrenergic mechanisms, not by a pineal circadian clock. Our results suggest that the pineal circadian clock may determine timing when Aa-Nat gene expression can respond to inputs from the master circadian clock in the suprachiasmatic nucleus, e.g. adrenergic stimulation.     

Circadian range of entrainment in the semilunar eclosion rhythm of the marine insect clunio marinus

The semilunar eclosion of the intertidal chironomid Clunio is controlled by a semilunar timing of pupation in combination with a daily timing of emergence. This results in reproductive activities of a laboratory population every 15 days at a distinct time of day (in nature mostly in correlation with the afternoon low water time on days with spring tides). The entrainment of the timing processes has been tested under various periods of the daily light-dark cycle in order to check the circadian organization of the timing mechanisms as suggested for the perception of the semilunar zeitgeber situation (a distinct phase relationship between the 24 h light-dark cycle and the 12.4 h tidal cycle recurring after every 15th light-dark cycle, named semimonthly zeitgeber cycle) as well as for the daily zeitgeber (the 24 h light-dark cycle). With respect to the semilunar timing, a strong entrainment was only possible in semimonthly zeitgeber cycles with light-dark cycle periods close to the 24-h day (light-dark cycles of 10:10 to 14:14). This limited circadian range of entrainment of an endogenous circasemilunar long-term rhythm (syn. oscillator) conforms with the hypothesis for a circadian clock component as an intrinsic part of the semilunar zeitgeber perception.The range of entrainment for the daily timing was obviously wider which may be discussed either in relation to a multioscillatory circadian organization of the midges or in relation to different coupling characteristics of one circadian oscillator during semilunar and daily timing.     

Circadian rhythm of the locomotor activity in Drosophila melanogaster and its mutants 'sine oculis' and 'small optic lobes'

ABSTRACT. The locomotor activity patterns of wildtype Drosophila melanogaster and the mutants so (sine oculis) and sol (small optic lobes) were investigated. In all strains the proportions showing circadian rhythmicity, arrhythmicity and more complex patterns which could not be thus classified were similar. The occurrence of abnormal activity patterns is thus not a property of the mutation as previously claimed (Mack & Engelmann, 1981). In flies with a distinct circadian rhythmicity, the period lengths (τ) varied between strains, τ for wildtype Italy and the mutant so was longer than for wildtype Berlin and the mutant sol. As different τ's have been reported by others, τ does not seem to be closely determined for Drosophila melanogaster. Many flies exhibited two rhythms simultaneously, one with τ shorter and one with τ longer than 24 h, apparently implying two-oscillator control of the locomotor activity. The eyeless so mutants were entrained by LD cycles, so the compound eyes are not necessary, and so must possess the relevant photoreceptor(s) elsewhere. This may therefore also be true for the wildtype. Histology of the so adults revealed no correlation between the degree of reduction in the medulla and the occurrence of abnormal activity patterns. Since the only structures common to the medulla of so and sol are known to be large tangential cells, it is concluded that either they are of importance for the rhythmic system, or the oscillator(s) controlling locomotor activity is (are) not located in the medulla.     

Circadian rhythm of autophagy proteins in hippocampus is blunted by sleep fragmentation

Autophagy is essential for normal cellular survival and activity. Circadian rhythms of autophagy have been studied in several peripheral organs but not yet reported in the brain. Here, we measured the circadian rhythm of autophagy-related proteins in mouse hippocampus and tested the effect of sleep fragmentation (SF). Expressions of the autophagy-related proteins microtubule‐associated protein 1 light chain 3 (LC3) and beclin were determined by western blotting and immunohistochemistry. Both the hippocampal LC3 signal and the ratio of its lipid-conjugated form LC3-II to its cytosolic form LC3-I showed a 24 h rhythm. The peak was seen at ZT6 (1 pm) and the nadir at ZT16 (1 am). The LC3 immunoreactivity in hippocampal CA1 pyramidal neurons also distributed differently, with more diffuse cytoplasmic appearance at ZT16. Chronic SF had a mild effect to disrupt the 24 h rhythm of LC3 and beclin expression. Interestingly, a greater effect of SF was seen after 24 h of recovery sleep when LC3-II expression was attenuated at both the peak and trough of circadian activities. Overall, the results show for the first time that the hippocampus has a distinct rhythm of autophagy that can be altered by SF.     

Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

The rabbit is particularly suitable for investigating the development of mammalian circadian function. Blind at birth, the pups are only visited by the mother to be nursed once every 24 h for about 3 min and so can be studied largely without maternal interference. They anticipate the mother's visit with increased behavioral arousal and with a rise in body temperature, both of which represent endogenous circadian rhythms. We now report that in newborn pups the suprachiasmatic nuclei of the hypothalamus (SCN; the main circadian pacemaker in mammals) show endogenous 24‐h rhythmicity in the expression of the clock genes Per1, Per2, and Bmal1. Pups nursed from postnatal days 1 to 7 and fasted to day 9 showed the same rhythms of clock gene expression as normally nursed controls. We also report that these rhythms are entrained by nursing. Pups killed on postnatal days 3–4 showed the same rhythms in gene expression as pups in the previous experiment, whereas littermates subsequently nursed from postnatal days 4 to 7 with nursing delayed 6 h showed a corresponding shift in the diurnal pattern of clock gene expression. Consistent with this, two groups of pups implanted with telemetric thermal sensors and nursed 6 h apart had daily patterns in body temperature synchronized with the two different nursing times. We conclude that the expression of clock genes associated with the newborn rabbit's circadian system is entrained by nonphotic cues accompanying nursing, the exact nature of which now needs to be clarified. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2009     

DSC1 channels are expressed in both the central and the peripheral nervous system of adult Drosophila melanogaster

DSC1 encodes a putative voltage-sensitive sodium channel α subunit in Drosophila melanogaster. We generated polyclonal antibodies raised against part of the DSC1 sequence to characterize the size and the distribution of these channels in the adult fly. Immunoblotting experiments indicated that the protein has a molecular weight of about 270 kDa. We also showed that DSC1 channels are found only in the neurons of the fly. The density of channels was high in synaptic regions and in most of the axonal processes that connect the various structures of the CNS. No signal was observed in the cortical cell bodies where the para channels are mainly present. The most striking result concerns the widespread distribution of DSC1 channels in the PNS, as confirmed by experiments done with the monoclonal antibody 22C10. These results strongly suggest that DSC1 and para channels may have complementary roles, at least in the adult stage. Electronic Publication     

Circadian oscillations of neuropeptide expression in the human biological clock

The mammalian suprachiasmatic nucleus is the principal component of a neural timing system implicated in the temporal organization of circadian and seasonal processes. The present study was performed to analyze the circadian profiles of two major neuropeptidergic cell groups in the human suprachiasmatic nucleus. To that end the brains of 40 human subjects collected at autopsy were investigated. The populations of arginine vasopressin- and vasoactive intestinal polypeptide-expressing neurons, located in the shell and core of the suprachiasmatic nucleus, respectively, showed marked circadian rhythms with an asymmetrical, bimodal waveform. Time series analysis revealed that these circadian cycles in neuronal activity could be described by a composite model consisting of a nonlinear periodic function, with mono- and diphasic cycles. The findings suggest that the 24-h biosynthesis of neuropeptides in the human suprachiasmatic nucleus, being part of the neural output pathway of the clock, is driven by a complex pacemaker system consisting of coupled nonlinear oscillators, in accordance with a multioscillator model of circadian timekeeping.Abbreviations AIC Akaikie's information criterion - ARMA autoregressive moving average - AVP arginine vasopressin - c-fos immediate early gene - Per period gene - SCN suprachiasmatic nucleus - VIP vasoactive intestinal polypeptide