Using Per gene expression to search for photoperiodic oscillators in the hamster suprachiasmatic nucleus

Iglesia, Horacio O. de la; Meyer, Jennifer L.; Schwartz, William J.

doi:10.1016/j.molbrainres.2004.05.018

Cited by 23 publications

(22 citation statements)

References 42 publications

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“…Importantly, our results revealed fundamental differences in the effects of light on Per expression when entrainment was accomplished by advances or delays. The dawn (advancing) light pulse of the short T cycle acted to acutely elevate Per1 mRNA from its low baseline level characteristic of the preceding subjective night; this was especially evident in the ventrolateral subregion of the SCN, as would be predicted in hamsters (20)(21)(22). In contrast, and surprisingly, the dusk (delaying) light pulse of the long T cycle had no acute effect on either Per1 or Per2 mRNA, but entrainment of the clock to the long T cycle somehow altered Per2 steady-state regulation, resulting in a Per2 mRNA rhythm with subjective day levels of increased amplitude and extended duration.…”

Section: Discussionmentioning

confidence: 79%

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Distinct patterns of Period gene expression in the suprachiasmatic nucleus underlie circadian clock photoentrainment by advances or delays

Schwartz¹,

Tavakoli-Nezhad²,

Lambert

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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The circadian clock in the mammalian hypothalamic suprachiasmatic nucleus (SCN) is entrained by the ambient light/dark cycle, which differentially acts to cause the clock to advance or delay. Light-induced changes in the rhythmic expression of SCN clock genes are believed to be a critical step in this process, but how the two entrainment modalities-advances vs. delays-engage the molecular clockwork remains incompletely understood. We investigated molecular substrates of photic entrainment of the clock in the SCN by stably entraining hamsters to T cycles (non-24-h light/ dark cycles) consisting of a single 1-h light pulse repeated as either a short (23.33-h) or a long (24.67-h) cycle; under these conditions, the light pulse of the short cycle acts as "dawn," whereas that of the long cycle acts as "dusk." Analyses of the expression of the photoinducible and rhythmic clock genes Period 1 and 2 (Per1 and Per2) in the SCN revealed fundamental differences under these two entrainment modes. Light at dawn advanced the clock, advancing the onset of the Per1 mRNA rhythm and acutely increasing mRNA transcription, whereas light at dusk delayed the clock, delaying the offset of the Per2 mRNA rhythm and tonically increasing mRNA stability. The results suggest that the underlying molecular mechanisms of circadian entrainment differ with morning (advancing) or evening (delaying) light exposure, and such differences may reflect how entrainment takes place in nocturnal animals under natural conditions. circadian synchronization | circadian clock resetting | light entrainment A fundamental feature of the circadian clock that regulates daily behavioral and physiological rhythmicity is its entrainment to the environmental cycle of light and darkness. By matching the clock's endogenous ("free-running") period to that of the ambient day/night cycle, entrainment ensures that the phase relationship between clock and external day remains stable over time, thereby synchronizing body rhythms to local time. Light is the clock's preeminent entraining cue (Zeitgeber), and the clock responds to light by changing its angular velocity and shifting its phase. To match its oscillation to that of the Zeitgeber, the clock can increase its velocity and advance its phase if the clock's freerunning period is too long, or it can decrease its velocity and delay its phase if its free-running period is too short (1, 2).In mammals, the master circadian clock is located in the suprachiasmatic nucleus (SCN) in the anterior hypothalamus (3). The SCN is composed of multiple, coupled single-cell circadian oscillators (4), and analyses of induced and spontaneous mutations, gene sequence homologies, and protein-protein interactions have identified candidate regulatory molecules and biochemical processes that are likely to constitute the basic intracellular oscillatory mechanism (5). Genes at the core of the clock function within autoregulatory feedback loops, with proteins rhythmically suppressing the transcription of their own mRNAs. When the basic helix-loop-hel...

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Section: Discussionmentioning

confidence: 79%

“…In situ hybridization with the radiolabeled cRNA probes was performed as previously described (22,39,40). Serial coronal sections were hybridized with the same probe at intervals of 75 μm (Figs.…”

Section: Methodsmentioning

confidence: 99%

Distinct patterns of Period gene expression in the suprachiasmatic nucleus underlie circadian clock photoentrainment by advances or delays

Schwartz¹,

Tavakoli-Nezhad²,

Lambert

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…Jagota et al showed two distinct peaks of electrophysiological activity in the horizontally sectioned SCN culture in hamsters (10) but not in rats and mice (11), which responded differentially to photoperiods. In addition, the circadian rhythms in Per1 and Per2 expression were reported to change in different photoperiods (12)(13)(14)(15)(16)(17)(18)(19)23). The duration of gene expression was extended in long photoperiods, whereas the rhythm amplitudes were increased in short photoperiods, suggesting that the mutual coupling of individual cell oscillations was altered by photoperiods.…”

Section: Discussionmentioning

confidence: 99%

Separate oscillating cell groups in mouse suprachiasmatic nucleus couple photoperiodically to the onset and end of daily activity

Inagaki

Honma

Ono

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

251

248

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The pattern of circadian behavioral rhythms is photoperioddependent, highlighted by the conservation of a phase relation between the behavioral rhythm and photoperiod. A model of two separate, but mutually coupled, circadian oscillators has been proposed to explain photoperiodic responses of behavioral rhythm in nocturnal rodents: an evening oscillator, which drives the activity onset and entrains to dusk, and a morning oscillator, which drives the end of activity and entrains to dawn. Continuous measurement of circadian rhythms in clock gene Per1 expression by a bioluminescence reporter enabled us to identify the separate oscillating cell groups in the mouse suprachiasmatic nucleus (SCN), which composed circadian oscillations of different phases and responded to photoperiods differentially. The circadian oscillation in the posterior SCN was phase-locked to the end of activity under three photoperiods examined. On the other hand, the oscillation in the anterior SCN was phase-locked to the onset of activity but showed a bimodal pattern under a long photoperiod [light-dark cycle (LD)18:6]. The bimodality in the anterior SCN reflected two circadian oscillatory cell groups of early and late phases. The anterior oscillation was unimodal under intermediate (LD12:12) and short (LD6:18) photoperiods, which was always phase-lagged behind the posterior oscillation when the late phase in LD18:6 was taken. The phase difference was largest in LD18:6 and smallest in LD6:18. These findings indicate that three oscillating cell groups in the SCN constitute regionally specific circadian oscillations, and at least two of them are involved in photoperiodic response of behavioral rhythm.bioluminescence reporter ͉ circadian rhythm ͉ clock gene ͉ photoperiod ͉ behavioral rhythm A daptation to seasonal changes in environment is critical to the survival of many organisms. Photoperiodic time measurement by the circadian clock is one of the strategies by which they conserve the phase relation between behavioral events such as the activity onset and dawn or dusk (1). A dramatic change induced by photoperiod is in the length of an activity band, the duration of activity in behavioral rhythms. Nocturnal rodents such as rats and mice exhibit compressed activity bands in long photoperiods and decompressed bands in short photoperiods. A long-standing hypothesis for the photoperiodic time measurement assumes two separate, but mutually coupled, circadian oscillators that drive the activity onset and end of activity, respectively, and respond to dawn and dusk differentially. Therefore, their phase-relationship encodes day lengths and changes the length of an activity band (1).The circadian clock in mammals is located in the suprachiasmatic nucleus (SCN) of the hypothalamus; it entrains to a light-dark cycle (LD) and determines the phases of overt circadian rhythms in behavior and physiology (2). Over the last decade, our understanding of the circadian clock in the SCN has advanced tremendously (3-5). The SCN consists of a number of oscillating cel...

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“…The "morning cells" seem to send a daily signal to reset the "evening cells", with no apparent interaction at intermediate times [46]. Anatomical [44], physiological [49,50], and behavioral data [51] strongly suggest that similar structures exist in mammals. Functionally, a clock system composed of a morning and an evening oscillator would be well suited to perform tasks such as tracking dawn and dusk.…”

Section: Process Cmentioning

confidence: 95%

Circadian control of the sleep–wake cycle

Beersma

Gordijn

2007

Physiology & Behavior

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It is beyond doubt that the timing of sleep is under control of the circadian pacemaker. Humans are a diurnal species; they sleep mostly at night, and they do so at approximately 24-h intervals. If they do not adhere to this general pattern, for instance when working night shifts or when travelling across time zones, they experience the stubborn influence of their circadian clock.In recent years much has been discovered about the organisation of the circadian clock. New photoreceptor cells in the retina have been found to influence the input to the clock, and much of the molecular machinery of the clock has been unravelled. It is now known that the circadian rhythm of sleep and wakefulness is only loosely coupled to the circadian rhythm of the pacemaker. New theories have been proposed for the functions of sleep and the sites at which those functions are executed. In spite of this rapid increase in knowledge of the circadian clock and of sleep regulatory processes, much remains to be discovered concerning the precise interaction between the biological clock and sleep timing. This is particularly unfortunate in view of the 24-h demands of our society for 7 days a week. Too little is known about the negative consequences of the societal pressures on well-being and performance.

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Using Per gene expression to search for photoperiodic oscillators in the hamster suprachiasmatic nucleus

Cited by 23 publications

References 42 publications

Distinct patterns of Period gene expression in the suprachiasmatic nucleus underlie circadian clock photoentrainment by advances or delays

Distinct patterns of Period gene expression in the suprachiasmatic nucleus underlie circadian clock photoentrainment by advances or delays

Separate oscillating cell groups in mouse suprachiasmatic nucleus couple photoperiodically to the onset and end of daily activity

Circadian control of the sleep–wake cycle

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