The circadian cycle of mPER clock gene products in the suprachiasmatic nucleus of the Siberian hamster encodes both daily and seasonal time (original) (raw)
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Seasonal molecular timekeeping within the rat circadian clock
Physiological research, 2004
In temperate zones duration of daylight, i.e. photoperiod, changes with the seasons. The changing photoperiod affects animal as well as human physiology. All mammals exhibit circadian rhythms and a circadian clock controlling the rhythms is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN consists of two parts differing morphologically and functionally, namely of the ventrolateral (VL) and the dorsomedial (DM). Many aspects of SCN-driven rhythmicity are affected by the photoperiod. The aim of the present overview is to summarize data about the effect of the photoperiod on the molecular timekeeping mechanism in the rat SCN, especially the effect on core clock genes, clock-controlled genes and clock-related genes expression. The summarized data indicate that the photoperiod affects i) clock-driven rhythm in photoinduction of c-fos gene and its protein product within the VL SCN, ii) clock-driven spontaneous rhythms in clock-controlled, i.e. arginine-vasopressin...
Sleep and Biological Rhythms, 2008
The circadian behavioral rhythms show seasonal changes not only in animals in the field but also in humans in urban environments. In nocturnal rodents the activity time is compressed or decompressed in response to day lengths. A two-oscillator model has been proposed to explain this photoperiodic response; an evening (E) oscillator is entrained to a dusk signal and drives activity onset, while a morning (M) oscillator is entrained to a dawn signal and controls the end of the active period. However, the location and the oscillation mechanism for these oscillators remain to be elucidated. Recent progress in understanding molecular circadian clock mechanisms and bioluminescent reporters for clock gene expressions enabled us to monitor the E and M clocks' tick separately. We measured clock gene Per1 expression levels continuously from individual cells as well as tissue explants of the hypothalamic suprachiasmatic nucleus (SCN) using transgenic mice carrying a luciferase reporter gene (Per1-luc mice) which were kept in different photoperiods. We found that there are two regionally specific oscillatory cell groups in the SCN that regulate activity onset and end separately in response to photoperiods, which we assume correspond to E and M oscillators. In addition, a third group of oscillatory cells was identified in the SCN only in a long photoperiod. These oscillatory cell networks change dynamically their clock gene expression pattern depending on environmental lights. Similar mechanisms may underlie seasonal changes in sleep time and melatonin rhythms of humans.
Current biology, 2003
exhibited significantly reduced paired testes weight ( ) and 24 hr plasma prolactin concentration ( ) compared to the LD group. However, following exposure to SD for 28 weeks (SD-R group), the paired testes weight and plasma prolactin concentration were significantly elevated back to LD-like values. There was no significant daily rhythm of prolactin over the 24 hr Oxford Road Manchester M13 9P sampling period for any of the groups ( ). Pineal melatonin concentration was elevated between zeit-United Kingdom geber time (ZT) 20 and 24 in LD and between ZT14 and ZT22 in both SD groups ( ). This finding is consistent with previous studies in this species [5, 6] Summary and indicates refractoriness of the reproductive and neuroendocrine axis to the SD photoperiod and prevail-In many seasonally breeding rodents, reproduction and metabolism are activated by long summer days ing SD melatonin profile.
Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis
Journal of Endocrinology, 2003
Melatonin-based photoperiod time-measurement and circannual rhythm generation are long-term time-keeping systems used to regulate seasonal cycles in physiology and behaviour in a wide range of mammals including man. We summarise recent evidence that temporal, melatonin-controlled expression of clock genes in specific calendar cells may provide a molecular mechanism for long-term timing. The agranular secretory cells of the pars tuberalis (PT) of the pituitary gland provide a model cell-type because they express a high density of melatonin (mt1) receptors and are implicated in photoperiod/circannual regulation of prolactin secretion and the associated seasonal biological responses. Studies of seasonal breeding hamsters and sheep indicate that circadian clock gene expression in the PT is modulated by photoperiod via the melatonin signal. In the Syrian and Siberian hamster PT, the high amplitude Per1 rhythm associated with dawn is suppressed under short photoperiods, an effect that is ...
European Journal of Neuroscience, 2007
In mammals, day length (photoperiod) is read and encoded in the main circadian clock, the suprachiasmatic nuclei (SCN). In turn, the SCN control the seasonal rhythmicity of various physiological processes, in particular the secretion pattern of the pineal hormone melatonin. This hormone then operates as an essential mediator for the control of seasonal physiological functions on some tissues, especially the pars tuberalis (PT). In the European hamster, both hormonal (melatonin) and behavioral (locomotor activity) rhythms are strongly affected by season, making this species an interesting model to investigate the impact of the seasonal variations of the environment. The direct (on SCN) and indirect (via melatonin on PT) effect of natural short and long photoperiod was investigated on the daily expression of clock genes, these being expressed in both tissues. In the SCN, photoperiod altered the expression of all clock genes studied. In short photoperiod, whereas Clock mRNA levels were reduced, Bmal1 expression became arrhythmic, probably resulting in the observed dramatic reduction in the rhythm of Avp expression. In the PT, Per1 and Rev-erba expressions were anchored to dawn in both photoperiods. The daily profiles of Cry1 mRNA were not concordant with the daily variations in plasma melatonin although we confirmed that Cry1 expression is regulated by an acute melatonin injection in the hamster PT. The putative role of such seasonal-dependent changes in clock gene expression on the control of seasonal functions is discussed.
The Circadian Timing System: Making Sense of day/night gene expression
Biological Research, 2004
The circadian time-keeping system ensures predictive adaptation of individuals to the reproducible 24-h day/ night alternations of our planet by generating the 24-h (circadian) rhythms found in hormone release and cardiovascular, biophysical and behavioral functions, and others. In mammals, the master clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus. The molecular events determining the functional oscillation of the SCN neurons with a period of 24-h involve recurrent expression of several clock proteins that interact in complex transcription/translation feedback loops. In mammals, a glutamatergic monosynaptic pathway originating from the retina regulates the clock gene expression pattern in the SCN neurons, synchronizing them to the light:dark cycle. The emerging concept is that neural/humoral output signals from the SCN impinge upon peripheral clocks located in other areas of the brain, heart, lung, gastrointestinal tract, liver, kidney, fibroblasts, and most of the cell phenotypes, resulting in overt circadian rhythms in integrated physiological functions. Here we review the impact of day/night alternation on integrated physiology; the molecular mechanisms and input/output signaling pathways involved in SCN circadian function; the current concept of peripheral clocks; and the potential role of melatonin as a circadian neuroendocrine transducer.
A positive role for PERIOD in mammalian circadian gene expression
Cell reports, 2014
In the current model of the mammalian circadian clock, PERIOD (PER) represses the activity of the circadian transcription factors BMAL1 and CLOCK, either independently or together with CRYPTOCHROME (CRY). Here, we provide evidence that PER has an entirely different function from that reported previously, namely, that PER inhibits CRY-mediated transcriptional repression through interference with CRY recruitment into the BMAL1-CLOCK complex. This indirect positive function of PER is consistent with previous data from genetic analyses using Per-deficient or mutant mice. Overall, our results support the hypothesis that PER plays different roles in different circadian phases: an early phase in which it suppresses CRY activity, and a later phase in which it acts as a transcriptional repressor with CRY. This buffering effect of PER on CRY might help to prolong the period of rhythmic gene expression. Additional studies are required to carefully examine the promoter- and phase-specific roles...
Circadian rhythms—mammalian aspects
Seminars in Cell & Developmental Biology, 1996
Across a large phylogenetic distance, circadian systems that regulate daily changes in physiology and behavior exhibit fundamental properties that are remarkably similar, suggesting either a conservation or constraint on the optimal organization of the biological clock. Whether or not this is a reflection of homologies in the genetic underpinnings of these clocks is unknown. Nonetheless, evidence for comparable organization from genetic, pharmacological and behavioral studies exists for diverse species. This allows insights into circadian organization to be drawn from a variety of models that provide access at different levels. Historically, mammalian models have been particularly useful for describing fundamental properties of clocks and their regulatory mechanisms. Recent discoveries of clock mutations in hamsters and mice will provide new opportunities for comprehensive studies involving multiple levels of organization