Circadian Systems and Metabolism

Roenneberg, Till; Merrow, Martha

doi:10.1177/074873099129001019

Cited by 90 publications

(57 citation statements)

References 58 publications

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“…Absent these data, a role for this FLO as a ''circadian rhythm generator,'' as previously suggested (13,16), seems unlikely. An extension of this conclusion is that the FRQ͞WCC TTFL is not simply required for light input to a postulated temperature-entrainable oscillator (13) but has a central role in the circadian oscillator.…”

Section: Discussionmentioning

confidence: 63%

“…Normal circadian entrainment in frq-null strains, i.e., strains lacking the TTFL, would have profound implications. In contemplating these implications, including self-sufficiency for the FLO and that the TTFL might not be necessary for circadian rhythmicity, the authors proposed a novel, ingenious, and speculative model in which the FLO was the underlying circadian oscillator and the TTFL part of the entraining mechanism to light (13,16). Because this model would require major revisions in circadian theory and in the interpretation of a great many previous results, we reexamined the premise and results on which it was based.…”

mentioning

confidence: 99%

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Assignment of an essential role for the Neurospora frequency gene in circadian entrainment to temperature cycles

Pregueiro

Price-Lloyd

Bell-Pedersen

et al. 2005

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

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Circadian systems include slave oscillators and central pacemakers, and the cores of eukaryotic circadian clocks described to date are composed of transcription and translation feedback loops (TTFLs). In the model system Neurospora, normal circadian rhythmicity requires a TTFL in which a White Collar complex (WCC) activates expression of the frequency (frq) gene, and the FRQ protein feeds back to attenuate that activation. To further test the centrality of this TTFL to the circadian mechanism in Neurospora, we used low-amplitude temperature cycles to compare WT and frq-null strains under conditions in which a banding rhythm was elicited. WT cultures were entrained to these temperature cycles. Unlike those normal strains, however, frq-null mutants did not truly entrain to the same cycles. Their peaks and troughs always occurred in the cold and warm periods, respectively, strongly suggesting that the rhythm in Neurospora lacking frq function simply is driven by the temperature cycles. Previous reports suggested that a FRQ-less oscillator (FLO) could be entrained to temperature cycles, rather than being driven, and speculated that the FLO was the underlying circadian-rhythm generator. These inferences appear to derive from the use of a phase reference point affected by both the changing waveform and the phase of the oscillation. Examination of several other phase markers as well as results of additional experimental tests indicate that the FLO is, at best, a slave oscillator to the TTFL, which underlies circadian rhythm generation in Neurospora.FRQ-less oscillator ͉ frq ͉ FRQ C ircadian programs in eukaryotes are widely perceived to be the output of multiple oscillatory systems based on cell intrinsic transcription and translation feedback loops (TTFLs) (1-3). In many animals and fungi, heterodimeric PAS domaincontaining transcription factors drive expression of genes encoding proteins that block the activity of their heterodimeric activators; such negative feedback loops generally are believed to make up the cores of these circadian clocks. In addition to these autonomous biological clocks, slave oscillators also exist within the panoply of circadian systems. Early studies on entrainment in Drosophila gave rise to models in which a pacemaker drove a slave oscillator that directly regulated an overt rhythmic event (4), and noncircadian slaves have since been experimentally described (e.g., ref. 5). However, because there are few molecular descriptions of slave oscillators, their existence and properties have so far chiefly been inferred from the behavior of the circadian system when exposed to Zeitgeber period lengths outside its innate frequency.At the core of the TTFL in the circadian model system Neurospora crassa are the products of the frequency ( frq), white collar-1 (wc-1), and wc-2 genes. Similar to animal systems, Neurospora possesses a feedback loop in which a heterodimeric activator, the White Collar complex (WCC) of the PAS proteins WC-1 and WC-2, activates expression of frq and thus FRQ, which in turn ...

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Section: Discussionmentioning

confidence: 63%

mentioning

confidence: 99%

Assignment of an essential role for the Neurospora frequency gene in circadian entrainment to temperature cycles

Pregueiro

Price-Lloyd

Bell-Pedersen

et al. 2005

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

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“…Hence, L-type VGCCs could contribute in coordinating rhythmic clock gene expression through the input pathway, even though the channels themselves are regulated by the circadian clocks and serve as outputs. Such an arrangement would formally similar to the model presented by Roenneberg and Merrow (1999), in which the input pathways that lead to entrainment of the 'core oscillator' can themselves be regulated by the oscillators as part of the output pathways. One important feature of this model is that it contains additional feedback loops at the cellular level, which can markedly enhance the stability of the overall oscillator system.…”

Section: Discussionmentioning

confidence: 95%

The expression of L‐type voltage‐gated calcium channels in retinal photoreceptors is under circadian control

Ko¹,

Liu²,

Dryer³

et al. 2007

Journal of Neurochemistry

202

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Photoreceptors are non-spiking neurons, and their synapses mediate the continuous release of neurotransmitters under the control of L-type voltage-gated calcium channels (VGCCs). Photoreceptors express endogenous circadian oscillators that play important roles in regulating photoreceptor physiology and function. Here, we report that the L-type VGCCs in chick cone photoreceptors are under circadian control. The L-type VGCC currents are greater when measured during the subjective night than during the subjective day. Using antibodies against the VGCCa1C and VGCCa1D subunits, we found that the immunofluorescence intensities of both VGCCa1C and VGCCa1D in photoreceptors are higher during the subjective night. However, the mRNA levels of VGCCa1D, but not VGCCa1C, are rhythmic. Nocturnal increases in L-type VGCCs are blocked by manumycin A, PD98059, and KN93, which suggest that the circadian output pathway includes Ras, Erk, and calcium-calmodulin dependent kinase II. In summary, four independent lines of evidence show that the L-VGCCs in cone photoreceptors are under circadian control. Keywords: avian, circadian, photoreceptor, retina, voltagegated calcium channel. Visual systems must anticipate daily changes in ambient illumination over 10-12 orders of magnitude. Circadian oscillators in the retina provide a mechanism for visual systems to initiate more sustained adaptive changes throughout the course of the day (Cahill and Besharse 1995;Green and Besharse 2004). The circadian oscillators in photoreceptors are endogenous and able to function independently in the absence of other retinal inputs (Cahill and Besharse 1993;Thomas et al. 1993;Ko et al. 2001). Photoreceptor circadian oscillators regulate retinomotor movement (Pierce and Besharse 1985;Burnside 2001), outer segment disc shedding and membrane renewal (LaVail 1980;Besharse and Dunis 1983), morphological changes at synaptic ribbons (Adly et al. 1999), gene expression (Korenbrot and Fernald 1989;Pierce et al. 1993;Haque et al. 2002), and the gating behavior of ion channels (Ko et al. 2001) among other photoreceptor activities. Importantly, photoreceptors are more sensitive to intense light damage at night than during the day, even in animals that have been maintained in constant darkness (DD) for several days after circadian lightdark (LD) cycle entrainment (Vaughan et al. 2002).Photoreceptors are non-spiking neurons, and they release glutamate continuously in the darkness as a result of depolarization-evoked activation of L-type voltage-gated calcium channels (VGCCs) (Barnes and Kelly 2002). The synthesis and release of the neurohormone melatonin in photoreceptors is also under circadian control (Cahill and Besharse 1993;Bernard et al. 1997;Ivanova and Iuvone 2003b), and melatonin synthesis and release can be blocked by dihydropyridine inhibitors of L-type VGCCs (Iuvone and Besharse 1986;Ivanova and Iuvone 2003a). In this regard, we previously showed that there is a circadian regulation of the apparent affinity of cGMP-gated ion channels (CNGCs) for cG...

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“…A connection between circadian gene regulation and metabolism/energy homeostasis has been established for numerous organisms across many phyla, including cyanobacteria, marine algae, fungi, higher plants, and fruit flies (Portaluppi et al 1996;Rabinowitz 1996;Hastings 1997;Roenneberg and Merrow 1999;Schibler and Lavery 1999). In fact, during the evolution of lower organisms, the adaptation of the metabolism to solar cycles may have been the major selective force in establishing circadian physiology.…”

Section: The Purpose Of Circadian Gene Expression In Peripheral Cell mentioning

confidence: 99%

Restricted feeding uncouples circadian oscillators in peripheral tissues from the central pacemaker in the suprachiasmatic nucleus

Damiola¹,

Minh²,

Preitner³

et al. 2000

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Circadian Systems and Metabolism

Cited by 90 publications

References 58 publications

Assignment of an essential role for the Neurospora frequency gene in circadian entrainment to temperature cycles

Assignment of an essential role for the Neurospora frequency gene in circadian entrainment to temperature cycles

The expression of L‐type voltage‐gated calcium channels in retinal photoreceptors is under circadian control

Restricted feeding uncouples circadian oscillators in peripheral tissues from the central pacemaker in the suprachiasmatic nucleus

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