Clock Evolution and Adaptation: Whence and Whither?

Johnson, Carl Hirschie; Kyriacou, Charalambos P.

doi:10.1002/9780470988527.ch10

Cited by 10 publications

(11 citation statements)

References 77 publications

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“…Consequently, an organism whose responses are merely constant will be out-competed by organisms that anticipate the predictable changes in their external environment by rhythmically preparing and altering their internal environment. To optimally adapt to a rhythmic environment, organisms must rhythmically regulate their behavior, physiology, and gene expression [55]. These studies show that insulin action and glucose metabolism are interwined with an internal timekeeping system that evolved to accommodate the environmental rhythmicity.…”

Section: Discussionmentioning

confidence: 99%

Circadian Disruption Leads to Insulin Resistance and Obesity

et al. 2013

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Summary Background Disruption of circadian (daily) timekeeping enhances the risk of metabolic syndrome, obesity, and Type 2 diabetes. While clinical observations have suggested that insulin action is not constant throughout the 24 hour cycle, its magnitude and periodicity have not been assessed. Moreover, when circadian rhythmicity is absent or severely disrupted, it is not known whether insulin action will lock to the peak, nadir or mean of the normal periodicity of insulin action. Results We used hyperinsulinemic-euglycemic clamps to show a bona fide circadian rhythm of insulin action; mice are most resistant to insulin during their daily phase of relative inactivity. Moreover, clock-disrupted Bmal1-knockout mice are locked into the trough of insulin action and lack rhythmicity in insulin action and activity patterns. When rhythmicity is rescued in the Bmal1-knockout mice by expression of the paralogous gene Bmal2, insulin action and activity patterns are restored. When challenged with a high fat diet, arhythmic mice (either Bmal1-knockout mice or wild type mice made arhythmic by exposure to constant light) were obese prone. Adipose tissue explants obtained from high-fat fed mice have their own periodicity that was longer than animals on a chow fed diet. Conclusions This study provides rigorous documentation for a circadian rhythm of insulin action and demonstrates that disturbing the natural rhythmicity of insulin action will disrupt the rhythmic internal environment of insulin sensitive tissue, thereby predisposing the animals to insulin resistance and obesity.

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Section: Discussionmentioning

confidence: 99%

Circadian Disruption Leads to Insulin Resistance and Obesity

et al. 2013

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“…One coping mechanism is the circadian oscillator or clock, which produces self-sustained rhythms with an approximately 24-h period. It is often suggested that the clock provides an adaptive advantage by allowing organisms to anticipate regular changes in the environment and temporally separate incompatible metabolic events [1]. The importance of these rhythms has in fact been demonstrated in both phytoplankton and higher plants: organisms that have an internal clock period matched to the external environment possess a competitive advantage over those that do not [2,3].…”

Section: Introductionmentioning

confidence: 99%

The Circadian Clock Regulates Auxin Signaling and Responses in Arabidopsis

2007

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The circadian clock plays a pervasive role in the temporal regulation of plant physiology, environmental responsiveness, and development. In contrast, the phytohormone auxin plays a similarly far-reaching role in the spatial regulation of plant growth and development. Went and Thimann noted 70 years ago that plant sensitivity to auxin varied according to the time of day, an observation that they could not explain. Here we present work that explains this puzzle, demonstrating that the circadian clock regulates auxin signal transduction. Using genome-wide transcriptional profiling, we found many auxin-induced genes are under clock regulation. We verified that endogenous auxin signaling is clock regulated with a luciferase-based assay. Exogenous auxin has only modest effects on the plant clock, but the clock controls plant sensitivity to applied auxin. Notably, we found both transcriptional and growth responses to exogenous auxin are gated by the clock. Thus the circadian clock regulates some, and perhaps all, auxin responses. Consequently, many aspects of plant physiology not previously thought to be under circadian control may show time-of-day–specific sensitivity, with likely important consequences for plant growth and environmental responses.

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“…However, no homologs of clock genes have so far been characterized from nonangiosperm land plants, which comprise a wide spectrum of species (Bowman et al, 2007;Lang et al, 2008). Even circadian rhythms of biological processes have only very rarely been observed in these relatively primitive plants (Oberschmidt et al, 1995;Christensen and Silverthorne, 2001;Johnson and Kyriacou, 2005;Aoki, 2006). In order to understand the evolution, diversity and origin(s) of plant circadian systems, it is crucial to study circadian clocks in species other than angiosperms; in particular, it would be informative to study the clock machineries of basal land plants (Bowman et al, 2007;Lang et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Functional characterization of CCA1/LHY homolog genes, PpCCA1a and PpCCA1b, in the moss Physcomitrella patens

et al. 2009

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SUMMARYThe evolution of circadian clocks in land plants is not understood, because circadian rhythms have received little attention in plants other than angiosperms. We have characterized two genes, PpCCA1a and PpCCA1b, homologs of the Arabidopsis thaliana clock genes CCA1/LHY, from the moss Physcomitrella patens. PpCCA1a and PpCCA1b, together with angiosperm CCA1/LHY homologs, belong to the clock-associated single-myb gene family of green plants (including green algae and land plants). The accumulation of PpCCA1a and PpCCA1b mRNA showed rhythms with a period of approximately 1 day, phased as are those of angiosperm homologs, under 24 h light/dark cycles or in continuous dark. However, in marked contrast to angiosperm homologs, both genes showed arrhythmic profiles in continuous light. The timing of the PpCCA1b peak is determined by the time of the last light to dark transition, suggesting that the arrhythmicity in continuous light is due to dysfunction of the core clock. We generated single and double disruptants for PpCCA1a and PpCCA1b, and found that the double disruptants showed: (i) short periodicity and damped amplitude in the PpCCA1b rhythm, (ii) similar changes in the rhythmically expressed genes PpSIG5 and PpPRRa, and (iii) de-repression of PpCCA1b transcription levels, indicating negative feedback regulation. These observations indicate that the two genes are not merely structural homologs but also functional counterparts of CCA1/LHY. Together, our results illustrate similarities as well as divergence of the clock machineries between P. patens and A. thaliana, two distantly placed species in land plant phylogeny.

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Clock Evolution and Adaptation: Whence and Whither?

Cited by 10 publications

References 77 publications

Circadian Disruption Leads to Insulin Resistance and Obesity

Circadian Disruption Leads to Insulin Resistance and Obesity

The Circadian Clock Regulates Auxin Signaling and Responses in Arabidopsis

Functional characterization of CCA1/LHY homolog genes, PpCCA1a and PpCCA1b, in the moss Physcomitrella patens

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