Circadian rhythms: Redox redux (original) (raw)
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Circadian rhythms from multiple oscillators: lessons from diverse organisms
Nature Reviews Genetics, 2005
| The organization of biological activities into daily cycles is universal in organisms as diverse as cyanobacteria, fungi, algae, plants, flies, birds and man. Comparisons of circadian clocks in unicellular and multicellular organisms using molecular genetics and genomics have provided new insights into the mechanisms and complexity of clock systems. Whereas unicellular organisms require stand-alone clocks that can generate 24-hour rhythms for diverse processes, organisms with differentiated tissues can partition clock function to generate and coordinate different rhythms. In both cases, the temporal coordination of a multi-oscillator system is essential for producing robust circadian rhythms of gene expression and biological activity.
Circadian Systems and Metabolism
Journal of Biological Rhythms, 1999
Circadian systems direct many metabolic parameters and, at the same time, they appear to be exquisitely shielded from metabolic variations. Although the recent decade of circadian research has brought insights into how circadian periodicity may be generated at the molecular level, little is known about the relationship between this molecular feedback loop and metabolism both at the cellular and at the organismic level. In this theoretical paper, we conjecture about the interdependence between circadian rhythmicity and metabolism. A mathematical model based on the chemical reactions of photosynthesis demonstrates that metabolism as such may generate rhythmicity in the circadian range. Two additional models look at the possible function of feedback loops outside of the circadian oscillator. These feedback loops contribute to the robustness and sustainability of circadian oscillations and to compensation for long-and short-term metabolic variations. The specific circadian property of temperature compensation is put into the context of metabolism. As such, it represents a general compensatory mechanism that shields the clock from metabolic variations.
Molecular biological approach to the circadian clock mechanism
Neuroscience Research the Official Journal of the Japan Neuroscience Society, 1995
Many circadian phenomena have been described in a diverse range of species, from single cellular organisms to higher species of plants and animals. From several lines of evidence from Drosophila and Neurospora, the oscillation of the circadian clock seems to involve cycling gene expression. Although a great deal of information concerning the anatomy, neurophysiology and neurochemistry of circadian pacemakers has been obtained over the last decade, molecular and cellular approaches to this problem have only just begun. I will summarize recent progress of the molecular biological approach to the circadian clock mechanism. Finally, the importance of' transcription factors to envision the common mechanism of circadian clock in the diverged species will be discussed considering with the existence of a hypothetical 'Time Box'.
Biological Rhythm Research, 2006
Evolution from prokaryotic to eukaryotic organisms was paralleled by a corresponding evolution in energy metabolism. From primeval fermentation, energy conservation progressed to anaerobic photosynthesis and then to carbon dioxide fixation with acceptance of electrons by water and the evolution of oxygen. In a progressively oxygenic biosphere, respiration developed with oxygen as a terminal electron acceptor. Evolving life was paralleled by a corresponding evolution of tropospheric O 2 /CO 2 composition and the feedback of oxygen on life processes via reactive oxygen and reactive nitrogen species, which as signalling molecules became crucial for the control of development of proand eukaryotic living systems. Adaptation to the seasonal variation in daylength resulted in photoperiodic control of development with a circadian rhythm in energy conservation and transformation to optimise energy harvesting by photosynthesis. Photosynthesis on the other hand acts as a lightdependent metabolic regulator via redox signals in addition to specific photoreceptors like phytochromes and cryptochromes. Finally, redox control integrates rhythmic gene expression in chloroplasts, mitochondria and the nucleus. The circadian rhythmic cell (cyanobacterial and eukaryotic) is a hydroelectro-chemical oscillator synchronised by the daily light -dark cycle with temporal compartmentation of metabolism and a network of metabolic sequences to compensate for oxidative stress in adapting to the light environment e.g. by separating N-fixation from oxygen production. In Chenopodium rubrum L. a circadian rhythm in overall energy transduction has been observed. This rhythm results from an oscillatory network between glycolysis and oxidative phosphorylation coupled to photophosphorylation. This network produces a circadian rhythm in adenylate energy charge and redox state (NADP/ NADPH 2 ). The nucleotide ratios themselves could, as rate effectors in compartmental feedback, fulfil the requirements for precise temperature-compensated time keeping. The integration of metabolic activity of Chenopodium plants on a hydraulic-electrochemical level is represented by a diurnal rhythm in compound surface membrane resting potential. Using molecular genetic techniques, research of the last 30 years has come to the conclusion that the core oscillator of circadian systems should reside in transcriptional and translational control loops (TTCL) involved in feedback regulation of clock genes. Considering the evolution of metabolic networks in response to environmental constraints, we proposed ) that circadian rhythms in redox state and phosphorylation potential, as an output from the network of energy transduction (Singh 1998), should be gating the TTCL for the circadian rhythmic production of proteins needed in the metabolic networks. A similar concept has been advanced for metabolic control of human circadian rhythms,
Circadian clocks - from genes to complex behaviour
Reproduction Nutrition Development, 1999
Circadian clocks control temporal structure in practically all organisms and on all levels of biology, from gene expression to complex behaviour and cognition. Over the last decades, research has begun to unravel the physiological and, more recently, molecular mechanisms that underlie this endogenous temporal programme. The generation of circadian rhythms can be explained, at the molecular level, by a model based upon a set of genes and their products which form an autoregulating negative feedback loop. The elements contributing to this transcriptional feedback appear to be conserved from insects to mammals. Here, we summarize the process of the genetic and molecular research that led to 'closing the molecular loop'. Now that the reductionist approach has led to the description of a detailed clock model at the molecular level, further insights into the circadian system can be provided by combining the extensive knowledge gained from decades of physiological research with molecular tools, thereby reconstructing the clock within the organism and its environment. We describe experiments combining old and new tools and show that they constitute a powerful approach to understanding the mechanisms that lead to temporal structure in complex behaviour. © Inra/Elsevier, Paris
The circadian cycle: is the whole greater than the sum of its parts?
Trends in Genetics, 2001
The term 'circadian rhythm' describes an oscillatory behavior in the absence of exogenous environmental cues, with a period of about a day. As yet, we don't fully understand which biological mechanisms join together to supply a stable and selfsustained oscillation with such a long period. By chipping away at the molecular mechanism with genetic approaches, some common features are emerging. In combining molecular analyses and physiological experiments, those features that are crucial for structuring a circadian day could be uncovered.
Light and circadian regulation of clock components aids flexible responses to environmental signals
New Phytol, 2014
The circadian clock measures time across a 24 h period, increasing fitness by phasing biological processes to the most appropriate time of day. The interlocking feedback loop mechanism of the clock is conserved across species; however, the number of loops varies. Mathematical and computational analyses have suggested that loop complexity affects the overall flexibility of the oscillator, including its responses to entrainment signals.
Interface focus, 2014
Biological rhythms, generated by feedback loops containing interacting genes, proteins and/or cells, time physiological processes in many organisms. While many of the components of the systems that generate biological rhythms have been identified, much less is known about the details of their interactions. Using examples from the circadian (daily) clock in three organisms, Neurospora, Drosophila and mouse, we show, with mathematical models of varying complexity, how interactions among (i) promoter sites, (ii) proteins forming complexes, and (iii) cells can have a drastic effect on timekeeping. Inspired by the identification of many transcription factors, for example as involved in the Neurospora circadian clock, that can both activate and repress, we show how these multiple actions can cause complex oscillatory patterns in a transcription-translation feedback loop (TTFL). Inspired by the timekeeping complex formed by the NMO-PER-TIM-SGG complex that regulates the negative TTFL in th...