Circadian regulation of the light input pathway in Neurospora crassa

Merrow, Martha; Franchi, Lisa; Dragovic, Zdravko; Görl, Margit; Johnson, J. P.; Brunner, Michael; Macino, Giuseppe; Roenneberg, Till

doi:10.1093/emboj/20.3.307

Cited by 114 publications

(155 citation statements)

References 55 publications

(129 reference statements)

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“…But what are appropriate zeitgebers for the frq NULL residual Neurospora clock? Light apparently is not useful because frq NULL strains are partially blind (11,18,25,26).…”

Section: Resultsmentioning

confidence: 99%

Demasking biological oscillators: Properties and principles of entrainment exemplified by the Neurospora circadian clock

Roenneberg

Dragovic

Merrow

2005

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

102

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Oscillations are found throughout the physical and biological worlds. Their interactions can result in a systematic process of synchronization called entrainment, which is distinct from a simple stimulus-response pattern. Oscillators respond to stimuli at some times in their cycle and may not respond at others. Oscillators can also be driven if the stimulus is strong (or if the oscillator is weak); i.e., they restart their cycle every time they receive a stimulus. Stimuli can also directly affect rhythms without entraining the underlying oscillator (masking): Drivenness and masking are often difficult to distinguish. Here we use the circadian biological clock to explore properties of entrainment. We confirm previous results showing that the residual circadian system in Neurospora can be entrained in a mutant of the clock gene frequency (frq 9 , a strain deficient in producing a functional FRQ protein). This finding has implications for understanding the evolution of circadian programs. By comparing data sets from independent studies, we develop a template for analyzing, modeling, and dissecting the interactions of entrained and masked components. These insights can be applied to oscillators of all periodicities.clock gene ͉ light ͉ masking ͉ model ͉ temperature

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“…But what are appropriate zeitgebers for the frq NULL residual Neurospora clock? Light apparently is not useful because frq NULL strains are partially blind (11,18,25,26).…”

Section: Resultsmentioning

confidence: 99%

Demasking biological oscillators: Properties and principles of entrainment exemplified by the Neurospora circadian clock

Roenneberg

Dragovic

Merrow

2005

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

102

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“…Immediate light responses are gated by the circadian clock such that identical light signals result in higher induction in the subjective morning (Heintzen et al 2001;Merrow et al 2001). Interestingly, the circadian response to light corresponds to the circadian phosphorylation and activity status of the WCC , suggesting that only a fraction of the WCC might be susceptible to light activation.…”

Section: Signal Transduction Of Lightmentioning

confidence: 99%

Transcriptional and post-transcriptional regulation of the circadian clock of cyanobacteria and Neurospora

Brunner¹,

Schafmeier²

2006

Genes Dev.

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Circadian clocks are self-sustained oscillators modulating rhythmic transcription of large numbers of genes. Clock-controlled gene expression manifests in circadian rhythmicity of many physiological and behavioral functions. In eukaryotes, expression of core clock components is organized in a network of interconnected positive and negative feedback loops. This network is thought to constitute the pacemaker that generates circadian rhythmicity. The network of interconnected loops is embedded in a supra-net via a large number of interacting factors that affect expression and function of core clock components on transcriptional and post-transcriptional levels. In particular, phosphorylation and dephosphorylation of clock components are critical processes ensuring robust self-sustained circadian rhythmicity and entrainment of clocks to external cues. In cyanobacteria, three clock proteins have the capacity to generate a self-sustained circadian rhythm of autophosphorylation and dephosphorylation independent of transcription and translation. This phosphorylation rhythm regulates the function of these clock components, which then facilitate rhythmic gene transcription, including negative feedback on their own genes. In this article, we briefly present the mechanism of clock function in cyanobacteria. We then discuss in detail the contribution of transcriptional feedback and protein phosphorylation to various functional aspects of the circadian clock of Neurospora crassa.Circadian rhythms are found in numerous light-perceiving organisms including cyanobacteria, algae, fungi, plants, insects, and vertebrates. The rhythms are supported by cell-autonomous circadian clocks, which regulate expression of a large number of genes on the level of transcription (for review, see Transcriptional/translational feedback loops are hallmarks of circadian clocks in all organisms. In eukaryotes, expression of core clock components is organized in a complex network of interconnected positive and negative feedback loops (for review, see Dunlap and Loros 2004;Gachon et al. 2004;Hardin 2005). This network of gene expression is assumed to generate circadian rhythmicity. Elimination of key components of these interconnected loops disrupts many, if not all, rhythmic outputs, depending on the organism. Expression, subcellular localization, assembly, function, and turnover of clock components are crucial for circadian rhythmicity, and thus, the core clock is embedded in a supra-net of cellular machinery regulating various aspects of clock function. Protein phosphorylation and dephosphorylation are important regulatory mechanisms that are critical for self-sustained circadian rhythmicity and entrainment of clocks to external cues. It is unclear to what extent reversible phosphorylations are mechanistically instrumental for generation of rhythmicity in eukaryotic clocks.Recent findings have shown that clock proteins in cyanobacteria generate a self-sustained circadian rhythm of autophosphorylation and dephosphorylation, which is independent of tra...

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“…The second common feature of many circadian oscillators is that they consist of not one but two or more oscillating gene products whose regulation is linked. This holds in organisms as different as the fungus Neurospora, the fruit fly Drosophila, and mammals (34,35,(40)(41)(42)(43)(44).…”

mentioning

confidence: 99%

Circuit topology and the evolution of robustness in two-gene circadian oscillators

Wagner

2005

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

141

122

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Many parameters driving the behavior of biochemical circuits vary extensively and are thus not fine-tuned. Therefore, the topology of such circuits (the who-interacts-with-whom) is key to understanding their central properties. I here explore several hundred different topologies of a simple biochemical model of circadian oscillations to ask two questions: Do different circuits differ dramatically in their robustness to parameter change? If so, can a process of gradual molecular evolution find highly robust topologies when starting from less robust topologies? I find that the distribution of robustness among different circuit topologies is highly skewed: Most show low robustness, whereas very few topologies are highly robust. To address the second evolutionary question, I define a topology graph, each of whose nodes corresponds to one circuit topology that shows circadian oscillations. Two nodes in this graph are connected if they differ by only one regulatory interaction within the circuit. For the circadian oscillator I study, most topologies are connected in this graph, making evolutionary transitions from low to high robustness easy. A similar approach has been used to study the evolution of robustness in biological macromolecules, with similar results. This suggests that the same principles govern the evolution of robustness on different levels of biological organization. The regulatory interlocking of several oscillating gene products in biological circadian oscillators may exist because it provides robustness. complexity ͉ gene networks

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Circadian regulation of the light input pathway in Neurospora crassa

Cited by 114 publications

References 55 publications

Demasking biological oscillators: Properties and principles of entrainment exemplified by the Neurospora circadian clock

Demasking biological oscillators: Properties and principles of entrainment exemplified by the Neurospora circadian clock

Transcriptional and post-transcriptional regulation of the circadian clock of cyanobacteria and Neurospora

Circuit topology and the evolution of robustness in two-gene circadian oscillators

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