Circadian Output, Input, and Intracellular Oscillators: Insights into the Circadian Systems of Single Cells

Loros, Jennifer J.; Dunlap, Jay C.; Larrondo, Luis F.; Shi, Mi; Belden, William J.; Gooch, Van D.; Chen, C.-H.; Baker, Christopher L.; Mehra, Arun; Colot, Hildur V.; Schwerdtfeger, Carsten; Lambreghts, Randy; Collopy, Patrick D.; Gamsby, Joshua J.; Hong, Christian I.

doi:10.1101/sqb.2007.72.067

Cited by 21 publications

(27 citation statements)

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“…During this time, analysis of rhythms moved from the use of genetics-which opened up the black box and exposed the feedback loops-to molecular biology, where the field is now. Although it is tempting to write about all the vistas that opened up during this time based on work in Neurospora, from clock mechanism to clock output, I have restricted this Perspectives to studies on the circadian mechanism and will leave output to other, highly capable hands (Loros 2008). It is an account of what drew me to rhythms work and to the Neurospora circadian system and of what led our lab to identify the factors and interactions that contributed to the denouement of the question of the molecular bases of circadian rhythms: the assembly, a little over a decade ago, of a complete interconnected regulatory cycle.…”

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confidence: 99%

Salad Days in the Rhythms Trade

Dunlap

2008

Genetics

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confidence: 99%

Salad Days in the Rhythms Trade

Dunlap

2008

Genetics

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“…The specifications of the TTFL began later with the mechanisms of interaction between mRNA and protein levels (Hardin et al 1990), and several molecular models have been published (Leloup and Goldbeter 2008;Dunlap et al 2007;Loros et al 2007;Mackey 2007;Lema and Auerbach 2006).…”

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confidence: 98%

“…The molecular mechanism has been studied intensively (review: Vitalini et al 2010;Dunlap et al 2007;Loros et al 2007). The gene frq, its mRNA, and product FRQ are essential components and belong to a negative limb of a feedback loop.…”

Section: The Circadian System Of Neurospora and Modelsmentioning

confidence: 99%

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How Light Resets Circadian Clocks

2014

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The daily revolutions of the earth around its axis are responsible for day and night and its annual orbit around the sun for the seasons with their fluctuations in day length. Most organisms have adapted to these diurnal and annual cycles. The strategies and mechanisms used are quite delicate and complicated.It came as a surprise that photosynthesis and many other processes are, however, additionally controlled by internal clocks. Thus, photosynthesis fluctuates not only during the daily light-dark cycle (=LD; see the List of Abbreviations and http://www.circadian.org/dictionary.html) but also when the plants are kept under LL and constant temperature (Hennessey and Field 1991). However, the period length (period for short) of this rhythmic event then deviates from exactly 24 h and is therefore called circadian (from Latin circa, about, and dies, day). If in the absence of LD and temperature cycles other 24 h time cues (also called zeitgeber, German for time giver) would control the rhythm, it should show an exact 24 h rhythm. This is not the case, demonstrating the endogenous nature of a clock that is locked to light signals (see Fig. 18.1). Spectrum of RhythmsEndogenous rhythms of organisms are not only tuned to the daily cycle of 24 h. The range of rhythms found in organisms covers ultradian (with periods of several hours to very short ones), circadian, and annual (with periods of about a year) rhythms. Other rhythms such as tidal, 14-day, and monthly ones cope with influences of the moon on the earth, mainly on the water movements of the oceans, and they are therefore found in organisms at the coasts and in the sea. Annual rhythms interact with the day-length changes during the year (see below). There are furthermore rhythms with periods covering several years. The following discussion of a "biological clock" is restricted to circadian rhythms. Even they are often not just composed of one clock type but form a "circadian system" consisting of two or more clocks with different prop- Function of Circadian ClocksThe term "clock" usually implies a time-measuring device or function. For instance, the day length (or night length) can be determined by an organism. Since day length is a function of the time of the year (long days in summer, short days in winter), it can be used to time certain events such as flowering or tuber formation of a plant or breeding of birds and mammals during the most appropriate season. These processes are denoted photoperiodism (see Chap. 19).However, a clock can also be used to set a certain temporal order. For instance, the circadian control of our sleepwake cycle ensures that we rise in the morning and fall asleep in the evening at a preferred time. Food intake and digestion are likewise controlled by this clock and gated to certain times of the day (Silver et al. 2011;Duguay and Cermakian 2009;Forsgren 1935). The circadian clock will time these events also under constant conditions. Furthermore, circadian clocks can serve as alarm clocks.

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“…The historical development of this field has been quite interesting but has been adequately reviewed elsewhere (21–29) and will not be re-developed in depth here. Instead we will aim for a succinct and comprehensible (at the expense of comprehensive) overview of how the circadian system works.…”

Section: The Neurospora Circadian Oscillatormentioning

confidence: 99%

Making Time: Conservation of Biological Clocks from Fungi to Animals

2017

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SUMMARY The capacity for biological timekeeping arose at least three times through evolution, in prokaryotic cyanobacteria, in cells that evolved into higher plants, and within the group of organisms that eventually became the Fungi and the Animals. Neurospora is a tractable model system for understanding the molecular bases of circadian rhythms in the last of these groups, and is perhaps the most intensively studied circadian cell type. Rhythmic processes described in fungi include growth rate, stress responses, developmental capacity and sporulation as well as much of metabolism; fungi use clocks to anticipate daily environmental changes. A negative feedback loop comprises the core of the circadian system in fungi and animals. In Neurospora, the best studied fungal model, it is driven by two transcription factors, WC-1 and WC-2, that form the White Collar Complex (WCC). WCC elicits expression of the frq gene. FRQ complexes with other proteins, physically interacts with the WCC, and reduces its activity; the kinetics of these processes is strongly influenced by progressive phosphorylation of FRQ. When FRQ become sufficiently phosphorylated that it loses the ability to influence WCC activity the circadian cycle starts again. Environmental cycles of light and temperature influence frq and FRQ expression and thereby reset the internal circadian clocks. The molecular basis of circadian output is also becoming understood. Taken together, molecular explanations are emerging for all the canonical circadian properties, providing a molecular and regulatory framework that may be extended to many members of the Fungal and Animal kingdoms, including humans.

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Circadian Output, Input, and Intracellular Oscillators: Insights into the Circadian Systems of Single Cells

Cited by 21 publications

References 131 publications

Salad Days in the Rhythms Trade

Salad Days in the Rhythms Trade

How Light Resets Circadian Clocks

Making Time: Conservation of Biological Clocks from Fungi to Animals

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