A Circadian Timing Mechanism in the Cyanobacteria

Williams, Stanly B.

doi:10.1016/s0065-2911(06)52004-1

Cited by 26 publications

(23 citation statements)

References 226 publications

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“…Records of DNA compaction and decompaction [29] clearly show that in modern cyanobacteria compaction occurs at night, not during the day. Of course, the current timing of the DNA compaction cycle may be due to a more recent adaptation to the altered atmosphere.…”

Section: Early Evolution Of Circadian Timing Mechanisms: 'Escape Frommentioning

confidence: 98%

Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod

Hut

Beersma

2011

Phil. Trans. R. Soc. B

178

193

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Virtually all species have developed cellular oscillations and mechanisms that synchronize these cellular oscillations to environmental cycles. Such environmental cycles in biotic (e.g. food availability and predation risk) or abiotic (e.g. temperature and light) factors may occur on a daily, annual or tidal time scale. Internal timing mechanisms may facilitate behavioural or physiological adaptation to such changes in environmental conditions. These timing mechanisms commonly involve an internal molecular oscillator (a 'clock') that is synchronized ('entrained') to the environmental cycle by receptor mechanisms responding to relevant environmental signals ('Zeitgeber', i.e. German for time-giver). To understand the evolution of such timing mechanisms, we have to understand the mechanisms leading to selective advantage. Although major advances have been made in our understanding of the physiological and molecular mechanisms driving internal cycles (proximate questions), studies identifying mechanisms of natural selection on clock systems (ultimate questions) are rather limited. Here, we discuss the selective advantage of a circadian system and how its adaptation to day length variation may have a functional role in optimizing seasonal timing. We discuss various cases where selective advantages of circadian timing mechanisms have been shown and cases where temporarily loss of circadian timing may cause selective advantage. We suggest an explanation for why a circadian timing system has emerged in primitive life forms like cyanobacteria and we evaluate a possible molecular mechanism that enabled these bacteria to adapt to seasonal variation in day length. We further discuss how the role of the circadian system in photoperiodic time measurement may explain differential selection pressures on circadian period when species are exposed to changing climatic conditions (e.g. global warming) or when they expand their geographical range to different latitudes or altitudes.

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Section: Early Evolution Of Circadian Timing Mechanisms: 'Escape Frommentioning

confidence: 98%

Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod

Hut

Beersma

2011

Phil. Trans. R. Soc. B

178

193

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“…The complex disassociates into its components before dawn and the cycle starts over for the next day ( Fig. 2) (for review, see Golden and Canales 2003;Iwasaki and Kondo 2004;Williams 2006).…”

Section: Synechococcus Elongatusmentioning

confidence: 99%

Biological Rhythms Workshop IA: Molecular Basis of Rhythms Generation

Mackey¹

2007

Cold Spring Harbor Symposia on Quantitative Biology

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Current circadian models are based on genetic, biochemical, and structural data that, when combined, provide a comprehensive picture of the molecular basis for rhythms generation. These models describe three basic elements-input pathways, oscillator, and output pathways-to which each molecular component is assigned. The lines between these elements are often blurred because some proteins function in more than one element of the circadian system. The end result of these molecular oscillations is the same in each system (near 24-hour timing), yet the proteins involved, the interactions among those proteins, and the regulatory feedback loops differ. Here, the current models for the molecular basis for rhythms generation are described for the prokaryotic cyanobacterium Synechococcus elongatus as well as the eukaryotic systems Neurospora crassa, Drosophila melanogaster, Arabidopsis thaliana, and mammals (particularly rodents).

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“…While the focus is on the molecular mechanisms of the Drosophila melanogaster circadian clock, advances in other circadian systems will also be discussed to illustrate conserved mechanisms. Readers interested in circadian clock mechanisms of other organisms are encouraged to read recent reviews (Hastings and Herzog 2004;Gardner et al 2006;Ko and Takahashi 2006;Williams 2006;Woelfle and Johnson 2006;Heintzen and Liu 2007;Levi and Schibler 2007).…”

mentioning

confidence: 99%

Probing the Relative Importance of Molecular Oscillations in the Circadian Clock

Zheng

Sehgal

2008

Genetics

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Circadian (24 hr) rhythms of behavior and physiology are driven by molecular clocks that are endogenous to most organisms. The mechanisms underlying these clocks are remarkably conserved across evolution and typically consist of auto-regulatory loops in which specific proteins (clock proteins) rhythmically repress expression of their own genes. Such regulation maintains 24-hr cycles of RNA and protein expression. Despite the conservation of these mechanisms, however, questions are now being raised about the relevance of different molecular oscillations. Indeed, several studies have demonstrated that oscillations of some critical clock genes can be eliminated without loss of basic clock function. Here, we describe the multiple levels at which clock gene/protein expression and function can be rhythmically regulated-transcription, protein expression, post-translational modification, and localization-and speculate as to which aspect of this regulation is most critical. While the review is focused on Drosophila, we include some discussion of mammalian clocks to indicate the extent to which the questions concerning clock mechanisms are similar, regardless of the organism under study. T HE light:dark cycle generated by the earth's rotation is the driving force of daily behavioral and physiological rhythms exhibited by most organisms. However, these daily (24 hr) rhythms are not just a passive response to the light:dark cycle; instead, an intrinsic timekeeping mechanism synchronizes physiological processes to the cyclic environment. The endogenous timekeeper is a self-sustained oscillator, termed the circadian clock, which can be entrained to environmental cues such as light and temperature (such environmental time signals are called zeitgebers), but more importantly, it free runs in constant conditions that lack environmental cues. In the past 20 years, genetic analysis of circadian rhythms in model organisms such as Drosophila, Neurospora, Arabidopsis, cyanobacteria, and mice has yielded considerable insight into the molecular mechanisms of circadian oscillators. Despite these advances, the question of how exactly a rhythm is generated is getting some attention again because a number of recent studies have challenged the simple models proposed initially. This review traces these developments in the field and then proposes a revised model that incorporates the old and new findings. While the focus is on the molecular mechanisms of the Drosophila melanogaster circadian clock, advances in other circadian systems will also be discussed to illustrate conserved mechanisms. Readers interested in circadian clock mechanisms of other organisms are encouraged to read recent reviews (Hastings and

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A Circadian Timing Mechanism in the Cyanobacteria

Cited by 26 publications

References 226 publications

Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod

Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod

Biological Rhythms Workshop IA: Molecular Basis of Rhythms Generation

Probing the Relative Importance of Molecular Oscillations in the Circadian Clock

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