The human biological clock, which regulates processes from gene expression to behaviour, like that of most organisms, synchronises to the Earth’s 24 hour rotation using signals from the environment (zeitgebers). This synchronisation is an active process called entrainment [1]. Daily rhythms also persist in temporal isolation [2], deviating modestly from 24 hours (hence circadian). Light is the ...

The biological clock of the suprachiasmatic nuclei drives numerous physiological and behavioural circadian rhythms. In this study, we addressed the question as to whether different components of the clock may control separately various circadian functions. Using the rat transpineal microdialysis tool, we analysed the effect of clock perturbation by exogenous melatonin injection on two hormonal ...

Synthetic biology, in which complex, dynamic biological systems are designed or reconstructed from basic biological components, can help elucidate the design principles of such systems. However, this engineering approach has only been applied to a few simple biological systems. The circadian clock is appropriate for this approach, since it is a dynamic system with complex transcriptional and po...

The circadian clocks that drive daily rhythms in animals are tightly coupled among the cells of some tissues. The coupling profoundly affects cellular rhythmicity and is central to contemporary understanding of circadian physiology and behavior. In contrast, studies of the clock in plant cells have largely ignored intercellular coupling, which is reported to be very weak or absent. We used luci...

Across phylogeny, the endogenous biological clock has been recognized as providing adaptive advantages to organisms through coordination of physiological and behavioral processes. Recent research has emphasized the role of circadian modulation of memory in generating peaks and troughs in cognitive performance. The circadian clock along with homeostatic processes also regulates sleep, which itse...

Like most organisms, plants have endogenous biological clocks that coordinate internal events with the external environment. We used high-density oligonucleotide microarrays to examine gene expression in Arabidopsis and found that 6% of the more than 8000 genes on the array exhibited circadian changes in steady-state messenger RNA levels. Clusters of circadian-regulated genes were found in path...

The environmental photoperiod regulates the synthesis of melatonin by the pineal gland, which in turn induces daily and seasonal adjustments in behavioral and physiological state. The mechanisms by which melatonin mediates these effects are not known, but accumulating data suggest that melatonin modulates a circadian biological clock, either directly or indirectly via neural inputs. The hypothe...

The biological clock in the suprachiasmatic nucleus (SCN) of the hypothalamus plays a well-defined role in regulating melatonin production by the pineal. Emerging evidence indicates that melatonin itself can feed back upon the SCN and thereby influence circadian functions. Melatonin administration has been shown to entrain activity rhythms in rodents and humans. Melatonin binds specifically wit...

The circadian clock located in the suprachiasmatic nuclei (SCN) was characterized in the fetal rat by using 14C-labeled deoxyglucose to monitor glucose utilization (metabolic activity) of the nuclei. A clear day-night oscillation of metabolic activity was detectable in the fetal SCN from the 19th through the 21st days of gestation; the nuclei were metabolically active during the subjective day ...

The eukaryotic biological clock involves a negative transcription-translation feedback loop in which clock genes regulate their own transcription and that of output genes of metabolic significance. While around 10% of the liver transcriptome is rhythmic, only about a fifth is driven by de novo transcription, indicating mRNA processing is a major circadian component. Here, we report that inhibit...