Circadian Biology and Molecular Mechanisms

Circadian biology examines endogenous rhythms of approximately 24 hours that regulate behaviour, physiology and metabolism across organisms. At the molecular level, these rhythms derive from transcription–translation feedback loops in which core clock components—such as BMAL1, CLOCK, PERIOD and CRYPTOCHROME proteins—undergo rhythmic expression and proteolysis. These oscillators are synchronised by a central pacemaker in the suprachiasmatic nucleus of the hypothalamus, which in turn aligns peripheral clocks in tissues via neural and endocrine signals. Entrainment by environmental cues, notably the light–dark cycle and feeding schedules, ensures coherence between internal timekeeping and external cycles. Disruption of these mechanisms can alter glucose homeostasis, immune function and cellular proliferation, implicating circadian dysregulation in metabolic disorders, cancer and psychiatric disease.

Research from Nature Portfolio

Investigations into primordial circadian systems have revealed structural and mechanistic insights in prokaryotic cyanobacteria. Studies of the KaiBC oscillator in species lacking the KaiA regulator demonstrate a novel dodecameric assembly of KaiC subunits, linked by a coiled-coil network that responds to ATP/ADP ratios and drives phosphorylation cycles. These findings illuminate the evolutionary origins of self-sustained timekeeping and the transition to more complex regulators. In parallel, analyses of seasonal gene expression in human blood and adipose tissue have uncovered annual oscillations in immune and metabolic transcripts. Inversion of expression patterns between hemispheres highlights the influence of photoperiod on inflammatory markers and cardiovascular risk factors, stressing the importance of circannual rhythms in human health.

Circadian Biology and Molecular Mechanisms publication trend

The graph below shows the total number of articles in circadian biology and molecular mechanisms across all publications each year (not limited to Nature Index journals).

Technical terms

Circadian oscillator: A molecular network generating self-sustained ∼24-hour rhythms through feedback loops.

Transcription–translation feedback loop: Coordinated cycles of gene expression and protein accumulation that create rhythmicity.

Suprachiasmatic nucleus: Hypothalamic structure serving as the central pacemaker synchronising peripheral clocks.

Entrainment: Adjustment of endogenous rhythms to external cues such as light or feeding time.

Post-translational modification: Chemical alteration of clock proteins that regulates stability and activity.

References

1. Timing to Perfection: The Biology of Central and Peripheral Circadian Clocks. Neuron (2012).
2. From primordial clocks to circadian oscillators. Nature (2023).
3. Widespread seasonal gene expression reveals annual differences in human immunity and physiology. Nature Communications (2015).
4. Circadian tumor infiltration and function of CD8+ T cells dictate immunotherapy efficacy. Cell (2024).
5. Meal Timing Regulates the Human Circadian System. Current Biology (2017).