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Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
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Circadian rhythms: pervasive, and often times evasive.

Luis F Larrondo1,2

  • 1ANID-Millennium Science Initiative Program-Millennium Institute for Integrative Biology (iBio), Santiago 8331150, Chile.

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
|January 22, 2025
PubMed
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Circadian clocks are widespread but not universally found. This review explores the evolution of circadian systems, emphasizing the need to study non-model organisms to understand clock functionality.

Keywords:
TTFLcircadian rhythmsconditional rhythmsevolutionfungal clocks

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Area of Science:

  • Biology
  • Evolutionary Biology
  • Chronobiology

Background:

  • Circadian clocks exhibit convergent evolution across diverse taxa, from cyanobacteria to humans.
  • However, homologs of known clock components are absent in several animal, protist, fungal, and bacterial phyla.
  • This raises questions about the evolutionary history and diversity of circadian systems.

Purpose of the Study:

  • To reflect on the challenges and open questions in the study of non-model circadian systems.
  • To emphasize the importance of investigating organisms lacking canonical clock components or observable rhythms.
  • To highlight the need for exploring novel experimental conditions for uncovering hidden circadian functionalities.

Main Methods:

  • Literature review and synthesis of current knowledge on circadian clock evolution.
  • Analysis of genomic data for core clock elements in diverse taxa.
  • Discussion of experimental approaches for studying rhythmicity in non-model organisms.

Main Results:

  • Genomic identification of core clock elements does not always correlate with observed rhythmicity.
  • Environmental cues (abiotic or nutritional) are often required to elicit rhythmic behavior in non-model systems.
  • The absence of known homologs or observable rhythms does not preclude the existence of functional circadian clocks.

Conclusions:

  • The study of non-model circadian systems is crucial for a comprehensive understanding of biological timing.
  • Further research is needed to elucidate the mechanisms conditioning clock functionality and the evolutionary pathways of circadian regulation.
  • Rethinking criteria for identifying functional clocks is essential, moving beyond reliance on canonical components and observable rhythms.