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The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent...
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Light Input to the Mammalian Circadian Clock.

Adam A Dannerfjord1,2, Laurence A Brown1, Russell G Foster1,2

  • 1Sleep and Circadian Neuroscience Institute (SCNi), Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.

Methods in Molecular Biology (Clifton, N.J.)
|December 7, 2020
PubMed
Summary

Mammals possess an internal biological clock in the brain

Keywords:
ClockLaser capture microdissection (LCM)Photosensitive retinal ganglion cells (pRGCs)RNA extractionSuprachiasmatic nuclei (SCN)Transcriptional translational feedback loop (TTFL)

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Area of Science:

  • Chronobiology
  • Neuroscience
  • Molecular Biology

Background:

  • Circadian rhythms are 24-hour cycles in physiology and behavior present in most organisms.
  • These rhythms are regulated by an internal biological clock, particularly in mammals, located in the suprachiasmatic nuclei (SCN).
  • The SCN clock relies on core clock genes forming a transcriptional-translational feedback loop.

Purpose of the Study:

  • To provide an overview of studies investigating the SCN's transcriptional response to light.
  • To elucidate the molecular signaling pathways involved in synchronizing the internal clock with external time cues.
  • To offer protocols for studying light-induced molecular responses in the SCN clock.

Main Methods:

  • Review of studies on the transcriptional response of the SCN to light stimuli.
  • Analysis of light detection mechanisms involving rods, cones, and photosensitive retinal ganglion cells (pRGCs).
  • Examination of the retinohypothalamic tract's role in conveying light information to the SCN.

Main Results:

  • Light is the primary time cue for the SCN molecular clock.
  • Specific photoreceptors, including melanopsin-expressing pRGCs, detect light.
  • Light triggers intracellular signaling cascades affecting key clock gene expression in the SCN.

Conclusions:

  • Understanding the molecular response of the SCN to light is crucial for comprehending circadian rhythm regulation.
  • The identified pathways highlight the intricate connection between light, vision, and the internal biological clock.
  • Protocols are provided to facilitate further research into these light-induced molecular mechanisms.