A blind circadian clock in cavefish reveals that opsins mediate peripheral clock photoreception

PLoS Biol. 2011 Sep;9(9):e1001142. doi: 10.1371/journal.pbio.1001142. Epub 2011 Sep 6.


The circadian clock is synchronized with the day-night cycle primarily by light. Fish represent fascinating models for deciphering the light input pathway to the vertebrate clock since fish cell clocks are regulated by direct light exposure. Here we have performed a comparative, functional analysis of the circadian clock involving the zebrafish that is normally exposed to the day-night cycle and a cavefish species that has evolved in perpetual darkness. Our results reveal that the cavefish retains a food-entrainable clock that oscillates with an infradian period. Importantly, however, this clock is not regulated by light. This comparative study pinpoints the two extra-retinal photoreceptors Melanopsin (Opn4m2) and TMT-opsin as essential upstream elements of the peripheral clock light input pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Circadian Clocks / physiology*
  • Circadian Rhythm / physiology*
  • Feeding Behavior
  • Gene Expression
  • Opsins / genetics
  • Opsins / metabolism*
  • Photic Stimulation
  • Photoreceptor Cells, Vertebrate / physiology*
  • Rod Opsins / genetics
  • Rod Opsins / metabolism
  • Zebrafish / physiology*


  • Opsins
  • Rod Opsins
  • melanopsin