MODELING APPROACHES OF THE CIRCADIAN CLOCK AND LIGHT ENTRAINMENT IN ZEBRAFISH
A circadian clock is the daily time-keeping mechanism internal to most living entities. It allows the organism to anticipate and thus adapt to environmental fluctuations. While these rhythms can free-run in constant conditions, such as constant darkness, they are usually entrained to the local time by environmental cues, often light.
Endogenous circadian oscillators can be found in many cells and peripheral organs, but in most higher organisms a central circadian pacemaker is present in the central nervous system, such as the suprachiasmatic nucleus in mammals. Interestingly, in zebrafish no central clock has been found, and instead all cells appear to be directly entrained by light, making it a unique and interesting vertebrate model.
The circadian clocks of several species have been modeled, with interlinked feedback loops as a recurring network motif. While the mechanisms that give rise to stable oscillations are now better understood, the way entrainment works requires more investigation. The direct light entrainability of zebrafish cells makes them a great model to look into this question.