Ruprecht-Karls-Universität Heidelberg
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Circadian Clock Biology

Prof. Dr. Nick Foulkes

Prof. Dr. Nick Foulkes
Fon +49 721 608 23394
Fax +49 721 608 23354
ude.tik TEA sekluof.salohcin

Using the zebrafish as a model system to study the vertebrate circadian clock

Circadian clock with zebra fishes

Almost every aspect of plant and animal biology shows day - night rhythms. Many persist even under constant conditions however with period lengths that are not precisely 24 hours and for this reason they are termed "circadian" (Circa - diem). Central to the generation of circadian rhythms is an endogenous circadian clock which is constantly reset ("entrained") by environmental factors such as light to ensure that it remains synchronised with the natural 24 hour cycle.

Where are clocks located? Are clocks generated by cell-cell interactions or are they cell autonomous? How are they entrained by light - dark cycles and how do they ultimately control physiology?

Classically, the circadian clock in vertebrates was shown to reside in so- called central "oscillator" or "pacemaker" structures. In mammals the suprachiasmatic nucleus (SCN) of the hypothalamus and the retina are both the sites of pacemakers while inlower vertebrates, the pineal gland also appears to contain an additional pacemaker.Within these structures, individual cells have been shown to contain clocks which are synchronised in the context of the tissue. In mammals, the SCN clock is entrainedby light via photoreceptors in the retina which appear to be distinct from the rod andcone ocular photoreceptor cells. However, more recently this centralized model forthe vertebrate clock has been challenged by the discovery of clock functions indiverse tissues and cell types.

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