Molecular Chronobiology

Chronobiology studies the temporal aspects of life on earth. We are especially interested in endogenous strategies to cope with the regular, highly predictable alterations in the environment that are due to the rotation of the earth. The daily cycles in light and darkness, in turn, produce changes in temperature and humidity, creating a challenge to primitive and complex organisms alike. Microbes, animals and plants all have pronounced daily rhythms from the level of gene expression to behaviour. The observation that these rhythms often persist in constant conditions led to the characterization of a daily biological oscillator, sometimes called a circadian (‘about a day’) clock, which serves to coordinate physiology at the level of the cell as well as in whole animals. Our circadian systems control our lives!

Does everything have a biological clock?

The daily biological clock maintains rhythms in many living organisms even in the absence of an apparent environmental stimulus. This so-called circadian (circa= approximately, dian=day) rhythm has a frequency of approximately 24-hours, although in nature it is typically synchronized to exactly 24h by the light/dark or temperature cycles that result from the rotation of the Earth. Within each individual, an orchestra of rhythms conducts essential biological processes. The clock creates an endogenous temporal framework in fungi, plants, and animals, and in at least some bacteria. In the case of humans, the timing program dictates when we sleep and awaken.

It has been estimated that there may be 15 to 30 million species of organisms living on earth. Do all of these have a biological clock?  Most organisms are exposed to 24-hour cycles in environmental conditions and they show corresponding cycles in physiology and behaviour.  Importantly, when the clock is physically removed or when so-called clock genes are mutated, an organism is out-competed by one with an intact circadian clock (see pioneering work by the Johnson lab at Vanderbuilt University), suggesting an evolutionary advantage to a functional daily timing system. We therefore project that endogenous timing systems will be pervasive throughout nature and indeed, circadian clocks have been found in organisms from unicells to, for instance, animals, with established experimental model systems in the bacteria, fungi, plants and animals.

People often ask about organisms that live in ‘constant conditions’ in nature, such as bacteria living around the ‘black smokers’ in the deep ocean or cave fish (see recent publications by the Foulkes lab). Although the environment as concerns light and temperature might be constant in these special niches, there should be echoes of the 24 hour daily cycle that leach into these environs. Anything in the environment that changes with a regular and predictable frequency (food source?) could possibly stimulate evolution of an endogenous temporal structure.

Entrainment of the circadian clock

Synchronization of the biological clock involves two oscillators coming together: a physical oscillation in the environment occurs each 24 hours (light/dark or warm/cold) and a biological clock that oscillates approximately once each 24 h when it is removed from the external cycle.

To synchronize (or entrain) to the cycle, the circadian biological clock must be getting signals from the environment (called zeitgebers - German for time givers).  Because the circadian clock is a complex genetic trait, each individual may synchronize differently (see how humans synchronize differently at www.euclock.org ).

Learn about your circadian clock

Get information on your own phase of entrainment – your chronotype – and how you are timing your behaviour relative to others. Go to www.euclock.org and indicate that you would like to learn about your chronotype.