Although the existence of circadian clocks is accepted as an ubiquitous feature of life, and their physiological mechanisms are becoming well understood, the role of circadian clocks in extreme environments, like the polar regions, has received very little attention. In polar environments the strength of the Zeitgeber is greatly reduced around the summer and winter solstices when the sun never sets or never rises. Polar organisms represent an excellent model in chronobiological studies.
Only a few studies have investigated activity patterns under polar conditions in the wild and the existing findings are inconsistent. Karl Stokkan and colleagues provide new molecular and behavioural evidence that suggests reindeer, living at high latitudes in the Arctic, lack the underlying biological clock necessary for generating circadian rhythmicity: they do not express 24-h locomotor activity rhythms in summer and winter, differently, during the equinoxes, animals express a circadian regulation of activity. The diversity of behavioural responses, even within the limited number of species tested, is surprising and suggests that a variety of genetic and physiological factors might be involved in regulating circadian plasticity
Lepidurus arcticus, an high Arctic invertebrate, is the ideal model (like drosophila) in which to develop this aspect because of its presence in all melt-water pools in Arctic, and because conspecifics can also be found at other latitudes, and gene expression and behaviour will be investigated.
Our aim is to understand the influence of the light on the biological clock of the high Arctic animals, and the adaptive significance of clocks and rhythms; moreover to develop a possible animal model for the study of the de-synchronization.
Only a few studies have been conducted to systematically investigate how working the biological clock in animals from non-rhythmic environment and the influence of the light on these animals. Studies on polar animals, in particular reindeer, showed that they produce melatonin at night during seasonal transitions of the equinox, lose these rhythms during the continuous winter nights of higher latitudes (1). Cultured fibroblasts from reindeer skin with transgenic constructs of clock gene promoters (mouse Bmal1 or Per2) driving a luciferase reporter were arrhythmic or showed unstable and transient oscillations of bioluminescence. These results are in line with the weak circadian central and peripheral organization in reindeer. It remains enigmatic whether the reindeer SCN cells also show a low amplitude of circadian rhythms at the molecular level or reduced synchronization in winter and summer (2). Behavioural, metabolic and genetic responses show that polar animals exhibit diverse responses to the continuous lighting conditions during summers and winters at high latitudes, which may reflect variance in the function of the biological clock, or in the ecological niches they occupy, as well as differences in their evolutionary histories. Functionality of persistent circadian rhythms in polar animals is generally thought to be linked to synchronization of physiology and behaviour with the geophysical environment, although persistent rhythmicity may also be adaptive due to interdependence between circadian clock function and homeostatic processes.
An animal model on high arctic invertebrate will permit us to study the master clock genes (and not peripheral clock gene as researches in literature) and metabolic and behavioural correlations, new data respect to the researches in the past.
1) Stokkan KA, van Oort BE, Tyler NJ, Loudon AS. 2007 Adaptations for life in the Arctic: evidence that melatonin rhythms in reindeer are not driven by a circadian oscillator but remain acutely sensitive to environmental photoperiod. J. Pineal. Res. 43, 289 ¿ 293.(doi:10.1111/j.1600-079X.2007.00476.x) 2) Paul MJ, Schwartz WJ. 2010 Circadian rhythms: how does a reindeer tell time?. Curr. Biol. 20, R280 ¿ R282. (doi:10.1016/j.cub.2010.02.008)