Molecular characterization of a diurnal rodent funambulus palmarum ( south indian palm squirrel ) : Cloning and characterization of period 2 from the suprachiasmatic nucleus

Abstract

Biological clocks are time keeping mechanisms that evolved in organisms allowing them to adapt and anticipate the various geophysical variations in their external habitat. The day-night cycle caused by Earth’s rotation on its axis has been the primary selective pressure to impose a rhythmic pattern to physiological and behavioral activities that nearly reflect the length of a day on earth. Such oscillations with a near (circa) 24h periodicity termed as circadian rhythms allows species- specific partitioning of specific activities across different parts of a diel (day) cycle conferring survival advantage to the bearer. Though light act as the major ‘Zeitgeber’ or ‘time giver’ to synchronize or ‘entrain’ the phase of these rhythms to that of the zeitgeber time (ZT), they also persists independent of any photic variable and therefore constitutes the hands of the clock which dictates the ‘circadian or endogenous time’ (CT) of any living entity. The internal ‘period’ varies across individuals of the same species but it is relatively consistent over a range of temperatures (temperature compensation). Apart from circadian rhythms cycles having shorter or longer intrinsic periods are also biologically significant. Ultradian rhythms, have periodicity of less than 20h whereas infradian rhythms are longer than 28h, they can be measured in weeks, months, years (circannual), and longer