2009 Volume 49 Issue 5 Pages 232-237
Most of organisms living on the earth have internal clocks and thus, the circadian rhythm represents a basic feature of life. In mammals, as in other many organisms, the cellular circadian core oscillator is thought to be composed of an autoregulatory transcription-(post)translation-based feedback loop involving a set of clock genes. The signal transduction cascade originating from this core oscillatory loop induces the expression of a variety of genes in a circadian fashion, and regulates many cellular functions such as cell division and energy metabolism. This cell oscillation system localizes in most of cells in the body. The circadian system has evolved in a close connection to light which synchronizes the internal phase to environmental rhythms. In mammals, the master clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, from which clock signals are transmitted through neuronal and hormonal oscillation conducting systems to the whole body. Arrived clock signals entrain the cell-clocks in peripheral organs, and the intracellular oscillating loop coordinates the timing of the expression of a variety of genes with specific cellular functions. Thus, the mammalian clock system displays a multidimensional complex structure constituting the central oscillator, oscillation conducting systems, and peripheral cellular oscillators.
