Introduction to circadian rhythms, clocks, and its genes

Abstract

From conception to death, life encompasses innumerable processes in continuous change and in many instances repetition; after all, life on earth has to cope from its origin with a highly cyclic environment. Thus, it is not surprising that cyclic phenomena are found in all living organisms and at all levels of organization. When this processes repeat in a regular manner, we refer to them as rhythmic. Biological rhythms occur in a wide range of frequencies, from cycles per seconds to cycles per year. Of particular interest are those rhythmic functions which repeat daily. These are the circadian rhythms whose organization and relevance are the interest of the present book. In this brief introduction, a general perspective of circadian rhythmicity and its mechanisms will be presented; we will start by a brief summary of the basic concepts and its biological relevance; then we will provide an account of the main ideas which lead to the characterization of circadian clocks among different species and levels of organization; and finally, we will provide a brief account on the characterization of the molecular mechanism underlying circadian oscillators, the so-called clock genes, and its distribution in mammalian tissues.