Crosstalk of epigenetics with biological rhythmicity in animal kingdom.

Biological rhythmicity plays a critical role in the pathophysiology and overall survival of an organism. Period (Per), cryptochrome (Cry), Bmal1 and CLOCK are four important gene families that affect the circadian rhythms to considerable level. However, our understanding regarding the genetic basis of biological rhythmicity is still in its infancy. Biological rhythms are generated through underlying gene expression which is regulated by various control systems. The finely regulated gene expression modulates biological rhythms through various molecular and cell-signaling pathways (metabolic state, endocrine activity and neural excitability). Epigenetics through modifications of histone tags, chromatin remodeling, non-coding RNAs and other mechanisms plays an important role as regulators of gene expression controlling biological rhythmicity in the animal kingdom. MicroRNAs like miR328, miR383, miR192/194, miR122, miRNA-219 and miRNA-132 are some of the noteworthy miRNAs reported to be functionally related to circadian rhythmicity controlling various biological events. Besides miRNAs, histone modification enzyme systems, RNA binding proteins and sirtuins form important ways to regulate the expression of genes related to biological clock in living organisms. In this review, we have made an attempt to understand the epigenetic basis of biological rhythmicity in mammalian organisms and analyze the progress made to date. [ABSTRACT FROM AUTHOR]