MicroRNAs--micro in size but macro in function.

MicroRNAs (miRNAs) are endogenous small RNAs that can regulate target mRNAs by binding to their 3'-UTRs. A single miRNA can regulate many mRNA targets, and several miRNAs can regulate a single mRNA. These have been reported to be involved in a variety of functions, including developmental transitions, neuronal patterning, apoptosis, adipogenesis metabolism and hematopoiesis in different organisms. Many oncogenes and tumor suppressor genes are regulated by miRNAs. Studies conducted in the past few years have demonstrated the possible association between miRNAs and several human malignancies and infectious diseases. In this article, we have focused on the mechanism of miRNA biogenesis and the role of miRNAs in human health and disease.