A study of microRNAs in silico and in vivo: emerging regulators of embryonic stem cells.

MicroRNAs (miRNAs) are noncoding regulatory RNAs that function via the degradation of target mRNAs and inhibition of translation. They are found widely in higher eukaryotic organisms, and in several species that have been closely examined, hundreds of miRNAs have thus far been discovered with mechanistically conserved, yet functionally diverse, roles necessary for the proper development, homeostasis and metabolism of the organisms. Mammalian cells produce miRNAs in a cell-type-specific manner and utilize them to regulate unique subsets of genes expressed in the host cells. This rule also appears to apply to the pluripotent embryonic stem cells, according to several recent studies that reported identification of specifically expressed miRNAs. Intense interest in these miRNAs stems in part from the possibility that they are one of the determinants of the salient characteristics of these cells: self-renewal capacity and pluripotency. As functional data supporting this hypothesis are beginning to accumulate, it can be envisioned that miRNAs may be useful as molecular tools for manipulating ESCs. This review focuses on the recent discovery and functional characterization of miRNAs in human and mouse ESCs and provides perspectives on future research directions.