Real-time PCR: Advancing RNA Interference and MicroRNA Studies

The endogenous small RNAs known as microRNAs (miRNAs) found in the genomes of both animals and plants are highly conserved by evolution, suggesting a fundamental biological function. MicroRNAs are cleaved from larger hairpin precursors (Figure 1), and it is the mature, cleaved, approxi-mately 22-nucleotide miRNA that currently is the focus of most research. The inherent homology between the longer pre-miRNA and the mature, active miRNA makes it difficult to preferentially detect the active molecule using traditional hybridization-based methods. This has contributed to the challenges of accurately quantifying and elucidating the role of miRNAs in different tissues, developmental stages and disease states. A total of approximately 850 unique miRNAs have been discovered so far, including 222 human miRNAs (about 250 miRNAs for each species have been predicted). Although miRNAs were only recently discovered, they are relatively abundant, accounting for approximately 1 % of the predicted genes in animals and plants (1). Despite their general abundance, the level o