Immense promises for tiny molecules: uncovering miRNA functions.

With the human genome fully sequenced, the need to obtain functional knowledge of many genes became apparent. Amongst them is a large set of recently discovered genes with powerful promise: the microRNA family. Accumulating data assigned functions in a wide array of biological processes to some miRNAs. Here we review the main approaches used to identify and validate miRNAs and describe ways to discover their functions. As potential effectors of many cellular pathways, mis-expression of miRNAs has been implicated in human cancer.