In the last decade, researchers have identified a novel mode of gene regulation in the form of a family of small RNAs. In 1993, investigators first identified in C. elegans a small RNA, lin-4, which affected developmental timing by forming a duplex with the 3′UTR of another gene, lin-14, thus preventing lin-14 translation.1 The identification of lin-4 represented the first small RNA-regulating target mRNA expression. In 2000, investigators identified another small RNA let-7 that regulated the gene let-4; however, unlike lin-4, let-7 was conserved across among several species.
