MicroRNAs (miRNAs) are small, non-coding RNAs that are thought to act as post-transcriptional modulators of gene expression, binding to miRNA Recognition Elements (MREs) in the 3′UTR of their target genes resulting in either the suppression of translation or degradation of mRNA transcripts or both (Filipowicz et al., 2008). However, recent reports have shown that MREs may also be found in the upstream elements (5′UTR) of a target mRNA (Lee et al., 2008; Lytle et al., 2007; Orom and Lund, 2010). Generally, miRNAs function as endogenous repressors of target mRNAexpression and/or translation although there are also instances where miRNAs have been shown to enhance mRNA translation (Manakov et al., 2009; Nielsen et al., 2009; Orom and Lund, 2010). The compounding effect of the multiple regulatory programs ultimately determines the protein profile of the cell.
