IntroductionMicroRNAs (miRNAs) are small noncoding RNAs approximately 22 nucleotides (nt) in length that are engaged in virtually all cellular processes [1, 2]. Generally, miRNAs negatively regulate gene expression by repressing translation or inducing degradation of target messenger RNAs(mRNAs). However, miRNAs can also positively regulategene expression by modulating promoter activity or activating translation [3–5]. In mammals, miRNAs are predicted to control the activity of ~50 % of all protein-coding genes, and deregulated expression of miRNAs has been implicated in a variety of human diseases including cancer [2].