MicroRNAs are small non-coding RNAs acting as regulatory elements in gene expression.57 miRNAs are transcribed as primary miRNA (pri-miRNA) and then cleaved by a nuclear complex, including the Drosha and Pasha proteins, resulting in the production of a precursor miRNA (pre-miRNA).58–60 Pre-miRNAs are then exported to the cytoplasm by exportin-5 and cleaved by the Dicer enzyme, yielding a double-stranded (ds) miRNA.61 Finally, miRNAs are loaded in the RNA-induced silencing complex (RISC) to suppress stability and/or translation of the mRNA target.62 miRNAs recognize and bind miRNA Regulatory Elements mostly located in the 3′UTR of target mRNAs;57 however miRNAs binding other regions, such as 5′UTR, have also been described.63
