A local stem-loop structure of pri-miRNAs is then cleaved in the nucleus by the dsRNA-specific ribonuclease Drosha/ Pasha to 70 nucleotides long precursor miRNA (pre-miRNA) [17] in a process known as "cropping" [18, 19] . Pre-miRNAs are then actively transported from the nucleus to the cytoplasm [20, 21] . In the cytoplasm, pre-miRNAs are subsequently cleaved by RNase III Dicer into~22-nt miRNA duplexes [17, 20] . One strand of the short-lived miRNA duplex is degraded ("passenger" strand, miR*), whereas the other ("guide", miR) strand is incorporated into the RNA-induced silencing complex (RISC) and serves as a functional, mature miRNA [8] . Selection of the "guide" strand is based on the base pairing stability of both dsRNA ends [22, 23] .