Up-Regulation of microRNA* Strands by Their Target Transcripts

During microRNA (miRNA) biogenesis, one strand of a 21-23 nucleotide RNA duplex is preferentially selected for entry into an RNA-induced silencing complex (RISC). The other strand, known as the miRNA* species, is typically thought to be degraded. Previous studies have provided miRNA* selection models, but it remains unclear how the dominance of one arm arises during the biogenesis of miRNA. Using miRNA sponge-like methods, we cloned four tandem target sequences (artificial target) of miR-7b* and then measured miR-7b* expression levels after transfection of the artificial target. miR-7b* levels were found to significantly increase after transfection of the artificial target. We postulate that the abundance of target transcripts drives miRNA arm selection.