Intronic MicroRNA (miRNA)

Nearly 97% of the human genome is composed of noncoding DNA,which varies from one species to another. Changes in thesesequences often manifest themselves in clinical and circumstantialmalfunction. Numerous genes in these non-protein-coding regionsencode microRNAs, which are responsible for RNA-mediatedgene silencing through RNA interference (RNAi)-like pathways.MicroRNAs (miRNAs), small single-stranded regulatory RNAs capableof interfering with intracellular messenger RNAs (mRNAs) withcomplete or partial complementarity, are useful for the design ofnew therapies against cancer polymorphisms and viral mutations. Currently, many varieties of miRNA are widely reported in plants, animals, and evenmicrobes. Intron-derived microRNA (Id-miRNA) is a new class ofmiRNA derived from the processing of gene introns. The intronicmiRNA requires type-II RNA polymerases (Pol-II) and spliceosomalcomponents for their biogenesis. Several kinds of Id-miRNA havebeen identified in C elegans, mouse, and human cells;however, neither function nor application has been reported. Here,we show for the first time that intron-derived miRNAs are able toinduce RNA interference in not only human and mouse cells, but inalso zebrafish, chicken embryos, and adult mice, demonstrating theevolutionary preservation of intron-mediated gene silencing viafunctional miRNA in cell and in vivo. These findings suggest anintracellular miRNA-mediated gene regulatory system, fine-tuningthe degradation of protein-coding messenger RNAs