Emerging roles of non-coding RNAs in gastric cancer: Pathogenesis and clinical implications

Figure 1 miRNAs biogenesis. Primary miRNA) (pri-miRNA) is transcribed by RNA polymerase II from miRNA genes. The long pri-miRNA is processed by the RNase III proteins Drosha and Pasha/DGCR8 into precursor miRNA (pre-miRNA) in the nucleus. The cleaved pre-miRNA is then exported to the cytoplasm by Exportin 5 and cleaved into about 18-22 nt miRNA duplex by the RNase III Dicer. Only one strand of the miRNA duplex becomes mature and incorporates into the RNA-induced silencing complex (RISC), whereas the other strand is degraded. miRNA regulates gene expression by forming base pairs mainly with the 3’-untranslated region of its target mRNAs. The imperfect and perfect base matching between miRNA and its target mRNAs leads to inhibition of mRNA translation and induction of mRNA degradation, respectively.