Fig. 1

The mechanism of RNA interference (RNAi). Extended double-stranded RNA (dsRNA) can be delivered to the cytoplasm, where it undergoes cleavage to generate small interfering RNA (siRNA) by the enzyme Dicer. siRNAs can also be introduced directly into a cell as long dsRNAs and then cleaved by RNase III (Dicer) in the cytoplasm to become small dsRNAs. dsRNA is processed into 21–30 nt-long short siRNA molecules that act as modules in the silencing mechanism [214]. Subsequently, siRNA is integrated into a multiprotein complex known as the RNA-induced silencing complex (RISC), leading to the fragmentation of the RNA sense strand through the action of Argonaute 2 (Ago2). The activated RISC-siRNA complex actively searches for, attaches to, and degrades mRNA molecules that have complementary sequences, thereby causing suppressing target gene expression. Moreover, the activated RISC-siRNA complex can be reactivated to target and eliminate additional mRNA molecules with identical sequences [72, 215, 216]