Figure 1: The two main delivery systems for RNAi: lipid-based nanoparticles and lentiviral vectors. Synthetic siRNA can be carried by lipid nanoparticles into the cytoplasm, where they are incorporated to the RNA-inducing silencing complex (RISC), which targets and degrades the complementary messenger RNA. Lentiviruses deliver the plasmid into the nucleus for transcription, and the shRNA sequences are then exported to the cytoplasm, where they are cleaved by the enzyme Dicer into siRNA duplexes before combining with RISC.