Figure 1.

Types of RNAi constructs introduced into target cells for silencing. Naked RNAi constructs can be introduced to target cells in forms of siRNA (small interfering RNA), esiRNA (endoribonuclease-prepared siRNA), or long dsRNA using variety of transfection protocols such as lipid-based transfection reagents or electroporation, or active uptake by target cells through receptor-mediated endocytosis. Once inside the cytoplasm, RNAi constructs can be further processed by host endonucleases or directly loaded into RISC (RNA-induced silencing complex) to facilitate gene expression knock down. Alternatively, for hard-to-transfect cells, RNAi can be introduced using viral vectors, such as lentivirus or adenovirus/adeno-associated virus (AAV) vectors carrying siRNA or shRNA expression cassettes. Once transcribed, shRNA can be further processed and exported out to cell cytoplasm for silencing gene expression.