The ability to knockdown the expression of an endogenous gene by RNAi has emerged as a powerful strategy for the rapid identification of specific gene functions. Vector-based constitutive expression of shRNA can result in stable and efficient knockdown of target genes. However, constitutive expression of shRNA imposes major limitations when analyzing the fimction of genes whose expression is vital for the survival of an organism. Inducible RNAi systems can circumvent this limitation by enabling the inhibition of expression of an essential gene only when the inducing agent is present, and the level of knockdown of the essential gene can be controlled and adjusted by the concentration of inducing agent. In this review, we briefly summarize the recent development of various inducible RNAi systems and their potential applications in drug target validation.
