[RNA interference for mammalian cells].

Knock-out of mammalian genes is technically troublesome and time-consuming compared to those of lower animals. RNA interference (RNAi) is a strategy of sequence-specific post-translational gene silencing, and it has been successfully applied for disruption of gene transcripts in C. elegans. Gene silencing by RNAi had not been accomplished in mammalian cells until recently, because bystander activation of DNA-dependent protein kinase (PKR) coincides to disturb gene silencing by long double-stranded RNA (dsRNA), resulting in non-specific repression of translation of many proteins. A breakthrough has come recently with a report suggesting that 20- or 21-bp duplex RNA with 2 bp 3' overhang are made by DICER protein that cleaves long dsRNA during RNAi reactions in vivo and the resultant short dsRNAs mediate RNAi. Those short dsRNAs, namely, small interference RNA (siRNA), barely activate PKR. Using synthesized 21 bp siRNA, T. Tuschl's group has challenged to establish an artificial RNAi method suitable for mammalian cells. Their report was favorable in that siRNA specifically suppressed targeted gene translation in mammalian cells during culture without activation of PKR. Recently K. Taira's group developed the vector-based siRNA expression system by which RNAi is feasible in mammalian cells. Almost all genes can be targeted by RNAi. RNAi methods require minimal time and labor; therefore, mammalian gene knockdown by RNAi will become popular in the near future.