![]() ![]() In addition to the therapeutic use in mammals, RNAi is also being explored as crop protection agent ( Zhang et al., 2017). Besides broad usage in basic research, siRNAs have now been developed to target genes for therapy and indeed the first siRNAs reached the market ( Dorsett and Tuschl, 2004 Sheridan, 2017). However, a breakthrough was reached when it was found that short siRNAs bypass immune sensing and can be used for gene knockdown also in higher organisms such as mammals ( Elbashir et al., 2001). However, long dsRNA is toxic for animal organisms with more sophisticated immune systems that are capable of sensing long dsRNA as “foreign” as such RNAs could, for example, result from viral infections ( Schlee and Hartmann, 2016). This process is commonly referred to as RNAi. This RNA is further processed to short interfering RNAs (siRNAs), which serve as guides for the RNA-induced silencing complex (RISC) that binds and sequence-specifically cleaves complementary target RNAs ( Zamore and Haley, 2005). dsRNA is generated by transcription or enzymes such as RNA-dependent RNA polymerases (RdRPs), which use single-stranded RNA as a template to generate long dsRNA ( Meister and Tuschl, 2004 Mello and Conte, 2004 Sharp and Zamore, 2000). Although these organisms are rather distant, the underlying mechanisms are remarkably conserved. Strategies such as RNA modifications or pooling of siRNAs have been developed and are used to reduce off-target effects.ĭouble-stranded RNA (dsRNA) as trigger for RNA interference (RNAi) has been discovered decades ago in plants and nematodes ( Baulcombe, 1996 Fire et al., 1998). Since siRNAs are widely used not only for screening but also for therapeutics as well as crop protection purposes, such miRNA-like off-target effects need to be minimized. SiRNAs, however, can function as miRNAs, and partial complementarity can lead to miRNA-like off-target effects in RNAi applications. This is due to only partial complementarity between the miRNA and the target RNA. In animals, endogenous microRNAs (miRNAs) function similarly but do not lead to direct cleavage of the target RNA but to translational inhibition followed by exonucleolytic decay. Within RISC, a member of the Argonaute protein family directly binds the guide strand and the siRNA guides RISC to fully complementary sites on-target RNAs, which are then sequence-specifically cleaved by the Argonaute protein-a process commonly referred to as RNA interference (RNAi). Short interfering RNAs (siRNAs) are processed from long double-stranded RNA (dsRNA), and a guide strand is selected and incorporated into the RNA-induced silencing complex (RISC). Regensburg Center for Biochemistry (RCB), Laboratory for RNA Biology, University of Regensburg, Regensburg, Germany. ![]()
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