RNA interference (RNAi) is an important pathway that is used in many different organisms to regulate gene expression. This animation introduces the principles of RNAi involving small interfering RNAs (siRNAs) and microRNAs (miRNAs). We take you on an audio-visual journey through the steps of gene expression and show you an up-to-date view of how RNAi can silence specific mRNAs in the cytoplasm.
RNA interference (RNAi) is an endogenous post-transcriptional gene regulatory mechanism mediated by non-coding RNA molecules known as microRNAs. microRNAs can target hundreds of genes simultaneous1, inducing subtle but reproducible shifts in gene expression and regulation.
This mechanism can be utilized for targeted gene silencing by introduction of nucleic acid based tools that are specially designed to trigger the RNAi mechanism. These molecules are taken up by the RNA induced silencing complex (RISC) to target specific mRNAs for degradation or to modulate endogenous microRNAs.
Currently, there are three primary categories of RNAi tools to perform these functions: small interfering RNA (siRNA), short hairpin RNA (shRNA), and microRNA mimics and inhibitors.
A schematic of the endogenous microRNA pathway, with points of entry for the three categories of RNAi tools.
The endogenous microRNA pathway begins with genomic DNA transcription to produce pri-microRNA, which is then processed by the microprocessor complex containing the DROSHA protein and other proteins to a pre-microRNA hairpin structure and exported from the nucleus by Exportin-5. In the cytoplasm, the pre-microRNA is further processed by the Dicer complex to double-strand anti-parallel RNA. One strand of this RNA duplex will load into the RISC complex and act to target a mRNA transcript for down-regulation by either (1) seed-mediated mRNA translational repression or (2) catalytic mRNA cleavage mediated by high sequence complementarity. The blue molecules to the right of the image illustrate different classes of RNAi research tools and where they enter the endogenous RNAi pathway.
These tools have enabled a shift from traditional gene knockout, antisense or ribozyme technologies towards RNAi as a standard technique for discovery biology and target validation. RNAi is routinely manipulated to perform individual gene functional analyses, as well as to dissect complex biological pathways or survey entire genomes in a high-throughput manner.
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