RNA interference (RNAi) is a post-transcriptional gene silencing phenomenon mediated by small double-stranded RNA with a length of 20-30nt. This life process is highly conserved during evolution and regulates the transcription and translation of many genes encoding functional proteins.

siRNA (Small interfering RNA) and miRNA (microRNA), as non-coding RNA, are common RNAi tools used in gene function research and disease treatment. siRNA is the simplest and most efficient way to knock down gene expression to study protein function in a wide range of cell types. It is also the best method for clinical treatment and drug development.

miRNA plays an important role as an endogenous gene regulator by mediating translation repression or promoting degradation of target mRNA. While the normal expression and function of miRNA is vital for physiological processes, aberrant expression of miRNAs has been proved to be closely related to the occurrence of various cancers. Perturbation of endogenous miRNA helps to study the function of specific miRNA and maintain therapeutic potential.

RNAi Mechanism

RNAi is activated by double-stranded RNA transported into the cytoplasm, and is represented by gene silencing induced by siRNA or shRNA that degrades the target mRNA or induces inhibition of specific mRNA translation. After exogenous dsRNA enters cells, it is first degraded into 21-25nt siRNA under the action of the Dicer enzyme. Subsequently, the antisense strand in the siRNA participates in the synthesis of the guide RNA-induced silencing complex (RISC), which then mediates cleavage of the region complementary to the siRNA antisense strand in the target mRNA molecule, thereby interfering with the function of target gene expression.

Figure 1. Schematic diagram of RNAi mechanism

Similarities and Differences Between siRNA and miRNA

siRNA miRNA
Characteristics Exogenous, resulting from viral infection or human import Time and tissue-specific. It is a mechanism of the organism itself that regulates the post-transcriptional horizontal expression of genes
Molecular Structure Double-stranded RNA Single-stranded RNA
Mechanism In the cytoplasm, the Dicer processes dsRNA into siRNA Pri-miRNA is processed by Drosha into pre-miRNA in the nucleus, and exportin-5 proteins are exported from the nucleus to the cytoplasm. In the cytoplasm, pre-miRNA is processed by the RNase III enzyme Dicer to become mature miRNA
Biological Function Silencing the target mRNA Regulate or degrade target mRNA
The Effect on RNA Target mRNA is degraded and the stability of mRNA is affected The target mRNA is degraded and the transcription level is regulated, but the stability of mRNA is not affected
Role Position Binds to any region that pairs with the target mRNA Binds to the 3’UTR base-paired region of the target mRNA
Complementary and Binding Specificity Completely matches to target mRNA with high binding specificity Completely matches to target mRNA, partially paired or mismatched, and had low binding specificity

Figure 2. Differences between siRNA and miRNA 

siRNA/miRNA Synthesis | Synbio Technologies 
Synbio Technologies’s chemical synthesis RNA services include a range of RNA products, siRNA and miRNA mimics, etc. Our high-quality services and products support researchers conducting gene function analysis and therapeutic strategy development around the world. 

Reference [1] Xu JZ, Zhang JL, et al. Antisense RNA: the new favorite in genetic research. J Zhejiang Univ Sci B. 2018 Oct.;19(10):739-749.[2] Jain, Ritesh G., et al. RNAi-based functional genomics in Hemiptera. Insects 11.9 (2020): 557. 

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