Small interfering RNA (siRNA) is a class of double-stranded RNA molecules, 20-25 base pairs in length, similar to miRNAs, and operates within the RNA interference pathway. It interferes with the post-transcriptional degradation of mRNAs that express specific genes with complementary nucleotide sequences, thereby preventing translation. siRNA production is catalyzed by an enzyme called Dicerase. This is a powerful tool for drug targeting and therapeutic development because it is used to regulate gene expression through transcriptional repression. In principle, any gene can be silenced by a synthetic siRNA with a complementary sequence. This makes them an important tool for drug targeting and verification of gene function.
Fig 1. Gene silencing mechanism through siRNA in eukaryotic cells by different pathways. (Danielle et al., 2022)
siRNA is one of the main tools of RNA interference. By complementary pairing with the mRNA sequence of a target gene, siRNA can induce the RNAi pathway, leading to the silencing of the target gene. The effect of this gene silencing can be either to degrade the target mRNA, thereby blocking protein synthesis, or to reduce protein production by inhibiting the translational process. siRNA's gene silencing function has been widely used to study gene function, to validate gene targets, and to explore the potential for disease treatment.
In addition to silencing specific genes, siRNAs can also be used to regulate gene expression. By designing appropriate siRNA sequences, the expression of specific genes can be selectively inhibited or promoted. This function is widely used to study gene signaling pathways, cell differentiation and the regulatory mechanisms of disease-related genes.
High-throughput screening using siRNA libraries is a common approach for discovering and validating key genes associated with specific diseases or biological processes. By simultaneously transfecting or transforming siRNA libraries in cell lines, a large number of genes can be silenced and genes associated with the process of interest can be identified by observing changes in cellular phenotype or function.
Small double-stranded siRNAs are transfected into cells where the guide strand is loaded into the RISC. This activated protein-nucleic acid complex can then trigger gene silencing by binding to individual target mRNA sequences through perfect complementarity, thereby targeting them for cleavage and degradation.
The method by which siRNA causes gene silencing is as follows:
siRNAs are widely used to assess the individual contribution of genes to a variety of cellular phenotypes, including cytoplasmic division, apoptosis, insulin signaling, and cellular differentiation. siRNA screening has been used to identify novel pathways and has had a major impact on validating targets for many cellular processes and diseases, including cancer, HIV infection, and hepatitis. Finally, in vivo RNAi has been used for target validation studies in animal disease models and has the potential to be used for therapeutic purposes to selectively target and inhibit disease-causing genes.