RNA interference (RNAi) is a biological process that suppresses gene expression in a sequence-specific manner through small RNA molecules.
Types of RNAi Molecules
- Small interfering RNA (siRNA): Double-stranded RNA molecules, 20–25 nucleotides long, either synthetically produced or generated by cleavage of longer dsRNA by Dicer. siRNAs guide the RNA-induced silencing complex (RISC) to complementary mRNA, leading to its cleavage and degradation, thus preventing protein translation.
- MicroRNA (miRNA): Endogenous, single-stranded RNA molecules about 21–23 nucleotides long, transcribed from specific genes. miRNAs bind imperfectly to the 3' untranslated region (UTR) of target mRNAs, causing translational repression or mRNA degradation. They regulate multiple genes and are involved in development, differentiation, and disease pathways.
- Short hairpin RNA (shRNA): Artificial RNA molecules expressed from DNA vectors inside cells, forming a hairpin loop structure. shRNA is processed by Dicer into siRNA-like molecules that induce gene silencing. shRNA allows stable, long-term gene knockdown, often used in research and therapeutic applications.
- PIWI-interacting RNA (piRNA): Although less commonly discussed in RNAi contexts, piRNAs are small RNAs involved mainly in silencing transposons and maintaining genome integrity, especially in germ cells.
Advantages of RNA Interference
- High specificity and efficiency: RNAi targets specific mRNA sequences, enabling precise and effective gene silencing with minimal off-target effects.
- Versatility: RNAi works in a wide range of organisms and cell types, making it a powerful tool for studying gene function and regulation across species.
- Temporal control: Synthetic siRNAs provide rapid, transient knockdown, while vector-expressed shRNAs allow stable and long-term gene silencing.
- Therapeutic potential: RNAi can target disease-related genes, including viral genes and oncogenes, offering promising approaches for treating cancers, viral infections, and genetic disorders.
- Reduced toxicity and immunogenicity: Advances in RNAi design and delivery (e.g., chemical modifications, nanoparticle carriers) improve stability and reduce immune responses.
- Multiple gene regulation: Particularly miRNAs can regulate multiple genes simultaneously, influencing complex biological pathways.
