RNA Interference
RNA Interference
• Over ten years ago, Andrew Fire and Craig Mello showed the ability of double stranded RNA molecules to inhibit the expression of homologous genes in C. elegans (Fire et al.
1998).
• For this achievement they were honoured with
the Nobel Prize for Medicine or Physiology in
2006.
RNAi Pathway
• RNA-interference (RNAi) is the sequence-specific silencing of gene expression triggered by short double-stranded RNAs.
• RNAi in mammalian systems begins in the nucleus with dsRNA synthesis and continues in the cytoplasm (Grimm and Kay 2007)
• The first step involves the processing of the long dsRNA into smaller fragments called siRNAs by the endonuclease Dicer. Generally siRNAs are 21 nucleotides long, of which 19 nucleotides form a helix and 2 nucleotides on each of the 3’ ends are unpaired. The ribonucleoprotein complex RISC (RNA-induced silencing complex), the main effector of the pathway, is guided by the siRNA to the complementary target mRNA. As a result, Ago2, the catalytic component of RISC, cleaves the target RNA at a specific site in the center of the duplex, 10 nucleotides from the 5’ end of the siRNA strand. 5' end cap and the poly-A tail which gives stability to mRNAs, are also removed from the target mRNA, therefore the cleaved mRNA is rapidly degraded by RNases. This will result in no protein synthesis from the corresponding gene (Kurreck 2009).
siRNA Delivery
• The modulators of RNAi include exogenously introduced double-stranded RNA (dsRNA) in the form of either short hairpin RNA (shRNA) or short interfering RNA (siRNA); or micro RNA (miRNA) which are the endogenous regulators of gene expression.
• As any other therapeutic agent, RNAi requires an effective and safe delivery vector.
• Moreover, specific tissue and cell targeting after systemic administration remain a formidable challenge.
• a number of different strategies have been developed for the in vitro and in vivo delivery of
• siRNA
