The RNA interference mechanism in molecular research in general, detailed in the model organism Caenorhabditis elegans as well as in term of nutritional research
RNAi is a gene silencing mechanism; two decades ago, Craig Mello and Andrew Fire discovered the knock-down phenomenon in C. elegans. In general the mechanism starts by cleavage of long double-stranded RNA by the RNase III enzyme dicer into 21-25nt long small interfering RNAs. After the activation of the RISC complex through ATP and the recognition of the small interfering RNA, the double-strand gets unwind by a helicase. The strand with the lower thermodynamic stability at the 5'-end enters
... (typically the antisense strand) while the other one (the sense strand), gets degraded. By perfect complementarities of the target mRNA and the siRNA, the target gets cleaved and destroyed, in contrast to imperfect complementarity, where siRNA works like microRNA and results in an translational repression by binding to the 3'UTR region of the target mRNA. Some specialties like the systemic effect, the inheritance, the transitive character, and the generation of secondary siRNA appear not in every organism. Mammals and Drosophila melanogaster lack the mechanism to generate secondary siRNAs. This depends on the missing homologous of RdRP enzymes, and results in the transient effect of RNAi in mammals. The spreading mechanism is established in plants, planarias, and C. elegans, but not in flies or mammals. This is based on the fact, that in those two organisms, homologous of rsd or sid are missing. RNA interference is next to the gene silencing mechanism involved in different natural functions such as heterochromatin modification and methylation, transposon silencing, works in lower organisms as an ancient defense system, and can induce an immune response in mammals. This results in the activation of the PKR pathway and the activation of the 2'-5' oligoadenylate synthase. This fact, as well as the possibility to induce off-target effects and cross interference, complicates the development of therapeutic agents.