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Top : New Forum Archives (2009-): : siRNA, microRNA and RNAi

Old threads on "siRNA, microRNA and RNAi" are achived here - (Feb/04/2009 )


I am quite confused about the differences between the mechanisms by which (i) antisense oligonucleotides, (ii) long dsRNA, and (iii) short 21-23 dsRNA act on RNAs to affect gene expression in human cells.

I heard that long piece of dsRNA (in both worms or plants) activate the RNAi pathway, in where the long dsRNA gets cleaved into siRNA (20-25nt) and ultimately cause SPECIFIC mRNA degradation via RISC. Does this mean I should talk about the exogenous siRNA here? But long dsRNA cause broad/global effect!! I am confused...

In addition, both siRNA and miRNA are in definition a size of 19-25nt, where both have larger sized precursors. I do need clarification on these definitions. In addtion, isn't miRNA as a definition a endogenous single-stranded RNA?


Hi, Your questions are really broad. I hope these links will at-least help you to find the answer. Yes, you are right, miRNA is endogenous single stranded RNA.


Good luck


These might also help.


Kole R, Krainer AR, Altman S. RNA therapeutics: beyond RNA interference and antisense oligonucleotides. Nat Rev Drug Discov. 2012 Jan 20. doi: 10.1038/nrd3625.


Summerton J. Morpholino, siRNA, and S-DNA Compared: Impact of Structure and Mechanism of Action on Off-Target Effects and Sequence Specificity. Med Chem. 2007;7(7):651-660

-Jon Moulton-