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Norwegian University of Science and Technology - Articles and news items

FIGURE 1 siRNA design principles. (A) Highly effective standard siRNAs have a guide strand (in green) with a less thermodynamically stable 5’ than 3’ end (indicated with dashed lines) and position-specific nucleotide preferences (indicated above guide strand). P and OH indicate 5’ phosphate groups and 3’ hydroxyl ends, respectively; blue region indicate seed region. (B) Bi-functional siRNAs targeting a single or (C) two different transcripts. (D) A dual-targeting siRNA where one strand (light green) targets EGFR and the other strand (dark green) targets CCND1

Unconventional RNA interference – recent approaches to robust RNAi

Genomics, Issue 5 2011 / 19 October 2011 / Marie Lundbæk, Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology and Pål Sætrom, Department of Cancer Research and Molecular Medicine & Department of Computer and Information Science, Norwegian University of Science and Technology

RNA interference (RNAi) is now a standard tool in molecular biology. Short interfering RNAs (siRNAs) for knocking down your favourite human gene are only a couple of mouse-clicks away at your favourite reagent supplier’s website. Moreover, in contrast to initial attempts at siRNA design, these siRNAs usually give potent target gene knockdown. Nevertheless, siRNAs are not always a cure-all; therapeutic settings often require combinatorial treatments and may necessitate effects that are incompatible with standard siRNAs, such as targeted gene up-regulation. Here, we review the features of standard siRNAs before describing three unconventional but therapeutically relevant approaches to RNAi: multi-targeting siRNAs, immunostimulatory siRNAs, and transcription-modulating siRNAs.

Fire and Mello coined the term RNA interference when they discovered that long doublestranded RNAs cause sequence specific gene inhibition in worms1,2. The enzyme Dicer processes such long double-stranded RNAs into short double-stranded ~22 nt duplexes with 2 nt 3’ overhangs – the siRNAs. Argonaute 2 (Ago2) then incorporates one of the siRNA strands and uses the strand as a guide to bind and cleave single-stranded RNAs such as messenger RNAs (mRNAs).

miRNA and viral infections in vertebrates

Issue 1 2009, Past issues / 7 February 2009 /

For plants and invertebrates, RNA interference is firmly established as an important antiviral mechanism. Even before Fire, Mello, and co-workers described RNA interference (RNAi) in worms in 19981 it was becoming clear that plants have an RNA-dependent pathway that protects against viral infections2. The pathway, then termed post-transcriptional gene silencing (PTGS), helps plants like tobacco recover from initial viral infections and ensures that plants are protected from subsequent infections from the same or similar viral strains3. Subsequent studies have revealed that plant PTGS and Fire and Mello’s RNAi are identical – the triggers are short RNAs derived from long double-stranded RNAs (dsRNA)4. Incorporated into the RNA-induced silencing complex (RISC), RISC cleaves transcripts like viral messenger RNAs (mRNAs) with antisense complementary to the short RNAs.


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