ps418

RNA interference is one of the most promising new genetic tools. It was voted breathrough of the year by Science last year (see Couzin, 2002). There are many potential applications for interference RNAs. For instance, when studying gene function in mice, drosophila, C. elegans, and so on, a standard research method has been the creation of knock-out lines, from which a gene of interest has been deleted. This produces what is known as the "null phenotype" for that gene. You can effectively do the same thing much more easily and cheaply with RNAi. According to this article, it may be possible to control the level of expression from high to medium to low levels, which is not possible with simple knockouts.

The interference is effected through the use of double-standed RNAs, or dsRNAs. First, dsRNAs which are homolous to the RNA transcript target, are introduced to the cell. The dsRNAs are cleaved into small RNA segments, 21-28 nucleotides long, referred to as small-interfering RNAs, or siRNAs, by a ribonuclease enzyme called Dicer. These siRNAs are then incorporated along with certain proteins into a RISC, or RNA-induced silencing complex. The RISCs then bind to and cleave those RNA transcripts that are complimentary to the siRNA in the RISC. The result is that even though an organism has a given gene, and the gene is producing RNA transcripts, the transcripts are rapidly degraded and proteins are not created from the RNA transcripts. See this Flash animation depicting the process, from Nature Reviews Genetics, 2; 110-119 (2001).


Think also of the possibilities for treating "genetic" diseases. If a disease is caused by the presence of a particular protein, and the individual is heterozygous for the gene for that protein, then potentially you could actually shut down production of that faulty protein using RNAi, without affecting production of the good protein. And cancer research should benefit greatly too, since overexpression of some genes is common in cancerous cells.

For instance this article discussed how RNAi may potentially be used to slow the onset of Huntington's disease by decreasing production the protein "Huntingtin," which is coded for by a gene on chromosome 4 called IT15. I'm sure its also possible that these could find application as a biological weapon, if there were some way to get the right dsRNA into one's target.

I'm confident we'll all be hearing alot about the wonders of RNA interference in the years to come. For more info, this page has a list of references on RNAi. This page also has alot of great resources on RNAi, but is not loading at the moment.

Patrick

Wounded King

Its not really all that new, they have been doing it in worms and plants since the late 90s.

It is cool though.

pz

And zebrafish...sometimes it seems like every other paper on my experimental animal of choice is a morphant paper.

ps418

In the late 90's, were they using dsRNA, or just antisense RNA strands?

Patrick

MortalWombat

Ngo H, Tschudi C, Gull K, Ullu E.
Double-stranded RNA induces mRNA degradation in Trypanosoma brucei.
Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):14687-92.


Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC.
Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans.
Nature. 1998 Feb 19;391(6669):806-11.

ps418

That answers my question. Thanks!

Patrick

Wounded King

I'd like to point out that 'morphants' refers to morpholino based studies and not to those using siRNA.

pz

Yes...which are antisense oligos used to interfere with expression.

Wounded King

But which aren't an example of RNAi. RNAi very specifically refers to the use of double stranded RNA, not to the whole range of RNA or other oligonucleotide based methods of gene knockdown. And since morpholinos aren't even RNA molecules it certainly doesn't include them.

It is the fact that it is the RNA doing the interfering that gives it its name, not that it is the RNA that is being interfered with.

If you wanted to find the earliest use of antisense oligos you would need to go back a couple of decades.

Aethari

On a side note, thanks for that link relating to Huntington's, pz...I'm sure my ex (whose mother has it) will be very interested.

~Aethari