knocking down mature miRNA with siRNA - is it possible to knockdown miRNA with siRNA? (Oct/04/2007 )

Can you knockdown a miRNA with the help of siRNA? Can we say that antisense oligonucleotide can be considered as a siRNA?

Yes you can. You can design siRNA to target precursor miRNA. Some companies such as Ambion and Dharmacon sell single-strand RNA called anti-miR or antagomiR to knockdown miRs. Here is the link to Ambion's site http://ambion.com/catalog/ProdGrp.html?fkA...p;fkProdGrp=344

A newly developed technique might helpful for such research
http://www.nature.com/nmeth/journal/v4/n9/.../nmeth1079.html

siRNA work by a different mechanism than other antisense oligos, and there are two other classes of antisense oligos which have distinct mechanisms.

siRNA - uses RISC complex to catalyze degradation of target RNA;
S-DNA (phosphorothioate) and other RNase-H competent antisense - uses RNase H to catalyze degradation of target RNA;
LNA, PNA, Morpholino and other RNase-H independent antisense - blocks processes by steric interference, no degradation of target.

For a comparison of the specificity and non-antisense effects associated with each of these classes, see this recent review:
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

Morpholinos are an alternative method for knocking down maturation and function of miRNA.
Kloosterman WP, Lagendijk AK, Ketting RF, Moulton JD, Plasterk RH. Targeted Inhibition of miRNA Maturation with Morpholinos Reveals a Role for miR-375 in Pancreatic Islet Development. PLoS Biol. 2007 Jul 24;5(8):e203 [Epub ahead of print]