ABSTRACT
Gene silencing by the conserved RNAi-pathway as first described in Caenorhabditis elegans is initiated by the introduction of double-stranded RNAs (dsRNA), resulting in sequence-specifi c degradation of homologous endogenous mRNA (Almeida and Allshire 2005). Later, RNAi has been shown to function in a similar manner in every metazoan and has been
applied to study a wide variety of phenotypes in vivo and in cells. Experiments in C. elegans and Drosophila primarily make use of long dsRNAs, which are intracellularly diced into functional 21mer short interfering RNAs (siRNAs). However, long dsRNAs are not effective in most mammalian cells due to the induction of antiviral pathways that lead to host cell shutdown. This can be counteracted by transfecting synthetic or plasmid-encoded siRNA that in most cases do not elicit an interferon or other host cell response (Amarzguioui and Prydz 2004). These approaches have been effectively used to study many different biological pathways in loss-of-function analysis and several large-scale efforts have recently generated libraries that target every predicted gene in major model organisms and humans.
