In light of the following from the source you gave, what are we to make of 'how the RNAi is derived?'... They first showed that siRNAs are produced even in the absence of RNAi using Drosophila embryo extract.
Ok, here's the way i understand it, excerpt from, never mind...
Double-stranded RNA (dsRNA) is a potent and specific inhibitor (RNAi) of gene activity in Drosophila. dsRNA corresponding to a single gene specifically interferes with expression of that gene by causing rapid degradation of the cytoplasmic mRNA product. A concentration of dsRNA that is an order-of-magnitude lower than the level of mRNA transcripts is sufficient to degrade most transcripts. Interference of gene expression can persist for at least fourteen days in an organism during which the body size increases 100-fold. These latter two properties indicate that the RNAi effect is amplified and highly stable. However, we find that RNAi is efficiently initiated only in the germline or early blastoderm-stage,suggesting that its normal function is limited to those stages. In order to understand the mechanism behind RNAi, we have undertaken a genetic screen for mutants that are resistant to RNAi. Results from the screen will be presented. In parallel, we are using a cell-free system derived from syncitial blastoderm extracts that mimics RNAi in vivo. Evidence from this in vitro system and from embryo experiments rule out RNA-directed RNA synthesis as a possible step in the RNAi process. This result is in contradiction to evidence that a similar phenomenon in plants and fungi use RNA synthesis.
Time flies like an arrow.
Fruit flies like a banana.
Drosophilia, eh? Seems fitting that the first test subjects would be AIDS patients then if the "cure" is extracted from Fruit Fly eggs.