The siPool strategy is beautifully simple:
By having many on-target siRNAs, each with a different seed sequence, you maintain on-target efficiency while diluting out off-target effects.
One analogy is the beauty of composite faces.
Which of these faces do you find most attractive?
If you’re like most people, you will have chosen the last face, which is actually a composite of the other 5 faces (source).
Each individual face has its flaw(s). Spock ears, mildly everted lips, incongruous eyebrows, etc. No face is ideal. But when combined, these flaws are evened out.
Same thing with siRNAs. Each individual siRNA has its own ugly off-target signature. But combined in a high-complexity siPool, the off-target warts are removed, and you’re left with a beautiful on-target phenotype.
And not all facial averages are equal. Perrett et al. found that a composite face created from faces pre-selected as being more attractive was preferred over a composite created from all available faces.
Likewise, siPools are composed of the best available individual siRNAs.
Being selective about what goes into a siPool is important, as we will discuss more in future posts.
I could not make good composites of lunatics ; their features are apt to be so irregular in different ways that it was impossible to blend them. I took a photographer with me to Hanwell, where it was arranged that the patients should sit two at a time on a bench. One of them was to be led forward and posted in front of the camera, while his place on the bench was filled by the second patient moving up into it, whose previous place was to be occupied by a third patient It happened that the second of the pair who were the first to occupy the bench considered himself to be a very mighty man, I forget whom, but let us say Alexander the Great. He boiled with internal fury at not being given precedence, and when the photographer had his head well under the velvet cloth, with his body bent, in the familiar attitude of photographers while focusing, Alexander the Great slid swiftly to his rear and administered a really good bite to the unprotected hinder end of the poor photographer, whose scared face emerging from under the velvet cloth rises vividly in my memory as I write this. The photographer guarded his rear afterwards by posting himself in a corner of the room. Memories of My Life, pp 262-263
Don’t get bitten by bad RNAi reagents.
See faceresearch.org for lots of information and interesting tools for facial analysis.
See this article for composite faces from different nations.