Guide vs passenger strand sorting - (Mar/06/2012 )
Within the siRNA/miRNA duplex, the guide strand should be the antisense strand to be complementary to the target mRNA (while the passenger strand is 'degraded'). But literature present evidence that it is the terminal nucleotides, its thermodynamic properties, destination argonaute protein, plant vs animal all dictate which strand will get loaded onto the RISC. If the sense strand gets loaded, then the target mRNA will be different. Can both strands potentially induce gene silencing???
Yes. There are many cases where both strands are processed. In those cases, there is a population of both strands loaded onto different RISC, and both may induce silencing. I don't have a citation handy, but look through miRBase and notice that for many hairpin maps, only a guide stand is shown colored (like this one):
For others, two strands are colored (and are thought to be processed and likely RISC-loaded):
One of these strands is still desicnated a star strand (*), but that doesn't mean it is not an active gene modulator.