mature star miRNA - (Oct/15/2009 )
In many of the miRNA microarray published data in which they compare a control and treated samples, there are many instances in which an increase in the levels of mature star form of the miRNA is observed but not on those of the leading mature miRNA. Does anyone know why? can degradation of the star form be inhibited by some treatments? Thank you
Answer that question and you probably have a Nature paper in your hand! There are a couple of points I'd make. Firstly, the fact that the miRNA* is hybridizing doesn't necessarily mean that the molecule is functional/loaded into RISC - it could have been protected from degradation by e.g. sequestration in P bodies and as such not functional. And this could be a global process - i.e. all small RNAs, including the star strand, are transported to P bodies upon a certain stimulus. Yet my guess would be that the helicase, or a co-factor of the helicase, that is responsible for the unwinding of the miRNA duplex selectively protects the star strand from degradation.
But I'd love to hear the thoughts and ideas of others on this board, as I think this is a really important question!
One more thing to add to miRNA Man's comments, many miRNA published in the papers and Sanger database were only found 1-3 times within the thousands (or hundred thousands) of sequences cloned in experiments. It may be biased and it may not represent the right statistics. I have done some reporter assay and found the start form was more abundant/active than its counterpart. So, I will say the database may not be 100% correct.