is it necessary to use RNAlater for tissue samples? - (Feb/16/2010 )
I work with drosophila crosses and collect embryos and freeze them in -80C for further use. When I need them, I thaw the tissue and extract RNA immediately and I never refreeze the left over. With this one-time freezing procedure, is the RNA in a good shape after thawing? How long the RNA remains good in the frozen tissue? Is it really necessary to use RNAlater?
In general, it is always best to have the highest quality of RNA possible. The best thing to do would be to use a BioAnalyzer to assess the quality of your RNA from immediately-frozen samples as well as from RNAlater-stabilized samples.
Here's a paper that examined the affect of RNA quality of flash-frozen vs. RNAlater samples (Fig 4 in particular):
That being said, no: it doesn't sound like you need RNAlater, because you are immediately freezing your samples and they are not going through multiple freeze–thaw cycles. However, that again depends on what you will be using the RNA for in downstream applications. Nevertheless, it would be worthwhile to assess the quality of your RNA with a BioAnalyzer...
As for RNA stability at -80ºC; I have had some tissues stored at -80ºC for almost a year (without RNAlater) before isolating the RNA and have had RNA Integrity Numbers of 8-9.5 (i.e. pretty-good-quality RNA).
Hope that helps!