Amounts of RNA

Dom Spinella dspinella at
Mon May 5 10:48:00 EST 1997

Patrick HJ Falckh writes:

> Hi Bruce,
> I have to disagree with Dom Spinella's comment that the amount of RNA 
> in a cell is mainly dependent on the protocol for isolating it; yes it 
> is important but does not define the actual RNA content in different 
> tissues.
> The amount of RNA will depend on the function and activity of the 
> cell, which also then takes in the cell type. For example heart atria 
> is a completely different tissue to liver and the amount of RNA is quite 
> different. This can be easily seen when there is induction of 
> metabolising enzymes: there is an increase in the amount of protein 
> which is related to an increase in the message and an increase in total 
> RNA. In the back of the Qiagen Product Guide there is a number of 
> appendices that includes a list of cell types and tissues and the 
> content of total and messenger RNA per 100mg. Admittedly this is for 
> mouse cells but clearly indicates the varying amount of both total and 
> mRNA present. 
> I have extracted total and mRNA from rat out of all the tissues listed 
> in the Qiagen list and the values are differnt for that rodent. In 
> addition I have extracted RNA from 3 differnt insect species, several 
> marine species and their differnt organs and foun quite a difference in 
> RNA content even though the method to extract the RNA is essentially the 
> same. Unfortunately, I don't know of a source that lists human tissues. 
> One of the numerous companies that makes the extraction kits must have a 
> listing somewhere of the differnt amounts in human tissues (one would 
> hope they have tessted their kits??!!).
> Hope this helps. 

I fear that Patrick has mis-interpreted my initial comments.  I do not
dispute that different cells and tissues have widely varying amounts of
RNA. Its just that different RNA isolation protocols vary in their
recovery efficiency depending on the tissue to which they are applied,
and are somewhat variable even when applied to the same tissue in
separate experiments (depending upon the amount of starting material for
example).  It has been my experience that this variance is as or more
important a contributor to RNA yield as actual RNA content of the cells.
But perhaps Patrick just has better hands than me ...
-- Dom Spinella

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