preserving dna

[Niklas Wahlberg]

Hi all,
     Here's my perspective on DNA samples from butterflies. I've been 
working with it almost daily for the past 4 years and I've extracted DNA 
from close to 1000 specimens. First of all, I never cut off the wings and 
put the body into the freezer, I extract the DNA from two legs (or one if 
it's a big one), leaving the rest of the specimen unharmed and maximally 
useful for taxonomic purposes (if necessary!). I store the extracted DNA in 
the freezer (enough for 50-200 PCRs depending on the freshness of the 
specimen). As far as I'm aware, water itself has not harmed my extracts. 
Many of my extracts are from dried specimens that colleagues and friends 
have sent from around the world. These can be tricky and this is where 
water can be a problem, through humidity. Specimens stored even briefly in 
humid conditions are generally useless for DNA work (this obviously applies 
to specimens relaxed in a humid box for spreading). The reason is most 
likely that bacteria and fungi (moulds) get into the butterfly and 
basically have a party, ie eat up anything and everything organic including 
DNA. I've been thinking of experimenting with different kinds of relaxing 
procedures to see whether some procedure would be less harmful to DNA, but 
I haven't had the time yet.
    As for storing specimens for future possible analysis, I reiterate what 
Catherine said in a previous post. Keep them frozen (the colder the 
better). Pure ethanol (70% ethanol is not good enough) is also an option if 
there is no freezer available. Drying specimens quickly works wonderfully 
if the specimen will be processed within 1-2 months of being killed. I 
haven't noticed any effects of the way a butterfly was killed (chloroform 
is used routinely in DNA extractions, so I can't see why it should destroy 
DNA) on the quality of DNA.
    I envision future holotypes of new species having their DNA extracted 
from a leg or two, with the DNA info complementing the more visible info. 
With the way things are going now, who knows, maybe in 20 years we will be 
sequencing the entire genome of new species routinely! I think it is worth 
preserving tissue (two legs...) from new taxa now, so that in the future, 
we can get even more information about what these beautiful creatures 
actually are.
     My two (euro) cents.

Cheers,
Niklas

At 00:33 2001.07.20 -0400, Ron Gatrelle wrote:

>Chris J. Durden <drdn at mail.utexas.edu> wrote:
>
> > I have heard that the latest, cutting edge research technique is to
> >         cut the wings off and dry in glassine envelopes
> >              put the body in absolute alcohol to preserve the DNA!
> >
>This brings up a good subject. My understanding is that water destroys the
>DNA and that a specific alcohol is to be used. Which?  Some may be
>preserving tissue for future analysis in vain if not using the correct
>medium.
>Ron
>
>
>
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Niklas Wahlberg
Department of Zoology
Stockholm University
S-106 91 Stockholm
SWEDEN

Phone: +46 8 164047
Fax:   +46 8 167715

http://www.zoologi.su.se/research/ihp/


 
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