Dolores,
maybe the formalin residue in the  fixed tissue (if not washed properly) 
inactivates the enzyme used for digestion. Also check the concentration of 
the sample.. too much DNA/protein from tissue might not spin down well in 
the Qiagen, ie get stuck, and not give a good result.

Louise Renton



>>>
>I don't know exactly why  we are having quite good results with
>parafin sections and not the same with only fixed tissue....may be
>because in parafin sections formalin rests have disappeared after
>washing with water and diferent changes in alcohol?...I really don't
>know, it's sure that somebody better than me in this field
>can solve the doubt.
>
>
>
>
>From:          "louise renton" 
>To:            TEC-LAB-DEP01@med.ub.es, histonet@pathology.swmed.edu
>Subject:       DNA extraction
>Date:          Tue, 23 Jul 2002 07:33:03 +0000
>
>Dolores,
>
>If the tissue is not embedded, but straight out of the fixative, wash the
>chopped up sample  for a couple of hours in several changes of sterile 
>water
>and then proceed as usual to the digestion step (spin down before each
>change to remove as much of the water as possible).
>Extraction of DNA  for PCR from long stored formalin fixed, paraffin wax
>embedded tissues can be a problem, as the DNA becomes degraded over time,
>(I tried to get PCRable DNA from blocks embedded  in 1942, with no joy) and
>standard phenol/coloform extraction (ref Maniatis) might be better and give
>larger yield than the Quigen kit.
>
>Hope this helps
>Louise Renton
>
>
> >From: Dolors Fuster 
> >To: histonet@pathology.swmed.edu
> >Subject: DNA
> >Date: Mon, 22 Jul 2002 20:26:41 +0100
> >
> >Hi histonetters !
> >
> >What do you recommend us to obtain the best results in DNA extraction
> >from formalin fixed tissue? should we do any kind of treatment before
> >starting the
> >extraction? (Water rinses, alcohol changes....)
> >
> >We are usin Qiagen kit with good results for parafin embeded samples
> >fresh tissue and other kind of samples (cell culture, serum...). but
> >are not successful with formalin fixed tissue
> >
> >Thanks in advance
> >Dolors Fuster
> >
> >Tecnic Especialista en
> >Anatomia Patologica
> >Departament d'Anatomia i Embriologia Humana
> >Facultat de Medicina (HCP)
> >Universitat de Barcelona
> >ICQ 14146798
> >
> >http://www.fashionmas.com/click/
>
>
>
>
>Louise Renton
>Bone Research Unit
>MRC
>Johannesburg
>South Africa
>Tel & fax +27 11 717 2298
>"Time flies like an arrow, friut flies like a banana"
>ex
>
>_________________________________________________________________
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>
>Dolors Fuster
>
>Tècnic Especialista en
>Anatomia Patològica
>Departament d'Anatomia i Embriologia Humana
>Facultat de Medicina (HCP)
>Universitat de Barcelona
>ICQ 14146798
>
>http://www.fashionmas.com/click/
>




Louise Renton
Bone Research Unit
MRC
Johannesburg
South Africa
Tel & fax +27 11 717 2298
"Time flies like an arrow, friut flies like a banana"


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