Multiple usage of slides for FISH

[Mario Nenno]

Dear Bernd Kazmierczak:
 
> can anybody give me a good method for washing off biotin-labelled probes
> from chromosome spreads after fluorescence in situ hybridization, so
> that the slides can be used again for other probes.

One possiblity is to denaturate your preparation/slides (again)
in 70% formamide/2x SSC at 70 degree Celsius. The time depends
on your chromosomes/nuclei on the slides (humans maybe 2 min).
In this way the hybridized probes, together with your detection
molecules, should be 'washed away' and your target DNA is 'free'
for the next probe. In my hands it works fine at least for short 
oligonucleotide probes.

Several colleagues, however, share the experience, that it is hard
to remove e.g. rDNA probes. One argument I've heard, is that a
complete rDNA is quite long.

So my advice is, first hybridize the shorter probe, then denaturate 
in 70% formamide/2x SSC at 70 degree C and subsequently hybridize the
longer probe.

Good luck, Mario
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