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Hi Ray.  I was recently imaging a GFP-tagged protein that, at high expression
levels, was localized throughout the cytoplasm.  Usually photo-toxicity does
not seem to be as much of a problem but in this particular case the cells
started retracting not long after initiating imaging.  I rarely see this and I
attributed it to the high amount of protein that seemed to be floating in the
cytoplasm (high fluorescent protein level, more reactive species produced by
photo-breakdown).  To limit the effects of Oxygen-radicals, we routinely use
Oxyrase (30uL/mL media), which the company claims is an oxygen scavenger.
Also, I try to limit expression be using weaker promoters and use lowest light
levels possible for your application.

Good Luck!  Hope this helps!

Mike

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>Hi,
>
>Has anyone noted a deleterious effect on GFP-labeled cells following
>observation of the cells using standard fluorescence microscopy?  The
>cells are looked at for a minute or two - pretty standard length of
>time.  The labeling in question is fairly uniform throughout the cytpoplasm.
>
>Thanks for any thoughts.
>
>Ray Hester
>Univ. of South Alabama
>Mobile, AL
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Michael C. Adams
Microscopy & Imaging Manager for Dr. Clare Waterman-Storer
Laboratory of Cell Motility Studies
Department of Cell Biology
The Scripps Research Institute
Attn: Mail Code CB-163
10550 North Torrey Pines Road
La Jolla, CA 92037

TEL 858.784.9244
FAX 858.784.7521
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