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We recently purchased anti-PCNA (and the corresponding blocking peptide) for
use as a marker of cell proliferation. Mouse proximal tubule cells (renal
epithelial cells) were grown on collagen-coated chamber slides or
semipermeable supports. Cells were fixed, treated with 10 mM citrate, pH 6,
(for antigen retrieval), permeabilized, and incubated with anti-PCNA (1:100)
followed by an AlexaFluor-IgG conjugate. Immunofluorescence showed that most
of the immunoreactive material (approximately 80%) was localized to the
cytosol, and only 10 - 20% was found in the nucleus. The blocking peptide
effectively competed away about 80% of the immunofluorescence. --- The
expectation was that most of the immunoreactive material would be found in
the nuclei of actively dividing cells and thus serve as a suitable marker of
proliferation. Only a small amount, if any, was expected in the cytosol. Can
you help explain my results? Alternatively, can you suggest another marker
for cell proliferation?

Thanks,

Phil