title: Protease-elicited TUNEL positivity of non-apoptotic fixed cells.
abstract: The appearance of free DNA ends in the chromatin is usually considered an indication of advanced apoptosis. Unexpectedly, the nuclei of non-apoptotic cells derived from mouse thymuses could be specifically labeled by terminal transferase after proteinase K treatment of the fixed, cytocentrifuged samples. Artifactual mechanical or contaminating nucleolytic factors have been ruled out as players in the generation of free DNA ends. The phenomenon was detected in both formaldehyde- and ethanol-fixed specimens, in agarose-embedded fixed cells, and in chromatin spreads. By urea-agarose gel electrophoresis, the average single-strand size of the DNA molecules carrying the free ends was found between 50 and 250 kb. We suggest that ss discontinuities preexisting in the fixed normal cells are unmasked by protease treatment eliciting TUNEL (terminal transferase-mediated nick end-labeling) positivity.
authors.affiliation: Department of Biophysics and Cell Biology, University Medical School of Debrecen, Debrecen, Hungary.
authors.forename: I
authors.initials: I
authors.lastname: Gál
authors.forename: T
authors.initials: T
authors.lastname: Varga
authors.forename: I
authors.initials: I
authors.lastname: Szilágyi
authors.forename: M
authors.initials: M
authors.lastname: Balázs
authors.forename: J
authors.initials: J
authors.lastname: Schlammadinger
authors.forename: G
authors.initials: G
authors.lastname: Szabó
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D016477:Artifacts; D004247:DNA / Q000378:metabolism*; D053938:DNA Fragmentation / Q000502:physiology; D004587:Electrophoresis, Agar Gel; D019286:Endopeptidase K; D020287:In Situ Nick-End Labeling; D051379:Mice; D008807:Mice, Inbred BALB C; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism
chemical_list: D004247:DNA; D019286:Endopeptidase K