Protease-elicited TUNEL Positivity of Non-apoptotic Fixed Cells

• Published in: The journal of histochemistry and cytochemistry Vol. 48; no. 7; pp. 963 - 969
• Main Authors: Gal, Istvan, Varga, Tamas, Szilagyi, Ildiko, Balazs, Margit, Schlammadinger, Jozsef, Szabo, Gabor, , Jr
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA Histochemical Soc 01.07.2000; SAGE Publications
• Subjects: Animals; Apoptosis - physiology; DNA - metabolism; DNA Fragmentation - physiology; Electrophoresis, Agar Gel; Endopeptidase K; In Situ Nick-End Labeling; Mice; Mice, Inbred BALB C; Thymus Gland - cytology; Thymus Gland - metabolism; protease; apoptosis; TUNEL; chromatin; fragmentation
• ISSN: 0022-1554; 1551-5044
• DOI: 10.1177/002215540004800709

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 transferasemediated nick end-labeling) positivity.