Assessment of apoptosis and necrosis by DNA fragmentation and morphological criteria

Apoptotic cells share a number of common features, such as phosphatidylserine (PS) exposure, cell shrinkage, chromatin cleavage, nuclear condensation, and formation of pyknotic bodies of condensed chromatin. Necrotic cells exhibit nuclear swelling, chromatin flocculation, loss of nuclear basophilia, breakdown of cytoplasmic structure and organelle function, and cytolysis by swelling. This unit describes some of the techniques most commonly used to detect cell death. A number of assays are used for characterizing and distinguishing apoptosis and necrosis. Morphological assays include trypan blue exclusion, differential staining, and Hoechst staining. Methods to detect chromatin cleavage include TUNEL assays for whole cells and paraffin sections, DNA fragmentation assays using whole cells, assays of total genomic DNA, analysis of DNA fragmentation by agarose gel electrophoresis, phenol extraction of DNA for analysis of fragmentation, a quantitative assay for DNA fragmentation, and detection of DNA fragmentation by pulsed-field gel electrophoresis. A protocol is also provided for Cytospin preparations from cell suspensions.