Electrophoretic DNA analysis for the detection of apoptosis.

There are many techniques available for the detection of apoptotic cells; some are based on morphological changes, others on biochemical events. However, electrophoretic detection of the systematic cleavage of DNA into oligonucleosomal multimers of 180-200 bp remains the "hallmark" of apoptosis. Conventional constant field agarose gel electrophoresis of DNA from apoptotic cells can be used to resolve the multimers into the characteristic DNA ladders indicative of apoptotic cell death. More recently, it has become clear that the generation of the lower molecular weight oligonucleosomal DNA is preceded by the generation of higher molecular weight fragments. In some cell types, DNA cleavage proceeds no further than the formation of 300 and/or 50 kbp cleavage products. DNA fragmentation of this size can only be resolved using a form of pulsed-field gel electrophoresis. Basic "starter" protocols for conventional and pulsed field electrophoresis for the detection of apoptotic cell DNA are described in this article.