A rapid and sensitive assay for the detection of DNA fragmentation during early phases of apoptosis

Apoptosis, or physiologic cell death, is an endogenous cellular process whereby senescent, DNA-damaged or diseased cells are eliminated from the body. Classically, apoptotic cells are identified by distinct morphological criteria in histological preparations (1). Apoptosis has been characterized biochemically by the activation of a nuclear endonuclease that cleaves the DNA into multimers of 180—200 basepairs and can be visualized as an 'oligosomal ladder' by standard agarose gel electrophoresis (2). Recently, however, it has become apparent that the 'ladder' formation in lymphocytes is a very late and probably terminal event in a highly regulated biochemical and molecular cascade of events leading to activation Of endonucleases, DNA degradation and cell death (3). Additional evidence suggests that apoptosis in cells of epithelial or mesenchymal origin may not involve DNA degradation into oligonucleosomal multimers and that different forms of the endonuclease appear to be active in different cell types (3,4). Research interest in the initial signal transduction pathway leading to the activation of the nuclear endonuclease(s) has escalated because it has become apparent that an understanding of the regulation and nature of the apoptotic endonuclease (5), has major implications for the genesis and prevention of cancer (5,6), teratogenesis (1) and normal and abnormal cell differentiation (7).