Detection of the initial stages of DNA fragmentation in apoptosis

DNA fragmentation during apoptosis proceeds through an ordered series of stages commencing with the production of DNA fragments of 300 kbp, which are then degraded to fragments of 50 kbp. The 50-kbp fragments are further degraded, in some but not all cells, to smaller fragments (10-40 kbp) and release the small oligonucleosome fragments that are recognized as the characteristic DNA ladder on conventional agarose gels. Methodology is presented for the detection of the initial stages of DNA fragmentation using pulsed-field gel electrophoresis or a combination of pulsed-field gel electrophoresis and conventional agarose gel electrophoresis that allows detection of the DNA ladder in the same sample. A new method for the detection of high molecular weight DNA fragments on conventional agarose gels is presented, together with a rationale for the analysis of DNA fragmentation during apoptosis.