Key morphological features of apoptosis may occur in the absence of internucleosomal DNA fragmentation.

Apoptosis, a major form of cell death, is characterized by chromatin condensation, a reduction in cell volume and endonuclease cleavage of DNA into oligonucleosomal length fragments. The detection of these fragments by gel electrophoresis, as a DNA ladder, is currently used as the major biochemical index of apoptosis. Here we report that key morphological changes of apoptosis can be dissociated experimentally from the DNA fragmentation produced by endonuclease activity. Internucleosomal cleavage of DNA is thus likely to be a later event in the apoptotic process.