FACS

PI staining for apoptosis
During apoptosis, the caspases can also activate other degradation enzymes such as DNases, which begin to cleave the DNA at the linker regions between oligonucleosomes2. The result of these biochemical events is the appearance of morphological changes in the cell and extensive DNA cleavage. The products of DNA degradation are nucleosomal and oligonucleosomal DNA fragments (180 bp and multiples of 180 bp), which generate a characteristic "ladder" pattern during agarose gel electrophoresis3

Because DNA fragments are lost from apoptotic nuclei and nuclear DNA content can be easily measured by flow cytometry, after nucleic acid staining with specific fluorochromes5, methods have been developed for a quantitative evaluation of apoptotic nuclei.

~ Nature Protocols 1, - 1458 - 1461 (2006)