In Situ Detection of Double-Strand DNA Breaks with Terminal 5OH Groups

DNA fragmentation is often used as a marker of programmed cell death in tissue sections. It is a sensitive indicator of apoptosis, particularly when utilized in combination with morphological verification. At least two types of DNA breaks are present in apoptotic cells: 1. Breaks with 3′OH and 5′PO₄ groups at the ends of the break, which can be generated by DNase I and DNase I-like nucleases; 2. Breaks with the inverted distribution of these chemical groups—3′ PO₄ /5′OH, produced by DNase II and DNase II-like nucleases (1-4 ).