Substantial Background Reduction in Ligase-Based Apoptosis Detection Using Newly Designed Hairpin Oligonucleotide Probes

A ligase-based assay for selective detection of apoptosis in tissue sections utilizing oligonucleotide probes was recently reported (1). This assay detects apoptosis when it is accompanied by internucleosomal DNA cleavage with the production of multiple double-strand breaks and electrophoretic ladder-type DNA fragmentation. Detection of double-strand breaks in apoptotic DNA in this assay is via ligation of labeled double-stranded DNA fragments to the ends of DNase I type breaks (1). Unlike conventional terminal transferase-based labeling (TUNEL), the assay stains apoptotic but not necrotic or transiently damaged cells (1,2). The major drawback of the assay, limiting its usefulness, is high background staining caused by nonspecific binding of the probe to the cells in the tissue sections.