In Situ Detection of Apoptosis by the TUNEL Assay: An Overview of Techniques
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Apoptosis, or programmed cell death, plays an important role in normal development and homeostasis of adult tissues. Apoptosis
has also been linked to many disease states, including cancer. One of the biochemical hallmarks of apoptosis is the generation
of free 3′-hydroxyl termini on DNA via cleavage of chromatin into single and multiple oligonuleosome-length fragments. The
TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay exploits this biochemical hallmark by labeling the exposed termini
of DNA, thereby enabling visualization of nuclei containing fragmented DNA. This review outlines the general method for in situ
TUNEL staining of cultured cells and tissue sections, and highlights recent improvements in the technique and limitations
of the assay.
