Cell biology. A widely used method for identifying dying cells.
TUNEL is the abbrevation for terminal transferase dUTP nick end labeling. DNA fragments that result from enzyme activity of endonucleases in apoptotic cells can be visualized by this method. The nucleotide dUTP labeled with a fluorescence marker is bound through the action of the enzyme terminal transferase onto fragmented DNA. The label incorporated at the damaged sites of DNA is visualized by fluorescence microscopy.