Apoptosis plays a significant role in various stages of cancer cell development growth or proliferation, disappearance, differentiation induced by physical factors (i.e., radiation, heat) and by chemical factors (i.e., medicine). One of the features of apoptotic cells is fragmentation of chromatin DNA at the nucleosome level (185 pb). This fragmented DNA can be detected histochemically by terminal labeling.
Principle
TUNEL, an acronym for Terminaldeoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, is an effective method for measuring the DNA fragments resulting from the apoptotic activation of intracellular endonucleases. Fluorochromelabeled nucleotides are incorporated in situ onto the ends of these DNA fragaments, allowing histologic localization and individual cells to be detected. TUNEL method uses Terminal deoxynucleotidyl Transferase to label 3'-OH ends of DNA fragments that are generated during the apoptosis process. The cells undergoing apoptosis are specifically labeled with fluorescein-dUTP with high sensitivity, allowing immediate detection by fluorescence microscopy. Since incorporated fluorescence can also be detected by a peroxidase-labeled anti-fluorescence antibody, it is also possible to detect with light microscopy.
