Top : Cell Biology : Apoptosis : Terminal Transferase dUTP Nick End Labeling (TUNEL) Assay

Summary: Terminal Transferase dUTP Nick End Labeling (TUNEL) Assay is a method used to detect DNA degradation in apoptotic cells because one of the hallmarks of late stage apoptosis is the fragmentation of nuclear chromatin which results in a multitude of 3’-hydroxyl termini of DNA ends. This property can be used to identify apoptotic cells by labeling the DNA breaks with fluorescent-tagged deoxyuridine triphosphate nucleotides (F-dUTP). The enzyme terminal deoxynucleotidyl transferase (TdT) catalyzes a template-independent addition of deoxyribonucleoside triphosphates to the 3’ hydroxyl ends of double- or single-stranded DNA generates DNA strands with exposed 3'-hydroxyl ends. Addition of the deoxythymidine analog 5‑bromo‑2'‑deoxyuridine 5'‑triphosphate(BrdUTP) to the TdT reaction serves to label the break sites. Once incorporated into the DNA, BrdU can be detected by an anti‑BrdU antibody using standard immunohistochemicaltechniques.Non-apoptotic cells do not incorporate much of the F-dUTP because of absence of exposed 3’-hydroxyl DNA ends.