Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick-End Labeling Assay (TUNEL Assay)

Definition - What does Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick-End Labeling Assay (TUNEL Assay) mean?

Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick-End Labeling (TUNEL) is a method that utilizes an enzyme called terminal deoxynucleotidyl transferase (TdT) for detecting sperm DNA damage. The TUNEL test can identify infertile men in whom sperm DNA damage may be contributing to infertility as evidenced by elevated sperm DNA fragmentation. DNA fragmentation is the breakage of the bonds between the two strands of the DNA.

FertilitySmarts explains Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick-End Labeling Assay (TUNEL Assay)

In most cases, male factor infertility is caused by semen abnormality such as a low count. However, it is now clear that sperm DNA damage can also contribute to repeated pregnancy losses as well as to the failure of assisted conception. There are several methods to detect sperm DNA damage. One of such assays is the TUNEL assay.

The TUNEL assay is performed with specialized kits following a strict protocol. The semen sample is run within these kits. An enzyme named TdT is allowed to interact with and label the blunt ends of double-stranded DNA breaks by catalyzing the addition of labeled dUTPs (deoxyuridine triphosphate) to one of the terminal ends of DNA. The incorporated dUTPs are detected using flow cytometry or fluorescent staining. The damaged cells will incorporate much of the dUTP owing to the presence of exposed or damaged DNA ends. In contrast, viable and relatively undamaged cells are unable to incorporate much of the dUTP because of the absence of exposed DNA ends.

The TUNEL assay has a limited value in correctly identifying infertile men. This shortcoming is probably due to the compact nature of the sperm chromatin, which prevents TdT from conveniently interacting with the DNA strand breaks.

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