American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

The Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay is a highly effective method for detecting apoptosis in tissues. This technique specifically labels DNA fragments that are generated during the later stages of apoptosis, allowing for the visualization of dying cells.

In the TUNEL assay, terminal deoxynucleotidyl transferase (TdT) enzyme incorporates modified nucleotides (usually dUTP conjugated to a fluorescent dye) at the sites of DNA strand breaks typical of apoptotic cells. Once the cells are prepared and treated with the TdT enzyme, the labeled cells can be visualized under a fluorescence microscope, revealing the extent and location of apoptosis within tissue sections.

This method is particularly valuable because it focuses on the hallmark feature of apoptosis: the fragmentation of DNA at the later stages of the cell death process. It is a reliable and established technique for researchers studying apoptosis in various biological contexts, such as cancer, neurodegenerative diseases, and developmental biology.