TUNEL assay
The TUNEL method ( TdT -mediated dUTP- biotin nick end labeling ) is used to represent nuclei of apoptotic cells. " TdT " stands for " Terminal deoxynucleotidyl transferase ", an enzyme which is used in an intermediate step of the art.
Method
During apoptosis, the deoxyribonucleic acid strand ( DNA strand ) of the nucleus due to the activity of endonucleases is fragmented. The resulting free hydroxy groups at the broken ends (3'- OH) groups are provided by the enzyme TdT using labeled nucleotides, which can be made , for example, on the basis of fluorescence visible with corresponding microscopes.
The method was first described in 1992. On the method was criticized in subsequent years, as a distinction between necrotic and apoptotic cell loss was only partially possible. In the following years it was described how the technique can be modified and improved with regard to occurring problems.