Figure 3
![Figure 3](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1477-7827-12-121/MediaObjects/12958_2014_Article_1289_Fig3_HTML.jpg)
Schematics of the DNA damage by the TUNEL assay. (1) Labeling of DNA strand breaks with TdT, which catalyzes the polymerization of labeled nucleotides to free 3′-OH DNA ends in a template-independent manner (TUNEL reaction) and (2) Fluorescein isothiocynate (FITC)-dUTP is incorporated into nucleotide polymers, and it can be directly detected and quantified by flow cytometry.