Quantifying Telomeric DNA Damage Foci

After deparaffinization, rehydration, and antigen retrieval, tissue sections were incubated with PNA probe (800 ng/ml, Panagene Inc., Daejeon, Korea) diluted in hybridization buffer (for 5 min at 80°C, then for 2 h at 37°C). After hybridization, sections were washed, incubated with blocking buffer, and finally stained for 53BP1, as described^{23 (link)}. To analyze the relationship between DNA damage foci and uncapped telomeres, potential colocalization of 53BP1-foci (IFM) and telomere signal (FISH) was quantified in epidermal cells by visual inspection. For every skin sample, at least 400 basal cells and/or 40 53BP1 + basal cells were analyzed for telomeric 53BP1-foci.