A. Average telomere length ratios in CD34+ stem, Lgr6+ stem, and basal cells from K14Cre;TRF2+/+;Terc+/+, K14Cre;TRF2f/f;Terc+/+, K14Cre;TRF2+/+;Terc-/-, and K14Cre;TRF2f/f;Terc-/- epidermis were determined by qPCR. Error bars represent SEM. Co-localization of 53BP1 (shown by immunofluorescence, AlexaFluor 488) at telomeres (shown by fluorescence in situ hybridization, Cy3) in histopathologic sections from K14Cre;TRF2+/+;Terc+/+ B., K14Cre;TRF2f/f;Terc-/- C., K14Cre;TRF2+/+;Terc-/- D., and K14Cre;TRF2f/f;Terc+/+ E. epidermis is shown. Nuclei are counterstained with DAPI. Scale bar = 5 μm. Phospho-ATM expression in histopathologic sections from K14Cre;TRF2+/+;Terc+/+ F., K14Cre;TRF2f/f;Terc-/- G., K14Cre;TRF2+/+;Terc-/- H., and K14Cre;TRF2f/f;Terc+/+ I. epidermis. Phospho-Chk2 expression in histopathologic sections from K14Cre;TRF2+/+;Terc+/+ J., K14Cre;TRF2f/f;Terc-/- K., K14Cre;TRF2+/+;Terc-/- L., and K14Cre;TRF2f/f;Terc+/+ M. epidermis. p53 protein expression in histopathologic sections from K14Cre;TRF2+/+;Terc+/+ N., K14Cre;TRF2f/f;Terc-/- O., K14Cre;TRF2+/+;Terc-/- P., and K14Cre;TRF2f/f;Terc+/+ Q. epidermis. Representative sections are shown.