Figure 6. SIRT6 overexpression in aged oocytes partly prevented the defective phenotype of early embryos. (A) Representative images of young, old, and SIRT6-OE two-cell embryos stained with antibodies against TRF1 (red) and γH2AX (green), and co-stained with Hoechst 33342 for chromosomes (blue). Scale bars, 25 µm. (B) Quantification of DNA damage-induced foci (TIFs) from (A). TIFs were detected by co-localization of TRF1 and γ-H2AX, and cells with at least 3 TIFs were scored (n=26 for young; n=28 for old; n=25 for old+SIRT6-OE). (C) TUNEL analysis of young, old, and SIRT6-OE embryos. Embryos were labeled with Hoechst 33342 (blue) for DNA and by TUNEL for fragmented DNA (red). Arrowheads point to the apoptotic cells in blastocysts. Scale bars, 25 μm. (D) Quantification of young (n=90), old (n=82), and SIRT6-OE (n=78) blastocysts with TUNEL positive nuclei. Data are expressed as mean percentage ± SD from three independent experiments. ** P<0.01, ***P<0.001.