(a) Mean number of TAF per cell increases exponentially with age in hepatocytes from male C57BL/6 mice (exponential curve provided best fit with R=0.98; P=0.01) mean±s.e.m. of n=3 per age group. (b) Percentage of TAF increase linearly with age in hepatocytes from male C57BJ6 mice (R=0.92; P=0.02) mean±s.e.m. of n=3 per age group. (c) Representative immuno-FISH images of hepatocytes from 12-month- (left) and 42-month-old (right) mice. Green: γH2A.X; red: telomeres; blue: DAPI, Scale bar: 3 μm. (d) Mean number of TAF per cells increases exponentially with age in the small intestine enterocytes from male C57BL/6 mice (exponential curve provided best fit with R=0.95; P=0.02), mean±s.e.m. of n=3 per age group. (e) Percentage of TAF increases linearly with age in enterocytes from male C57BL/6 mice (R=0.98; P=0.007) mean±s.e.m. of n=3 per age group. (f) Representative immuno-FISH images in mice crypts at different ages. Boxed areas indicate colocalization between γH2A.X and telomeres, and are shown at higher magnification on the right (telomeres: red; γH2A.X: green and nucleus: DAPI; images are from one single Z plane), Scale bar: 20 μm. (g) Immuno-FISH images of 12-, 22-, 36- and 42-month-old mice colour coded according to degree of colocalization between γH2A.X and telomeres (white: low colocalization; red: high colocalization). (h) Histograms showing telomere intensity for telomeres colocalizing (bottom) or not colocalizing (top) with DNA damage foci in both the liver and gut from 36-month-old mice (n=3); red dotted line represents median intensity. Mann–Whitney test shows no significant difference in telomere intensities distribution between TAF and non-TAF for the small intestine (gut) (P=0.08) and a slight increase in liver telomere intensity in non-TAF (P=0.002). Intensity of 1,000 telomeres was analysed per condition. (i) Mean number of non-TAF per cell does not increase with age in small intestinal enterocytes from male C57BL/6 mice (linear curve provided best fit with R=0.77; P=0.12) mean±s.e.m. of n=3 per age group. (j) Mean number of non-TAF per cell does not increase with age in hepatocytes from male C57BL/6 mice (exponential curve provided best fit with R=0.86; P=0.07) mean±s.e.m. of n=3 per age group.