AAV9-Tert treatment causes telomere elongation in blood and bone marrow. (A) Longitudinal HT-Q-FISH analysis of telomere length in peripheral blood monocytes (Trf1^lox/loxMx1-Cre–transplanted mice; see also Figure 2A). Blood was extracted at 4 different time points (time point 1, before pI:pC treatment; time point 2, after 5 weeks of pI:pC treatment and before AAV9 injection; time point 3, 2 months after AAV9 injection; and time point 4, 4 months after AAV9 injection). Relative variation (Δ) of telomere length in AAV9-Tert-treated and AAV9-empty-treated animals between time points 2 and 4 (B) and between time points 1 and 4 (C). (D) Relative telomere length in bone marrow sections from AAV9-Tert-treated and AAV9-empty-treated mice shown as arbitrary units of fluorescence (a.u.f.). Each square and triangle represents the mean telomere length per nucleus of an individual mouse. (E) Frequency distribution blot of telomere length showing a higher abundance of short telomeres in the AAV9-empty-treated group compared with AAV9-Tert-treated mice (pooled data from panel D). (F) Representative images of bone marrow sections from AAV9-Tert-treated and AAV9-empty-treated mice used for Q-FISH analysis. Cell nuclei are stained blue (DAPI) and telomeres are stained red (Cy3). White arrowheads indicate nonspecific extranuclear signals and yellow arrowheads indicate specific telomere signals within DAPI-stained nuclei. Bars represent 20 μm (top) and 10 μm (bottom). In all graphs, n indicates number of mice. Data are mean ± SEM. Statistical analysis: 2-way analysis of variance in panel A; 2-sided Student t test in panels B and C; P values are shown. a.u., arbitrary units.