TRF1 deletion progressively leads to pancytopenia and histopathologically proven BMF but not to telomere shortening. (A) PCR for wild-type and floxed TRF1 confirmed the absence of remaining recipient wild-type bone marrow in TRF1^flox/floxMx1-wt (lane 3 + 4) and TRF1^flox/floxMx1-Cre (lane 5 + 6). Genomic control DNA of TRF1^wt and TRF1^flox/flox are shown (lane 1 + 2). (B) Hematoxylin and eosin staining of the sternal bone marrow of TRF1^flox/floxMx1-wt and TRF1^flox/floxMx1-Cre animals without Cre induction and after +18 days. Image was captured with ×10 magnification (blue bar represents 200 μm), small image shows ×40 magnification. (C) Peripheral blood counts measured twice a week of TRF1^flox/floxMx1-wt and TRF1^flox/floxMx1-Cre mice. No statistical difference was found at day 0 in all subpopulations between TRF1^flox/floxMx1-wt and TRF1^flox/floxMx1-Cre mice (all P > .05) except for thrombocytes (P = .005). At day +18, all TRF1^flox/floxMx1-Cre mice showed statistically significant lower peripheral blood counts (all P < .005) except for hemoglobin levels (P = .55). Two-sided t test was used for statistical comparison. (D) Western blot analysis of TRF1 protein levels of bone marrow protein extracts of TRF1^flox/floxMx1-wt and TRF1^flox/floxMx1-Cre animals without pI-pC injections and after +18 days. Two different exposure times are shown. (E) Quantification of TRF1 protein levels in relation to actin protein levels (without pI-pC, dark gray bars and with pI-pC, light gray bars). Two-sided t test was used for statistical comparison. (F) Telomere length analysis using Q-FISH of sternal bone marrow sections of TRF1^flox/floxMx1-wt and TRF1^flox/floxMx1-Cre animals without (dark gray bars) and after 18 days of pI-pC treatment (light gray bars). Two-sided t test was used for statistical comparison.