Fig. 3. TUNEL staining of growth plate chondrocytes at P1 and P10. Longitudinal femur sections of wild-type (WT), TgFGF, Stat1^-/- and TgFGF/Stat1^-/- mice at P1 (A) and P10 (B) were analyzed for the presence of apoptotic chondrocytes in the epiphyseal region as well as in the metaphyseal growth plates. Apoptotic chondrocytes were present at high frequency around the secondary centers of ossification in TgFGF at P10 as well as in the proliferating zone. WT femurs show low frequency of chondrocyte DNA fragmentation in the epiphyseal region and in the proliferating zone. In Stat1^-/- mice, the levels of apoptosis is near absent along the femur, except in the hypertrophic zone.