Fig. 2. BrdU incorporation in metatarsal chondrocytes. E15.5 metatarsals were maintained in organ culture for 48 hours and were labeled with 50 µg BrdU/ml for the last 6 hours of the culture. Histological sections (5 µm) were stained with specific anti-BrdU antibody. The positive cells were visualized by DAB staining. Sections were counterstained with Alcian Blue. (A) Metatarsals from TgFGF are shorter and wider than those of wild type (WT) and Stat1^-/-. Loss of the Stat1 gene in TgFGF (TgFGF/Stat1^-/-) increases the length of the metatarsals in TgFGF/Stat1^-/- mice. (B) Chondrocytes in the proliferating zone labeled with BrdU. The rate of DNA synthesis is higher in WT (62±1%) and Stat1^-/- (66±0.8%) versus TgFGF (34±0.6%). Absence of Stat1 in TgFGF attenuates the inhibitory effect of TgFGF on chondrocyte proliferation (TgFGF/Stat1^-/-, 44±0.5%).