Fig. 5. Apoptosis in Vegfa conditional knockout (CKO) bones. Histological sections through the center of E18.5 unaffected (A,C) and Vegfa CKO (B,D) humerus. Areas within the squares in A and B are shown at high magnification in C and D. In the affected epiphysis (D), the presence of apoptotic cells with shrunken cytoplasm and condensed nuclei is observed. TUNEL assay of E18.5 unaffected (E) and Vegfa CKO (F) humerus and Vegfa CKO tibia and femur (G) shows strong TUNEL-positive signals in regions of apoptotic cells (arrowheads) in the Vegfa CKO bones (E and F are serial sections of A and B, while G is serial section of Fig. 4 D). Histological sections of E16.5 Prx1/Vegfa CKO scapula and humerus show misshapen bones with extensive regions of dead cells (H, arrowheads).