Fig. 9. Vascularization in the vicinity of Vegfa conditional knockout (CKO) cartilaginous elements. CD31 immunostaining of unaffected (A) and Vegfa CKO (B,C,D) tibias at E16.0. Comparison of histologically comparable sections of unaffected (A) and Vegfa CKO (B) knee joint regions reveals no major difference in CD31 immunostaining (arrowheads). Extensive vascularization in the vicinity of the diaphyses and the epiphyses of Vegfa CKO knee joint region (C, arowheads). In D, an area indicated by a square in B shown at high magnification, CD31-positive blood vessels are seen in the vicinity of a region of initial cell death between the femur (f), tibia (t), and the anterior cruciate ligament (l).