Fig. 4. VEGF-lacZ expression in developing limb and calvarium. At E13.5, there is robust expression of VEGF in the periochondrium and surrounding tissues (arrow) of the radius (r) and ulna (u) as observed in whole-mount (A) and histological sections (B). In the calvarium at E13.5, expression of VEGF can be seen (C, arrows; b, brain), and this expression is stronger at E14.5 in the region of mesenchyme that is destined to differentiate into osteoblasts (D, area of expression defined by bracket; b, brain). At E14.5, VEGF expression is associated with cells covering the surface of calvarial bone (E, arrows; c, cranial base cartilage) in regions where osteoid and mineral are being deposited.