Fig. 5. Expression analysis of VEGF and its receptors, VEGFR1 (vR1), VEGFR2 (vR2) and neuropilin 2 (np2) in the developing tibia. No significant differences are observed in VEGF expression between wild-type (A) and VEGF^120/120 (B) mice at E15.5 (arrowheads define the regions of VEGF expression). At E15.5, there is significantly higher level of expression of VEGFR1 and VEGFR2 in wild-type tibia (C,E, arrowheads) than in VEGF^120/120 tibia (D,F, arrowheads). No significant differences are observed in neuropilin 2 expression between wild-type (G) and VEGF^120/120 (H) mice at E15.5. At E16.5, there is a significantly stronger signal for VEGFR-1 and VEGFR-2 in wild-type tibia (I,K, arrowheads) than in VEGF^120/120 tibia (J,L, arrowheads). At E16.5, there is a dramatic difference in the expression of neuropilin 2 in wild-type mice (M, arrows) when compared with VEGF^120/120 mice (N, arrows).