Vasculo-angiogenesis in P-Sp culture. P-Sp explants derived from E9.5 CBP homozygous mutant embryos and CBP wild-type littermates were cultured on OP9 stromal cells. Note that vascular bed and vascular network formation were defective in mutant embryo explants compared with that of wild-type littermates. VEGF (100 ng/mL) was added to the culture system as noted above. Vascular bed (vb) and vascular network (vn) formation were partially rescued in CBP homozygous mutants by addition of VEGF. However, note that vascular bed and network formation of P-Sp explants from CBP homozygous mutant embryos was poorer than that of wild-type littermates. Scale bar indicates 50 μm.