Vascular defects in Tie2-Cre conditional and full Nrp1-null mutants. (A-D) PECAM immunohistochemistry of E12.5 SVP vessels of the indicated genotypes. Clear arrowheads indicate examples of vascular tufts; clear arrows and solid arrows indicate examples of vascular interconnections in the SVP versus deeper brain layers, respectively. Scale bar represents 100 μm. (E) Quantitation of SVP branchpoints at E12.5; error bars represent SD; asterisks indicate P values; **P < .001; ***P < .0001.