NRP1 and microphthalmia: Because endothelial-specific Nrp1 null mutants display microphthalmia and vascular brain abnormalities similar to those of full Nrp1 null and Vegfa120/120 mutants (Gu et al., 2003; Fantin et al., 2010), reduced eye size or defective blood vessel patterning cannot explain the decreased midline crossing of RGC axons in the absence of VEGF164/NRP1 signaling.