NRP1 expression by neural progenitors is not essential for brain vascularization. (A-A″) Single xy scan through an E10.5 hindbrain carrying the constitutively active Nes-Cre transgene and the Rosa26^Yfp reporter, labeled for YFP (green), NRP1 (red), and IB4 (blue), all shown together in (A) or as double YFP/IB4 (A′) and single NRP1 (A″) channels. Scale bar represents 50 μm. (B-D) Immunofluorescent staining for NRP1 of 20-μm thin, frozen sections from E10.5 control Nrp1^fl/+, Nrp1^fl/–, and mutant Nes-Cre;Nrp1^fl/– hindbrains. Scale bar represents 50 μm. (E,F) PECAM immunohistochemistry of E12.5 littermate hindbrains of the indicated genotypes; scale bar represents 100 μm. (G) Quantitation of SVP branchpoints at E12.5; error bars represent SD; n.s., not significant.