VE-PTP is predominantly expressed on arterial endothelium. (A) Whole-mount β-galactosidase staining of an E12.5 VE-PTP^+/mt embryo showing a distinct vascular pattern of VE-PTP transcriptional activity (represented by the lacZ expression pattern), whereas the same staining of a wild-type littermate (B) was negative. (C-E) Cryosections of an adult VE-PTP^+/mt heterozygous kidney. (C) An arterial vessel (ar) is immunolabeled for PECAM-1 (red) and endothelial nuclei are β-galactosidase stained (blue), recording VE-PTP transcriptional activity. (D) Immunolabeling for VE-PTP with mAb 109.3 (red) and β-galactosidase staining (arrows depict endothelial nuclei). Note that VE-PTP protein and transcriptional expression are more prominent in arterial endothelium (ar) than in venular endothelium (ve). (E) Immunolabeling for endomucin (red) stains predominantly venular endothelium (ve), whereas the β-galactosidase staining is more prominent in nuclei of arterial endothelium (ar). (F) Cryosection of an E12.5 VE-PTP^+/mt embryo stained like sections in panel E. Note transcriptional activity of VE-PTP in the dorsal aorta (da, blue), but only weakly in neighboring venules (v), stained for endomucin (red). Bars represent 500 μm (A-B) and 20 μm. Objectives used: (A-B) Plan S 1 ×/0.085 numeric aperture (NA); (C-F) Plan Apochromat 20 ×/0.60 NA.