Developmental defects in VE-PTP-lacZ homozygous embryos. (A) Normal vascularization in an E9.5 wild-type yolk sac. (B) Pale yolk sac of a VE-PTP^mt/mt embryo with blood islands (arrows). (C) Growth retardation in a rare E10.0 homozygous VE-PTP mutant, stained for β-galactosidase. The VE-PTP^+/mt embryo on the left had 25 somite pairs, whereas its VE-PTP^mt/mt littermate on the right was less than half the size and had only 10 somite pairs. (D) Pale-looking E9.5 VE-PTP homozygous mutant embryo with severely enlarged pericardium (asterisk). d indicates dorsal; v, ventral. (E-H) E9.0 embryos immunostained as whole mounts for PECAM-1. (E) Well-organized cerebral vascular network (arrows) in an E9.0 wild-type embryo brain. (F) Disconnected clusters of endothelial cells (arrows) in a VE-PTP^mt/mt littermate. (G) Well-defined intersomitic sprouts (asterisks) in an E9.0 wild-type embryo, whereas intersomitic vessels (arrows) failed to develop in a homozygous mutant embryo (H). Bars represent 1 mm. A Plan S 1 ×/0.085 NA objective was used to visualize all images in these panels.