Loss of Endosialin leads to a defect in selective vessel regression. (A) Retinas from littermate Endosialin^+/+, Endosialin^+/−, and Endosialin^−/− C57BL/6 mice were stained with FITC–isolectin B4 (green), the basement membrane marker collagen IV (red), and DAPI (blue). Left panel, representative confocal images from P5 retinas. Arrowheads show collagen IV–positive, isolectin B4–negative empty sleeves indicating vessel regression. Scale bar indicates 25 μm. Right panels, quantification of mean number of empty sleeves ± SEM. Endosialin^+/+: P4, n = 4; P5, n = 7. Endosialin^+/−: P4, n = 5; P5, n = 5. Endosialin^−/−: P4, n = 3; P5, n = 3. (B) B16-F0 melanoma xenografts grown for 14 days in Endosialin^+/+ or Endosialin^−/− mice (mean tumor diameter, 7.1 mm) were formalin fixed, paraffin embedded, and sections were stained for collagen IV (green) and endomucin (red). Nuclei were counterstained with DAPI (blue). Arrowheads show collagen IV–positive, endomucin-negative empty sleeves. Scale bar indicates 100 μm. Graphs show the distribution of vessel size and the number of empty sleeves as a percentage of total vessels ± SEM. Endosialin^+/+: n = 3; Endosialin^−/−: n = 3.