Sprouting angiogenesis is not affected by loss of Endosialin. Retinas were stained with FITC–isolectin B4 (green) and NG2 followed by Alexa Fluor 555–anti–rabbit Ig (red). (A) Confocal images of P3 Endosialin^+/+ and Endosialin^−/− 129/SvJ retinas taken at the sprouting front of the expanding vasculature showing no difference in the alignment of tip cell filopodia (arrowheads) with the underlying NG2-positive astrocyte network (arrows). Scale bars indicate 50 μm. Graph shows quantification of tip cell number. (B) Vessel density in the sprouting plexus was analyzed immediately behind the sprouting front (indicated by asterisk in panel A). Graph shows quantification of vessel density at the sprouting front ± SEM. No significant difference was observed at any time point. For panels A and B, 129/SvJ Endosialin^+/+: P3, n = 6; P4, n = 3; Endosialin^−/− P3, n = 8; P4, n = 4. C57BL/6 Endosialin^+/+: P2, n = 3; P3, n = 7; P4, n = 4. Endosialin^+/− P2, n = 4; P3, n = 4; P4 = 4. Endosialin^−/−: P2, n = 2; P3, n = 3; P4, n = 7. (C) Left panels show representative low-power images of 129/SvJ P3 retinas. Scale bar indicates 500 μm. Right panels show quantification of the radial expansion of the vascular plexus at each time point ± SD. No significant difference was observed at any time point. 129/SvJ; Endosialin^+/+: P3, n = 3; P4, n = 4; P5, n = 4; P6, n = 4, P7, n = 2. Endosialin^−/−: P3, n = 2; P4, n = 2; P5, n = 3; P6, n = 4, P7, n = 3. C57BL/6; Endosialin^+/+: P2, n = 3; P3, n = 3; P4, n = 3. Endosialin^+/−: P2, n = 4; P3, n = 2; P4, n = 4. Endosialin^−/−: P2, n = 2; P3, n = 3; P4, n = 4.