PTN neutralization attenuates Fgfr-1^−/−–mediated vascularization. (A) Fgfr-1^−/− embryoid bodies treated with PTN neutralizing antibodies (anti-PTN, 3 μg/mL) from day 4 to day 8 showed reduced CD31 immunostaining (red) compared with control IgG treatment (control IgG). Bars represent 100 μm. (B) Quantification of CD31⁺ vessel length in Fgfr-1^−/− embryoid bodies treated with anti-PTN or control IgG. *P < .001. (C) CD31 immunoreactivity (red) in Fgfr-1^+/− or Fgfr-1^−/− embryoid bodies kept in basal medium (control) or treated with CM^−/− with and without anti-PTN antibodies (3 μg/mL) as indicated from day 4 to day 8. Bars represent 100 μm. Lower panels show higher magnification. Bars represent 100 μm. (D) Quantification of CD31⁺ length in the embryoid body cultures (n = 6-8 for each condition) kept in the different conditions in panel C. Statistical analysis of the different conditions (FGFR-1^+/− CM^−/− compared with FGFR-1^+/− Control, and FGFR-1^+/− CM^−/− α-PTN compared with FGFR-1^+/− CM^−/−) showed significant differences (*P < .028).