Transfer of the Fgfr-1^−/− phenotype to Fgfr^+/− embryoid bodies by conditioned medium. (A) Immunohistochemical staining for CD31 expression in Fgfr-1^+/− embryoid bodies kept in Fgfr-1^+/−–conditioned medium (CM^+/−), Fgfr-1^−/− embryoid bodies in basal medium (control), and Fgfr-1^+/− embryoid bodies in Fgfr-1^−/−–conditioned medium (CM^−/−). Note the change in vessel morphology in Fgfr-1^+/− embryoid bodies in CM^−/−, mimicking that in Fgfr-1^−/− embryoid bodies. Bottom row of panels shows representative magnifications of the top panels. Bars represent 100 μm. (B) Real-time PCR analyses of Cd31, Vegfr2, and Cd41 transcript levels in embryoid bodies cultured as indicated. (C) Immunostaining for CD41 in Fgfr-1^+/− embryoid bodies kept in basal medium (control) or in CM^−/−. Bars represent 100 μm. (D) Quantification of CD41⁺ area showed significantly lower expression of CD41 in Fgfr-1^+/− embryoid bodies cultured in CM^−/− compared with the regular culture medium (control). *P = .005.