Expression of vascular markers in differentiating ES cell cultures.

Wt (^+/+) (A,D,G,J), flt-1^+/−(B,E,H,K), and flt-1^−/− (C,F,I,L) ES cell cultures were fixed on day 5 (A-F) or day 6 (G-L) and labeled with antibodies to PECAM (A-C,G-I) or VE-cadherin (D-F,J-L), and the appropriate fluorescent-labeled secondary antibody. Arrows (C,F) point to sparse PECAM⁺ and VE-cadherin⁺ cells in day 5 flt-1^−/− cultures. Original magnifications ×20, except D-F at ×40.