Fig. 6. Bmp signaling is essential for blood vessel formation and is a mediator of the vasculogenic activity of Foxf1. Explants of E8.25 allantoic buds (A-F) and Smo^-/- E9.5 yolk sacs (G,H) were cultured in vitro for 24 hours followed by staining with Pecam antibody to visualize the capillary network. (A-C) Allantoic explants from wt mouse embryos grown in the absence (A) or presence (B,C) of the Bmp antagonist noggin at 1 (B) or 10 (C) ng/ml. (D-F) Rescue of blood vessel formation in Foxf1^-/- explants by exogenous Bmp4. (D) Normal vasculogenesis in Foxf1^-/+ explant. (E) Foxf1^-/- allantoic cells express Pecam, but fail to form a distinct vascular plexus. (F) Addition of 0.1 ng/ml Bmp4 to Foxf1^-/- explants restored formation of the capillary network. (G,H) The yolk sac from an E9.5 Smo^-/- embryo was dissected, cut in half and left- and right-hand sides spread on separate filters with (H) or without (G) Bmp4 (0.1 ng/ml) in the medium. After 24 hours in culture, explants were fixed and stained with Pecam antibody. Low-magnification images (top) show the entire explants and higher magnification views (bottom) show the formation of a vascular plexus in response to Bmp4.