Fig. 3. Runx1 expression in the allantois and chorion does not require chorio-allantoic fusion. (A) Allantois (al) explant culture on plastic (48 hours) from a Runx1^lz/+ conceptus showing Runx1 expression (blue) (3.2x). (B) Chorion (ch) explant culture on plastic from a Runx1^lz/+ conceptus (3.2x). (C) Allantois sphere cultures (48 hours) from Runx1^lz/+ (lz/+) and wild-type (+/+) conceptuses (left). Right hand panels are nuclear fast red stained histological sections of whole mount preparations of allantoic spheres showing Runx1 expression predominantly in mesothelium on the surface of the sphere. (D) Tg(Ly6a/GFP) (Sca-1) expression from the freshly isolated allantois and chorion and following 24 hours of culture on OP9 cells.