In vitro characterization of interaction between yolk sac–derived E10.5 definitive hematopoietic progenitors and stromal cells. (A) Total number of CAFCs per yolk sac of E10.5 F2 embryos. Data represent means (± SD) of 3 independent experiments. *P < .05, TGRac1^Flox/null versus littermate controls (N = 3). (B) Survival of definitive hematopoietic progenitors from the yolk sac at E10.5 in a hanging drop organ culture with AFT024 stroma cells (“Methods”). Data represent means (± SD) of 3 independent experiments (N = 3). There was no significant difference between genotypes. ■ indicates littermate control; □, TGRac1^Flox/null.