Fig. 4. CFU-GEMM colonies obtained from E15 placenta, yolk sac and liver cells after 14 days of culture in methylcellulose-based medium. (A-C) Phase contrast. (D-F) May-Grünwald-Giemsa staining. (A,D) Placenta. (B,E) Yolk sac. (C,F) Liver. Placenta colonies are characterized by a very large, highly hemoglobinized center. Cytology reveals a different degree of erythroid maturity depending on the organs: early erythroblasts predominate in the placenta; late erythroblasts (small, deeply basophilic, arrows in E) are numerous in the yolk sac; fetal liver displays mainly erythrocytes expelling their nucleus (arrows in F).