Analysis of gene expression and colony formation of ES-EPs. (A) Semiquantitative RT-PCR analysis of hematopoietic-specific genes expressed in undifferentiated ES cells (ES), 20-day-old ES-EP cultures from day 7 EBs, and freshly prepared bone marrow (BM) is shown. ES-EPs express erythroid-specific genes but none of the tested genes characteristic of myeloid or B-lymphoid cells. (B) ES-EPs express adult but not fetal globins, as shown by semiquantitative RT-PCR analysis of the globin chains indicated. (C) Colony formation ability of ES-EPs was measured. Mean values of 3 independent experiments plus or minus the standard deviation (SD) are shown.