Bcl-x is dispensable for normal development of primitive erythroid colonies. (A) Primitive erythroid (EryP) precursors were enumerated after secondary replating of 6-day-old embryoid bodies derived from in vitro differentiation of bcl-x^+/− and bcl-x^−/− ES cells. EryP colonies were generated in methylcellulose cultures containing Epo. Similar results were obtained using two independently derived bcl-x^−/− ES cell clones (nos. 48 and 99). Bcl-x^−/− EryP colonies shown in B are from clone no. 48. Error bars represent standard error of the mean from three separate cultures. (B) bcl-x^+/− and bcl-x^−/− EryP colonies exhibit similar morphologies. Five-day-old colonies are shown. Original magnification × 400.