Fig. 6. Relationship between the GFP^–Flk1^–, GFP⁺Flk1^– and GFP⁺Flk1⁺ subpopulations. (A) At day 3 of differentiation, GFP-Bry EBs were harvested, dissociated and cells fractionated by cell sorting based on their respective GFP and Flk1 expression levels (pre-culture). Each subpopulation was allowed to reaggregate in culture for 20 hours. At this stage, EB-like structures were harvested, dissociated and stained for Flk1 expression (post-culture). (B) Blast-CFC potential of the GFP^–Flk1^–, GFP⁺Flk1^– and GFP⁺Flk1⁺ populations immediately after cell sorting (pre-culture) or after the 20-hour culture step (post-culture). Colonies were scored after 4 days of culture. (C) Hematopoietic potential of the same fractions as above. Cells were replated in methylcellulose cultures containing cytokines appropriate for hematopoiesis differentiation. Colonies were scored after 6 to 8 days of culture and designated as follows: Mac, macrophages; Mix, multi-lineage; EryP, primitive erythroid. Data are presented as the mean number of colonies from three dishes. Bars, where visible, represent s.e. of the mean.