Fig. 5. Blast potential and gene expression patterns of Flk1/GFP-Bry subpopulations. (A) At day 2.5 of differentiation, GFP-Bry EBs were harvested, dissociated and cells fractionated by cell sorting based on their respective GFP and Flk1 expression levels. (B) Blast-CFC potential of the GFP^–Flk1^–, GFP⁺Flk1^– and GFP⁺Flk1⁺ populations. Colonies were scored following 4 days of culture. Data are presented as the mean number of colonies from three dishes. Bars, where visible, represent s.e. of the mean. The purity of sorted cells was 95%. (C) RNA extraction was performed on each fraction as well as the starting population (presort). Gene expression patterns were analyzed by RT-PCR using specific primers for each of the indicated genes. ß-actin expression was used to equilibrate the relative amount of each cDNA.