Induction of differentiation of ES cells in vitro. (A) CCE ES cells were allowed to differentiate in a type IV collagen-coated dish for 4 days. Expression of FLK1 and E-cadherin on the CCE cells before (left panel, day 0) and after (middle panel, day 4) the induction was analyzed by flow cytometry. FLK1⁺E-cadherin⁻ cells were sorted and reanalyzed (right panel). (B) The ES cell-derived FLK1⁺E-cadherin⁻ cells were cultured in a gelatin-coated dish for 3 days. Expression of CD45, TER119, and 4-integrin on the total cells (left panel) and VE-cadherin and 4-integrin on the CD45⁻ TER119⁻ cells (right panel) was analyzed. The numbers indicate the percentage of cells that appeared in each quadrant. The result shown is a representative of more than five independent experiments.