Fig. 3. Hypoxia influences the kinetics of mesoderm differentiation. Flow cytometry was performed on dissociated cells obtained from EBs harvested at the indicated time points. (A) The number of FLK1⁺ cells detected in differentiated Arnt^+/+ EBs is increased by hypoxic conditions. In direct contrast, the number of FLK1⁺ cells in two independent Arnt^–/– cell lines is reduced in normoxia and is not enhanced by 3% O₂. (B) Hypoxia stimulates the production of GFP⁺ cells in GFP-BRY ES cells as early as day 2 of differentiation.