Fig. 9. (A) Cardiac cell differentiation in wild-type (wt) and HIF-1^-/- ES cells. Expression of CT-1 during differentiation (B) and upon incubation with menadione (20 µM) and CoCl₂ (50 µM) (C,D). In HIF-1^-/- ES cells cardiomyogenesis was completely absent as evaluated by counting the number of spontaneously contracting embryoid bodies (A). Furthermore, no upregulation of CT-1 mRNA was observed in HIF-1^-/- compared with the wild type (B). Menadione as well as CoCl₂ failed to upregulate CT-1 mRNA (C) and protein (D) in HIF-1^-/- cells. ^*P<0.05, significantly different to levels in wild-type embryoid bodies.