Flt-1^−/− ES cell cultures have an elevated endothelial cell mitotic index.

Days 6 and 7 WT (^+/+) and flt-1^−/−triple-labeled images were used to calculate nonendothelial cell and endothelial cell mitotic indices for 2 separate differentiation experiments (Table 1). Endothelial cell mitotic indices were expressed as a percentage of the nonendothelial cell mitotic index calculated for each experimental condition. The dotted black line represents the nonendothelial mitotic index for each experiment converted to 100%, and it was used as a baseline for comparison of endothelial mitotic indices.