(a) Erythroblasts (EB; mitochondriahigh Syto16high), reticulocytes (RC; mitochondriahigh Syto16low) and EC (EC; Ter119+ PBC) were collected from the indicated embryos (E18.5), and the expression of each protein was examined by western blot. The asterisk indicates a nonspecific band. Uncropped images are shown in Supplementary Figs 11 and 12. 