Smad4^Δ/Δ mice display severe iron deficiency anemia. (A) Hypochromic erythrocytes in Smad4^Δ/Δ mice. Cell volume was plotted against hemoglobin concentration. (Left) Normal control. (Right) Hypochromic red blood cells (< 220 g/L) and volume increase (> 75 fl) due to reticulocytosis in Smad4^Δ/Δ. (B) In liver, Smad4 and hepcidin (Hepc) expression are almost abrogated, and ferroportin 1 (Fpn) is slightly decreased. Cytochrome b reductase 1 (Dcytb), divalent metal transporter 1 (Dmt1), and transferrin (Tf) were unchanged. (C) In duodenum, Smad4, Fpn, hephaestin (Heph), major histocompatibility complex class I–like protein (Hfe), transferrin receptor 1 (Tfr1), and stimulator of Fe transport (Sft) were unchanged, and Dmt1, Dcytb, and transferrin receptor 2 (Tfr2) were dramatically increased. Smad4^fl/fl littermates were chosen as controls. The P values were calculated by Student t test.