Hepcidin up-regulation reduces ferroportin expression and causes an anemic phenotype in Tmprss6^−/− mice. Wright-Giemsa–stained blood smears from Tmprss6^+/+ (A) and Tmprss6^−/− (B) littermate mice. The figure shows the severe hypochromia found in mutant erythrocytes in comparison to wild-type ones. (C) Representative Northern blot analysis of liver tissues from wild-type and Tmprss6^−/− mice showing the increased hepcidin mRNA expression in mutant mice. (D) TaqMan real-time PCR analysis of hepcidin expression in liver samples from 7-week-old Tmprss6^+/+ and Tmprss6^−/− mice. mRNA levels on the y-axis are expressed relative to β-actin levels. The average relative expression of hepcidin in wild-type mice was assigned an arbitrary value of 100. Values are means (± SEM). *P < .05; n = 5 mice per group. Perls Prussian blue stain for iron in sections of duodenal villi of 5-week-old Tmprss6^+/+ (E) and Tmprss6^−/− (F) mice shows iron accumulation in Tmprss6-null enterocytes. Representative immunostaining of ferroportin in duodenal tissue from 5-week-old Tmprss6^+/+ (G) and Tmprss6^−/− (H) mice. Arrow points to the basal expression of ferroportin in wild-type enterocytes, whereas positive basal staining is absent in Tmprss6-null cells. Bars represent 10 μm, magnification 100×/1.25 NA (A,B); bars 20 μm, magnification 60×/0.80 NA (E-H).