Hamp mRNA levels are suppressed in double-knockout mice treated with a low-iron diet. (A-B left) Smad1^fl/fl;Smad5^fl/fl;Cre⁺ mice and littermate Cre⁻ controls were fed a standard or low-iron diet (FeD) for 3 weeks upon weaning. (A-B right) Smad1^fl/fl;Smad5^fl/fl;Cre⁺ mice were fed a low-iron diet for 2 weeks upon weaning and switched to standard diet for 1 week, coupled with 4 intraperitoneal injections of phosphate-buffered saline (PBS) or a mixture of neutralizing BMP2/4 (10 mg/kg of body weight) and BMP6 (5 mg/kg of body weight) antibodies in PBS administered every other day. Livers were harvested to measure Hamp mRNA levels (A) and nonheme iron concentrations (B; n = 3-8 per group). Values represent mean ± standard error of the mean. *P < .05; **P < .01 relative to mice on a standard diet of the same genotype (left) or relative to PBS-treated mice (right) by Student t test.