Reduced TfR1 expression in the bone marrow of IRP2-deficient mice. (A) TfR1 mRNA levels in the bone marrow were assayed by RNase protection in groups of 4 wild-type versus 4 Irp2^-/- mice. β-Actin was used as a standard. The bands corresponding to full-length probes (TfR1: 490 nt, β-actin: 276 nt) and to the β-actin (250 nt) and TfR1 (371 nt) mRNAs are indicated by arrows. The signals were quantified using a phosphorimager. The histogram represents the levels of TfR1 mRNA after normalization for β-actin expression. Error bars indicate standard deviation. TfR1 mRNA levels are significantly reduced in mutant mice compared with wild-type mice (Student St test). (B) TfR1 protein levels (middle panel) were analyzed in 4 wild-type versus 4 Irp2^-/- mice (top panel) by Western blotting using β-actin as a standard (bottom panel).