Iron-independent reduction of ferH mRNA translation in proliferating and differentiating primary ebls. The SCF-dependent erythroid progenitors were grown from chicken bone marrow as described.25 Maturation was induced by removal of self-renewal factors (SCF and IGF-1) and addition of avian Epo (high-titer anemic serum) and insulin to the medium (see Materials and Methods). Self-renewing SCF-ebls and cells induced to differentiate for 48 or 96 hours were treated with low (0.03 mg/mL) or high levels of iron-saturated Tf (1 mg/mL) or high ferric ammonium citrate concentrations (FeCit; 50 μg/mL, lowest panel at 48 hours) for 24 hours. Sucrose gradient analysis and densitometrical quantitation were performed as described in the legend to Fig 1. (○) ferH mRNA; (•) eALAS mRNA.