Requirement of Transferrin for Iron-Induced Hepcidin Expression in the Zebrafish.

Abstract The zebrafish mutant gavi was identified in a large-scale chemical mutagenesis screen for embryonic anemia. Two alleles were discovered: gaviHE067 and gaviIT029, both of which have a homozygous recessive pattern of inheritance. The gavi mutants developed severe hypochromic anemia at 48 hours post-fertilization and died by 14 days post-fertilization. To determine the cause of the hypochromic anemia, low resolution genetic mapping was performed which revealed transferrin as a candidate gene. Sequencing of transferrin cDNA from the mutants confirmed that each allele of gavi harbors a mutation that results in aberrant splicing, while quantitative realtime RT-PCR demonstrated virtually absent transferrin expression in the mutants. Our previous work demonstrated that expression of hepcidin, an iron regulatory gene, is upregulated 18 hours following iron dextran injection of the zebrafish embryo. This effect was not impaired by a defect in ferroportin1 (Fraenkelet al., (2005) J Clin Invest115:1532–1541), an iron exporter and ligand for hepcidin. To evaluate the effects of iron loading on transferrin-deficient mutants, gaviIT029 homozygotes at 48 hours post-fertilization were either anesthetized and injected with iron dextran, or anesthetized but not injected. Transferrin expression was assayed 18 hours post-treatment. gaviIT029 homozygote embryos exhibited low levels of hepcidin expression that failed to increase following iron injection. These findings provide the first evidence to support the hypothesis that transferrin is required for the induction of hepcidin expression in response to iron loading in vivo.