The synthesis of hemoglobin involves globin chain production, heme-biosynthesis and iron utilization. We have undertaken a genetic approach to understanding the process of hemoglobin production using the zebrafish as a model system. Mutagenesis screens have previously identified five complementation groups of zebrafish mutants with defects in hemoglobin production. In the previous grant period, we isolated the sauternes gene, which encodes ALAS2, the first enzyme in the home-biosynthesis pathway. Mutations in ALAS2 cause congenital sideroblastic anemia in humans, and the zebrafish sau mutant represents an animal model of this disease. We also isolated the ferroportin 1 gene as the defect in the weissherbst mutant. Ferroportin 1 proved to act as the basolateral iron transporter of the gut as well as the placental iron transporter in mammals. Subsequently, it was found that mutations in ferroportin 1 are associated with hemochromatosis in humans. Our studies established the fish system as a means to study human disease and to isolate novel genes. During this new grant period, we will further sequence and characterize the zebrafish globins and establish the structure of the globin loci. We plan to isolate and characterize two newly identified hypochromic mutant genes. A dominant suppressor screen will be done to delineate genes that participate in the ferroportin 1 pathway of iron utilization. A chemical genetics approach will be used to understand hemoglobin production. A library of sixteen thousand compounds will be examined for effects on rescue of our hypochromic mutant phenotypes and another screen will look for chemicals that induce fetal globin gene expression in adults. These pharmaceutical compounds may ameliorate disease conditions in other vertebrates. Our studies should provide a better understanding of the basic biology of hemoglobin production and may have a therapeutic impact on patients with thalassemia, sickle cell anemia, and hemochromatosis.
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