Iron has a fundamental role in many metabolic processes, including electron transport, deoxyribonucleotide synthesis, oxygen transport and many essential redox reactions involving haemoproteins and Fe–S cluster proteins. Defective iron homeostasis results in either iron deficiency or iron overload1. Precise regulation of iron transport in mitochondria is essential for haem biosynthesis2, haemoglobin production and Fe–S cluster protein assembly3,4 during red cell development. Here we describe a zebrafish mutant, frascati (frs)5, that shows profound hypochromic anaemia and erythroid maturation arrest owing to defects in mitochondrial iron uptake. Through positional cloning, we show that the gene mutated in the frs mutant is a member of the vertebrate mitochondrial solute carrier family (SLC25)6 that we call mitoferrin (mfrn). mfrn is highly expressed in fetal and adult haematopoietic tissues of zebrafish and mouse. Erythroblasts generated from murine embryonic stem cells null for Mfrn (also known as Slc25a37) show maturation arrest with severely impaired incorporation of 55Fe into haem. Disruption of the yeast mfrn orthologues, MRS3 and MRS4, causes defects in iron metabolism and mitochondrial Fe–S cluster biogenesis7,8,9,10. Murine Mfrn rescues the defects in frs zebrafish, and zebrafish mfrn complements the yeast mutant, indicating that the function of the gene may be highly conserved. Our data show that mfrn functions as the principal mitochondrial iron importer essential for haem biosynthesis in vertebrate erythroblasts.
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We thank C. Lawrence, A. Walker and C. Belair for zebrafish animal husbandry; M. Halpern for sptb333 zebrafish; S. Johnson for SJD zebrafish; W. Shu Wu for mouse bone marrow cDNA; C. Roy for advice on preparing 55Fe-saturated transferrin; M. Kaku and Y. Fujiwara for advice on ES cell culture and selection; H. Wohlrab for advice on SLC25 biochemistry; K. Dooley for the frsij001 allele from the Tübingen 2000 screen; M. Ocaña for help with confocal fluorescence images; S. Dallaire and C. Lee for karyotyping the Mfrn-null ES cells; A. B. Cantor for advice on generating Hox-11-immortalized haematopoietic cells; and E. Shafizadeh, S.-K. Choe, C. Burns, Y. Houvras, D. Langenau, W. Tse, H. Wolhrab, J. Kanki and G. M. Shaw for critically reading the manuscript. This work was supported in part by the William Randolph Hearst Foundation (B.H.P.); the March of Dimes Birth Defects Foundation Basil O'Connor Award (B.H.P.); the Swiss National Science Foundation (G.E.A.); the Belgian National Research Fund (E.M.); the NIH (L.L.P., L.I.Z., J.K., M.J.W., B.H.P.); and the Howard Hughes Medical Institute (L.I.Z.).
Text to accompany the above Supplementary Figures.