Mitoferrin is essential for normal development in Drosophila melanogaster

• Mitochondria are crucial to iron metabolism, being the unique site for heme synthesis and the major site for iron-sulfur (Fe-S) cluster biosynthesis. Iron is transported into the mitochondrion by an iron metal transporter, mitoferrin, in the inner membrane of mitochondria. By studying different dmfrn Drosophila mutants we have previously showed that dmfrn and mitochondrial iron metabolism have an important role during spermatogenesis and that a functional dmfrn is essential for male fertility (Metzendorf & Lind, 2010). During the spermatogenesis study, we characterized two fly strains with deletions in the dmfrn gene, which is located on the right arm of chromosome three. In the strain with the small deletion dmfrnDf13, which we recovered during P-element mobilization, a third of the 5´ untranslated region is deleted. In the strain Df(3R)ED6277, the genes dmfrn and CG5514 are deleted and half of the 5´ untranslated regions of genes Mes-4 and Gp93 are removed. We found that deletion of dmfrn, (homozygous dmfrnDf13, transheterozygous dmfrnDf13/Df(3R)ED6277 or homozygous Df(3R)ED6277) causes lethality at larval stage.In the current study we analyzed the developmental phenotype in further detail. As fertility of the hypomorph dmfrn P element mutant strains is depended on the level of dietary iron (Metzendorf & Lind, 2010), we were interested if the deletion mutants might show a similar dependence. Using a third chromosome balancer with markers, Tb (Tubby will result in shorter larvae and pupae) and Sb (stubble: bristles short and stubby) that allows distinguishing between heterozygous and transheterozygous flies at the larval, pupal and adult stage makes it possible to quantify the genotypes. We found that transheterozygous (dmfrnDf13/Df(3R)ED6277) flies develop to third instar larvae and very seldom start puparation (<0.25%) when the flies was fed with low iron food. On normal food, transheterozygous flies develop to the pupal stage (~17%), but very few flies eclose as adults (~6%). Knocking down dmfrn expression by Gal4/UAS driven RNA interference (RNAi) with a ubiquitous driver, resulted in a phenotype similar to that of the dmfrn deletion strains. Introduction of the genomic construct dmfrnvenusB32 (a fluorescently (venus) tagged transgenic dmfrn) rescued dmfrn deletion flies to pupal stage on low iron food, and increased the fraction of eclosed adults with the dmfrn deletion alleles on normal and high iron food. The presence of third instar larvae without the balancer indicates that dmfrn deletion might not cause larval lethality, but may either slow down development or cause developmental arrest. We concluded that mitoferrin is essential for normal development and that the developmental phenotype of mitoferrin deletion mutants can be rescued to some degree by addition of dietary iron, showing that the developmental lethality or arrest is due to mitochondrial iron deficiency.Metzendorf , C. and Lind M.I. (2010) Drosophila mitoferrin is essential for male fertility: evidence for a role of mitochondrial iron metabolism during spermatogenesis. BMC Developmental Biology, 10, 68.

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