Characterization of Drosophila mitoferrin and CG18317 mutants

Introduction: Mitochondria are the site of iron-sulfur cluster synthesis and insertion of iron into heme, two essential prosthetic groups. Mrs3/4/mitoferrins are mitochondrial carrier proteins, which are involved in the mitochondrial iron transport. Yeast mutants suggest that a low-affinity iron transport system exists. Previous analysis of Drosophila mitoferrin P element mutants revealed an involvement of dmfrn in spermatogenesis. The ubiquitous expression of dmfrn in several adult male tissues, did however suggest a more general role. Results: Here we analyzed stocks with deletions in dmfrn and find that on low iron food dmfrn deletion inhibits development to adulthood, whereas on normal and high iron food some escapers do eclose. RNAi of dmfrn driven by the ubiquitous Actin5C-Gal4 driver recapitulates the phenotype on low iron food, but not on normal or high iron food. Overexpression of dmfrn from an UAS-dmfrn transgenic construct that contains only the coding region of dmfrn also resulted in the failure to develop to adulthood on low iron food. We identified CG18317 as putative Drosophila homolog of yeast Rim2p/Mrs12p, a mitochondrial pyrimidine carrier that is implicated in low affinity iron transport. CG18317 is ubiquitously expressed in several tissues of the male fly and the second exon is alternatively spliced resulting in a 21 nucleotides shorter transcript. An initial study of transposon mutants and deletion mutants of this gene showed sensitivity of one transposon mutant to low iron food conditions. Preliminary results indicate that increased expression of CG18317 might rescue development of dmfrn deletion mutants to at least pupal stage. Conclusions: In contrast to yeast MRS3/4, Drosophila mitoferrin is an essential gene, necessary for development of Drosophila to adulthood. The presence of escapers does however suggest, that dmfrn is either not the only mitochondrial iron carrier or that dmfrn modulates activity of a mitochondrial iron transport system