Drosophila mitoferrinis essential for male fertility: evidence for a role of mitochondrial iron metabolism during spermatogenesis

Christoph Metzendorf,Maria I Lind

doi:10.1186/1471-213x-10-68

Abstract

BackgroundMammals and Drosophila melanogaster share some striking similarities in spermatogenesis. Mitochondria in spermatids undergo dramatic morphological changes and syncytial spermatids are stripped from their cytoplasm and then individually wrapped by single membranes in an individualization process. In mammalian and fruit fly testis, components of the mitochondrial iron metabolism are expressed, but so far their function during spermatogenesis is unknown. Here we investigate the role of Drosophila mitoferrin (dmfrn), which is a mitochondrial carrier protein with an established role in the mitochondrial iron metabolism, during spermatogenesis.ResultsWe found that P-element insertions into the 5'-untranslated region of the dmfrn gene cause recessive male sterility, which was rescued by a fluorescently tagged transgenic dmfrn genomic construct (dmfrnvenus). Testes of mutant homozygous dmfrnSH115 flies were either small with unorganized content or contained some partially elongated spermatids, or testes were of normal size but lacked mature sperm. Testis squashes indicated that spermatid elongation was defective and electron micrographs showed mitochondrial defects in elongated spermatids and indicated failed individualization. Using a LacZ reporter and the dmfrnvenus transgene, we found that dmfrn expression in testes was highest in spermatids, coinciding with the stages that showed defects in the mutants. Dmfrn-venus protein accumulated in mitochondrial derivatives of spermatids, where it remained until most of it was stripped off during individualization and disposed of in waste bags. Male sterility in flies with the hypomorph alleles dmfrnBG00456 and dmfrnEY01302 over the deletion Df(3R)ED6277 was increased by dietary iron chelation and suppressed by iron supplementation of the food, while male sterility of dmfrnSH115/Df(3R)ED6277 flies was not affected by food iron levels.ConclusionsIn this work, we show that mutations in the Drosophila mitoferrin gene result in male sterility caused by developmental defects. From the sensitivity of the hypomorph mutants to low food iron levels we conclude that mitochondrial iron is essential for spermatogenesis. This is the first time that a link between the mitochondrial iron metabolism and spermatogenesis has been shown. Furthermore, due to the similar expression patterns of some mitochondrial iron metabolism genes in Drosophila and mammals, it is likely that our results are applicable for mammals as well.

Highlights

Mammals and Drosophila melanogaster share some striking similarities in spermatogenesis
It was recovered during a screen for recessive lethal genes [19], which would be in agreement with iron-sulfur clusters being essential co-factors [3] and the proposed general function of mitoferrin2 in mitochondrial iron transport in non-erythroid tissues [11]
In the current study we show that the mitochondrial iron metabolism plays a role during spermatogenesis for the first time directly, through the male sterility phenotypes caused by P-element insertions into dmfrn and the dependence of the hypomorph mutant on dietary iron, and indirectly, through the expression of fh and dmfrn in testes

Summary

Introduction

Mammals and Drosophila melanogaster share some striking similarities in spermatogenesis. In mammalian and fruit fly testis, components of the mitochondrial iron metabolism are expressed, but so far their function during spermatogenesis is unknown. We investigate the role of Drosophila mitoferrin (dmfrn), which is a mitochondrial carrier protein with an established role in the mitochondrial iron metabolism, during spermatogenesis. Transport of iron into mitochondria, is facilitated by the mitochondrial carrier proteins Mrs3p and Mrs4p (Mrs3/4p) [5,6] in yeast. MRS3/4 genes have been shown to genetically interact with frataxin [7] in the delivery of iron to heme [8] and ISC synthesis [9] in mitochondria. Another less effective mitochondrial iron transport mechanism seems to exist, as MRS3/4 mutants only manifest phenotypes at low iron conditions [10]

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