Abstract
Drosophila melanogaster sperm reach an extraordinary long size, 1.8 mm, by the end of spermatogenesis. The mitochondrial derivatives run along the entire flagellum and provide structural rigidity for flagellar movement, but its precise function and organization is incompletely understood. The two mitochondrial derivatives differentiate and by the end of spermatogenesis the minor one reduces its size and the major one accumulates paracrystalline material inside it. The molecular constituents and precise function of the paracrystalline material have not yet been revealed. Here we purified the paracrystalline material from mature sperm and identified by mass spectrometry Sperm-Leucylaminopeptidase (S-Lap) family members as important constituents of it. To study the function of S-Lap proteins we show the characterization of classical mutants and RNAi lines affecting of the S-Lap genes and the analysis of their mutant phenotypes. We show that the male sterile phenotype of the S-Lap mutants is caused by defects in paracrystalline material accumulation and abnormal structure of the elongated major mitochondrial derivatives. Our work shows that S-Lap proteins localize and accumulate in the paracrystalline material of the major mitochondrial derivative. Therefore, we propose that S-Lap proteins are important constituents of the paracrystalline material of Drosophila melanogaster sperm.
Highlights
Insects are the record-holders for the sperm size; they have the smallest and the biggest flagellated sperm among the animals
Our results strongly indicate that S-Lap proteins are the crucial components of the paracrystalline material of the major mitochondrial derivative of D. melanogaster sperm
Despite the general occurrence of paracrystalline material in mitochondrial derivatives of insect sperm, there are no data about its molecular components
Summary
Insects are the record-holders for the sperm size; they have the smallest and the biggest flagellated sperm among the animals. The widest sperm described so far belongs to Zorotypus impolitus with a 1:13 axoneme: mitochondria size ratio [4]. The two mitochondrial derivatives elongate along the entire length of the mature sperm tail and stay in close association with the axoneme. In almost all examined insects, the complete sperm enters the egg at fertilization and degraded in the first stages of the embryonic development; it is not clear whether the paracrystalline material of the mitochondrial derivatives has a role in fertilization or after it [6,7]. There are electron microscopic observations of the structure of the sperm mitochondrial paracrystalline material from D. hydei and D. melanogaster, wherein a periodic pattern is observed with 300 Å and 260 Å periodicity in the longitudinal sections [8].
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