Abstract
Mitochondria are essential organelles of developing spermatids in Drosophila, which undergo dramatic changes in size and shape after meiotic division, where mitochondria localized in the cytoplasm, migrate near the nucleus, aggregate, fuse and create the Nebenkern. During spermatid elongation the two similar mitochondrial derivatives of the Nebenkern start to elongate parallel to the axoneme. One of the elongated mitochondrial derivatives starts to lose volume and becomes the minor mitochondrial derivative, while the other one accumulates paracrystalline and becomes the major mitochondrial derivative. Proteins and intracellular environment that are responsible for cyst elongation and paracrystalline formation in the major mitochondrial derivative need to be identified. In this work we investigate the function of the testis specific big bubble 8 (bb8) gene during spermatogenesis. We show that a Minos element insertion in bb8 gene, a predicted glutamate dehydrogenase, causes recessive male sterility. We demonstrate bb8 mRNA enrichment in spermatids and the mitochondrial localisation of Bb8 protein during spermatogenesis. We report that megamitochondria develop in the homozygous mutant testes, in elongating spermatids. Ultrastructural analysis of the cross section of elongated spermatids shows enlarged mitochondria and the production of paracrystalline in both major and minor mitochondrial derivatives. Our results suggest that the Bb8 protein and presumably glutamate metabolism has a crucial role in the normal development and establishment of the identity of the mitochondrial derivatives during spermatid elongation.
Highlights
Insects have some of the longest sperm in the animal kingdom, they contain the same components as the mammalian sperm, namely compact nucleus, acrosome, axoneme, mitochondria and plasma membrane
We demonstrate that the protein is localized in the mitochondria and show that the lack of Bb8 results in the formation of megamitochondria and abnormal distribution of paracrystalline, which appears in both mitochondrial derivatives of the spermatids
We found that mitochondrial bb8, a putative glutamate dehydrogenase is expressed exclusively in the testis and the bb8 mRNA is enriched in the post-meiotic stages of spermatogenesis
Summary
Insects have some of the longest sperm in the animal kingdom, they contain the same components as the mammalian sperm, namely compact nucleus, acrosome, axoneme, mitochondria and plasma membrane. Mitochondria are essential organelles of both somatic and germ cells. In addition to providing energy for the cells through oxidative phosphorylation, mitochondria play important roles in signalling, differentiation and cell death. Mitochondria change shape and localization during Drosophila spermatogenesis [1]. During early stages of spermatogenesis, the number and appearance of mitochondria are similar to the mitochondria of somatic cells. They are distinct and dispersed through the cytoplasm.
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