Microtubule Organizing Centers Contain Testis-Specific γ-TuRC Proteins in Spermatids of Drosophila

Versatile gamma-tubulin complexes contribute to the dynamic organization of MTOCs during Drosophila spermatogenesis

The initiation of microtubule formation is facilitated by γ-tubulin and γ-Tubulin Ring Complex (γ-TuRC) in various microtubule-organizing centers (MTOCs). While the heterogeneity of tissue-specific MTOCs and γ-TuRC in Drosophila testis has been described, their molecular composition and physiological significance are poorly understood. We investigated the testis-specific distribution and biochemical interaction of the canonical γ-TuRC proteins Grip163 and Grip84. We found that while Grip163 is present on the centrosome and basal body, Grip84 localizes to the centrosome and Golgi in spermatocytes and colocalizes with the testis-specific γ-Tubulin complexes (t-γ-TuC) at the basal body, apical nuclear tip, and near the elongated mitochondria after meiosis. We also showed the apical nuclear tip localization of some γ-TuRC interacting partners and proved their binding to t-γ-TuC proteins. These results highlight and prove the importance of the different γ-TuRCs in organizing the diverse MTOCs present during the extensive rearrangement of cell organelles during the spermatogenesis of Drosophila.

Adenine nucleotide translocase 2 (Ant2) is required for individualization of spermatogenesis of Drosophila melanogaster

Successful completion of spermatogenesis is crucial for the perpetuation of the species. In Drosophila, spermatid individualization, a process involving changes in mitochondrial structure and function is critical to produce functional mature sperm. Ant2, encoding a mitochondrial adenine nucleotide translocase, is highly expressed in male testes and plays a role in energy metabolism in the mitochondria. However, its molecular function remains unclear. Here, we identified an important role of Ant2 in spermatid individualization. In Ant2 knockdown testes, spermatid individualization complexes composed of F-actin cones exhibited a diffuse distribution, and mature sperms were absent in the seminal vesicle, thus leading to male sterility. The most striking effects in Ant2-knockdown spermatids were decrease in tubulin polyglycylation and disruption of proper mitochondria derivatives function. Excessive apoptotic cells were also observed in Ant2-knockdown testes. To further investigate the phenotype of Ant2 knockdown in testes at the molecular level, complementary transcriptome and proteome analyses were performed. At the mRNA level, 868 differentially expressed genes were identified, of which 229 genes were upregulated and 639 were downregulated induced via Ant2 knockdown. iTRAQ-labeling proteome analysis revealed 350 differentially expressed proteins, of which 117 proteins were upregulated and 233 were downregulated. The expression of glutathione transferase (GstD5, GstE5, GstE8, and GstD3), proteins involved in reproduction were significantly regulated at both the mRNA and protein levels. These results indicate that Ant2 is crucial for spermatid maturation by affecting mitochondrial morphogenesis.

Mitochondrial Differentiation during Spermatogenesis: Lessons from Drosophila melanogaster

Numerous diseases can arise as a consequence of mitochondrial malfunction. Hence, there is a significant focus on studying the role of mitochondria in cancer, ageing, neurodegenerative diseases, and the field of developmental biology. Mitochondria could exist as discrete organelles in the cell; however, they have the ability to fuse, resulting in the formation of interconnected reticular structures. The dynamic changes between these forms correlate with mitochondrial function and mitochondrial health, and consequently, there is a significant scientific interest in uncovering the specific molecular constituents that govern these transitions. Moreover, the specialized mitochondria display a wide array of variable morphologies in their cristae formations. These inner mitochondrial structures are closely associated with the specific functions performed by the mitochondria. In multiple cases, the presence of mitochondrial dysfunction has been linked to male sterility, as it has been observed to cause a range of abnormal spermatogenesis and sperm phenotypes in different species. This review aims to elucidate the dynamic alterations and functions of mitochondria in germ cell development during the spermatogenesis of Drosophila melanogaster.

Nuclear elongation during spermiogenesis depends on physical linkage of nuclear pore complexes to bundled microtubules by Drosophila Mst27D

Spermatozoa in animal species are usually highly elongated cells with a long motile tail attached to a head that contains the haploid genome in a compact and often elongated nucleus. In Drosophila melanogaster, the nucleus is compacted two hundred-fold in volume during spermiogenesis and re-modeled into a needle that is thirty-fold longer than its diameter. Nuclear elongation is preceded by a striking relocalization of nuclear pore complexes (NPCs). While NPCs are initially located throughout the nuclear envelope (NE) around the spherical nucleus of early round spermatids, they are later confined to one hemisphere. In the cytoplasm adjacent to this NPC-containing NE, the so-called dense complex with a strong bundle of microtubules is assembled. While this conspicuous proximity argued for functional significance of NPC-NE and microtubule bundle, experimental confirmation of their contributions to nuclear elongation has not yet been reported. Our functional characterization of the spermatid specific Mst27D protein now resolves this deficit. We demonstrate that Mst27D establishes physical linkage between NPC-NE and dense complex. The C-terminal region of Mst27D binds to the nuclear pore protein Nup358. The N-terminal CH domain of Mst27D, which is similar to that of EB1 family proteins, binds to microtubules. At high expression levels, Mst27D promotes bundling of microtubules in cultured cells. Microscopic analyses indicated co-localization of Mst27D with Nup358 and with the microtubule bundles of the dense complex. Time-lapse imaging revealed that nuclear elongation is accompanied by a progressive bundling of microtubules into a single elongated bundle. In Mst27D null mutants, this bundling process does not occur and nuclear elongation is abnormal. Thus, we propose that Mst27D permits normal nuclear elongation by promoting the attachment of the NPC-NE to the microtubules of the dense complex, as well as the progressive bundling of these microtubules.

A germline-specific role for unconventional components of the γ-tubulin complex in Caenorhabditis elegans

The γ-tubulin complex (γTuC) is a widely conserved microtubule nucleator, but some of its components, namely GCP4, GCP5 and GCP6 (also known as TUBGCP4, TUBGCP5 and TUBGCP6, respectively), have not been detected in Caenorhabditis elegans. Here, we identified two γTuC-associated proteins in C. elegans, GTAP-1 and GTAP-2, for which apparent orthologs were detected only in the genus Caenorhabditis. GTAP-1 and GTAP-2 were found to localize at centrosomes and the plasma membrane of the germline, and their centrosomal localization was interdependent. In early C. elegans embryos, whereas the conserved γTuC component MZT-1 (also known as MOZART1 and MZT1) was essential for the localization of centrosomal γ-tubulin, depletion of GTAP-1 and/or GTAP-2 caused up to 50% reduction of centrosomal γ-tubulin and precocious disassembly of spindle poles during mitotic telophase. In the adult germline, GTAP-1 and GTAP-2 contributed to efficient recruitment of the γTuC to the plasma membrane. Depletion of GTAP-1, but not of GTAP-2, severely disrupted both the microtubule array and the honeycomb-like structure of the adult germline. We propose that GTAP-1 and GTAP-2 are unconventional components of the γTuC that contribute to the organization of both centrosomal and non-centrosomal microtubules by targeting the γTuC to specific subcellular sites in a tissue-specific manner.

GST-IVTT pull-down: a fast and versatile in vitro method for validating and mapping protein-protein interactions

Over the past few decades, dozens of in vitro methods have been developed to map, investigate and validate protein-protein interactions. However, most of these approaches are time-consuming and labour-intensive or require specialised equipment or substantial amounts of purified proteins. Here, we describe a fast and versatile research protocol that is suitable for the in vitro analysis of the physical interaction between proteins or for mapping the binding surfaces. The principle of this method is based on the immobilisation of the protein/domain of interest to a carrier followed by its incubation with a labelled putative binding partner, which is generated by a coupled in vitro transcription/translation reaction. Interacting proteins are removed from the carrier, fractionated and visualised by SDS/PAGE autoradiography (or western blotting). This simple and cheap method can be easily carried out in every wet lab.

Mutation in Drosophila concentrative nucleoside transporter 1 alters spermatid maturation and mating behavior

Concentrative nucleoside transporters (Cnts) are unidirectional carriers that mediate the energy-costly influx of nucleosides driven by the transmembrane sodium gradient. Cnts are transmembrane proteins that share a common structural organization and are found in all phyla. Although there have been studies on Cnts from a biochemical perspective, no deep research has examined their role at the organismal level. Here, we investigated the role of the Drosophila melanogaster cnt1 gene, which is specifically expressed in the testes. We used the CRISPR/Cas9 system to generate a mutation in the cnt1 gene. The cnt1 mutants exhibited defects in the duration of copulation and spermatid maturation, which significantly impaired male fertility. The most striking effect of the cnt1 mutation in spermatid maturation was an abnormal structure of the sperm tail, in which the formation of major and minor mitochondrial derivatives was disrupted. Our results demonstrate the importance of cnt1 in male fertility and suggest that the observed defects in mating behavior and spermatogenesis are due to alterations in nucleoside transport and associated metabolic pathways.

Comparative analysis unveils the cadmium-induced reproductive toxicity on the testes of Pardosa pseudoannulata

Cadmium (Cd) pollution is one of the most serious heavy metal pollutions in the world, which has been demonstrated to cause different toxicities to living organisms. Cd has been widely suggested to cause reproductive toxicity to vertebrates, yet its reproductive toxicity to invertebrates is not comprehensive. In this study, the wolf spider Pardosa pseudoannulata was used as a bioindicator to evaluate the male reproductive toxicity of invertebrates under Cd stress. Cd stress had no effect on the color, size and length of testis. However, Cd significantly increased the contents of catalase, glutathione peroxidase and malondialdehyde, the antioxidants in the testis of P. pseudoannulata. Then we analyzed the transcriptome of testis exposed to Cd, and identified a total of 4739 differentially expressed genes (DEGs) compared to control, with 2368 up-regulated and 2371 down-regulated. The enrichment analysis showed that Cd stress could affect spermatogenesis, sperm motility, post-embryonic development, oxidative phosphorylation and metabolism and synthesis of male reproductive components. At the same time, the protein-protein interaction network was constructed with the generated DEGs. Combined with the enrichment analysis of key modules, it revealed that Cd stress could further affect the metabolic process in testis. In general, the analysis of testicular damage and transcriptome under Cd stress can provide a novel insight into the reproductive toxicity of Cd on rice filed arthropods and offer a reference for the protection of rice filed spiders under Cd pollution.