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

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.

Deficiency of ValRS-m Causes Male Infertility in Drosophila melanogaster

Drosophila spermatogenesis involves the renewal of germline stem cells, meiosis of spermatocytes, and morphological transformation of spermatids into mature sperm. We previously demonstrated that Ocnus (ocn) plays an essential role in spermatogenesis. The ValRS-m (Valyl-tRNA synthetase, mitochondrial) gene was down-regulated in ocn RNAi testes. Here, we found that ValRS-m-knockdown induced complete sterility in male flies. The depletion of ValRS-m blocked mitochondrial behavior and ATP synthesis, thus inhibiting the transition from spermatogonia to spermatocytes, and eventually, inducing the accumulation of spermatogonia during spermatogenesis. To understand the intrinsic reason for this, we further conducted transcriptome-sequencing analysis for control and ValRS-m-knockdown testes. The differentially expressed genes (DEGs) between these two groups were selected with a fold change of ≥2 or ≤1/2. Compared with the control group, 4725 genes were down-regulated (dDEGs) and 2985 genes were up-regulated (uDEGs) in the ValRS-m RNAi group. The dDEGs were mainly concentrated in the glycolytic pathway and pyruvate metabolic pathway, and the uDEGs were primarily related to ribosomal biogenesis. A total of 28 DEGs associated with mitochondria and 6 meiosis-related genes were verified to be suppressed when ValRS-m was deficient. Overall, these results suggest that ValRS-m plays a wide and vital role in mitochondrial behavior and spermatogonia differentiation in Drosophila.

BdTTLL3B-mediated polyglycylation is involved in the spermatogenesis in Bactrocera dorsalis

Polyglycylation is a post-translational modification that generates glycine side chains in the C-terminal domains of both α- and β-tubulins. To date, the patterns and significance of polyglycylation across insect species remain largely unknown. The TTLL3B was thought to be a polyglycylase and be essential for polyglycylation in dipteran insects. In this study, the TTLL3B of Bactrocera dorsalis (BdTTLL3B) was identified and characterized. The BdTTLL3B expressed remarkably higher in adult males, especially in testes. The spatio-temporal patterns of polyglycylation were consistent with that of BdTTLL3B. Along with spermatogenesis, the intensity of polyglycylation was enhanced steadily and concentrated in elongated flagella. The expression of recombinant BdTTLL3B in Hela cells, which are genetically deficient in polyglycylation, catalyzed intracellular polyglycylation, validating the identity of BdTTLL3B as a polyglycylase. Knockout of BdTTLL3B significantly suppressed polyglycylation in testes and impaired male fertility, probably due to abnormal morphology of mitochondrial derivatives and over-accumulation of paracrystalline. Taken together, these findings indicated that the BdTTLL3B-mediated polyglycylation is involved in the spermatogenesis and play an important role in fertility of adult B. dorsalis. Therefore, the BdTTLL3B can be considered as a candidate target gene for the management of B. dorsalis, such as developing gene silencing/knockout-based sterile insect technology (SIT).

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.

Structure and molecular basis of spermatid elongation in the Drosophila testis

Spermatid elongation is a crucial event in the late stage of spermatogenesis in the Drosophila testis, eventually leading to the formation of mature sperm after meiosis. During spermatogenesis, significant structural and morphological changes take place in a cluster of post-meiotic germ cells, which are enclosed in a microenvironment surrounded by somatic cyst cells. Microtubule-based axoneme assembly, formation of individualization complexes and mitochondria maintenance are key processes involved in the differentiation of elongated spermatids. They provide important structural foundations for accessing male fertility. How these structures are constructed and maintained are basic questions in the Drosophila testis. Although the roles of several genes in different structures during the development of elongated spermatids have been elucidated, the relationships between them have not been widely studied. In addition, the genetic basis of spermatid elongation and the regulatory mechanisms involved have not been thoroughly investigated. In the present review, we focus on current knowledge with regard to spermatid axoneme assembly, individualization complex and mitochondria maintenance. We also touch upon promising directions for future research to unravel the underlying mechanisms of spermatid elongation in the Drosophila testis.

Delineating Purinergic Signaling in Drosophila

Simplistic models can aid in discovering what is important in the context of normal and pathological behavior. First recognized as a genetic model more than 100 years ago, to date, fruit flies (Drosophila melanogaster) still remain an astonishingly good laboratory stand-in for scientists to study development and physiology and to investigate the molecular mechanisms of human diseases. This is because fruit flies indeed represent a simplistic model. Furthermore, about 75% of human disease-related genes have their counterparts in the Drosophila genome, added to the fact that fruit flies are inexpensive and extremely easy to maintain, being invertebrates and, moreover, lacking any ethical concern issues. Purinergic signaling is, by definition, mediated by extracellular purinergic ligands, among which ATP represents the prototype molecule. A key feature that has progressively emerged when dissecting the purinergic mechanisms is the multilayer and dynamic nature of the signaling sustained by purinergic ligands. Indeed, these last are sequentially metabolized by several different ectonucleotidases, which generate the ligands that simultaneously activate several different purinergic receptors. Since significant purinergic actions have also been described in Drosophila, the aim of the present work is to provide a comprehensive picture of the purinergic events occurring in fruit flies.