Single-cell RNA-sequencing reveals the transcriptional landscape of ND-42 mediated spermatid elongation via mitochondrial derivative maintenance in Drosophila testes

CG9920 is necessary for mitochondrial morphogenesis and individualization during spermatogenesis in Drosophila melanogaster

Drosophila melanogaster is an ideal model organism for investigating spermatogenesis due to its powerful genetics, conserved genes and visible morphology of germ cells during sperm production. Our previous work revealed that ocnus (ocn) knockdown resulted in male sterility, and CG9920 was identified as a significantly downregulated protein in fly abdomen after ocn knockdown, suggesting a role of CG9920 in male reproduction. In this study, we found that CG9920 was highly expressed in fly testes. CG9920 knockdown in fly testes caused male infertility with no mature sperms in seminal vesicles. Immunofluorescence staining showed that depletion of CG9920 resulted in scattered spermatid nuclear bundles, fewer elongation cones that did not migrate to the anterior region of the testis, and almost no individualization complexes. Transmission electron microscopy revealed that CG9920 knockdown severely disrupted mitochondrial morphogenesis during spermatogenesis. Notably, we found that CG9920 might not directly interact with Ocn, but rather was inhibited by STAT92E, which itself was indirectly affected by Ocn. We propose a possible novel pathway essential for spermatogenesis in D. melanogaster, whereby Ocn indirectly induces CG9920 expression, potentially counteracting its inhibition by the JAK-STAT signaling pathway.

Exposure to Titanium Dioxide Nanoparticles Leads to Specific Disorders of Spermatid Elongation via Multiple Metabolic Pathways in Drosophila Testes

Titanium dioxide nanoparticles (TiO2 NPs) have been extensively utilized in various applications. However, the regulatory mechanism behind the reproductive toxicity induced by TiO2 NP exposure remains largely elusive. In this study, we employed a Drosophila model to assess potential testicular injuries during spermatogenesis and conducted bulk RNA-Seq analysis to elucidate the underlying mechanisms. Our results reveal that while prolonged exposure to lower concentrations of TiO2 NPs (0.45 mg/mL) for 30 days did not manifest reproductive toxicity, exposure at concentrations of 0.9 and 1.8 mg/mL significantly impaired spermatid elongation in Drosophila testes. Notably, bulk RNA-seq analysis revealed that TiO2 NP exposure affected multiple metabolic pathways including carbohydrate metabolism and cytochrome P450. Importantly, the intervention of glutathione (GSH) significantly protected against reproductive toxicity induced by TiO2 NP exposure, as it restored the number of Orb-positive spermatid clusters in Drosophila testes. Our study provides novel insights into the specific detrimental effects of TiO2 NP exposure on spermatid elongation through multiple metabolic alterations in Drosophila testes and highlights the protective role of GSH in countering this toxicity.

Integrative analysis of single-nucleus RNA-seq and bulk RNA-seq reveals germline cells development dynamics and niches in the Pacific oyster gonad

Gametogenesis drives the maturation of germ cell precursors into functional gametes, facilitated by interactions with the niche environment. However, the molecular mechanisms, especially in invertebrates, remain incompletely understood. In this study, the gonadal microenvironment and gametogenic processes in the Pacific oyster, a model for diffuse gonadal organization and periodic gametogenesis, are investigated. We combine single-nucleus RNA-seq and bulk RNA-seq to analyze gonadal microenvironments in oysters. Twenty-three male and nineteen female gonadal cell clusters are identified, revealing four male and three female germ cell types, alongside follicular cells in females and Sertoli/Leydig cells in males. The NOTCH and BMP (bone morphogenetic protein) signaling pathways play a significant role in the male germline niche, suggesting similarities with mammalian germ cell microenvironment. This study offers valuable insights into germ cell developmental transitions and microenvironmental characteristics.

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.

Single-cell transcriptome characteristics of testicular terminal epithelium lineages during aging in the Drosophila

Aging is a complex biological process leading to impaired functions, with a variety of hallmarks. In the testis of Drosophila, the terminal epithelium region is involved in spermatid release and maturation, while its functional diversity and regulatory mechanism remain poorly understood. In this study, we performed single-cell RNA-sequencing analysis (scRNA-seq) to characterize the transcriptomes of terminal epithelium in Drosophila testes at 2-, 10 and 40-Days. Terminal epithelium populations were defined with Metallothionein A (MtnA) and subdivided into six novel sub-cell clusters (EP0-EP5), and a series of marker genes were identified based on their expressions. The data revealed the functional characteristics of terminal epithelium populations, such as tight junction, focal adhesion, bacterial invasion, oxidative stress, mitochondrial function, proteasome, apoptosis and metabolism. Interestingly, we also found that disrupting genes for several relevant pathways in terminal epithelium led to male fertility disorders. Moreover, we also discovered a series of age-biased genes and pseudotime trajectory mediated state-biased genes during terminal epithelium aging. Differentially expressed genes during terminal epithelium aging were mainly participated in the regulation of several common signatures, e.g. mitochondria-related events, protein synthesis and degradation, and metabolic processes. We further explored the Drosophila divergence and selection in the functional constraints of age-biased genes during aging, revealing that age-biased genes in epithelial cells of 2 Days group evolved rapidly and were endowed with greater evolutionary advantages. scRNA-seq analysis revealed the diversity of testicular terminal epithelium populations, providing a gene target resource for further systematic research of their functions during aging.

Single-cell RNA sequencing analysis to evaluate antimony exposure effects on cell-lineage communications within the Drosophila testicular niche

The increasing production and prevalence of antimony (Sb)-related products raise concerns regarding its potential hazards to reproductive health. Upon environmental exposure, Sb reportedly induces testicular toxicity during spermatogenesis; moreover, it is known to affect various testicular cell populations, particularly germline stem cell populations. However, the cell-cell communication resulting from Sb exposure within the testicular niche remains poorly understood. To address this gap, herein we analyzed testicular single-cell RNA sequencing data from Sb-exposed Drosophila. Our findings revealed that the epidermal growth factor receptor (EGFR) and WNT signaling pathways were associated with the stem cell niche in Drosophila testes, which may disrupt the homeostasis of the testicular niche in Drosophila. Furthermore, we identified several ligand-receptor pairs, facilitating the elucidation of intercellular crosstalk involved in Sb-mediated reproductive toxicology. We employed scRNA-seq analysis and conducted functional verification to investigate the expression patterns of core downstream factors associated with EGFR and WNT signatures in the testes under the influence of Sb exposure. Altogether, our results shed light on the potential mechanisms of Sb exposure-mediated testicular cell-lineage communications.

Insect Insights at the Single-Cell Level: Technologies and Applications

Single-cell techniques are a promising way to unravel the complexity and heterogeneity of transcripts at the cellular level and to reveal the composition of different cell types and functions in a tissue or organ. In recent years, advances in single-cell RNA sequencing (scRNA-seq) have further changed our view of biological systems. The application of scRNA-seq in insects enables the comprehensive characterization of both common and rare cell types and cell states, the discovery of new cell types, and revealing how cell types relate to each other. The recent application of scRNA-seq techniques to insect tissues has led to a number of exciting discoveries. Here we provide an overview of scRNA-seq and its application in insect research, focusing on biological applications, current challenges, and future opportunities to make new discoveries with scRNA-seq in insects.