Matrix metalloproteinase 2 is required for ovulation and corpus luteum formation in Drosophila

Actomyosin contraction in the follicular epithelium provides the major mechanical force for follicle rupture during Drosophila ovulation

Ovulation is critical for sexual reproduction and consists of the process of liberating fertilizable oocytes from their somatic follicle capsules, also known as follicle rupture. The mechanical force for oocyte expulsion is largely unknown in many species. Our previous work demonstrated that Drosophila ovulation, as in mammals, requires the proteolytic degradation of the posterior follicle wall and follicle rupture to release the mature oocyte from a layer of somatic follicle cells. Here, we identified actomyosin contraction in somatic follicle cells as the major mechanical force for follicle rupture. Filamentous actin (F-actin) and nonmuscle myosin II (NMII) are highly enriched in the cortex of follicle cells upon stimulation with octopamine (OA), a monoamine critical for Drosophila ovulation. Pharmacological disruption of F-actin polymerization prevented follicle rupture without interfering with the follicle wall breakdown. In addition, we demonstrated that OA induces Rho1 guanosine triphosphate (GTP)ase activation in the follicle cell cortex, which activates Ras homolog (Rho) kinase to promote actomyosin contraction and follicle rupture. All these results led us to conclude that OA signaling induces actomyosin cortex enrichment and contractility, which generates the mechanical force for follicle rupture during Drosophila ovulation. Due to the conserved nature of actomyosin contraction, this work could shed light on the mechanical force required for follicle rupture in other species including humans.

Matrix metalloproteinase 2 degrades collagen I to regulate ovarian development by association with an insulin-like peptide

The ovary generally undergoes tissue remodeling during larval to pupal transition, which includes membrane degeneration and ovariole growth. At the same time, the hormones produced by insects significantly change during metamorphosis. However, the regulatory mechanism for ovarian development and hormones is not fully understood in insects. Herein, we found that matrix metalloproteinase 2 (MMP2) was highly expressed in the ovarian capsules and ovarioles, and the development was abnormal after knocking out MMP2 in Bombyx mori. The process of abnormal degradation of collagen I due to MMP2 deletion, which resulted in abnormal development of ovarioles and eggs, was analyzed in detail. The proteomics of ovaries in the MMP2-knock out and wild type strains showed a critically significant difference in the expression of a protein, insulin-like peptide (ILP). Additional analysis revealed significant alteration of ILP during ovarian development, and abnormal expression of ILP significantly affected ovarian development in vivo and MMP2 expression in vitro and in vivo. These results showed that MMP2 regulation of ovarian tissue remodeling is closely related to ILP expression. Our study provides new insights into the regulatory mechanism of MMP2 and ovarian development in B. mori.

Role of nuclear protein Akirin in the modulation of female reproduction in Nilaparvata lugens (Hemiptera: Delphacidae)

Introduction: Akirin as a highly conserved transcription factor, exerts a profound influence on the growth, development, immune response, and reproductive processes in animals. The brown planthopper (BPH), Nilaparvata lugens, a major pest in rice production in Asia, possesses high reproductive capacity, a critical factor contributing to reduced rice yields. The aims of this study were to demonstrate the regulatory role of Akirin in the reproduction of BPH. Methods: In this study, quantitative PCR (qPCR) was used to detect the mRNA expression of genes. RNA interference (RNAi) was used to downregulate the expression of Akirin gene, and RNA sequencing (RNA-seq) was used to screen for differentially expressed genes caused by Akirin downregulation. Hormone contents were measured with the enzyme linked immunosorbent assay (ELISA), and protein content was evaluated with the bicinchoninic acid (BCA) method. Results: Using BPH genome data, we screened for an Akirin gene (NlAkirin). An analysis of tissue-specific expressions showed that NlAkirin was expressed in all tissues tested in female BPH, but its expression level was highest in the ovary. After inhibiting the mRNA expression of NlAkirin in BPH females, the number of eggs laid, hatching rate, and number of ovarioles decreased. Transcriptome sequencing was performed, following a NlAkirin double-stranded RNA treatment. Compared with the genes of the control, which was injected with GFP double-stranded RNA, there were 438 upregulated genes and 1012 downregulated genes; the expression of vitellogenin (Vg) and vitellogenin receptor (VgR) genes as well as the mRNA expression of genes related to the target of rapamycin (TOR), juvenile hormone (JH), and insulin pathways involved in Vg synthesis was significantly downregulated. As a result of NlAkirin knockdown, the titers of JH III and Ecdysone (Ecd) were downregulated in unmated females but returned to normal levels in mated females. The ovarian protein contents in both unmated and mated females were downregulated. Discussion and conclusion: Our results suggest that NlAkirin affects female BPH reproduction by regulating the mRNA expression of genes related to the Vg, VgR, TOR, JH, and insulin signaling pathways, in addition to the titers of JH III and Ecd. The findings of this research provide novel insights into the regulatory role of Akirin in insect reproductive capacity.

Professional phagocytes are recruited for the clearance of obsolete nonprofessional phagocytes in the Drosophila ovary

Cell death is an important process in the body, as it occurs throughout every tissue during development, disease, and tissue regeneration. Phagocytes are responsible for clearing away dying cells and are typically characterized as either professional or nonprofessional phagocytes. Professional phagocytes, such as macrophages, are found in nearly every part of the body while nonprofessional phagocytes, such as epithelial cells, are found in every tissue type. However, there are organs that are considered "immune-privileged" as they have little to no immune surveillance and rely on nonprofessional phagocytes to engulf dying cells. These organs are surrounded by barriers to protect the tissue from viruses, bacteria, and perhaps even immune cells. The Drosophila ovary is considered immune-privileged, however the presence of hemocytes, the macrophages of Drosophila, around the ovary suggests they may have a potential function. Here we analyze hemocyte localization and potential functions in response to starvation-induced cell death in the ovary. Hemocytes were found to accumulate in the oviduct in the vicinity of mature eggs and follicle cell debris. Genetic ablation of hemocytes revealed that the presence of hemocytes affects oogenesis and that they phagocytose ovarian cell debris and in their absence fecundity decreases. Unpaired3, an IL-6 like cytokine, was found to be required for the recruitment of hemocytes to the oviduct to clear away obsolete follicle cells. These findings demonstrate a role for hemocytes in the ovary, providing a more thorough understanding of phagocyte communication and cell clearance in a previously thought immune-privileged organ.

Local Ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

Orthologs of NOX5 and EC-SOD/SOD3: dNox and dSod3 Impact Egg Hardening Process and Egg Laying in Reproductive Function of Drosophila melanogaster

The occurrence of ovarian dysfunction is often due to the imbalance between the formation of reactive oxygen species (ROS) and the ineffectiveness of the antioxidative defense mechanisms. Primary sources of ROS are respiratory electron transfer and the activity of NADPH oxidases (NOX) while superoxide dismutases (SOD) are the main key regulators that control the levels of ROS and reactive nitrogen species intra- and extracellularly. Because of their central role SODs are the subject of research on human ovarian dysfunction but sample acquisition is low. The high degree of cellular and molecular similarity between Drosophila melanogaster ovaries and human ovaries provides this model organism with the best conditions for analyzing the role of ROS during ovarian function. In this study we clarify the localization of the ROS-producing enzyme dNox within the ovaries of Drosophila melanogaster and by a tissue-specific knockdown we show that dNox-derived ROS are involved in the chorion hardening process. Furthermore, we analyze the dSod3 localization and show that reduced activity of dSod3 impacts egg-laying behavior but not the chorion hardening process.

Sast1-mediated manifold effects inhibit Plutella xylostella fertility

BACKGROUND

Plutella xylostella (Linnaeus) is a destructive pest of cruciferous crops due to its strong reproductive capacity and extensive resistance to pesticides. Seminal fluid proteins (SFPs) are the main effective factors that determine the reproductive physiology and behaviour of both sexes. Although an increasing number of SFPs have been identified, the effects of astacins in SFPs on agricultural pests have not yet been reported. Here, we elucidated the mechanisms by which Sast1 (seminal astacin 1) regulates the fertility of Plutella xylostella (L.).

RESULTS

PxSast1 was specifically expressed in the testis and accesssory gland. CRISPR/Cas9-induced PxSast1 knockout successfully constructed two homozygous mutant strains. Sast1 impaired the fertility of P. xylostella by separately regulating the reproductive capacity of males and females. Loss of PxSast1, on the one hand, significantly decreased the ability of males to mate and fertilize, mainly manifested as shortened mating duration, reduced mating competitiveness and decreased eupyrene sperm production; on the other hand, it significantly inhibited the expression of chorion genes in females, resulting in oogenesis deficits. Simultaneously, for mated females, the differentially expressed genes in signalling pathways related to oogenesis and chorion formation were significantly enriched after PxSast1 knockout.

CONCLUSION

These analyses of the functions of PxSast1 as the regulator of spermatogenesis and oogenesis establish its importance in the fertility process of P. xylostella, as well as its potential as a promising target for genetic regulation-based pest control. © 2024 Society of Chemical Industry.

Comparative transcriptomic characterization of the ovary in the spawning process of the mud crab Scylla paramamosain

Oviposition is induced upon mating in most insects. Spawning is a physiological process that is fundamental for the reproduction of Scylla paramamosain. However, the molecular mechanisms underlying the spawning process in this species are poorly understood. Herein, comprehensive ovary transcriptomic analysis was conducted at the germinal vesicle breakdown stage (GVBD), spawning stage, 0.5 h post-spawning stage, and 24 h post-spawning stage of S. paramamosain for gene discovery. A total of 67,230 unigenes were generated, and 27,975 (41.61%) unigenes were annotated. Meanwhile, the differentially expressed genes (DEGs) between the different groups were identified, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was subsequently conducted. These results suggested that octopamine (OA) and tyramine (TA) could induce oviposition, while dopamine (DA) and serotonin (5-hydroxytryptamine [5-HT]) inhibit oviposition. The 20-hydroxyecdysone (20E) and methyl farnesoate (MF) signal pathways might be positively associated with oviposition. Furthermore, numerous transcripts that encode neuropeptides and their G-protein-coupled receptors (GPCRs), such as CNMamide, RYamide, ecdysis-triggering hormone (ETH), GPA2/GPB5 receptor, and Moody receptor, appear to be differentially expressed during the spawning process. Eleven unigenes were selected for qRT-PCR and the pattern was found to be consistent with the transcriptome expression pattern. Our work is the first spawning-related investigation of S. paramamosain focusing on the ovary at the whole transcriptome level. These findings assist in improving our understanding of spawning regulation in S. paramamosain and provide information for oviposition studies in other crustaceans.

ETS transcription factors regulate precise matrix metalloproteinase expression and follicle rupture in Drosophila

Drosophila matrix metalloproteinase 2 (MMP2) is specifically expressed in posterior follicle cells of stage-14 egg chambers (mature follicles) and is crucial for the breakdown of the follicular wall during ovulation, a process that is highly conserved from flies to mammals. The factors that regulate spatiotemporal expression of MMP2 in follicle cells remain unknown. Here, we demonstrate crucial roles for the ETS-family transcriptional activator Pointed (Pnt) and its endogenous repressor Yan in the regulation of MMP2 expression. We found that Pnt is expressed in posterior follicle cells and overlaps with MMP2 expression in mature follicles. Genetic analysis demonstrated that pnt is both required and sufficient for MMP2 expression in follicle cells. In addition, Yan was temporally upregulated in stage-13 follicle cells to fine-tune Pnt activity and MMP2 expression. Furthermore, we identified a 1.1 kb core enhancer that is responsible for the spatiotemporal expression of MMP2 and contains multiple pnt/yan binding motifs. Mutation of pnt/yan binding sites significantly impaired the Mmp2 enhancer activity. Our data reveal a mechanism of transcriptional regulation of Mmp2 expression in Drosophila ovulation, which could be conserved in other biological systems.

Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

Identification of genes regulated by 20-Hydroxyecdysone in Macrobrachium nipponense using comparative transcriptomic analysis

BACKGROUND

Macrobrachium nipponense is a freshwater prawn of economic importance in China. Its reproductive molt is crucial for seedling rearing and directly impacts the industry's economic efficiency. 20-hydroxyecdysone (20E) controls various physiological behaviors in crustaceans, among which is the initiation of molt. Previous studies have shown that 20E plays a vital role in regulating molt and oviposition in M. nipponense. However, research on the molecular mechanisms underlying the reproductive molt and role of 20E in M. nipponense is still limited.

RESULTS

A total of 240.24 Gb of data was obtained from 18 tissue samples by transcriptome sequencing, with > 6 Gb of clean reads per sample. The efficiency of comparison with the reference transcriptome ranged from 87.05 to 92.48%. A total of 2532 differentially expressed genes (DEGs) were identified. Eighty-seven DEGs associated with molt or 20E were screened in the transcriptomes of the different tissues sampled in both the experimental and control groups. The reliability of the RNA sequencing data was confirmed using Quantitative Real-Time PCR. The expression levels of the eight strong candidate genes showed significant variation at the different stages of molt.

CONCLUSION

This study established the first transcriptome library for the different tissues of M. nipponense in response to 20E and demonstrated the dominant role of 20E in the molting process of this species. The discovery of a large number of 20E-regulated strong candidate DEGs further confirms the extensive regulatory role of 20E and provides a foundation for the deeper understanding of its molecular regulatory mechanisms.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

The Drosophila drop-dead gene is required for eggshell integrity

The eggshell of the fruit fly Drosophila melanogaster is a useful model for understanding the synthesis of a complex extracellular matrix. The eggshell is synthesized during mid-to-late oogenesis by the somatic follicle cells that surround the developing oocyte. We previously reported that female flies mutant for the gene drop-dead (drd) are sterile, but the underlying cause of the sterility remained unknown. In this study, we examined the role of drd in eggshell synthesis. We show that eggs laid by drd mutant females are fertilized but arrest early in embryogenesis, and that the innermost layer of the eggshell, the vitelline membrane, is abnormally permeable to dye in these eggs. In addition, the major vitelline membrane proteins fail to become crosslinked by nonreducible bonds, a process that normally occurs during egg activation following ovulation, as evidenced by their solubility and detection by Western blot in laid eggs. In contrast, the Cp36 protein, which is found in the outer chorion layers of the eggshell, becomes crosslinked normally. To link the drd expression pattern with these phenotypes, we show that drd is expressed in the ovarian follicle cells beginning in mid-oogenesis, and, importantly, that all drd mutant eggshell phenotypes could be recapitulated by selective knockdown of drd expression in the follicle cells. To determine whether drd expression was required for the crosslinking itself, we performed in vitro activation and crosslinking experiments. The vitelline membranes of control egg chambers could become crosslinked either by incubation in hyperosmotic medium, which activates the egg chambers, or by exogenous peroxidase and hydrogen peroxide. In contrast, neither treatment resulted in the crosslinking of the vitelline membrane in drd mutant egg chambers. These results indicate that drd expression in the follicle cells is necessary for vitelline membrane proteins to serve as substrates for peroxidase-mediated cross-linking at the end of oogenesis.

Secretory oviducts contribute to the high egg-laying rate of physogastric termite queens (Isoptera: Termitidae)

Physogastric termite queens are characterized by a notorious enlargement of the abdomen triggered by an equal development of the ovaries. Other physogastry-related modifications have been reported on the fat body, cuticle, midgut, tracheal system, and hemolymph. Surprisingly, modifications on the lateral oviducts of these females, important sites for ovulation and egg transport, have received little attention. Here we took advantage of the high fecundity of physogastric queens in three termitid species to evaluate ovary development and also to compare the morphophysiological features of the lateral oviducts between early-mated and physogastric queens of Cornitermes cumulans. Older queens show well-developed ovaries, with numerous ovarioles connected to the lateral oviducts through pedicels. At these sites, several corpora lutea were observed, residual follicle cells from previous ovulation events. Such features were absent among early-mated queens and reflect then the maturity and ageing of the queens. Histological and histochemical analyses indicated that secretory activity of the lateral oviducts was also restricted to physogastric queens, in which proteins, but not polysaccharides, are secreted into the oviduct lumen. The likely function of these proteins, based on previous studies, is to lubricate the lateral oviducts and stimulate muscular contractions to the egg transport. The physogastry of termite queens is a notorious feature, characterized by several body modifications, especially concerning the ovaries. Our results shed light on the physogastry-related changes in the lateral oviducts of termite queens, as their increasing secretory activity is in agreement with the high number of eggs produced and transporting through these structures. Thus, such changes correspond to an important step allowing the high egg-laying rate shown by physogastric termite queens.

The bHLH-PAS transcriptional complex Sim:Tgo plays active roles in late oogenesis to promote follicle maturation and ovulation

Across species, ovulation is a process induced by a myriad of signaling cascades that ultimately leads to the release of encapsulated oocytes from follicles. Follicles first need to mature and gain ovulatory competency before ovulation; however, the signaling pathways regulating follicle maturation are incompletely understood in Drosophila and other species. Our previous work has shown that the bHLH-PAS transcription factor Single-minded (Sim) plays important roles in follicle maturation downstream of the nuclear receptor Ftz-f1 in Drosophila. Here, we demonstrate that Tango (Tgo), another bHLH-PAS protein, acts as a co-factor of Sim to promote follicle cell differentiation from stages 10 to 12. In addition, we discover that re-upregulation of Sim in stage-14 follicle cells is also essential to promote ovulatory competency by upregulating octopamine receptor in mushroom body (OAMB), matrix metalloproteinase 2 (Mmp2) and NADPH oxidase (NOX), either independently of or in conjunction with the zinc-finger protein Hindsight (Hnt). All these factors are crucial for successful ovulation. Together, our work indicates that the transcriptional complex Sim:Tgo plays multiple roles in late-stage follicle cells to promote follicle maturation and ovulation.

split-intein Gal4 provides intersectional genetic labeling that is repressible by Gal80

The split-Gal4 system allows for intersectional genetic labeling of highly specific cell types and tissues in Drosophila. However, the existing split-Gal4 system, unlike the standard Gal4 system, cannot be repressed by Gal80, and therefore cannot be controlled temporally. This lack of temporal control precludes split-Gal4 experiments in which a genetic manipulation must be restricted to specific timepoints. Here, we describe a split-Gal4 system based on a self-excising split-intein, which drives transgene expression as strongly as the current split-Gal4 system and Gal4 reagents, yet which is repressible by Gal80. We demonstrate the potent inducibility of "split-intein Gal4" in vivo using both fluorescent reporters and via reversible tumor induction in the gut. Further, we show that our split-intein Gal4 can be extended to the drug-inducible GeneSwitch system, providing an independent method for intersectional labeling with inducible control. We also show that the split-intein Gal4 system can be used to generate highly cell type-specific genetic drivers based on in silico predictions generated by single-cell RNAseq (scRNAseq) datasets, and we describe an algorithm ("Two Against Background" or TAB) to predict cluster-specific gene pairs across multiple tissue-specific scRNA datasets. We provide a plasmid toolkit to efficiently create split-intein Gal4 drivers based on either CRISPR knock-ins to target genes or using enhancer fragments. Altogether, the split-intein Gal4 system allows for the creation of highly specific intersectional genetic drivers that are inducible/repressible.

Regulation of morphogen pathways by a Drosophila chondroitin sulfate proteoglycan Windpipe

Morphogens provide quantitative and robust signaling systems to achieve stereotypic patterning and morphogenesis. Heparan sulfate (HS) proteoglycans (HSPGs) are key components of such regulatory feedback networks. In Drosophila, HSPGs serve as co-receptors for a number of morphogens, including Hedgehog (Hh), Wingless (Wg), Decapentaplegic (Dpp) and Unpaired (Upd, or Upd1). Recently, Windpipe (Wdp), a chondroitin sulfate (CS) proteoglycan (CSPG), was found to negatively regulate Upd and Hh signaling. However, the roles of Wdp, and CSPGs in general, in morphogen signaling networks are poorly understood. We found that Wdp is a major CSPG with 4-O-sulfated CS in Drosophila. Overexpression of wdp modulates Dpp and Wg signaling, showing that it is a general regulator of HS-dependent pathways. Although wdp mutant phenotypes are mild in the presence of morphogen signaling buffering systems, this mutant in the absence of Sulf1 or Dally, molecular hubs of the feedback networks, produces high levels of synthetic lethality and various severe morphological phenotypes. Our study indicates a close functional relationship between HS and CS, and identifies the CSPG Wdp as a novel component in morphogen feedback pathways.

Knockdown of the salivary protein gene NlG14 caused displacement of the lateral oviduct secreted components and inhibited ovulation in Nilaparvata lugens

Saliva plays important roles in insect feeding, but its roles in insect reproduction were rarely reported. Here we reported that the knockdown of a salivary gland-specific gene NlG14 disrupted the reproduction through inhibiting the ovulation of the brown planthopper (BPH), Nilaparvata lugens (Stål), one of the most devastating rice pests in Asia. NlG14 knockdown caused the displacement of the lateral oviduct secreted components (LOSC), leading to the ovulation disorder and the accumulation of mature eggs in the ovary. The RNAi-treated females laid much less eggs than their control counterparts, though they had the similar oviposition behavior on rice stems as controls. NlG14 protein was not secreted into the hemolymph, indicating an indirect effect of NlG14 knockdown on BPH reproduction. NlG14 knockdown caused the malformation of A-follicle of the principal gland and affected the underlying endocrine mechanism of salivary glands. NlG14 reduction might promote the secretion of insulin-like peptides NlILP1 and NlILP3 from the brain, which up-regulated the expression of Nllaminin gene and then caused the abnormal contraction of lateral oviduct muscle. Another explanation was NlG14 reduction disrupted the ecdysone biosynthesis and action through the insulin-PI3K-Akt signaling in ovary. Altogether, this study indicated that the salivary gland specific protein NlG14 indirectly mediated BPH ovulation process, which established a connexon in function between insect salivary gland and ovary.

split-intein Gal4 provides intersectional genetic labeling that is fully repressible by Gal80

The split-Gal4 system allows for intersectional genetic labeling of highly specific cell-types and tissues in Drosophila . However, the existing split-Gal4 system, unlike the standard Gal4 system, cannot be repressed by Gal80, and therefore cannot be controlled temporally. This lack of temporal control precludes split-Gal4 experiments in which a genetic manipulation must be restricted to specific timepoints. Here, we describe a new split-Gal4 system based on a self-excising split-intein, which drives transgene expression as strongly as the current split-Gal4 system and Gal4 reagents, yet which is fully repressible by Gal80. We demonstrate the potent inducibility of "split-intein Gal4" in vivo using both fluorescent reporters and via reversible tumor induction in the gut. Further, we show that our split-intein Gal4 can be extended to the drug-inducible GeneSwitch system, providing an independent method for intersectional labeling with inducible control. We also show that the split-intein Gal4 system can be used to generate highly cell-type specific genetic drivers based on in silico predictions generated by single cell RNAseq (scRNAseq) datasets, and we describe a new algorithm ("Two Against Background" or TAB) to predict cluster-specific gene pairs across multiple tissue-specific scRNA datasets. We provide a plasmid toolkit to efficiently create split-intein Gal4 drivers based on either CRISPR knock-ins to target genes or using enhancer fragments. Altogether, the split-intein Gal4 system allows for the creation of highly specific intersectional genetic drivers that are inducible/repressible.

Significance statement

The split-Gal4 system allows Drosophila researchers to drive transgene expression with extraordinary cell type specificity. However, the existing split-Gal4 system cannot be controlled temporally, and therefore cannot be applied to many important areas of research. Here, we present a new split-Gal4 system based on a self-excising split-intein, which is fully controllable by Gal80, as well as a related drug-inducible split GeneSwitch system. This approach can both leverage and inform single-cell RNAseq datasets, and we introduce an algorithm to identify pairs of genes that precisely and narrowly mark a desired cell cluster. Our split-intein Gal4 system will be of value to the Drosophila research community, and allow for the creation of highly specific genetic drivers that are also inducible/repressible.

Presence of non-symbiotic yeasts in a symbiont-transferring organ of a stag beetle that lacks yeast symbionts found in other stag beetles

Dispersal from wood to wood is essential for wood-inhabiting fungi and wood-inhabiting insects play an important role in the dispersal success of such fungi. However, it is poorly understood whether wood-inhabiting insects which change the habitats from wood to non-wood environments can contribute to the fungal dispersal. Larvae of most stag beetles (Coleoptera: Lucanidae) are wood feeders, while adults are sap feeders. Female adults of lulcanids possess specialized organs (mycetangia) for transportation of fungal symbionts and harbor specific yeasts (e.g., Scheffersomyces spp.) within. Here, we report that the lucanid Aegus subnitidus harbors non-specific yeasts facultatively in mycetangia. We conducted yeast isolation from mycetangia and hindguts of female adults, in a larval gallery in wood-associated materials, and in female-visiting fermented tree sap using culture-dependent methods. Less than half of the females carried a total of 20 yeast species with small amounts using mycetangia and a female harbored up to five species, suggesting the absence of an intimate association with specific yeasts that are found in other lucanids. Yeast species compositions markedly differed between the larval gallery and sap. Most yeasts from the larval galley exhibited xylose-assimilation abilities, while few yeasts from sap did. Mycetangial yeasts comprised a combination from both sources. In hindguts, most yeasts were found in sap (> 70%) with no yeasts in the larval gallery. Sap-associated yeasts in each female mycetangium were also obtained from the female-visiting sap patch, while mycetangial, larval gallery-associated yeasts were absent from the patch, suggesting the survival success of larval gallery-associated yeasts in mycetangia through sap patches. Therefore, wood-inhabiting insects that possess mycetangia can potentially act as vectors of non-symbiotic wood-inhabiting yeasts dispersing from wood to wood via other environments.

The Vast Utility of Drosophila Oogenesis

In this chapter, we highlight examples of the diverse array of developmental, cellular, and biochemical insights that can be gained by using Drosophila melanogaster oogenesis as a model tissue. We begin with an overview of ovary development and adult oogenesis. Then we summarize how the adult Drosophila ovary continues to advance our understanding of stem cells, cell cycle, cell migration, cytoplasmic streaming, nurse cell dumping, and cell death. We also review emerging areas of study, including the roles of lipid droplets, ribosomes, and nuclear actin in egg development. Finally, we conclude by discussing the growing conservation of processes and signaling pathways that regulate oogenesis and female reproduction from flies to humans.

Assessing Ovulation in Drosophila melanogaster

Ovulation is a critical reproductive process by which a mature oocyte is released from the ovary for fertilization. This process requires the coordination of multiple cellular and molecular events including the spatiotemporal breakdown of the follicle wall. Recent work has shown that ovulation in Drosophila utilizes conserved cellular processes and molecular pathways as in mammals. Thus, Drosophila ovulation can serve as a good model to decipher the fundamental mechanisms of ovulation utilized across species. In past decades, several methods have been developed to study Drosophila ovulation, but all of them have drawbacks. This chapter offers a strategy and detailed protocols for performing and analyzing the necessary assays to evaluate the ovulation process in Drosophila.

Insulin-like peptide 8 (Ilp8) regulates female fecundity in flies

Introduction: Insulin-like peptides (Ilps) play crucial roles in nearly all life stages of insects. Ilp8 is involved in developmental stability, stress resistance and female fecundity in several insect species, but the underlying mechanisms are not fully understood. Here we report the functional characterization of Ilp8s in three fly species, including Bactrocera dorsalis, Drosophila mercatorum and Drosophila melanogaster. Methods: Phylogenetic analyses were performed to identify and characterize insect Ilp8s. The amino acid sequences of fly Ilp8s were aligned and the three-dimensional structures of fly Ilp8s were constructed and compared. The tissue specific expression pattern of fly Ilp8s were examined by qRT-PCR. In Bactrocera dorsalis and Drosophila mercatorum, dsRNAs were injected into virgin females to inhibit the expression of Ilp8 and the impacts on female fecundity were examined. In Drosophila melanogaster, the female fecundity of Ilp8 loss-of-function mutant was compared with wild type control flies. The mutant fruit fly strain was also used for sexual behavioral analysis and transcriptomic analysis. Results: Orthologs of Ilp8s are found in major groups of insects except for the lepidopterans and coleopterans, and Ilp8s are found to be well separated from other Ilps in three fly species. The key motif and the predicted three-dimensional structure of fly Ilp8s are well conserved. Ilp8 are specifically expressed in the ovary and are essential for female fecundity in three fly species. Behavior analysis demonstrates that Ilp8 mutation impairs female sexual attractiveness in fruit fly, which results in decreased mating success and is likely the cause of fecundity reduction. Further transcriptomic analysis indicates that Ilp8 might influence metabolism, immune activity, oocyte development as well as hormone homeostasis to collectively regulate female fecundity in the fruit fly. Discussion: Our findings support a universal role of insect Ilp8 in female fecundity, and also provide novel clues for understanding the modes of action of Ilp8.

Search performance and octopamine neuronal signaling mediate parasitoid induced changes in Drosophila oviposition behavior

Making the appropriate responses to predation risk is essential for the survival of an organism; however, the underlying mechanisms are still largely unknown. Here, we find that Drosophila has evolved an adaptive strategy to manage the threat from its parasitoid wasp by manipulating the oviposition behavior. Through perception of the differences in host search performance of wasps, Drosophila is able to recognize younger wasps as a higher level of threat and consequently depress the oviposition. We further show that this antiparasitoid behavior is mediated by the regulation of the expression of Tdc2 and Tβh in the ventral nerve cord via LC4 visual projection neurons, which in turn leads to the dramatic reduction in octopamine and the resulting dysfunction of mature follicle trimming and rupture. Our study uncovers a detailed mechanism underlying the defensive behavior in insects that may advance our understanding of predator avoidance in animals.

Nuclear Progestin Receptor-mediated Linkage of Blood Coagulation and Ovulation

Ovulation is a dramatic remodeling process that includes rupture of blood capillaries and clotting, but coagulation is not thought to directly regulate this process. Herein, we report remarkable increases of coagulation factors V (f5, ~3145-fold) and tissue factor (f3a, ~120-fold) in zebrafish ovarian follicle cells during ovulation. This increase was mediated through the nuclear progestin receptor (Pgr), which is essential for ovulation in zebrafish, and was totally abolished in ovarian follicular cells from pgr-/- mutants. In addition, promoter activities of f5 and f3a were significantly enhanced by progestin (DHP) via Pgr. Similar regulation of human F5 promoter activity was induced via human PGRB, suggesting a conserved mechanism. Site-directed mutagenesis of the zebrafish f5 promoter further demonstrated a direct regulation of coagulation factors via progestin response elements. Moreover, a stark increase of erythrocytes occurred in capillaries meshed in wild-type preovulatory follicles but was absent in pgr-/- mutants. Interestingly, anticoagulants significantly inhibited ovulation both in vitro and in vivo, respectively. Furthermore, reduced fecundity was observed in f5+/- female zebrafish. Taken together, our study provides plausible evidence for steroid regulation of coagulation factors, and a new hypothesis for blood clotting-triggered ovulation in vertebrates.

Proteome and Transcriptome Analysis of Gonads Reveals Intersex in Gigantidas haimaensis

Sex has proven to be one of the most intriguing areas of research across evolution, development, and ecology. Intersex or sex change occurs frequently in molluscs. The deep-sea mussel Gigantidas haimaensis often dominates within Haima cold seep ecosystems, but details of their reproduction remain unknown. Herein, we conducted a combined proteomic and transcriptomic analysis of G. haimaensis gonads to provide a systematic understanding of sexual development in deep-sea bivalves. A total of 2,452 out of 42,238 genes (5.81%) and 288 out of 7,089 proteins (4.06%) were significantly differentially expressed between ovaries and testes with a false discovery rate (FDR) <0.05. Candidate genes involved in sexual development were identified; among 12 differentially expressed genes between sexes, four ovary-biased genes (β-catenin, fem-1, forkhead box L2 and membrane progestin receptor α) were expressed significantly higher in males than females. Combining histological characteristics, we speculate that the males maybe intersex undergoing sex change, and implied that these genes may be involved in the process of male testis converting into female gonads in G. haimaensis. The results suggest that this adaptation may be based on local environmental factors, sedentary lifestyles, and patchy distribution, and sex change may facilitate adaptation to a changing environment and expansion of the population. The findings provide a valuable genetic resource to better understand the mechanisms of sex change and survival strategies in deep-sea bivalves.

Roles of matrix metalloproteinases in development, immunology, and ovulation in fruit Fly (Drosophila)

Matrix metalloproteinase (MMP), a protease enzyme, participates in proteolytic cleavage of extracellular matrix proteins from Drosophila and mammals. But, recent studies have revealed other physiologically important roles of MMP in Drosophila. MMP contributes to cardioblast movement and distribution of collagen proteins during cardiogenesis in developing Drosophila. Tissue remodeling, especially tracheal development is also maintained by MMP. MMP regulates certain immunological functions in Drosophila such as wound repairing, plasmatocyte assemblage at the injured site of the basement membrane and glial response to axon degeneration in Drosophila nervous system. But, the contribution of MMP to tumor formation and metastasis in Drosophila has made it an interesting topic among researchers. Ovulation and egg laying are also found to be affected positively by MMP in Drosophila.

Omics Studies for the Identification of Ascidian Peptides, Cognate Receptors, and Their Relevant Roles in Ovarian Follicular Development

Omics studies contribute to the elucidation of genomes and profiles of gene expression. In the ascidian Ciona intestinalis Type A (Ciona robusta), mass spectrometry (MS)-based peptidomic studies have detected numerous Ciona-specific (nonhomologous) neuropeptides as well as Ciona homologs of typical vertebrate neuropeptides and hypothalamic peptide hormones. Candidates for cognate G protein-coupled receptors (GPCRs) for these peptides have been found in the Ciona transcriptome by two ways. First, Ciona homologous GPCRs of vertebrate counterparts have been detected by sequence homology searches of cognate transcriptomes. Second, the transcriptome-derived GPCR candidates have been used for machine learning-based systematic prediction of interactions not only between Ciona homologous peptides and GPCRs but also between novel Ciona peptides and GPCRs. These data have ultimately led to experimental evidence for various Ciona peptide-GPCR interactions. Comparative transcriptomics between the wildtype and Ciona vasopressin (CiVP) gene-edited Ciona provide clues to the biological functions of CiVP in ovarian follicular development and whole body growth. Furthermore, the transcriptomes of follicles treated with peptides, such as Ciona tachykinin and cionin (a Ciona cholecystokinin homolog), have revealed key regulatory genes for Ciona follicle growth, maturation, and ovulation, eventually leading to the verification of essential and novel molecular mechanisms underlying these biological events. These findings indicate that omics studies, combined with artificial intelligence and single-cell technologies, pave the way for investigating in greater details the nervous, neuroendocrine, and endocrine systems of ascidians and the molecular and functional evolution and diversity of peptidergic regulatory networks throughout chordates.

Proteolysis in Reproduction: Lessons From Gene-Modified Organism Studies

The physiological roles of proteolysis are not limited to degrading unnecessary proteins. Proteolysis plays pivotal roles in various biological processes through cleaving peptide bonds to activate and inactivate proteins including enzymes, transcription factors, and receptors. As a wide range of cellular processes is regulated by proteolysis, abnormalities or dysregulation of such proteolytic processes therefore often cause diseases. Recent genetic studies have clarified the inclusion of proteases and protease inhibitors in various reproductive processes such as development of gonads, generation and activation of gametes, and physical interaction between gametes in various species including yeast, animals, and plants. Such studies not only clarify proteolysis-related factors but the biological processes regulated by proteolysis for successful reproduction. Here the physiological roles of proteases and proteolysis in reproduction will be reviewed based on findings using gene-modified organisms.

The dual roles of three MMPs and TIMP in innate immunity and metamorphosis in the silkworm, Bombyx mori

The matrix metalloproteinases (MMPs) and their endogenous inhibitory factors, tissue inhibitors of metalloproteinases (TIMPs), are implicated in many diseases. However, the mammalian MMPs (> 20) and TIMPs (> 3) are larger in number, and so little is known about their individual roles in organisms. Hence, we have systematically studied the roles of all three MMPs and one TIMP in silkworm innate immunity and metamorphosis. We observed that MMPs and TIMP are highly expressed during the pupation stage of the silkworms, and TIMP could interact with each MMPs. High-activity MMPs and low-activity TIMP may enhance the infection of B. mori nucleopolyhedrovirus in both in vitro and in vivo. MMPs' knockout and TIMP overexpression delayed silkworm development and even caused death. Interestingly, different MMPs' knockout led to different tubular tissue dysplasia. These findings provide insights into the conserved functions of MMPs and TIMP in human organogenesis and immunoregulation.

Metalloproteases in gonad formation and ovulation

Changes in expression or activation of various metalloproteases including matrix metalloproteases (Mmp), a disintegrin and metalloprotease (Adam) and a disintegrin and metalloprotease with thrombospondin motif (Adamts), and their endogenous inhibitors (tissue inhibitors of metalloproteases, Timp), have been shown to be critical for ovulation in various species from studies in past decades. Some of these metalloproteases such as Adamts1, Adamts9, Mmp2, and Mmp9 have also been shown to be regulated by luteinizing hormone (LH) and/or progestin, which are essential triggers for ovulation in all vertebrate species. Most of these metalloproteases also express broadly in various tissues and cells including germ cells and somatic gonad cells. Thus, metalloproteases likely play roles in gonad formation processes comprising primordial germ cell (PGC) migration, development of germ and somatic cells, and sex determination. However, our knowledge on the functions and mechanisms of metalloproteases in these processes in vertebrates is still lacking. This review will summarize our current knowledge on the metalloproteases in ovulation and gonad formation with emphasis on PGC migration and germ cell development.

On the Origin and Evolution of Drosophila New Genes during Spermatogenesis

The origin of functional new genes is a basic biological process that has significant contribution to organismal diversity. Previous studies in both Drosophila and mammals showed that new genes tend to be expressed in testes and avoid the X chromosome, presumably because of meiotic sex chromosome inactivation (MSCI). Here, we analyze the published single-cell transcriptome data of Drosophila adult testis and find an enrichment of male germline mitotic genes, but an underrepresentation of meiotic genes on the X chromosome. This can be attributed to an excess of autosomal meiotic genes that were derived from their X-linked mitotic progenitors, which provides direct cell-level evidence for MSCI in Drosophila. We reveal that new genes, particularly those produced by retrotransposition, tend to exhibit an expression shift toward late spermatogenesis compared with their parental copies, probably due to the more intensive sperm competition or sexual conflict. Our results dissect the complex factors including age, the origination mechanisms and the chromosomal locations that influence the new gene origination and evolution in testes, and identify new gene cases that show divergent cell-level expression patterns from their progenitors for future functional studies.

Juvenile hormone signaling promotes ovulation and maintains egg shape by inducing expression of extracellular matrix genes

It is well documented that the juvenile hormone (JH) can function as a gonadotropic hormone that stimulates vitellogenesis by activating the production and uptake of vitellogenin in insects. Here, we describe a phenotype associated with mutations in the Drosophila JH receptor genes, Met and Gce: the accumulation of mature eggs with reduced egg length in the ovary. JH signaling is mainly activated in ovarian muscle cells and induces laminin gene expression in these cells. Meanwhile, JH signaling induces collagen IV gene expression in the adult fat body, from which collagen IV is secreted and deposited onto the ovarian muscles. Laminin locally and collagen IV remotely contribute to the assembly of ovarian muscle extracellular matrix (ECM); moreover, the ECM components are indispensable for ovarian muscle contraction. Furthermore, ovarian muscle contraction externally generates a mechanical force to promote ovulation and maintain egg shape. This work reveals an important mechanism for JH-regulated insect reproduction.

Drosophila Accessory Gland: A Complementary In Vivo Model to Bring New Insight to Prostate Cancer

Prostate cancer is the most common cancer in aging men. Despite recent progress, there are still few effective treatments to cure its aggressive and metastatic stages. A better understanding of the molecular mechanisms driving disease initiation and progression appears essential to support the development of more efficient therapies and improve patient care. To do so, multiple research models, such as cell culture and mouse models, have been developed over the years and have improved our comprehension of the biology of the disease. Recently, a new model has been added with the use of the Drosophila accessory gland. With a high level of conservation of major signaling pathways implicated in human disease, this functional equivalent of the prostate represents a powerful, inexpensive, and rapid in vivo model to study epithelial carcinogenesis. The purpose of this review is to quickly overview the existing prostate cancer models, including their strengths and limitations. In particular, we discuss how the Drosophila accessory gland can be integrated as a convenient complementary model by bringing new understanding in the mechanisms driving prostate epithelial tumorigenesis, from initiation to metastatic formation.

Mating-Induced Trade-Offs upon Egg Production versus Fertilization and Offspring's Survival in a Sawfly with Facultative Parthenogenesis

Investigation of mating-induced trade-offs between reproduction and survival is conducive to provide evolutionary insights into reproductive strategies and aging. Here, we used RNAseq and bioinformatics to reveal mating-induced changes of genes and pathways related to reproduction and survival in female Cephalcia chuxiongica, a pine defoliator with facultative parthenogenesis and long larval dormancy. Results showed that mating induced substantial downregulation on genes and pathways associated to immunity, stress response, and longevity. However, mating induced divergent reproductive response, with downregulation on genes and pathways related to egg production while upregulation on genes and pathways related to egg fertilization. Considering the nature of limited resources in adults, low fecundity, and egg protection behavior in C. chuxiongica, we suggest that mating triggers trade-offs between reproduction and survival in this insect and females of this species may have evolved specific strategies to adapt to the environmental and hosts' conditions, e.g., restrict whole fecundity to ensure higher fertilization and offspring's survival. Moreover, mating induced significant responses on genes and pathways that play important roles in vertebrate reproduction while their function in insects are unclear, such as the progesterone-mediated oocyte maturation pathway; the significant regulation after mating suggests that their function may be evolutionarily conserved in animal kingdom.

A platform utilizing Drosophila ovulation for nonhormonal contraceptive screening

A significant unmet need for new contraceptive options for both women and men remains due to side-effect profiles, medical concerns, and the inconvenience of many currently available contraceptive products. Unfortunately, the development of novel nonsteroidal female contraceptive medicine has been stalled in the last couple of decades due to the lack of effective screening platforms. Drosophila utilizes conserved signaling pathways for follicle rupture, a final step in ovulation that is essential for female reproduction. Therefore, we explored the potential to use Drosophila as a model to screen compounds that could inhibit follicle rupture and be nonsteroidal contraceptive candidates. Using our ex vivo follicle rupture assay, we screened 1,172 Food and Drug Administration (FDA)-approved drugs and identified six drugs that could inhibit Drosophila follicle rupture in a dose-dependent manner. In addition, we characterized the molecular actions of these drugs in the inhibition of adrenergic signaling and follicle rupture. Furthermore, we validated that three of the four drugs consistently inhibited mouse follicle rupture in vitro and that two of them did not affect progesterone production. Finally, we showed that chlorpromazine, one of the candidate drugs, can significantly inhibit mouse follicle rupture in vivo. Our work suggests that Drosophila ovulation is a valuable platform for identifying lead compounds for nonsteroidal contraceptive development and highlights the potential of these FDA-approved drugs as novel nonsteroidal contraceptive agents.

Dissection of the Ovulatory Process Using ex vivo Approaches

Ovulation is a unique physiological phenomenon that is essential for sexual reproduction. It refers to the entire process of ovarian follicle responses to hormonal stimulation resulting in the release of mature fertilization-competent oocytes from the follicles and ovaries. Remarkably, ovulation in different species can be reproduced out-of-body with high fidelity. Moreover, most of the molecular mechanisms and signaling pathways engaged in this process have been delineated using in vitro ovulation models. Here, we provide an overview of the major molecular and cytological events of ovulation observed in frogs, primarily in the African clawed frog Xenopus laevis, using mainly ex vivo approaches, with the focus on meiotic oocyte maturation and follicle rupture. For the purpose of comparison and generalization, we also refer extensively to ovulation in other biological species, most notoriously, in mammals.

Neuronal octopamine signaling regulates mating-induced germline stem cell increase in female Drosophila melanogaster

Stem cells fuel the development and maintenance of tissues. Many studies have addressed how local signals from neighboring niche cells regulate stem cell identity and their proliferative potential. However, the regulation of stem cells by tissue-extrinsic signals in response to environmental cues remains poorly understood. Here we report that efferent octopaminergic neurons projecting to the ovary are essential for germline stem cell (GSC) increase in response to mating in female Drosophila. The neuronal activity of the octopaminergic neurons is required for mating-induced GSC increase as they relay the mating signal from sex peptide receptor-positive cholinergic neurons. Octopamine and its receptor Oamb are also required for mating-induced GSC increase via intracellular Ca²⁺ signaling. Moreover, we identified Matrix metalloproteinase-2 as a downstream component of the octopamine-Ca²⁺ signaling to induce GSC increase. Our study provides a mechanism describing how neuronal system couples stem cell behavior to environmental cues through stem cell niche signaling.

NADPH Oxidase 5 Is Essential for Molting and Oviposition in a Rice Planthopper Nilaparvata lugens

The brown planthopper Nilaparvata lugens is a typical monophagous insect herbivore that feeds exclusively on rice sap. This insect pest causes serious damage to rice crops throughout East Asian countries. Chemical control remains the first choice for managing N. lugens populations; however, the use of insecticides has given rise to planthopper resurgence and additional environmental risks. Nilaparvata lugens is a model insect of Hemiptera because its whole genome sequence has been elucidated and is susceptible to RNA interference. In this study, our findings revealed that a superoxide-generating gene, NADPH oxidase 5 (Nox5), is essential for molting and oviposition in a Hemipteran insect Nilaparvata lugens. Knockdown of Nox5 transcript levels by RNA interference in 2nd-5th-instar nymphs results in significantly lethal deficits in the molting transitions from nymph-nymph and nymph-adult. Nox5 knockdown leads to a reduction of hydrogen peroxide in female ovaries and failure of oviposition from the insect ovipositor into the rice leaf sheath. Here, we provide in vivo evidence demonstrating that Nox5 is a key enzyme for regulating molting and oviposition in this insect species.

Drosophila Insulin-Like Peptide 8 (DILP8) in Ovarian Follicle Cells Regulates Ovulation and Metabolism

In Drosophila melanogaster eight insulin-like peptides (DILP1-8) are encoded on separate genes. These DILPs are characterized by unique spatial and temporal expression patterns during the lifecycle. Whereas, functions of several of the DILPs have been extensively investigated at different developmental stages, the role of DILP8 signaling is primarily known from larvae and pupae where it couples organ growth and developmental transitions. In adult female flies, a study showed that a specific set of neurons that express the DILP8 receptor, Lgr3, is involved in regulation of reproductive behavior. Here, we further investigated the expression of dilp8/DILP8 and Lgr3 in adult female flies and the functional role of DILP8 signaling. The only site where we found both dilp8 expression and DILP8 immunolabeling was in follicle cells around mature eggs. Lgr3 expression was detected in numerous neurons in the brain and ventral nerve cord, a small set of peripheral neurons innervating the abdominal heart, as well as in a set of follicle cells close to the oviduct. Ovulation was affected in dilp8 mutants as well as after dilp8-RNAi using dilp8 and follicle cell Gal4 drivers. More eggs were retained in the ovaries and fewer were laid, indicating that DILP8 is important for ovulation. Our data suggest that DILP8 signals locally to Lgr3 expressing follicle cells as well as systemically to Lgr3 expressing efferent neurons in abdominal ganglia that innervate oviduct muscle. Thus, DILP8 may act at two targets to regulate ovulation: follicle cell rupture and oviduct contractions. Furthermore, we could show that manipulations of dilp8 expression affect starvation resistance suggesting effects on metabolism. Possibly this reflects a feedback signaling between ovaries and the CNS that ensures nutrients for ovary development. In summary, it seems that DILP8 signaling in regulation of reproduction is an ancient function, conserved in relaxin signaling in mammals.

Role of Biogenic Amines in Oviposition by the Diamondback Moth, Plutella xylostella L

Oviposition is an important reproductive behavior that is triggered by mating in insects, and biogenic amines might be involved in its regulation. The effects of biogenic amines on oviposition have only been studied in a few insect species, and the findings to date have not been conclusive. In addition, there are few studies on the effects of biogenic amines on oviposition of the diamondback moth, Plutella xylostella L. Here, we tested how mating and biogenic amines regulate oviposition of P. xylostella by injecting amines and amine receptor antagonists into virgin and mated females and counting the number of eggs laid afterward. Biogenic amines of octopamine and tyramine could induce virgin adults of P. xylostella to lay eggs, while dopamine and serotonin had no such effect on oviposition. Furthermore, the octopamine antagonists mianserin, epinastine, and phentolamine inhibited oviposition by mated females. The tyramine antagonist yohimbine, dopamine antagonist SCH23390, and serotonin antagonist ketanserin did not block oviposition by mated females, and octopamine and tyramine-inducing oviposition by virgin females could be inhibited by the octopamine antagonists mianserin and epinastine instead of the tyramine antagonist yohimbine. We conclude that octopamine and its receptors are involved in mating-triggered oviposition in P. xylostella, while tyramine acts as a subsidiary. Further, the inducing effect of tyramine on oviposition is achieved via octopamine receptors instead of tyramine receptors. This experiment is helpful to further understand the role of biogenic amines in mating regulation and to provide a new strategy for controlling P. xylostella.

Nuclear receptor Ftz-f1 promotes follicle maturation and ovulation partly via bHLH/PAS transcription factor Sim

The NR5A-family nuclear receptors are highly conserved and function within the somatic follicle cells of the ovary to regulate folliculogenesis and ovulation in mammals; however, their roles in Drosophila ovaries are largely unknown. Here, we discover that Ftz-f1, one of the NR5A nuclear receptors in Drosophila, is transiently induced in follicle cells in late stages of oogenesis via ecdysteroid signaling. Genetic disruption of Ftz-f1 expression prevents follicle cell differentiation into the final maturation stage, which leads to anovulation. In addition, we demonstrate that the bHLH/PAS transcription factor Single-minded (Sim) acts as a direct target of Ftz-f1 to promote follicle cell differentiation/maturation and that Ftz-f1’s role in regulating Sim expression and follicle cell differentiation can be replaced by its mouse homolog steroidogenic factor 1 (mSF-1). Our work provides new insight into the regulation of follicle maturation in Drosophila and the conserved role of NR5A nuclear receptors in regulating folliculogenesis and ovulation.

When animals reproduce, females release eggs from their ovaries which then get fertilized by sperm from males. Each egg needs to properly mature within a collection of cells known as follicle cells before it can be let go. As the egg matures, so do the follicle cells surrounding it, until both are primed and ready to discharge the egg from the ovary. Mammals rely on a protein called SF-1 to mature their follicle cells, but it is unclear how this process works.

Most animals – from humans to fruit flies – release their eggs in a very similar way, using many of the same proteins and genes. For example, the gene for SF-1 in mammals is similar to a gene in fruit flies which codes for another protein called Ftz-f1. Since it is more straightforward to study ovaries in fruit flies than in humans and other mammals, investigating this protein could shed light on how follicle cells mature. However, it remained unclear whether Ftz-f1 plays a similar role to its mammalian counterpart.

Here, Knapp et al. show that Ftz-f1 is present in the follicle cells of fruit flies and is required for them to properly mature. Ftz-f1 controlled this process by regulating the activity of another protein called Sim. Further experiments found that the gene that codes for the SF-1 protein in mice was able to compensate for the loss of Ftz-f1 and drive follicle cells to mature.

Studying how ovaries release eggs is an essential part of understanding female fertility. This work highlights the similarities between these processes in mammals and fruit flies and may help us understand how ovaries work in humans and other mammals. In the future, the findings of Knapp et al. may lead to new therapies for infertility in females and other disorders that affect ovaries.

A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis

Oogenesis is a complex developmental process that involves spatiotemporally regulated coordination between the germline and supporting, somatic cell populations. This process has been modeled extensively using the Drosophila ovary. Although different ovarian cell types have been identified through traditional means, the large-scale expression profiles underlying each cell type remain unknown. Using single-cell RNA sequencing technology, we have built a transcriptomic data set for the adult Drosophila ovary and connected tissues. Using this data set, we identified the transcriptional trajectory of the entire follicle-cell population over the course of their development from stem cells to the oogenesis-to-ovulation transition. We further identify expression patterns during essential developmental events that take place in somatic and germline cell types such as differentiation, cell-cycle switching, migration, symmetry breaking, nurse-cell engulfment, egg-shell formation, and corpus luteum signaling. Extensive experimental validation of unique expression patterns in both ovarian and nearby, nonovarian cells also led to the identification of many new cell type-and stage-specific markers. The inclusion of several nearby tissue types in this data set also led to our identification of functional convergence in expression between distantly related cell types such as the immune-related genes that were similarly expressed in immune cells (hemocytes) and ovarian somatic cells (stretched cells) during their brief phagocytic role in nurse-cell engulfment. Taken together, these findings provide new insight into the temporal regulation of genes in a cell-type specific manner during oogenesis and begin to reveal the relatedness in expression between cell and tissues types.

Mating status and the evolution of eusociality: Oogenesis is independent of mating status in the solitary bee Osmia bicornis

The fundamental trait underlying eusociality is the reproductive division of labour. In honeybees (Apis mellifera), queens lay eggs while workers forage, defend and care for brood. The division of labour is maintained by pheromones including queen mandibular pheromone (QMP) produced by the queen. QMP constrains reproduction in adult honeybee workers, but in the absence of their queen workers can activate their ovaries and, although they cannot mate, they lay haploid male eggs. The reproductive ground plan hypothesis suggests that reproductive constraint may have evolved by co-opting mechanisms of reproductive control in solitary ancestors. In many insects mating is required to activate or accelerate oogenesis. Here, we use the solitary bee Osmia bicornis (Megachilidae) to test whether reproductive constraint evolved from ancestral control of reproduction by mating status. We present a structural study of the O. bicornis ovary, and compare key stages of oogenesis with honeybee workers. Importantly, we show that mating does not affect any aspect of the reproductive physiology of O. bicornis. We therefore conclude that mechanisms governing reproductive constraint in honeybees were unlikely to have been co-opted from mechanisms pertaining to mating status.

Downregulation of homeodomain protein Cut is essential for Drosophila follicle maturation and ovulation

Proper development and maturation of a follicle is essential for successful ovulation and reproduction; however, the molecular mechanisms for follicle maturation, particularly for somatic follicle cell differentiation, are poorly understood. During Drosophila oogenesis, the somatic follicle cells encasing oocytes undergo two distinct well-established transitions: the mitotic to endocycle switch at stage 6/7 and the endocycle to gene amplification switch at stage10A/10B. Here, we identify a novel third follicle cell transition that occurs in the final stages of oogenesis (stage 13/14). This late follicle cell transition is characterized by upregulation of the transcription factor Hindsight (Hnt), and downregulation of the homeodomain transcription factor Cut and the zinc-finger transcription factor Tramtrack-69 (Ttk69). We demonstrate that inducing expression of Cut in stage 14 follicle cells is sufficient to inhibit follicle rupture and ovulation through its negative regulation of Hnt and promotion of Ttk69 expression. Our work illustrates the importance of the stage13/14 transition for follicle maturation and demonstrates the complex regulation required for somatic follicle cells to differentiate into a state primed for follicle rupture and ovulation.

Multiple Pools of Nuclear Actin

While nuclear actin was reported ~50 years ago, it's in vivo prevalence and structure remain largely unknown. Here, we use Drosophila oogenesis, that is, follicle development, to characterize nuclear actin. We find that three different reagents-DNase I, anti-actin C4, and anti-actin AC15-recognize distinct pools of nuclear actin. DNase I labels monomeric or G-actin, and, during follicle development, G-actin is present in the nucleus of every cell. Some G-actin is recognized by the C4 antibody. In particular, C4 nuclear actin colocalizes with DNase I to the nucleolus in anterior escort cells, follicle stem cells, some mitotic follicle cells, and a subset of nurse cells during early oogenesis. C4 also labels polymeric nuclear actin in the nucleoplasm of the germline stem cells, early cystoblasts, and oocytes. The AC15 antibody labels a completely distinct pool of nuclear actin from that of DNase I and C4. Specifically, AC15 nuclear actin localizes to the chromatin in the nurse and follicle cells during mid-to-late oogenesis. Within the oocyte, AC15 nuclear actin progresses from localizing to puncta surrounding the DNA, to forming a filamentous cage around the chromosomes. Together these findings reveal that nuclear actin is highly prevalent in vivo, and multiple pools of nuclear actin exist and can be recognized using different reagents. Additionally, our localization studies suggest that nuclear actin may regulate stemness, nucleolar structure and function, transcription, and nuclear structure. Such findings call for further studies to explore the prevalence, diversity, and functions of nuclear actin across tissues and organisms. Anat Rec, 301:2014-2036, 2018. © 2018 Wiley Periodicals, Inc.

Activating embryonic development in Drosophila

The transition from oocyte to embryo marks the onset of development. This process requires complex regulation to link developmental signals with profound changes in mRNA translation, cell cycle control, and metabolism. This control is beginning to be understood for most organisms, and research in the fruit fly Drosophila melanogaster has generated new insights. Recent findings have increased our understanding of the roles played by hormone and Ca2+ signaling events as well as metabolic remodeling crucial for this transition. Specialized features of the structure and assembly of the meiotic spindle have been identified. The changes in protein levels, mRNA translation, and polyadenylation that occur as the oocyte becomes an embryo have been identified together with key aspects of their regulation. Here we highlight these important developments and the insights they provide on the intricate regulation of this dramatic transition.

Matrix metalloproteinases promote fat body cell dissociation and ovary development in Bombyx mori

Matrix metalloproteinases (Mmps) are pivotal extracellular proteinases participating in tissue remodeling. Three Mmps genes have been identified from the silkworm, Bombyx mori, and their expression levels and enzyme activity are consistent with progressive fat body cell dissociation during the early pupal stages. Using both loss-of-function and gain-of-function experiments, we have demonstrated that Mmps are functionally required for fat body cell dissociation and ovary development in female pupae. Moderate inhibition of Mmps activity via inhibitor treatments delayed fat body cell dissociation and ovary development, while severe inhibition blocked these developmental processes and eventually led to pupal lethality. Individual RNAi knockdown of each Mmp delayed fat body cell dissociation, with the strongest and weakest phenotypes occurring for Mmp3 and Mmp1, respectively. By contrast, overexpression of each Mmp promoted fat body cell dissociation and ovary development, with the strongest stimulatory effects for Mmp3 overexpression and the weakest effects for Mmp1 overexpression. This is the first time to show that Mmps induce fat body cell dissociation in Lepidoptera, and we also hypothesize that Mmps-induced fat body cell dissociation is required for ovary development in this insect species.

The Drosophila Hox gene Ultrabithorax controls appendage shape by regulating extracellular matrix dynamics

Although the specific form of an organ is frequently important for its function, the mechanisms underlying organ shape are largely unknown. In Drosophila, the wings and halteres, homologous appendages of the second and third thoracic segments, respectively, bear different forms: wings are flat, whereas halteres are globular, and yet both characteristic shapes are essential for a normal flight. The Hox gene Ultrabithorax (Ubx) governs the difference between wing and haltere development, but how Ubx function in the appendages prevents or allows flat or globular shapes is unknown. Here, we show that Ubx downregulates Matrix metalloproteinase 1 (Mmp1) expression in the haltere pouch at early pupal stage, which in turn prevents the rapid clearance of Collagen IV compared with the wing disc. This difference is instrumental in determining cell shape changes, expansion of the disc and apposition of dorsal and ventral layers, all of these phenotypic traits being characteristic of wing pouch development. Our results suggest that Ubx regulates organ shape by controlling Mmp1 expression, and the extent and timing of extracellular matrix degradation.

NADPH oxidase-generated reactive oxygen species in mature follicles are essential for Drosophila ovulation

Ovarian reactive oxygen species (ROS) are believed to regulate ovulation in mammals, but the details of ROS production in follicles and the role of ROS in ovulation in other species remain underexplored. In Drosophila ovulation, matrix metalloproteinase 2 (MMP2) is required for follicle rupture by degradation of posterior follicle cells surrounding a mature oocyte. We recently demonstrated that MMP2 activation and follicle rupture are regulated by the neuronal hormone octopamine (OA) and the octopamine receptor in mushroom body (OAMB). In the current study, we investigated the role of the superoxide-generating enzyme NADPH oxidase (NOX) in Drosophila ovulation. We report that Nox is highly enriched in mature follicle cells and that Nox knockdown in these cells leads to a reduction in superoxide and to defective ovulation. Similar to MMP2 activation, NOX enzymatic activity is also controlled by the OA/OAMB-Ca²⁺ signaling pathway. In addition, we report that extracellular superoxide dismutase 3 (SOD3) is required to convert superoxide to hydrogen peroxide, which acts as the key signaling molecule for follicle rupture, independent of MMP2 activation. Given that Nox homologs are expressed in mammalian follicles, the NOX-dependent hydrogen peroxide signaling pathway that we describe could play a conserved role in regulating ovulation in other species.