Notch Signaling during Oogenesis in Drosophila melanogaster

RNAi screen in the Drosophila wing of genes encoding proteins related to cytoskeleton organization and cell division

Cell division and cytoskeleton organization are fundamental processes participating in the development of Drosophila imaginal discs. In this manuscript we describe the phenotypes in the adult fly wing generated by knockdowns of 85% of Drosophila genes encoding proteins likely related to the regulation of cell division and cytoskeleton organization. We also compile a molecular classification of these proteins into classes that describe their expected or known main biochemical characteristics, as well as mRNA expression in the wing disc and likely protein subcellular localization for a subset of these genes. Finally, we analyze in more detail one protein family of cytoskeleton genes (Arp2/3 complex), and define the consequences of interfering with cell division for wing growth and patterning.

Gaining Wings to FLY: Using Drosophila Oogenesis as an Entry Point for Citizen Scientists in Laboratory Research

Citizen science is a productive approach to include non-scientists in research efforts that impact particular issues or communities. In most cases, scientists at advanced career stages design high-quality, exciting projects that enable citizen contribution, a crowdsourcing process that drives discovery forward and engages communities. The challenges of having citizens design their own research with no or limited training and providing access to laboratory tools, reagents, and supplies have limited citizen science efforts. This leaves the incredible life experiences and immersion of citizens in communities that experience health disparities out of the research equation, thus hampering efforts to address community health needs with a full picture of the challenges that must be addressed. Here, we present a robust and reproducible approach that engages participants from Grade 5 through adult in research focused on defining how diet impacts disease signaling. We leverage the powerful genetics, cell biology, and biochemistry of Drosophila oogenesis to define how nutrients impact phenotypes associated with genetic mutants that are implicated in cancer and diabetes. Participants lead the project design and execution, flipping the top-down hierarchy of the prevailing scientific culture to co-create research projects and infuse the research with cultural and community relevance.

New Mutations in the 5′ Region of the Notch Gene Affect Drosophila melanogaster Oogenesis

The Notch pathway is an important and evolutionarily conserved signaling system involved in the development of multicellular organisms. Notch signaling plays an important role in the regulation of proliferation and differentiation of many cell types. In this study, we report new aspects of Notch gene participation in oogenesis using our previously generated mutations. The mutations consist of an insertion of an auxiliary element of a transgene construct into the first intron of the gene and a series of directed deletions within the 5′ regulatory region of Notch. We showed that some of these mutations affect Drosophila oogenesis. This insertion, either alone or in combination with the deletion of an insulator sequence, led to lower expression of Notch in the ovaries. As a result, the formation of egg chambers was disturbed in middle oogenesis. These abnormalities have not been described previously and imply one more function of Notch in oogenesis. It can be assumed that Notch is associated with not only follicular epithelium morphogenesis but also cellular mechanisms of oocyte growth.

Whole-Genome Re-sequencing and Transcriptome Reveal Oogenesis-Related Genes in Autotetraploid Carassius auratus

Oogenesis involves a series of biochemical and physiological transformations and numerous regulated genes. The autotetraploid Carassius auratus (4nRR) originated from whole-genome duplication of Carassius auratus red var. (RCC), which produces diploid eggs through pairing of diploid-like chromosome during female meiosis. To explore the molecular mechanisms underlying oogenesis in 4nRR, we used the Illumina sequencing platform to characterize the ovaries of 4nRR and RCC. Transcriptome and whole-genome re-sequencing were performed to uncover the key genes and potential genetic mutations related to oogenesis. Each sample produced paired-end reads in the range of 66.97 to 98.36 million via Illumina HiSeq™ 2500. After comparing of the transcriptome profiles between the 4nRR and RCC, we uncovered 8562 differentially expressed genes (DEGs). The DEGs were enriched in oogenesis-related processes, including oogenesis, oocyte development, ubiquitin-mediated proteolysis, the signaling pathways of MAPK and calcium, and oocyte meiosis as investigated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Additionally, whole-genome re-sequencing revealed 34,058,834 SNPs and 6,153,711 InDels, including 6,677,638 non-synonymous variations (SNPs) and 706,210 frame-shift InDels in the 8510 DEGs of 4nRR fish. Subsequently, whole-genome re-sequencing and transcriptomatic analyses revealed the genes that participate in oogenesis associated processes. Specifically, genes involved in ubiquitin-mediated proteolysis (SMURF1, UBE2I), calcium transport (CALM3, CAMK4), and meiosis (MAPK3, GRB2, CPEB1, CCNB2, YWHAE) were related to oogenesis in 4nRR. These findings enrich our understanding of oogenesis in the autopolyploid fish.

Post-transcriptional regulation of insect metamorphosis and oogenesis

Metamorphic transformation from larvae to adults along with the high fecundity is key to insect success. Insect metamorphosis and reproduction are governed by two critical endocrines, juvenile hormone (JH), and 20-hydroxyecdysone (20E). Recent studies have established a crucial role of microRNA (miRNA) in insect metamorphosis and oogenesis. While miRNAs target genes involved in JH and 20E-signaling pathways, these two hormones reciprocally regulate miRNA expression, forming regulatory loops of miRNA with JH and 20E-signaling cascades. Insect metamorphosis and oogenesis rely on the coordination of hormones, cognate genes, and miRNAs for precise regulation. In addition, the alternative splicing of genes in JH and 20E-signaling pathways has distinct functions in insect metamorphosis and oogenesis. We, therefore, focus in this review on recent advances in post-transcriptional regulation, with the emphasis on the regulatory role of miRNA and alternative splicing, in insect metamorphosis and oogenesis. We will highlight important new findings of miRNA interactions with hormonal signaling and alternative splicing of JH receptor heterodimer gene Taiman.

Arthropod segmentation

There is now compelling evidence that many arthropods pattern their segments using a clock-and-wavefront mechanism, analogous to that operating during vertebrate somitogenesis. In this Review, we discuss how the arthropod segmentation clock generates a repeating sequence of pair-rule gene expression, and how this is converted into a segment-polarity pattern by ‘timing factor’ wavefronts associated with axial extension. We argue that the gene regulatory network that patterns segments may be relatively conserved, although the timing of segmentation varies widely, and double-segment periodicity appears to have evolved at least twice. Finally, we describe how the repeated evolution of a simultaneous (Drosophila-like) mode of segmentation within holometabolan insects can be explained by heterochronic shifts in timing factor expression plus extensive pre-patterning of the pair-rule genes.

An update on ecdysone signaling during insect oogenesis

An overview is presented of the different functions of ecdysone signaling during insect oogenesis. An extensive genetic toolkit allowed analysis with unprecedented temporal and spatial detail in Drosophila where functions were revealed in stem cell proliferation and niche maintenance, germline cyst differentiation and follicle formation, integration of nutrient and lipid signaling, follicle maturation and ovulation. Besides putative autocrine/paracrine signaling, hormonal networks were identified that integrate ecdysone with other endocrine signaling pathways. In other insects, progress in oogenesis has lagged behind although recently RNAi emerged as a new tool to analyze gene function in ovaries in hemimetabolous insects and Tribolium.

Parental and preimaginal exposure to methylmercury disrupts locomotor activity and circadian rhythm of adult Drosophila melanogaster

Methylmercury (MeHg) is a well-known toxic pollutant. However, little is known about the effects of this toxic agent in an adult as a consequence of a parental or preimaginal exposure. This study used Drosophila melanogaster to investigate whether a parental or a preimaginal (eggs-larvae-pupae stages) exposure could impact parameters as viability, locomotor activity, and sleep patterns of fruit flies. Thus, we performed two exposure protocols. One where just parents were exposed to MeHg (0-12 µM) during 24 h, then flies were transferred to lay eggs in a healthy medium (without MeHg). In the other, flies were set to lay eggs in a MeHg medium, same concentrations, and discarded after this (preimaginal exposure). Viability was evaluated from egg to adult flies. F1 progeny was collected within 24 h and transferred to a fresh healthy medium. Sleep behavior analysis was performed using Drosophila Active Monitoring System (DAMS), and the locomotor activity was evaluated by climbing assay. Results have shown that the parental exposure had a significant impact on F1 progeny reducing viability and locomotor activity performance, but no significant circadian rhythm alterations. Whereas the preimaginal exposure had a stronger effect decreasing viability and locomotor activity, it also disrupted sleep patterns. MeHg preimaginal exposure showed a longer sleep duration and lower daily activity. Results corroborate the hypothesis that low MeHg exposure could trigger subclinical symptoms related to a 'neurotoxicological development effect'. Complementary investigations could clarify the underlying mechanisms of MeHg effects in neural functions due to parental and early development exposure to this toxicant.

Reelin and aromatase cooperate in ovarian follicle development

Reelin plays an important role in cerebral cortex development and synaptogenesis. In the hippocampus, the neurosteroid estrogen affects reelin expression. In this study we tested a potential crosstalk between estradiol and reelin, thus the possibility of a reelin-induced activation of the estradiol synthesizing enzyme aromatase. As a model system, we used ovaries, which express reelin and are a major source of estradiol. We found that in wild-type mice, reelin and aromatase are expressed in granulosa cells of growing follicles. The expression of reelin varies with the estrus cycle and is highest shortly before ovulation, when estradiol serum levels are at their maximum. In ovaries of reelin-deficient reeler mice, aromatase mRNA and protein are significantly reduced, as evidenced by real-time PCR, western blot analysis, and quantitative immunohistochemistry in granulosa cells of preovulatory follicles. In line with reduced estradiol synthesis, ovarian estrus cycle length is prolonged in reeler mice. Most importantly, treating cultured granulosa cells with recombinant reelin results in significant upregulation of aromatase mRNA and protein and increased secretion of estradiol into the supernatant. Our data provide evidence of a local increase of aromatase expression by reelin. Regarding reproduction, this crosstalk may contribute to follicular stability and counteract luteinization in ovaries.

The dynamic landscape of gene regulation during Bombyx mori oogenesis

BACKGROUND

Oogenesis in the domestic silkworm (Bombyx mori) is a complex process involving previtellogenesis, vitellogenesis and choriogenesis. During this process, follicles show drastic morphological and physiological changes. However, the genome-wide regulatory profiles of gene expression during oogenesis remain to be determined.

RESULTS

In this study, we obtained time-series transcriptome data and used these data to reveal the dynamic landscape of gene regulation during oogenesis. A total of 1932 genes were identified to be differentially expressed among different stages, most of which occurred during the transition from late vitellogenesis to early choriogenesis. Using weighted gene co-expression network analysis, we identified six stage-specific gene modules that correspond to multiple regulatory pathways. Strikingly, the biosynthesis pathway of the molting hormone 20-hydroxyecdysone (20E) was enriched in one of the modules. Further analysis showed that the ecdysteroid 20-hydroxylase gene (CYP314A1) of steroidgenesis genes was mainly expressed in previtellogenesis and early vitellogenesis. However, the 20E-inactivated genes, particularly the ecdysteroid 26-hydroxylase encoding gene (Cyp18a1), were highly expressed in late vitellogenesis. These distinct expression patterns between 20E synthesis and catabolism-related genes might ensure the rapid decline of the hormone titer at the transition point from vitellogenesis to choriogenesis. In addition, we compared landscapes of gene regulation between silkworm (Lepidoptera) and fruit fly (Diptera) oogeneses. Our results show that there is some consensus in the modules of gene co-expression during oogenesis in these insects.

CONCLUSIONS

The data presented in this study provide new insights into the regulatory mechanisms underlying oogenesis in insects with polytrophic meroistic ovaries. The results also provide clues for further investigating the roles of epigenetic reconfiguration and circadian rhythm in insect oogenesis.

Comparative Proteomic Profiling Reveals Molecular Characteristics Associated with Oogenesis and Oocyte Maturation during Ovarian Development of Bactrocera dorsalis (Hendel)

Time-dependent expression of proteins in ovary is important to understand oogenesis in insects. Here, we profiled the proteomes of developing ovaries from Bactrocera dorsalis (Hendel) to obtain information about ovarian development with particular emphasis on differentially expressed proteins (DEPs) involved in oogenesis. A total of 4838 proteins were identified with an average peptide number of 8.15 and sequence coverage of 20.79%. Quantitative proteomic analysis showed that a total of 612 and 196 proteins were differentially expressed in developing and mature ovaries, respectively. Furthermore, 153, 196 and 59 potential target proteins were highly expressed in early, vitellogenic and mature ovaries and most tested DEPs had the similar trends consistent with the respective transcriptional profiles. These proteins were abundantly expressed in pre-vitellogenic and vitellogenic stages, including tropomyosin, vitellogenin, eukaryotic translation initiation factor, heat shock protein, importin protein, vitelline membrane protein, and chorion protein. Several hormone and signal pathway related proteins were also identified during ovarian development including piRNA, notch, insulin, juvenile, and ecdysone hormone signal pathways. This is the first report of a global ovary proteome of a tephritid fruit fly, and may contribute to understanding the complicate processes of ovarian development and exploring the potentially novel pest control targets.

The Notch pathway regulates both the proliferation and differentiation of follicular cells in the panoistic ovary of Blattella germanica

The Notch pathway is an essential regulator of cell proliferation and differentiation during development. Its involvement in insect oogenesis has been examined in insect species with meroistic ovaries, and it is known to play a fundamental role in cell fate decisions and the induction of the mitosis-to-endocycle switch in follicular cells (FCs). This work reports the functions of the main components of the Notch pathway (Notch and its ligands Delta and Serrate) during oogenesis in Blattella germanica, a phylogenetically basal species with panoistic ovary. As is revealed by RNAi-based analyses, Notch and Delta were found to contribute towards maintaining the FCs in an immature, non-apoptotic state. This ancestral function of Notch appears in opposition to the induction of transition from mitosis to endocycle that Notch exerts in Drosophila melanogaster, a change in the Notch function that might be in agreement with the evolution of the insect ovary types. Notch was also shown to play an active role in inducing ovarian follicle elongation via the regulation of the cytoskeleton. In addition, Delta and Notch interactions were seen to determine the differentiation of the posterior population of FCs. Serrate levels were found to be Notch-dependent and are involved in the control of the FC programme, although they would appear to play no crucial role in panoistic ovary oogenesis.

Notch signalling mediates reproductive constraint in the adult worker honeybee

The hallmark of eusociality is the reproductive division of labour, in which one female caste reproduces, while reproduction is constrained in the subordinate caste. In adult worker honeybees (Apis mellifera) reproductive constraint is conditional: in the absence of the queen and brood, adult worker honeybees activate their ovaries and lay haploid male eggs. Here, we demonstrate that chemical inhibition of Notch signalling can overcome the repressive effect of queen pheromone and promote ovary activity in adult worker honeybees. We show that Notch signalling acts on the earliest stages of oogenesis and that the removal of the queen corresponds with a loss of Notch protein in the germarium. We conclude that the ancient and pleiotropic Notch signalling pathway has been co-opted into constraining reproduction in worker honeybees and we provide the first molecular mechanism directly linking ovary activity in adult worker bees with the presence of the queen.

In honeybees, pheromones produced by the queen inhibit reproduction by workers and enforce a eusocial division of labour. Here, Duncan, Hyink and Dearden show that this inhibition is mediated by the Notch signalling pathway in the workers' ovaries.

Comparative transcriptomic analysis of silkworm Bmovo-1 and wild type silkworm ovary

The detailed molecular mechanism of Bmovo-1 regulation of ovary size is unclear. To uncover the mechanism of Bmovo-1 regulation of ovarian development and oogenesis using RNA-Seq, we compared the transcriptomes of wild type (WT) and Bmovo-1-overexpressing silkworm (silkworm^+Bmovo-1) ovaries. Using a pair-end Illumina Solexa sequencing strategy, 5,296,942 total reads were obtained from silkworm^+Bmovo-1 ovaries and 6,306,078 from WT ovaries. The average read length was about 100 bp. Clean read ratios were 98.79% for silkworm^+Bmovo-1 and 98.87% for WT silkworm ovaries. Comparative transcriptome analysis showed 123 upregulated and 111 downregulated genes in silkworm^+Bmovo-1 ovaries. These differentially expressed genes were enriched in the extracellular and extracellular spaces and involved in metabolism, genetic information processing, environmental information processing, cellular processes and organismal systems. Bmovo-1 overexpression in silkworm ovaries might promote anabolism for ovarian development and oogenesis and oocyte proliferation and transport of nutrients to ovaries by altering nutrient partitioning, which would support ovary development. Excessive consumption of nutrients for ovary development alters nutrient partitioning and deters silk protein synthesis.

Transcriptomic study of the red palm weevil Rhynchophorus ferrugineus embryogenesis

The red palm weevil (RPW), Rhynchophorus ferrugineus (Coleoptera: Curculionidae), is an invasive, concealed and destructive tissue borer, and it becomes a lethal pest of the palm family of plants and has been reported to attack 20 palm species around the globe. Here we report a systematic transcriptomic study on embryogenesis of RPW, where we analyze the transcriptomes across five developmental stages of RPW embryogenesis, involving four embryonic stages (E1, E2, E3 and E4) and one larval stage (L1). Using the RNA-seq and next-generation platforms, we generated 80 to 91 million reads for each library and assemble 22 532 genes that are expressed at different embryonic stages. Among the total transcripts from the five embryonic development stages, we found that 30.45 % are differentially expressed, 10.10 % show stage-specificity and even a larger fraction, 62.88 %, exhibit constitutive expression in all the stages. We also analyzes the expression dynamics of several conserved signaling pathways (such as Hedgehog, JAK-STAT, Notch, TGF-β, Ras/MAPK and Wnt), as well as key developmental genes, including those related to apoptosis, axis formation, Hox complex, neurogenesis and segmentation. The datasets provide an essential resource for gene annotation and RPW functional genomics, including studies by using tools and concepts from multiple disciplines, such as development, physiology, biochemistry, molecular biology and genetics.

Unlike in Drosophila Meroistic Ovaries, hippo represses notch in Blattella germanica Panoistic ovaries, triggering the mitosis-endocycle switch in the follicular cells

During insect oogenesis, the follicular epithelium undergoes both cell proliferation and apoptosis, thus modulating ovarian follicle growth. The Hippo pathway is key in these processes, and has been thoroughly studied in the meroistic ovaries of Drosophila melanogaster. However, nothing is known about the role of the Hippo pathway in primitive panoistic ovaries. This work examines the mRNA expression levels of the main components of the Hippo pathway in the panoistic ovary of the basal insect species Blattella germanica, and demonstrates the function of Hippo through RNAi. In Hippo-depleted specimens, the follicular cells of the basal ovarian follicles proliferate without arresting cytokinesis; the epithelium therefore becomes bilayered, impairing ovarian follicle growth. This phenotype is accompanied by long stalks between the ovarian follicles. In D. melanogaster loss of function of Notch determines that the stalk is not developed. With this in mind, we tested whether Hippo and Notch pathways are related in B. germanica. In Notch (only)-depleted females, no stalks were formed between the ovarian follicles. Simultaneous depletion of Hippo and Notch rescued partially the stalk to wild-type. Unlike in the meroistic ovaries of D. melanogaster, in panoistic ovaries the Hippo pathway appears to regulate follicular cell proliferation by acting as a repressor of Notch, triggering the switch from mitosis to the endocycle in the follicular cells. The phylogenetically basal position of B. germanica suggests that this might be the ancestral function of Hippo in insect ovaries.

Regulation of broad by the Notch pathway affects timing of follicle cell development

During Drosophila oogenesis, activation of Notch signaling in the follicular epithelium (FE) around stage 6 of oogenesis is essential for entry into the endocycle and a series of other changes such as cell differentiation and migration of subsets of the follicle cells. Notch induces the expression of zinc finger protein Hindsight and suppresses homeodomain protein Cut to regulate the mitotic/endocycle (ME) switch. Here we report that broad (br), encoding a small group of zinc-finger transcription factors resulting from alternative splicing, is a transcriptional target of Notch nuclear effector Suppressor of Hairless (Su(H)). The early pattern of Br in the FE, uniformly expressed except in the polar cells, is established by Notch signaling around stage 6, through the binding of Su(H) to the br early enhancer (brE) region. Mutation of the Su(H) binding site leads to a significant reduction of brE reporter expression in follicle cells undergoing the endocycle. Chromatin immunoprecipitation results further confirm Su(H) binding to the br early enhancer. Consistent with its expression in follicle cells during midoogenesis, loss of br function results in a delayed entry into the endocycle. Our findings suggest an important role of br in the timing of follicle cell development, and its transcriptional regulation by the Notch pathway.

Notch pathway regulates female germ cell meiosis progression and early oogenesis events in fetal mouse

A critical process of early oogenesis is the entry of mitotic oogonia into meiosis, a cell cycle switch regulated by a complex gene regulatory network. Although Notch pathway is involved in numerous important aspects of oogenesis in invertebrate species, whether it plays roles in early oogenesis events in mammals is unknown. Therefore, the rationale of the present study was to investigate the roles of Notch signaling in crucial processes of early oogenesis, such as meiosis entry and early oocyte growth. Notch receptors and ligands were localized in mouse embryonic female gonads and 2 Notch inhibitors, namely DAPT and L-685,458, were used to attenuate its signaling in an in vitro culture system of ovarian tissues from 12.5 days post coitum (dpc) fetus. The results demonstrated that the expression of Stra8, a master gene for germ cell meiosis, and its stimulation by retinoic acid (RA) were reduced after suppression of Notch signaling, and the other meiotic genes, Dazl, Dmc1, and Rec8, were abolished or markedly decreased. Furthermore, RNAi of Notch1 also markedly inhibited the expression of Stra8 and SCP3 in cultured female germ cells. The increased methylation status of CpG islands within the Stra8 promoter of the oocytes was observed in the presence of DAPT, indicating that Notch signaling is probably necessary for maintaining the epigenetic state of this gene in a way suitable for RA stimulation. Furthermore, in the presence of Notch inhibitors, progression of oocytes through meiosis I was markedly delayed. At later culture periods, the rate of oocyte growth was decreased, which impaired subsequent primordial follicle assembly in cultured ovarian tissues. Taken together, these results suggested new roles of the Notch signaling pathway in female germ cell meiosis progression and early oogenesis events in mammals.

Notch2 is required in somatic cells for breakdown of ovarian germ-cell nests and formation of primordial follicles

Background

In the mouse ovary, oocytes initially develop in clusters termed germ-cell nests. Shortly after birth, these germ-cell nests break apart, and the oocytes individually become surrounded by somatic granulosa cells to form primordial follicles. Notch signaling plays essential roles during oogenesis in Drosophila, and recent studies have suggested that Notch signaling also plays an essential role during oogenesis and ovary development in mammals. However, no in vivo loss-of-function studies have been performed to establish whether Notch family receptors have an essential physiological role during normal ovarian development in mutant mice.

Results

Female mice with conditional deletion of the Notch2 gene in somatic granulosa cells of the ovary exhibited reduced fertility, accompanied by the formation of multi-oocyte follicles, which became hemorrhagic by 7 weeks of age. Formation of multi-oocyte follicles resulted from defects in breakdown of the primordial germ-cell nests. The ovaries of the Notch2 conditional mutant mice had increased numbers of oocytes, but decreased numbers of primordial follicles. Oocyte numbers in the Notch2 conditional mutants were increased not by excess or extended cellular proliferation, but as a result of decreased oocyte apoptosis.

Conclusions

Our work demonstrates that Notch2-mediated signaling in the somatic-cell lineage of the mouse ovary regulates oocyte apoptosis non-cell autonomously, and is essential for regulating breakdown of germ-cell nests and formation of primordial follicles. This model provides a new resource for studying the developmental and physiological roles of Notch signaling during mammalian reproductive biology.