Regulation of the vitellogenin receptor during Drosophila melanogaster oogenesis

Lipids in Insect Reproduction: Where, How, and Why

Modern insects have inhabited the earth for hundreds of millions of years, and part of their successful adaptation lies in their many reproductive strategies. Insect reproduction is linked to a high metabolic rate that provides viable eggs in a relatively short time. In this context, an accurate interplay between the endocrine system and the nutrients synthetized and metabolized is essential to produce healthy offspring. Lipids guarantee the metabolic energy needed for egg formation and represent the main energy source consumed during embryogenesis. Lipids availability is tightly regulated by a complex network of endocrine signals primarily controlled by the central nervous system (CNS) and associated endocrine glands, the corpora allata (CA) and corpora cardiaca (CC). This endocrine axis provides hormones and neuropeptides that significatively affect tissues closely involved in successful reproduction: the fat body, which is the metabolic center supplying the lipid resources and energy demanded in egg formation, and the ovaries, where the developing oocytes recruit lipids that will be used for optimal embryogenesis. The post-genomic era and the availability of modern experimental approaches have advanced our understanding of many processes involved in lipid homeostasis; therefore, it is crucial to integrate the findings of recent years into the knowledge already acquired in the last decades. The present chapter is devoted to reviewing major recent contributions made in elucidating the impact of the CNS/CA/CC-fat body-ovary axis on lipid metabolism in the context of insect reproduction, highlighting areas of fruitful research.

Endolysosomal trafficking controls yolk granule biogenesis in vitellogenic Drosophila oocytes

Endocytosis and endolysosomal trafficking are essential for almost all aspects of physiological functions of eukaryotic cells. As our understanding on these membrane trafficking events are mostly from studies in yeast and cultured mammalian cells, one challenge is to systematically evaluate the findings from these cell-based studies in multicellular organisms under physiological settings. One potentially valuable in vivo system to address this challenge is the vitellogenic oocyte in Drosophila, which undergoes extensive endocytosis by Yolkless (Yl), a low-density lipoprotein receptor (LDLR), to uptake extracellular lipoproteins into oocytes and package them into a specialized lysosome, the yolk granule, for storage and usage during later development. However, by now there is still a lack of sufficient understanding on the molecular and cellular processes that control yolk granule biogenesis. Here, by creating genome-tagging lines for Yl receptor and analyzing its distribution in vitellogenic oocytes, we observed a close association of different endosomal structures with distinct phosphoinositides and actin cytoskeleton dynamics. We further showed that Rab5 and Rab11, but surprisingly not Rab4 and Rab7, are essential for yolk granules biogenesis. Instead, we uncovered evidence for a potential role of Rab7 in actin regulation and observed a notable overlap of Rab4 and Rab7, two Rab GTPases that have long been proposed to have distinct spatial distribution and functional roles during endolysosomal trafficking. Through a small-scale RNA interference (RNAi) screen on a set of reported Rab5 effectors, we showed that yolk granule biogenesis largely follows the canonical endolysosomal trafficking and maturation processes. Further, the data suggest that the RAVE/V-ATPase complexes function upstream of or in parallel with Rab7, and are involved in earlier stages of endosomal trafficking events. Together, our study provides s novel insights into endolysosomal pathways and establishes vitellogenic oocyte in Drosophila as an excellent in vivo model for dissecting the highly complex membrane trafficking events in metazoan.

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.

Infection with 'Candidatus Liberibacter asiaticus' improves the fecundity of Diaphorina citri aiding its proliferation: A win-win strategy

The evolution of insect vector-pathogen relationships has long been of interest in the field of molecular ecology. One system of special relevance, due to its economic impacts, is that between Diaphorina citri and 'Candidatus Liberibacter asiaticus' (CLas), the cause of the severe Asian form of huanglongbing. CLas-positive D. citri are more fecund than their CLas-negative counterparts, boosting opportunities for pathogens to acquire new vector hosts. The molecular mechanism behind this life-history shift remains unclear. Here, we found that CLas promoted ovarian development and increased the expression of the vitellogenin receptor (DcVgR) in ovaries. DcVgR RNAi significantly decreased fecundity and CLas titer in ovaries, extended the preoviposition period, shortened the oviposition period and blocked ovarian development. Given their importance in gene regulation, we explored the role of miRNAs in shaping these phenotypes and their molecular triggers. Our results showed that one miRNA, miR-275, suppressed DcVgR expression by binding to its 3' UTR. Overexpression of miR-275 knocked down DcVgR expression and CLas titer in ovaries, causing reproductive defects that mimicked DcVgR knockdown phenotypes. We focused, further, on roles of the Juvenile Hormone (JH) pathway in shaping the observed fecundity phenotype, given its known impacts on ovarian development. After CLas infection, this pathway was upregulated, thereby increasing DcVgR expression. From these combined results, we conclude that CLas hijacks the JH signalling pathway and miR-275, thereby targeting DcVgR to increase D. citri fecundity. These changes simultaneously increase CLas replication, suggesting a pathogen-vector host mutualism, or a seemingly helpful, but cryptically costly life-history manipulation.

Tyraminergic control of vitellogenin production and release in the blood-feeding insect, Rhodnius prolixus

In insects, the biogenic amine tyramine (TA) has been shown to control several physiological processes. Recently, the involvement of the type 1 tyramine receptor (TAR1) in reproductive processes has been demonstrated in different insects. Here, we investigate the putative role of Rhodnius prolixus TAR1 (RpTAR1) in reproduction in female R. prolixus. RpTAR1 transcript was highly expressed in tissues associated with egg development. Moreover, after a blood meal, which is the stimulus for full egg development, RpTAR1 transcript was upregulated in the ovaries and in the fat body. After RNAi-mediated RpTAR1 knockdown, an ovarian phenotype characterized by the absence or reduction of egg production was observed. Furthermore, protein and Vg accumulation in the fat body was observed, suggesting an impairment in protein release from the fat body into the hemolymph. However, even though fewer eggs were produced and laid, there was no difference in hatching ratio of those laid, in comparison to the controls, indicating that the overall low protein uptake by the ovaries did not influence the viability of individual eggs produced. Interestingly, the eggs from dsTAR1-treated insects appeared more red, indicating a higher content of RHBP compared to the control. A higher colocalization between Vg and Rab11, a marker for the recycling endosome pathway, was observed after dsTAR1 injection, suggesting that a more active lysosome degradation pathway in response to the Vg accumulation may occur. In addition to the Vg accumulation in the fat body, dsTAR1 treatment altered JH pathway. However, it remains to be elucidated whether this event is either directly related to the RpTAR1 downregulation or for a consequence to the Vg accumulation. Lastly, the RpTAR1 action on Vg synthesis and release in the fat body was monitored in the presence or absence of yohimbine, the antagonist of TAR1, in an ex-vivo experiment. Yohimbine antagonises the TAR1 stimulated release of Vg. These results provide critical information concerning the role of TAR1 in Vg synthesis and release in R. prolixus. Furthermore, this work opens the way for further investigation into innovative methods for controlling R. prolixus.

Self-organized intracellular twisters

Life in complex systems, such as cities and organisms, comes to a standstill when global coordination of mass, energy, and information flows is disrupted. Global coordination is no less important in single cells, especially in large oocytes and newly formed embryos, which commonly use fast fluid flows for dynamic reorganization of their cytoplasm. Here, we combine theory, computing, and imaging to investigate such flows in the Drosophila oocyte, where streaming has been proposed to spontaneously arise from hydrodynamic interactions among cortically anchored microtubules loaded with cargo-carrying molecular motors. We use a fast, accurate, and scalable numerical approach to investigate fluid-structure interactions of 1000s of flexible fibers and demonstrate the robust emergence and evolution of cell-spanning vortices, or twisters. Dominated by a rigid body rotation and secondary toroidal components, these flows are likely involved in rapid mixing and transport of ooplasmic components.

Modulation of ecdysteroid and juvenile hormone signaling pathways by bisphenol analogues and polystyrene beads in the brackish water flea Diaphanosoma celebensis

Owing to its high production and world-wide usage, plastic pollution is an increasing concern in marine environments. Plastic is decomposed into nano- and micro-sized debris, which negative affect reproduction and development in aquatic organisms. Bisphenol A (BPA), an additive of plastic, is released into the water column upon plastic degradation, and is known as a representative endocrine-disrupting chemical. However, the reproductive effects of plastics and bisphenols at the molecular level have not yet been explored in small marine crustaceans. In this study, we investigated the effects of polystyrene (PS) beads (0.05, 0.5, and 6 - μm) and bisphenol analogues (BPs; BPA, BPS, and BPF) on reproduction and development of small marine crustaceans. Effects on transcriptional changes in ecdysteroid and juvenile hormone (JH) signaling pathway-related genes were examined in the brackish water flea Diaphanosoma celebensis exposed to PS beads and BPs for 48 h. As results, BPs and PS beads delayed emergence time of first offspring, and increased fecundity in a concentration-dependent manner. BPs differentially modulated the expression of ecdysteroid and JH signaling pathway-related genes, indicating that BP analogs can disrupt endocrine systems via mechanisms different from those of BPA. PS beads was also changed the gene expression of both pathway, depending on their size and concentration. Our findings suggest that BP analogues and PS beads disrupt the endocrine system by modulating the hormonal pathways, affecting reproduction negatively. This study provides a better understanding of the molecular mode of action of BPs and PS beads in the reproduction of small crustaceans.

Cell-to-Cell Interactions during Early Drosophila Oogenesis: An Ultrastructural Analysis

Drosophila oogenesis requires the subsequent growth of distinct egg chambers each containing a group of sixteen germline cells surrounded by a simple epithelium of follicle cells. The oocyte occupies a posterior position within the germ cells, thus giving a distinct asymmetry to the egg chamber. Although this disposition is critical for the formation of the anterior–posterior axis of the embryo, the interplay between somatic and germ cells during the early stages of oogenesis remains an open question. We uncover by stage 2, when the egg chambers leaved the germarium, some unique spatial interactions between the posterior follicle cells and the oocyte. These interactions are restricted to the surface of the oocyte over the centriole cluster that formed during early oogenesis. Moreover, the posterior follicle cells in front of the oocyte display a convoluted apical membrane with extensive contacts, whereas the other follicle cells have a flat apical surface without obvious surface protrusions. In addition, the germ cells located at the posterior end of the egg chamber have very elongated protrusions that come into contact with each other or with facing follicle cells. These observations point to distinct polarization events during early oogenesis supporting previous molecular data of an inherent asymmetry between the anterior and the posterior regions of the egg chambers.

Quantitative models for building and growing fated small cell networks

Small cell clusters exhibit numerous phenomena typically associated with complex systems, such as division of labour and programmed cell death. A conserved class of such clusters occurs during oogenesis in the form of germline cysts that give rise to oocytes. Germline cysts form through cell divisions with incomplete cytokinesis, leaving cells intimately connected through intercellular bridges that facilitate cyst generation, cell fate determination and collective growth dynamics. Using the well-characterized Drosophila melanogaster female germline cyst as a foundation, we present mathematical models rooted in the dynamics of cell cycle proteins and their interactions to explain the generation of germline cell lineage trees (CLTs) and highlight the diversity of observed CLT sizes and topologies across species. We analyse competing models of symmetry breaking in CLTs to rationalize the observed dynamics and robustness of oocyte fate specification, and highlight remaining gaps in knowledge. We also explore how CLT topology affects cell cycle dynamics and synchronization and highlight mechanisms of intercellular coupling that underlie the observed collective growth patterns during oogenesis. Throughout, we point to similarities across organisms that warrant further investigation and comment on the extent to which experimental and theoretical findings made in model systems extend to other species.

Regulation of vtg and VtgR in mud crab Scylla paramamosain by miR-34

BACKGROUND

Vitellogenin (Vtg) is the precursor of major yolk protein and plays a crucial role in the maturation of oocytes and the production of eggs in oviparous animals. Vitellogenin receptor (VtgR) mediates the transport of Vtg explicitly to oocytes in the membrane. In a previous study, we found that miR-34 can regulate the expression of some eyestalk genes and affect reproduction in mud crab Scylla paramamosain, one of the most important economic crabs on the coasts of southern China.

METHODS AND RESULTS

In this study, firstly, we found that miR-34 can target at 3'-UTR of Vtg and VtgR genes by using bioinformatic tools and predicted miR-34 might depress the expression of Vtg and VtgR. Secondly, the relative luciferase activity of HEK293T cells co-transfected with miRNA mimic and pmir-RB-REPORTTM-Vtg/VtgR-3'UTR was significantly lower than those of cells co-transfected with mimic NC and pmir-RB-REPORTTM-Vtg/VtgR-3'UTR. Finally, in vivo experiments showed that agomiR-34 could repress the expression of Vtg and VtgR genes, while Antigomir-34 could promote the expression of these two genes.

CONCLUSIONS

These results confirm our hypothesis and previous published results that miR-34 may indirectly regulate ovarian development by binding to the 3'-UTR of Vtg and VtgR genes and inhibiting their expression.

The Drosophila ribosome protein S5 paralog RpS5b promotes germ cell and follicle cell differentiation during oogenesis

Emerging evidence suggests that ribosome heterogeneity may have important functional consequences in the translation of specific mRNAs within different cell types and under various conditions. Ribosome heterogeneity comes in many forms, including post-translational modification of ribosome proteins (RPs), absence of specific RPs and inclusion of different RP paralogs. The Drosophila genome encodes two RpS5 paralogs: RpS5a and RpS5b. While RpS5a is ubiquitously expressed, RpS5b exhibits enriched expression in the reproductive system. Deletion of RpS5b results in female sterility marked by developmental arrest of egg chambers at stages 7-8, disruption of vitellogenesis and posterior follicle cell (PFC) hyperplasia. While transgenic rescue experiments suggest functional redundancy between RpS5a and RpS5b, molecular, biochemical and ribo-seq experiments indicate that RpS5b mutants display increased rRNA transcription and RP production, accompanied by increased protein synthesis. Loss of RpS5b results in microtubule-based defects and in mislocalization of Delta and Mindbomb1, leading to failure of Notch pathway activation in PFCs. Together, our results indicate that germ cell-specific expression of RpS5b promotes proper egg chamber development by ensuring the homeostasis of functional ribosomes.

The vitellogenin receptor functionality of the migratory locust depends on its phosphorylation by juvenile hormone

Vitellogenin receptor (VgR) plays a pivotal role in ovarian vitellogenin (Vg) uptake and vertical transmission of pathogenic microbes and Wolbachia symbionts. However, the regulatory mechanisms of VgR action as an endocytic receptor and translocation from oocyte cytoplasm to the membrane remain poorly understood. Here, by using the migratory locust Locusta migratoria as a model system, we report that juvenile hormone (JH) promotes VgR phosphorylation at Ser¹³⁶¹ in the second EGF-precursor homology domain. A signaling cascade including GPCR, PLC, extracellular calcium, and PKC-ι is involved in JH-stimulated VgR phosphorylation. This posttranslational regulation is a prerequisite for VgR binding to Vg on the external surface of the oocyte membrane and subsequent VgR/Vg endocytosis. Acidification, a condition in endosomes, induces VgR dephosphorylation along with the dissociation of Vg from VgR. Phosphorylation modification is also required for VgR recycling from oocyte cytoplasm to the membrane. Additionally, VgR phosphorylation and its requirement for Vg uptake and VgR recycling are evolutionarily conserved in other representative insects including the cockroach Periplaneta americana and the cotton bollworm Helicoverpa armigera This study fills an important knowledge gap of low-density lipoprotein receptors in posttranslational regulation, endocytosis, and intracellular recycling.

Receptor-mediated yolk uptake is required for oskar mRNA localization and cortical anchorage of germ plasm components in the Drosophila oocyte

The Drosophila germ plasm is responsible for germ cell formation. Its assembly begins with localization of oskar mRNA to the posterior pole of the oocyte. The oskar translation produces 2 isoforms with distinct functions: short Oskar recruits germ plasm components, whereas long Oskar remodels actin to anchor the components to the cortex. The mechanism by which long Oskar anchors them remains elusive. Here, we report that Yolkless, which facilitates uptake of nutrient yolk proteins into the oocyte, is a key cofactor for long Oskar. Loss of Yolkless or depletion of yolk proteins disrupts the microtubule alignment and oskar mRNA localization at the posterior pole of the oocyte, whereas microtubule-dependent localization of bicoid mRNA to the anterior and gurken mRNA to the anterior-dorsal corner remains intact. Furthermore, these mutant oocytes do not properly respond to long Oskar, causing defects in the actin remodeling and germ plasm anchoring. Thus, the yolk uptake is not merely the process for nutrient incorporation, but also crucial for oskar mRNA localization and cortical anchorage of germ plasm components in the oocyte.

A study of the fruit fly Drosophila reveals that receptor-mediated yolk uptake is not merely a nutrient storage process for future embryogenesis, but is also required for localization of Oskar mRNA and cortical anchorage of germ plasm components in the oocyte during oogenesis.

Nuclear receptors linking physiology and germline stem cells in Drosophila

Maternal nutrition and physiology are intimately associated with reproductive success in diverse organisms. Despite decades of study, the molecular mechanisms linking maternal diet to the production and quality of oocytes remain poorly defined. Nuclear receptors (NRs) link nutritional signals to cellular responses and are essential for oocyte development. The fruit fly, Drosophila melanogaster, is an excellent genetically tractable model to study the relationship between NR signaling and oocyte production. In this review, we explore how NRs in Drosophila regulate the earliest stages of oocyte development. Long-recognized as an essential mediator of developmental transitions, we focus on the intrinsic roles of the Ecdysone Receptor and its ligand, ecdysone, in oogenesis. We also review recent studies suggesting broader roles for NRs as regulators of maternal physiology and their impact specifically on oocyte production. We propose that NRs form the molecular basis of a broad physiological surveillance network linking maternal diet with oocyte production. Given the functional conservation between Drosophila and humans, continued experimental investigation into the molecular mechanisms by which NRs promote oogenesis will likely aid our understanding of human fertility.

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.

Molecular Characterization of Neoseiulus barkeri Vitellogenin Genes and Vitellogenin Receptor during Reproductive Diapause

The relationship between reproductive diapause and the genes related to vitellogenin (Vg) and its receptor (VgR) in insectoid ovarian development is still unclear. Accordingly, in the present study, we used hematoxylin and eosin staining to study the ovarian structure in the predatory mite Neoseiulus barkeri, a species that shows promise as a biological pest control agent. Staining revealed the presence of oocytes on ovary surfaces, and the oocytes were deposited as yolk granules through the intake of Vg and other nutrients with the development of the ovary. Development of the ovary stopped at the oocyte stage in diapausing adult mites, and this stage presented the same characteristics as the first day of adulthood in non-diapause female adults, where oocytes with nutrient cells, but no yolk granules are observed. In order to further explore the effects of the Vg gene and its receptor on reproduction, the sequences of the N. barkeri vitellogenin genes NbVg1, NbVg2, NbVg3, and NbVgR were analyzed using bioinformatics, and the expression levels of the NbVgs and the VgR at different developmental stages were determined by quantitative polymerase chain reaction (qPCR). The results showed that the NbVgs and NbVgR have complete domains and that the positions of many conservative regions and conservative motif are consistent. The expression levels of the NbVgs and NbVgR were highest in the ovipositional period, followed by those in the preovipositional period. The expression levels of the NbVgs and the VgR in non-diapause female adult mites were significantly higher than those in reproductive diapause female adult mites.

Identification of potential candidate genes involved in the sex determination cascade in an aquatic firefly, Sclerotia aquatilis (Coleoptera, Lampyridae)

Sexual differentiation, dimorphism, and courtship behavior are the downstream developmental programs of the sex determination cascade. The sex determination cascade in arthropods often involves key genes, transformer (tra), doublesex (dsx), transformer-2 (tra2), and fruitless (fru). These genes are conserved among insect taxa; however, they have never been reported in fireflies. In this study, the candidate genes for these key genes were identified for the first time in an aquatic firefly, Sclerotia aquatilis using transcriptome analysis. A comparative protein-protein interaction (PPI) network of sex determination cascade was reconstructed for S. aquatilis based on a network of a model insect, Drosophila melanogaster. Subsequently, a sex determination cascade in S. aquatilis was proposed based on the amino acid sequence structures and expression profiles of these candidates. This study describes the first efforts toward understanding the molecular control of sex determination cascade in fireflies.

Modulation of Cell-Cell Interactions in Drosophila Oocyte Development

The Drosophila ovary offers a suitable model system to study the mechanisms that orchestrate diverse cellular processes. Oogenesis starts from asymmetric stem cell division, proper differentiation and the production of fully patterned oocytes equipped with all the maternal information required for embryogenesis. Spatial and temporal regulation of cell-cell interaction is particularly important to fulfill accurate biological outcomes at each step of oocyte development. Progress has been made in understanding diverse cell physiological regulation of signaling. Here we review the roles of specialized cellular machinery in cell-cell communication in different stages of oogenesis.

MicroRNAs bmo-miR-2739 and novel-miR-167 coordinately regulate the expression of the vitellogenin receptor in Bombyx mori oogenesis

Vitellogenin receptors (VgRs) play critical roles in oogenesis by mediating endocytosis of vitellogenin and other nutrients in ovipara. We conducted small RNA sequencing and screening with a luciferase reporter system, and found that bmo-miR-2739 and a novel miRNA (novel-miR-167) coordinately regulate the expression of VgR in Bombyx mori (BmVgR). Further analyses suggested that these two miRNAs direct target repression by binding directly to the BmVgR 3ʹ untranslated region. Forced expression of either miRNA using the piggyBac system blocked vitellogenin (Vg) transport and retarded ovariole development. Antagomir silencing of bmo-miR-2739 or novel-miR-167 resulted in increased amounts of BmVgR protein in the ovaries and BmVgR mRNA in the fat body. This evidence combined with spatiotemporal expression profiles revealed that these two miRNAs function together to fine-tune the amount of BmVgR protein for ovarian development. Additionally, novel-miR-167 mainly switched on the posttranscriptional repression of BmVgR in non-ovarian tissues. The results of this study contribute to a better understanding of the function of miRNA during ovarian development of a lepidopteran and suggest a new strategy for controlling insect reproduction.

Novel cis-regulatory regions in ecdysone responsive genes are sufficient to promote gene expression in Drosophila ovarian cells

The insect steroid hormone ecdysone is a key regulator of oogenesis in Drosophila melanogaster and many other species. Despite the diversity of cellular functions of ecdysone in oogenesis, the molecular regulation of most ecdysone-responsive genes in ovarian cells remains largely unexplored. We performed a functional screen using the UAS/Gal4 system to identify non-coding cis-regulatory elements within well-characterized ecdysone-response genes capable of driving transcription of an indelible reporter in ovarian cells. Using two publicly available transgenic collections (the FlyLight and Vienna Tiles resources), we tested 62 Gal4 drivers corresponding to ecdysone-response genes EcR, usp, E75, br, ftz-f1 and Hr3. We observed 31 lines that were sufficient to drive a UAS-lacZ reporter in discrete cell populations in the ovary. Reporter expression was reproducibly observed in both somatic and germ cells at distinct stages of oogenesis, including those previously characterized as critical points of ecdysone regulation. Our studies identified several useful new reagents, adding to the UAS/Gal4 toolkit available for genetic analysis of oogenesis in Drosophila. Further, our study provides novel insight into the molecular regulation of ecdysone signaling in oogenesis.

Intracellular localization of vitellogenin receptor mRNA and protein during oogenesis of a parthenogenetic tick, Haemaphysalis longicornis

BACKGROUND

Vitellogenin (Vg), a key molecule for oocyte development synthesized in the fat body during blood-feeding, is released into the hemolymph and then taken into the oocytes via Vg receptor (VgR) in ticks. Previously, we showed that VgR mRNA is expressed in the ovary at the adult stage of parthenogenetic Haemaphysalis longicornis ticks and its expression increases after blood-feeding. However, intracellular localization of VgR mRNA and protein at each developmental stage of oocytes during oogenesis remains largely unclear.

METHODS

mRNA and protein expression profiles of H. longicornis VgR (HlVgR) in the oocytes from the unfed to oviposition periods were analyzed by real-time PCR, in situ hybridization, and immunostaining. To elucidate the timing of the onset of Vg uptake, RNA interference (RNAi)-mediated gene silencing of HlVgR was performed.

RESULTS

In situ hybridization revealed that HlVgR mRNA was detected in the cytoplasm of stage I-III oocytes, and weaker positive signals for HlVgR mRNA were found in the cell periphery of stage IV and V oocytes. Likewise, HlVgR protein was detected by immunostaining in the cytoplasm of stage I-III oocytes and in the cell periphery of stage IV and V oocytes. Each developmental stage of the oocytes showed distinct patterns of mRNA and protein expression of HlVgR. Moreover, RNAi of HlVgR caused delayed or arrested development in the oocytes. The ovaries of control ticks showed all developmental stages of oocytes, whereas stage I-III oocytes were found in the ovaries of HlVgR-RNAi ticks at 5 days after engorgement.

CONCLUSIONS

These results suggest that active uptake of Vg is required for development from stage III to stage IV during oogenesis. Our data clearly revealed an apparent shift in the intracellular localization of VgR for both mRNA and protein level in oocytes during oogenesis.

Vitellogenin transcytosis in follicular cells of the honeybee Apis mellifera and the wasp Polistes simillimus

Vitellogenin receptor (VgR) is a low-density lipoprotein receptor responsible for the mediated endocytosis of vitellogenin (Vg) during egg formation in insects. The maturing oocyte is enveloped by a follicular epithelium, which has large intercellular spaces during Vg accumulation (patency). However, Vg has been reported in the cytoplasm of follicular cells, indicating that there may be a transcellular route for its transport. This study verified the presence of VgR in the follicular cells of the ovaries of the honeybee Apis mellifera and the wasp Polistes simillimus in order to evaluate if Vg is transported via transcytosis in these insects. Antibodies specific for vitellogenin receptor (anti-VgR), vitellogenin (anti-Vg), and clathrin (anti-Clt) were used for immunolocalization. The results showed the presence of VgR on the apical and basal plasma membranes of follicular cells of the vitellogenic follicles in both species, indicating that VgR may have been transported from the basal to the apical cell domain, followed by its release into the perivitelline space, evidenced by the presence of apical plasma membrane projections containing VgR. Co-localization proved that Vg bind to VgR and that the transport of this protein is mediated by clathrin. These data suggest that, in these social insects, Vg is transported via clathrin-mediated VgR transcytosis in follicular cells.

Effects of the synthetic estrogen 17-α-ethinylestradiol on Drosophila melanogaster: Dose and gender dependence

17-a-ethinylestradiol (EE2) belongs to the increasing list of Endocrine Disruptors Chemicals (EDCs), able to interfere with the endocrine system in both vertebrates and invertebrates. Regardless of its great dispersion in the environment, to date there is still little knowledge about its action mechanisms and harmful effects in invertebrates. To better evaluate its potential role in invertebrates, we used the model system Drosophila melanogaster, an insect in which the hormonal response has been widely described. The effects of EE2 in D.melanogaster adults have been evaluated by using life traits as well as molecular endpoints. It was found that EE2 significantly decreases survival and fertility in both sexes, with a higher effect in female flies, as well as affects the expression of the Ecdysone Receptor (EcR), Estrogen Related Receptor (ERR), Yolk protein2 (Yp2) and yolkless (yl) genes. In conclusion, our results suggest that EE2 treatment may have potential toxic and endocrine effects on Drosophila melanogaster adults of both sexes. In particular, our data provide an indication that, after EE2 treatment, two of the genes involved in the vitellogenesis process (yl and Yp2) are transcribed in adult males where are mostly silent, and suggest future studies forward their use as potential molecular markers to EDCs exposure in Drosophila male.

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.

Collective Growth in a Small Cell Network

Theoretical studies suggest that many of the emergent properties associated with multicellular systems arise already in small networks [1, 2]. However, the number of experimental models that can be used to explore collective dynamics in well-defined cell networks is still very limited. Here we focus on collective cell behavior in the female germline cyst in Drosophila melanogaster, a stereotypically wired network of 16 cells that grows by ∼4 orders of magnitude with unequal distribution of volume among its constituents. We quantify multicellular growth with single-cell resolution and show that proximity to the oocyte, as defined on the network, is the principal factor that determines cell size; consequently, cells grow in groups. To rationalize this emergent pattern of cell sizes, we propose a tractable mathematical model that depends on intercellular transport on a cell lineage tree. In addition to correctly predicting the divergent pattern of cell sizes, this model reveals allometric growth of cells within the network, an emergent property of this system and a feature commonly associated with differential growth on an organismal scale [3].

The repertoire of epithelial morphogenesis on display: Progressive elaboration of Drosophila egg structure

Epithelial structures are foundational for tissue organization in all metazoans. Sheets of epithelial cells form lateral adhesive junctions and acquire apico-basal polarity perpendicular to the surface of the sheet. Genetic analyses in the insect model, Drosophila melanogaster, have greatly advanced our understanding of how epithelial organization is established, and how it is modulated during tissue morphogenesis. Major insights into collective cell migrations have come from analyses of morphogenetic movements within the adult follicular epithelium that cooperates with female germ cells to build a mature egg. Epithelial follicle cells progress through tightly choreographed phases of proliferation, patterning, reorganization and migrations, before they differentiate to form the elaborate structures of the eggshell. Distinct structural domains are organized by differential adhesion, within which lateral junctions are remodeled to further shape the organized epithelia. During collective cell migrations, adhesive interactions mediate supracellular organization of planar polarized macromolecules, and facilitate crawling over the basement membrane or traction against adjacent cell surfaces. Comparative studies with other insects are revealing the diversification of morphogenetic movements for elaboration of epithelial structures. This review surveys the repertoire of follicle cell morphogenesis, to highlight the coordination of epithelial plasticity with progressive differentiation of a secretory epithelium. Technological advances will keep this tissue at the leading edge for interrogating the precise spatiotemporal regulation of normal epithelial reorganization events, and provide a framework for understanding pathological tissue dysplasia.

Transfer of Dorsoventral and Terminal Information from the Ovary to the Embryo by a Common Group of Eggshell Proteins in Drosophila

The Drosophila eggshell is an extracellular matrix that confers protection to the egg and also plays a role in transferring positional information from the ovary to pattern the embryo. Among the constituents of the Drosophila eggshell, Nasrat, Polehole, and Closca form a group of proteins related by sequence, secreted by the oocyte, and mutually required for their incorporation into the eggshell. Besides their role in eggshell integrity, Nasrat, Polehole, and Closca are also required for embryonic terminal patterning by anchoring or stabilizing Torso-like at the eggshell. Here, we show that they are also required for dorsoventral patterning, thereby unveiling that the dorsoventral and terminal systems, hitherto considered independent, share a common extracellular step. Furthermore, we show that Nasrat, Polehole, and Closca are required for proper Nudel activity, a protease acting both in embryonic dorsoventral patterning and eggshell integrity, thus providing a means to account for the role of Nasrat, Polehole, and Closca. We propose that a Nasrat/Polehole/Closca complex acts as a multifunctional hub to anchor various proteins synthesized at oogenesis, ensuring their spatial and temporal restricted function.

Mobile-phone radiation-induced perturbation of gene-expression profiling, redox equilibrium and sporadic-apoptosis control in the ovary of Drosophila melanogaster

The daily use by people of wireless communication devices has increased exponentially in the last decade, begetting concerns regarding its potential health hazards. Drosophila melanogaster four days-old adult female flies were exposed for 30 min to radiation emitted by a commercial mobile phone at a SAR of 0.15 W/kg and a SAE of 270 J/kg. ROS levels and apoptotic follicles were assayed in parallel with a genome-wide microarrays analysis. ROS cellular contents were found to increase by 1.6-fold (x), immediately after the end of exposure, in follicles of pre-choriogenic stages (germarium - stage 10), while sporadically generated apoptotic follicles (germarium 2b and stages 7-9) presented with an averaged 2x upregulation in their sub-population mass, 4 h after fly's irradiation with mobile device. Microarray analysis revealed 168 genes being differentially expressed, 2 h post-exposure, in response to radiofrequency (RF) electromagnetic field-radiation exposure (≥1.25x, P < 0.05) and associated with multiple and critical biological processes, such as basic metabolism and cellular subroutines related to stress response and apoptotic death. Exposure of adult flies to mobile-phone radiation for 30 min has an immediate impact on ROS production in animal's ovary, which seems to cause a global, systemic and non-targeted transcriptional reprogramming of gene expression, 2 h post-exposure, being finally followed by induction of apoptosis 4 h after the end of exposure. Conclusively, this unique type of pulsed radiation, mainly being derived from daily used mobile phones, seems capable of mobilizing critical cytopathic mechanisms, and altering fundamental genetic programs and networks in D. melanogaster.

The temporally controlled expression of Drongo, the fruit fly homolog of AGFG1, is achieved in female germline cells via P-bodies and its localization requires functional Rab11

To achieve proper RNA transport and localization, RNA viruses exploit cellular vesicular trafficking pathways. AGFG1, a host protein essential for HIV-1 and Influenza A replication, has been shown to mediate release of intron-containing viral RNAs from the perinuclear region. It is still unknown what its precise role in this release is, or whether AGFG1 also participates in cytoplasmic transport. We report for the first time the expression patterns during oogenesis for Drongo, the fruit fly homolog of AGFG1. We find that temporally controlled Drongo expression is achieved by translational repression of drongo mRNA within P-bodies. Here we show a first link between the recycling endosome pathway and Drongo, and find that proper Drongo localization at the oocyte's cortex during mid-oogenesis requires functional Rab11.

The fenpropathrin resistant Tetranychus cinnabarinus showed increased fecundity with high content of vitellogenin and vitellogenin receptor

Carmine spider mite, Tetranychus cinnabarinus (Boisduval), an agricultural pest of economically important crops, has developed resistance to a group of pesticides. We have selected a fenpropathrin-resistant strain (FeR) of T. cinnabarinus from the isogenous and susceptible strain (SS), and found that the FeR not only showed resistance but its fecundity also increased. According to the numbers of eggs laid per day of both strains, the FeR was more fertile than SS throughout the life span. To investigate the underlying reason, the protein contents of vitellogenin (vg) and vitellogenin receptor (vgr) were detected, and the results showed both of them were significantly higher in FeR than in SS. Then, the mRNA-expressions of vg and vgr genes were compared between FeR and SS. From the transcriptome data of T. cinnabarinus, we classified two vg genes (designated as Tcvg1 and Tcvg2, respectively) and a vgr gene (designated as Tcvgr). The expressions of Tcvg1, Tcvg2 and Tcvgr were highly associated with the fecundity of the mites that their mRNAs were extremely abundant at the adult stage, but hardly detectable during the developmental period (from egg to deutonymph). In accordance with the protein content, the expression levels of the three genes were all significantly higher in FeR than they were in SS. These results suggested that after resistance selection with fenpropathrin in T. cinnabarinus, the fecundity and the expression of reproduction-related genes (vg and vgr) were significantly higher in fenpropathrin resistant strain than that in susceptible strain.

Transcriptome analysis provides insight into venom evolution in a seed-parasitic wasp, Megastigmus spermotrophus

One of the most striking host range transitions is the evolution of plant parasitism from animal parasitism. Parasitoid wasps that have secondarily evolved to attack plants (ie gall wasps and seed-feeders) demonstrate intimate associations with their hosts, yet the mechanism of plant-host manipulation is currently not known. There is, however, emerging evidence suggesting that ovipositional secretions play a role in plant manipulation. To investigate whether parasites have modified pre-existing adaptations to facilitate dramatic host shifts we aimed to characterize the expression of venom proteins in a plant parasite using a collection of parasitoid venom sequences as a guide. The transcriptome of a seed-feeding wasp, Megastigmus spermotrophus, was assembled de novo and three putative venoms were found to be highly expressed in adult females. One of these putative venoms, aspartylglucosaminidase, has been previously identified as a major venom component in two distantly related parasitoid wasps (Asobara tabida and Leptopilina heterotoma) and may have originated via gene duplication within the Hymenoptera. Our study shows that M. spermotrophus, a specialized plant parasite, expresses putative venom transcripts that share homology to venoms identified in Nasonia vitripennis (both superfamily Chalcidoidea), which suggests that M. spermotrophus may have co-opted pre-existing machinery to develop as a plant parasite.

RNA sequencing to characterize transcriptional changes of sexual maturation and mating in the female oriental fruit fly Bactrocera dorsalis

BACKGROUND

Female reproductive potential plays a significant role in the survival and stability of species, and sexual maturation and mating processes are crucial. However, our knowledge of the reproductive genes involved in sexual maturation and mating has been largely limited to model organisms. The oriental fruit fly Bactrocera dorsalis is a highly invasive agricultural pest, known to cause major economic losses; thus, it is of great value to understand the transcriptional changes involved in sexual maturation and mating processes as well as the related genes. Here, we used a high-throughput sequencing method to identify multiple genes potentially involved in sexual maturation and mating in female B. dorsalis.

RESULTS

We sequenced 39,999 unique genes with an average length of 883 bp. In total, 3264 differentially expressed genes (DEGs) were detected between mature virgin and immature Bactrocera dorsalis libraries, whereas only 83 DEGs were identified between flies that had mated or were mature virgins. These DEGs were functionally annotated using the GO and KEGG pathway annotation tools. Results showed that the main GO terms associated with the DEGs from the mature virgin vs. immature groups were primarily assigned to the metabolic and developmental processes, which we focused on, whereas those from the mated vs. mature virgin group largely belonged to the response to stimulus and immune system processes. Additionally, we identified multiple DEGs during sexual maturation that are involved in reproduction, and expression pattern analysis revealed that the majority DEGs detected were highly enriched in those linked to the ovaries or fat bodies. Several mating responsive genes differentially expressed after mating were also identified, and all antimicrobial peptides detected were highly enriched in fat body and significantly up-regulated approximately 2- to 10-fold at 24 h after mating.

CONCLUSION

This study supplied female reproductive genes involved in sexual maturation and the post-mating response in B. dorsalis, based on RNA-seq. Our data will facilitate molecular research related to reproduction and provide abundant target genes for effective control of this agricultural pest.

The ecdysone receptor signalling regulates microvilli formation in follicular epithelial cells

Epithelial morphogenesis contributes greatly to the development and homeostasis of the organs and body parts. Here, we analysed the consequences of impaired ecdysone receptor (EcR) signalling in the Drosophila follicular epithelium. Besides governing cell growth, the three EcR isoforms act redundantly in controlling follicle cell positioning. Flattening of the microvilli and an aberrant actin cytoskeleton arise from defective EcR signalling in follicle cells, and these defects impact on the organisation of the oocyte membrane. We found that this signalling governs a complex molecular network since its impairment affects key molecules as atypical protein kinase C and activated Moesin. Interestingly, the activity of the transcription factor Tramtrack69 isoform is required for microvilli and their actin core morphogenesis as well as for follicle cell positioning. In conclusion, our findings provide evidence of novel roles for EcR signalling and Tramtrack69 transcription factor in controlling stage-specific differentiation events that take place in the follicular epithelium.

A NONOVARY-SPECIFIC VITELLOGENIN RECEPTOR FROM THE ORIENTAL FRUIT FLY, Bactrocera dorsalis (HENDEL)

The yolk protein precursor, vitellogenin (Vg), is absorbed into growing oocytes via receptor-mediated endocytosis for embryonic development. In this study, a Vg receptor (VgR) cDNA of the oriental fruit fly (Bactrocera dorsalis Hendel) was cloned via RT-PCR and RACE (GenBank accession no. KR535603) and its expression analyzed. The BdVgR cDNA has a length of 6,585 bp encoding 1,923 amino acids. It has a conserved motif arrangement with other insect VgRs, and showed high identity to the B. cucurbitae VgR (91.4%). The expression of BdVgR mRNA and proteins was shown in both ovary and fat body. This is the first report on a nonovary-specific VgR from a nonsocial insect. In ovary, the expression of BdVgR mRNA and proteins was inconsistent, with the transcription, but not protein, level high on D0. In fat body, the expression levels of BdVgR mRNA and proteins were high on days 5 and 6. The function of BdVgR in the fat body is not clear. However, it may be involved in reuptake of yolk proteins from the hemolymph as an amino acid reservoir or as autocrine regulation of yolk protein expression.

β carbonic anhydrase is required for female fertility in Drosophila melanogaster

Background

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous enzymes that catalyze the reversible hydration reaction of carbon dioxide. CAs are present as six structurally divergent enzyme families: α, β, γ, δ, ζ and η. β-CAs have a wide distribution across different species including invertebrates. Previously, we showed that Drosophila melanogaster β-CA is a highly active mitochondrial enzyme. In this study, we investigated the function of Drosophila β-CA by silencing the expression of the β-CA gene using UAS/GAL4-based RNA interference (RNAi) in Drosophila in vivo.

Results

Crossing β-CA RNAi lines over ubiquitous Actin driver flies did not produce any viable progeny, indicating that β-CA expression is required for fly development. RNAi silencing of β-CA ubiquitously in adult flies did not affect their survival rate or function of mitochondrial electron transport chain. Importantly, β-CA RNAi led to impaired reproduction. All β-CA knockdown females were sterile, and produced few or no eggs. Whole ovaries of knockdown females looked normal but upon cadherin staining, there was an apparent functional defect in migration of border cells, which are considered essential for normal fertilization.

Conclusions

These results indicate that although Drosophila β-CA is dispensable for survival of adult flies, it is essential for female fertility.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-015-0111-3) contains supplementary material, which is available to authorized users.

Efficient Endocytic Uptake and Maturation in Drosophila Oocytes Requires Dynamitin/p50

Dynactin is a multi-subunit complex that functions as a regulator of the Dynein motor. A central component of this complex is Dynamitin/p50 (Dmn). Dmn is required for endosome motility in mammalian cell lines. However, the extent to which Dmn participates in the sorting of cargo via the endosomal system is unknown. In this study, we examined the endocytic role of Dmn using the Drosophila melanogaster oocyte as a model. Yolk proteins are internalized into the oocyte via clathrin-mediated endocytosis, trafficked through the endocytic pathway, and stored in condensed yolk granules. Oocytes that were depleted of Dmn contained fewer yolk granules than controls. In addition, these oocytes accumulated numerous endocytic intermediate structures. Particularly prominent were enlarged endosomes that were relatively devoid of Yolk proteins. Ultrastructural and genetic analyses indicate that the endocytic intermediates are produced downstream of Rab5. Similar phenotypes were observed upon depleting Dynein heavy chain (Dhc) or Lis1. Dhc is the motor subunit of the Dynein complex and Lis1 is a regulator of Dynein activity. We therefore propose that Dmn performs its function in endocytosis via the Dynein motor. Consistent with a role for Dynein in endocytosis, the motor colocalized with the endocytic machinery at the oocyte cortex in an endocytosis-dependent manner. Our results suggest a model whereby endocytic activity recruits Dynein to the oocyte cortex. The motor along with its regulators, Dynactin and Lis1, functions to ensure efficient endocytic uptake and maturation.

Accumulation of the Drosophila Torso-like protein at the blastoderm plasma membrane suggests that it translocates from the eggshell

The eggshell serves as a depository for proteins that play an important role in early embryonic development. In particular, the Drosophila eggshell is responsible for transferring asymmetries from the egg chamber to specify the regions at both ends of the embryo through the uneven activation of the Torso (Tor) receptor in its membrane. This process relies on the restricted expression of the gene torso-like (tsl) in subpopulations of follicle cells during oogenesis and its protein accumulation at both poles of the eggshell, but it is not known how this signal is transmitted to the embryo. Here, we show that Tsl accumulates at the embryonic plasma membrane, even in the absence of the Tor receptor. However, during oogenesis, we detected Tsl accumulation only at the eggshell. These results suggest that there is a two-step mechanism to transfer the asymmetric positional cues from the egg chamber into the early embryo: initial anchoring of Tsl at the eggshell as it is secreted, followed by its later translocation to the egg plasma membrane, where it enables Tor receptor activation. Translocation of anchored determinants from the eggshell might then regulate the spatial and temporal control of early embryonic developmental processes.

Ethylparaben affects lifespan, fecundity, and the expression levels of ERR, EcR and YPR in Drosophila melanogaster

Parabens, which mainly include methylparaben (MP), ethylparaben (EP), propylparaben (PP), and butylparaben (BP), are widely used as cosmetic and food preservatives. Although these chemicals, when used as preservatives, are thought to be safe for humans, many studies have demonstrated that they have estrogenic effects, and can affect the normal development and functions of the reproductive systems in a number of animal species. By treating fruit flies (Drosophila melanogaster) with EP, here we show that lower concentration of EP (0.02%) enhanced fertility while higher concentration of EP (0.10% and 0.20%) shortened the lifespan and reduced the fecundity of fruit flies. When we analyzed the expression levels of the estrogen-related receptor gene (ERR), ecdysone receptor gene (EcR) and Yolk protein receptor gene (YPR) from control and EP-treated fruit flies by using quantitative real-time PCR, we found that the expression levels of all three genes were significantly changed by EP treatment, and that female fruit flies are more sensitive to EP than males. Our data suggests that the estrogenic and the toxic effects of EP to fruit flies may have a molecular basis through the hormonal effect of EP.

Ultrasensitive proteome analysis using paramagnetic bead technology

In order to obtain a systems-level understanding of a complex biological system, detailed proteome information is essential. Despite great progress in proteomics technologies, thorough interrogation of the proteome from quantity-limited biological samples is hampered by inefficiencies during processing. To address these challenges, here we introduce a novel protocol using paramagnetic beads, termed Single-Pot Solid-Phase-enhanced Sample Preparation (SP3). SP3 provides a rapid and unbiased means of proteomic sample preparation in a single tube that facilitates ultrasensitive analysis by outperforming existing protocols in terms of efficiency, scalability, speed, throughput, and flexibility. To illustrate these benefits, characterization of 1,000 HeLa cells and single Drosophila embryos is used to establish that SP3 provides an enhanced platform for profiling proteomes derived from sub-microgram amounts of material. These data present a first view of developmental stage-specific proteome dynamics in Drosophila at a single-embryo resolution, permitting characterization of inter-individual expression variation. Together, the findings of this work position SP3 as a superior protocol that facilitates exciting new directions in multiple areas of proteomics ranging from developmental biology to clinical applications.

Endophilin B is required for the Drosophila oocyte to endocytose yolk downstream of Oskar

The nutritional environment is crucial for Drosophila oogenesis in terms of controlling hormonal conditions that regulate yolk production and the progress of vitellogenesis. Here, we discovered that Drosophila Endophilin B (D-EndoB), a member of the endophilin family, is required for yolk endocytosis as it regulates membrane dynamics in developing egg chambers. Loss of D-EndoB leads to yolk content reduction, similar to that seen in yolkless mutants, and also causes poor fecundity. In addition, mutant egg chambers exhibit an arrest at the previtellogenic stage. D-EndoB displayed a crescent localization at the oocyte posterior pole in an Oskar-dependent manner; however, it did not contribute to pole plasm assembly. D-EndoB was found to partially colocalize with Long Oskar and Yolkless at the endocytic membranes in ultrastructure analysis. Using an FM4-64 dye incorporation assay, D-EndoB was also found to promote endocytosis in the oocyte. When expressing the full-length D-endoB(FL) or D-endoB(ΔSH3) mutant transgenes in oocytes, the blockage of vitellogenesis and the defect in fecundity in D-endoB mutants was restored. By contrast, a truncated N-BAR domain of the D-EndoB only partially rescued these defects. Taken together, these results allow us to conclude that D-EndoB contributes to the endocytic activity downstream of Oskar by facilitating membrane dynamics through its N-BAR domain in the yolk uptake process, thereby leading to normal progression of vitellogenesis.

Visualization of clathrin-mediated endocytosis in live Drosophila egg chambers

In oviparous animals, clathrin-dependent endocytosis is often critical to stockpile a necessary supply of yolk within the maturing oocyte, which enables subsequent embryonic development. In the physically linked chains of maturing egg chambers within the Drosophila melanogaster ovary, a distinct, morphologically discernable subset undergoes a massive burst clathrin-mediated endocytosis to accumulate yolk in a process termed vitellogenesis. Here, we describe how to prepare isolated ovaries to follow endocytosis, and detail approaches to follow live uptake of soluble reporters into vitellogenic Drosophila egg chambers.

Transcriptome analysis of female reproductive tissues of Anastrepha obliqua and molecular evolution of eggshell proteins in the fraterculus group

The investigation of cDNA libraries has been an important tool for the identification of new genes in nonmodel species such as the fruit flies from the Anastrepha fraterculus group. In the present study, we constructed a cDNA library from the female reproductive tissues of Anastrepha obliqua aiming to identify genes with high evolutionary rates. We sequenced 2304 clones obtained from the female reproductive tissues of A. obliqua flies. The expressed sequence tags generated a total of 816 unigenes which were classified into different protein classes. Among these,we identified chorionic and vitelline protein genes as being among the most highly expressed. We used unigene sequences to amplify a set of chorionic and vitelline genes, involved in the formation of the eggshell,in species of the fraterculus group. Four chorionic genes and two vitelline genes showed evidence of positive selection along the Anastrepha and/or Tephritidae lineage. The signal of selection detected for Vm26Aa was possibly generated by a gene duplication event. The rapid evolutionary rates indicate that these genes could serve as important markers in population and evolutionary studies, not only for species of this group, but possibly also for other Diptera.

Unscrambling butterfly oogenesis

Background

Butterflies are popular model organisms to study physiological mechanisms underlying variability in oogenesis and egg provisioning in response to environmental conditions. Nothing is known, however, about; the developmental mechanisms governing butterfly oogenesis, how polarity in the oocyte is established, or which particular maternal effect genes regulate early embryogenesis. To gain insights into these developmental mechanisms and to identify the conserved and divergent aspects of butterfly oogenesis, we analysed a de novo ovarian transcriptome of the Speckled Wood butterfly Pararge aegeria (L.), and compared the results with known model organisms such as Drosophila melanogaster and Bombyx mori.

Results

A total of 17306 contigs were annotated, with 30% possibly novel or highly divergent sequences observed. Pararge aegeria females expressed 74.5% of the genes that are known to be essential for D. melanogaster oogenesis. We discuss the genes involved in all aspects of oogenesis, including vitellogenesis and choriogenesis, plus those implicated in hormonal control of oogenesis and transgenerational hormonal effects in great detail. Compared to other insects, a number of significant differences were observed in; the genes involved in stem cell maintenance and differentiation in the germarium, establishment of oocyte polarity, and in several aspects of maternal regulation of zygotic development.

Conclusions

This study provides valuable resources to investigate a number of divergent aspects of butterfly oogenesis requiring further research. In order to fully unscramble butterfly oogenesis, we also now also have the resources to investigate expression patterns of oogenesis genes under a range of environmental conditions, and to establish their function.

Vitellogenin receptor mutation leads to the oogenesis mutant phenotype "scanty vitellin" of the silkworm, Bombyx mori

In insects, the vitellogenin receptor (VgR) mediates the uptake of vitellogenin (Vg) from the hemolymph by developing oocytes. The oogenesis mutant scanty vitellin (vit) of Bombyx mori (Bm) lacks vitellin and 30-kDa proteins, but B. mori egg-specific protein and BmVg are normal. The vit eggs are white and smaller compared with the pale yellow eggs of the wild type and are embryonic lethal. This study found that a mutation in the B. mori VgR gene (BmVgR) is responsible for the vit phenotype. We cloned the cDNA sequences encoding WT and vit BmVgR. The functional domains of BmVgR are similar to those of other low-density lipoprotein receptors. When compared with the wild type, a 235-bp genomic sequence in vit BmVgR is substituted for a 7-bp sequence. This mutation has resulted in a 50-amino acid deletion in the third Class B region of the first epidermal growth factor (EGF1) domain. BmVgR is expressed specifically in oocytes, and the transcriptional level is changed dramatically and consistently with maturation of oocytes during the previtellogenic periods. Linkage analysis confirmed that BmVgR is mutated in the vit mutant. The coimmunoprecipitation assay confirmed that mutated BmVgR is able to bind BmVg but that BmVg cannot be dissociated under acidic conditions. The WT phenotype determined by RNA interference was similar to that of the vit phenotype for nutritional deficiency, such as BmVg and 30-kDa proteins. These results showed that BmVgR has an important role in transporting proteins for egg formation and embryonic development in B. mori.

The apoptotic engulfment protein Ced-6 participates in clathrin-mediated yolk uptake in Drosophila egg chambers

During oogenesis in Drosophila, the phagocytic engulfment protein Ced-6 recognizes the atypical endocytic sorting signal within the vitellogenin receptor Yolkless. Because Ced-6 displays all of the features of an authentic clathrin adaptor, an unrecognized clathrin dependence for Ced-6/Gulp operation during phagocytosis is possible.

Clathrin-mediated endocytosis and phagocytosis are both selective surface internalization processes but have little known mechanistic similarity or interdependence. Here we show that the phosphotyrosine-binding (PTB) domain protein Ced-6, a well-established phagocytosis component that operates as a transducer of so-called “eat-me” signals during engulfment of apoptotic cells and microorganisms, is expressed in the female Drosophila germline and that Ced-6 expression correlates with ovarian follicle development. Ced-6 exhibits all the known biochemical properties of a clathrin-associated sorting protein, yet ced-6–null flies are semifertile despite massive accumulation of soluble yolk precursors in the hemolymph. This is because redundant sorting signals within the cytosolic domain of the Drosophila vitellogenin receptor Yolkless, a low density lipoprotein receptor superfamily member, occur; a functional atypical dileucine signal binds to the endocytic AP-2 clathrin adaptor directly. Nonetheless, the Ced-6 PTB domain specifically recognizes the noncanonical Yolkless FXNPXA sorting sequence and in HeLa cells promotes the rapid, clathrin-dependent uptake of a Yolkless chimera lacking the distal dileucine signal. Ced-6 thus operates in vivo as a clathrin adaptor. Because the human Ced-6 orthologue GULP similarly binds to clathrin machinery, localizes to cell surface clathrin-coated structures, and is enriched in placental clathrin-coated vesicles, new possibilities for Ced-6/Gulp operation during phagocytosis must be considered.

Cryo-section immunolabelling of difficult to preserve specimens: advantages of cryofixation, freeze-substitution and rehydration

BACKGROUND INFORMATION

Electron microscopic immunolabelling of ultrathin thawed cryo-sections, according to the method of Tokuyasu, is widely used as a very sensitive high-resolution localization technique. Its main advantages are that antigens remain in a hydrated environment prior to immunolabelling, and that antigen accessibility is improved compared with resin section labelling. However, the quality of structural appearance and antigenicity depends highly on the limitations of the initial conventional chemical fixation step, such as slow diffusion and selective reaction/cross-linking of fixative molecules.

RESULTS AND CONCLUSIONS

Cryofixation, instead of conventional chemical fixation, followed by freeze-substitution/chemical fixation, rehydration and further processing for Tokuyasu cryo-sectioning leads to an improved preservation of both ultrastructure and antigenicity. This is especially true for tissues which are difficult to preserve by conventional chemical fixation at ambient temperatures, such as plant material, Drosophila embryos or nematode tissue. In particular labile and highly dynamic structures (for example, microtubules and Golgi apparatus) are remarkably better preserved. These improvements are also valid for light microscopic applications.