Biosynthesis of mosquito vitellogenin

Vitellogenin genes are transcribed in Culex quinquefasciatus ovary

BACKGROUND

Culex quinquefasciatus, a cosmopolitan, domestic, and highly anthropophilic mosquito, is a vector of pathogenic arboviruses such as West Nile virus and Rift Valley virus, as well as lymphatic filariasis. The current knowledge on its reproductive physiology regarding vitellogenin expression in different tissues is still limited.

OBJECTIVES

In this study, we analysed the transcriptional profiles of vitellogenin genes in the fat body and ovaries of C. quinquefasciatus females during the first gonotrophic cycle.

METHODS

C. quinquefasciatus ovaries and/or fat bodies were dissected in different times during the first gonotrophic cycle and total RNA was extracted and used for reverse transcription polymerase chain reaction, quantitative real time-PCR, and in situ hybridisation.

FINDINGS

We confirmed the classical descriptions of the vitellogenic process in mosquitoes by verifying that vitellogenin genes are transcribed in the fat bodies of C. quinquefasciatus females. Using RNA in situ hybridisation approach, we showed that vitellogenin genes are also transcribed in developing ovaries, specifically by the follicle cells.

MAIN CONCLUSIONS

This is the first time that vitellogenin transcripts are observed in mosquito ovaries. Studies to determine if Vg transcripts are translated into proteins and their contribution to the reproductive success of the mosquito need to be further investigated.

Human blood microRNA hsa-miR-21-5p induces vitellogenin in the mosquito Aedes aegypti

Mosquito vectors transmit various diseases through blood feeding, required for their egg development. Hence, blood feeding is a major physiological event in their life cycle, during which hundreds of genes are tightly regulated. Blood is a rich source of proteins for mosquitoes, but also contains many other molecules including microRNAs (miRNAs). Here, we found that human blood miRNAs are transported abundantly into the fat body tissue of Aedes aegypti, a key metabolic center in post-blood feeding reproductive events, where they target and regulate mosquito genes. Using an artificial diet spiked with the mimic of an abundant and stable human blood miRNA, hsa-miR-21-5p, and proteomics analysis, we found over 40 proteins showing differential expression in female Ae. aegypti mosquitoes after feeding. Of interest, we found that the miRNA positively regulates the vitellogenin gene, coding for a yolk protein produced in the mosquito fat body and then transported to the ovaries as a protein source for egg production. Inhibition of hsa-miR-21-5p followed by human blood feeding led to a statistically insignificant reduction in progeny production. The results provide another example of the involvement of small regulatory molecules in the interaction of taxonomically vastly different taxa.

Fat and Happy: Profiling Mosquito Fat Body Lipid Storage and Composition Post-blood Meal

The fat body is considered the insect analog of vertebrate liver and fat tissue. In mosquitoes, a blood meal triggers a series of processes in the fat body that culminate in vitellogenesis, the process of yolk formation. Lipids are stored in the fat body in specialized organelles called lipid droplets that change in size depending on the nutritional and metabolic status of the insect. We surveyed lipid droplets in female Aedes aegypti fat body during a reproductive cycle using confocal microscopy and analyzed the dynamic changes in the fat body lipidome during this process using LC/MS. We found that lipid droplets underwent dynamic changes in volume after the mosquito took a blood meal. The lipid composition found in the fat body is quite complex with 117 distinct lipids that fall into 19 classes and sublcasses. Our results demonstrate that the lipid composition of the fat body is complex as most lipid classes underwent significant changes over the course of the vitellogenic cycle. This study lays the foundation for identifying unknown biochemical pathways active in the mosquito fat body, that are high-value targets for the development of novel mosquito control strategies.

Gut-Expressed Vitellogenin Facilitates the Movement of a Plant Virus across the Midgut Wall in Its Insect Vector

Many viral pathogens of global importance to plant and animal health are persistently transmitted by insect vectors. Midgut of insects forms the first major barrier that these viruses encounter during their entry into the vectors. However, the vector ligand(s) involved in the movement of plant viruses across the midgut barrier remains largely uncharacterized. Begomoviruses, many of which are disease agents of some major crops worldwide, are persistently transmitted by whiteflies (Bemisia tabaci). Here, in order to identify whitefly midgut proteins that interact with a devastating begomovirus, tomato yellow leaf curl virus (TYLCV), we performed midgut-specific TYLCV coat protein (CP) immunoprecipitation followed by high-throughput mass spectrometry proteomic analysis. We find that vitellogenin (Vg), a critical insect reproductive protein that has been considered to be synthesized by the fat body, is also synthesized by and interacts with TYLCV CP in the whitefly midgut. TYLCV appears to be internalized into midgut epithelial cells as a complex with Vg through endocytosis. Virus-containing vesicles then deliver the virus-Vg complexes to early endosomes for intracellular transport. Systematic silencing of Vg or midgut-specific immune blocking of Vg inhibited virus movement across the midgut wall and decreased viral acquisition and transmission by whitefly. Our findings show that a functional Vg protein is synthesized in the midgut of an insect and suggest a novel Vg mechanism that facilitates virus movement across the midgut barrier of its insect vector.

IMPORTANCE An essential step in the life cycle of many viruses is transmission to a new host by insect vectors, and one critical step in the transmission of persistently transmitted viruses is overcoming the midgut barrier to enter vectors and complete their cycle. Most viruses enter vector midgut epithelial cells via specific interaction between viral structural proteins and vector cell surface receptor complexes. Tomato yellow leaf curl virus (TYLCV) is persistently transmitted by the whitefly Bemisia tabaci between host plants. Here, we find that TYLCV coat protein interacts with vitellogenin (Vg) in the whitefly midgut. This interaction is required for the movement of the virus crossing the midgut wall and thus facilitates viral acquisition and transmission by whitefly. This study reveals a novel mechanism of virus overcoming the insect midgut barrier and provides new insights into the function of Vg beyond serving as nutrition for developing embryos in insects.

The 20-hydroxyecdysone agonist, halofenozide, promotes anti-Plasmodium immunity in Anopheles gambiae via the ecdysone receptor

Mosquito physiology and immunity are integral determinants of malaria vector competence. This includes the principal role of hormonal signaling in Anopheles gambiae initiated shortly after blood-feeding, which stimulates immune induction and promotes vitellogenesis through the function of 20-hydroxyecdysone (20E). Previous studies demonstrated that manipulating 20E signaling through the direct injection of 20E or the application of a 20E agonist can significantly impact Plasmodium infection outcomes, reducing oocyst numbers and the potential for malaria transmission. In support of these findings, we demonstrate that a 20E agonist, halofenozide, is able to induce anti-Plasmodium immune responses that limit Plasmodium ookinetes. We demonstrate that halofenozide requires the function of ultraspiracle (USP), a component of the canonical heterodimeric ecdysone receptor, to induce malaria parasite killing responses. Additional experiments suggest that the effects of halofenozide treatment are temporal, such that its application only limits malaria parasites when applied prior to infection. Unlike 20E, halofenozide does not influence cellular immune function or AMP production. Together, our results further demonstrate the potential of targeting 20E signaling pathways to reduce malaria parasite infection in the mosquito vector and provide new insight into the mechanisms of halofenozide-mediated immune activation that differ from 20E.

Comparative iTRAQ proteomic profiling of proteins associated with the adaptation of brown planthopper to moderately resistant vs. susceptible rice varieties

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a destructive pest that poses a significant threat to rice plants worldwide. To explore how BPHs adapt to the resistant rice variety, we analyzed proteomics profiles of two virulent N. lugens populations. We focused on Biotype Y, which can survive on the moderately resistant rice variety YHY15, and Biotype I, which can survive on the susceptible rice variety TN1. We performed protein quantitation using the isobaric tag for relative and absolute quantification (iTRAQ) and then compared the expression patterns between two virulent N. lugens populations and found 258 differentially expressed proteins (DEPs). We found that 151 of the DEPs were up-regulated, while 107 were down-regulated. We evaluated transcript levels of 8 expressed genes from the iTRAQ results by qRT-PCR, which revealed transcriptional changes that were consistent with the changes at the protein level. The determination of the protein changes in two virulent N. lugens populations would help to better understanding BPH adaptation to resistant rice varieties and facilitate the better design of new control strategies for host defense against BPH.

Residual vitellus and energetic state of wolf spiderlings Pardosa saltans after emergence from egg-sac until first predation

The aim of this study was to evaluate energetic source used by juveniles of a terrestrial oviparous invertebrate during the earliest periods of their life. Growth, behavioural activities and energy contents of Pardosa saltans spiderlings' residual vitellus were monitored during 8 days after their emergence from their egg-sac until they disperse autonomously. The life-cycle of juvenile after emergence can be divided into three periods: a gregarious while juveniles are aggregated on their mother, dismounting off their mother's back and dispersion. We present the first biochemical study of residual vitellus and energy expenditure during these three periods. At emergence, the mean weight of juveniles was 0.59 mg and energy stock from residual vitellus averaged 51 cal/g wet mass. During gregarious period, the weight of the juveniles aggregated on their mother did not vary significantly and juveniles utilized only 1 cal/day from their residual vitellus. During the period from dismounting until their first exogenous feed, juveniles lost weight and used 30% of their residual vitellus stock. Proteins from the residual vitellus contributed principally to their energy expenditure during this period: 1.5 µg protein/day. Juveniles' first exogenous feeding was observed 7-8 days after emergence, when 70% of residual vitellus energy had been utilized. Juveniles dispersed after eating, reconstituting an energy stock comparable to that observed at emergence from egg-sac (50 cal/g wet mass). This new energy stock contains mainly lipids unlike the energy stock from the residual vitellus.

A survey of proteins in midgut contents of the tick, Haemaphysalis flava, by proteome and transcriptome analysis

Tick blood meals are stored and digested in their midguts. Blood digestion is complex, and many proteins are involved. Study of the tick-derived proteins in the midgut content may aid in the discovery of active molecules that would be useful for anti-tick vaccines. We analyzed the midgut content proteomes of partially engorged female Haemaphysalis flava, fully engorged female H. flava, and hedgehog serum using liquid chromatography tandem-mass spectrometry and label-free quantitation. In this study, high-confidence protein profiling of tick midgut content was determined. Based on the search against our in-house transcriptome database, the 28 high-confidence proteins were identified. Of these, 17 were identified as tick-derived, and the rest were of unspecified origin (proteins that could not be differentiated as host-derived or tick-derived proteins). The function of these midgut content proteins identified here may involve nutrient transportation, anti-coagulation, erythrocyte lysis, detoxification, lipid metabolism, and immunization. The presence of hemoglobin suggested that the red blood cells were lysed in the gut lumen. The midgut contents contain a large amount of fibrinogen and it has the ability to clot immediately. The midgut contained mostly host-derived proteins, and these host proteins provide rich nutrients for tick development and reproduction. However, some intracellular proteins were also identified, suggesting the possibility of shedding of the midgut epithelium and ingestion of saliva during feeding. This finding advances our understanding of the digestive mechanism and will be useful in the screening of vaccine antigens.

Proteomic analysis of saliva from partially and fully engorged adult female Rhipicephalus microplus (Acari: Ixodidae)

Rhipicephalus microplus salivary gland secretes a number of complex bioactive proteins during feeding. These components are important in feeding and affect anti-coagulation, anti-inflammation and also have anti-microbial effects. In this study, tick saliva was collected from partially engorged female (PEF) and fully engorged female (FEF) ticks. Liquid chromatography tandem-mass spectrometry (LC-MS/MS) and isobaric tags for relative and absolute quantification (iTRAQ) were used to identify and quantify R. microplus salivary proteins. A total of 322 unique peptides were detected and 151 proteins were characterized in both PEF and FEF. Of these, 41 proteins are considered as high-confidence proteins. Fifteen high-confidence proteins were upregulated and six high-confidence proteins were downregulated (p < 0.05; PEF:FEF ratio ≥ 1.2 or PEF:FEF ratio ≤ 0.83); 17 high-confidence proteins are slightly changed (PEF:FEF ratio > 0.83 and < 1.2). These high-confidence proteins are involved in several physiological roles, including egg development, transportation of proteins, immunity and anti-microorganism, anti-coagulant, and adhesion. In comparison with PEF, the number of upregulated proteins exceeded the number of proteins downregulated. Salivary protein may be induced by the blood-meal and these proteins contribute to successful feeding.

Vitellogenesis in spiders: first analysis of protein changes in different reproductive stages of Polybetes pythagoricus

Vitellogenesis represents one of the most vital processes of oviparous species during which various proteins, carbohydrates, and lipids are synthesized and stored inside the developing oocytes. Through analyzing protein changes in the midgut diverticula, hemolymph, and ovaries of females throughout the different vitellogenic stages of the spider Polybetes pythagoricus, we determined the origin of the different proteins involved in the formation of lipovitellins (LVs) along with the existence of a linkage between the hemocyanin and this vital process. An increase in the total protein content of the midgut diverticula, hemolymph, and ovary occurred throughout vitellogenesis followed by a decrease in those levels after laying. The presence of hemocyanin in egg and in LV2, as well as its accumulation in the ovary throughout the vitellogenesis process, was determined. Considering that all biologic processes depend on the correct structure and function of proteins, this study establishes, for the first time for the Order Araneae, the coexistence of three different origins of vitellogenesis-related proteins: one predominantly ovarian involving peptides of 120, 75, 46, and 30 kDa; another extraovarian one originated from the midgut diverticula and represented by a 170 kDa peptide, and a third hemolymphatic one, represented by the 67 kDa peptide.

Identification and Expression Patterns of Three Vitellogenin Genes and Their Roles in Reproduction of the Alligatorweed Flea Beetle Agasicles hygrophila (Coleoptera: Chrysomelidae)

The alligatorweed flea beetle Agasicles hygrophila is an insect used for biological control of the aquatic weed Alternanthera philoxeroides (alligatorweed). Because these insects are oviparous, synthesis, and transportation of yolk proteins is integral to reproduction. Vitellin, the chief protein constituent in egg yolk, is mainly synthesized in the fat body and its synthesis is regulated by the transcript levels of Vitellogenin (Vg). In our study, we first cloned and characterized three Vg genes from A. hygrophila and quantified the expression levels of these Vgs in different tissues and developmental stages by RT-qPCR. Analysis of the full-length cDNA sequences of the three A. hygrophila Vg genes revealed that the open reading frames of AhVg1, AhVg2, and AhVg3 were 5175, 5346, and 5385 bp, encoding 1724, 1781, and 1794 amino acids, respectively. RT-qPCR analysis revealed that these three AhVgs have similar expression patterns; expression in the fat body was significantly higher than that in other tissues, and the highest expression was observed in the adult developmental stage. RNA interference was used to explore the functions of the AhVgs. A. hygrophila female adults injected with dsRNA targeting the AhVg genes showed decreased AhVg gene expression. Down regulation of all three AhVgs significantly affected ovary development, reduced egg laying capacity, and reduced the egg hatch rate compared with the control groups. Our findings provide the basis for further study of the functions of Vg genes in other insect species.

De novo characterization of Phenacoccus solenopsis transcriptome and analysis of gene expression profiling during development and hormone biosynthesis

The cotton mealybug Phenacoccus solenopsis is a devastating pest of cotton causing tremendous loss in the yield of crops each year. Widespread physiological and biological studies on P. solenopsis have been carried out, but the lack of genetic information has constrained our understanding of the molecular mechanisms behind its growth and development. To understand and characterize the different developmental stages, RNA-Seq platform was used to execute de-novo transcriptome assembly and differential gene expression profiling for the eggs, first, second, third instar and adult female stages. About 182.67 million reads were assembled into 93,781 unigenes with an average length of 871.4 bp and an N50 length of 1899 bp. These unigenes sequences were annotated and classified by performing NCBI non-redundant (Nr) database, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Clusters of Orthologous Groups (COG), Gene ontology (GO), the Swiss-Prot protein database (Swiss-Prot), and nearest related organism Acyrthosiphon pisum (pea aphid) database. To get more information regarding the process of metamorphosis, we performed a pairwise comparison of four developmental stages and obtained 29,415 differentially expressed genes. Some of the differentially expressed genes were associated with functional protein synthesis, anti-microbial protection, development and hormone biosynthesis. Functional pathway enrichment analysis of differentially expressed genes showed the positive correlation with specific physiological activities of each stage, and these results were confirmed by qRT-PCR experiments. This study gives a valuable genomics resource of P. solenopsis covering all its developmental stages and will promote future studies on biological processes at the molecular level.

Protein profiling as early detection biomarkers for TiO2 nanoparticle toxicity in Daphnia magna

The mode of action for nanoparticle (NP) toxicity in aquatic organisms is not yet fully understood. In this work, a strategy other than toxicity testing was applied to Daphnia magna exposed to TiO₂-NPs: the use of nuclear microscopy and the assessment of protein profile. D. magna is a keystone species broadly used as a model system in ecotoxicology. Titanium (Ti) was found in the D. magna digestive tract, mainly in the gut. The penetration of Ti into the epithelial region was greater at higher exposure levels and also observed in eggs in the brood pouch. The protein profile of individuals exposed to different concentrations showed that 2.8 and 5.6 mg/L TiO₂-NP concentrations induced an over-expression of the majority of proteins, in particular proteins with molecular weight of ∼120, 85 and 15 kDa, while 11.2 mg/L TiO₂-NP had an inhibitory effect on protein expression. The Matrix-assisted laser desorption ionization with tandem time of flight mass spectrometry (MALDI-TOF/TOF MS) analysis of these proteins consistently identified them as vitellogenin (Vtg)-like proteins, associated with enzymes involved in redox balance. These results indicate that Vtg-like proteins are up-regulated in D. magna exposed to TiO₂-NPs. Vitellogenesis is associated with the reproduction system, suggesting that TiO₂-NP exposure can impair reproduction by affecting this process. The precise mode of action of TiO₂-NPs is still unclear and the results from this study are a first attempt to identify specific proteins as potential markers of TiO₂-NP toxicity in D. magna, providing useful information for future research.

Insect tissue-specific vitellogenin facilitates transmission of plant virus

Insect vitellogenin (Vg) has been considered to be synthesized in the fat body. Here, we found that abundant Vg protein is synthesized in Laodelphax striatellus hemocytes as well. We also determined that only the hemocyte-produced Vg binds to Rice stripe virus (RSV) in vivo. Examination of the subunit composition of L. striatellus Vg (LsVg) revealed that LsVg was processed differently after its expression in different tissues. The LsVg subunit able to bind to RSV exist stably only in hemocytes, while fat body-produced LsVg lacks the RSV-interacting subunit. Nymph and male L. striatellus individuals also synthesize Vg but only in hemocytes, and the proteins co-localize with RSV. We observed that knockdown of LsVg transcripts by RNA interference decreased the RSV titer in the hemolymph, and thus interfered with systemic virus infection. Our results reveal the sex-independent expression and tissue-specific processing of LsVg and also unprecedentedly connect the function of this protein in mediating virus transmission to its particular molecular forms existing in tissues previously known as non-Vg producing.

Comparative proteome analysis reveals that blood and sugar meals induce differential protein expression in Aedes aegypti female heads

Aedes aegypti females ingest sugar or blood to obtain the nutrients needed to maintain cellular homeostasis. During human blood ingestion, female mosquitoes may transmit different viruses such as dengue, yellow fever and, more recently, zika and chikungunya. Here, we report changes in protein expression in the heads of adult female Ae. aegypti mosquitoes in response to the ingestion of blood or sugar. Proteins extracted from the heads of Ae. aegypti fed exclusively on blood (BF) or sugar (SF) were trypsin hydrolyzed (off-gel) and analyzed by the reverse-phase nano-liquid chromatography coupled with hybrid mass spectrometry. A total of 1139 proteins were identified in female heads, representing 7.4% of the predicted proteins in Ae. aegypti genome (total = 15 419 active genes). Gene ontology annotation and categories showed that, in this insect, the head was rich in proteins involved in the metabolic process, proton transport, organelle, macromolecular complex, structural molecule activity, antioxidant activity, and catalytic activity. Our report is the first indicating that many of the annotated genes are translated into functional proteins in heads of adult female Ae. aegypti. Interestingly, we identified 8.7 times more exclusively expressed proteins involved in signal transduction, replication-transcription-translation (5.5 x), and transport (2.9 x) activity in BF than in SF groups. This paper discusses the protein profile of Ae. aegypti female heads and its implications for blood ingestion and carbohydrate intake.

DsRNA-mediated targeting of ribosomal transcripts RPS6 and RPL26 induces long-lasting and significant reductions in fecundity of the vector Aedes aegypti

Ribosomal transcripts produce critical proteins that are involved in most cellular production processes. Targeting ribosomal transcripts has produced mortality in mites and ticks but the effect of ribosomal transcript knockdown has not been thoroughly examined in mosquitoes. We examine the effects of triggers targeting four ribosomal proteins (RP) transcripts. Although no significant mortality was observed after dsRNA microinjection and subsequent blood feeding, significant contrasts were observed on fecundity. Triggers targeting RPS6 and RPL26 effectively reduced gene expression but more importantly, reduced reproductive output by more than 96% and 91% at the first oviposition while triggers targeting RPL1 and RPS2 did not cause a reduction although gene expression was reduced. Significantly reduced fecundity continued through a second oviposition cycle in dsRPS6 and dsRPL26 cohorts, although the effect was not as strong. Relative gene expression levels confirmed specific transcript knockdown up to 20days post-injection in mosquitoes that did not oviposit or produced reduced clutch sizes. Dissections at 36h post-blood meal indicated defects in oocyte provisioning. The strong phenotype produced by dsRPS6 allowed us to examine the effects in various tissues as well as the dose response, trigger format, delivery method and trigger specificity in Aedes aegypti. Strong knockdown was observed in the abdomen and the ovaries. Greater than 50ng of dsRPS6 significantly reduced fecundity but not when delivered in a sugar meal or as an siRNA. Similar bioassays with mutated dsRPS6 triggers indicates that up to three mismatches per possible siRNA are still effective in reducing fecundity. These studies indicate that while active and effective triggers can be developed for vector species, the lack of an efficient delivery method is the biggest barrier to use as a potential control method.

Complexity of Yolk Proteins and Their Dynamics in the Sea Star Patiria miniata

Oviparous animals store yolk proteins within the developing oocyte. These proteins are used in gametogenesis and as a nutritional source for embryogenesis. Vitellogenin and the major yolk protein are two of the most important yolk proteins among diverse species of invertebrates and vertebrates. Among the echinoderms, members of the subphyla Echinozoa (sea urchins and sea cucumbers) express the major yolk protein (MYP) but not vitellogenin (Vtg), while an initial report has documented that two Asterozoa (sea stars) express a vitellogenin. Our results show that sea stars contain two vitellogenins, Vtg 1 and Vtg 2, and MYP. In Patiria miniata, these genes are differentially expressed in the somatic and germ cells of the ovary: Vtg 1 is enriched in the somatic cells of the ovary but not in the oocytes, and Vtg 2 accumulates in both oocytes and somatic cells; MYP is not robustly present in either. Remarkably, Vtg 2 and MYP mRNA reappear in larvae; Vtg 2 is detected within cells of the ectoderm, and MYP accumulates in the coelomic pouches, the intestine, and the posterior enterocoel (PE), the site of germ line formation in this animal. Additionally, the Vtg 2 protein is present in oocytes, follicle cells, and developing embryos, but becomes undetectable following gastrulation. These results help elucidate the mechanisms involved in yolk dynamics, and provide molecular information that allows for greater understanding of the evolution of these important gene products.

Dynamics of expression of two vitellogenin genes in the Chagas' disease vector Triatoma infestans: Analysis throughout pre-vitellogenesis and vitellogenesis

The reproductive success of all oviparous species depends on vitellogenin (Vg) biosynthesis and its accumulation in the developing oocytes. The expression levels of two Vg genes (Vg1 and Vg2) were analyzed by qPCR and western blot in fat body and ovaries of adult females, at different times after ecdysis (pre-vitellogenic phase) and after blood feeding of females (vitellogenic phase). Vg genes were also evaluated in fat bodies of adult males as well as in female fifth instar nymphs. No trace of Vg mRNA was detected in adult males or in nymphs. Vg1 and Vg2 were expressed in the fat bodies and ovaries of adult females. The Vg genes start to be expressed slightly in both tissues of adult females during pre-vitellogenesis. After blood feeding, Vg1 and Vg2 were up regulated and significant levels of Vg transcripts as well as protein expression were observed in fat bodies sampled throughout vitellogenesis. During this period however, the distribution patterns of Vg1 and Vg2 transcripts showed two peaks around early and advanced vitellogenesis (days 4 and 12 post-feeding, respectively). In the ovaries, levels of mRNAs increased from the day 10 post-blood feeding onwards. In addition, the immunofluorescence assays showed a strong signal for vitellin in the yolk bodies of terminal follicles of vitellogenic females. The involvement of fat body and ovary in the synthesis of Vg suggests different roles of Vgs in supporting the growth of oocytes.

cDNA isolation and characterization of two vitellogenin genes in the Chagas' disease vector Triatoma infestans (Hemiptera, Reduviidae)

Two vitellogenin genes (Vg1 and Vg2) were identified in the Chagas' disease vector Triatoma infestans. The putative coding sequence corresponding to Vg2 was found to be 5553bp long, encoding 1851 amino acids in a single open reading frame. The comparative analysis of the deduced amino acid sequences from Vg1 and Vg2 cDNA fragments of T. infestans revealed 58.94% of identity with 76.43% of homology. The phylogenetic tree based on the complete Vg amino acid sequences of hemimetabolous insects unambiguously supported two clusters, one consisting of Vg sequences from dictyopteran and the other containing Vg sequences of hemipteran. The Vg1 and Vg2 mRNAs were detected in fat bodies and ovaries of adult females with the highest levels of both Vg transcripts in the first tissue. Quantitative PCR showed low expression of Vg2 in head and muscle of adult females, while the Vg1 transcript was not present in these organs. Neither Vg1 nor Vg2 was expressed in fifth instar nymph fat bodies or in adult male fat bodies, heads, and muscles.

The major yolk protein vitellogenin interferes with the anti-plasmodium response in the malaria mosquito Anopheles gambiae

Functional gene analysis in malaria mosquitoes reveals molecules underpinning the trade-off between efficient reproduction and the antiparasitic response.

When taking a blood meal on a person infected with malaria, female Anopheles gambiae mosquitoes, the major vector of human malaria, acquire nutrients that will activate egg development (oogenesis) in their ovaries. Simultaneously, they infect themselves with the malaria parasite. On traversing the mosquito midgut epithelium, invading Plasmodium ookinetes are met with a potent innate immune response predominantly controlled by mosquito blood cells. Whether the concomitant processes of mosquito reproduction and immunity affect each other remains controversial. Here, we show that proteins that deliver nutrients to maturing mosquito oocytes interfere with the antiparasitic response. Lipophorin (Lp) and vitellogenin (Vg), two nutrient transport proteins, reduce the parasite-killing efficiency of the antiparasitic factor TEP1. In the absence of either nutrient transport protein, TEP1 binding to the ookinete surface becomes more efficient. We also show that Lp is required for the normal expression of Vg, and for later Plasmodium development at the oocyst stage. Furthermore, our results uncover an inhibitory role of the Cactus/REL1/REL2 signaling cassette in the expression of Vg, but not of Lp. We reveal molecular links that connect reproduction and immunity at several levels and provide a molecular basis for a long-suspected trade-off between these two processes.

Malaria annually claims the lives of almost 1 million infants and imposes a major socio-economic burden on Africa and other tropical regions. Meanwhile, the detailed biological interactions between the malaria parasite and its Anopheles mosquito vector remain largely enigmatic. What we do know is that the majority of malaria parasites are normally eliminated by the mosquito's immune response. Mosquitoes accidentally acquire an infection by sucking parasite-laden blood, but this belies the primary function of the blood in the provisioning of nutrients for egg development in the insect's ovaries. We have found that the molecular processes involved in delivering blood-acquired nutrients to maturing eggs diminish the efficiency of parasite killing by the mosquito immune system. Conversely, molecular pathways that set the immune system on its maximal capacity for parasite killing preclude the efficient development of the mosquito's eggs. Our results reveal some of the molecules that underpin this example of the trade-offs between reproduction and immunity, a concept that has long intrigued biologists.

Molecular characterization and expression pattern of Spodoptera litura (Lepidoptera: Noctuidae) vitellogenin, and its response to lead stress

Vitellogenin (Vg) cDNA from Spodoptera litura Fabricius was cloned and sequenced. The open reading frame (ORF) of Vg cDNA was 5247 nucleotides in length (GenBank Accession no. EU095334), which encoded for a protein of 1748 amino acids. S. litura Vg comprised three conserved regions (Vitellogenin-N domain, DUF1943 and von Willebrand factor type D domain (VWD)), a 17 amino-acid signal peptide and a RXXR cleavage signal (RTIR). The highly conserved GL/ICG motif, the DGXR motif and cysteine residues were found in the C-terminus of the Vg. Vg mRNA was found specifically in the female fat body. Vg expression was first transcribed in 6th day female pupae and levels increased with insect development. The maximum level of Vg mRNA appeared in 24-h-old adults. When S. litura larvae were exposed to lead (Pb) (25-200 mg Pb/kg), there was a significant inhibition in Vg of female adults. The start of Vg expression was advanced ahead by Pb, from 6th day pupae to 3rd day or 4th day pupae. Low levels of Vg in male adults were also induced by low concentrations of Pb (12.5 and 25 mg Pb/kg). These data show that Pb stress elicits an important Vg response in S. litura.

Molecular characteristics of insect vitellogenins

Vitellogenins (Vgs) are precursors of the major egg storage protein, vitellin (Vn), in many oviparous animals. Insects Vgs are large molecules ( approximately 200-kD) synthesized in the fat body in a process that involves substantial structural modifications (e.g., glycosylation, lipidation, phosphorylation, and proteolytic cleavage, etc.) of the nascent protein prior to its secretion and transport to the ovaries. However, the extent to which Vgs are processed in the fat body varies greatly among different insect groups. We provide evidence by cloning and peptide mapping of four Vg molecules from two cockroach species (Periplaneta americana and Leucophaea maderae) that, in hemimetabolous insects, the pro-Vg is cleaved into several polypeptides (ranging from 50-to 180-kD), unlike the holometabolans where the Vg precursor is cleaved into two polypeptides (one large and one small). An exception is the Vg of Apocrita (higher Hymenoptera) where the Vg gene product remains uncleaved. The yolk proteins (YPs) of higher Diptera (such as Drosophila) form a different family of proteins and are also not cleaved. So far, Vgs have been sequenced from 25 insect species; 9 of them belong to Hemimetabola and 16 to Holometabola. Alignment of the coding sequences revealed that some features, like the GL/ICG motif, cysteine residues, and a DGXR motif upstream of the GLI/CG motif, were highly conserved near the carboxy terminal of all insect Vgs. Moreover, a consensus RXXR cleavage sequence motif exists at the N-terminus of all sequences outside the Apocrita except for Lymantria dispar where it exists at the C-terminus. Phylogenetic analysis using 31 Vg sequences from 25 insect species reflects, in general, the current phylogenies of insects, suggesting that Vgs are still phylogenetically bound, although a divergence exists among them.

Expression of clottable protein of tiger shrimp (Penaeus monodon) in gonads and its possible role as nutrient source for the embryo

We have investigated the expression of clottable protein (CP) in gonad of tiger shrimp (Penaeus monodon) and extent of its phosphorylation. Polyclonal antibodies against purified CP were prepared from rabbit serum. Using this anti-CP antiserum, the temporal expression of CP in gonads of tiger shrimp was analyzed. It was found that the CP occurs only in mature ovaries but not in immature ovaries and testes. Results of RT-PCR confirmed that these tissues expressed low levels of CP mRNA transcripts. Upon eyestalk-ablation, the ovaries in female shrimps were induced to develop, and the CP expression levels in ovaries were traced chronically by RT-PCR analyses. The expression level peaked on day 3 with an increase of about 40 folds relative to the basal level and returned to normal level (as the control shrimp) at day 12. The shrimp embryos at different intervals from spawning to 16h post-spawning were also collected, and it was found that CP contents were gradually decreased in the embryos until the nauplii were hatched. In addition, purified CP was shown to react with specific anti-phosphoserine, anti-phosphothreonine, and anti-phosphotyrosine antibodies suggesting that CP is a phosphoprotein with all types of phosphorylations. Taken together the results suggest that expression of CP in shrimp ovaries is coupled to ovarian development and CP possibly supply nutrition for shrimp embryo.

Vitellogenin functions as a multivalent pattern recognition receptor with an opsonic activity

Background

Vitellogenin (Vg), a major reproductive protein, has been associated with infection-resistant response in fish. However, the underlying mechanisms by which Vg is involved in anti-infectious response are not understood.

Methodology/Results

By both protein-microbe interaction analysis and enzyme-linked immunosorbent assay as well as phagocytosis test, we demonstrate for the first time that fish Vg acts as a pattern recognition molecule with multiple specificities that can recognize bacteria as well as fungus rather than self components from fish, and functions as an opsonin that can enhance macrophage phagocytosis.

Conclusions

This study shows that fish Vg plays an integrative function in regulating immunity via its pleiotropic effects on both recognizing pathogen-associated molecular patterns and promoting macrophage phagocytosis. It also supports the notion that factors normally involved in control of female reproduction are associated with immunity in organisms that rely on Vg for oocyte development.

Sequence and the developmental and tissue-specific regulation of the first complete vitellogenin messenger RNA from ticks responsible for heme sequestration

The first full-length mRNA for vitellogenin (Vg) from ticks was sequenced. This also represents the first complete sequence of Vg from the Chelicerata and of a heme binding Vg. The Vg cDNA from the American dog tick, Dermacentor variabilis was 5744nt in length (GenBank Accession number AY885250), which coded for a protein of 1843 aa with a calculated molecular weight of 208 kD. This protein had an 18 aa signal sequence, a single RXXR cleavage signal that would generate two subunits (49.5 and 157K in molecular weight) and lipoprotein N-terminal and carboxy von Willebrand factor type D domains. Tryptic digest MS analysis of vitellin protein confirmed the function of the cDNA as the tick yolk protein. Apparently, vitellin in D. variabilis is oligomeric (possibly dimeric) and is comprised of a mixture of the uncleaved monomer and subunits that were predicted from the single RXXR cleavage signal. The highly conserved GL/ICG motif close to the C-terminus in insect Vg genes was different in the tick Vg message, i.e., GLCS. This variant was also present in a partial sequence of Vg from Boophilus microplus. Phylogenic analysis showed that the full length Vg cDNA from D. variabilis and the partial cDNA from B. microplus were distinct from insects and Crustacea. The Vg message was not found in whole body RNA from unfed or fed males or in unfed and partially fed (virgin) females as determined by Northern blotting. The message was found in replete (mated) pre-ovipositional females, increased to higher levels in ovipositing females and was absent after egg laying was complete. The endocrine regulation of the Vg mRNA is discussed. The tissue sources of the Vg message are both the gut and fat body. Tryptic digest MS fingerprinting suggests that a second Vg mRNA might be present in the American dog tick, which needs further study.

Construction of gender-enriched cDNA archives for adult Oesophagostomum dentatum by suppressive-subtractive hybridization and a microarray analysis of expressed sequence tags

In the present study, we constructed gender-enriched cDNA libraries for the adult stage of the parasitic nematode Oesophagostomum dentatum (order Strongylida) using suppressive-subtractive hybridization (SSH), sequenced clones from the female-library and male-library (480 from each) and conducted bioinformatic and microarray analyses of the expressed sequence tags (ESTs). In total, 873 ESTs (440 male and 433 female) were obtained, achieving a sequencing success of 91%The nucleotide sequences reported in this article (Tables 1-5) have been deposited in the EMBL, GenBank and DDJB databases under the Accession nos. AM157797-AM158083. Microarray analyses of 516 unique ESTs representing both gender-enriched libraries revealed differential hybridization for 391 of them (75.8%). Of these, 220 (56.3%) had significantly greater signal intensities in the female than in the male, and 154 (70%) of these were predicted to have homologues in C. elegans. These homologues were predicted to be involved in key biological processes, including embryonic nutrition, gametogenesis, molecular binding/transport or metabolism, nucleic acid synthesis and function, and signal transduction. Of the 171 ESTs with statistically higher signal intensities in male O. dentatum, 43.8% had homologues in C. elegans. These homologues included major sperm proteins (MSPs) or MSP-like molecules, keratin-like molecules, molecules involved in metabolism, PDZ domain-containing proteins, sugar binding proteins, protein kinases, serine proteases or protease inhibitors, molecules involved in proteolysis and other proteins, such as enzymes and various putative proteins. Of the 287 ESTs (from both gender-enriched cDNA libraries) with no known homologues in C. elegans, 50 (17.4%) had homologues in other nematodes, 8 had homologues in various other organisms and 104 (36.2%) had no homology to any sequence in current gene databases. The present study lays a foundation for the isolation and molecular, biochemical and functional characterization of selected genes from the gender-enriched cDNA archives established for O. dentatum.

Determination and distribution of a female-specific protein in the brown planthopper, Nilaparvata lugens Stal (Homoptera: Delphacidae)

Electrophoretic analyses of hemolymph and body or ovary homogenates from reproducing females, males, and 5th instar nymphs of the brown planthopper, Nilaparvata lugens Stal, revealed a protein band of 175 kDa in females. An immunoblot test using antibody against this protein showed a positive reaction with a 175 kDa protein from female body or ovary homogenates. It is likely that this protein in hemolymph is vitellogenin (Vg). Distribution of Vg was determined by immunofluorescence and immunogold labeling techniques. The results showed that the positive immunofluorescence reactions were present in yolk particles, the intercellular space of follicle cells, hemolymph, and the epithelial plug of ovarioles. In addition, the yeast-like symbiotes (YLS) in mycetocytes of adults and various nymphal instars as well as those free in hemolymph or entering oocytes also exhibited a positive reaction. Electron micrographs showed that immunogold particles were found most in yolk mass and YLS over other tissues. Especially the YLS in various developmental stages all contained immunogold particles, implying that the symbiote is somewhat related with production of the female-specific protein.

Vitellogenin of the parasitoid wasp, Encarsia formosa (Hymenoptera: Aphelinidae): gene organization and differential use by members of the genus

The vitellogenin (Vg) gene of the parasitoid wasp, Encarsia formosa (Hymenoptera: Aphelinidae), has been cloned and sequenced. The gene codes for a protein consisting of 1814 amino acids in seven exons. The position of the six introns in the E. formosa gene align with those inferred for the Vg gene of the honeybee, Apis mellifera. The position of two introns in the hymenopteran sequences are shared with every full-length insect Vg gene characterized to date. The deduced amino acid sequence of the E. formosa Vg gene most closely resembles that of the ichneumonid parasitoid, Pimpla nipponica (38% identity). The gene product, less the putative signal peptide, contains large quantities of serine (11.3% of total residues) but lacks the extensive polyserine tracts found in the Vgs of insects outside the apocritan Hymenoptera. The gene also codes for the highest level of lysine (9.5%), and lowest levels of phenylalanine (2.6%) and tyrosine (2.3%), observed in any insect Vg characterized to date. The mature gene product retains 12 cysteine residues in positions conserved in other insect Vgs. Ovary homogenates suggest that processed Vg is stored in the egg as an uncleaved molecule of approximately 200 kDa. Vg expression was examined in three additional Encarsia species. The protein was found in female E. sophia and E. luteola, but not in male E. luteola or female E. pergandiella. Despite extensive screening of a phage library prepared from E. pergandiella genomic DNA, a Vg gene was not detected in this species.

Characterization of an ecto-phosphatase activity in malpighian tubules of hematophagous bug Rhodnius prolixus

We have characterized a phosphatase activity present on the external surface of intact Malpighian tubules in Rhodnius prolixus. This phosphatase hydrolyses the substrate p-nitrophenyl phosphate at a rate of 3.38 +/- 0.07 nmol Pi x mg(-1) x min(-1). Phosphatase activity decreased with the increase of the pH from 6.4 to 7.6 pH, a range in which tubules cellular integrity was maintained for at least 1 h. Classical inhibitors of acid phosphatase, such as ammonium molybdate, fluoride, vanadate, mpV-PIC, and bpV-PHEN, caused different patters of inhibition. The ecto-phosphatase present an apparent Km of 1.67 +/- 0.34 mM and Vmax of 5.71 +/- 0.37 nmol Pi x mg(-1) x min(-1) for p-NPP. Zinc chloride inhibited 78.2% of ecto-phosphatase activity, with Ki of 0.35 mM. Such inhibition was reversed by incubation with cysteine and GSH, but not DTT, serine, and GSSG, showing that cysteine residues are important for enzymatic activity. Phosphatase activity increased 141% three days after blood meal, and returned to basal levels 2 days later. These results suggest that ecto-phosphatase activity could be involved in a diuretic mechanism, essential in the initial days after a blood meal for the control of Rhodnius homeostasis.

The early gene E74B isoform is a transcriptional activator of the ecdysteroid regulatory hierarchy in mosquito vitellogenesis

In the mosquito Aedes aegypti, blood feeding activates vitellogenesis that involves yolk protein precursor (YPP) genes in an insect metabolic tissue, the fat body. Vitellogenesis is regulated by the 20-hydroxyecdysone (20E) regulatory hierarchy, in which the Ets-domain protein E74 is a key transcriptional regulator. The mosquito AaE74 gene encodes two isoforms-AaE74A and AaE74B. Both AaE74 isoforms are 20E-inducible early gene products. AaE74B reaches its maximal expression at 10(-7)M of 20E, while AaE74A requires 10(-6)M of 20E, a concentration at which the YPP genes reach their maximal induction level. In transfection assay, AaE74B is capable of activating a reporter construct containing E74-response elements, while expression of AaE74A has no effect on the basal levels of the reporter. The AaE74B binding activity is present in the fat body nuclei only during active vitellogenesis. Taken together, our findings demonstrate that AaE74B isoform plays the role of a transcriptional activator during vitellogenesis.

Blood meal induces global changes in midgut gene expression in the disease vector, Aedes aegypti

Blood feeding is an essential developmental process for many arthropods and plays a significant role in disease transmission. Understanding physiological responses in the midgut is important because it is the primary site of blood meal digestion and pathogenic infection. Processes that occur in the midgut in response to a blood meal have been studied but are poorly understood. Here, we use cDNA microarrays to examine midgut gene expression on a global level in response to blood feeding to assist in unraveling these processes. We have developed Aedes aegypti microarrays consisting of clones obtained from an expressed sequence tag project. Individual clones were amplified by polymerase chain reaction and printed onto glass slides. These microarrays were used to study the effects of a blood meal on midgut gene expression over a 72-h time course. As a result, a number of genes involved in processes such as nutrient uptake and metabolism, cellular stress responses, ion balance, and PM formation, as well as a number of unknown genes were induced or repressed in response to a blood meal based on this microarray data.

Instability of crab vitellogenin and its immunological relatedness with mammalian atherogenic lipoproteins

Vitellogenesis is the process of accumulation of vitellogenin (Vg) in rapidly growing oocytes of oviparous animals and its' subsequent transformation into lipovitellin (Lv). Lipovitellin, which forms the major yolk protein, serves as a principal nutrient reserve for the developing embryo. In the present study, Vg and Lv were purified from the hemolymph and ovary, respectively of the crab Scylla serrata by gel filtration followed by preparative gel electrophoresis. It was observed that purified Vg, but not Lv, possessed an intrinsic protease activity with which it underwent autoproteolysis giving rise to several smaller proteins. Furthermore, urea-mediated unfolding studies by UV-spectral analysis revealed clearly that Vg was easily disrupted by urea whereas Lv was resistant. Taken together, these results suggest that although Lv had a stable conformation, its precursor Vg was labile and highly sensitive to degradation. Another aspect that was investigated in the present study was the immunological kinship of crab Vg and Lv to mammalian atherogenic lipoproteins, the low density lipoprotein (LDL), very low density lipoprotein (VLDL), and apolipoprotein B (apoB). By Western blot analysis, it was demonstrated that crab Vg and Lv were immunoreactive to antibodies to human LDL, VLDL, and apoB. These observations suggest the existence of common epitope recognition sites in crab Vg and mammalian lipid transferring proteins. This corroborates well with our earlier study on the recognition of crab Vg receptor by mammalian lipoproteins.

Breeding biology of the intertidal sand crab, Emerita (Decapoda: Anomura)

Emerita is a burrowing mole crab or sand crab, adapted to life in wave-washed sandy beaches of temperate and tropical seas. The reproductive biology of this anomuran crab presents several peculiarities, all contributing to its adaptation to this harsh environmental niche. We discuss the following aspects: 1) sex ratio and size at sexual maturity, 2) neoteny and protandric hermaphroditism, 3) mating behaviour and sperm transfer strategy, 4) synchronisation of moulting and reproduction, 5) environmental impact on reproductive cycle and egg production, 6) biochemistry of yolk utilisation and energetics, 7) larval development, dispersal and settlement and 8) the value of Emerita as indicator species. These aspects are discussed in the light of the life history pattern, comprising a sedentary adult and pelagic larval phases. The successful colonisation of the physically challenging habitat of the sandy beach by Emerita is attributable largely to reproductive strategy and the larval developmental and recruitment pattern. Sensitivity to changing environmental conditions, including pollution, make this intertidal crab an indicator species for monitoring anthropogenic impact.

Cyclic nucleotide-independent phosphorylation of vitellin by casein kinase II purified from Rhodnius prolixus oocytes

In this study we show that Vitellin (VT) phosphorylation in chorionated oocytes of Rhodnius prolixus is completely inhibited by heparin (10 microg/ml), a classical casein kinase II (CK II) inhibitor. VT phosphorylation is not affected by modulators of cyclic nucleotide-dependent protein kinases such as c-AMP (10 microM), H-8 (1 microM) and H-89 (0.1 microM). We have obtained a 3000-fold VT-free enriched preparation of CK II. Autophosphorylation of this enzyme preparation in the presence of (32)P-ATP demonstrated that it lacks any endogenous substrates. Rhodnius CK II is strongly inhibited by heparin (Ki = 9 nM) and uses ATP (Km = 36 microM) or GTP (Km = 86 microM) as phosphate donors. Incubation of VT with purified Rhodnius CK II and (32)P-ATP led to the incorporation of 2 mols of phosphate/mol VT. However, the total number of phosphorylation sites available can be altered by previous incubation of VT with alkaline phosphatase. These data show that an insect yolk protein contain phosphorylation sites for a cyclic nucleotide-independent protein kinase such as CK II.

Rhodnius prolixus vitellin is composed of three different populations: comparison with vitellogenin

Rhodnius prolixus oocyte extracts were chromatographed on an ion exchange column in order to purify vitellin (VT). Three VT heterogeneous populations were identified and named VT(1), VT(2), and VT(3) according to their order of elution from the column. The phosphate content of each population was determined, after lipid extraction, and a heterogeneous distribution was found: VT(1) being the less phosphorylated (50 mol P/mol protein) and VT(3) the heavily phosphorylated population (281 mol P/mol protein). Analysis of radioactivity associated with each VT population purified from animals fed with (32)Pi showed the same phosphorylation profile. Due to the fact that vitellogenin is the known precursor of VT, we have also chromatographed 32P-VG in the same way as we purified VT. Only one VG's population was detected and resembled to VT(3) with respect to its elution profile. All VT populations contain the same neutral lipids, but they were heterogeneous with respect to phospholipid composition. VT(1) presents phosphatidylcholine and phosphatidylethanolamine whereas VT(2) and VT(3) also showed cardiolipin and probably phosphatidylserine. Sugar composition of VT(2) and VT(3) includes mannose as the main associated carbohydrate but VT(1) also contains glucose resembling VG. Although VG and VT are similar with respect to the elution profile, their sugar composition is different. These results suggest a post-endocytosis processing on VG molecule. The possible biological function of VT heterogeneous populations is discussed.

The major yolk protein in sea urchins is a transferrin-like, iron binding protein

The major yolk protein (MYP) in sea urchins has historically been classified as a vitellogenin based on its abundance in the yolk platelets. Curiously, it is found in both sexes of sea urchins where it is presumed to play a physiological role in gametogenesis, embryogenesis, or both. Here we present the primary structure of MYP as predicted from cDNAs of two sea urchins species, Strongylocentrotus purpuratus and Lytechinus variegatus. The sequence from these two species share identity to one another, but bear no resemblance to other known vitellogenins. Instead the sequence shares identity to members of the transferrin superfamily of proteins. In vitro iron binding assays, including both (59)Fe overlay assays of MYP enriched coelomic fluid and immunoprecipitation of native iron-bound MYP from coelomic fluid, support this classification. We suggest that one of MYP's transferrin-like properties is to shuttle iron to developing germ cells.

Hepatopancreas is the extraovarian site of vitellogenin synthesis in black tiger shrimp, Penaeus monodon

The site of yolk protein synthesis in crustaceans has long been a subject of controversy. The vitellogenin gene structure was partially reported only very recently in Macrobrachium rosenbergii, after which the hepatopancreas was confirmed as the extraovarian site of vitellogenin synthesis in that species. Ovaries are the most frequently reported as the site of yolk protein synthesis in penaeid shrimp. Using cDNA reversed-transcribed from mRNA isolated from the hepatopancreas of vitellogenic female shrimp, Penaeus monodon, we found that its deduced amino acid sequence had high identity of 48% with that from M. rosenbergii vitellogenin. A similar location of the intron in the sequenced region of genomic DNA was also found between these two species. We therefore concluded that the hepatopancreas the extraovarian site of vitellogenin synthesis in P. monodon in vivo. The partial structure of vitellogenin gene is presented in this study.

Sex- and tissue-specific expression of aspartic proteinases in Danio rerio (zebrafish)

Full-length zebrafish cDNAs encoding two aspartic proteinases were cloned and sequenced. One of the two cDNAs was a 1708 bp product with an open reading frame of 398 amino acid residues corresponding to a cathepsin D. The other was a 1383 bp product encoding a polypeptide chain of 416 amino acids homologous to nothepsin, an aspartic proteinase first identified by us in the liver of Antarctic Notothenioidei. Gene expression assessed by RT-PCR and northern blot hybridization of RNA from different tissues showed that the expression was tissue- and sex-specific. Whereas the cathepsin D gene was expressed in all the tissues examined independently of the sex, the nothepsin gene was expressed exclusively in female livers.

Differential regulation of ribosomal protein gene expression in Aedes aegypti mosquitoes before and after the blood meal

In fat body of the mosquito, Aedes aegypti, a cycle of ribosome accumulation and degradation accompanies synthesis of the yolk protein precursor, vitellogenin. Here we compare the transcription and translation of ribosomal proteins rpS6, rpL8 and rpL34, relative to rRNA and vitellogenin genes in Aedes aegypti fat body after eclosion, and in response to a blood meal. Analysis using Northern blots and reverse-transcription polymerase chain reactions (RT-PCR) showed that the rpS6, rpL8 and rpL34 genes are coordinately regulated with respect to one another, and that ribosomal protein gene expression in this system was predominantly regulated by transcription during the 3-4 days between adult eclosion and blood feeding. After a blood meal, ribosomal protein mRNA levels remained similar to those in unfed females during the first 18 h, then declined to minimum levels by 48 h after the blood meal. These data indicate that transcription of ribosomal protein genes is low in vitellogenic mosquitoes, relative to previtellogenic females. Experiments with the dissected fat body, however, showed that levels of acetic acid-soluble proteins increased by approximately threefold between 12 and 24 h after the blood meal. Taken together, these observations suggest that the active translation of ribosomal proteins from stable mRNA accompanies ribosome biosynthesis after the blood meal. Thus, in the fat body of adult female mosquitoes, the expression of ribosomal protein genes is regulated at the level of transcription before the blood meal, while translational control is the predominant regulatory mechanism after the blood meal.

Lipophorin as a yolk protein precursor in the mosquito, Aedes aegypti

We examined expression of the lipophorin (Lp) gene, lipophorin (Lp) synthesis and secretion in the mosquito fat body, as well as dynamic changes in levels of this lipoprotein in the hemolymph and ovaries, during the first vitellogenic cycle of females of the yellow fever mosquito, Aedes aegypti. Lipophorin was purified by potassium bromide (KBr) density gradient ultracentrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Polyclonal antibodies were produced against individual Lp apoproteins, apolipoprotein-I (apoLp-I) and apolipoprotein-II (apoLp-II), with molecular weights of 240 and 75 kDa, respectively. We report here that in the mosquito A. aegypti, Lp was synthesized by the fat body, with a low level of the Lp gene expression and protein synthesis being maintained in pre- and postvitellogenic females. Following a blood meal, the Lp gene expression and protein synthesis were significantly upregulated. Our findings showed that the fat body levels of Lp mRNA and the rate of Lp secretion by this tissue reached their maximum at 18 h post-blood meal (PMB). 20-Hydroxyecdysone was responsible for an increase in the Lp gene expression and Lp protein synthesis in the mosquito fat body. Finally, the immunocytochemical localization of Lp showed that in vitellogenic female mosquitoes, this protein was accumulated by developing oocytes where it was deposited in yolk granules.

Lipid utilization for ovarian development in an autogenous mosquito, Culex pipiens molestus (Diptera: Culicidae)

During the first ovarian cycle, autogenous female mosquitoes develop their ovaries in the absence of blood feeding. In autogenous Culex pipiens molestus (Forskal), complete yolk deposition was observed 2 d after emergence, even when no feeding was allowed (starved). Neutral lipids in Cx. p. molestus increased during the pupal stage, abruptly declined after emergence, and again increased on day 3. In contrast, neutral lipids decreased in anautogenous Anopheles stephensi (Liston) and Cx. p. pallens (Coquillett) and starved females died within 2-3 d after emergence. High ratios of two major neutral lipids, free fatty acid and triglyceride, were isolated by thin-layer chromatography (TLC) from the lipid contents of both Cx. p. molestus and An. stephensi fourth-instars and newly emerged females. Fatty acid analyses using gas liquid chromatography (GLC) and GLC-mass spectrometry (GLC-MS) showed higher proportions of unsaturated than saturated fatty acids in Cx. p. molestus at both stages and two major neutral lipids: free fatty acids and triglycerides. The percentage composition of linoleic acid (C18:2), which is a precursor of arachidonic acid, was higher in Cx. p. molestus than in An. stephensi. Our results indicated that elevated lipid content before emergence may play a role of inducing ovarian development in autogenous mosquitoes.

Synthesis of vitellogenin by the follicle cells of Rhodnius prolixus

The synthesis and secretion of vitellogenin by the ovary of Rhodnius prolixus was investigated. Using whole ovary or epithelial cells isolated from follicles of different sizes, it is shown that the follicle cells are a site of synthesis for this protein in the ovary. The ovaries or follicle cells were incubated in vitro with [(35)S]-methionine or (32)Pi and the secretion of newly synthesized ovarian vitellogenin (O-Vg) was estimated by the radioactivity associated with the immunoprecipitate or acid-precipitate proteins in the culture medium. The radioactive O-Vg was analyzed by SDS-PAGE followed by autoradiography or after elution from a DEAE-Toyopearl column. The presence of O-Vg inside the follicle cells was detected by immunofluorescence and immunogold labels. Both methods revealed strong labeling inside the follicle cells. While the capacity for total protein synthesis by the follicle cells was maximal during the early phase of vitellogenesis (in small follicles), the synthesis of O-Vg reached its peak during the late phase of oocyte growth, just before formation of the chorion. A possible role for ovarian vitellogenin in Rhodnius and its relationship with Vg synthesis by the fat body is discussed.