Vitellogenin motifs conserved in nematodes and vertebrates

Vitellogenin accumulation leads to reproductive senescence by impairing lysosomal function

The maintenance of proteostasis is essential for cellular and organism healthspan. How proteostasis collapse influences reproductive span remains largely unclear. In Caenorhabditis elegans, excess accumulation of vitellogenins, the major components in yolk proteins, is crucial for the development of the embryo and occurs throughout the whole body during the aging process. Here, we show that vitellogenin accumulation leads to reproduction cessation. Excess vitellogenin is accumulated in the intestine and transported into the germline, impairing lysosomal activity in these tissues. The lysosomal function in the germline is required for reproductive span by maintaining oocyte quality. In contrast, autophagy and sperm depletion are not involved in vitellogenin accumulation-induced reproductive aging. Our findings provide insights into how proteome imbalance has an impact on reproductive aging and imply that improvement of lysosomal function is an effective approach for mid-life intervention for maintaining reproductive health in mammals.

Somatic aging pathways regulate reproductive plasticity in Caenorhabditis elegans

In animals, early-life stress can result in programmed changes in gene expression that can affect their adult phenotype. In C. elegans nematodes, starvation during the first larval stage promotes entry into a stress-resistant dauer stage until environmental conditions improve. Adults that have experienced dauer (postdauers) retain a memory of early-life starvation that results in gene expression changes and reduced fecundity. Here, we show that the endocrine pathways attributed to the regulation of somatic aging in C. elegans adults lacking a functional germline also regulate the reproductive phenotypes of postdauer adults that experienced early-life starvation. We demonstrate that postdauer adults reallocate fat to benefit progeny at the expense of the parental somatic fat reservoir and exhibit increased longevity compared to controls. Our results also show that the modification of somatic fat stores due to parental starvation memory is inherited in the F1 generation and may be the result of crosstalk between somatic and reproductive tissues mediated by the germline nuclear RNAi pathway.

Molecular evolution of bumble bee vitellogenin and vitellogenin-like genes

Vitellogenin (Vg), a storage protein, has been significantly studied for its egg yolk precursor role in oviparous animals. Recent studies found that vitellogenin and its Vg-like homologs were fundamentally involved in many other biological processes in social insects such as female caste differences and oxidative stress resilience. In this study, we conducted the first large-scale molecular evolutionary analyses of vitellogenin coding genes (Vg) and Vg-like genes of bumble bees, a primitively eusocial insect belonging to the genus Bombus. We obtained sequences for each of the four genes (Vg, Vg-like-A, Vg-like-B, and Vg-like-C) from 27 bumble bee genomes (nine were newly sequenced in this study), and sequences from the two closest clades of Bombus, including five Apis species and five Tetragonula species. Our molecular evolutionary analyses show that in bumble bee, the conventional Vg experienced strong positive selection, while the Vg-like genes showed overall relaxation of purifying selection. In Apis and Tetragonula; however, all four genes were found under purifying selection. Furthermore, the conventional Vg showed signs of strong positive selection in most subgenera in Bombus, apart from the obligate parasitic subgenus Psithyrus which has no caste differentiation. Together, these results indicate that the conventional Vg, a key pleiotropic gene in social insects, is the most rapidly evolving copy, potentially due to its multiple known social functions for both worker and queen castes. This study shows that concerted evolution and purifying selection shaped the evolution of the Vg gene family following their ancient gene duplication and may be the leading forces behind the evolution of new potential protein function enabling functional social pleiotropy.

Tick Ecdysteroid Hormone, Global Microbiota/Rickettsia Signaling in the Ovary versus Carcass during Vitellogenesis in Part-Fed (Virgin) American Dog Ticks, Dermacentor variabilis

The transovarial transmission of tick-borne bacterial pathogens is an important mechanism for their maintenance in natural populations and transmission, causing disease in humans and animals. The mechanism for this transmission and the possible role of tick hormones facilitating this process have never been studied. Injections of physiological levels of the tick hormone, 20-hydroxyecdysone (20E), into part-fed (virgin) adult females of the American dog tick, Dermacentor variabilis, attached to the host caused a reduction in density of Rickettsia montanensis in the carcass and an increase in the ovaries compared to buffer-injected controls. This injection initiates yolk protein synthesis and uptake by the eggs but has no effect on blood feeding. Francisella sp. and R. montanensis were the predominant bacteria based on the proportionality in the carcass and ovary. The total bacteria load increased in the carcass and ovaries, and bacteria in the genus Pseudomonas increased in the carcass after the 20E injection. The mechanism of how the Rickettsia species respond to changes in tick hormonal regulation needs further investigation. Multiple possible mechanisms for the proliferation of R. montanensis in the ovaries are proposed.

Vitellogenins - Yolk Gene Function and Regulation in Caenorhabditis elegans

Vitellogenins are a family of yolk proteins that are by far the most abundant among oviparous animals. In the model nematode Caenorhabditis elegans, the 6 vitellogenins are among the most highly expressed genes in the adult hermaphrodite intestine, which produces copious yolk to provision eggs. In this article we review what is known about the vitellogenin genes and proteins in C. elegans, in comparison with vitellogenins in other taxa. We argue that the primary purpose of abundant vitellogenesis in C. elegans is to support post-embryonic development and fertility, rather than embryogenesis, especially in harsh environments. Increasing vitellogenin provisioning underlies several post-embryonic phenotypic alterations associated with advancing maternal age, demonstrating that vitellogenins can act as an intergenerational signal mediating the influence of parental physiology on progeny. We also review what is known about vitellogenin regulation - how tissue-, sex- and stage-specificity of expression is achieved, how vitellogenins are regulated by major signaling pathways, how vitellogenin expression is affected by extra-intestinal tissues and how environmental experience affects vitellogenesis. Lastly, we speculate whether C. elegans vitellogenins may play other roles in worm physiology.

A Vitellogenin Antibody in Honey Bees (Apis mellifera): Characterization and Application as Potential Biomarker for Insecticide Exposure

The insect yolk precursor vitellogenin is a lipoglycoprotein synthesized and stored in the fat body and secreted into the hemolymph. In honey bees, vitellogenin displays crucial functions in hormone signaling, behavioral transition of nurse bees to foragers, stress resistance, and longevity in workers. Plant protection products such as neonicotinoids, pyrethroids, and organophosphates alter the transcriptional expression of vitellogenin. To assess plant protection product-induced alterations on the protein level, we developed a rabbit polyclonal vitellogenin antibody. After characterization, we assessed its specificity and vitellogenin levels in different tissues of worker bees. The vitellogenin antibody recognized full-length 180-kDa vitellogenin and the lighter fragment of 150 kDa in fat body, hemolymph, and brain. In hemolymph, a band of approximately 75 kDa was detected. Subsequent mass spectrometric analysis (liquid chromatography-mass spectrometry) confirmed the 180- and 150-kDa bands as vitellogenin. Subsequently, we evaluated vitellogenin expression in brain, fat body, and hemolymph on 24-h exposure of bees to 3 ng/bee to the neonicotinoid clothianidin. Full-length vitellogenin was upregulated 3-fold in the fat body, and the 150-kDa fragment was upregulated in the brain of exposed honey bees, whereas no alteration occurred in the hemolymph. Upregulation of the vitellogenin protein by the neonicotinoid clothianidin is in line with the previously shown induction of its transcript. We conclude that vitellogenin might serve as a potential biomarker for neonicotinoid and other pesticide exposure in bees. Environ Toxicol Chem 2019;00:1-10. © 2019 SETAC.

A microRNA program in the C. elegans hypodermis couples to intestinal mTORC2/PQM-1 signaling to modulate fat transport

In this study, Dowen et al. identified a microRNA-regulated developmental timing pathway that coordinates the mobilization of intestinal fat stores to the germline during C. elegans development. Their results show that lin-4 and let-7 microRNAs promotes mTOR signaling, which regulates intestinal fat metabolism, thereby providing insight into a novel function for microRNAs.

Animals integrate metabolic, developmental, and environmental information before committing key resources to reproduction. In Caenorhabditis elegans, adult animals transport fat from intestinal cells to the germline to promote reproduction. We identified a microRNA (miRNA)-regulated developmental timing pathway that functions in the hypodermis to nonautonomously coordinate the mobilization of intestinal fat stores to the germline upon initiation of adulthood. This developmental timing pathway, which is controlled by the lin-4 and let-7 miRNAs, engages mTOR signaling in the intestine. The intestinal signaling component is specific to mTORC2 and functions in parallel to the insulin pathway to modulate the activity of the serum/glucocorticoid-regulated kinase (SGK-1). Surprisingly, SGK-1 functions independently of DAF-16/FoxO; instead, SGK-1 promotes the cytoplasmic localization of the PQM-1 transcription factor, which antagonizes intestinal fat mobilization at the transcriptional level when localized to the nucleus. These results revealed that a non-cell-autonomous developmental input regulates intestinal fat metabolism by engaging mTORC2 signaling to promote the intertissue transport of fat reserves from the soma to the germline.

Specific polyunsaturated fatty acids modulate lipid delivery and oocyte development in C. elegans revealed by molecular-selective label-free imaging

Polyunsaturated fatty acids (PUFAs) exhibit critical functions in biological systems and their importance during animal oocyte maturation has been increasingly recognized. However, the detailed mechanism of lipid transportation for oocyte development remains largely unknown. In this study, the transportation of yolk lipoprotein (lipid carrier) and the rate of lipid delivery into oocytes in live C. elegans were examined for the first time by using coherent anti-Stokes Raman scattering (CARS) microscopy. The accumulation of secreted yolk lipoprotein in the pseudocoelom of live C. elegans can be detected by CARS microscopy at both protein (~1665 cm⁻¹) and lipid (~2845 cm⁻¹) Raman bands. In addition, an image analysis protocol was established to quantitatively measure the levels of secreted yolk lipoprotein aberrantly accumulated in PUFA-deficient fat mutants (fat-1, fat-2, fat-3, fat-4) and PUFA-supplemented fat-2 worms (the PUFA add-back experiments). Our results revealed that the omega-6 PUFAs, not omega-3 PUFAs, play a critical role in modulating lipid/yolk level in the oocytes and regulating reproductive efficiency of C. elegans. This work demonstrates the value of using CARS microscopy as a molecular-selective label-free imaging technique for the study of PUFA regulation and oocyte development in C. elegans.

Vitellogenin of Fujian oyster, Crassostrea angulata: Synthesized in the ovary and controlled by estradiol-17β

In this study, we cloned a full-length cDNA encoding vitellogenin (Vg) in the Fujian oyster Crassostrea angulata. The complete Vg cDNA consists of 5160 nucleotides with a long open reading frame encoding 1641 amino acid residues. The deduced amino acid sequence shared high similarity with the Vgs of other mollusc, fish, nematode and arthropod species, particularly in the N-terminal region. We analyzed the spatiotemporal expression of caVg transcripts by Real-time Quantitative PCR. In common with other mollusc Vgs, the caVg gene was expressed primarily in the ovary, and the levels were 348 and 177 times higher in maturation and ripeness stages (P<0.01), respectively, than in the partially spent stage. There was negligible expression in male oysters. In situ hybridization analysis further localized caVg mRNA to the follicle cells (also named auxiliary cells) surrounding the oocytes in the ovary. Moreover, in vivo waterborne exposure experiments in early gametogenesis oysters showed that estradiol-17β (E2) administration resulted in a significant increase in caVg mRNA expression. We conclude that caVg is synthesized in the follicle cell surrounding the vitellogenic oocyte in C. angulata, and directly passed to oocytes through the extracellular space without mediation through hemolymph. Also, we hypothesize that this process is mediated by E2 in a dose dependent.

Yolk formation in a stony coral Euphyllia ancora (Cnidaria, Anthozoa): insight into the evolution of vitellogenesis in nonbilaterian animals

Vitellogenin (Vg) is a major yolk protein precursor in numerous oviparous animals. Numerous studies in bilateral oviparous animals have shown that Vg sequences are conserved across taxa and that Vgs are synthesized by somatic-cell lineages, transported to and accumulated in oocytes, and eventually used for supporting embryogenesis. In nonbilateral animals (Polifera, Cnidaria, and Ctenophora), which are regarded as evolutionarily primitive, although Vg cDNA has been identified in 2 coral species from Cnidaria, relatively little is known about the characteristics of yolk formation in their bodies. To address this issue, we identified and characterized 2 cDNA encoding yolk proteins, Vg and egg protein (Ep), in the stony coral Euphyllia ancora. RT-PCR analysis revealed that expression levels of both Vg and Ep increased in the female colonies as coral approached the spawning season. In addition, high levels of both Vg and Ep transcripts were detected in the putative ovarian tissue, as determined by tissue distribution analysis. Further analyses using mRNA in situ hybridization and immunohistochemistry determined that, within the putative ovarian tissue, these yolk proteins are synthesized in the mesenterial somatic cells but not in oocytes themselves. Furthermore, Vg proteins that accumulated in eggs were most likely consumed during the coral embryonic development, as assessed by immunoblotting. The characteristics of Vg that we identified in corals were somewhat similar to those of Vg in bilaterian oviparous animals, raising the hypothesis that such characteristics were likely present in the oogenesis of some common ancestor prior to divergence of the cnidarian and bilaterian lineages.

Transcriptome sequencing of Zhikong scallop (Chlamys farreri) and comparative transcriptomic analysis with Yesso scallop (Patinopecten yessoensis)

Background

Bivalves play an important role in the ecosystems they inhabit and represent an important food source all over the world. So far limited genetic research has focused on this group of animals largely due to the lack of sufficient genetic or genomic resources. Here, we performed de novo transcriptome sequencing to produce the most comprehensive expressed sequence tag resource for Zhikong scallop (Chlamys farreri), and conducted the first transcriptome comparison for scallops.

Results

In a single 454 sequencing run, 1,033,636 reads were produced and then assembled into 26,165 contigs. These contigs were then clustered into 24,437 isotigs and further grouped into 20,056 isogroups. About 47% of the isogroups showed significant matches to known proteins based on sequence similarity. Transcripts putatively involved in growth, reproduction and stress/immune-response were identified through Gene ontology (GO) and KEGG pathway analyses. Transcriptome comparison with Yesso scallop (Patinopecten yessoensis) revealed similar patterns of GO representation. Moreover, 38 putative fast-evolving genes were identified through analyzing the orthologous gene pairs between the two scallop species. More than 46,000 single nucleotide polymorphisms (SNPs) and 350 simple sequence repeats (SSRs) were also detected.

Conclusion

Our study provides the most comprehensive transcriptomic resource currently available for C. farreri. Based on this resource, we performed the first large-scale transcriptome comparison between the two scallop species, C. farreri and P. yessoensis, and identified a number of putative fast-evolving genes, which may play an important role in scallop speciation and/or local adaptation. A large set of single nucleotide polymorphisms and simple sequence repeats were identified, which are ready for downstream marker development. This transcriptomic resource should lay an important foundation for future genetic or genomic studies on C. farreri.

Regulation of lipoprotein assembly, secretion and fatty acid β-oxidation by Krüppel-like transcription factor, klf-3

Lipid metabolism is coordinately regulated through signaling networks that integrate biochemical pathways of fat assimilation, mobilization and utilization. Excessive diversion of fat for storage is a key risk factor for many fat-related human diseases. Dietary lipids are absorbed from the intestines and transported to various organs and tissues to provide energy and maintain lipid homeostasis. In humans, disparity between triglycerides (TG) synthesis and removal, via mitochondrial β-oxidation and VLDL (very low density lipoprotein) secretion, causes excessive TG accumulation in the liver. The mutation in Caenorhabditis elegans KLF-3 leads to high TG accumulation in the worm's intestine. Our previous data suggested that klf-3 regulates lipid metabolism by promoting fatty acid β-oxidation. Depletion of cholesterol in the diet has no effect on fat deposition in klf-3 (ok1975) mutants. Addition of vitamin D in the diet, however, increases fat levels in klf-3 worms. This suggests that excess vitamin D may be lowering the rate of fatty acid β-oxidation, with the eventual increase in fat accumulation. We also demonstrate that mutation in klf-3 reduces expression of C. elegans dsc-4 and/or vit genes, the orthologs of mammalian microsomal triglyceride transfer protein and apolipoprotein B, respectively. Both microsomal triglyceride transfer protein and apolipoprotein B are essential for mammalian lipoprotein assembly and transport, and mutation in both dsc-4 (qm182) and vit-5 (ok3239) results in high fat accumulation in worm intestine. Genetic interactions between klf-3 and dsc-4, as well as vit-5 genes, suggest that klf-3 may have an important role in regulating lipid assembly and secretion.

Vitellogenins are new high molecular weight components and allergens (Api m 12 and Ves v 6) of Apis mellifera and Vespula vulgaris venom

BACKGROUND/OBJECTIVES

Anaphylaxis due to hymenoptera stings is one of the most severe clinical outcomes of IgE-mediated hypersensitivity reactions. Although allergic reactions to hymenoptera stings are often considered as a general model for the underlying principles of allergic disease, venom immunotherapy is still hampered by severe systemic side effects and incomplete protection. The identification and detailed characterization of all allergens of hymenoptera venoms might result in an improvement in this field and promote the detailed understanding of the allergological mechanism. Our aim was the identification and detailed immunochemical and allergological characterization of the low abundant IgE-reactive 200 kDa proteins of Apis mellifera and Vespula vulgaris venom.

METHODS/PRINCIPAL FINDINGS

Tandem mass spectrometry-based sequencing of a 200 kDa venom protein yielded peptides that could be assigned to honeybee vitellogenin. The coding regions of the honeybee protein as well as of the homologue from yellow jacket venom were cloned from venom gland cDNA. The newly identified 200 kDa proteins share a sequence identity on protein level of 40% and belong to the family of vitellogenins, present in all oviparous animals, and are the first vitellogenins identified as components of venom. Both vitellogenins could be recombinantly produced as soluble proteins in insect cells and assessed for their specific IgE reactivity. The particular vitellogenins were recognized by approximately 40% of sera of venom-allergic patients even in the absence of cross-reactive carbohydrate determinants.

CONCLUSION

With the vitellogenins of Apis mellifera and Vespula vulgaris venom a new homologous pair of venom allergens was identified and becomes available for future applications. Due to their allergenic properties the honeybee and the yellow jacket venom vitellogenin were designated as allergens Api m 12 and Ves v 6, respectively.

Evolution of yolk protein genes in the Echinodermata

Vitellogenin genes (vtg) encode large lipid transfer proteins (LLTPs) that are typically female-specific, functioning as precursors to major yolk proteins (MYPs). Within the phylum Echinodermata, however, the MYP of the Echinozoa (Echinoidea + Holothuroidea) is expressed by an unrelated transferrin-like gene that has a reproductive function in both sexes. We investigated egg proteins in the Asterozoa (Asteroidea + Ophiuroidea), a sister clade to the Echinozoa, showing that eggs of the asteroid Parvulastra exigua contain a vitellogenin protein (Vtg). vtg is expressed by P. exigua, a species with large eggs and nonfeeding larvae, and by the related asterinid Patiriella regularis which has small eggs and feeding larvae. In the Asteroidea, therefore, the reproductive function of vtg is conserved despite significant life history evolution. Like the echinozoan MYP gene, asteroid vtg is expressed in both sexes and may play a role in the development of both ovaries and testes. Phylogenetic analysis indicated that a putative Vtg from the sea urchin genome, a likely pseudogene, does not clade with asteroid Vtg. We propose the following sequence as a potential pathway for the evolution of YP genes in the Echinodermata: (1) the ancestral echinoderm produced YPs derived from Vtg, (2) bisexual vtg expression subsequently evolved in the echinoderm lineage, (3) the reproductive function of vtg was assumed by a transferrin-like gene in the ancestral echinozoan, and (4) redundant echinozoan vtg was released from stabilizing selection.

Comparative proteomic analysis reveals differentially expressed proteins in Caenorhabditis elegans pgl-1 mutants grown at 20°C and 25°C

PGL-1 is an RNA-binding protein component of germ granules and essential for fertility in Caenorhabditis elegans. To clarify the molecular function of PGL-1, we performed comparative proteomic analysis using 2-D DIGE and LC-MS/MS. Five groups of synchronized adult hermaphrodites were analyzed: (1) wild-type N2 grown at 20°C, (2) pgl-1(bn101) mutants grown at 20°C, (3) pgl-1(bn101) mutants grown at 20°C then upshifted to 25°C after the L1 stage, (4) pgl-1(ct131) mutants grown at 20°C, and (5) pgl-1(ct131) mutants grown at 20°C then upshifted to 25°C after the L1 stage. The five groups were divided into two experimental sets for 2-D DIGE: set A included N2 and pgl-1(bn101) mutants, and set B included N2 and pgl-1(ct131) mutants. Dunnett's test indicated 90 and 100 specific spots, respectively, with significantly different expression levels from the rest of the experimental set (q≤0.1). Among them, 69 and 58 spots, respectively, were analyzed by LC-MS/MS. Finally, we identified 19 proteins from 24 specific spots common to both the experimental sets. RNAi analysis indicated that decreased eef-1G expression is strongly associated with the temperature-sensitive sterile phenotype of pgl-1. Our results suggest that PGL-1 is closely involved in translational processes during C. elegans germline development.

Regulation of behaviorally associated gene networks in worker honey bee ovaries

Several lines of evidence support genetic links between ovary size and division of labor in worker honey bees. However, it is largely unknown how ovaries influence behavior. To address this question, we first performed transcriptional profiling on worker ovaries from two genotypes that differ in social behavior and ovary size. Then, we contrasted the differentially expressed ovarian genes with six sets of available brain transcriptomes. Finally, we probed behavior-related candidate gene networks in wild-type ovaries of different sizes. We found differential expression in 2151 ovarian transcripts in these artificially selected honey bee strains, corresponding to approximately 20.3% of the predicted gene set of honey bees. Differences in gene expression overlapped significantly with changes in the brain transcriptomes. Differentially expressed genes were associated with neural signal transmission (tyramine receptor, TYR) and ecdysteroid signaling; two independently tested nuclear hormone receptors (HR46 and ftz-f1) were also significantly correlated with ovary size in wild-type bees. We suggest that the correspondence between ovary and brain transcriptomes identified here indicates systemic regulatory networks among hormones (juvenile hormone and ecdysteroids), pheromones (queen mandibular pheromone), reproductive organs and nervous tissues in worker honey bees. Furthermore, robust correlations between ovary size and neuraland endocrine response genes are consistent with the hypothesized roles of the ovaries in honey bee behavioral regulation.

Partner in fat metabolism: role of KLFs in fat burning and reproductive behavior

The abnormalities caused by excess fat accumulation can result in pathological conditions which are linked to several interrelated diseases, such as cardiovascular disease and obesity. This set of conditions, known as metabolic syndrome, is a global pandemic of enormous medical, economic, and social concern affecting a significant portion of the world’s population. Although genetics, physiology and environmental components play a major role in the onset of disease caused by excessive fat accumulation, little is known about how or to what extent each of these factors contributes to it. The worm, Caenorhabditis elegans offers an opportunity to study disease related to metabolic disorder in a developmental system that provides anatomical and genomic simplicity relative to the vertebrate animals and is an excellent eukaryotic genetic model which enable us to answer the questions concerning fat accumulation which remain unresolved. The stored triglycerides (TG) provide the primary source of energy during periods of food deficiency. In nature, lipid stored as TGs are hydrolyzed into fatty acids which are broken down through β-oxidation to yield acetyl-CoA. Our recent study suggests that a member of C. elegans Krüppel-like factor, klf-3 regulates lipid metabolism by promoting FA β-oxidation and in parallel may contribute in normal reproduction and fecundity. Genetic and epigenetic factors that influence this pathway may have considerable impact on fat related diseases in human. Increasing number of studies suggest the role of mammalian KLFs in adipogenesis. This functional conservation should guide our further effort to explore C. elegans as a legitimate model system for studying the role of KLFs in many pathway components of lipid metabolism.

Transcriptome sequencing and de novo analysis for Yesso scallop (Patinopecten yessoensis) using 454 GS FLX

BACKGROUND

Bivalves comprise 30,000 extant species, constituting the second largest group of mollusks. However, limited genetic research has focused on this group of animals so far, which is, in part, due to the lack of genomic resources. The advent of high-throughput sequencing technologies enables generation of genomic resources in a short time and at a minimal cost, and therefore provides a turning point for bivalve research. In the present study, we performed de novo transcriptome sequencing to first produce a comprehensive expressed sequence tag (EST) dataset for the Yesso scallop (Patinopecten yessoensis).

RESULTS

In a single 454 sequencing run, 805,330 reads were produced and then assembled into 32,590 contigs, with about six-fold sequencing coverage. A total of 25,237 unique protein-coding genes were identified from a variety of developmental stages and adult tissues based on sequence similarities with known proteins. As determined by GO annotation and KEGG pathway mapping, functional annotation of the unigenes recovered diverse biological functions and processes. Transcripts putatively involved in growth, reproduction and stress/immune-response were identified. More than 49,000 single nucleotide polymorphisms (SNPs) and 2,700 simple sequence repeats (SSRs) were also detected.

CONCLUSION

Our data provide the most comprehensive transcriptomic resource currently available for P. yessoensis. Candidate genes potentially involved in growth, reproduction, and stress/immunity-response were identified, and are worthy of further investigation. A large number of SNPs and SSRs were also identified and ready for marker development. This resource should lay an important foundation for future genetic or genomic studies on this species.

Deconstructing honeybee vitellogenin: novel 40 kDa fragment assigned to its N terminus

Vitellogenin, an egg-yolk protein precursor common to oviparous animals, is found abundantly in honeybee workers - a caste of helpers that do not usually lay eggs. Instead, honeybee vitellogenin (180 kDa) participates in processes other than reproduction: it influences hormone signaling, food-related behavior, immunity, stress resistance and longevity. The molecular basis of these functions is largely unknown. Here, we establish and compare the molecular properties of vitellogenin from honeybee hemolymph (blood) and abdominal fat body, two compartments that are linked to vitellogenin functions. Our results reveal a novel 40 kDa vitellogenin fragment in abdominal fat body tissue, the main site for vitellogenin synthesis and storage. Using MALDI-TOF combined with MS/MS mass-spectroscopy, we assign the 40 kDa fragment to the N terminus of vitellogenin, whereas a previously observed 150 kDa fragment corresponded to the remainder of the protein. We show that both protein units are N glycosylated and phosphorylated. Focusing on the novel 40 kDa fragment, we present a homology model based on the structure of lamprey lipovitellin that includes a conserved β-barrel-like shape, with a lipophilic cavity in the interior and two insect-specific loops that have not been described before. Our data indicate that the honeybee fat body vitellogenin experiences cleavage unlike hemolymph vitellogenin, a pattern that can suggest a tissue-specific role. Our experiments advance the molecular understanding of vitellogenin, of which the multiple physiological and behavioral effects in honeybees are well established.

TBC-2 is required for embryonic yolk protein storage and larval survival during L1 diapause in Caenorhabditis elegans

C. elegans first stage (L1) larvae hatched in the absence of food, arrest development and enter an L1 diapause, whereby they can survive starvation for several weeks. The physiological and metabolic requirements for survival during L1 diapause are poorly understood. However, yolk, a cholesterol binding/transport protein, has been suggested to serve as an energy source. Here, we demonstrate that C. elegans TBC-2, a RAB-5 GTPase Activating Protein (GAP) involved in early-to-late endosome transition, is important for yolk protein storage during embryogenesis and for L1 survival during starvation. We found during embryogenesis, that a yolk::green fluorescent protein fusion (YP170::GFP), disappeared much more quickly in tbc-2 mutant embryos as compared with wild-type control embryos. The premature disappearance of YP170::GFP in tbc-2 mutants is likely due to premature degradation in the lysosomes as we found that YP170::GFP showed increased colocalization with Lysotracker Red, a marker for acidic compartments. Furthermore, YP170::GFP disappearance in tbc-2 mutants required RAB-7, a regulator of endosome to lysosome trafficking. Although tbc-2 is not essential in fed animals, we discovered that tbc-2 mutant L1 larvae have strongly reduced survival when hatched in the absence of food. We show that tbc-2 mutant larvae are not defective in maintaining L1 diapause and that mutants defective in yolk uptake, rme-1 and rme-6, also had strongly reduced L1 survival when hatched in the absence of food. Our findings demonstrate that TBC-2 is required for yolk protein storage during embryonic development and provide strong correlative data indicating that yolk constitutes an important energy source for larval survival during L1 diapause.

Suppression of ovarian development and vitellogenin gene expression in the adult diapause of the two-spotted spider mite Tetranychus urticae

Tetranychus urticae (Acari: Tetranychidae) possesses a sac-like ovary with characteristic oocytes that protrude from the ovarian surface. In nondiapause females, transparent oocytes became opaque with yolk deposition between days 0 and 1 in the adult stage at 20 degrees C. In diapause females, however, ovarian development ceased at a stage having transparent oocytes without yolk deposition; this stage corresponded to the day-0 stage of the nondiapause females. Four partial fragments of the vitellogenin (Vg) genes of T. urticae were isolated. This is the first report on the Vg genes of mites. The deduced amino acid sequences of these four Vg gene fragments contained the von Willebrand factor D domain and the GLCG motif, which were reported to be the common features of Vg sequences in insects and ticks. Northern blot analysis did not detect Vg mRNA in the diapause adult females of T. urticae. It is, therefore, suggested that diapause mites do not synthesize Vg mRNA and that vitellogenesis is regulated at the transcriptional level in diapause.

Confirmation of sex-specific transcripts from Ancylostoma caninum adult worms by semi-quantitative RT-PCR

In a previous work Ancylostoma caninum sex-specific genes had being identified, however without confirmation, by using an non specific RT-PCR comparing male and female cDNA. In this work more fragments had been identified and a semi-quantitative RT-PCR carried out in order to confirm the sex-specific character of the transcripts obtained. Four fragments were confirmed as sex-specific or as being expressed more in one sex than the other.

Precursor structure of egg proteins in the coral Galaxea fascicularis

In the egg of the reef coral Galaxea fascicularis, four proteins (named GfEP-1 to -4) are stored in high abundance. In the present study, a cDNA containing a full-length open reading frame for GfEP-1 was cloned, and the translated protein sequence was compared to the N-terminal sequences of GfEP-2, -3, and -4. GfEP-1 and -2 were shown to be generated by processing of a precursor of 1439 amino acids, and GfEP-3 turned out to be a partial fragment of GfEP-2. The precursor protein contained regions which exhibited similarities to vitellogenins (Vgs) in bilaterian animals (oviparous vertebrates and invertebrates including nematodes, arthropods, and molluscs). This study reports the first cloning and characterization of a full-length cDNA encoding a Vg in a non-bilaterian animal, and argues that the emergence of Vg as a precursor of egg yolk proteins predated the divergence of the cnidarian and bilaterian lineages.

Downregulation of vitellogenin gene activity increases the gustatory responsiveness of honey bee workers (Apis mellifera)

In the honey bee (Apis mellifera), young workers usually perform tasks in the nest while older workers forage in the field. The behavioral shift from nest-task to foraging activity is accompanied by physiological and sensory changes so that foragers can be characterized by a higher juvenile hormone (JH) level, a lower vitellogenin protein titer, and an increased responsiveness to water and sucrose stimuli. JH was hypothesized to be the key mediator of behavioral development, physiology, and sensory sensitivity in honey bee workers. Recent research, however, has shown that JH is controlled by the hemolymph vitellogenin level, which implies that the fat body specific vitellogenin gene can be a key regulator of behavioral change. Here, we show that downregulation of vitellogenin activity by RNA interference (RNAi) causes an increase in the gustatory responsiveness of worker bees. Our observations suggest that vitellogenin is an important regulator of long-term changes in honey bee behavior.

Complex social behaviour derived from maternal reproductive traits

A fundamental goal of sociobiology is to explain how complex social behaviour evolves, especially in social insects, the exemplars of social living. Although still the subject of much controversy, recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes to result in sib-care, the hallmark of highly evolved social life in insects. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers.

Reproductive protein protects functionally sterile honey bee workers from oxidative stress

Research on aging shows that regulatory pathways of fertility and senescence are closely interlinked. However, evolutionary theories on social species propose that lifelong care for offspring can shape the course of senescence beyond the restricted context of reproductive capability. These observations suggest that control circuits of aging are remodeled in social organisms with continuing care for offspring. Here, we studied a circuit of aging in the honey bee (Apis mellifera). The bee is characterized by the presence of a long-lived reproductive queen caste and a shorter-lived caste of female workers that are life-long alloparental care givers. We focus on the role of the conserved yolk precursor gene vitellogenin that, in Caenorhabditis elegans, shortens lifespan as a downstream element of the insulin/insulin-like growth factor signaling cascade. Vitellogenin protein is synthesized at high levels in honey bee queens and is abundant in long-lived workers. We establish that vitellogenin gene activity protects worker bees from oxidative stress. Our finding suggests that one mechanistic explanation for patterns of longevity in bees is that a reproductive regulatory pathway has been remodeled to extend life. This perspective is of considerable relevance to research on longevity regulation that builds largely on inference from solitary model species.

Chromosomal clustering and GATA transcriptional regulation of intestine-expressed genes in C. elegans

We used mRNA tagging to identify genes expressed in the intestine of C. elegans. Animals expressing an epitope-tagged protein that binds the poly-A tail of mRNAs (FLAG::PAB-1) from an intestine-specific promoter (ges-1) were used to immunoprecipitate FLAG::PAB-1/mRNA complexes from the intestine. A total of 1938 intestine-expressed genes (P<0.001) were identified using DNA microarrays. First, we compared the intestine-expressed genes with those expressed in the muscle and germline, and identified 510 genes enriched in all three tissues and 624 intestine-, 230 muscle- and 1135 germ line-enriched genes. Second, we showed that the 1938 intestine-expressed genes were physically clustered on the chromosomes, suggesting that the order of genes in the genome is influenced by the effect of chromatin domains on gene expression. Furthermore, the commonly expressed genes showed more chromosomal clustering than the tissue-enriched genes, suggesting that chromatin domains may influence housekeeping genes more than tissue-specific genes. Third, in order to gain further insight into the regulation of intestinal gene expression, we searched for regulatory motifs. This analysis found that the promoters of the intestine genes were enriched for the GATA transcription factor consensus binding sequence. We experimentally verified these results by showing that the GATA motif is required in cis and that GATA transcription factors are required in trans for expression of these intestinal genes.

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.

Vitellogenesis in the sand shrimp, metapenaeus ensis: the contribution from the hepatopancreas-specific vitellogenin gene (MeVg2)

An additional vitellogenin gene (MeVg2) that is structurally different from MeVg1 was cloned and characterized from the shrimp Metapenaeus ensis. The MeVg2 gene consists of fewer exons-introns and is most likely evolved from the MeVg1 gene. The cDNA for MeVg2 is 8.0 kilobases (kb) in size, and the deduced MeVg2 precursor shared an overall 54% amino sequence identity to the MeVg1 gene of the same shrimp. As compared to the MeVg1 precursor, MeVg2 precursor consists of more potential subunit cleavage sites, suggesting that the precursor may be processed into many smaller subunits. The MeVg2 is expressed only in the hepatopancreas, and the expression level of MeVg2 in adult female increases from the early vitellogenic stage, reaching a maximum at the middle vitellogenic stage, and remains high toward the end of vitellogenic cycle. In addition to the 8-kb mRNA, smaller transcripts of 1.5-2.5 kb for MeVg2 were identified, and the 8-kb transcript only constitutes less than 10% of the overall MeVg2-derived transcripts. To confirm the presence of the small transcripts, we screened the shrimp hepatopancreas cDNA library and isolated two smaller MeVg2-specific cDNA clones. These clones shared greater than 99% overall identity to the corresponding C-terminal region of the MeVg2 precursor, suggesting that an alternative expression/ splicing of the MeVg2 gene occurred. By immunohistochemical analysis, vitellin-immunopositive signals were localized in the lumen and extracellular fraction of the hepatopancreas. Amino acid sequence determination of the tissue protein and secreted protein from the hepatopancreas revealed that the 76-kDa vitellogenin subunit is most likely processed into smaller-sized subunits. Taken together, these results suggest that the hepatopancreas is an important organ for the synthesis of vitellogenin and may contribute to vitellogenesis by producing a large quantity of smaller MeVg2 subunit for ovarian uptake.

Redox regulation of germline and vulval development in Caenorhabditis elegans

In vitro studies have indicated that reactive oxygen species (ROS) and the oxidation of signaling molecules are important mediators of signal transduction. We have identified two pathways by which the altered redox chemistry of the clk-1 mutants of Caenorhabditis elegans acts in vivo on germline development. One pathway depends on the oxidation of an analog of vertebrate low density lipoprotein (LDL) and acts on the germline through the Ack-related tyrosine kinase (ARK-1) kinase and inositol trisphosphate (IP3) signaling. The other pathway is the oncogenic ras signaling pathway, whose action on germline as well as vulval development appears to be modulated by cytoplasmic ROS.

Cleavage site of a major yolk protein (MYP) determined by cDNA isolation and amino acid sequencing in sea urchin, Hemicentrotus pulcherrimus

The overall sequence of cDNA encoding vitellogenin (Vg), a precursor to major yolk protein (MYP), of Hemicentrotus pulcherrimus was determined. Its nucleotide sequence has an open reading frame of 4041 bp encoding 1346 amino acids. The amino acid sequence showed little similarity to other Vgs in vertebrates, insects or nematodes, but resembled members of the vertebrate and invertebrate transferrin family. The N-terminal amino acid sequence of the protein fragments dominant in the later embryonic stage was analyzed in order to determine the cleavage site of MYP. Determination of the cleavage site in MYP and analysis of MYP proteolysis in vitro suggested that MYP has a specific molecular shape to permit its proteolytic fragmentation at a definite site. The functional region of transferrin in MYP is conserved after proteolytic processing. Considering these results and those from other work, the protein called sea urchin Vg is not a true Vg. Therefore, a new name, echinoferrin, is proposed for this protein.

Eggshell and egg yolk proteins in fish: hepatic proteins for the next generation: oogenetic, population, and evolutionary implications of endocrine disruption

The oocyte is the starting point for a new generation. Most of the machinery for DNA and protein synthesis needed for the developing embryo is made autonomously by the fertilized oocyte. However, in fish and in many other oviparous vertebrates, the major constituents of the egg, i.e. yolk and eggshell proteins, are synthesized in the liver and transported to the oocyte for uptake. Vitellogenesis, the process of yolk protein (vitellogenin) synthesis, transport, and uptake into the oocyte, and zonagenesis, the synthesis of eggshell zona radiata proteins, their transport and deposition by the maturing oocyte, are important aspects of oogenesis. The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role. The ability of many synthetic chemical compounds to mimic this estrogen can lead to unscheduled hepatic synthesis of vitellogenin and zona radiata proteins, with potentially detrimental effects to the adult, the egg, the developing embryo and, hence, to the recruitment to the fish population. This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms. The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

Drosophila yolk protein produced in E. coli is accumulated by mosquito ovaries

Despite similar functions, the yolk proteins of the higher dipteran flies and the vitellogenins found in other insects are unrelated at the sequence level and have evolved from different genes. Both are selectively endocytosed into the ovary via receptors belonging to the LDLR receptor subfamily. We cloned the Drosophila yp1 gene into an E. coli expression vector and showed that the yolk protein produced by E. coli is taken up into ovaries of both Drosophila melanogaster and the malaria mosquito Anopheles gambiae, which normally uses vitellogenin.

Deciphering endocytosis in Caenorhabditis elegans

We discuss in this review recent studies using the worm Caenorhabditis elegans to decipher endocytic trafficking in a multicellular organism. Recent advances, including in vivo assay systems, new genetic screens, comparative functional analysis of conserved proteins, and RNA-mediated interference (RNAi) in C. elegans, are being used to study the functions of known membrane trafficking factors and to identify new ones. The ability to monitor endocytosis in vivo in worms allows one to test current endocytosis models and to demonstrate the physiological significance of factors identified by genetic and biochemical methods. The available human genome sequence facilitates comparative studies where human homologs of new factors identified in C. elegans can be quickly assayed for similar function using traditional cell biological methods in mammalian cell systems. New studies in C. elegans have used a combination of these techniques to reveal novel metazoan-specific trafficking factors required for endocytosis. Many more metazoan-specific trafficking factors and insights into the mechanisms of endocytosis are likely to be uncovered by analysis in C. elegans.

Analysis of developmentally regulated genes of the parasite Haemonchus contortus

Differential regulation of gene expression in the development of Haemonchus contortus was analysed using RNA arbitrarily-primed PCR. A study of third-stage larval and adult H. contortus revealed large differences between the two stages; 32 and 30% unique third-stage larval and adult RNA arbitrarily-primed PCR products, respectively. This finding is consistent with a high degree of differential gene expression between these developmental stages. A number of adult products were sequenced, revealing 11 molecules to be similar to deposits within sequence databases. Four other molecules that did not have significant similarity to sequences in the databases may represent developmentally regulated genes specific to H. contortus. Northern analysis of the putative adult-expressed molecules with homologues in the databases confirmed that four were expressed only in adults, while four were expressed in both stages, but had different sized transcripts. This may reflect differential splicing, or expression of closely related but different molecules at different life cycle stages. Two molecules were present in mRNA populations from both stages, suggesting these were false stage-associated molecules. No transcript was detected for one molecule by Northern analysis, probably due to low level of expression. In situ hybridisation analysis was used to localise expression of transcripts in the adult parasite, in particular, to gain some insight into the nature of those molecules with no known predicted function.

Distribution and transport of cholesterol in Caenorhabditis elegans

Cholesterol transport is an essential process in all multicellular organisms. In this study we applied two recently developed approaches to investigate the distribution and molecular mechanisms of cholesterol transport in Caenorhabditis elegans. The distribution of cholesterol in living worms was studied by imaging its fluorescent analog, dehydroergosterol, which we applied to the animals by feeding. Dehydroergosterol accumulates primarily in the pharynx, nerve ring, excretory gland cell, and gut of L1-L3 larvae. Later, the bulk of dehydroergosterol accumulates in oocytes and spermatozoa. Males display exceptionally strong labeling of spermatids, which suggests a possible role for cholesterol in sperm development. In a complementary approach, we used a photoactivatable cholesterol analog to identify cholesterol-binding proteins in C. elegans. Three major and several minor proteins were found specifically cross-linked to photocholesterol after UV irradiation. The major proteins were identified as vitellogenins. rme-2 mutants, which lack the vitellogenin receptor, fail to accumulate dehydroergosterol in oocytes and embryos and instead accumulate dehydroergosterol in the body cavity along with vitellogenin. Thus, uptake of cholesterol by C. elegans oocytes occurs via an endocytotic pathway involving yolk proteins. The pathway is a likely evolutionary ancestor of mammalian cholesterol transport.

Sorting and transport in C. elegans: aA model system with a sequenced genome

In the past few years, yeast and cultured cells have been the model systems of choice for the study of protein sorting and transport. Recently, there has been a surge in research in these areas in Caenorhabditis elegans, with advances in experimental techniques and genomics. New in vivo assays that monitor endocytosis and neuronal transport have been used to delineate roles for several genes in these processes.

A simple and rapid method for cloning insect vitellogenin cDNAs

We describe a simple and rapid method for cloning insect vitellogenin (Vg) cDNAs. The method relies on the facts that insect Vg amino acid sequences can be aligned confidently along their entire lengths and that a short, highly conserved GL/ICG motif and up to nine cysteine residues that follow at conserved locations are present near the C-termini. An adaptor-ligated double-strand cDNA library is constructed from poly(A)+ RNA prepared from vitellogenic female fat body tissues using a commercial kit, and subjected to PCR with each of the degenerate nucleotide sequences for the GL/ICG motif and the adaptor sequence as primers. The PCR products (0.7-0.9 kb, representing the 3' portion) are cloned, the nucleotide sequences are determined, and the deduced amino acid sequences are aligned with the known insect Vg sequences starting from the GL/ICG motif. Gene-specific primers corresponding to the sequences near the 5'-termini of the initial clones and the adaptor sequence are employed to obtain the remaining 5' portion of the Vg cDNAs. The method was successfully applied to the bean bug Plautia stali (Heteroptera), revealing three Vg genes.

Receptor-mediated endocytosis in the Caenorhabditis elegans oocyte

The Caenorhabditis elegans oocyte is a highly amenable system for forward and reverse genetic analysis of receptor-mediated endocytosis. We describe the use of transgenic strains expressing a vitellogenin::green fluorescent protein (YP170::GFP) fusion to monitor yolk endocytosis by the C. elegans oocyte in vivo. This YP170::GFP reporter was used to assay the functions of C. elegans predicted proteins homologous to vertebrate endocytosis factors using RNA-mediated interference. We show that the basic components and pathways of endocytic trafficking are conserved between C. elegans and vertebrates, and that this system can be used to test the endocytic functions of any new gene. We also used the YP170::GFP assay to identify rme (receptor-mediated endocytosis) mutants. We describe a new member of the low-density lipoprotein receptor superfamily, RME-2, identified in our screens for endocytosis defective mutants. We show that RME-2 is the C. elegans yolk receptor.

Site of vitellogenin synthesis determined from a cDNA encoding a vitellogenin fragment in the freshwater giant prawn, Macrobrachium rosenbergii

Vitellogenesis is an important part of reproductive process in crustaceans, and the process is characterized by the synthesis and accumulation of yolk protein in the developing oocytes. The yolk proteins in crustaceans mainly consist of vitellogenin (Vg) and vitellin (Vn), which are respectively present in extra-oocyte tissues and intra-oocytes. The site and the process of yolk protein synthesis in crustaceans are still controversial. The synthesis site of Vg in a crustacean species, Macrobrachium rosenbergii, is determined by immunological and immunohistochemical techniques, and molecular cloning of a cDNA encoding the primary structure of Vn in this study. The hepatopancrease is clearly shown to be the synthesis site of Vg in this species. The length of Vg mRNA was estimated as about 6 kb from Northern blotting analysis. The partial primary structure of Vg gene is presented, and the post-translational processing are further discussed. For the first time, the partial primary structure of Vg gene and the synthesis site of Vg approached by molecular cloning in crustaceans are presented.

Similarity of DNA binding and transcriptional regulation by Caenorhabditis elegans MAB-3 and Drosophila melanogaster DSX suggests conservation of sex determining mechanisms

Although most animals occur in two sexes, the molecular pathways they employ to control sexual development vary considerably. The only known molecular similarity between phyla in sex determination is between two genes, mab-3 from C. elegans, and doublesex (dsx) from Drosophila. Both genes contain a DNA binding motif called a DM domain and they regulate similar aspects of sexual development, including yolk protein synthesis and peripheral nervous system differentiation. Here we show that MAB-3, like the DSX proteins, is a direct regulator of yolk protein gene transcription. We show that despite containing different numbers of DM domains MAB-3 and DSX bind to similar DNA sequences. mab-3 mutations deregulate vitellogenin synthesis at the level of transcription, resulting in expression in both sexes, and the vitellogenin genes have potential MAB-3 binding sites upstream of their transcriptional start sites. MAB-3 binds to a site in the vit-2 promoter in vitro, and this site is required in vivo to prevent transcription of a vit-2 reporter construct in males, suggesting that MAB-3 is a direct repressor of vitellogenin transcription. This is the first direct link between the sex determination regulatory pathway and sex-specific structural genes in C. elegans, and it suggests that nematodes and insects use at least some of the same mechanisms to control sexual development.

A novel piscine vitellogenin gene: structural and functional analyses of estrogen-inducible promoter

The Oreochromis aureus vitellogenin, OaVtg, gene spans 9 kb and contains 34 exons. Its transcription start site is located 15 bp upstream of the translational start codon. Although the OaVtg promoter has a nonconsensus TATA, transient transfection assay showed that this promoter is capable of driving basal transcription. Two imperfect estrogen response elements: EREp (proximal) and EREd (distal) are located in the promoter at - 532 and - 1352, respectively. In competition gel mobility-shift assays, only EREp exhibited specific binding of the recombinant estrogen receptor protein, GST-C/D OaER. Another imperfect ERE (EREexon2) was detected within exon 2 of the OaVtg gene. This is a novel finding for a vitellogenin (Vtg) gene. EREexon2 similarly showed specific recognition of GST-C/D OaER. Both EREp and EREexon2 showed comparable binding affinities as consensus ERE. In transient transfections, the OaVtg promoter, EREp and EREd elicited significant increase in estrogen-dependent synthesis of CAT protein. Hence, we propose that the non-consensus OaVtg EREs contribute to the estrogen-dependent regulation of the OaVtg gene in vivo.

Differential gene expression in insects: transcriptional control

Studies on transcriptional control of gene expression play a pivotal role in many areas of biology. In non-Drosophilid insects, the cuticle, chorion, immune response, silk gland, storage proteins, and vitellogenin are foci for advances in basic research on promoter elements and transcription factors. Insects offer other advantages for gene regulation studies, including the availability of applied problems. In non-Drosophilid insects, the most serious problem for transcriptional control studies is the lack of homologous in vivo expression systems. Once this deficiency is addressed, the full impact of research on transcription control will be realized throughout the field of entomology.

Structure of a fish (Oncorhynchus mykiss) vitellogenin gene and its evolutionary implication

In this paper we describe the first complete structure of a fish vitellogenin gene. A 22 kb genomic region from rainbow trout (Oncorhynchus mykiss) was cloned and analysed. This region was shown to contain two tandemly arranged vitellogenin genes. Both genes are 98.7% similar, indicating that they result from a recent local duplication. The complete sequence encoding one of the two genes was determined and the gene organization was established. The gene is 10.3 kb long and has 34 exons, it lacks one exon compared to amphibian and avian vitellogenin genes. Exons 22 and 23 of the Xenopus and chicken genes were shown to be merged into a single exon in the trout genome. Other splicing sites appeared highly conserved between the three vertebrate genes. In contrast, little similarity between invertebrate and vertebrate vitellogenin genes was observed with respect to the number and organization of introns. The comparison of 17 independent invertebrate splicing sites with the 34 vertebrate sites indicated that a few sites are probably ancient. However, most of the splicing junctions compared appeared unrelated. Results suggest that vitellogenin genes have been reshaped through multiple insertions and deletions of intervening sequences during evolution.

Structure of the gypsy moth vitellogenin gene

Genomic clones containing the vitellogenin (Vg) gene from the gypsy moth were isolated from two genomic libraries and characterized. The nucleotide sequence of a 16,132 bp region of the gypsy moth genome was determined which included a 3,666 bp region upstream from the transcription initiation site and 499 bp region downstream from the transcribed region. Primer extension analysis was performed to identify the transcription initiation site. Gene sequence confirmed the sequence of VgmRNA recently reported [Hiremath and Lehtoma, J. Insect Biochem. Mol. Biol. (1997) 27:27-35] and indicated that the gypsy moth Vg gene contains seven exons interrupted by six introns. Sequence analysis of the promoter region revealed presence of several motifs associated with sex-specific and developmentally regulated genes in other systems. The nucleotide sequence comparison analyses showed that the gypsy moth Vg gene had considerably similarity with the Bombyx mori Vg gene but not with those from Anthonomous grandis and Aedes aegypti.