Precursor-product relationship between vitellogenin and the yolk proteins as derived from the complete sequence of a Xenopus vitellogenin gene

Proteomic Analysis of Egg Yolk Proteins During Embryonic Development in Wanxi White Goose

To investigate the alterations of yolk protein during embryonic development in Wanxi white goose, the egg yolk protein composition at days 0, 4, 7, 14, 18, and 25 of incubation (D0, D4, D7, D14, D18, and D25) was analyzed by two-dimensional gel electrophoresis combined with mass spectrometry. A total of 65 spots representing 11 proteins with significant abundance changes were detected. Apolipoprotein B-100, vitellogenin-1, vitellogenin-2-like, riboflavin-binding protein, and serotransferrin mainly participated in nutrient (lipid, riboflavin, and iron ion) transport, and vitellogenin-2-like showed a lower abundance after D14. Ovomucoid-like were involved in endopeptidase inhibitory activity and immunoglobulin binding and exhibited a higher expression after D18, suggesting a potential role in promoting the absorption of immunoglobulin and providing passive immune protection for goose embryos after D18. Furthermore, myosin-9 and actin (ACTB) were involved in the tight junction pathway, potentially contributing to barrier integrity. Serum albumin mainly participated in cytolysis and toxic substance binding. Therefore, the high expression of serum albumin, myosin-9, and ACTB throughout the incubation might protect the developing embryo. Apolipoprotein B-100, vitellogenin-1, vitellogenin-2-like, riboflavin-binding protein, and serotransferrin might play a crucial role in providing nutrition for embryonic development, and VTG-2-like was preferentially degraded/absorbed.

Biomarkers of reproduction in endangered green sea turtles (Chelonia mydas) nesting at Tortuguero, Costa Rica

Understanding the timing of vitellogenesis is essential for identifying threats to the reproductive success of endangered oviparous vertebrate species, such as sea turtles. We measured concentrations of testosterone (T) and vitellogenin (VTG) in green sea turtles (Chelonia mydas) nesting at Tortuguero, Costa Rica, as biomarkers of ovarian development. Testosterone concentration increased from the first to second month and VTG concentration increased at the third week of sampling. These results show that Tortuguero green sea turtles were still producing both biomarkers early into the nesting season. VTG concentration was negatively correlated with female weight, suggesting that larger females start nesting earlier at Tortuguero and that we may have sampled larger females further into their reproductive cycle.

Effects of dietary icariin supplementation on the ovary development-related transcriptome of Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab (Eriocheir sinensis) is an economically important aquaculture species in China, with distinct differences in ovarian maturation status between crabs fed with natural diets and artificial diets during the listing period, thus, leading to selling price differentiation. Our previous study showed that dietary supplementation with 100 mg/kg icariin can effectively promote ovarian development of E. sinensis. However, the internal molecular mechanism has not yet been elucidated because of a lack of comprehensive genome sequence information. We compared the ovary transcriptomes of E. sinensis fed with two diets containing 0 and 100 mg/kg ICA using the BGISEQ-500 platform. This yielded 12.54 Gb clean bases and 54,794 unigenes, 13,832 of which were found to be differentially expressed after icariin exposure. Twenty pathways closely related to gonadal development were selected through KEGG analysis. Seven differentially expressed genes relevant to vitellogenesis and oocyte maturation (serine/threonine-protein kinase mos-like, Eg2, cytoplasmic polyadenylation element-binding protein, cyclin B, vitellogenin 1, cathepsin D, and juvenile hormone esterase-like carboxylesterase 1) were validated by qRT-PCR, and four proteins (MEK1/2, ERK1/2, Cyclin B and Cdc2) associated with the progesterone mediated oocyte maturation pathway (i.e., MAPK/MPF pathway) were analyzed by western-blot. The results showed that icariin could promote the synthesis, processing and deposition of vitellogenin in oocytes, and that it also has the potential to promote oocyte maturation (resumption of Meiosis I) by altering the expression of the relevant genes and proteins.

Bactericera cockerelli vitellogenin-6 like, a vitellogenin without a direct reproductive function?

Vitellogenin-like proteins are members of the large lipid transfer proteins, a family of proteins involved in reproduction, lipid circulation and immune defences. In this study, we identified a new Bactericera cockerelli vitellogenin-like (Vg-like) transcript, and named it BcVg6-like based on its similarity to Acyrthosiphon pisum Vg6. In silico analyses predicted different conserved domains in BcVg6-like compared with the conventional Ba. cockerelli vitellogenin, BcVg1-like, previously described by our research group. Phylogenetic analyses determined that BcVg6-like clustered with Vg-like-B proteins and not the conventional vitellogenins involved in vitellogenesis. Also, the expression analyses showed differences in BcVg6-like transcript expression between 7-day-old males and 3- and 7-day-old females. BcVg6-like was not upregulated after exogenous application of juvenile hormone III, but its relative expression increased significantly in alimentary canals of adult females exposed to tomato plants infected by the bacterial plant pathogen 'Candidatus Liberibacter solanacearum'. Our results suggest that in Ba. cockerelli, both vitellogenin genes may have different functions: BcVg1-like is a conventional vitellogenin that conserved its ancestral function as an egg yolk precursor whereas BcVg6-like might have acquired a function in lipid and/or other molecule transport, and could potentially play a role in immune defence.

Identification and expression analyses of vitellogenin in Bactericera cockerelli (Šulc)

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a phloem-feeding insect with preference for Solanaceae. This insect species is vector of the pathogenic bacteria 'Candidatus Liberibacter solanacearum' the causative agent of zebra chip, an important disease of commercial potatoes in several countries worldwide. The recent classification of psyllids among the most dangerous vectors has promoted their study, but still many biological processes such as reproduction and vitellogenesis need to be investigated. As a first step towards the elucidation of vitellogenesis in B. cockerelli, one candidate vitellogenin transcript (6622 bases long) was identified and the expression of the transcript and the protein were analyzed in virgin and mated females between 1 and 7days old. In virgin females, Vg expression increased up to 5days old; while mating significantly up-regulated Vg expression in 5- and 7-day-old females. To determine the role of juvenile hormone in B. cockerelli Vg expression, topical applications of juvenile hormone III were performed on virgin females, resulting in an up-regulation of Vg expression and an increase in the number of mature oocytes present in female reproductive organs. Overall, this study represents the first step to understand vitellogenesis of B. cockerelli and it highlights the role of JH III in the hormonal regulation of Vg expression and oocyte development.

An in vivo assay performed using multiple biomarkers related to testosterone synthesis and conversion for assessing the androgenic potency of refuse leachate

Refuse leachate is likely an important source of androgens. However, common in vitro bioassays underestimate the potential androgenic activity of leachate, owing to non-receptor-mediated mechanisms that modify the balance of sex hormones and promote the accumulation of endogenous androgens. This study aimed to develop an in vivo assay by using multiple biomarkers related to testosterone synthesis and conversion for assessing the potential androgenic activity of refuse leachate sampled from a municipal solid waste treatment plant in Qingdao, China. The results indicated that exposure to leachate increased the levels of testosterone and luteinizing hormone, but decreased those of 17β-estradiol in both male and female goldfish (Carassius auratus), suggesting a potential androgenic activity. Further, Leydig cell hyperplasia and decreased gonadal P450 aromatase mRNA levels were observed; these alterations might promote the biosynthesis of testosterone and hinder the conversion of testosterone to 17β-estradiol, which in turn enhance testosterone accumulation. Exposure to leachate also resulted in reproductive impairments, including decreased gonadosomatic index and plasma vitellogenin levels of female goldfish, as well as decreased testicular enzyme activities in male goldfish. The integrated use of biochemical, molecular, and histological markers not only improved our understanding of the androgenic effects of leachate but also verified the reliability and validity of the results. Therefore, the in vivo bioassay described in this study might allow the investigation of the androgenic effects of other complex contaminant mixtures in the future.

Vitellogenin2: spermatozoon specificity and immunoprotection in mud crabs

As the precursor of vitellin (Vn), vitellogenin (Vg) has initially been considered as a female-specific protein involved in vitellogenesis, while it was also present in males induced by hormones or organs manipulation. Distinct from vtg1 we previously found in female mud crab Scylla paramamosain, vtg2 was intriguingly detected in male testis under normal physiological conditions in this study. Sequence analysis showed that vtg2 and vtg1 were actually two isoforms of Vg caused by different types of alternative splicing. PCR and in situ hybridization analysis revealed that vtg2 was localized only in the testicular spermatozoa, while Vn was detected in both the spermatozoa of the testis and seminal vesicle. Therefore, we speculated that Vn was initially translated in testicular spermatozoa, then migrated with spermatozoa, and finally stored in the seminal vesicle, where spermatozoa gradually accomplished maturation. We presumed that vtg2/Vn might act as an immune-relevant molecule in the male reproduction system. In the subsequent experiment, the expression of vtg2/Vn in testis was significantly induced in response to lipopolysaccharide (LPS) and lipoteichoic acid (LTA) injection at both transcriptional and translational levels. In the light of the results presented above, we deemed that vtg2/Vn is a novel candidate of immune-relevant molecules involved in immunoprotection during the spermatozoon maturation, and this research helps to open a new avenue for further exploring the role of Vg.

Resveratrol potentiates vitamin D and nuclear receptor signaling

The 1,25-dihydroxyvitamin D3 (1,25D) hormone is derived from vitamin D generated in skin or obtained from the diet, and binds to and activates the vitamin D receptor (VDR) in target tissues including kidney, colon/small intestine, and bone/muscle. We tested resveratrol for its ability to modulate VDR signaling, using vitamin D responsive element (VDRE) and mammalian 2-hybrid (M2H) transcriptional system technology. Via VDRE-based assays in kidney, colon and myoblast cells, VDR-mediated transcription was activated by resveratrol, and a cooperative effect on transactivation was observed with resveratrol plus 1,25D. The M2H assay revealed a modest, resveratrol-induced dimerization of VDR with its retinoid X receptor (RXR) heteropartner. Cells treated with both resveratrol and 1,25D displayed synergistic stimulation of VDR-RXR heterodimerization, while resveratrol antagonized rexinoid-mediated RXR-RXR homodimerization. Increased transactivation in response to resveratrol was also observed with a subset of other nuclear receptors and their respective cognate responsive elements. Evaluation of wild-type versus a ligand-binding domain mutant VDR revealed that hormone-responsiveness to 1,25D was severely depressed, while the response to resveratrol was only moderately attenuated. Moreover, radiolabeled 1,25D-displacement assays demonstrated an increase in VDR-bound 1,25D in the presence of resveratrol. Thus, resveratrol may affect VDR and other nuclear receptors indirectly, likely via the ability of resveratrol to: (1) potentiate 1,25D binding to VDR; (2) activate RXR; and/or (3) stimulate SIRT1, an enzyme known to deacetylate nuclear receptors. The results of this study elucidate a possible pathway for crosstalk between two nutritionally derived lipids, vitamin D and resveratrol, both of which converge on VDR signaling.

FOXL2 down-regulates vitellogenin expression at mature stage in Eriocheir sinensis

The present study highlights that forkhead transcription factor (FOXL)2 down-regulates vitellogenin (VTG) synthesis not only through the regulation of follicular cell apoptosis with DEAD-box RNA helicase 20 (DDX20), but also may through the steroidogenic pathway with fushi tarazu factor (FTZ-F)1 at mature stage in Eriocheir sinensis.

Ovarian development in crustaceans is characterized by rapid production of egg yolk protein in a process called vitellogenesis. In the present study, we investigated the involvement of a DEAD (Asp-Glu-Ala-Asp) box RNA helicase 20 (DDX20), forkhead transcription factor (FOXL)2 and fushi tarazu factor (FTZ-F)1 in the regulation of vitellogenesis. Based on ESTs from the testis and accessory gland of Eriocheir sinensis, we cloned the full-length cDNAs of foxl2 and fushitarazu factor 1 (ftz-f1), which include the conserved structural features of the forkhead family and nuclear receptor 5A (NR5A) family respectively. The expression of foxl2 mRNA surged at the mature stage of the ovary, when vtg mRNA swooped, suggesting that foxl2 negatively affects the vitellogenin (VTG) synthesis at this developmental stage. Etoposide (inducing germ cell apoptosis) treatment up-regulated FOXL2 and DDX20 at both the mRNA and the protein levels, primarily in the follicular cells as shown by immunofluorescence analysis. Furthermore, foxl2, ddx20 and ftz-f1 mRNA levels increased significantly with right-eyestalk ablation. Interactions between FOXL2 and DDX20 or FTZ-F1 were confirmed by co-immunoprecipitation and the forkhead domain of FOXL2 was identified as the specific structure interacting with FTZ-F1. In conclusion, FOXL2 down-regulates VTG expression by binding with DDX20 in regulation of follicular cell apoptosis and with FTZ-F1 to repress the synthesis of VTG at the mature stage. This report is the first to describe the molecular mechanism of VTG synthesis in E. sinensis and may shed new light on the regulation of cytochrome P450 enzyme by FOXL2 and FTZ-F1 in vitellogenesis.

An integrated approach combining chemical analysis and an in vivo bioassay to assess the estrogenic potency of a municipal solid waste landfill leachate in Qingdao

Various adverse effects related to landfill leachate have made leachates an important issue in past decades, and it has been demonstrated that landfill leachate is an important source of environmental estrogens. In this study, we employed chemical analysis of some already evaluated estrogenic substances, in combination with a bioassay using several specific biomarkers (e.g., plasma vitellogenin and sex steroids, enzyme activity of gonad gamma-glutamyl transpeptidase, and gonadosomatic index) to evaluate the estrogenic activities in outlets from different stages of the leachate treatment process. The results indicated that 5 environmental estrogens (4-t-octylphenol, bisphenol A, di-ethyl phthalate, di-n-butyl phthalate, and diethylhexyl phthalate) were detected by a gas chromatography-mass spectrometry, and the concentrations in leachate samples were 6153 ng/L, 3642 ng/L, 2139 ng/L, 5900 ng/L, and 9422 ng/L, respectively. Leachate (1∶200 diluted) induced the synthesis of plasma vitellogenin and led to decreased enzyme activity of gonad gamma-glutamyl transpeptidase and gonadosomatic index in male goldfish (Carassius auratus) after a 28-day exposure, while increased circulating 17β-estradiol level was also observed in males exposed to treated effluent. Although the target EEs were partially removed with removal rates varying from 87.2% to 99.77% by the “membrane bioreactor+reverse osmosis+aeration zeolite biofilter” treatment process, the treated effluent is still estrogenic to fish. The method combined chemical techniques with the responses of test organisms allowing us to identify the group of estrogen-like chemicals so that we were able to evaluate the overall estrogenic effects of a complex mixture, avoiding false negative assessments.

Miniature inverted-repeat transposable elements: discovery, distribution, and activity

Eukaryotic organisms have dynamic genomes, with transposable elements (TEs) as a major contributing factor. Although the large autonomous TEs can significantly shape genomic structures during evolution, genomes often harbor more miniature nonautonomous TEs that can infest genomic niches where large TEs are rare. In spite of their cut-and-paste transposition mechanisms that do not inherently favor copy number increase, miniature inverted-repeat transposable elements (MITEs) are abundant in eukaryotic genomes and exist in high copy numbers. Based on the large number of MITE families revealed in previous studies, accurate annotation of MITEs, particularly in newly sequenced genomes, will identify more genomes highly rich in these elements. Novel families identified from these analyses, together with the currently known families, will further deepen our understanding of the origins, transposase sources, and dramatic amplification of these elements.

The molecular and structural characterization of two vitellogenins from the free-living nematode Oscheius tipulae

This paper describes the purification of yolk proteins, which are important for the reproduction of egg-laying animals, and the structural characterization of two vitellogenins, VT1 and OTI-VIT-6, of the nematode Oscheius tipulae. O. tipulae is an alternative model organism to its relative, the widely used Caenorhabditis elegans, and is a good model to understand reproduction in insect parasitic nematodes of the genus Heterorhabditis. The native purified O. tipulae vitellogenin is composed of three polypeptides (VT1, VT2 and VT3), whereas in C. elegans, vitellogenin is composed of four polypeptides. The gene (Oti-vit-1) encoding yolk polypeptide VT1 has been recently identified in the genome of O. tipulae. Immunoblotting and N-terminal sequencing confirmed that VT1 is indeed coded by Oti-vit-1. Utilizing the same experimental approaches, we showed that the polypeptides VT2 and VT3 are derived from the proteolytic processing of the C- and N-terminal portions of the precursor OTI-VIT-6, respectively. We also showed that the recombinant polypeptide (P40), corresponding to the N-terminal sequence of OTI-VIT-6, preferentially interacts with a 100-kDa polypeptide found in adult worm extracts, as we have previously shown for the native vitellins of O. tipulae. Using the putative nematode vitellogenin amino acid sequences available in the UniProtKB database, we constructed a phylogenetic tree and showed that the O. tipulae vitellogenins characterized in this study are orthologous to those of the Caenorhabditis spp. Together, these results represent the first structural and functional comparative study of nematode yolk proteins outside the Caenorhabditis genus and provide insight into the evolution of these lipoproteins within the Nematode Phylum.

Lipovitellin constitutes the protein backbone of glycoproteins involved in sperm-egg interaction in the amphibian Discoglossus pictus

Our knowledge of the molecules that interact with sperm at the egg membrane is restricted to a short list. In the eggs of Discoglossus pictus, fusion with sperm is limited to a differentiated structure, the dimple, offering several advantages for detecting molecules involved in fertilization. Previous studies have identified fucosylated glycoproteins of 200, 260, and 270 kDa located at the surface of the dimple that are able to bind sperm in vitro. Here, we show that dimple glycoproteins and a protein represented by a 120-kDa band released following gel-into-gel SDS-PAGE of both glycoproteins share the same N-terminal amino acid sequence, which itself is similar to the N-termini of Xenopus liver-synthesized vitellogenin (VTG) and the lipovitellin 1. MALDI/MS mass spectrometry indicated that the 120-kDa band is part of both gps 200 and 270/260. A 117-kDa major protein of the egg lysate exhibits the same MALDI/MS spectrum, and LC-MSMS indicates that this is a lipovitellin 1 (DpLIV) that coincides with the 120-kDa band and is responsible for the formation of the 200-270-kDa dimers. Therefore, lipovitellin 1 constitutes the protein backbone of the dimple glycoconjugates. In vitro assays using polystyrene beads coated with DpLIV or with its dimers indicate that significant sperm binding occurs only with DpLIV dimers. In amphibians, VTG is taken up by the oocyte, where it releases lipovitellins destined to form yolk. In Discoglossus, our data suggest that yolk proteins are also synthesized by the oocyte. The dimple forms in the ovulated oocyte following the exocytosis of vesicles that likely expose DpLIVs at their membrane. Indeed, in whole mounts of immunostained eggs, anti-vitellogenin antibodies label only the surface of the dimple.

Vitellogenesis in Bufo arenarum: identification, characterization and immunolocalization of high molecular mass lipovitellin during oogenesis

Vitellogenin (Vtg), a large lipoglycophosphoprotein, is the most important precursor of the yolk proteins, and the major source of nutrients for the developing embryo in oviparous species. After its uptake by the oocytes, Vtg is converted into lipovitellins (high and light) and phosvitin, which are deposited into crystalline yolk platelets. We describe here the presence of two high molecular mass lipovitellin isoforms in Bufo arenarum mature oocytes with masses of 113 and 100 kDa, respectively. The amino acid sequence analysis of p113 and p100 peptides showed a high sequence homology between both polypeptides and the complete reported sequences of Xenopus laevis vitellogenin. Using specific antibodies, we determined that the Vtg uptake begins early during oogenesis, at the previtellogenic stage, and continues until oocytes have reached their mature status. In addition, we found that large endocytic vesicles mediate Vtg uptake in stage I oocytes, and that the size of the endocytic vesicles declines with oogenesis progression. In terms of the Vtg protein trafficking, we detected the Vtg precursor (190 kDa) in the liver of estradiol-injected females. Finally, we propose a subclassification of B. arenarum stage II oocytes into three physiologically and morphologically distinct periods (early, mid and late).

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.

Vitellogenin, a biomarker for environmental estrogenic pollution, of Reeves' pond turtles: analysis of similarity for its amino acid sequence and cognate mRNA expression after exposure to estrogen

Vitellogenin (VTG), a biomarker for environmental estrogenic pollution, can be detected in the bloodstream of oviparous animals before morphological and functional abnormalities appear due to exposure to environmental estrogens. Reports observing VTG in turtles have been limited. We therefore cloned and sequenced a partial cDNA of VTG in Reeves' pond turtle, Chinemys reevesii. The cloned cDNA fragment possessed the start codon and 2,229 bp, encoding 743 amino acid residues. A sequence of deduced amino acid from the cDNA did not contain a high serine content, such as that which exists in phosvitin. Two N-glycosylation sites were found in the sequence. The sequence was compared to those of two birds (chicken and herring gull), one amphibian (Xenopus), and five fishes (carp, zebrafish, eel, haddock, and red seabream). The C. reevesii VTG was similar to that of herring gull (78%, value of positives), chicken (76%), Xenopus (69%), eel (63%), red seabream (62%), haddock (62%), carp (62%), and zebrafish (61%). The phylogenetic tree showed that C. reevesii VTG existed between the amphibian and birds, and it was present far from fish VTGs. A reverse transcription-polymerase chain reaction method was employed to detect the mRNA expression of the C. reevesii VTG through the use of primers designed from our sequence. The VTG mRNA expression (292 bp) was proven in the total RNA extraction from the liver of the juvenile turtles which were treated with estradiol-17beta. The information herein would be useful for ecotoxicological studies using freshwater turtles and these findings are expected to contribute positively towards wildlife conservation.

Vitellogenin and Its Messenger RNA During Ovarian Development in the Female Blue Crab, Callinectes sapidus: Gene Expression, Synthesis, Transport, and Cleavage1

Blue crab vitellogenin (VTG) cDNA encodes a precursor that, together with two other Brachyuran VTGs, forms a distinctive cluster within a phylogenetic tree of crustacean VTGs. Using quantitative RT-PCR, we found that VTG was primarily expressed in the hepatopancreas of a vitellogenic female, with minor expression in the ovary. VTG expression in the hepatopancreas correlated with ovarian growth, with a remarkable 8000-fold increase in expression from stage 3 to 4 of ovarian development. In contrast, the VTG levels in the hepatopancreas and hemolymph decreased in stage 4. Western blot analysis and N-terminal sequencing revealed that vitellin is composed of three subunits of approximately 78.5 kDa, 119.42 kDa, and 87.9 kDa. The processing pathway for VTG includes an initial hepatopancreatic cleavage of the primary precursor into approximately 78.5-kDa and 207.3-kDa subunits, both of which are found in the hemolymph. A second cleavage in the ovary splits the approximately 207.3-kDa subunit into approximately 119.4-kDa and approximately 87.9-kDa subunits. The hemolymph VTG profiles of mated and unmated females during ovarian development indicate that early vitellogenesis and ovarian development do not require mating, which may be essential for later stages, as VTG decreased to the basal level at stage 4 in the unmated group but remained high in the mated females. Our results encompass comprehensive overall temporal and spatial aspects of vitellogenesis, which may reflect the reproductive physiology of the female blue crab, e.g., single mating and anecdysis in adulthood.

Vertebrate Yolk Complexes and the Functional Implications of Phosvitins and Other Subdomains in Vitellogenins1

In nonplacental or nontrophotenic vertebrates, early development depends on the maternal provision of egg yolk, which is mainly derived from large multidomain vitellogenin (Vtg) precursors. To reveal the molecular nature of the protein pools in vertebrate oocytes, published data on the N-termini of yolk proteins has been mapped to the deduced primary structures of their parent Vtgs. The available evidence shows that the primary cleavage sites of Vtgs are conserved, whereas the cleavage products exist as multidomain variants in the yolk protein pool. The serine-rich phosvitin (Pv) domains are linearly related to the molecular masses of the lipovitellin heavy chain. The 3-D localization of Pv maps to the outer edges of the Vtg monomer, where it is proposed to form amphipathic structures that loop up over the lipid pocket. At this locus, it is proposed that Pv stabilizes the nascent Vtg while it receives its lipid cargo, thereby facilitating the hepatic loading and locking of lipid within the Vtg (C-sheet)-(A-sheet)-(LvL) cavity, and enhances its solubility following secretion to the circulating plasma. The C-terminal regions of Vtgs are homologous to human von Willebrand factor type D domains (Vwfd), which are conserved cysteine-rich molecules with homologous regions that are prevalent in Vtgs, lipophorins, mucins, integrins, and zonadhesins. Unlike human VWFD, lower vertebrate Vwfds do not contain RGD motifs, which are associated with extracellular matrix binding. Although its function in Vtg is unknown, the lubricant properties associated with mucins and the cell adhesion properties associated with integrins and zonadhesins implicate Vwfd in the genesis of hemostatic platelet aggregation. Similarly, the proteolytic inhibitory properties associated with the binding of factor VIII in humans suggest that Vwfd stabilizes Vtg during passage in the systemic circulation.

Characterization of vitellogenin in the shrimp Metapenaeus ensis: expression studies and hormonal regulation of MeVg1 transcription in vitro

During gonad maturation, female shrimp accumulate the major egg yolk protein vitellin (Vn) in premolt stage, and the process of molting and reproduction is synchronized. Using a polyclonal anti-Vn antibody, immunopositive signals could be detected in the ovary and among the proteins secreted by the hepatopancreas by Western blot. In the ovary, Vn immunoreactivity was located in the posterior lobe. Hepatopancreas proteins with sizes identical to ovary vitellogenin (Vg) subunits (i.e., 78 and 157 kDa) were immunoreactive to the Vn antibody and these proteins included amino acid sequences identical to parts of the MeVg1 precursor. A major 7.8 kb MeVg1 transcript, was detected in the ovary. In the hepatopancreas, the transcripts were primarily small (<2.3 kb) and while the 7.8 kb transcript which constitutes <50% of the total Vg mRNA. MeVg1 transcript could be detected in the hepatopancreas of juvenile females with a maximum level during late intermolt and early premolt. To study the effect of different hormones on expression of MeVg1, explant cultures of hepatopancreas and ovary were developed. Although several hormones (20-hydroxyecdysone, estradiol (ES), farnesoic acid (FA), juvenile hormone (JH) III, methyl farnesoate, and progesterone (PG)) apparently stimulated MeVg1 gene expression, only FA consistently stimulated MeVg1 expression by the hepatopancreas explants, while both FA and 20-hydroxyecdysone were stimulated ovarian explants. In summary, (i) Vg transcripts can be detected in both reproductive and nonreproductive females; (ii) the presence of large quantities of smaller Vg transcripts and the absence of a large Vg precursor from the hepatopancreas suggests that smaller MeVg1 transcripts provide an important contribution to Vg synthesis in shrimp. Our results suggest that there is differential processing of the MeVg1 precursor in the ovary and hepatopancreas of shrimp.

Vertebrate vitellogenin gene duplication in relation to the "3R hypothesis": correlation to the pelagic egg and the oceanic radiation of teleosts

The spiny ray-finned teleost fishes (Acanthomorpha) are the most successful group of vertebrates in terms of species diversity. Their meteoric radiation and speciation in the oceans during the late Cretaceous and Eocene epoch is unprecedented in vertebrate history, occurring in one third of the time for similar diversity to appear in the birds and mammals. The success of marine teleosts is even more remarkable considering their long freshwater ancestry, since it implies solving major physiological challenges when freely broadcasting their eggs in the hyper-osmotic conditions of seawater. Most extant marine teleosts spawn highly hydrated pelagic eggs, due to differential proteolysis of vitellogenin (Vtg)-derived yolk proteins. The maturational degradation of Vtg involves depolymerization of mainly the lipovitellin heavy chain (LvH) of one form of Vtg to generate a large pool of free amino acids (FAA 150-200 mM). This organic osmolyte pool drives hydration of the ooctye while still protected within the maternal ovary. In the present contribution, we have used Bayesian analysis to examine the evolution of vertebrate Vtg genes in relation to the "3R hypothesis" of whole genome duplication (WGD) and the functional end points of LvH degradation during oocyte maturation. We find that teleost Vtgs have experienced a post-R3 lineage-specific gene duplication to form paralogous clusters that correlate to the pelagic and benthic character of the eggs. Neo-functionalization allowed one paralogue to be proteolyzed to FAA driving hydration of the maturing oocytes, which pre-adapts them to the marine environment and causes them to float. The timing of these events matches the appearance of the Acanthomorpha in the fossil record. We discuss the significance of these adaptations in relation to ancestral physiological features, and propose that the neo-functionalization of duplicated Vtg genes was a key event in the evolution and success of the teleosts in the oceanic environment.

Endocrine disrupters with (anti)estrogenic and (anti)androgenic modes of action affecting reproductive biology of Xenopus laevis: I. Effects on sex steroid levels and biomarker expression

Adult Xenopus laevis were exposed in vivo to ethinylestradiol, tamoxifen, methyldihydrotestosterone and flutamide as (anti)estrogenic and (anti)androgenic compounds, respectively, for four weeks at a concentration of 10(-8) M and to Lambro river water, a polluted river from Italy. Effects of the treatments were analysed by mRNA expression of retinol-binding protein (RBP), transferrin (TF), transthyretin (TTR) and vitellogenin (VTG) in the liver of male and female X. laevis, to analyse the potential of these genes to detect endocrine disrupting compounds (EDC) with different modes of action. In addition, plasma VTG and sex steroid levels, estradiol-17beta (E(2)) and testosterone (T), were analysed. Sex steroids were depressed by ethinylestradiol in both sexes whereas tamoxifen increased E(2) in females. The induction of VTG protein plasma levels was more pronounced at the protein level compared to hepatic VTG mRNA expression in response to estrogenic treatment but VTG mRNA expression detected both, estrogenic and antiestrogenic EDC. The mRNA expression of TF was decreased by estrogenic and increased by antiestrogenic treatment while TTR mRNA expression was down-regulated and RBP mRNA up-regulated by estrogenic exposure. The other treatments did not affect the mRNA expression of the examined genes.

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.

Vitellogenesis in the red crab Charybdis feriatus: Hepatopancreas-specific expression and farnesoic acid stimulation of vitellogenin gene expression

Vitellogenesis in the mature female crab Charybdis feriatus occurs all year round during which active synthesis of the vitellogenin (Vg) precursor occurs. Several polypeptides from the ovaries were shown to be immuno-reactive to the shrimp vitellin (Vn) antibody. N-terminal amino acid sequence determination revealed that several ovarian polypeptides and one polypeptide secreted by the hepatopancreas were identical to part of the C. feriatus Vg (CfVg) precursor. The full-length cDNA sequence encoding a protein with high amino acid sequence similarity to the Vg of the shrimp Metapenaeus ensis was cloned. In common with the shrimp M. ensis MeVg2, the crab vitellogenin gene is expressed only in the hepatopancreas. The expression level of CfVg is undetectable in the non-reproductive females, increases to maximum at the middle stages of vitellogenesis and drops to a lower level in late vitellogenesis. Expression of CfVg also extended to females that are undergoing brooding of developing larvae. Although the 8 kb transcript for the full-length cDNA was detected, smaller transcripts specific to CfVg mRNA were also detected, suggesting the occurrence of alternative splicing/expression of the CgVg gene to produce the smaller transcripts. Using a short term in vitro hepatopancreas explant culture assay, we have demonstrated that low concentrations of farnesoic acid (FA) stimulate CfVg gene expression in the hepatopancreas. Although both methyl farnesoate (MF) and juvenile hormone III also caused up-regulation of the CfVg gene, their effects are only significant at much higher concentrations.

Derivation of major yolk proteins from parental vitellogenins and alternative processing during oocyte maturation in Fundulus heteroclitus

Various Coomassie blue-staining yolk proteins (YPs) present in oocytes and eggs of Fundulus heteroclitus, a teleost that produces low hydrated, demersal eggs (benthophil species), were subjected to N-terminal microsequencing. Four YPs were N-terminally blocked, while five yielded sequence information. Of the latter, four corresponded to internal sequences of vitellogenin 1 (Vg1), whereas a fifth band corresponded to the N-terminal sequence of Vg2. Phosphorylated YPs (phosvitins and phosvettes) derived from the polyserine domain of Vg were not successfully sequenced. The major N-terminally blocked 122-and 103-kDa YPs both represented the lipovitellin heavy chain of Vg1 (LvH1), and thus most of the oocyte YPs were derived from Vg1. During oocyte maturation in vivo and in vitro, the LvH1 122 is degraded, concomitant with an increased enzymatic activity of cathepsin B, while the 45-kDa YP is converted to a 42-kDa YP. The LvH1 122 was found to contain a consensus site for proteolytic degradation (PEST) near its C-terminus, which is missing from its stable, but truncated twin sequence, LvH1 103. We suggest that this site becomes exposed to cathepsin B during the hydration process that accompanies oocyte maturation and renders the LvH1 122 susceptible to proteolysis. PEST sites are found in Vg sequences from other benthophil fish, whereas, interestingly, they are missing in marine teleosts that spawn highly hydrated, pelagic eggs (pelagophil species), displaying a different pattern of Vg incorporation into YPs and LvH1 and LvH2 processing to that found in F. heteroclitus. Thus, different models of Vg/YP precursor/product relationship and further processing during oocyte maturation and hydration are proposed for pelagophil and benthophil teleosts.

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.

Molecular analysis of a major soluble egg protein in the scleractinian coral Favites chinensis

Soluble proteins were extracted from eggs of the scleractinian coral Favites chinensis, and analyzed using SDS-polyacrylamide gel electrophoresis. Two major proteins, named FcEP-1 and 2, were detected, and two partial amino acid sequences of FcEP-1 were determined. A cDNA encoding FcEP-1 was identified, using reverse transcription PCR with degenerate oligonucleotide primers designed based on the amino acid sequences, and rapid amplification of cDNA ends. Upon translation of the cDNA, FcEP-1 was predicted to consist of 648 amino acids, and the protein sequence exhibited similarity to vertebrate and invertebrate vitellogenins. FcEP-1 transcripts were already present approximately 6 months before spawning, when the size of oocytes was approximately 1/60 of the mature egg, and could be detected throughout the vitellogenic period. These observations suggest that detection of FcEP-1 transcripts may be useful to monitor the vitellogenic activity in F. chinensis.

Multihormonal control of vitellogenesis in lower vertebrates

The comparative approach on how and when vitellogenesis occurs in the diverse reproductive strategies displayed by aquatic and terrestrial lower vertebrates is presented in this chapter; moreover, attention has been paid to the multihormonal control of hepatic vitellogenin synthesis as it is related to seasonal changes and to vitellogenin use by growing oocytes. The hormonal mechanisms regulating vitellogenin synthesis are also considered, and the effects of environmental estrogens on the feminization process in wildlife and humans have been reported. It is then considered how fundamental nonmammalian models appear to be, for vitellogenesis research, addressed to clarifying the yolkless egg and the evolution of eutherian viviparity.

Mr 25 000 protein, a substrate for protein serine/threonine kinases, is identified as a part of Xenopus laevis vitellogenin B1

A phosphorylated protein with a molecular mass of 25 000 (pp25) previously purified from the cytosolic fraction of Xenopus laevis oocytes is an effective phosphate acceptor for casein kinases and protein kinase C. In this study, based on the partial amino acid sequence of pp25, a cDNA was isolated that encodes a new yolk precursor protein, Xenopus vitellogenin B1, which contained the sequence encoding pp25. Both mRNA and protein of vitellogenin B1 were expressed in all of the female organs examined. In agreement with a previous report, the amount of vitellogenin B1 protein in the liver increased after stimulation with estrogen. These results suggest that pp25 is a cytosolic non-crystallized yolk protein nutrient source, but it might also play a role in rapid development.

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.

Organization of the shrimp vitellogenin gene: evidence of multiple genes and tissue specific expression by the ovary and hepatopancreas

Vitellogenin is the major egg yolk protein synthesized in female shrimp during gonad maturation. Although there are several reports for the cloning of vitellogenin complementary DNA (cDNA) in different crustaceans, little is known of the gene organization of this protein. This study reports the first cloning and characterization of a full-length gene encoding the vitellogenin precursor from the shrimp Metapenaeus ensis. By genomic DNA library screening, six different lambda clones were isolated using shrimp partial gene sequence as probe. Initial DNA sequence determination revealed that these clones are derived from different genes with coding sequence similar to other crustacean vitellogenins. Two of these clones were used for further analysis. One of the lambda clones (lambda 3.3) carries most of the coding sequence that correspond to the M. ensis vitellogenin gene (MeVg1) and the other clone (lambda 8.3) carries a smaller portion of the coding sequence of a different vitellogenin gene (MeVg2). The lambda 3.3 clone was chosen for further characterization. To clone the remaining 5' end upstream promoter region, 5' untranslated region and the remaining coding sequence of MeVg1, a polymerase chain reaction (PCR)-based gene walking approach was used. Subsequently, a PCR clone with overlapping sequence identical to the genomic clone was obtained and the organization of MeVg1 gene was constructed. The MeVg1 gene consists of 15 exons and 14 introns spanning approximately 10 kb. Several potential cleavage sites were identified from the deduced vitellogenin precursor. Cleaving of the precursor in these sites would result in the production of several vitellogenin subunits. To clone the cDNA for the vitellogenin, 5' and 3' rapid amplification of cDNA ends was performed using ovary cDNA of the shrimp. A 4.4 kb 5' cDNA clone and a 4 kb 3' end cDNA clone were isolated. The size of the reconstructed cDNA for M. ensis Vg is 7.97 kb and consists of the longest open reading frame of 7776 bp. Unlike the vitellogenin precursor of most insects and vertebrates, the deduced vitellogenin precursor lacks the polyserine domain important for receptor-mediated endocytosis. Phylogenetic analysis revealed a closer relationship of the MeVg1 with other crustacean vitellogenins but distantly related to other invertebrate and vertebrate vitellogenins. By reverse transcription-PCR, we have demonstrated that the shrimp MeVg1 gene is expressed only in the ovary and hepatopancreas while the MeVg2 gene is expressed exclusively in the hepatopancreas. In conclusion, the shrimp ovary also contribute significantly in the production of vitellogenin at transcription level and the gene organization of the shrimp protein may provide an insight in the evolution of this group of important proteins.

Lipovitellins and phosvitins of the fertilized eggs during embryo growth in the oviparous lizard Podarcis sicula

In the lizard Podarcis sicula, the major vitellogenin (VTG)-derived yolk proteins, lipovitellins and phosvitins, were extracted from the yolk globules of laid and fertilized eggs at different periods of incubation up to 44 days close to hatching. Embryonic development was almost over at this time. Yolk proteins were isolated by precipitation in saturated (NH(4))(2)SO(4), separated on SDS-PAGE and detected by Western blotting with homologous polyclonal anti/VTG antibody. Two lipovitellins of 110 and 116 kDa were always present in the yolk of laid eggs after 1, 10, 18, and 44 days from oviposition. Both these proteins were glycosylated and were recognized by the anti/VTG antibody; their N-terminal sequences were analyzed. Four phosvitins were detected in freshly laid eggs, but their number decreased during incubation, and after 44 days only a single protein of approximately 6.5 kDa was present. The results indicated that, in this lizard, during embryonic development, lipovitellins remain unchanged, whereas the phosphorylated components of yolk undergo continuous degradation.

Regulation of pathways of mRNA destabilization and stabilization

The level of an mRNA in the cytoplasm represents a balance between the rate at which the mRNA precursor is synthesized in the nucleus and the rates of nuclear RNA processing and export and cytoplasmic mRNA degradation. Although most studies of gene expression have focused on gene transcription and in the area of eukaryotic mRNA degradation, but to provide a short general discussion of the importance of mRNA degradation and its regulation and a brief overview of recent findings and present knowledge. The overview is followed by a more in-depth discussion of one of the several pathways for mRNA degradation. We concentrate on the pathway for regulated mRNA degradation mediated by mRNA-binding proteins and endonucleases that cleave within the body of mRNAs. As a potential example of this type of control, we focus on the regulated degradation of the egg yolk precursor protein vitellogenin on the mRNA-binding protein vigilin and the mRNA endonuclease polysomal ribonuclease 1 (PMR-1).

Vitellogenin-derived yolk proteins of white perch, Morone americana: purification, characterization, and vitellogenin-receptor binding

The objectives of this study were to 1) purify and characterize vitellogenin-derived yolk proteins of white perch (Morone americana), 2) develop a nonisotopic receptor binding assay for vitellogenin, and 3) identify the yolk protein domains of vitellogenin recognized by the ovarian vitellogenin receptor. Four yolk proteins derived from vitellogenin (YP1, YP2 monomer [YP2m] and dimer [YP2d], and YP3) were isolated from ovaries of vitellogenic perch by selective precipitation, ion exchange chromatography, and gel filtration. The apparent molecular masses of purified YP1, YP2m, and YP2d after gel filtration were 310 kDa, 17 kDa, and 27 kDa, respectively. YP3 appeared in SDS-PAGE as a approximately 20-kDa band plus some diffuse smaller bands that could be visualized by staining for phosphoprotein with Coomassie Brilliant Blue complexed with aluminum nitrate. Immunological and biochemical characteristics of YP1, YP2s, and YP3 identified them as white perch lipovitellin, beta'-components, and phosvitin, respectively. A novel receptor-binding assay for vitellogenin was developed based on digoxigenin (DIG)-labeled vitellogenin tracer binding to ovarian membrane proteins immobilized in 96-well plates. Lipovitellin from white perch and vitellogenin from perch and other teleosts effectively displaced specifically bound DIG-vitellogenin in the assay, but phosvitin and the beta'-component could not, demonstrating for the first time that the lipovitellin domain of teleost vitellogenin mediates its binding to the oocyte receptor. Lipovitellin was less effective than vitellogenin in this regard, suggesting that the remaining yolk protein domains of vitellogenin may interact with its lipovitellin domain to facilitate binding of vitellogenin to its receptor.

Immunodissection of yolk lipovitellin (LV1) demonstrates the existence of different LV1-domains and suggests a complex family of vitellogenin genes in the lizard Anolis pulchellus

In the tropical lizard Anolis pulchellus vitellogenin (Vtg), the plasma precursor of egg-yolk proteins, consists of a family of five polypeptides ranging between 116 and 226 kDa. In addition, lipovitellin-LV1, the main yolk protein, resolves electrophoretically into several forms. This suggests that yolk LV1 is a mixture of similar but distinct peptides that presumably correspond to the LV1 domains of the plasma Vtgs. Here, we test the hypothesis that each component of yolk LV1 is distinct enough to be antigenically different and that these components correspond to cleavage products of plasma Vtg polypeptides. Our experimental approach is based on adsorptions of a polyclonal antiserum against purified LV1 with membrane-immobilized Vtgs. This immunochemical design permitted us to dissect sub-populations of LV1 antibodies that specifically reacted with one of the plasma Vtgs. The presence of unique epitopes in the LV1 components directly indicates differences among the structures of their plasma Vtg precursors and supports the idea of a heterogeneous multigene Vtg family in Anolis. These results also show the potential of this immunoadsorption approach for the identification, and even separation of proteins sharing a high degree of similarity in their molecular structures.

Changes in hepatic vitellogenin mRNA levels during oocyte development in the Japanese eel, Anguilla japonica

The induction of vitellogenesis is a complex process requiring coordinated control and expression of many hepatic gene products, such as vitellogenin (VTG). To investigate the regulation of VTG synthesis, knowledge of the molecular genetics of VTG is required. Here, the authors have isolated a partial cDNA encoding Japanese eel VTG using an immunoscreening technique. This cDNA contained an open reading frame of 1629 bp, predicted to encode 543 amino acid residues, the sequence of which showed high homology with the VTG of other fishes. Northern blot analysis yielded a VTG transcript of approximately 5.8 kb from eel hepatic tissue. Experimentally, VTG synthesis could be induced by treatment with salmon pituitary homogenate. The levels of VTG mRNA in the liver during the artificial maturation of female Japanese eels correspond well to levels of E2 and VTG in the serum.

Measurement of vitellogenin gene expression by RT-PCR as a tool to identify endocrine disruption in Japanese medaka (Oryzias latipes)

In order to monitor vitellogenin gene expression in the Japanese medaka (Oryzias latipes), a reverse transcription-polymerase chain reaction (RT-PCR) system was developed. To date cDNA for medaka vitellogenin has not been published; therefore, initially a sequence fragment had to be obtained and compared with other known vertebrate vitellogenins. For this, a 1.2 kb cDNA of medaka vitellogenin (M-Vg1.2) was amplified by RT-PCR and cloned into a pCRR H-TOPO bacterial vector. On Northern blot analysis, the antisense cRNA of M-Vg1.2 stained a 5.5 kb gene product found exclusively in female fish, but not in males. Additionally, the 5'-end of medaka vitellogenin cDNA was amplified by 5'-RACE-PCR. The analysed nucleotide sequence of 1.6 kb shared significant similarities with vitellogenins known from other fish species: approximately 72% similarity with mummichog (Fundulus heteroclitus) vitellogenin I and approximately 62% with fathead minnow (Pimephales promelas) vitellogenin. To develop a semiquantitative RT-PCR for the measurement of vitellogenin gene expression, primers specific to a 500 bp sequence of the vitellogenin cDNA (M-Vg0.5) were constructed using the gene product of elongation factor 1 alpha as internal standard. Induction of vitellogenin gene expression was measured in male medaka exposed to 0, 2, 20 and 50 micrograms l-1 nonylphenol and 0, 2.5, 25 and 100 ng l-1 17 alpha-ethinyloestradiol for 7 days. The LOECs for vitellogenin induction in male medaka were 20 micrograms l-1 and 25 ng l-1 for nonylphenol and 17 alpha-ethinyloestradiol, respectively.

Development of an ELISA for vitellogenin in whole body homogenate of zebrafish (Danio rerio)

The yolk protein, lipovitellin (Lv) was purified from ovaries of mature female zebrafish (Danio rerio) by gel filtration and anion exchange chromatography. Polyclonal antibodies against Lv were raised in rabbits. Anti-Lv IgG was purified by affinity chromatography. SDS-PAGE followed by Western blotting was performed to analyse the specificity of the antibody and the immunological similarities between Lv and vitellogenin (Vtg). Anti-Lv IgG was used to develop a direct non-competitive sandwich ELISA to measure Vtg concentrations of whole body homogenate (WBH) in zebrafish. The intra- and interassay variabilities were 5.8% and 10.4%, respectively. The sensitivity was 0.2 ng Vtg x ml(-1) and the practical detection limit was 40 ng Vtg x g(-1) fish (wet weight). Adult male zebrafish were exposed to a nominal water concentration of 10 ng x l(-1) of ethinylestradiol (EE2) in a semi-static exposure system for 7 days. Compared with the control group, exposure to 10 ng EE2 x l(-1) induced a 200-fold increase in Vtg levels.

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.

Wee1-regulated apoptosis mediated by the crk adaptor protein in Xenopus egg extracts

Many of the biochemical reactions of apoptotic cell death, including mitochondrial cytochrome c release and caspase activation, can be reconstituted in cell-free extracts derived from Xenopus eggs. In addition, because caspase activation does not occur until the egg extract has been incubated for several hours on the bench, upstream signaling processes occurring before full apoptosis are rendered accessible to biochemical manipulation. We reported previously that the adaptor protein Crk is required for apoptotic signaling in egg extracts (Evans, E.K., W. Lu, S.L. Strum, B.J. Mayer, and S. Kornbluth. 1997. EMBO (Eur. Mol. Biol. Organ.) J. 16:230-241). Moreover, we demonstrated that removal of Crk Src homology (SH)2 or SH3 interactors from the extracts prevented apoptosis. We now report the finding that the relevant Crk SH2-interacting protein, important for apoptotic signaling in the extract, is the well-known cell cycle regulator, Wee1. We have demonstrated a specific interaction between tyrosine-phosphorylated Wee1 and the Crk SH2 domain and have shown that recombinant Wee1 can restore apoptosis to an extract depleted of SH2 interactors. Moreover, exogenous Wee1 accelerated apoptosis in egg extracts, and this acceleration was largely dependent on the presence of endogenous Crk protein. As other Cdk inhibitors, such as roscovitine and Myt1, did not act like Wee1 to accelerate apoptosis, we propose that Wee1-Crk complexes signal in a novel apoptotic pathway, which may be unrelated to Wee1's role as a cell cycle regulator.

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.

Isolation and characterization of bone morphogenetic protein-binding proteins from the early Xenopus embryo

Using a surface plasmon resonance biosensor as a sensitive and specific monitor, we have isolated two distinct bone morphogenetic protein (BMP)-binding proteins, and identified them as lipovitellin 1 and Ep45, respectively. Lipovitellin 1 is an egg yolk protein that is processed from vitellogenin. Both vitellogenin and Ep45 are synthesized under estrogen control in the liver, secreted, and taken up by developing oocytes. In this paper, we have shown that of the TGF-beta family members tested, Ep45 can bind only to BMP-4, whereas lipovitellin 1 can bind to both BMP-4 and activin A. Because of this difference in specificity, we have focused on and further studied Ep45. Kinetic parameters were determined by surface plasmon resonance studies and showed that Ep45 associated rapidly with BMP-4 (k(a) = 1.06 x 10(4) M(-1)s(-1)) and dissociated slowly (k(d) = 1.6 x 10(-4) s(-1)). In Xenopus embryos microinjected with Ep45 mRNA, Ep45 blocked the ability of follistatin to inhibit BMP activity and to induce a secondary body axis in a dose-dependent manner, whereas it had no effect on other BMP antagonists, chordin and noggin. These results support the possibility that Ep45 interacts with BMP to modulate its activities in vivo.

Two forms of vitellogenin, yielding two distinct lipovitellins, play different roles during oocyte maturation and early development of barfin flounder, Verasper moseri, a marine teleost that spawns pelagic eggs

Two forms of vitellogenin (Vg), Vg A and Vg B, were identified in serum from estrogen-treated barfin flounder (Verasper moseri). Structural changes of lipovitellins (Lvs) derived from the two Vgs were examined during vitellogenesis and oocyte maturation. Two Lvs, vLv A and vLv B, were identified electrophoretically and immunologically in postvitellogenic oocytes. Each appeared to be composed of distinct heavy chains (vLvH A, M(r) 107,000, and vLvH B, M(r) 94,000) and light chains (vLvL A, M(r) 30,000, and vLvL B, M(r) 28,000) when analyzed by SDS-PAGE. Results from N-terminal amino acid sequencing and Western blotting using antisera to vLvH A and vLvH B verified that there are two Vg polypeptides in serum from estrogen-treated fish, Vg A (M(r) 168,000) and Vg B (M(r) 175,000), which give rise to vLvH A-vLvL A and vLvH B-vLvL B, respectively. N-terminal sequencing revealed two sequences for both phosvitin and beta'-component, supporting the concept of duality for all three classes of Vg-derived yolk proteins. During oocyte maturation, native dimeric vLv B was dissociated into a native M(r) 170,000 monomer (oLv B). Meanwhile, vLv A was extensively cleaved including complete degradation of vLvH A into free amino acids. We propose that the quantitative ratio of vLv A to vLv B in postvitellogenic oocytes regulates the buoyancy of the spawned pelagic eggs by controlling availability of free amino acids which function as osmotic effectors during oocyte hydration. The vLv A/vLv B ratio likely also controls the proportional availability of different types of nutrients, free amino acids versus Lv, for use during embryonic development.

A common binding site on the microsomal triglyceride transfer protein for apolipoprotein B and protein disulfide isomerase

The assembly of triglyceride-rich lipoproteins requires the formation in the endoplasmic reticulum of a complex between apolipoprotein B (apoB), a microsomal triglyceride transfer protein (MTP), and protein disulfide isomerase (PDI). In the MTP complex, the amino-terminal region of MTP (residues 22-303) interacts with the amino-terminal region of apoB (residues 1-264). Here, we report the identification and characterization of a site on apoB between residues 512 and 721, which interacts with residues 517-603 of MTP. PDI binds in close proximity to this apoB binding site on MTP. The proximity of these binding sites on MTP for PDI and amino acids 512-721 of apoB was evident from studies carried out in a yeast two-hybrid system and by co-immunoprecipitation. The expression of PDI with MTP and apoB16 (residues 1-721) in the baculovirus expression system reduced the amount of MTP co-immunoprecipitated with apoB by 73%. The interaction of residues 512-721 of apoB with MTP facilitates lipoprotein production. Mutations of apoB that markedly reduced this interaction also reduced the level of apoB-containing lipoprotein secretion.

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.