Purification, characterization and immunoassay of striped bass (Morone saxatilis) vitellogenin

Structural modeling and gene expression analysis of phosvitinless vitellogenin (vgc) in the Indian freshwater murrel, Channa punctatus (Bloch, 1793)

Vitellogenin (Vg) is a female-specific egg-yolk precursor protein, synthesized in the liver of fish in response to estrogens. In the present study, complete gene of phosvitinless vitellogenin (vgc) was sequenced, its 3D structure was predicted and validated by web-based softwares. The complete nucleotide sequence of vgc was 4126 bp which encodes for 1272 amino acids and showed the presence of three conserved domains viz. LPD_N, DUF1943 and DUF1944. The retrieved amino acid sequence of VgC protein was subjected to in silico analysis for understanding the structural and functional properties of protein. mRNA levels of multiple vg genes have also been quantified during annual reproductive cycle employing qPCR. A correlation has been observed between seasonal changes in gonadosomatic index with estradiol levels and hepatic expression of three types of vg genes (vga, vgb, vgc) during ovarian cycle of murrel. During preparatory phase, when photoperiod and temperature are low; low titre of E2 in blood induces expression of vgc gene. A rapid increase in the levels of E2 favours induction of vgb and vga genes in liver of murrel during early pre-spawning phase when photoperiod is long and temperature is high in nature. These results suggest that among three vitellogenin proteins, VgC is synthesized earlier than VgA and VgB during oogenesis.

Estrogen-induced yolk precursors in European sea bass, Dicentrarchus labrax: Status and perspectives on multiplicity and functioning of vitellogenins

The estrogen-inducible egg yolk precursor, vitellogenin, of the European sea bass (Dicentrarchus labrax) has received considerable scientific attention by virtue of its central importance in determination of oocyte growth and egg quality in this important aquaculture species. However, the multiplicity of vitellogenins in the sea bass has only recently been examined. Recent cloning and homology analyses have revealed that the sea bass possesses the three forms of vitellogenin, VtgAa, VtgAb and VtgC, reported to occur in some other highly evolved teleosts. Progress has been made in assessing the relative abundance and special structural features of the three Vtgs and their likely roles in oocyte maturation and embryonic nutrition. This report discusses these findings in the context of our prior knowledge of vitellogenesis in this species and of the latest advances in our understanding of the evolution and function of multiple Vtgs in acanthomorph fishes.

Multiple vitellogenins and product yolk proteins in striped bass, Morone saxatilis: molecular characterization and processing during oocyte growth and maturation

The multiple vitellogenin (Vtg) system of striped bass, a perciform species spawning nearly neutrally buoyant eggs in freshwater, was investigated. Vitellogenin cDNA cloning, Western blotting of yolk proteins (YPs) using Vtg and YP type-specific antisera, and tandem mass spectrometry (MS/MS) of the YPs revealed the complex mechanisms of yolk formation and maturation in this species. It was discovered that striped bass possesses a tripartite Vtg system (VtgAa, VtgAb, and VtgC) in which all three forms of Vtg make a substantial contribution to the yolk. The production of Vtg-derived YPs is generally similar to that described for other perciforms. However, novel amino-terminal labeling of oocyte YPs prior to MS/MS identified multiple alternative sites for cleavage of these proteins from their parent Vtg, revealing a YP mixture far more complex than reported previously. This approach also revealed that the major YP product of each form of striped bass Vtg, lipovitellin heavy chain (LvH), undergoes limited degradation to smaller polypeptides during oocyte maturation, unlike the case in marine fishes spawning buoyant eggs in which LvHAa undergoes extensive proteolysis to osmotically active free amino acids. These differences likely reflect the lesser need for hydration of pelagic eggs spawned in freshwater. The detailed characterization of Vtgs and their proteolytic fate(s) during oocyte growth and maturation establishes striped bass as a freshwater model for investigating teleost multiple Vtg systems.

Purification and partial characterization of vitellogenin from spotted wolffish (Anarhichas minor) and development of an enzyme-linked immunosorbent assay for the determination of gender and sexual maturity

Vitellogenin (VTG) from spotted wolffish, Anarhichas minor, a candidate species for cold-water marine aquaculture, was purified by MgCl₂/EDTA precipitation followed by a two-step chromatographic procedure. VTG had an apparent molecular mass of 470 kDa, as determined by gel filtration, and an amino acid composition similar to those of other teleosts. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the purified VTG revealed a major band with a relative molecular weight of 166 kDa and some minor bands. Spotted wolffish VTG (sw-VTG) is relatively robust to in vitro degradation, as shown when samples of purified VTG and plasma from mature females subjected to various storage conditions or multiple freeze/thaw cycles were analyzed by Western blot. We developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) using an antibody against Atlantic wolffish (Anarhichas lupus) VTG and purified sw-VTG. The ELISA had a detection limit of 6.7 ng/ml and a working range of 16.2-787.5 ng/ml, with intra- and inter-assay coefficients of variation ranging from 1.5 to 7.3 % and 7.1 to 14.3 %, respectively. The assay could distinguish males from immature females and discriminate maturing females at different stage of oocyte development. These results suggest that the sw-VTG ELISA would be useful in spotted wolffish aquaculture to determine sex and monitor female maturation.

Isolation and partial characterization of Asian sea bass (Lates calcarifer) Vitellogenin

A study was conducted to isolate, partial characterize Asian sea bass (Lates calcarifer) vitellogenin (vtg). Two-year-old juvenile L. calcarifer (n = 10) were given three intraperitoneal injections of 17-β estradiol (E2) at a dose of 2 mg/kg body weight to induce vitellogenesis. Blood was collected 3 days after the last injection, and plasma was purified through gel filtration chromatography. A broad single symmetrical peak consisting of vtg molecule was produced. Protein concentration was 0.059 mg/ml as determined by Bradfrod assay using bovine serum albumin as a standard. The protein appeared as one circulating form in Native PAGE considering the dimeric form of putative vtg with molecular weight of 545 kDa. In SDS-PAGE under reducing conditions, two major bands appeared at 232.86 and 118.80 kDa and minor bands at 100.60, 85.80 and 39.92 kDa, respectively. The purified vtg was used to generate a polyclonal antibody, and the specificity of antibody was assessed by Western blot analysis. Two major bands were immunoreacted, but no cross-reactivity was observed with plasma from non-induced males. The protein was characterized as phosphoglycolipoprotein as it positively stained for the presence of lipid, phosphorus and carbohydrate using Sudan Black B, methyl green and periodic acid/Schiff reagent solution, respectively. The amino acid composition was analyzed by high sensitivity amino acid analysis that showed high percentage of non-polar amino acids (~48 %). The results suggest the potential utilization of vtg as a basis tool to further study about reproductive physiology of this important economical species.

Characterization of vitellogenin and its derived yolk proteins in cloudy catshark (Scyliorhinus torazame)

Elasmobranchs (sharks and rays) exhibit unique reproductive characteristics and, in contrast to the situation in teleosts, very little is known about the identity, structure and physical characteristics of their egg yolk proteins. The aims of this study were to (1) detect and purify the vitellogenin (Vtg; egg yolk precursor) and yolk proteins (YPs) of the cloudy catshark (Scyliorhinus torazame), (2) examine the relationships between Vtg and YPs and (3) characterize and classify the deduced primary structure of the Vtg transcript (vtg). The apparent molecular weights of purified Vtg and putative Vtg-related YPs (lipovitellin: Lv, phosvitin: Pv) were determined by gel filtration and were ~560, >669 and ~58 kDa, respectively. Following SDS-PAGE, these purified products (i.e., Vtg, Lv and Pv) appeared as bands of ~210, ~110 and ~22 kDa, respectively. On Western blots, antisera against purified Vtg, Lv and Pv recognized the ~210 kDa Vtg band. Catshark Pv, in contrast to teleost Pvs, had a very low serine content. The catshark Vtg cDNA sequence (vtg) appeared to contain an open-reading frame consisting of domains encoding Lv, Pv and β'-component (β'-c). A phylogenetic analysis, with a consideration of genome duplication events, placed catshark vtg into the 'vtgAB type.' It is concluded that at least a single major type of Vtg protein, which is transcribed and translated from catshark vtgAB gene, is the precursor of three egg yolk proteins (Lv, Pv and β'-c) in catshark.

An ovary transcriptome for all maturational stages of the striped bass (Morone saxatilis), a highly advanced perciform fish

Background

The striped bass and its relatives (genus Morone) are important fisheries and aquaculture species native to estuaries and rivers of the Atlantic coast and Gulf of Mexico in North America. To open avenues of gene expression research on reproduction and breeding of striped bass, we generated a collection of expressed sequence tags (ESTs) from a complementary DNA (cDNA) library representative of their ovarian transcriptome.

Results

Sequences of a total of 230,151 ESTs (51,259,448 bp) were acquired by Roche 454 pyrosequencing of cDNA pooled from ovarian tissues obtained at all stages of oocyte growth, at ovulation (eggs), and during preovulatory atresia. Quality filtering of ESTs allowed assembly of 11,208 high-quality contigs ≥ 100 bp, including 2,984 contigs 500 bp or longer (average length 895 bp). Blastx comparisons revealed 5,482 gene orthologues (E-value < 10^-3), of which 4,120 (36.7% of total contigs) were annotated with Gene Ontology terms (E-value < 10^-6). There were 5,726 remaining unknown unique sequences (51.1% of total contigs). All of the high-quality EST sequences are available in the National Center for Biotechnology Information (NCBI) Short Read Archive (GenBank: SRX007394). Informative contigs were considered to be abundant if they were assembled from groups of ESTs comprising ≥ 0.15% of the total short read sequences (≥ 345 reads/contig). Approximately 52.5% of these abundant contigs were predicted to have predominant ovary expression through digital differential display in silico comparisons to zebrafish (Danio rerio) UniGene orthologues. Over 1,300 Gene Ontology terms from Biological Process classes of Reproduction, Reproductive process, and Developmental process were assigned to this collection of annotated contigs.

Conclusions

This first large reference sequence database available for the ecologically and economically important temperate basses (genus Morone) provides a foundation for gene expression studies in these species. The predicted predominance of ovary gene expression and assignment of directly relevant Gene Ontology classes suggests a powerful utility of this dataset for analysis of ovarian gene expression related to fundamental questions of oogenesis. Additionally, a high definition Agilent 60-mer oligo ovary 'UniClone' microarray with 8 × 15,000 probe format has been designed based on this striped bass transcriptome (eArray Group: Striper Group, Design ID: 029004).

Purification and partial characterization of vitellogenin from shorthead redhorse (Moxostoma macrolepidotum) and copper redhorse (Moxostoma hubbsi) and detection in plasma and mucus with a heterologous antibody

Vitellogenin (VTG), the egg yolk precursor protein, was purified from plasma of estradiol-3-benzoate (E2B)-treated male shorthead redhorse (Moxostoma macrolepidotum) and immature copper redhorse (Moxostoma hubbsi) by a two-step chromatographic procedure without precipitation. Intact VTGs appeared as dimers with apparent molecular masses, determined by gel filtration, of approximately 425 kDa (copper redhorse) and approximately 450 kDa (shorthead redhorse). In native polyacrylamide gel electrophoresis (PAGE), dimeric redhorse VTGs appeared as a 520 kDa band. Both VTGs were reduced to a single monomer of approximately 150 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and nonreducing conditions, indicating that monomers are not linked by disulfide bonds in the dimer form. The purified proteins were characterized as phospholipoglycoproteins. Isoelectric focusing of both VTGs revealed components with isoelectric points ranging from 5.3 to 6.0, suggesting charge heterogeneity. The amino acid composition of both VTGs contains a high proportion of nonpolar amino acids and was similar to those of other teleosts. An antibody developed against carp (Cyprinus carpio) VTG showed cross-reactivity with VTG from both redhorse species. Using this antibody, VTG was detected in plasma and surface mucus of E2B-treated redhorse. This is the most extensive report on purification and characterization of vitellogenin from catostomidid species.

Quantification of Greenland halibut serum vitellogenin: a trip from the deep sea to the mass spectrometer

This paper focuses on the sequential steps involved in developing a technique for quantifying Greenland halibut vitellogenin, a serum protein biomarker, using a comprehensive mass spectrometric approach. In the first phase of this study, in-gel trypsin digestions of serum proteins separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A characteristic band around a molecular mass of 185 kDa, present in the mature female specimens, but absent in the male samples, was identified as vitellognin according to the peptide mass fingerprint obtained by MALDI-MS. Subsequently, MALDI and electrospray ionization tandem mass spectrometry (ESI-MS/MS) analyses were performed on the digest of the vitellogenin band for de novo sequencing. From these studies, a characteristic 'signature' peptide (sequence: FFGQEIAFANIDK) was selected from a list of candidate peptides as a surrogate analytical standard used for quantification purposes. Sample preparation for vitellogenin quantification consisted of a simple one-step overnight trypsin digestion. Samples were spiked with an isotopologue signature peptide standard and analyzed by high-performance liquid chromatography (HPLC) coupled in-line to an electrospray quadrupole-hexapole-quadrupole tandem mass spectrometer, operated in selective reaction monitoring mode. Transitions [(m/z 750.0 --> 1020.4 and 750.0 --> 1205.4) and (754.8 --> 1028.6 and 754.8 --> 1213.2)] were monitored for the signature peptide and the internal standard, respectively. Samples obtained from the field showed that vitellogenin levels were in accordance with fish maturity determined by macroscopic examination of the gonad, proving this technique suitable for measuring vitellogenin as a serum protein biomarker for reproductive maturity in female fish.

Conserved and variant molecular and functional features of multiple egg yolk precursor proteins (vitellogenins) in white perch (Morone americana) and other teleosts

Three complete cDNAs encoding different forms of vitellogenin (Vtg) were isolated from a white perch (Morone americana) liver cDNA library and characterized with respect to immunobiochemical and functional features of the three Vtgs and their product yolk proteins (YPs) in this species and in the congeneric striped bass (Morone saxatilis). The two longest cDNAs encoded Vtgs with a complete suite of yolk protein domains that, based on comparisons with vtg sequences from other species, were categorized as VtgAa and VtgAb using the current nomenclature for multiple teleost Vtgs. The shorter cDNA encoded a Vtg that lacked a phosvitin domain, had a shortened C-terminus, and was categorized as VtgC. Mapping of peptide sequences from the purified Vtgs and their derived YPs to Vtg sequences deduced from the cDNAs definitively identified the white perch VtgAa, VtgAb, and VtgC proteins. Detailed comparisons of the primary structures of each Vtg with partial or complete sequences of Morone yolk proteins or of Vtgs from other fishes revealed conserved and variant structural elements of teleost Vtgs with functional significance, including, as examples, signal peptide cleavage sites, dimerization sites, cathepsin D protease recognition sites, and receptor-binding domains. These comparisons also yielded an interim revision of the classification scheme for multiple teleost Vtgs.

Induction and partial characterization of California halibut (Paralichthys californicus) vitellogenin

The egg yolk precursor protein, vitellogenin (Vg), was isolated by size exclusion and ion exchange chromatography from plasma of California halibut (Paralichthys californicus) treated with estrogen. MALDI TOF mass spectrometry (MS) analysis resulted in a molecular mass of 188 kDa. MS/MS de novo sequencing identified the protein as Vg by matching sequences of tryptic peptides to the known sequences of several other species. Matches were also made to two different forms of Vg in haddock, medaka, and mummichog, providing evidence that California halibut has more than one form of Vg. Native PAGE and Western blot with an antibody to turbot (Scophthalmus maximus) Vg confirmed the identity of the protein. Protein resolved on the SDS PAGE as a double band of approximately the same mass as determined with MALDI TOF, and two lower mass bands that were also immunoreactive. MALDI TOF and MS/MS de novo sequencing were useful for determining the molecular mass, identification, and exploring the multiplicity of Vg. The potential of using other MS methods to understand the structure and function of Vg is discussed.

Cytochrome P450 aromatase in grey mullet: cDNA and promoter isolation; brain, pituitary and ovarian expression during puberty

In a study towards elucidating the role of aromatases during puberty in female grey mullet, the cDNAs of the brain (muCyp19b) and ovarian (muCyp19a) aromatase were isolated by RT-PCR and their relative expression levels were determined by quantitative real-time RT-PCR. The muCyp19a ORF of 1515bp encoded 505 predicted amino acid residues, while that of muCyp19b was 1485 bp and encoded 495 predicted amino acid residues. The expression level of muCyp19b significantly increased in the brain as puberty advanced; however, its expression level in the pituitary increased only slightly with pubertal development. In the ovary, the muCyp19a expression level markedly increased as puberty progressed. The promoter regions of the two genes were also isolated and their functionality evaluated in vitro using luciferase as the reporter gene. The muCyp19a promoter sequence (650 bp) contained a consensus TATA box and putative transcription factor binding sites, including two half EREs, an SF-1, an AhR/Arnt, a PR and two GATA-3 s. The muCyp19b promoter sequence (2500 bp) showed consensus TATA and CCAAT boxes and putative transcription binding sites, namely: a PR, an ERE, a half ERE, a SP-1, two GATA-binding factor, one half GATA-1, two C/EBPs, a GRE, a NFkappaB, three STATs, a PPAR/RXR, an Ahr/Arnt and a CRE. Basal activity of serially deleted promoter constructs transiently transfected into COS-7, alphaT3 and TE671 cells demonstrated the enhancing and silencing roles of the putative transcription factor binding sites. Quinpirole, a dopamine agonist, significantly reduced the promoter activity of muCyp19b in TE671. The results suggest tissue-specific regulation of the muCyp19 genes and a putative alternative promoter for muCyp19b.

Vitellogenin synthesis in primary cultures of fish liver cells as endpoint for in vitro screening of the (anti)estrogenic activity of chemical substances

Concern over possible adverse effects of endocrine-disrupting compounds on fish has caused the development of appropriate testing methods. In vitro screening assays may provide initial information on endocrine activities of a test compound and thereby may direct and optimize subsequent testing. Induction of vitellogenin (VTG) is used as a biomarker of exposure of fish to estrogen-active substances. Since VTG induction can be measured not only in vivo but also in fish hepatocytes in vitro, the use of VTG induction response in isolated fish liver cells has been suggested as in vitro screen for identifying estrogenic-active substances. The main advantages of the hepatocyte VTG assay are considered its ability to detect effects of estrogenic metabolites, since hepatocytes in vitro remain metabolically competent, and its ability to detect both estrogenic and anti-estrogenic effects. In this article, we critically review the current knowledge on the VTG response of cultured fish hepatocytes to (anti)estrogenic substances. In particular, we discuss the sensitivity, specificity, and variability of the VTG hepatocyte assay. In addition, we review the available data on culture factors influencing basal and induced VTG production, the response to natural and synthetic estrogens as well as to xenoestrogens, the detection of indirect estrogens, and the sources of assay variability. The VTG induction in cultured fish hepatocytes is clearly influenced by culture conditions (medium composition, temperature, etc.) and culture system (hepatocyte monolayers, aggregates, liver slices, etc.). The currently available database on estrogen-mediated VTG induction in cultured teleost hepatocytes is too small to support conclusive statements on whether there exist systematic differences of the VTG response between in vitro culture systems, VTG analytical methods or fish species. The VTG hepatocyte assay detects sensitively natural and synthetic estrogens, whereas the response to xenoestrogens appears to be more variable. The detection of weak estrogens can be critical due to the overshadow with cytotoxic concentrations. Moreover, the VTG hepatocyte assay is able to detect antiestrogens as well as indirect estrogens, i.e substances which require metabolic activation to induce an estrogenic response. Nevertheless, more chemicals need to be analysed to corroborate this statement. It will be necessary to establish standardized protocols to minimize assay variability, and to develop a set of pass-fail criteria as well as cut-offs for designating positive and negative responses.

Purification of vitellogenin from smooth flounder (Pleuronectes putnami) and measurement in plasma by homologous ELISA

Male smooth flounder (Pleuronectes putnami) were induced to produce vitellogenin (VTG) by injection of 17beta-estradiol (E2). Anion exchange chromatography of precipitated plasma from E2-injected resulted in a single peak consisting of VTG. Smooth flounder VTG has an approximate molecular mass of approximately 520 kDa, determined by gel filtration with molecular weight standards. Purified VTG was used to develop a homologous enzyme-linked immunosorbent assay (ELISA). The flounder VTG ELISA is an indirect antigen competition assay with a detection limit of 15 ng.ml(-1) and a useful range of 30-950 ng.ml(-1) of diluted sample. Intra- and inter-assay precision (as %CV, n=7) ranged from 1.3% to 6.0% and 5.1%, respectively. The ELISA was evaluated using plasma samples collected from a smooth flounder population captured in the Saint Lawrence Estuary. The ELISA is sensitive enough to differentiate males and non-vitellogenic females from vitellogenic individuals during early vitellogenesis.

Endocrine disruption and altered gonadal development in white perch (Morone americana) from the lower Great Lakes region

High prevalences of gonadal intersex have been observed in wild fish populations in areas affected by domestic and industrial effluents. For this study, fish were collected in 1998 from the Cootes Paradise region of Hamilton Harbour in western Lake Ontario, Canada, to determine whether gonadal abnormalities, including intersex, were present in young of the year (YOY) fish. No gonadal abnormalities were observed in goldfish (Carassius auratus), common carp (Cyprinus carpio), gizzard shad (Dorosoma cepedianum), brown bullhead (Ictalurus ameiurus), pumpkinseed (Lepomis gibbosus), and bluegill (Lepomis macrochirus). However, intersex gonads were observed in 8 of 16 male white perch (Morone americana) examined in this survey. Subsequently, in 1999 and 2000 white perch estimated to be YOY to approximately 2 years of age were collected from Cootes Paradise and from two other sites in the lower Great Lakes region. Gonadal intersex was observed in male white perch collected from the Bay of Quinte (22-44%) and Lake St. Clair (45%), although the prevalence and the extent of the intersex condition were lower relative to the 83% prevalence in white perch collected in Cootes Paradise. Intersex was not observed in hatchery-reared white perch or in white perch collected from an uncontaminated reference site (i.e., Deal Lake) in the United States. An analysis of plasma collected in the spring of 2002 from male adult white perch in Cootes Paradise revealed high concentrations of vitellogenin, ranging from 49 to 1,711 microg/mL. These observations indicate that male white perch are exposed to estrogenic endocrine-disrupting substances that may be responsible for the induction of gonadal intersex.

Bluegill (Lepomis macrochirus) vitellogenin: purification and enzyme-linked immunosorbent assay for detection of endocrine disruption by papermill effluent

Vitellogenin (VTG) is a highly specific marker of exposure to environmental estrogens and has been used extensively in field and laboratory studies of estrogenic endocrine disruption in fishes. The purpose of this study was to develop and validate a sensitive, competitive, enzyme-linked immunosorbent assay (ELISA) specific for bluegill (Lepomis macrochirus) vitellogenin. Bluegill VTG was purified by anion exchange chromatography on DEAE-agarose. The polypeptide had an apparent mass of 170 kDa and was specifically recognized by the rabbit antiserum raised against bluegill female-specific plasma protein. Plasma samples from vitellogenic females diluted in parallel with the purified VTG standard curve in the ELISA. The detection limit of the assay was 29 ng/ml and the working range extended to 2700 ng/ml. Recovery of purified VTG was 85.8+/-9.5%, intra-assay variation was 6.4% and interassay variation was 12.3%. We used this ELISA to analyze the seasonal cycle of vitellogenesis in female bluegill and to evaluate potential disruption of this process by exposure to bleached kraft mill effluent (BKME). Captive female bluegill stocked in outdoor experimental streams in New Bern, NC had the lowest levels of VTG, estradiol-17beta (E2), and testosterone (T) and the smallest oocyte diameters in January, but these variables increased in March and remained elevated through August, suggesting an extended spawning season. Plasma VTG, E2, T and oocyte diameter were unaffected by exposure to BKME concentrations as high as 30%. Development of the VTG ELISA allowed rapid and convenient analysis of plasma samples to evaluate exposure to potential endocrine disrupting compounds.

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

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

The effects of long-term estradiol-17beta treatment on the growth and physiology of female triploid brook trout (Salvelinus fontinalis)

Triploid female fish show impaired gonadal development, which results in the production of only a few oocytes relative to diploids. The rate of maturation of these few oocytes in much slower relative to those of diploids and is attributed to an insufficient estradiol-17beta (E(2)) stimulus. Female triploid brook trout, aged 2+, were fed E(2) for seven months (i.e., July 1998 to February 1999) in an attempt to increase plasma E(2) comparable to diploid levels and thereby accelerate rates of oocyte growth. Compared to triploids fed a normal diet (i.e., control-triploids), the administration of 30 mg E(2)/kg feed to triploids (i.e., E(2)-treated-triploids) led to the development of secondary sex characteristics, a significant reduction in hematocrit and total blood hemoglobin level, a decrease in plasma testosterone and no weight gain. Plasma vitellogenin was significantly higher in E(2)-treated-triploids than in control-triploids and diploids at every month except October 1999. Although greater than in the control-triploids, plasma E(2) for the E(2)-treated-triploids did not attain the high levels shown by the diploids during the months of peak vitellogenesis (i.e., September and October). Following maturation and spawning of diploids, sacrificed E(2)-treated and control-triploids showed no differences in ovarian development or liver size. The E(2) dose for the treated-triploids was increased to 80 mg E(2)/kg feed for approximately seven more weeks in a further attempt to increase plasma E(2), with no success. It is suggested that the low plasma E(2) of the treated-triploids was the result of a high metabolic clearance rate.

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.

Development and validation of a homologous zebrafish (Danio rerio Hamilton-Buchanan) vitellogenin enzyme-linked immunosorbent assay (ELISA) and its application for studies on estrogenic chemicals

Vitellogenin (VTG) was isolated by anion exchange chromatography from plasma of female zebrafish (Danio rerio) induced with 17alpha-ethinylestradiol (EE2). The purity of the VTG isolate was confirmed by polyacrylamide gel electrophoresis (SDS-PAGE). Purified VTG was used to raise polyclonal antibodies in rabbits and the specificity of the antisera for VTG confirmed by Western blot analysis of plasma proteins separated by SDS-PAGE. The antibodies cross-reacted with two proteins in the plasma of female zebrafish, with molecular masses of approximately 142 and 171 kDa. No cross-reactivity was observed with any other plasma proteins. A competitive enzyme-linked immunosorbent assay (ELISA) was developed using the polyclonal zebrafish VTG (z-VTG) antibodies and purified z-VTG as ligand and standard, respectively. The z-VTG ELISA was sensitive with a detection limit of between 2.0 and 3.0 ng purified VTG/ml, and a working range between 3 and 500 ng/ml (30-85% binding). The ELISA demonstrated precision, with inter- and intra-assay variations of 7.5+/-2.7 and 4.9+/-1.4%, respectively. Plasma from adult zebrafish and whole body homogenates from juvenile zebrafish diluted parallel with the z-VTG standard in the ELISA, validating the assay for quantifying z-VTG in both of these tissues. Exposure of adult male zebrafish to EE2 via water induced a concentration-dependent induction of VTG with a lowest observed effect concentration (LOEC) < or =1.67 ng EE2/l (for a 21-day exposure). The homologous z-VTG ELISA provides a valuable tool for the study of environmental estrogens in zebrafish.

Purification and characterization of a putative vitellogenin from the ovary of amphioxus (Branchiostoma belcheri tsingtaunese)

An oocyte-yolk protein was purified by double-step chromatography from amphioxus ovaries. The purified protein appeared to exist as a homodimer of approximately 320 kDa in native polyacrylamide gel electrophoresis (PAGE), and was reduced to a single monomer of approximately 160 kDa in sodium dodecyl sulfate-PAGE (SDS-PAGE). The protein was characterized as a phospholipoglycoprotein by native PAGE and staining of gels for phosphorus with methyl green, for lipids with oil red O and Sudan black B, and for carbohydrates using periodic acid/Schiff reagent. In addition, the amino acid composition of the oocyte-yolk protein was generally similar to that of vitellogenins (Vgs) isolated from different phyla of animals including both vertebrates and invertebrates. The purified phospholipoglycoprotein is thus considered as putative amphioxus Vg.

Sex steroids relative to alternative mating behaviors in the simultaneous hermaphrodite Serranus subligarius (Perciformes: Serranidae)

This study is the first investigation of reproductive endocrinology in a simultaneously hermaphroditic teleost, the belted sandfish (Serranus subligarius). We address two questions: (1) Do steroid hormone levels vary during the spawning season or during the daily spawning cycle of sandfish? (2) Do hormone levels vary relative to an individual's phenotype-size, frequency of spawning and aggressive behaviors, and proportion of testis in the gonad? We analyzed circulating estradiol-17beta (E2), testosterone (T), 11-ketotestosterone (11KT), 17alpha,20beta,21-trihydroxy-4-pregnen-3-one (20betaS), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) concentrations in a field population. Only E2 levels were significantly higher at the new and full moon, suggesting peak periods of vitellogenesis at these times. Naturally spawning sandfish were sampled every 2 h during the photophase of a 25-h period (12 pm to 1 pm the following day) and gonadosomatic index, degree of oocyte hydration and ovulation, and plasma levels of E2, T, DHP, and 20betaS were analyzed. E2 and T levels did not vary during photophase, suggesting continuous recruitment of oocytes into vitellogenesis. The 20betaS levels peaked around the time of final oocyte maturation. Since frequency of spawning behaviors changes with body size, we captured individuals of various sizes throughout the spawning season and analyzed circulating levels of hormones. 11KT and 20betaS levels increased significantly with body size. In 1992, we quantified frequency of spawning and aggressive behaviors, circulating T and 11KT levels and testicular mass relative to ovotestis mass in focal animals. 11KT levels tended to be positively correlated with frequency of courting male behavior, but were unrelated to the frequency of aggressive behavior or testis mass. Because hormone levels increased with size and frequency of each spawning behavior changes with size, we propose that sex steroids influence growth-related changes in spawning tactics of individuals.

Gonadal development and plasma steroid levels during pubertal development in captive-reared striped bass, Morone saxatilis

Puberty is the period during which full sexual development occurs and the capacity to reproduce is acquired. Despite its importance, our understanding of the endocrine regulation of puberty in lower vertebrates is still limited. The objective of the present study was to describe the changes in gonadal development and plasma steroid levels in a relatively late maturing species, the striped bass, during the first four years of life. In about 65% of the females, puberty was initiated during the third year. Although gonadosomatic index (GSI) and oocyte diameter increased during this year, this first cycle was characterized by a heterogeneous population of developing oocytes, a relatively low mean maximum oocyte diameter, and an absence of yolk granules in the oocytes. Plasma 17beta-estradiol (E(2)) levels were low in all three-year-old fish, suggesting that an insufficient stimulation of vitellogenin production by E(2) may underlie the lack of vitellogenin incorporation into developing oocytes. All monitored parameters increased during the fourth year, but were still below the values attained by older females. In about 60% of the males, puberty was initiated during the first year and all males were mature by the third year. During the first two years, several immature males initiated spermatogenesis without reaching full maturity. In mature males, mean GSI, plasma testosterone, and 11-ketotestosterone levels increased simultaneously, reaching higher values each subsequent year. Our results indicate that, similar to the situation in mammals, more than one reproductive cycle is required in striped bass before complete adulthood is reached.

Fathead minnow (Pimephales promelas) vitellogenin: purification, characterization and quantitative immunoassay for the detection of estrogenic compounds

The egg yolk precursor protein, vitellogenin (VTG), was purified from blood plasma of 17beta-estradiol (E2)-treated male fathead minnows (Pimephales promnelas) by anion-exchange chromatography on DEAE-agarose. A rabbit antiserum was raised against their blood plasma and then adsorbed with plasma from untreated (control) males to render the antiserum specific to VTG. The adsorbed antiserum was used to detect fathead minnow VTG (fVTG) in Western and dot blotting experiments and in an enzyme-linked immunosorbent assay (ELISA). The antiserum recognised fVTG as a approximately 156 kDa protein in plasma from vitellogenic females and E2-injected males but not untreated males. Its identity was confirmed by analysis of: (1) amino acid composition; (2) an internal amino acid sequence; (3) reactivity to the homologous antiserum; and (4) recognition by monoclonal antibodies prepared against the VTG from common carp (Cyprinus carpio) and brown bullhead (Ameiurus nebulosus). Specificity of the homologous antiserum to fVTG was confirmed by Western blotting of serially diluted plasma from vitellogenic females. Utility of the antiserum and purified fVTG for detecting exposure of male fathead minnows to estrogenic compounds was verified using a dot blotting immunoassay of fVTG and detected by chemiluminescence. Adult male fish were exposed to various concentrations of E2 (10(-8), 10(-9) and 10(-10) M) in their rearing water and plasma assayed for the presence of VTG at different time points (2, 7, 14 and 21 days). A competitive, antibody-capture, quantitative ELISA was then developed based on the purified fVTG and its respective antiserum. The ELISA was validated by demonstrating parallel binding slopes of dilution curves prepared with plasma from E2-injected males, vitellogenic females, and aqueous egg extracts as compared with purified fVTG standard. Plasma concentrations of VTG as low as 3 ng ml(-1) were detected in the ELISA, for which inter- and intra-assay coefficients of variation were both less than 5%. Furthermore, plasma from control males was unreactive with the fVTG antiserum. The VTG ELISA could be useful for the detection of estrogenic properties associated with certain compounds and could be easily incorporated into standard laboratory toxicity assays using this species.

An enzyme-linked immunosorbent assay (ELISA) for measuring vitellogenin in English sole (Pleuronectes vetulus): development, validation and cross-reactivity with other pleuronectids

Vitellogenin (Vtg) is a yolk protein produced in the liver of oviparous animals in response to estrogen. Vitellogenesis is normally observed only in sexually mature females, but it can be induced in male and juvenile animals by exposure to exogenous estradiol (E2) or substances that mimic estrogens. The abnormal production of Vtg by males can, therefore, be used as a biological indicator for exposure to xenoestrogens. In this study, an enzyme-linked immunosorbent assay (ELISA) for measuring Vtg in English sole (Pleuronectes vetulus) was developed and validated. Plasmatic Vtg was purified from E2-injected male English sole using DEAE ion-exchange and Sepharose size-exclusion chromatography, and polyclonal antibodies against the purified Vtg protein were generated in rabbits. In this assay, a competition for the Vtg antibody was established between Vtg coated onto microtiter plate wells and free Vtg. Detection of adsorbed antigen-antibody complexes was achieved using a horseradish peroxidase conjugated anti-rabbit secondary antibody whose enzyme activity was revealed with 3,3',5,5'-tetramethyl benzidine (TMB) substrate. Assay conditions provided a detectable Vtg range of 10-450 ng ml-1 (85-20% of binding) of diluted sample. Plasma dilution curves from vitellogenic female and E2-treated male English sole showed parallelism with the standard dilution curve. We are presently conducting field and laboratory studies to investigate estrogenic and anti-estrogenic activity resulting from exposure to contaminants.

Effects of long-term testosterone, gonadotropin-releasing hormone agonist, and pimozide treatments on gonadotropin II levels and ovarian development in juvenile female striped bass (Morone saxatilis)

The ability of the juvenile female reproductive axis to respond to hormonal stimulation was investigated in a Perciform fish, the striped bass (Morone saxatilis) using various combinations of testosterone (T), GnRH agonist (GnRHa), and pimozide. A long-term treatment with T alone, or T in combination with GnRHa, increased pituitary gonadotropin II (GtH II) levels 2- and 3-fold, respectively, suggesting that T and GnRHa each stimulate GtH II accumulation. Release of the accumulated GtH II could be induced only by high doses of GnRHa in combination with T, indicating that GtH II synthesis and release require different levels of GnRH stimulation. The addition of the dopamine antagonist pimozide did not affect pituitary and plasma GtH II levels but, in response to an additional acute GnRHa challenge, inhibited the release of GtH II. Although ovarian development was slightly stimulated by a combined T and GnRHa treatment, vitellogenesis was generally not initiated. The present study demonstrated that the juvenile striped bass pituitary is responsive to hormonal stimulation, resulting in elevated levels of GtH II in the pituitary and plasma. However, increased plasma levels of GtH II did not result in precocious puberty, suggesting that additional factors are required for the initiation of ovarian development in this teleost.

Endocrine profiles of female striped bass (Morone saxatilis) in captivity, during postvitellogenesis and induction of final oocyte maturation via controlled-release GnRHa-delivery systems

Plasma levels of reproductive and thyroid hormones were measured in captive striped bass females during postvitellogenesis and the spawning period (March-June). Circulating gonadotropin II (GtH II), 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P), and 17,20beta, 21-trihydroxy-4-pregnen-3-one (17,20beta,21-P) remained low and unchanged in nonmaturing females, while 17beta-estradiol (E2) and testosterone (T) declined throughout postvitellogenesis. Plasma thyroxine (T4) declined significantly in mid-April, while triiodothyronine (T3) increased in mid-May. The only female that ovulated spontaneously had markedly different E2, T, and T3 profiles during postvitellogenesis, and had a surge in plasma GtH II during final oocyte maturation (FOM). The lack of a GtH II surge is presumably responsible for the absence of FOM, but earlier, and as of yet unknown, endocrine disruptions during postvitellogenesis may determine the female's ability to undergo FOM. Treatment of females with a gonadotropin-releasing hormone agonist (GnRHa)-delivery system induced FOM and ovulation within 3 and 10 days, respectively, and resulted in the production of fertile eggs. Plasma GtH II increased continually after GnRHa implantation, even in the presence of declining GnRHa plasma levels. Plasma E2 increased first and peaked prior to FOM, whereas T peaked at the peripheral germinal vesicle (GV) stage. Plasma 17,20beta-P and 17,20beta,21-P increased dramatically at the GV breakdown (GVBD) stage. Plasma T4 was unaffected by the GnRHa treatment, whereas T3 decreased after GnRHa implantation and remained low throughout FOM. Based on the observed hormonal profiles, FOM can be separated into an early phase (lipid-droplet coalescence, GV migration) associated with E2 and T elevations, and a late phase (yolk-globule coalescence, GVBD) associated with 17,20beta-P and 17,20beta,21-P elevation.

Purification and partial characterization of English sole (Pleuronectes vetulus) vitellogenin

Vitellogenin (VTG) was purified by double-step chromatography from plasma of male English sole treated with 17 beta-estradiol. The intact protein appeared to exist as a dimer in two forms of approximately 300 and 320 kDa and had an isoelectric point of 6.63. In SDS-PAGE, it was reduced to a single monomer of approximately 130 kDa. In immunoblotting, the protein showed cross-reactivity with coho salmon VTG antiserum. Native PAGE (sample not treated with the reducing agent mercaptoethanol) and immunoblotting of plasma from control and estradiol-treated male sole and gravid female sole demonstrated that the putative English sole VTG was normally female specific and estradiol inducible in males. It was immunocytochemically localized in liver and ovary of English sole, rock sole and starry flounder, using polyclonal antiserum to the purified protein from the estradiol-treated male English sole. The protein was characterized as a phospholipoglycoprotein by native PAGE, staining the gels for phosphorus with methyl green, for lipid with Sudan black B and for carbohydrate by an improved periodic-acid Fuchsin sulfite method. The amino acid composition of the putative VTG was generally similar to that of VTGs from other teleosts, with the non-polar amino acids alanine, valine, leucine and isoleucine accounting for one-third of the total amino acids present. However, English sole vitellogenin contained a higher proportion of leucine and a lower proportion of glycine than most other teleost vitellogenins isolated to date.

Transition of serum vitellogenin cycle in Sakhalin taimen (Hucho perryi)

A specific and sensitive enzyme-linked immunosorbent assay (ELISA) and a single radial immunodiffusion (SRID) were developed for measurement of serum vitellogenin (Vg) levels in Sakhalin taimen (Hucho perryi). Regarding specificity for serum Vg, an antiserum raised against lipovitellin of taimen (a-Lv) was adequate for both assays. ELISA and SRID could detect Vg in serum at concentrations as low as 10 ng/ml and 25 micrograms/ml, respectively. In estrogen administration experiments, the level of serum Vg began clearly increasing within 12 to 24 hr after injection of immature females with estradiol-17 beta (E2). The appearance and levels of Vg in males treated with E2 were delayed and smaller, respectively, than for females. Vg levels varied throughout natural vitellogenesis from 0-4 micrograms/ml (3 years old) to approximately 30 mg/ml (5-6 years old). We observed an early transitory peak of serum Vg levels (primary reaction) at the time of early vitellogenesis and chronic high Vg levels (for 6-7 months) in winter period before ovulation. Changes of serum E2 levels were correlated with Vg levels. However, E2 levels decreased a month earlier than Vg levels near ovulation. It appears that the duration of vitellogenesis in taimen is considerably longer than that in other salmonids, lasting more than 2 years.

Characterization of a heat-stable fraction of lipovitellin and development of an immunoassay for vitellogenin and yolk protein in winter flounder (Pleuronectes americanus)

An enzyme-linked immunoabsorbent assay was developed for detection and quantification of the yolk protein lipovitellin (Lv) and its plasma precursor, vitellogenin (Vg), in winter flounder (Pleuronectes americanus). Native Lv was found to be a mixture of heat-stable and heat-labile molecules in mature, ovulated eggs. A heat-stable Lv fraction was purified from extracts of unfertilized eggs by brief heat treatment and gel permeation chromatography on Bio-Gel A-1.5. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of heat-stable Lv revealed a single polypeptide of 94 kD, while native Lv also possessed several smaller polypeptides, suggesting that heat-labile Lv contains proteolytic cleavages of the 94-kD polypeptide which destabilize its structure. The Stokes radius of the native protein on Bio-Gel A-1.5 was estimated at 4.50 nm, while the Stokes radii of heat-stable and heat-labile Lv were 4.26 nm and 5.17 nm, respectively. Heat-stable Lv was used to produce a rabbit polyclonal antiserum which reacted with a single 175-kD polypeptide in Western blots of vitellogenic female winter flounder serum, but did not react with any component of male serum. Ouchterlony double diffusion using this antiserum demonstrated immunological identity of Lv, heat-stable Lv, and Vg. The anti-Lv anti-serum was used to construct an homologous ELISA with a linear response between 25 and 300 ng/ml. This assay was used to characterize a Bio-Gel A-1.5 column profile of serum from an estradiol-treated male winter flounder, and a single peak, with Stokes radius of 6.70 nm, was identified as Vg. Winter flounder Vg was confirmed to be a dimer, while Lv from mature eggs was found to be a monomer of a lower molecular weight polypeptide.

Characterization of vitellogenin induced by estradiol-17β in protandrous black porgy,Acanthopagrus schlegeli

The objectives of this study were to isolate and characterize vitellogenin from plasma of estradiol-treated protandrous black porgy,Acanthopagrus schlegeli. Vitellogenin concentrations in plasma measured by a validated enzyme-linked immunosorbent assay (ELISA) were also compared. Two-year-old black porgy (n=20) were fed with estradiol-17β (4 mg kg(-1) of feed). Plasma was collected for purification of vitellogenin. Two forms of vitellogenin were found in plasma after chromatography on Sepharose CL-2B column and hydroxylapatite, and polyacrylamide gel electrophoresis. Black porgy vitellogenins are phospho-lipo-glycoproteins based on their chemical staining properties. The apparent molecular weights of the two forms of vitellogenin were 636 kDa and 321 kDa, respectively. The amino acid composition of purified vitellogenin was also analyzed after acid hydrolysis. The presence of immunoreactive vitellogenin was identified in the plasma and mucus extract from control and estradiol-induced females on the basis of Western blotting. Serial dilution of the plasma and mucus extract taken from estradiol-induced black porgy showed reactivity to an antiserum against lipovitellin in the ELISA, whereas mucus extract and plasma from male fish did not. Significantly higher concentrations of plasma vitellogenin were detected in estradiol-stimulated black porgy than in the control males.

Vitellogenins of Oreochromis niloticus: identification, isolation, and biochemical and immunochemical characterization

Two native forms of vitellogenin (EIP1 and EIP2) were identified in the plasma of Oreochromis niloticus. They were present in females and were estrogen-inducible in males. Both were phosphoglycolipoproteins and both immunoreacted with the antiserum raised against egg proteins. Two prominent bands (EIpp1 and EIpp2; corresponding to 185 and 120 kDa, respectively), observed on sodium dodecyl sulfate-polyacrylamide gels, were induced by estradiol treatment of males and immunoreacted with the antiserum against egg proteins. EIP1 and EIP2 were isolated by precipitation with Mg2+ ions and ethylenediamine tetraacetic acid, preparative polyacrylamide gel electrophoresis, and electroelution. During purification the fractions containing EIP1 and EIP2 also retained EIpp2 and EIpp1, respectively. Immunoblot analyses using affinity-purified antibodies against EIP1, EIP2, EIpp1, and EIpp2 confirmed that EIP1 and EIP2 were at least composed of EIpp2 and EIpp1, respectively. These results suggest that at least two immunochemically different proteins are induced and are secreted into the blood to serve as vitellogenin and to provide a source of nutrient for the developing embryo of Oreochromis niloticus.