Purification and identification of vitellogenin and its immunohistochemical detection in growing oocytes of the teleost,Oryzias latipes

Critical Role of the Cortical Alveolus Protease Alveolin in Chorion Hardening In Vivo at Medaka Fertilization

Alveolin is a cortical alveolus proteinase that is secreted in the perivitelline space (PVS) at fertilization to act on the chorion. Purified alveolin is known to induce chorion hardening in vitro by processing zona pellucida B (ZPB), a major chorion component. However, in vivo function of alveolin remains unclear; thus, in this study, the effects of alveolin efficiency (Alv-/-) at the organism level were investigated using the medaka, Oryzias latipes. The Alv-/- fertilized eggs were mechanically fragile; however, they developed normally and left offspring as long as they were carefully handled before hatching. A mechanical press test showed that the Alv-/- fertilized eggs were six times more fragile than the wild-type eggs. They were 35% larger owing to the enlarged PVS, 34% thinner, and permeable to even 10 kDa FITC-dextran. These results are consistent with the transmission electron microscopy observation that the periphery of the inner layers was highly porous in the Alv-/- chorion. In chorion hardening, the alveolin-mediated processing of ZPB and the transglutaminase (TGase)-mediated crosslinking of chorion components are the key steps. This study was the first to show that alveolin also processed TGase concomitantly with ZPB, which greatly facilitated the crosslinking. Thus, alveolin was concluded to be the primary trigger for chorion hardening in vivo. Furthermore, fertilization in a balanced salt solution could partially improve the impaired chorion hardening of the Alv-/- eggs fertilized in water, probably through an alveolin-independent mechanism.

Characterization of incomplete vitellogenin (VgC) in the Indian freshwater murrel, Channa punctatus (Bloch)

A novel incomplete vitellogenin (VgC) was purified from the plasma of estradiol-treated male murrel, Channa punctatus, by gel filtration chromatography. The native mass of VgC protein was 180 kDa, and it resolved as a single peptide of 100 kDa on SDS-PAGE. The peptide on subjecting to matrix-assisted laser desorption/ionization-time of flight produced a peptide mass fingerprint. On tandem mass spectrometry, some of these peptides showed mass to charge (m/z) ratio and amino acid sequence similarity with VgC peptides of other teleosts. Phylogenetic analysis revealed a similarity of murrel VgC with fish species of the order Perciformes. Semi-quantitative RT-PCR assay was developed to study expression of vgc gene at variable levels of estradiol exposure. Presence of VgC in males indicates that fish has been exposed to estrogens; hence, it can be used as a biomarker for estrogenic exposure.

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.

Role of maternally derived immunity in fish

Maternal immunity is of paramount importance for protection of young ones at early stage of life since the immune factors of an immunocompetent female are transferred transplacentally or through colostrum, milk or yolk to an immunologically naive neonate. Both innate and adaptive type of immunity are transferred of from mother to offspring in fishes. These factors include immunoglobulin (Ig)/antibody, complement factors, lysozymes, protease inhibitors like alpha macroglobulin, different types of lectins and serine proteases like molecules. Among different types of Ig viz. IgM, IgD, IgT/IgZ and IgM-IgZ chimera types, IgM is present in most of the teleostean fishes. In teleosts, IgM either as a reduced/breakdown product or monomeric form is usually transferred to the offsprings. The maternally derived IgM usually persists for a limited duration, exhausts within the completion of yolk absorption process, and completely disappears thereafter during larval stages. Maternal transfer of immunity which provides defense to embryo and larvae depends upon the health as well as the immune status of brood fish. The overall health status of brood fish can affect breeding performances, quality seed production and protection of offsprings. However, factors such as age, maturation, reproductive behaviour and nutrition (micro and macro-nutrients) may affect the immunity in brood fishes. Besides these, seasonal changes such as photoperiods, temperature, adverse environmental conditions, and stress conditions like handling, crowding, and water pollution/contamination can also affect the immunity of brood fishes. The maintenance of the brood stock immunity at high level during vitellogenesis and oogenesis, is utmost important for reducing mortalities at larval/post larval stages through maximum/optimum transfer of maternal immunity. Brood stock immunization prior to breeding as well as selective breeding among the disease resistant families might be the ideal criteria for producing quality seed.

Establishment of ELISA for murrel vitellogenin and choriogenin, as biomarkers of potential endocrine disruption

Vitellogenin (Vg) and choriogenin (Chg) are sensitive biomarkers for testing endocrine disruption in fish. Therefore, we have developed immunoassays for Vg and Chg in the Indian freshwater murrel, Channa punctatus. Vg is a known precursor of egg-yolk proteins, whereas Chg contributes to the formation of egg-envelope. Vg and Chg were induced in male murrel by administration of estradiol-17beta. Chg had an apparent native molecular mass of 180 kDa. It consisted of a single peptide with a molecular mass of 110 kDa, whereas native Vg protein (530 kDa) contained 175 kDa peptide. Highly specific polyclonal antibodies against purified plasma proteins, Vg and Chg, were employed for developing competitive enzyme linked immunosorbent assays (ELISAs). The sensitivity of Vg assay was 3.9 ng/mL (working range 15-500 ng/mL) and of Chg assay was 1.56 ng/mL (working range 6-200 ng/mL). The inter- and intra-assay variations were well within acceptable limits. The two antisera did not cross-react with male plasma proteins. Antiserum to Vg did not cross-react with Chg. Similarly, antiserum to Chg showed no correlation with Vg. Further, immunofluorescence and Western blotting confirmed the specificity of Vg and Chg antisera.

Purification of two lipovitellins and development of immunoassays for two forms of their precursors (vitellogenins) in medaka (Oryzias latipes)

Two distinct yolk proteins (YP1 and YP2) were purified from the ovary of medaka, and specific antisera against YPs were generated to characterize YPs and reveal their relation to two vitellogenins (Vg1 and Vg2). The molecular masses of purified YP1 and YP2 on gel filtration were 270 and 380 kDa, respectively. YPs were confirmed to be lipoproteins by staining with Sudan black. Amino acid compositions of YP1 and YP2 were similar to those of Vg1 and Vg2, respectively. In double immunodiffusion using anti-Vg1, a precipitin line of YP1 formed a spur against the Vg1 line. YP2 and Vg2 were reacted with anti-Vg2, and a precipitin line of YP2 formed a fuse against the Vg2 line. These biochemical and immunological analyses of purified YPs revealed that YP1 is lipovitellin 1 (Lv1) derived from Vg1 and YP2 is lipovitellin 2 (Lv2) derived from Vg2. Using specific antibodies against Lvs and Vgs, specific, high sensitivity chemiluminescent immunoassays (CLIAs) for two Vgs were developed to reveal basal Vg levels and response to exogenous estradiol-17beta (E2). The measurable range of both CLIAs was from 0.975 to 1000 ng/ml. The cross-reactivity to the alternative Vg in each CLIA was extremely low (<or=0.57%). When immature fish were immersed in water containing E2 for 1 h, both Vgs were induced by 0.5 microg/L of E2 at 24 h after treatment. Vg1 increased in a concentration-dependant manner up to 100 microg/L E2, while Vg2 reached a plateau at 10 microg/L of E2. The ratio of Vg1:Vg2 in E2-treated fish changed in a concentration-dependent manner from 1.5:1 to 8.5:1. The results from E2-treatment suggest that differential regulation may control the expression of medaka Vgs.

Vitellogenin-immunohistochemistry in the Liver and the Testis of the Medaka, Oryzias latipes, Exposed to 17β-estradiol andp-nonylphenol

Vitellogenin (VTG) produced in male fish has been used for a biomarker to study endocrine disrupters. However, the characteristics of VTG produced in male fish have not been studied well. In this study, we investigated the localization of VTG in the liver and the testis of male medaka (Oryzias latipes) treated with 17beta-estradiol (E2) and p-nonylphenol (NP). The male fish were exposed to 1 microg/L E2 and 500 microg/L NP for 1-12 days. Control groups were kept in water including only vehicle. The frozen sections of the liver and the testis were stained with immunohistochemical methods using an antiserum against medaka VTG as the first antibody. In the E2 and NP treated liver, the hepatocytes showed immunoreactivity. In particular, the cytoplasm close to the cell membrane surrounding the sinusoids was strongly immunopositive. In the testis of both treatments, the interstitial tissues and the cells (spermatocytes) in the seminiferous tubules were immunopositive. The concentration of VTG became gradually higher in both tissues with longer treatments. These results suggest that germ cells in the testis treated with E2 and NP are able to incorporate and accumulate VTG.

Comparison of vitellogenin responses in zebrafish and rainbow trout following exposure to environmental estrogens

In this comparative study, the suitability of the commonly used in vivo biomarker for estrogenicity, vitellogenin (VTG), upon waterborne exposure to known environmental estrogens is evaluated in both male zebrafish (Danio rerio) and juvenile rainbow trout (Oncorhynchus mykiss). The results from initial experiments in which both species were exposed to 4-tert-octylphenol (OP) or 17 alpha-ethynylestradiol under semistatic conditions for 3 weeks demonstrated a difference in species sensitivity for OP exposure. Additional dose-response studies (semistatic, 3 weeks) with 4-nonylphenol (20, 100, and 500 microg/L), bisphenol A (40, 200, and 1000 microg/L), dibutylphthalate (40, 200, and 1000 microg/L DBP), and 17beta-estradiol (20 and 100 ng/L E2) were conducted. All these compounds, except for DBP, were found to be estrogenic to both fish species. The results demonstrated a difference in species sensitivity for NP with the zebrafish being about 5 times less sensitive. For the other compounds tested, no indications for a difference in species sensitivity was found. The results from this study demonstrated that both fish species can be used for the detection of VTG as biomarker for estrogenicity, taken into the potential interspecies differences in sensitivity which might be important for the evaluation of fish population effects.

Purification and identification of a second form of vitellogenin from ascites of medaka (Oryzias latipes) treated with estrogen

Estrogen treatment of medaka leads to accumulation of ascites, in which vitellogenin (Vg) and choriogenins (precursors to vitelline envelope) are abundant. Besides those female-specific proteins, we detected a new component in ascites that cross-reacts with antiserum against egg yolk proteins. We tentatively named it egg yolk-related protein (YRP). YRP was purified from ascites by hydroxylapatite chromatography followed by gel filtration. Purified YRP had a molecular mass of 460 kDa in intact state while 570 kDa for Vg. The molecular weight of purified YRP on SDS-PAGE under both reducing and nonreducing conditions was 130 kDa. YRP was confirmed to be a lipoglycophosphoprotein by staining with Sudan black, periodic acid-Schiff (PAS) and methyl green. Amino acid composition of YRP resembled that of Vg except for a relatively low content of serine. A specific antiserum against YRP was raised in a rabbit. Antiserum against YRP specifically immunostained its antigen but not Vg or choriogenins. YRP was detected as a female-specific protein in serum of breeding medaka. The antiserum also cross-reacted with a band at 29 kDa in egg extracts, which is not immunoreactive to antiserum against Vg. These data show that YRP is a precursor to some egg yolk proteins with differing antigenicity from Vg (Hamazaki et al. '87). We thus conclude that YRP is a second form of medaka Vg and rename YRP as Vg 2 while formerly reported Vg as Vg 1.

Inhibition of oocyte development in Japanese medaka (Oryzias latipes) exposed to di-2-ethylhexyl phthalate

Di-2-ethylhexyl phthalate (DEHP) is a widely used plasticizer known to be a suspected endocrine disrupter, but its precise effects on aquatic organisms are not yet known. When Japanese medaka (Oryzias latipes) were exposed from the time of hatching to 3 months of age to an aqueous DEHP solution at nominal concentrations of 1, 10, and 50 microg/l, DEHP-treated female fish showed distinct reproductive effects as follows. First, blood vitellogenin levels in all treated test subjects markedly decreased. Second, Gonado Somatic Index (GSI) decreased to 33% and 38% of the control GSI in 10 microg/l and 50 microg/l treated female fish, respectively. Third, 54% of female fish in the control treatment had completely matured oocytes in their ovaries, but only 37%, 0% and 22% of female fish matured to the last stage in the 1, 10 and 50 microg/l treated test subjects, respectively. Unlike female fish, no change or adverse effects were observed in the male fish. In summary, DEHP hinders the development of reproductive organs in the female Japanese medaka. In this work, the possibility o f anti-estrogenic activity of DEHP is proposed as the cause.

An in vitro vitellogenin bioassay for oestrogenic substances in the medaka (Oryzias latipes)

We developed an in vitro bioassay for oestrogenic compounds based on vitellogenin as a biomarker. To quantify the induction of vitellogenin in medaka (Oryzias latipes) we established a sandwich enzyme-linked immunosorbent assay (ELISA). This ELISA was carried out with two different monoclonal antibodies specific for the yolk precursor protein vitellogenin and the high molecular weight yolk proteins (lipovitellin) of medaka. Purified lipovitellin of medaka was used as a standard for the ELISA and could be quantified down to a concentration of 9 ng/ml. The calibration curve was linear up to at least 600 ng/ml and the intra-assay coefficient of variance was 3.2%. The application of the sandwich ELISA was tested using blood samples of males and females as well as primary hepatocyte cultures of medaka. Vitellogenin synthesis in cultured liver cells of males was induced by 1 and 100 nM of the xenoestrogen 17alpha-ethynylestradiol (EE(2)). The first production of vitellogenin was detected 6 days after hormone application. In contrast, isolated liver cells of sexually mature females, which were treated in the same manner, showed vitellogenin expression from the beginning of cultivation and its synthesis increased and remained high at 100 nM EE(2). However, the induction of vitellogenin synthesis in male hepatocytes in vitro could be maintained for at least one month and this indicated viable and differentiated liver cells. The hepatocyte cultures of male medaka in combination with the sandwich ELISA were shown to be a suitable tool to detect and quantify oestrogenic activity of chemicals.

Development and application of a monoclonal antibody-based sandwich ELISA for quantification of Japanese medaka (Oryzias latipes) vitellogenin

Vitellogenin (Vtg) was purified from ascitic fluid of a 17beta-estradiol (E2)-treated female Japanese medaka by anion-exchange chromatography. The molecular mass of medaka Vtg by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), corresponding to the Vtg monomer, was 200 kDa. BALB/c mice were immunized with purified-Vtg and two hybridoma clones producing specific antibodies against medaka Vtg were selected. The specificity of these monoclonal antibodies (mAbs) was evaluated by Western blot analysis of the plasma proteins separated on SDS-PAGE, and no cross-reactivity was observed with plasma proteins from control males. A sandwich enzyme-linked immunosorbent assay (ELISA) for quantification of medaka Vtg was developed using these mAbs. The assay range was between 1 and 100 ng/ml, and the intra- and inter-assay variations determined from plasma samples were within 7.7 and 8.5%, respectively. Recovery of medaka Vtg added to plasma was 92-111%. In a plasma dilution test, plots of Vtg concentration gave a straight line. After exposure of male medaka to E2 (10 ng/l), Vtg appeared in liver and plasma on the first day and reached a maximum on the 3rd to 5th day. The sandwich ELISA could be useful for the detection of estrogenic properties, and the medaka Vtg bioassay could be a very sensitive and good tool for screening of endocrine disrupting compounds.

Fish test for endocrine-disruption and estimation of water quality of Japanese rivers

The LC50 values (72 h) of 17beta-estradiol (E2), p-nonylphenol (NP) and bis-phenol-A (BPA) to adult male and female medaka were 3.5 and 3.5, 0.85 and 0.87, and 6.8 and 8.3 mg L(-1), respectively; the LC50 values to embryos were 0.46, 0.13 and 5.1 mg L(-1), respectively. The IC50 values for inhibition to egg hatching were 0.47, 0.85 and 9.0 mg L(-1), respectively. These values were much higher than concentrations detected in river water in Japan and the chemicals were considered to have no lethal effect on the fish in an aquatic environment. Mature male medaka was continuously exposed to 0.005, 0.05 or 1.0 microg L(-1) of E2, or to 0.1, 10 or 100 microg L(-1) of NP or BPA. Female specific proteins (FSP) were induced in the blood of male medaka that were exposed for 5 weeks to E2 higher than 0.005 microg L(-1), NP higher than 0.1 microg L(-1), or BPA higher than 10 microg L(-1). Based on these FSP inducible concentrations and reported concentrations of E2, NP and BPA in Japanese river water, some river water contaminated by E2 or NP could be estimated as the FSP inducible in male medaka.

Vitellogenin-derived yolk proteins in a hybrid sturgeon, bester (Huso huso x Acipencer ruthenus): identification, characterization and course of proteolysis during embryogenesis

Vitellogenin (Vg) and its corresponding yolk protein (YP) products, YP1, YP2 and YP3, were isolated from serum of estrogen-treated hybrid sturgeon (bester; Huso huso X Acipencer ruthenus) and eggs from untreated fish, respectively. Vitellogenin had an apparent molecular mass of 580 kDa and appeared as two major bands corresponding to 180 kDa and 120 kDa after SDS-PAGE. Apparent molecular weights of YP1, YP2 and YP3 were 370 kDa, 88 kDa and 19 kDa, respectively. After SDS-PAGE, YP1 appeared as a main band of 110 kDa, while YP2 was resolved as a single band of 94 kDa and 29 kDa band under non-reducing and reducing conditions, respectively. Yolk protein 3 appeared as a diffuse band corresponding to 16 kDa and two faint bands below 14.4 kDa after SDS-PAGE. However, the 16 kDa band alone was observed after dephosphorylation with alkaline phosphatase. The course of cleavage of yolk proteins in bester embryos and alevins was observed by SDS-PAGE and Western blotting from fertilization onward. After hatching, the main 110 kDa band of YP1 was degraded into smaller peptides during development, while YP2 hardly showed any such structural changes. The amino acid compositions of purified yolk proteins indicated that YP1, YP2 and YP3 were bester lipovitellin, beta-component, and phosvitin, respectively.

Gilthead seabream (Sparus aurata) vitellogenin: purification, partial characterization, and validation of an enzyme-linked immunosorbent assay (ELISA)

VTG was purified from seabream Sparus aurata plasma by ion exchange chromatography on a DEAE-Sepharose column. The vitellogenin was characterized and its properties were determined. The molecular mass of the native form, obtained by Sephadex G-200 column, was around 450 kDa, whereas an apparent molecular mass of 180 kDa was detected by electrophoresis under denaturing and reducing conditions, suggesting a dimeric form for the native protein. The presence of carbohydrates was determined using concanavalin A, while the presence of phosphate groups was detected by Stains-all, a cationic stain. These data together with the sex specificity, the estrogen inducibility, and the cross-reactivity of the abVTG against the major yolk proteins identifies this protein as vitellogenin. The validated ELISA was used for a rapid and reliable measurement of plasma VTG changes related with those of estradiol-17beta in female broodstock.

Plasma vitellogenin of grouper (Epinephelus malabaricus): isolation and properties

Radiolabelled vitellogenin produced by juvenile grouper following injection of 3H-leucine, 32P-orthophosphate and estradiol-stimulation was purified by anion-exchange and gel filtration chromatography and characterized by electrophoresis and chemical analysis. The radiolabelled product was found to exist in two heterogeneous molecular weight forms by electrophoresis under nondenaturing conditions on polyacrylamide gel with M(r), of 260,000 and 525,000. It showed two protein monomers (M(r) 113,000 and 140,000) on electrophoresis under denaturing condition on a sodium dodecyl sulphate-polyacrylamide gel. The purified material contained 17.2% total lipid with 1.3% cholesterol and 2.1% triglycerides, 8-21 micrograms/mg protein total carbohydrate and 6.8 micrograms phosphate/mg protein; amino acid analysis showed a profile comparable to that found for vitellogenins isolated from the grouper, medaka, goldfish and rainbow trout. The study showed grouper vitellogenin to be a glycophospholipoprotein similar in composition to vitellogenins from other teleosts and demonstrated that vitellogenins can be induced in juveniles by injection with estradiol-17 beta.

Protease activity appeared after trypsin treatment of the purified vitellogenin from eel Anguilla japonica

Density gradient ultracentrifugation and anion-exchange chromatography combination were effective for the purification of the eel vitellogenin from the plasma of estradiol-treated eels. The vitellogenin was very high density glycolipoprotein (P = 1.27 g/ml) and its apolipoprotein was M(r) 196 k in both reduced and non-reduced conditions by SDS-PAGE. The major lipid component was phospholipid. The N-terminal amino-acid sequence of the vitellogenin was as follows: (Ac)Thr-Pro-Ala-Leu/Ala-Asp-Tyr. Amino-acid composition of the eel vitellogenin was similar to those of other teleosts. The protease activity appeared in the trypsinized vitellogenin, but was not detected in the purified vitellogenin. The protease was separated from the used trypsin and the other cleaved vitellogenin by a dextran sulfate cellulose column. The molecular weight of the protease was determined by zymogram using SDS-polyacrylamide gel containing casein and was 50 k. It was concluded that the eel vitellogenin possesses the protease activity as a latent form.

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.

Formation of the vitelline envelope precedes the active uptake of vitellogenin during oocyte development in the rainbow trout, Oncorhynchus mykiss

In order to study the initial formation of the vitelline envelope and the appearance of vitellogenin in oocytes of rainbow trout, females were sampled monthly from 19 to 5 mo before ovulation. Immunohistochemistry revealed that the formation of the vitelline envelope starts when the oocytes reach a diameter of about 450 microns. Oocytes of this size were first found in females sampled a year before ovulation at the time when plasma levels of estradiol-17 beta increased from 0.2 to 0.6 ng/ml. An antiserum directed against vitellogenin crossreacted with small vesicles (around 2 microns) present just inside the oolemma, when the oocytes reached a diameter of 600 microns. This was interpreted as an active uptake of vitellogenin. Oocytes of this size were first found in females sampled 9 mo before ovulation at the time when estradiol-17 beta levels increased from 0.6 to 1.0 ng/ml and the gonadal somatic index was doubled. Oocytes with a diameter of 600 microns had an immunoreactive vitelline envelope with a thickness of about 3 microns. It is apparent that the initial formation of the vitelline envelope starts before the active uptake of vitellogenin and that the low previtellogenic plasma levels of estradiol-17 beta observed in females are of physiological significance.

Isolation of H-SF substances, the high-molecular-weight precursors of egg envelope proteins, from the ascites accumulated in the oestrogen-treated fish, Oryzias latipes

High- and low-molecular weight spawning-female-specific (H-SF and L-SF) substances are liver-derived putative precursors of the inner layer of egg envelope of the medaka Oryzias latipes, and are also found in the ascites which are accumulated in the male fish on prolonged treatment with oestrogen. In the present study, the H-SF substances purified from the ascites of the oestrogen-treated male medaka were found to consist of three proteins. Their molecular weights ranged from 74,000 to 76,000, which corresponds to those of ZI-1 and ZI-2, the major components of medaka egg envelope. The amino acid composition of the H-SF substances was characterised by high contents of proline (17.58 mol%) and glutamic acid/glutamine (13.34 mol%). The characteristics were almost identical to those of ZI-1 and ZI-2 but differed from those of L-SF substance, a precursor of ZI-3, another major component of the egg envelope. These results confirm our view that H-SF substances are the precursors of ZI-1 and ZI-2. The average amino acid compositions of H-SF substances and L-SF substance coincided with the amino acid composition of whole egg envelope. This result strongly suggests that an equal amount of H-SF substances and L-SF substance would construct the inner layer of egg envelope after a little modification.

Vitellogenin in tilapia (Oreochromis mossambicus): Induction of two forms by estradiol, quantification in plasma and characterization in oocyte extract

Two forms of vitellogenin were isolated by DEAE agarose ion-exchange chromatography from plasma of the tilapia, Oreochromis mossambicus. The monomers have apparent molecular masses of 200 and 130 kDa, as indicated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), and a total amount of phosphorus of 1.7 and 0.1%, respectively. Antibodies specific to the two forms, designated tVTG-200 and tVTG-130, were generated in rabbits and used to develop enzyme-linked immunosorbent assays (ELISAs) and in Western blot analyses of plasma and oocyte extract. SDS-PAGE of the oocyte extract showed a major protein band at 106.6, minor bands at 26.6, 24.2, and 23.7 kDa, and very faint bands at 83.4 and 17.5 kDa. Western blots of the oocyte extract revealed that the antiserum to tVTG-200 recognized strongly the protein bands at 24.2 and 23.7 kDa, and less strongly the bands at 25.1 and 22.6 kDa, whereas the antiserum to tVTG-130 recognized mainly the protein band at 106.6 kDa. The presence of both VTGs in untreated male tilapia was detected with the ELISAs using relatively high plasma volumes. Their presence in males was confirmed by VTG-like immunoreactive materials eluting from the ion-exchange column at the same positions as tVTG-200 and tVTG-130. The concentrations of the VTGs in males were several orders of magnitude lower than in vitellogenic females. Treatment of male tilapia with estradiol-17β (E2) induced both VTGs within 24h. After 7 days, tVTG-130 reached a maximum concentration in plasma, whereas tVTG-200 continued to increase. Our findings demonstrate that the two vitellogenins are biochemically distinct, possibly differentially regulated, and made by both sexes.

Oogenesis in Fundulus heteroclitus. VI. Establishment and verification of conditions for vitellogenin incorporation by oocytes in vitro

A procedure was developed for studying vitellogenin (VTG) incorporation by vitellogenic oocytes of Fundulus heteroclitus in vitro. Since homologous VTG can be obtained from this animal only with great difficulty, the use of [32P]VTG from Xenopus laevis was explored as an alternative. Vitellogenic as well as maturational-stage oocytes were found to sequester X. laevis [32P]VTG from the medium, and incorporation was found to be linear with time for at least up to 12 hr. Once incorporated into the oocyte, [32P]VTG did not appear to undergo turnover. The effect of different [32P]VTG concentrations on incorporation indicated that the uptake mechanism was saturable. Unlabeled F. heteroclitus VTG and X. laevis VTG were also found to compete effectively with X. laevis [32P]VTG, whereas bovine serum albumin did not. These results represent the first documentation of a successful culture system for receptor-mediated VTG incorporation by teleost oocytes.

The purification and partial characterization of carp, Cyprinus carpio, vitellogenin

A procedure is described for the isolation of intact vitellogenin (c-VTG) from the carp, Cyprinus carpio. VTG was induced in juvenile females using oestradiol-17β and purified from the plasma using a combination of gel-filtration chromatography on Sepharose 6B and ion exchange chromatography on DEAE-cellulose. Purification procedures were conducted at low temperatures (below 9°C) in the presence of the proteolytic enzyme inhibitor aprotinin to prevent degradation. Intact c-VTG had an apparent molecular mass of 390,000 Daltons, but when extracted from plasma in the absence of aprotinin it underwent proteolysis into at least 2 protein fragments (apparent molecular masses of 230,000 and 96,000 Daltons), showing an instability of the native dimer. An amino acid analysis of c-VTG showed that its composition was almost identical to goldfish VTG, a species closely allied to the true carps and also similar to other oviparous vertebrate VTGs. Collectively, these data indicate that using these purification procedures VTG from carp, and probably other teleost species, can be isolated in an intact, highly purified form.

A glycoprotein from the liver constitutes the inner layer of the egg envelope (zona pellucida interna) of the fish, Oryzias latipes

A glycoprotein from the liver, which shares epitopes with chorion (egg envelope or zona pellucida) glycoproteins, is present only in the spawning female fish, Oryzias latipes, under natural conditions. This spawning female-specific (SF) substance is distinct from vitellogenin but closely resembles a major glycoprotein component, ZI-3, of the inner layer (zona radiata interna) of the ovarian egg envelope with respect to some biochemical and immunochemical characteristics. Here we report that the [125I]SF substance, injected into the abdominal cavity of the spawning female fish, was rapidly transported by the blood circulation into the ovary and incorporated into the inner layer of egg envelope of the growing oocytes. The result strongly suggests that the SF substance from the liver is a precursor substance of the major component, ZI-3, of the inner layer of egg envelope in the fish.

Vitellogenin induction by estradiol in channel catfish, Ictalurus punctatus

In oviparous vertebrates estrogens induce hepatic synthesis of vitellogenin (VG), a blood protein sequestered in vitellogenic oocytes and from which lipovitellin (LV) and phosvitin are derived. Our objective was to identify VG in the channel catfish, Ictalurus punctatus. An intraperitoneal injection of estradiol-17 beta into adult male fish induced a dose-dependent accumulation of a 150 kDa protein (EP) in the plasma. EP was detectable in Coomassie blue-stained polyacrylamide gels within 24 hr after injection of 2 mg hormone/100 g body weight. During the next 4 days, EP increased from 5 to about 25% of the total plasma protein. Electrophoretic mobility, peptide mapping, and immunological crossreactivity showed EP to be indistinguishable from a plasma protein in adult females with vitellogenic ovaries. Two major yolk polypeptides, YP1 (120 kDa) and YP2 (29.6 kDa), were precipitated by (NH4)2SO4 from a yolk protein extract. YP1 but not YP2 reacted with an anti-EP polyclonal antiserum in Western blots. Peptide mapping after proteolysis with trypsin showed YPs 1 and 2 to be unique and revealed structural homologies between YP1 and EP. Liver but not pancreatic explants from an estradiol-treated male synthesized and secreted a [35S]methionine-labeled, 150 kDa protein beginning about 2 hr after initial exposure to the label. We tentatively conclude that EP and YP1 represent VG and LV, respectively. YP2 remains unidentified.