Tilapia (Oreochromis niloticus) vitellogenins: development of homologous and heterologous ELISAs and analysis of vitellogenin pathway through the ovarian follicle

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.

Immuno-Enzymatic and Proteomic Approaches for Sexing the African Bonytongue (Heterotis niloticus Cuvier, 1829)

Heterotis niloticus is an African species of Osteoglossiformes that presents biological peculiarities and zootechnical performances favorable for fish farming. However, the absence of a sexual dimorphism hinders the optimization of its reproduction in captivity and limits the understanding of its reproductive behavior. This study is aimed at developing a minimally invasive and reliable sexing method to detect vitellogenin (Vtg) in female plasma. A commercial sexing kit (Acobium, Montpellier, France) for Arapaima gigas—a phylogenetically sister species of H. niloticus—successfully identified only 20% of mature H. niloticus females. Enzyme-linked immunosorbent assays (ELISA) were carried out using three Vtg antibodies. The A. gigas Vtg1 antibody cross-reacted significantly with plasma dilutions of female H. niloticus ranging from 1:1000 to 1:10,000, but with relatively low intensity. The Vtg antibody from Osteoglossum bicirrhosum, another species of Osteoglossiformes, showed non-specific binding with the Vtg of H. niloticus female plasma. Finally, an antibody for H. niloticus Vtg developed in this study allowed us to differentiate the two sexes with plasma coating dilutions ranging from 1:1000 to 1:10,000. The results of the assay were validated by a proteomic approach showing that Vtg-targeted mass spectrometry analysis of H. niloticus blood protein extracts could be used to accurately determine the presence of Vtg in the plasma of mature females. The final validation of the ELISA technique using the H. niloticus Vtg antibody was confirmed by visual sexing of a significant number of blood-sampled fish gonads; 100% of the fish were correctly sexed by the ELISA method.

Vitellogenesis in the Patagonian toothfish (Dissostichus eleginoides) conditioned to a recirculating aquaculture system

The Patagonian toothfish (Dissostichus eleginoides) is a new promising fish species for diversifying the aquaculture industry in Chile because of its high economic value and high international demand. However, when attempting to start aquaculture of a new species, one of the major challenges is successfully achieving conditions to reproduce them. This is particularly difficult when the information on the biology and physiology of the reproduction process of the species in question is scarce, as is the case with D. eleginoides. Additionally, female reproductive dysfunction is more prevalent under culture conditions and it is very important to have tools to evaluate the progress of oocyte maturation. Therefore, evaluation of the vitellogenesis process in addition to measuring gonadosomatic index (GSI) and oocyte diameter is an important parameter for allowing the monitoring of females from a broodstock that will spawn in the reproductive season. This study aimed to develop an enzyme-linked immunosorbent assay (ELISA) specific for the Patagonian toothfish (D. eleginoides) vitellogenine (Vtg) and quantify the plasma level in the fishes, maintained in a recirculation aquaculture system (RAS), throughout their reproductive cycle. A polyclonal antibody was prepared using the isolated major egg protein as antigen. This antibody was specific to the major plasma phosphoprotein identified as Vtg and was used to develop and standardize an indirect ELISA assay. The assay standard curve was linear from 0.1 to 1 µg/ml purified egg yolk protein and the average r² was 0.995. We corroborated our ELISA assay by demonstrating a strong correlation between high levels of plasma Vtg obtained by the assay and the intensity of the corresponding bands in both SDS-PAGE coomassie stained gels and Western Blot. During the two reproductive seasons analyzed, the highest Vtg plasma level was obtained in the majority of the females in the last three months before spawning (December-January). This differs from the wild population in which the spawning occurs during the austral winter (June-September). Therefore, the RAS condition established to maintain in captivity the D. eleginoides allows females to develop mature oocytes normally, as was evidenced by picks of Vtg plasma levels.

Identification and structural characterization of the factors involved in vitellogenesis and its regulation in the African Osteoglossiforme of aquacultural interest Heterotis niloticus (Cuvier, 1829)

The African bonytongue (Heterotis niloticus) is an excellent candidate for fish farming because it has outstanding biological characteristics and zootechnical performances. However, the absence of sexual dimorphism does not favor its reproduction in captivity or the understanding of its reproductive behavior. Moreover, no molecular data related to its reproduction is yet available. This study therefore focuses on the structural identification of the different molecular actors of vitellogenesis expressed in the pituitary gland, the liver and the ovary of H. niloticus. A transcriptomic approach based on de novo RNA sequencing of the pituitary gland, ovary and liver of females in vitellogenesis led to the creation of three transcriptomes. In silico analysis of these transcriptomes identified the sequences of pituitary hormones such as prolactin (PRL), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and their ovarian receptors (PRLR, FSHR, LHR). In the liver and ovary, estrogen receptors (ER) beta and gamma, liver vitellogenins (VtgB and VtgC) and their ovarian receptors (VLDLR) were identified. Finally, the partial transcript of an ovarian Vtg weakly expressed compared to hepatic Vtg was identified based on structural criteria. Moreover, a proteomic approach carried out from mucus revealed the presence of one Vtg exclusively in females in vitellogenesis. In this teleost fish that does not exhibit sexual dimorphism, mucus Vtg could be used as a sexing biomarker based on a non-invasive technique compatible with the implementation of experimental protocols in vivo.

Development of ELISAs for the detection of vitellogenin in three marine fish from coastal areas of China

Estrogenic pollution has aroused great concern for its adverse effects on marine organisms. This study aimed to establish biomarker-based methods for detecting environmental estrogens using vitellogenin (Vtg) of teleost fishes inhabiting coastal areas of China. Firstly, Vtgs in marbled flounder (Pseudopleuronectes yokohamae), black rockfish (Sebastes schlegelii) and fat greenling (Hexagrammos otakii) were purified, characterized and used to prepare antibodies. Then, Vtg ELISA for each species was developed using purified Vtg and its antibody. Marbled flounder Vtg ELISA had a working range of 3.9-500 ng/mL and a detection limit of 2.1 ng/mL, and black rockfish Vtg ELISA had strong cross-reactivity with marbled flounder Vtg. Furthermore, Vtg induction in male marbled flounder exposed to pentadecafluorooctanoic acid (PFOA) was measured by developed ELISA. Plasma Vtg concentrations were significantly increased with PFOA concentrations in seawater and fish muscle. Therefore, Vtg ELISAs for these species might be useful tools for monitoring marine environmental estrogens.

Short-term induction of vitellogenesis in the immature male yellowfin seabream (Acanthopagrus latus) exposed to bisphenol A and 17β-estradiol

Bisphenol A (BPA) is a known environmental endocrine-disrupting chemical that is widely used in plastics manufacturing. BPA enters in the aquatic environment mainly through urban and industrial sewage effluents, thereby posing a potential threat to organisms living in these ecosystems. This study was conducted to investigate the effect of BPA on VTG production with direct (sodium dodecyl sulfate-polyarylamide gel electrophoresis) and indirect (alkali-labile phosphate (ALP), total plasma calcium and protein) methods in immature male yellowfin seabream ( Acanthopagrus latus) as a marine fish model. Fish were randomly distributed into seven groups that were administered 1, 10, 50, and 100 µg g−1 week−1 of BPA and 2 µg g−1week−1 of 17β-estradiol (E2) over a period of 2 weeks. Solvent controls received olive oil, whereas controls were not injected. The fish were sampled on days 0, 7, and 14, and their blood plasma and liver were obtained. The results showed that the hepatosomatic index of all treated fish was elevated in comparison with controls. Direct and indirect indicators showed that fish VTG protein was induced by BPA and E2 exposure. The protein was found to have two bands with molecular weights around 210 and 190 KDa. ALP, total plasma calcium and protein levels were increased in dose- and time-dependent manners. The results of this study demonstrated that short-term exposure of yellowfin seabream to BPA induced adverse effects in the reproductive system of hermaphrodite fish.

Purification and development of ELISAs for two forms of vitellogenin in Indian walking catfish, Clarias batrachus (L.)

Two forms of vitellogenin (Vg: Vg1 and Vg2) were purified from the plasma of estradiol-17β (E₂)-treated Indian walking catfish, Clarias batrachus, by gel filtration and adsorption chromatography. Native Vg1 and Vg2 had apparent molecular masses of 375 and 450 kDa, respectively, and both Vgs resolved into two similar major bands (95 and 67 kDa) in SDS-PAGE under reducing condition. Polyclonal antisera raised against each form of Vg were absorbed with a combination of hypophysectomized male catfish serum proteins and alternate Vg to ensure specificity. Immunological analyses verified the presence of Vg1 and Vg2 in the plasma of female catfish. Homologous ELISAs were developed for Vg1 and Vg2 using their respective harvested antisera, which exhibited the detection limit of 100 ng ml^-1 for Vg1 and 40 ng ml^-1 for Vg2, and low level of cross-reactivity (not parallel to the standard) was found with alternate Vg in each assay. Treatment of male catfish with E₂ induced both Vgs showing a proportionate ratio of Vg1 to Vg2 at 5.6:1. Plasma concentrations of both Vgs measured by ELISAs at different reproductive phases of field collected female catfish increased in accordance with the ovarian development, keeping the proportionate ratio of Vg1 to Vg2 at about 2:1 in fish undergoing vitellogenesis during prespawning period and 1:20 during spawning period, suggesting that Vg1 may be the major Vg to contribute in yolk formation, whereas Vg2, besides its role in yolk formation, may facilitate other physiological functions. The present study, thus, demonstrates the occurrence of two unequally synthesized Vgs in the catfish.

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.

Molecular cloning of vitellogenin gene and mRNA expression by 17alpha-ethinylestradiol from slender bitterling

Indigenous aquatic population such as fish could be used as a successful test species for evaluating the ecological effects in aquatic environment. In the present study, vitellogenin (Vtg) from slender bitterling (Acheilognathus yamatsutae), an indigenous aquatic species in Korea, was cloned and sequenced to determine if the Vtg gene possesses an important characteristic so as to act as a sensitive biomarker for estrogenic endocrine disrupting chemicals (EEDCs). The sbVtg cDNA is 5010 bp in length, containing a 4653 bp open reading frame, which encodes 1550 amino acid residues. The sbVtg cDNA was divided into lipovitellin heavy chain (LvH), phosvitin (Pv), lipovitellin light chain (LvL) as well as a beta'-component (beta'-c) domain, and belongs to VtgAo2. SbVtg has conserved important sequences for Vtg functions such as signal peptide, VtgR-binding region, and disulfide bond formation, all of which are consistent with those of other teleosts. In addition, the male slender bitterling aqueous exposed to 17 alpha-ethinylestradiol (EE2, 12.5, 25, and 50 ng/L) produced a statistically significant and concentration-dependent increase in hepatic Vtg mRNA expression, which showed a similar pattern to biliary estrogenic activity, measured by ERE-reporter gene assay. Thus, this study clearly indicates that the induction of Vtg in slender bitterling might be a suitable biomarker in toxicological research of EEDCs.

Hybrid ELISAs for vitellogenins of the endangered copper redhorse Moxostoma hubbsi and the shorthead redhorse Moxostoma macrolepidotum (Cypriniformes, catostomidae)

The shorthead redhorse (sr) Moxostoma macrolepidotum is endemic in North America, while in Canada the copper redhorse (cr) Moxostoma hubbsi is classified as endangered. A commercial heterologous carp vitellogenin (VTG) sandwich ELISA underestimates VTGs in these species. Hybrid ELISAs, using anti-carp VTG antibodies and purified sr- and cr-VTGs as standards, were validated to measure VTGs in plasma and surface mucus of redhorse species. The hybrid ELISAs showed good precision, sensitivity and accuracy. Following induction with beta-estradiol 3-benzoate (E2B), levels of plasma VTG (mean+/-SEM) in male sr increased from 2.7+/-1.5 microg/ml to 16.5+/-2.2mg/ml. In immature cr, plasma VTG increased to 70.1+/-13.8 mg/ml after induction, from an initial value of 37.7+/-51.0 microg/ml. Levels of VTG in mucus from E2B-injected fish were highly correlated (p<0.0001) with levels in plasma, but not in a non-induced mature female. Hybrid assays are a good compromise between homologous and heterologous assays, especially for small-bodied or endangered fish species. The performance of the hybrid assays strongly suggests they could be used to determine exposure of these species to estrogenic contaminants and contribute to restoration efforts of the copper redhorse.

Towards a universal scale to assess sexual maturation and related life history traits in oviparous teleost fishes

The literature presents a confusing number of macroscopic maturation scales for fish gonads, varying from over-simplified scales comprising three to four stages to highly specific and relatively complicated nine-stage scales. The estimation of some important life history traits are dependent on a correct assessment and use of the gonadal maturation scales, and frequent mistakes have been made in many studies. The goal of this report is to provide a synthetic, relatively simple, yet precise maturation scale that works for most oviparous teleost fishes. The synthetic scale proposed here is based on the correspondence between key physiological and cytological processes of gamete development and corresponding modifications observed at the macroscopic level. It is based on previous and ongoing studies of several fish species pertaining to some of the most important African and Neotropical taxa, including Characiformes, Siluriformes, Osteoglossiformes and Perciformes. This scale should allow for standardized protocols of field studies and improve intra- and inter-specific comparisons of life history traits. Guidelines on the correct use of this scale to estimate these life history traits are provided.

Gender determination in the Paiche or Pirarucu (Arapaima gigas) using plasma vitellogenin, 17beta-estradiol, and 11-ketotestosterone levels

Arapaima gigas is an air-breathing giant fish of Amazonian rivers. Given its great economic and cultural importance, the aquaculture development of this species represents an evident solution to face the decline of wild populations. In captivity, reproduction occurs generally in large earthen ponds where stocks of a few tens of brooders are maintained together at the beginning of the rainy season (December-March in the Peruvian Amazon). Fry production relies on the spontaneous formation of male and female pairs, which build a nest, delimit a territory and guard the offspring for at least 20 days from other congeners and predators. However, as sex determination of A. gigas is not possible by morphological criteria, it is very difficult to optimize reproduction conditions and fry production in each pond, which seriously hampers the culture of this species. This situation prompted us to develop sexing methodologies based on (1) the detection of female specific plasma Vitellogenin (Vtg) using an enzyme immuno assay (EIA), and (2) the determination of plasma 17beta-estradiol and 11-ketotestosterone levels for immature specimens. The Vtg purification was performed by electro-elution after polyacrilamide gel electrophoresis (PAGE) from plasma of 17beta-estradiol treated A. gigas juveniles. Two different Vtg molecules were isolated, (Vtg(1) and Vtg(2)) with 184 and 112 kDa apparent molecular masses, respectively, and two antibodies were raised in rabbits for each Vtg molecule. Adult fish were 100% accurately sexed by Vtg EIA, while 100% of immature fish and 95% of adults were accurately sexed by 17beta-Estradiol and 11-Ketestosterone ratios. We also observed different color pattern development in male and female adult fish (6-year-olds) around the reproductive period.

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.

Vitellogenin cleavage products as indicators for toxic stress in zebra fish embryos: a proteomic approach

Vitellogenins (Vtgs) are the major yolk proteins in all oviparous animals. Systematic and regulated processing of these during embryogenesis is crucial for embryonic development. In the present study, toxicant-induced disturbance of Vtg degradation processes during Danio rerio (DR) embryogenesis was analysed to establish a sensitive tool for monitoring toxic stress at the molecular level. A 2-DE-based proteomic approach for whole DR embryos was established to study Vtg cleavage products (lipovitellin (Lv) derivatives). Ethanol was chosen as a positive control for a toxicity related change in the proteome of whole zebra fish embryos. Protein extracts from embryos treated with two ethanol concentrations, 0.5 and 2% v/v, showing either no or very strong visible effects, like absent heartbeat and blood circulation, were examined. Significant changes in the Lv pattern were detected for both conditions. The results are interpreted as scope for the use of the high abundant Lv derivatives as sensitive stress indicators in zebra fish embryos reflecting the overall fitness of the intact organisms.

Induction of three vitellogenins by 17beta-estradiol with concurrent inhibition of the growth hormone-insulin-like growth factor 1 axis in a euryhaline teleost, the tilapia (Oreochromis mossambicus)

The objective of the present study was to utilize the male Mozambique tilapia (Oreochromis mossambicus) as a model for examining the molecular mechanisms that mediate the physiological transition between somatic and gonadal growth in female teleost fish, and in vertebrates in general. Partial cDNAs that encode multiple forms of vitellogenin (Vtg), which is the major precursor of yolk proteins, were cloned from estrogen-treated males and utilized to develop real-time quantitative RT-PCR assays, which were supplemented by an assay for Vtg immunoreactivity in the plasma. Alignment analyses of the amino acid sequences deduced from the vtg cDNAs revealed three distinct tilapia Vtgs, which were categorized as Aa-, Ab-, and C-type Vtgs. A single injection of male tilapias with 17beta-estradiol (E(2)) at 5 microg/g body weight significantly increased the plasma E(2) and hepatic levels of all three vtg transcripts within 1 day. Plasma E(2) levels declined after 3 days, whereas the plasma Vtg immunoreactivity and hepatic levels of the three vtg transcripts continued to increase. Hepatic expression of the estrogen receptor (esr) 1 gene, but not the esr2 gene, also increased markedly 1 day after E(2) injection and remained elevated for 5 days. While plasma growth hormone (Gh) levels were unaffected, hepatic expression of transcripts that encoded the Gh receptor and insulin-like growth factor 1 (Igf1) was suppressed by E(2), as were the plasma Igf1 levels. These results clearly suggest a distinct negative interplay between the growth and reproductive axes at the molecular level of key hepatic regulatory pathways involved in the control of energy utilization by gonadal and somatic growth processes.