Cloning and characterization of vitellogenin cDNA from the common Japanese conger (Conger myriaster) and vitellogenin gene expression during ovarian development

Health Effects and Life Stage Sensitivities in Zebrafish Exposed to an Estrogenic Wastewater Treatment Works Effluent

A wide range of health effects in fish have been reported for exposure to wastewater treatment work (WwTW) effluents including feminized responses in males. Most of these exposure studies, however, have assessed acute health effects and chronic exposure effects are less well established. Using an Estrogen Responsive Element-Green Fluorescent Protein (ERE-GFP)-Casper transgenic zebrafish, we investigated chronic health effects and life stage sensitivities for exposure to an estrogenic WwTW effluent and the synthetic estrogen 17α-ethinylestradiol (EE2). Exposure to the WwTW effluent (at full strength;100%) and to 10 ng/L (nominal) EE2 delayed testis maturation in male fish but accelerated ovary development in females. Exposure to 50% and 100% effluent, and to 10 ng/L EE2, also resulted in skewed sex ratios in favor of females. Differing patterns of green fluorescent protein (GFP) expression, in terms of target tissues and developmental life stages occurred in the ERE-GFP- zebrafish chronically exposed to 100% effluent and reflected the estrogenic content of the effluent. gfp and vitellogenin (vtg) mRNA induction were positively correlated with measured levels of steroidal estrogens in the effluent throughout the study. Our findings illustrate the importance of a fish's developmental stage for estrogen exposure effects and demonstrate the utility of the ERE-GFP zebrafish for integrative health analysis for exposure to estrogenic chemical mixtures.

Purification, characterization and expression of two vitellogenins in the Indian freshwater murrel Channa punctatus

The present study was undertaken to characterize different vitellogenins in Channa punctatus. Protein purification by gel chromatography followed by fast protein liquid chromatography (FPLC) revealed existence of two different Vg forms. Liquid chromatography tandem mass spectrophotometry (LC-MS/MS) suggested the existence of Vga and Vgb. Cloning of partial sequences of vga and vgb mRNA and phylogenetic analysis substantiated the existence of two vitellogenins. Real time PCR for vga and vgb genes from liver of estradiol-17β (E2) treated fish reveals difference in expression levels of transcripts of these two genes. vgb is expressed at lower dose of estradiol suggesting a higher sensitivity to estradiol. The present study thus proposes different regulatory control for the expression of these two genes and vgb as a superior biomarker than vga to assess exposure of C. punctatus to environmental estrogens.

Composition and phylogenetic analysis of vitellogenin coding sequences in the Indonesian coelacanth Latimeria menadoensis

The coelacanth Latimeria menadoensis, a living fossil, occupies a key phylogenetic position to explore the changes that have affected the genomes of the aquatic vertebrates that colonized dry land. This is the first study to isolate and analyze L. menadoensis mRNA. Three different vitellogenin transcripts were identified and their inferred amino acid sequences compared to those of other known vertebrates. The phylogenetic data suggest that the evolutionary history of this gene family in coelacanths was characterized by a different duplication event than those which occurred in teleosts, amniotes, and amphibia. Comparison of the three sequences highlighted differences in functional sites. Moreover, despite the presence of conserved sites compared with the other oviparous vertebrates, some sites were seen to have changed, others to be similar only to those of teleosts, and others still to resemble only to those of tetrapods.

Molecular cloning and mRNA expression of the vitellogenin and nuclear receptor gene induced by 17β-estradiol in the mud carp, Cirrhinus molitorella

Vitellogenins (VTGs), the precursors of yolk proteins, are crucial for the embryonic development of teleosts, and have also been studied extensively as biomarkers for environmental estrogenic mimics. The cDNA of a VTG was isolated from the liver of male mud carp (Cirrhinus molitorella) following induction by 17β-estradiol (E(2)) using 3'- and 5'-RACE methods. It was 4,216 bp in length, and encoded a putative protein of 1,342 amino acids. This putative VTG contained complete portions of lipovitellin I (LVI) and phosvitin, but lacked the C-terminal half of LVII and was thus classed as a type I vitellogenin. In addition, the partial cDNA of estrogen receptors (ERα and ERβ) and androgen receptors (AR) were cloned. The mRNA expression of VTG, ERα, ERβ and AR were examined in the liver of juvenile mud carp exposed to E(2) (0, 5, 50 and 500 ng/l) in the water for 2, 4, 6 and 8 days. Quantitative reverse transcription PCR (RT-PCR) revealed a significant increase in transcript levels of VTG and ERα but not of ERβ and AR. VTG and ERα were expressed in a time-dose-dependent manner. Our results imply that ERα may be the principal subtype that regulates VTG, and that VTG mRNA of mud carp is an ideal biomarker to detect environmental estrogens.

Influence of temperature regime on endocrine parameters and vitellogenesis during experimental maturation of European eel (Anguilla anguilla) females

We examined the effect of temperature in European silver eels during their maturation induced by injections of carp pituitary extract on endocrine parameters: pituitary fshβ and lhβ expression, plasma 17β-estradiol (E2) and vitellogenin, estrogen receptor 1 (esr1), and vitellogenin 2 (vtg2) expression in liver. A variable thermal regime (T10) that increased from 10° to 14° and 17°C was compared with a constant 20°C regime (T20) during 12 weeks. T10 caused a faster development until week 8, higher fshβ, lhβ, esr1 expression, and higher E2 levels. The results strongly suggest that T10 is inducing a higher endogenous FSH level which increases the E2 circulating level during vitellogenesis. A variable thermal regime induced an fshβ expression and E2 profile in vitellogenic hormonally matured eel females that were more similar to the profile observed in other naturally maturing fish.

Cloning, expression, and induction by 17-beta estradiol (E2) of a vitellogenin gene in the white cloud mountain minnow Tanichthys albonubes

Vitellogenins (Vtgs), the precursors for the yolk proteins, are very important for the embryonic development of teleosts, and have also been studied extensively as biomarkers for environmental estrogenic mimics. The cDNA for a Vtg was isolated from the liver of the female white cloud mountain minnow (Tanichthys albonubes) by 3'- and 5'-RACE methods. It is 4,171 bp in full length, and encodes a putative protein of 1,326 amino acids. This putative Vtg, designated as wcmmVtg, contains complete portions of LVI and PV, but lacks the C-terminal half of LVII and thus belongs to type I vitellogenin. In addition to the liver of the female fish, wcmmVtg was also shown to be expressed in the ovary. During ovarian development, the mRNA expression of wcmmVtg in both the liver and ovary was continuously increased from the previtellogenic to late vitellogenic stages, but then decreased significantly at post-spawning stage. In the male fish, expression of wcmmVtg mRNA was induced in the liver by treatment with E2 (10 and 100 ng/l) for 14 days. These results suggest that the Vtg originated from the ovary of the white cloud mountain minnow may also contribute to the accumulation of yolk proteins during oocyte growth, and that the male white cloud mountain minnow is sensitive to the estrogenic treatment in terms of Vtg mRNA expression, which could also be applied to monitor the environmental estrogenic mimics.

Characterization of vtg-1 mRNA expression during ontogeny in Oreochromis mossambicus (PETERS)

The yolk-precursor lipoprotein, vitellogenin (VTG) has been widely recognized as a biomarker for the detection of estrogenic activity in water-borne chemical pollutants. We characterized the expression status of this important constituent of reproduction in the Mozambique tilapia (Oreochromis mossambicus), a tilapiine freshwater fish species indigenous to Southern Africa, and investigated its utility in detection of exposure to estrogen using a quantitative real-time polymerase chain reaction (QPCR) assay. We initially isolated a 3kb upstream promoter region of the vtg gene and identified putative binding sites for several regulatory factors including estrogen receptor (ESR). Evidence for the expression of several splice-site vtg mRNA variants was found in a number of tissue types. A quantitative real-time polymerase chain reaction (QPCR) assay was subsequently developed based upon a specific primer pair (OMV6/9) that selectively amplified the liver-enriched transcript. The level of this transcript in liver tissue was high in females and lower, but detectable, in males and was significantly increased in male fish following laboratory exposure to 17beta-estradiol (E(2)). This study further established that juvenile whole body homogenates (WBHs) contained extremely low levels of liver-specific vtg mRNA between 5 and 110 days post-fertilization (dpf) compared to adult male liver. Subsequent exposure of 20 dpf juveniles to E(2) showed a substantial increase in this transcript within hours, and when compared to classic male model under same conditions, the juveniles were remarkably more sensitive. We therefore conclude that the quantification, using QPCR methodology, of vtg mRNA expression in 20 dpf O. mossambicus juveniles has promise for assessing estrogenic EDC activity in aquatic sources.

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.

Effects of adrenergic agonists on the extrahepatic expression of vitellogenin Ao1 in heart and brain of the Chinese rare minnow (Gobiocypris rarus)

Teleost vitellogenins (VTGs) are large multidomain apolipoproteins and traditionally considered as the estrogen responsive precursors of the major egg yolk proteins. We identified five clones encoding VTGs, about 16% of the random EST clones from our constructed cDNA library from Chinese rare minnow liver tissue treated with 17beta-estradiol (E2). Full-length vtgAo1 has been obtained based on the sequence information of four partial cDNA inserts by RACE. The inducibility of the vtgAo1 expression in liver by E2 was confirmed by RT-PCR. The presence of vtgAo1 transcripts have been observed primarily in liver. However, a significant level of the vtgAo1 was found in an unexpected location, heart, particularly in atrial cells by RT-PCR and whole mount in situ hybridization analyses. The vtgAo1 mRNA expression in heart and liver tissue could be suppressed by both alpha-adrenergic agonist, phenylephrine (PE) and beta-adrenergic agonist, isoproterenol (ISO). The expression of VTG in the heart observed in the present studies suggested it may provide protection from surplus intracellular lipids in fish cardiomyocytes as triglyceride transport proteins do in mammals. The results also indicated that the production of teleost vtg in vivo can be regulated by not only estrogenic agents, but adrenergic signals as well.

Ovarian follicle cells are the site of vitellogenin synthesis in the Pacific abalone Haliotis discus hannai

Only a few biochemical and molecular studies on yolk proteins (vitellins) have been carried out in mollusks, mainly in bivalves, while information on prosobranch vitellogenesis is still limited. In this study, we cloned a full-length cDNA encoding vitellogenin (Vg) in the Pacific abalone Haliotis discus hannai. The complete Vg cDNA consists of 7753 nucleotides with a long open reading frame encoding 2391 amino acid residues. The deduced primary structure contains the N-terminal amino acid sequences of the 95 kDa and 150 kDa subunits of vitellin of the abalone and shows similarities to Vgs of other mollusk, fish, nematode and coral species. In common with bivalve Vgs, the abalone Vg gene was expressed only in the ovary. In situ hybridization analysis further localized Vg mRNA to the follicle cells in the ovary. We conclude that the follicle cells are the site of Vg synthesis in H. discus hannai.

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

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