Molecular cloning and expression analysis of estrogen receptor betas (ERβ1 and ERβ2) during gonad development in the Korean rockfish, Sebastes schlegeli

Molecular cloning of estrogen receptor and its function on vitellogenesis in pompano (Trachinotus ovatus)

Estrogen receptors (ERs) play a critical role in vitellogenesis (Vtgs). However, the contribution of each ER for the regulation of vtgs expression was not analyzed clearly in teleosts. In the present study, three ers isoforms (erα, erβ1, and erβ2) were cloned in pompano (Trachinotus ovatus). Real-time PCR and enzyme-linked immunosorbent assay (ELISA) was used to detect the effects of 17β-estradiol (E2) on ERs and Vtgs in the liver of pompano. In vivo injection experiments showed that E2 significantly increased the expressions of ers and vtgs. ER broad spectrum antagonist Fulvestrant significantly attenuated the E2- induced up-regulation of ers and vtgs in a dose-dependent manner. ERα antagonist Methyl-piperidino pyrazole (MPP) significantly attenuated the up-regulation of erα, erβ2, vtg-B and vtg-C, and promoted the expressions of erβ1 and vtg-A. ERβ antagonist Cyclofenil significantly inhibited the expressions of erβ1, erβ2, vtg-A and vtg-C, and promoted the expressions of erα and vtg-B. In addition, E2 significantly increased the protein level of Vtg, while Fulvestrant, MPP and Cyclofenil significantly inhibited the protein level of Vtg in a dose-dependent manner. Our results indicate that E2 may regulate the expression of each vtg with different subtypes of ERs, and shows a distinct compensatory expression effect on the regulation for ers and vtgs, which provides a theoretical basis for reproductive endocrinology study in pompano.

Comparative transcriptomic analysis of gonadal development and renewal in the ovoviviparous black rockfish (Sebastes schlegelii)

BACKGROUND

The black rockfish (Sebastes schlegelii) has an ovoviviparous reproductive pattern and long-term sperm storage, resulting in asynchronous gonadal development between the sexes. However, the comprehensive understanding of gonadal development in black rockfish has not yet been achieved. Here, we studied gonadal development and germ cell renewal using histology and RNA-seq.

RESULTS

In this study, RNA-seq was performed on testes and ovaries to characterize key pathways and genes that are active during development and gamete maturation in black rockfish. Differentially expressed genes (DEGs) were identified and annotated in 4 comparisons (F_III vs. F_IV, F_IV vs. F_V, M_III vs. M_IV and M_IV vs. M_V). Based on analysis of DEGs enriched in the testis, 11 and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were mapped to the M_III vs. M_IV group and the M_IV vs. M_V group, respectively. DEGs in ovarian development were also classified into 10 groups according to their biological functions. The expression patterns of the selected genes determined by qPCR were significantly correlated with the RNA-Seq results, supporting the reliability and accuracy of the RNA-Seq analysis. E2 levels showed down regulation from previtellogenesis to mature stage in female and T level showed down regulation from spermatogenesis to regressed stage in the male.

CONCLUSIONS

The categories "intercellular interaction and cytoskeleton", "molecule amplification" and "repair in the cell cycle" were revealed to be crucial in testis development and spermatogenesis, as was the biosynthesis of a series of metabolites. Our results provide comprehensive insight into black rockfish gonadal development and provide a basis for further study of reproductive physiology and molecular biology in ovoviviparity teleosts.

Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE2) than other common model teleosts: A comparative review of reproductive effects

The environmental estrogen 17α-ethinylestradiol (EE₂) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE₂. This relative insensitivity to EE₂ exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE₂ in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE₂ accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE₂ has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE_2, it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E₂) by full grown ovarian follicles remains high; unlike other teleost models where E₂ synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE₂. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE₂ exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE₂ exposure between mummichog and other commonly used model teleosts.

Transcriptional Activity of an Estrogen Receptor β Subtype in the Medaka Oryzias dancena

In vertebrate reproductive system, estrogen receptor (ER) plays a pivotal role in mediation of estrogenic signaling pathways. In the present study, we report the cDNA cloning, expression analysis, and transcriptional activity of ERβ1 subtype from medaka Oryzias dancena. The deduced O. dancena ERβ1 (odERβ1; 519 amino acids) contained six characteristic A/B to E/F domains with very short activation function 2 region (called AF2). A phylogenetic analysis indicated that odERβ1 was highly conserved among teleost ERβ1 subgroup. A conventional RT-PCR revealed that the odERβ1 transcripts were widely distributed in the multiple tissues, the ovary, brain, gill, intestine, kidney, and muscle. Further, the relatively higher odERβ1 expressions in the ovary and brain were clearly reproduced in RT-qPCR assay. When HA-fused odERβ1 expression vector was transfected into HEK293 cells, an immunoreactivity for odERβ1 was mainly detected in the nucleus part. Finally, an estrogen responsive element driven luciferase reporter assays demonstrated that the transcriptional activity of odERβ1 significantly increased by estradiol-17β (E2) in a dose dependent manner (p<0.05). However, fold-activation of odERβ1 in the presence of E2 was markedly weak, when it compared with those of O. latipes ERβ1. Taken together, these data suggest that odERβ1 represents a functional variant of teleost ERβ subtype and provides a basic tool allowing future studies examining the function of F domain of ERβ1 subtype and expanding our knowledge of ERβ evolution.

Involvement of Estrogen and Its Receptors in Morphological Changes in the Eyes of the Japanese Eel, Anguilla japonica, in the Process of Artificially-Induced Maturation

During the long migration from river habitats to the spawning ground, the Japanese eel undergoes sexual maturation. This spawning migration occurs concurrently with morphological changes, such as increases in eye size; however, the mechanisms by which sex steroids and their receptors influence these changes in peripheral tissues remain unclear. The aim of this study was to investigate changes in the eyes of female Japanese eels during sexual maturation, and our research focused on estrogen receptor (ER)α and ERβ transcripts. During ovarian development, the gonadosomatic index increased and yolk-laden oocytes developed rapidly. These changes occurred in conjunction with a steady increase in plasma levels of estradiol-17β (E₂). Concomitant increases in transcript levels of ERα and ERβ in eye, brain, pituitary, and ovary were also observed. Fluorescence in-situ hybridization analyses revealed that ERα and ERβ transcripts were present in the choriocapillary layer and photoreceptor layer of the eyes, and the analysis also revealed that their signals in these layers became stronger in mature females compared to those observed in immature females, suggesting that under the influence of gonadotropins, morphological changes in the eyes are regulated by E₂ through the activation of its receptors. In conclusion, E₂ plays a crucial role in physiological adaptations that occur in peripheral tissues during the spawning migration.

Comparison of steroidogenic gene expression in mummichog (Fundulus heteroclitus) testis tissue following exposure to aromatizable or non-aromatizable androgens

Androgens are a recognized class of endocrine disrupting compounds with the ability to impact reproductive status in aquatic organisms. The current study utilized in vitro exposure of mummichog (Fundulus heteroclitus) testis tissue to either the aromatizable androgen 17α-methyltestosterone (MT) or the non-aromatizable androgen 5α-dihydrotestosterone (DHT) over the course of 24 h to determine if there were differential effects on steroidogenic gene expression. Testis tissue was exposed to androgen concentrations of 10^-12 M, 10^-9 M and 10^-6 M for 6, 12, 18 or 24 h, after which a suite of steroidogenic genes, including steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase (3βhsd) and cytochrome P450 17A1 (cyp17a1), were quantified using real-time polymerase chain reaction. Both androgens affected steroidogenic gene expression, with most alterations occurring at the 24-hour time point. The gene with the highest fold-change, and shortest interval to expression alteration, was 3βhsd for both androgens. Potential differences between the two model androgens were observed in increased expression of cyp17a1 and 11β-hydroxysteroid dehydrogenase (11βhsd), which were only altered after exposure to DHT and in expression levels of cytochrome P450 11A1 (cyp11a1), which was upregulated by MT but not altered by DHT. Results from this study show both androgens interact at the gonadal level of the hypothalamus-pituitary-gonadal axis and may possess some distinct gene expression impacts. These data strengthen the current research initiatives of establishing in vitro test systems that allow toxic potential of untested chemicals to be predicted from molecular perturbations.

Identification of suh gene and evidence for involvement of notch signaling pathway on gonadal differentiation of Yellow River carp (Cyprinus carpio)

The suh gene is crucial in Notch pathway and regulates mammalian gonad development. In this study, the sequences of suh1 and suh2 genes in Yellow River carp (Cyprinus carpio) were verified. The partial 5'-flanking regions of suh1 and suh2 were analyzed and several potential transcription factor-binding sites were identified. Phylogenetic, gene structure, and chromosome synteny analyses revealed that carp suh1 and suh2 were orthologs and homologous to vertebrate suh. Investigation of the expression profiles of suh1 and suh2 with qPCR showed that these genes were abundant in the brain and gonad of carp, with suh1 exhibiting sexual dimorphism expression pattern in gonad. To study the relationship between gonad differentiation and Notch signaling, primordial gonads were exposed to DAPT, an inhibitor of Notch signaling, in vitro and in vivo. The results revealed a significant downregulation of suh1 and other Notch genes in vitro. In addition, expression of male-biased genes, such as amh, dmrt1, etc., was downregulated, whereas that of female-biased genes, such as foxl2, gdf9, etc., was upregulated. When the primordial gonads were subjected to long-term DAPT exposure, an increased proportion of ovary and delay in testis development were observed. These results suggest that suh gene may have a conservative function between teleosts and mammals. Furthermore, Notch signaling was found to be involved in gonad differentiation in Yellow River carp, and DAPT was noted to inhibit and enhance the expression of male- and female-biased genes, respectively, and induce the increase in number of females.

Molecular characterization and quantification of estrogen receptors in turbot (Scophthalmus maximus)

Estrogens regulate various reproductive processes via estrogen receptor (ER)-mediated signaling pathway in vertebrates. In this study, full-length sequences coding for ERα, ERβ1 and ERβ2 were isolated from female turbot (Scophthalmus maximus) by homology cloning and a strategy based on rapid amplification of cDNA end-polymerase chain reaction (RACE-PCR). The nucleotide and amino acid sequences of turbot ERs showed high homologies with the corresponding sequences of other fish species and significant homology with the Japanese flounder (Paralichthys olivaceus) and the European sea bass (Dicentrarchus labrax). Turbot ERs contained six typical nuclear receptor-characteristic domains and exhibited high evolutionary conservation in the functional domains. Quantitative real-time polymerase chain reaction analysis revealed that the erα and erβ (β1, β2) mRNAs were abundant in the liver and ovary, respectively. Furthermore, hepatic mRNA levels of erα and vitellogenin (vtg) were found increased gradually from pre-vitellogenesis to late-vitellogenesis stages, with the highest values observed at the late-vitellogenesis stage, and then decreased from migratory-nucleus to atresia stages. However, mRNA levels of erα in the ovary remained unchanged during ovarian development. Hepatosomatic index, gonadosomatic index, serum estradiol-17β and the mRNA levels of erβ1 and erβ2 in the ovary manifested results similar to the expression of erα mRNAs in the liver. These findings indicated that ERα is mainly involved in hepatic vitellogenesis, and ERβs may play crucial roles to regulate ovarian development in turbot. Overall, this study improves understanding of the physiological functions of turbot ERs, which will be valuable for fish reproduction and broodstock management.

Cloning, expression and functional characterization on vitellogenesis of estrogen receptors in Scatophagus argus

Estrogen receptors (Er) play a critical role in vitellogenesis. Three ers (erα, erβ1 and erβ2) and vitellogenins (vtg-A, vtg-B and vtg-C) subtypes were isolated in various fish species, while the contribution of each Er to the regulation of vtgs expression was not analyzed in detail. Here, erα, erβ1 and erβ2 were cloned and all were found to be expressed in female liver in Scatophagus argus. During proteic vitellogenesis stage, erα was simultaneously up-regulated, while erβ1 and erβ2 were not, with three vtgs in female liver. The effects of 17β-estradiol (E₂) alone or combined with Er antagonists on ers, vtgs mRNA expressions and Vtg protein content in incubated male liver were examined by real-time PCR and enzyme-linked immunosorbent assay (ELISA), respectively. The expressions of erα, erβ1, vtgs mRNA and Vtg protein increased significantly after 24h incubation with E₂ (0.1, 1 and 10μM), while Er nonselective antagonist ICI 182 780 (0.01, 0.1 and 1μM) significantly attenuated the up-regulation effects of E₂ on ers, vtgs mRNA and Vtg protein in a dose-dependent manner. Erα selective antagonist Methyl-piperidinopyrazole (MPP) (0.01, 0.1 and 1μM) significantly attenuated the up-regulation effects of E₂ on erα, vtg-B, vtg-C mRNA and Vtg protein, while promoted the expression of erβ1 and vtg-A. Erβ selective antagonist Cyclofenil (0.01, 0.1 and 1μM) attenuated the up-regulation effects of E₂ on erβ1, erβ2, vtg-A, vtg-C mRNA and Vtg protein while promoted the expression of erα and vtg-B. Our results suggest that the regulation of Ers on different vtgs was divergent in S. argus.

Cloning, Characterization, and Expression Profile of Estrogen Receptor in Common Chinese Cuttlefish, Sepiella japonica

Sex steroid hormones are widely detected in molluscs and play important roles in sex determination, gonadal tissue maturation, and gametogenesis. Nevertheless, the signaling pathways of sex steroids in cephalopod have not yet been clearly elucidated. In the present study, a full-length sequence encoding the estrogen receptor (ER) was isolated from common Chinese cuttlefish, Sepiella japonica. The sjER cDNA clone was found to contain 1,788 nucleotides including a 1,470 bp open reading frame encoding 489 amino acid (aa) residues. The deduced ER protein consisted of six nuclear receptor characteristic domains. Based on a phylogenetic analysis, the ER DNA-binding domain and ligand-binding domain are highly conserved compared to other mollusc ERs. Highest aa identities were found for sjER with common octopus (Octopus vulgaris) ER (89%) and pacific oyster (Crassostrea gigas) ER (61%). Tissue expression analysis confirmed that sjER was widely distributed among tissues and predominantly expressed in the brain, liver, gonad (testis and ovary), and other accessory sexual gland (nidamental gland). The ER expression was temporally upregulated in the brain, liver, and ovary during the early sexual maturation period in S. japonica, which is coincident with the fluctuation of ovary estradiol content. These suggest that sjER may be involved in regulating the reproductive cycle of S. japonica. A fusion protein transient transfections assay showed that sjER was mainly located in the nucleus, suggesting a possible orthodox working mechanism of S. japonica ER in the nucleus through a ligand-dependent activation of specific gene transcription.

Three nuclear and two membrane estrogen receptors in basal teleosts, Anguilla sp.: Identification, evolutionary history and differential expression regulation

Estrogens interact with classical intracellular nuclear receptors (ESR), and with G-coupled membrane receptors (GPER). In the eel, we identified three nuclear (ESR1, ESR2a, ESR2b) and two membrane (GPERa, GPERb) estrogen receptors. Duplicated ESR2 and GPER were also retrieved in most extant teleosts. Phylogeny and synteny analyses suggest that they result from teleost whole genome duplication (3R). In contrast to conserved 3R-duplicated ESR2 and GPER, one of 3R-duplicated ESR1 has been lost shortly after teleost emergence. Quantitative PCRs revealed that the five receptors are all widely expressed in the eel, but with differential patterns of tissue expression and regulation. ESR1 only is consistently up-regulated in vivo in female eel BPG-liver axis during induced sexual maturation, and also up-regulated in vitro by estradiol in eel hepatocyte primary cultures. This first comparative study of the five teleost estradiol receptors provides bases for future investigations on differential roles that may have contributed to the conservation of multiple estrogen receptors.

Selection of reference genes for reverse transcription quantitative real-time PCR normalization in black rockfish (Sebastes schlegeli)

Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is a technique widely used for quantification of mRNA transcription. Data normalization is an indispensable process for RT-qPCR and reference genes are most commonly used to normalize RT-qPCR and to reduce possible errors generated in the quantification of genes among several proposed methods. To date, RT-qPCR has been used in terms of gene expression studies in black rockfish (Sebastes schlegeli) but the majority of published RT-qPCR studies still lack proper validation of the reference genes. In the present study, mRNA transcription profiles of eight putative reference genes (18S rRNA, ACTB, GAPDH, TUBA, RPL17, EF1A, HPRT, and B2M) were examined using RT-qPCR in different tissues and larvae developmental stages of black rockfish. Three common statistical algorithms (geNorm, NormFinder, and BestKeeper) were used to assess expression stability and select the most stable genes for gene normalization. Two reference genes, RPL17 and EF1A showed high stability in black rockfish tissue analysis, while GAPDH was the least stable gene. During larvae developmental stages, EF1A, RPL17 and ACTB were identified as the optimal reference genes for data normalization, whereas B2M appeared unsuitable as the reference gene. In summary, our results could provide a useful guideline for reference gene selection and enable more accurate normalization of gene expression data in gene expression studies of black rockfish.