Isolation of estrogen receptor subtypes and vitellogenin genes: Expression in female Chalcalburnus tarichi

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.

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.

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.

Alterations in histology and antioxidant defense system in the testes of the lake Van fish (Alburnus tarichi Güldenstädt, 1814)

Recent reports have demonstrated gonadal abnormalities in the Lake Van fish (Alburnus tarichi) from Lake Van caused by increasing pollution. In the present study, the fish was collected from an area of Lake Van receiving mainly sewage treatment plant effluent at prespawning period (April) and from a river (Karasu) which is close to the polluted area of the lake and where the fish migrates at spawning period (May). Collected specimens were examined for testicular alterations, gonadosomatic index (GSI), condition factor (CF), and antioxidant defense system biomarkers based on comparison with a reference lake (Erçek) and a reference freshwater inlet (Memedik River). Histological examinations of the testes of fish from the polluted area and the connected river showed various alterations consisting of macrophage aggregates, vacuolation, pyknosis, germ cell degeneration, seminiferous tubule dilation, disorganization of tubules, reduced spermatozoa, and fibrosis. A lower GSI and CF were also observed. Moreover, alterations in the antioxidant system biomarkers were determined in the testis tissues of fish from the Lake Van and Karasu River, indicating oxidative stress. These results suggest that the abnormalities in the testes are causally related to the increased oxidative stress, and pollution in Lake Van may have adversely affected the reproductive health of the lake Van fish.

Sequence Evolution and Expression of the Androgen Receptor and Other Pathway-Related Genes in a Unisexual Fish, the Amazon Molly, Poecilia formosa, and Its Bisexual Ancestors

The all-female Amazon molly (Poecilia formosa) originated from a single hybridization of two bisexual ancestors, Atlantic molly (Poecilia mexicana) and sailfin molly (Poecilia latipinna). As a gynogenetic species, the Amazon molly needs to copulate with a heterospecific male, but the genetic information of the sperm-donor does not contribute to the next generation, as the sperm only acts as the trigger for the diploid eggs' embryogenesis. Here, we study the sequence evolution and gene expression of the duplicated genes coding for androgen receptors (ars) and other pathway-related genes, i.e., the estrogen receptors (ers) and cytochrome P450, family19, subfamily A, aromatase genes (cyp19as), in the Amazon molly, in comparison to its bisexual ancestors. Mollies possess-as most other teleost fish-two copies of the ar, er, and cyp19a genes, i.e., arα/arβ, erα/erβ1, and cyp19a1 (also referred as cyp19a1a)/cyp19a2 (also referred to as cyp19a1b), respectively. Non-synonymous single nucleotide polymorphisms (SNPs) among the ancestral bisexual species were generally predicted not to alter protein function. Some derived substitutions in the P. mexicana and one in P. formosa are predicted to impact protein function. We also describe the gene expression pattern of the ars and pathway-related genes in various tissues (i.e., brain, gill, and ovary) and provide SNP markers for allele specific expression research. As a general tendency, the levels of gene expression were lowest in gill and highest in ovarian tissues, while expression levels in the brain were intermediate in most cases. Expression levels in P. formosa were conserved where expression did not differ between the two bisexual ancestors. In those cases where gene expression levels significantly differed between the bisexual species, P. formosa expression was always comparable to the higher expression level among the two ancestors. Interestingly, erβ1 was expressed neither in brain nor in gill in the analyzed three molly species, which implies a more important role of erα in the estradiol synthesis pathway in these tissues. Furthermore, our data suggest that interactions of steroid-signaling pathway genes differ across tissues, in particular the interactions of ars and cyp19as.

Relation between increased oxidative stress and histological abnormalities in the ovaries of Alburnus tarichi in Lake Van, Turkey

Recent studies have shown reproductively arrested gonad development in female Alburnus tarichi (Güldenstädt, 1814) (Cyprinidae) from the eastern coastline of Lake Van, Turkey, due to increasing pollution. In the reproductively arrested females (RAF), oocytes were developmentally blocked and arrested at the previtellogenic stage and gonadosomatic indices (GSI) were very low, while reproductively non-arrested females (RNF) found at the same site displayed relatively normal ovarian development and higher GSI. The present study investigated various oxidative stress biomarkers in the ovaries of RAF and RNF collected from a polluted site at Lake Van at the mid-vitellogenic phase, compared with reference fish from a non-polluted site (Lake Erçek). Ovarian total protein content, biometric indices, and histology were also evaluated. The oxidative stress biomarkers used were levels of lipid peroxidation (LPO) and glutathione (GSH), and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione-S-transferase (GST). High levels of LPO and GSH and activities of SOD, GPx and GST were found in the ovaries of RAF compared with the reference fish. GSH content and activities of GPx and GST were also higher in the RNF. The total protein content and biometric indices decreased significantly in the RAF compared with the RNF and reference fish. The histology of the ovaries revealed atresia, melano-macrophage centers, encapsulated follicle cysts, and severe fibrosis in the RAF. The results of this study suggest that abnormalities in the ovaries of A. tarichi are causally related to increased oxidative stress as a result of pollution.

Cytotoxic effects of 4-octylphenol on fish hepatocytes

The present study was conducted to determine cytotoxic effects of 4-octylphenol (4-OP) on primary cultured hepatocytes of pearl mullet (Alburnus tarichi). Lactate dehydrogenase (LDH) release, malondialdehyde (MDA) level, antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST)] and glutathione (GSH) content were measured after 24-h exposure to 4-OP. 4-OP caused dose- and time-dependent increases in LDH release. Significant induction of MDA level and decrease in GSH content were found. SOD and GPx activities were decreased while GST activity was increased. These findings suggest that 4-OP leads to cytotoxicity by depressing antioxidant defenses in fish hepatocytes.

Vitellogenin in the male Lake Van fish (Chalcalburnus tarichi Pallas, 1811)

Chalcalburnus tarichi is an endemic cyprinid species living in Lake Van, Turkey. In the present study, we investigated vitellogenin (Vtg) in the plasma of adult male C. tarichi, sampled monthly from Edremit, Campus and Çarpanak sites of Van Edremit Gulf (VEG) of lake, between October 2004 and May 2005. The fish living around VEG winters in deep water around Edremit site. University and Çarpanak sites are also on fish migration way from VEG to fresh water (Karasu River). The levels of measured plasma Vtg changed from trace levels to 26.35 µg/mL. The highest level of plasma Vtg was detected in April, with a concentration of 21.60 ± 1.29 µg/mL. We also performed immunohistochemical Vtg staining in the liver sections of male fish and determined Vtg positive hepatocytes in the liver of 1/10 sampled fish. Our results indicated that C. tarichi living in Lake Van might be exposed to endocrine-disrupting chemicals.