Exposure to estrogenic chemicals induces ectopic expression of vtg in the testis of rainbowfish, Melanotaenia fluviatilis

Reproductive endocrine disruption and gonadal intersex induction in male Japanese medaka chronically exposed to betamethasone at environmentally relevant levels

The broad utilization of betamethasone in medical treatments may pose a significant ecotoxicological risk to aquatic organisms, yet its potential reproductive toxicity remains unclear. The present study examined the impacts of environmental exposure on male reproduction using Japanese medaka (Oryzias latipes). After 110 days of betamethasone exposure at environmentally relevant concentrations (0, 20 and 200 ng/L), LH/FSH synthesis and release in the pituitary was inhibited, and the production of sex hormones and their signaling pathways in the gonads of male medaka were greatly influenced. This synthetic glucocorticoid restrained testosterone (T) synthesis and gave rise to a significant increase in E₂/T and E₂/11-KT ratios. Furthermore, chronic betamethasone exposure (20 and 200 ng/L) led to the suppression of androgen receptor (AR) signaling and enhancement of estrogen receptors (ERs) signaling. An increase in hepatic vitellogenin contents was also detected, and testicular oocytes were observed in both 20 and 200 ng/L betamethasone-treated groups. It showed that 20 and 200 ng/L betamethasone could induce male feminization and even intersex, triggering abnormal spermatogenesis in medaka males. With its adverse effects on male fertility, betamethasone could potentially influence the fishery productivity and population dynamics in aquatic ecosystems.

Vitellogenins and choriogenins are biomarkers for monitoring Oryzias curvinotus juveniles exposed to 17 β - estradiol

The effect of estrogens on Oryzias curvinotus juveniles were investigated by sequencing the transcriptome of O. curvinotus juveniles exposed to 17 β - estradiol for 24 h. A total of 69,071,524 and 71,210,528 raw reads were obtained for the control group (NC) and 17 β - estradiol exposure group (E2), respectively. After de novo assembly, total 133,210 unigenes were identified, and 85,837 unigenes (64.44% of 133,210) were annotated. Analysis of the transcriptome showed that exposure to 2 μg/L 17 β - estradiol led to the up-regulation of 19 genes and down-regulation of 18 genes. The eef1b and rps4x was most suitable as controls for quantitative real-time PCR (qPCR) using Reffinder. Different expression genes enrichment analysis found that exposed to 2 μg/L 17 β - estradiol affected various physiological processes, including spliceosome, phototransduction, amino sugar and nuclear sugar metabolism, hypotaurine metabolism, and renin-angiotensin system, etc. Exposing O. curvinotus juveniles to increasing concentrations of 17 β - estradiol (2 ng/L, 20 ng/L, 200 ng/L and 2 μg/L) led to significant up-regulation of vitellogenins (vtgs) and choriogenins (chgs) mRNA expression. The present study is the first high-throughput transcriptome sequencing of O. curvinotus juveniles, which will be useful for future functional analysis of genes related to environmental estrogen exposed, and development of biomarkers.

Effects of environmental chemicals on fish thyroid function: Implications for fisheries and aquaculture in Australia

Numerous environmental stressors exert acute or chronic effects on the fish thyroid cascade. Such effects could be mediated via thyroidal alterations, imbalance of plasma T4 and T3 levels or damage to the structure of the thyroidal tissues (thyroid hypertrophy, hyperplasia). The thyroidal system is intricately linked to other endocrine systems in vertebrates including the control of reproduction. Disruption of fish thyroid function by environmental stressors has the potential to result in deleterious effects including the inhibition of sperm production, reduction in egg production, gonad development, ovarian growth, swimming activity, fertilisation and increase in larval mortality. Thyroid hormones play a major role in the development and growth of fish, particularly during their early life stages, thus, thyroid disruption by environmental stressors could inhibit the growth of fish larvae and juveniles in wild fish and cultured species, limit fish seed production and result in a decline in wild fisheries. This review highlights the effects of several environmental toxicants including PBDE, PCBs, PCDD and PCDF, PAH/oil, phthalates, metals, pesticides, mixed pollutants/chemicals, cyanide; and other stressors including acid (low pH) and ammonia, on fish thyroid function. Environmental sources of chemical stressors and appropriate water quality guidelines to protect the freshwater and marine species for the relevant pollutants are also discussed including (when available) the Australian guidelines (2000) and Canadian water quality guidelines (where Australian guidelines are not available). To date there has been no published research on the effects of anthropogenic environmental pollutants on the thyroid system of any native Australian fish species. However, the detection of high risk chemicals (notably PBDEs, PCBs, PAHs, metals and pesticides) in Australian waterways and Australian fish and shellfish implies that thyroid disruption of Australian wild fish and aquacultured species could occur. It is therefore imperative that the effects of such pollutants on the thyroid system of Australian native fish be investigated.

The occurrence of endocrine disrupting compounds in off-shore sediments from the southern Baltic Sea

This paper presents the study on the occurrence and spatial distribution of polybrominated diphenyl ethers (PBDEs), butyltin compounds (BTCs), bisphenol A (BPA), and alkylphenols (APs) in sediments. The study focused mainly on off-shore surface sediments collected from the southern Baltic Sea. The pollutant concentrations were as follows: <LOQ-0.158 μg kg(-1) dw ∑9PBDEs, 0.02-1.06 μg kg(-1) dw BDE-209; <LOQ-20.13 μg Sn kg(-1) dw ∑BTCs and 2.7-1001 μg kg(-1) dw nonylphenols (NPs). The spatial distribution of the analyzed compounds was highly related to the organic matter content in the sediments. Only BDE-209 concentrations were the highest in sandy sediments collected near the point source of pollution. This suggests the fresh anthropogenic input of BDE-209 into the marine environment. The principal component analysis (PCA) confirms these observations-the distribution of ∑BTCs, NPs, and ∑9PBDEs was mainly determined by the physicochemical properties of the sediments, while the distribution of BDE-209 was also related to other factors, such as proximity to the pollution source. According to the environmental standards applied in this work, NPs, and to a lesser extent TBT, might pose a risk to aquatic life in the present study area as they occur in some sediments in concentrations higher than those that might cause adverse effects on biota.

Ectopic synthesis of vitellogenin in testis and epididymis of estrogen-treated lizard Podarcis sicula

In oviparous vertebrates, vitellogenin (VTG) is the major yolk precursor synthesized in the liver of sexually mature females during the reproductive period. In males, the VTG gene is silent, but it may be activated by estradiol-17β (E2) or estrogen-like substances. Until now, extra-hepatic expression and synthesis of VTG after estrogen exposure has been reported only for aquatic vertebrates. This study demonstrates the ability of testis and epididymis of the terrestrial oviparous lacertid Podarcis sicula to synthesize VTG following E2 exposure. The results of in situ hybridization and immunohistochemistry analysis show the presence of both VTG mRNA and protein in these districts besides the known induction in the liver. The possible contemporaneous uptake of the E2-induced hepatic VTG by means of the specific vitellogenin receptor has been also evaluated. Finally, histological analysis shows that the E2-treatment during the mating season impairs spermatogenesis.

Effects of bisphenol A and fadrozole exposures on cyp19a1 expression in the Murray rainbowfish, Melanotaenia fluviatilis

Several endocrine-disrupting chemicals (EDCs) have been attributed to the alteration of reproduction in fish through disrupting endogenous sex steroidogenic pathways including aromatisation of androgens to oestrogen by CYP19 aromatase. Here we investigate this hypothesis in adult male and female Melanotaenia fluviatilis by examining the mRNA expression of cyp19a1 isoforms after exposure for ≤96 h to two EDCs with contrasting modes of action: one a weak oestrogen mimic, bisphenol A [BPA (100 or 500 μg/L)], and the other a nonsteroidal aromatase inhibitor, fadrozole [FAD (10 or 50 µg/L)]. The results suggest that BPA did not affect cyp19a1a expression significantly at both concentrations, whereas 50 µg/L of FAD significantly upregulated its expression in ovary. In contrast, BPA exposures increased expression of cyp19a1b in brain of both males and females, whilst FAD had contrasting effects in brain: It increased in males but decreased in females. Similar contrasting responses of cyp19a1b were induced by BPA in gonads: upregulation in ovary and downregulation in testis. FAD did not have a significant effect on gonadal expression of cyp19a1b. Collectively, the results suggest that BPA and FAD can disrupt cyp19a1b activity more readily than can cyp19a1a, albeit with contrasting effects in either a tissue- or sex-specific context that is conceivably consistent with their (BPA and FAD) opposing modes of action. Enhanced spatial and temporal sensitivity of cyp19a1b compared with cyp19a1a suggests that brain sex of fish is more susceptible to disruption by environmental pollutants such as BPA and FAD. Therefore, we propose that the response of cyp19a1b in brain tissue of M. fluviatilis is a more suitable indicator of oestrogenic pollution in the aquatic environment.