Androstenedione and 17α-methyltestosterone induce early ovary development of Anguilla japonica

Influence of 17α-Methyltestosterone on Morphological Deformities and Pigmentation Development in Juvenile Japanese Eels, Anguilla japonica

17α-methyltestosterone (MT) is a synthetic steroid used to induce masculinization when administered during the larval stage of fish. However, the side effects of MT on eel are still poorly understood and, in this study, we examined the various effects of MT on juvenile eel A. japonica (100.63 ± 8.56 mm total length (TL)). To further investigate growth and sex differentiation, juvenile eels (n = 1000) were exposed to 25 µg/g MT for 6 months. We analyzed growth-related factors, sex steroid hormones, skin pigmentation, and color-related gene expression. Through this study, we found a 90% sex conversion of juvenile eels to males using MT treatment. In the MT-treated eel group (285.97 ± 26.21 mm TL) where sexual maturity was induced, spermatogonia stages were observed in the gonads. In contrast, the control group (395.97 ± 27.72 mm TL) exhibited an 80% immaturity rate, with only 20% of the subjects that were rapidly developing displaying early oogonia. ELISA analysis results showed that the level of growth hormone, which is known to be secreted from spermatogonia, did not change as a result of MT treatment. We confirmed that MT delayed growth and caused morphological changes, particularly a shortened snout length and pigmentation of the fin. The total length, body weight, and snout length were considerably lower in the experimental group than in the control group. In addition, in histological analysis we also observed that some of the MT-treated group (5 out of 10 fish) showed liver atrophy and inflammation, and physiological analysis showed that the cortisol concentration increased in the MT-treated eels. Interestingly, we found that some pigment color-related genes, such as melanocortin 1 receptor (MC1R), tyrosinase (Tyr), and dopachrome tautomerase (DCT), were significantly overexpressed in the fins of MT-treated eels. These results suggest that the treatment of A. japonica larvae with MT induced masculinization but also causes growth side effects from the use of synthetic hormones.

Dietary steroids promote body weight growth and induce gametogenesis by increasing the expressions of genes related to cell proliferation of sea cucumber (Apostichopus japonicus)

Steroids play a vital role in animal survival, promoting growth and development when administered appropriate concentration exogenously. However, it remains unclear whether steroids can induce gonadal development and the underlying mechanism. This study assessed sea cucumber weights post-culturing, employing paraffin sections and RNA sequencing (RNA-seq) to explore gonadal changes and gene expression in response to exogenous steroid addition. Testosterone and cholesterol, dissolved in absolute ethanol, were incorporated into sea cucumber diets. After 30 days, testosterone and cholesterol significantly increased sea cucumber weights, with the total weight of experimental groups surpassing the control. The testosterone-fed group exhibited significantly higher eviscerated weight than the control group. In addition, dietary steroids influenced gonad morphology and upregulated genes related to cell proliferation，such as RPL35, PC, eLF-1, MPC2, ADCY10 and CYP2C18. Thees upregulated differentially expressed genes were significantly enriched in the organic system, metabolism, genetic information and environmental information categories. These findings imply that steroids may contribute to the growth and the process of genetic information translation and protein synthesis essential for gonadal development and gametogenesis.

Tissue-specific promoters regulate the transcription of cyp19a1 in the brain-pituitary-gonad axis of Japanese eel (Anguilla japonica)

Aromatase is a key enzyme that catalyzes the biosynthesis of estrogens. Previous study indicated that putative tissue-specific promoters of the one aromatase gene (cyp19a1) may drive the differential regulatory mechanisms of cyp19a1 expression in Anguilla japonica. In the present study, for elucidating the transcription characteristics and the function of putative tissue-specific promoters of cyp19a1 in the brain-pituitary-gonad (BPG) axis during vitellogenesis, we investigated the transcriptional regulation of cyp19a1 by 17β-estrogen (E2), testosterone (T), or human chorionic gonadotropin (HCG) in A. japonica. The expression of estrogen receptor (esra), androgen receptor (ara), or luteinizing hormone receptor (lhr) was up-regulated as cyp19a1 in response to E2, T, or HCG, respectively in the telencephalon, diencephalon, and pituitary. The expression of cyp19a1 was also upregulated in the ovary by HCG or T in a dose-dependent manner. Unlike in the brain and pituitary, the expression of esra and lhr, rather than ara, was upregulated by T in the ovary. Subsequently, four primary subtypes of 5'-untranslated terminal regions of cyp19a1 transcripts and the corresponding two 5' flanking regions (promoter P.I and P.II) were identified. The P.II existed in all BPG axis tissues, whereas the P.I with strong transcriptional activity was brain- and pituitary-specific. Furthermore, the transcriptional activity of promoters, the core promoter region, and the three putative hormone receptor response elements were validated. The transcriptional activity did not change when the HEK291T cells co-transfected with P.II and ar vector were exposed to T. These results suggested that the expression of cyp19a1 was upregulated indirectly through esra and lhr rather than ara by T in the ovary, whereas the expression of cyp19a1 was upregulated directly through androgen receptor and the downstream androgen response element of tissue-specific P.I in the brain and pituitary. The results of the study reveal the regulatory mechanisms of estrogen biosynthesis and provide a reference for optimizing the technology of artificially induced maturation in eels.

An effect assessment of microplastics and nanoplastics interacting with androstenedione on mosquitofish (Gambusia affinis)

An increasing number of microplastics have been detected in aquatic environments, causing various damage to organisms. The size of microplastics affects the toxicity once they enter the organisms. Meanwhile, there is an increasing variety of Endocrine-disrupting chemicals (EDCs) present in aquatic environments. Androstenedione (AED) is a typical EDC. In this study, we used polystyrene microspheres of 80 nm (NPs) and 8 μm (MPs) as materials to simulate environmental contaminants in the aquatic environment with AED. We used female mosquitofish (Gambusia affinis) as the research object to investigate the effects of microplastics on fish in waters containing AED. We compared different sizes of particles accumulation in some tissues of fish and variation of enzyme activities (SOD, LDH, CAT), and the content of MDA in the gut. MPs, NPs, and AED combined exposure test investigated mRNA profiles of immune-related genes (IL-1β, IL-6, IL-8, IL-10) and hormone receptor genes (ARα, ARβ, ERα, ERβ) in the liver of fish. Our results indicated that MPs emerged in various tissues (gill, gut, and liver) of mosquitofish. Besides, NPs and MPs caused enteric abnormal enzyme activity after 48 h of exposure, which was particularly pronounced in the MPs-AED group. MPs induced significant upregulation of inflammatory factors and gonadal factor genes after 96 h of exposure, which was more pronounced when co-exposed with AED. In conclusion, NPs and MPs caused mechanisms of immune damage and inflammatory response. MPs were found to be more likely to cause adverse reactions than NPs, and these responses were enhanced by the combined effects of AED. This study demonstrated that AED can exacerbate the negative effects of MPs and NPs on mosquitofish. It provided an important basis for the effective assessment of MPs and NPs on bioaccumulation and biochemical status of mosquitofish. Additionally, it serves as a foundation to investigate the interactive effects of microplastics and EDCs in living organisms.

Effects of 17α-Methyltestosterone on the Transcriptome and Sex Hormones in the Brain of Gobiocypris rarus

17α-Methyltestosterone (MT), a synthetic environmental endocrine disruptor with androgenic effects, has been shown to disrupt the reproductive system and inhibit germ cell maturation in Gobiocypris rarus. To further investigate the regulation of gonadal development by MT through the hypothalamic-pituitary-gonadal (HPG) axis, G. rarus were exposed to 0, 25, 50, and 100 ng/L of MT for 7, 14, and 21 days. We analyzed its biological indicators, gonadotropin-releasing hormone (GnRH), gonadotropins, reproduction-related gene expression, and brain tissue transcriptome profiles. We found a significant decrease in the gonadosomatic index (GSI) in G. rarus males exposed to MT for 21 days compared to the control group. GnRH, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels, as well as the expressions of the gnrh3, gnrhr1, gnrhr3, fshβ, and cyp19a1b genes, were significantly reduced in the brains of both male and female fish when exposed to 100 ng/L MT for 14 days compared to the controls. Therefore, we further constructed four RNA-seq libraries from 100 ng/L MT-treated groups of male and female fish, obtaining 2412 and 2509 DEGs in male and female brain tissue, respectively. Three common pathways were observed to be affected in both sexes after exposure to MT, namely, nicotinate and nicotinamide metabolism, focal adhesion, and cell adhesion molecules. Furthermore, we found that MT affected the PI3K/Akt/FoxO3a signaling pathway through the upregulation of foxo3 and ccnd2, and the downregulation of pik3c3 and ccnd1. Therefore, we hypothesize that MT interferes with the levels of gonadotropin-releasing hormone (GnRH, FSH, and LH) in G. rarus brains through the PI3K/Akt/FoxO3a signaling pathway, and affects the expression of key genes in the hormone production pathway (gnrh3, gnrhr1 and cyp19a1b) to interfere with the stability of the HPG axis, thus leading to abnormal gonadal development. This study provides a multidimensional perspective on the damaging effects of MT on fish and confirms that G. rarus is a suitable model animal for aquatic toxicology.

Transgenerational effects of androstadienedione and androstenedione at environmentally relevant concentrations in zebrafish (Danio rerio)

Androgens androstadienedione (ADD) and androstenedione (AED) are predominant steroid hormones in surface water, and can disrupt the endocrine system in fish. However, little is known about the transgenerational effects of ADD and AED in fish. In the present study, F0 generation was exposed to ADD and AED from 21 to 144 days post-fertilization (dpf) at nominal concentrations of 5 (L), 50 (M) and 500 (H) ng L^-1, and F1 generation was domesticated in clear water for 144 dpf. The sex ratio, histology and transcription in F0 and F1 generations were examined. In the F0 generation, ADD and AED tended to be estrogenic in zebrafish, resulting in female biased zebrafish populations. In the F1 generation, ADD at the H level caused 63.5% females, while AED at the H level resulted in 78.7% males. In brain, ADD and AED had similar effects on circadian rhythm in the F0 and F1 generations. In the F1 eleutheroembryos, transcriptomic analysis indicated that neuromast hair cell related biological processes (BPs) were overlapped in the ADD and AED groups. Taken together, ADD and AED at environmentally relevant concentrations had transgenerational effects on sex differentiation and transcription in zebrafish.

Dynamic transcriptome analysis of ovarian follicles in artificial maturing Japanese eel (Anguilla japonica)

Inducing maturation of the ovaries to enable the production of good-quality eggs is critical for the successful artificial breeding of Anguilla japonica. During the spawning season, however, the ovaries of A. japonica have been found to develop into asynchronous clutches, impeding the success of artificial breeding on a commercial scale. The dynamic molecular regulation of follicular development in the same individual was assessed by transcriptome analysis of the five stages of follicles, the pre-vitellogenic, early vitellogenic, midvitellogenic, late vitellogenic, and migratory nucleus stages in artificial maturing A. japonica. Comparisons across these developmental stages identified a total of 19,298 differentially expressed transcripts (DETs). Short time-series expression miner analysis across these DETs revealed four significant expression profiles. Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses found that some of the significantly enriched biological processes and metabolic pathways included those related to steroid hormone biosynthesis (cyp11a1, cyp17a1, cyp17a2, hsd17b1, and hsd17b12), cargo receptor activity (vtgr and vldlr), meiosis and ovulation (pgrs and mPRγ), hydration (cts and aqp1), and egg coat formation (zp). These genes and pathways were associated with serum 17β-estradiol concentrations and morphological changes. The levels of hsd17b12 and mPRγ mRNAs were much higher during the migratory nucleus stage, suggesting their respective involvement in the biosynthesis and functional pathway of the maturation-inducing steroid 17α,20β-dihydroxy-4-pregnen-3-one. The gene subtypes aqp1b and ctsd may regulate water influx into oocytes and yolk protein proteolysis, respectively. To our knowledge, the present study is the first to describe combined transcriptome profiling of asynchronously developing follicles in the same individual. The findings suggest that steroid hormone synthesis and nutrient absorption in follicular somatic cells play important roles during follicular development and maturation, despite the same external physiological surroundings.

Integrated Analysis of mRNA- and miRNA-Seq in the Ovary of Rare Minnow Gobiocypris rarus in Response to 17α-Methyltestosterone

17α-Methyltestosterone (MT) is a synthetic androgen. The objective of this study was to explore the effects of exogenous MT on the growth and gonadal development of female rare minnow Gobiocypris rarus. Female G. rarus groups were exposed to 25–100 ng/L of MT for 7 days. After exposure for 7 days, the total weight and body length were significantly decreased in the 50-ng/L MT groups. The major oocytes in the ovaries of the control group were vitellogenic oocytes (Voc) and cortical alveolus stage oocytes (Coc). In the MT exposure groups, some fish had mature ovaries with a relatively lower proportion of mature oocytes, and the diameter of the perinucleolar oocytes (Poc) was decreased compared with those of the control group. Ovarian VTG, FSH, LH, 11-KT, E2, and T were significantly increased after exposure to 50 ng/L of MT for 7 days. Unigenes (73,449), 24 known mature microRNAs (miRNAs), and 897 novel miRNAs in the gonads of G. rarus were found using high-throughput sequencing. Six mature miRNAs (miR-19, miR-183, miR-203, miR-204, miR-205, and miR-96) as well as six differentially expressed genes (fabp3, mfap4, abca1, foxo3, tgfb1, and zfp36l1) that may be associated with ovarian development and innate immune response were assayed using qPCR. Furthermore, the miR-183 cluster and miR-203 were differentially expressed in MT-exposed ovaries of the different G. rarus groups. This study provides some information about the role of miRNA–mRNA pairs in the regulation of ovarian development and innate immune system, which will facilitate future studies of the miRNA–RNA-associated regulation of teleost reproduction.

Effects of 2,4-dichlorophenol exposure on zebrafish: Implications for the sex hormone synthesis

2,4-Dichlorophenol (2,4-DCP), an estrogenic endocrine disruptor, is widely spread in aquatic environments and may interfere with normal physiological functions in fish. However, the influence of this chemical on the synthesis of sex hormones is not well understood. In the present study, zebrafish (Danio rerio) were exposed to 2,4-DCP (80 and 160 μg/L) with or without fadrozole (an aromatase inhibitor which inhibits the synthesis of estradiol) from 20 to 40 days post fertilization. Then, the sex ratio, the content of vitellogenin (VTG) and sex hormones (androstenedione (ASD), estrone (E1), 17β-estradiol (E2), estriol (E3), testosterone (T) and 11-ketotestosterone (11-KT)) were studied. Furthermore, the expression of genes involved in synthesis of sex hormones (cyp19a1a, cyp19a1b, 17β-hsd, 11β-hsd and cyp11b) along with the DNA methylation in cyp19a1a and cyp19a1b promoters was analyzed. The results showed that 2,4-DCP exposure led to female-biased ratio, increased the content of ASD, E2 and VTG, as well as the ratio of E2/11-KT, while decreased the levels of androgens (T and 11-KT). The sex hormonal change can be explained by the significant up-regulation of cyp19a1a, cyp19a1b, 17β-hsd and 11β-hsd genes. In addition, hypomethylation of cyp19a1a promoter was involved in this process. Notably, fadrozole can partly attenuate 2,4-DCP-induced feminization, and recover the levels of ASD, E2 and 11-KT. Thus, these results demonstrate that 2,4-DCP induces feminization in fish by disrupting the synthesis of sex hormones.

Effects of 17 α-methyltestosterone on the transcriptome, gonadal histology and sex steroid hormones in Pseudorasbora parva

In recent years, the increasing use of environmental endocrine disruptors has caused serious environmental pollution and hurt aquatic organisms. It is still risky for aquatic species and humans exposed to 17α-methyltestosterone (MT), however, the harmful effect of MT on fish is still poorly understood. The main purpose of this study is to evaluate the influence of MT on Pseudorasbora parva at multi-levels. We analyzed gonadal histology, the sex steroid hormones, steroidogenic genes expression, and transcriptome profiling of gonads in response to MT in adult P. parva. Through this study, we found MT could inhibit the gonadal development of P. parva, and the growth and development of fish could be delayed by exposure to MT at 200 ng/L. MT could produce disruption effects on fish from multiple pathways, while its interference to the HPGL axis happens primarily through the steroidogenic pathway, e.g., disturbing the expression of crucial genes and sex steroids synthesis. Besides, we constructed 4 RNAseq libraries and obtained 7758 and 11,543 DEGs in females and males, respectively. Interestingly, we found MT had more obvious disruption effects on males than the females, mainly reflected in the immune system. Interestingly, we found three common pathways in both sexes after MT exposure, i.e., cell adhesion molecules, cytokine-cytokine receptor interaction, and neuroactive ligand-receptor interaction. These results confirm the suitability of P. parva as a model fish for aquatic toxicological study and provide us a multidimensional sight for the disruption effects of MT on fish.

Correlation between the ovarian status and the androgen sensibility in the cultured Japanese eel, Anguilla japonica

Different responsive abilities of different types of eels (cultured, cultured feminized, and wild silver eels) during artificial maturation are recognized, and maturity status at the beginning of artificial maturation might be important. Maturity may represented by the distribution pattern of oocyte diameters. Androgens have been demonstrated to stimulate ovarian development in eels. To determine the initial status, operations were performed on eels to identify sex and to sample ovarian tissue. The recovered eels were then treated with 17α-methyltestosterone (17MT), and the responses of individual eels to 17MT were determined by the fold change in the mean oocyte diameter before and after treatment. Sampled ovarian tissues were fixed in Bouin's solution, oocytes were isolated, and the diameter of isolated oocytes was measured. The ovarian status, determined by kernel density estimation (KDE), was presented by the probability density of measured oocyte diameters; compared with histograms, a description method, KDE, provided more subtle information on the investigated ovary. Our data indicated a correlation between the initial ovarian status (density pattern) and the consequence of treatment (change of ovary); we also argued the semelparity of the Japanese eel. Our results supported the hypothesis that the initial ovarian status is an important factor affecting artificial maturation and that androgens could ameliorate the initial status of the eel ovary.