Gene knockout of nuclear progesterone receptor provides insights into the regulation of ovulation by LH signaling in zebrafish

Far from Their Origins: A Transcriptomic Investigation on How 2,4-Di-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl) Phenol Affects Rainbow Trout Alevins

Benzotriazole ultraviolet stabilizers (BUVSs) are a group of widely used chemicals added to a variety of consumer (e.g., plastics) and industrial (e.g., metal coating) goods. Although detected globally as an environmentally persistent pollutant, BUVSs have received relatively little toxicological attention and only recently have been acknowledged to affect development and the endocrine system in vivo. In our previous study, altered behavior, indicative of potential neurotoxicity, was observed among rainbow trout alevins (day 14 posthatching) that were microinjected as embryos with a single environmentally relevant dose of 2,4-di-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl) phenol (UV-327). In the present follow-up study, we performed whole-transcriptome profiling (RNA sequencing) of newly hatched alevins from the same batch. The primary aim was to identify biomarkers related to behavior and neurology. Dose-specifically, 1 to 176 differentially expressed genes (DEGs) were identified. In the group presenting altered behavior (273.4 ng g-1), 176 DEGs were identified, yet only a fraction was related to neurological functions, including water, calcium, and potassium homeostasis; acetylcholine transmission and signaling; as well insulin and energy metabolism. The second objective was to estimate the transcriptomic point of departure (tPOD) and assess if point estimate(s) are protective of altered behavior. A tPOD was established at 35 to 94 ng UV-327 g-1 egg, making this tPOD protective of behavioral alterations. Holistically, these transcriptomic alterations provide a foundation for future research on how BUVSs can influence rainbow trout alevin development, while providing support to the hypothesis that UV-327 can influence neurogenesis and subsequent behavioral endpoints. The exact structural and functional changes caused by embryonic exposure to UV-327 remain enigmatic and will require extensive investigation before being deciphered and understood toxicologically. Environ Toxicol Chem 2024;43:2026-2038. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The induction of oocyte maturation and ovulation in the European eel (Anguilla anguilla): in vitro and in vivo comparison of progesterone with 17α,20β-dihydroxy-4-pregnen-3-one

Ovulation in European eel is induced by injection of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) as the maturation-inducing hormone (MIH). Female eels need to ovulate within 18 h after injection to release good quality eggs. Progesterone (P), as an upstream precursor of DHP, may promote endogenous DHP production and improve egg quality. The purpose of this study was therefore to compare treatment of P with DHP on batch level, in vitro, to determine dose-response effects, and in vivo, at a single dose. For the in vitro experiment, ovarian tissue was extracted and placed in culture plates containing hormone-free medium and media supplemented with the treatment: DHP at 1, 10 and 100 ng mL-1, or P at 10, 100 and 1,000 ng mL-1. At the start of incubation, the folliculated oocytes were sampled for histology, microscopy and qPCR. After incubation for 12 and 18 h, the oocytes were sampled for microscopy and qPCR analysis. For the in vivo experiment, females were either injected with DHP or P at a dose of 2 mg kg-1 to assess their effects on ovulation and reproductive success. At the moment of release, eggs were sampled for RNA sequencing to compare effects of DHP and P on the expression of genes involved in egg quality aspects. Remaining eggs were fertilized and larval viability was recorded. Both DHP and P were able to induce GVBD (DHP at 10 and 100 ng mL-1, P at 100 and 1,000 ng mL-1) in vitro. Expression of genes involved in oocyte maturation and ovulation was similar in vitro for both DHP and P treatments. Regarding the in vivo results, RNAseq results reflected similar DHP and P effects on the expression of genes involved in egg quality aspects. Females injected with either DHP or P ovulated, released eggs, and were equally able to produce larvae without any differences in reproductive success. Our results support the conclusion that DHP and P work equally well in vitro and in vivo. P is more attractive to apply as the price is 3,000 times lower than the price of DHP.

cAMP signaling in ovarian physiology in teleosts: A review

Ovarian function in teleosts, like in other vertebrates, is regulated by two distinct gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin effects are mediated by membrane-bound G protein-coupled receptors localized on the surface of follicle cells. Gonadotropin receptor activation results in increased intracellular cAMP, the most important second cellular signaling molecule. FSH stimulation induces the production of 17β-estradiol in the cells of growing follicles to promote vitellogenesis in oocytes. In contrast, in response to LH, fully grown post-vitellogenic follicles gain the ability to synthesize maturation-inducing steroids, which induce meiotic resumption and ovulation. All these events were induced downstream of cAMP. In this review, we summarize studies addressing the role of the cAMP pathway in gonadotropin-induced processes in teleost ovarian follicles. Furthermore, we discuss future problems concerning cAMP signaling in relation to teleost ovarian function and the differences and similarities in the gonadotropin-induced cAMP signaling pathways between mammals and teleosts.

Exposure to acetaminophen impairs gametogenesis and fertility in zebrafish (Danio rerio)

Acetaminophen (ACE; paracetamol) is one of the most widely used nonsteroidal anti-inflammatory drugs worldwide and is often found in aquatic systems, where it can act on nontarget species and impair fish reproduction. This study aimed to investigate the effects of chronic exposure to environmentally relevant ACE concentrations (0.5, 5 and 50 µg/L) on multiple reproductive parameters in zebrafish (Danio rerio). Gametogenesis was analyzed using histology, morphometry, cell proliferation, and apoptosis. This study also evaluated sex steroids, and prostaglandin E₂ (PGE₂) levels, gene expression for sex steroids and PGE₂ receptors, fertilization rate, and semen quality. In females, exposure to 5 and 50 µg/L ACE induced larger and more abundant vitellogenic follicles and increased follicular atresia. In these treatments, males showed a lower proportion and proliferation of undifferentiated spermatogonia and a higher proportion of TUNEL-positive differentiated spermatogonia, spermatids, and spermatozoa, resulting in lower sperm production. ACE increased 17β-estradiol (E₂) and reduced 11-ketotestosterone levels in the testis, whereas only E₂ increased in the ovaries. In both sexes, gonadal PGE₂ levels were reduced. ACE at 50 µg/L induced an increase in the gene expression of androgen, estrogen, and PGE₂ receptors in the ovaries, and reduced expression in the testes. Results also showed lower egg production and fertilization rate from 28 days of exposure with reduced sperm quality. These results demonstrated that ACE impairs the reproductive performance of zebrafish, affecting multiple reproductive parameters, which may be caused by the synergistic action of the imbalance of sex steroids, with a reduction of PGE₂ and its receptors.

Association of ADAMTS proteoglycanases downregulation with IVF-ET outcomes in patients with polycystic ovary syndrome: a systematic review and meta-analysis

BACKGROUND

A disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) is involved in inflammation and fertility in women with polycystic ovary syndrome (PCOS). This study aims to assess the role of ADAMTS level in the outcomes of in vitro fertilization and embryo transfer (IVF-ET) in women with PCOS, using a meta-analytic approach.

METHODS

We systematically searched Web of Science, PubMed, EmBase, and the Cochrane library to identify potentially eligible studies from inception until December 2021. Study assess the role of ADAMTS levels in patients with PCOS was eligible in this study. The pooled effect estimates for the association between ADAMTS level and IVF-ET outcomes were calculated using the random-effects model.

RESULTS

Five studies involving a total of 181 patients, were selected for final analysis. We noted that ADAMTS-1 levels were positively correlated to oocyte maturity (r = 0.67; P = 0.004), oocyte recovery (r = 0.74; P = 0.006), and fertilization (r = 0.46; P = 0.041) rates. Moreover, ADAMTS-4 levels were positively correlated to oocyte recovery (r = 0.91; P = 0.001), and fertilization (r = 0.85; P = 0.017) rates. Furthermore, downregulation of ADAMTS-1, ADAMTS-4, ADAMTS-5, and ADAMTS-9 was associated with elevated follicle puncture (ADAMTS-1: weighted mean difference [WMD], 7.24, P < 0.001; ADAMTS-4: WMD, 7.20, P < 0.001; ADAMTS-5: WMD, 7.20, P < 0.001; ADAMTS-9: WMD, 6.38, P < 0.001), oocytes retrieval (ADAMTS-1: WMD, 1.61, P < 0.001; ADAMTS-4: WMD, 3.63, P = 0.004; ADAMTS-5: WMD, 3.63, P = 0.004; ADAMTS-9: WMD, 3.20, P = 0.006), and Germinal vesicle oocytes levels (ADAMTS-1: WMD, 2.89, P < 0.001; ADAMTS-4: WMD, 2.19, P < 0.001; ADAMTS-5: WMD, 2.19, P < 0.001; ADAMTS-9: WMD, 2.89, P < 0.001). Finally, the oocytes recovery rate, oocyte maturity rate, fertilization rate, cleavage rate, good-quality embryos rate, blastocyst formation rate, and clinical pregnancy rate were not affected by the downregulation of ADAMTS-1, ADAMTS-4, ADAMTS-5, and ADAMTS-9 (P > 0.05).

CONCLUSIONS

This study found that the outcomes of IVF-EF in patients with PCOS could be affected by ADAMTS-1 and ADAMTS-4; further large-scale prospective studies should be performed to verify these results.

Changes in Ovulation-Related Gene Expression during Induced Ovulation in the Amur Sturgeon (Acipenser schrenckii) Ovarian Follicles

The luteinizing hormone (LH) and maturation-inducing steroids (MIS), such as 17α,20β-dihydroxy-4-pregnen-3-one, regulate the final oocyte maturation in teleosts. Oocyte maturational competence (OMC) and ovulatory competence measure the sensitivity to MIS for oocyte maturation and ovulation, respectively. However, the molecular mechanisms underlying the acquisition of ovulatory competence remain unknown. Sturgeons are an excellent research model for investigating these mechanisms. We examined the seasonal profiles of OMC and ovulatory competence in vitro and the expression of 17 ovulation-related gene candidates using quantitative PCR in Amur sturgeon ovarian follicles. The ovulatory competence was induced by the LH-releasing hormone analog (LHRHa) priming injection after acquiring the OMC, which was spontaneously induced in spring or autumn. Seven genes, including the tissue-type plasminogen activator (plat), were enhanced following the LHRHa priming injection in ovarian follicles sampled from anovulated and ovulated fish. The activin receptor type 1 (acvr1) and prostaglandin G/H synthase 2 (ptgs2) were only upregulated in ovulated fish. Our results suggest that plat/plasmin and prostaglandin (PG)/PG receptor systems are essential for sturgeon ovulation, similar to other vertebrates. Notably, successful ovulation depends on a sufficient PG synthesis, and mediators activating the PG/PG receptor system are essential for acquiring the ovulatory competence. We provide the first report of ovulation-related gene alterations in the ovarian follicles of Amur sturgeons.

Transcriptomic Interaction between Young Fecal Transplantation and Perfluorobutanesulfonate in Aged Zebrafish Gonads

The transfer of young fecal microbiota has been found to significantly refresh the reproductive endocrine system and effectively ameliorate the toxicity of perfluorobutanesulfonate (PFBS) in aged zebrafish recipients. However, the mechanisms underlying the antagonistic action of young fecal microbiota against the reproductive endocrine toxicity of PFBS remain largely unknown. In this study, the aged zebrafish were transplanted with feces from young donors and then exposed to PFBS for 14 days. After exposure, the shift in the transcriptomic fingerprint of the gonads was profiled by using high-throughput sequencing, aiming to provide mechanistic clues into the interactive mode of action between young fecal transplantation and PFBS's innate toxicity. The results showed that the gene transcription pattern associated with protein and lipid synthesis in the gonads of the aged individuals was quite different from the young counterparts. It was intriguing that the transplantation of young feces established a youth-like transcriptomic phenotype in the elderly recipients, thus attenuating the functional decline and maintaining a healthy aging state of the gonads. A sex specificity response was clearly observed. Compared to the aged females, more metabolic pathways (e.g., glycine, serine, and threonine metabolism; glyoxylate and dicarboxylate metabolism; pyrimidine metabolism) were significantly enriched in aged males receiving young feces transplants. PFBS dramatically altered the transcriptome of aged testes, while a much milder effect was observable in aged ovaries. Accordingly, a suite of biological processes related to germ cell proliferation were disrupted by PFBS in aged males, including the ECM-receptor interaction, retinol metabolism, and folate biosynthesis. In aged ovaries exposed to PFBS, mainly the fatty acid and arginine biosynthesis pathway was significantly affected. However, these transcriptomic disorders caused by PFBS were largely mitigated in aged gonads by transferring young feces. Overall, the present findings highlighted the potential of young fecal transplantation to prevent the functional compromise of gonads resulting from aging and PFBS.

Nuclear Progestin Receptor-mediated Linkage of Blood Coagulation and Ovulation

Ovulation is a dramatic remodeling process that includes rupture of blood capillaries and clotting, but coagulation is not thought to directly regulate this process. Herein, we report remarkable increases of coagulation factors V (f5, ~3145-fold) and tissue factor (f3a, ~120-fold) in zebrafish ovarian follicle cells during ovulation. This increase was mediated through the nuclear progestin receptor (Pgr), which is essential for ovulation in zebrafish, and was totally abolished in ovarian follicular cells from pgr-/- mutants. In addition, promoter activities of f5 and f3a were significantly enhanced by progestin (DHP) via Pgr. Similar regulation of human F5 promoter activity was induced via human PGRB, suggesting a conserved mechanism. Site-directed mutagenesis of the zebrafish f5 promoter further demonstrated a direct regulation of coagulation factors via progestin response elements. Moreover, a stark increase of erythrocytes occurred in capillaries meshed in wild-type preovulatory follicles but was absent in pgr-/- mutants. Interestingly, anticoagulants significantly inhibited ovulation both in vitro and in vivo, respectively. Furthermore, reduced fecundity was observed in f5+/- female zebrafish. Taken together, our study provides plausible evidence for steroid regulation of coagulation factors, and a new hypothesis for blood clotting-triggered ovulation in vertebrates.

Signal pathway of LH-induced expression of nuclear progestin receptor in vertebrate ovulation

Nuclear progestin receptor (PGR), which is induced in the follicles destined to undergo ovulation, is believed to be obligatory for rupture of the follicles during ovulation in vertebrates. Studies in some mammals and teleost medaka have revealed the outline of the central signaling pathway that leads to the PGR expression in the preovulatory follicles at ovulation. In this review, we summarize the current knowledge on what signaling mediators are involved in the LH-induced follicular expression of PGR at ovulation in these animals. LH-inducibility of follicular PGR expression is conserved. In both group of animals, activation of the LH receptor on the granulosa cell surface with LH commonly results in the increase of intracellular cAMP levels, while the downstream signaling cascades activated by high level of cAMP are totally different between mice and medaka. PGR is currently presumed to be induced via PKA/CREB-mediated transactivation and ERK1/2-dependent signaling in mice, but the receptor is induced via EPAC/RAP and AKT/CREB pathways in the teleost medaka. The differences and similarities in the signaling pathways for PGR expression between them is discussed from comparative and evolutionary aspects. We also discussed questions concerning PGR expression and its regulation needed to be investigated in future.

Inhibition of oocyte maturation by nitric oxide synthase 1 (NOS1) in zebrafish

It is well-documented that nitric oxide (NO) is an important regulator of oocyte maturation in mammals. Conversely, the function of NO during oocyte maturation has received little attention in nonmammalian vertebrates. NO is produced from L-arginine through the action of the enzyme NO synthase (NOS). Herein, we examined the expression, hormonal regulation, and involvement of NOS in meiotic signaling in zebrafish oocyte maturation. Three types of nos genes, nos1, nos2a, and nos2b, have been identified in zebrafish. We found that the expression of nos1 was highest in the ovary among the three nos genes, with maximal expression in full-grown (FG)-stage follicles during folliculogenesis. In addition, the concentration of NO was reduced during oocyte maturation and this corresponded with the decreased expression of nos1 in the follicular cell layers, suggesting that NOS1-derived NO may be one of the inhibitors of oocyte maturation in zebrafish. This is the first description of nos1 involvement in oocyte maturation in vertebrates. Moreover, the NO donor SNAP (S-nitroso-l-acetyl penicillamine) partially attenuates human chorionic gonadotropin (hCG)- and 17,20β-P-induced GVBD (germinal vesicle breakdown), perhaps by increasing cGMP levels during oocyte maturation. Finally, our results showed that SNAP and the cGMP analog 8-Br-cGMP inhibited hCG-induced mitogen-activated protein kinase (MAPK) activation, further indicating that NO and cGMP block oocyte maturation in zebrafish.

Single-Cell Atlas of the Chinese Tongue Sole (Cynoglossus semilaevis) Ovary Reveals Transcriptional Programs of Oogenesis in Fish

Oogenesis is a highly orchestrated process that depends on regulation by autocrine/paracrine hormones and growth factors. However, many details of the molecular mechanisms that regulate fish oogenesis remain elusive. Here, we performed a single-cell RNA sequencing (scRNA-seq) analysis of the molecular signatures of distinct ovarian cell categories in adult Chinese tongue sole (Cynoglossus semilaevis). We characterized the successive stepwise development of three germ cell subtypes. Notably, we identified the cellular composition of fish follicle walls, including four granulosa cell types and one theca cell type, and we proposed important transcription factors (TFs) showing high activity in the regulation of cell identity. Moreover, we found that the extensive niche–germline bidirectional communications regulate fish oogenesis, whereas ovulation in fish is accompanied by the coordination of simultaneous and tightly sequential processes across different granulosa cells. Additionally, a systems biology analysis of the homologous genes shared by Chinese tongue sole and macaques revealed remarkably conserved biological processes in germ cells and granulosa cells across vertebrates. Our results provide key insights into the cell-type-specific mechanisms underlying fish oogenesis at a single-cell resolution, which offers important clues for exploring fish breeding mechanisms and the evolution of vertebrate reproductive systems.

Augmentation of progestin signaling rescues testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling

Disruption of androgen signaling is known to cause testicular malformation and defective spermatogenesis in zebrafish. However, knockout of cyp17a1, a key enzyme responsible for the androgen synthesis, in ar-/- male zebrafish paradoxically causes testicular hypertrophy and enhanced spermatogenesis. Because Cyp17a1 plays key roles in hydroxylation of pregnenolone and progesterone (P4), and converts 17α-hydroxypregnenolone to dehydroepiandrosterone and 17α-hydroxyprogesterone to androstenedione, we hypothesize that the unexpected phenotype in cyp17a1-/-;androgen receptor (ar)-/- zebrafish may be mediated through an augmentation of progestin/nuclear progestin receptor (nPgr) signaling. In support of this hypothesis, we show that knockout of cyp17a1 leads to accumulation of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) and P4. Further, administration of progestin, a synthetic DHP mimetic, is sufficient to rescue testicular development and spermatogenesis in ar-/- zebrafish, whereas knockout of npgr abolishes the rescue effect of cyp17a1-/- in the cyp17a1-/-;ar-/- double mutant. Analyses of the transcriptomes among the mutants with defective testicular organization and spermatogenesis (ar-/-, ar-/-;npgr-/- and cyp17a-/-;ar-/-;npgr-/-), those with normal phenotype (control and cyp17a1-/-), and rescued phenotype (cyp17a1-/-;ar-/-) reveal a common link between a downregulated expression of insl3 and its related downstream genes in cyp17a-/-;ar-/-;npgr-/- zebrafish. Taken together, our data suggest that genetic or pharmacological augmentation of the progestin/nPgr pathway is sufficient to restore testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling.

Metalloproteases in gonad formation and ovulation

Changes in expression or activation of various metalloproteases including matrix metalloproteases (Mmp), a disintegrin and metalloprotease (Adam) and a disintegrin and metalloprotease with thrombospondin motif (Adamts), and their endogenous inhibitors (tissue inhibitors of metalloproteases, Timp), have been shown to be critical for ovulation in various species from studies in past decades. Some of these metalloproteases such as Adamts1, Adamts9, Mmp2, and Mmp9 have also been shown to be regulated by luteinizing hormone (LH) and/or progestin, which are essential triggers for ovulation in all vertebrate species. Most of these metalloproteases also express broadly in various tissues and cells including germ cells and somatic gonad cells. Thus, metalloproteases likely play roles in gonad formation processes comprising primordial germ cell (PGC) migration, development of germ and somatic cells, and sex determination. However, our knowledge on the functions and mechanisms of metalloproteases in these processes in vertebrates is still lacking. This review will summarize our current knowledge on the metalloproteases in ovulation and gonad formation with emphasis on PGC migration and germ cell development.

Neuroendocrine Control of Reproduction in Teleost Fish: Concepts and Controversies

During the teleost radiation, extensive development of the direct innervation mode of hypothalamo-pituitary communication was accompanied by loss of the median eminence typical of mammals. Cells secreting follicle-stimulating hormone and luteinizing hormone cells are directly innervated, distinct populations in the anterior pituitary. So far, ∼20 stimulatory and ∼10 inhibitory neuropeptides, 3 amines, and 3 amino acid neurotransmitters are implicated in the control of reproduction. Positive and negative sex steroid feedback loops operate in both sexes. Gene mutation models in zebrafish and medaka now challenge our general understanding of vertebrate neuropeptidergic control. New reproductive neuropeptides are emerging. These include but are not limited to nesfatin 1, neurokinin B, and the secretoneurins. A generalized model for the neuroendocrine control of reproduction is proposed. Hopefully, this will serve as a research framework on diverse species to help explain the evolution of neuroendocrine control and lead to the discovery of new hormones with novel applications. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

ADAMTS1 is regulated by the EP4 receptor in the zebrafish ovary

Prostaglandins (PGs) are a class of fatty-acid derived hormones that are essential in ovulation of teleosts, but their exact role remains unknown. One putative target of PGs in ovulation is regulation of the expression of members of the A Disintegrin and Metalloproteinase with Thrombospondin motifs (ADAMTS) family, which are implicated in follicular rupture. This study investigated the regulation of ADAMTS, other proteases, and their inhibitors in response to treatment with PGE₂ or PGF_2α. Four members of the ADAMTS family, ADAMTS1, ADAMTS5, ADAMTS9, and ADAMTS16 were shown to be expressed in the ovary of zebrafish, but only adamts1 was upregulated in full-grown follicles following treatment with PGE₂. Inhibitors of the PG receptors EP1 and EP2 had no effect on PGE₂-stimulated adamts1 expression, while treatment of full-grown follicles with both PGE₂ and GW627368x, an inhibitor of EP4 function, prevented the PGE₂-induced increase in adamts1 expression. Treatment of full-grown follicles with the maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) in vitro had no effect on the expression of adamts1 mRNA. These findings suggest that expression of ADAMTS1 in zebrafish ovarian follicles is regulated by the prostaglandin PGE₂ via the EP4 series prostaglandin receptor.

Nuclear progesterone receptor regulates ptger4b and PLA2G4A expression in zebrafish (Danio rerio) ovulation

Previous studies have implicated the nuclear progesterone receptor (Pgr or nPR) as being critical to ovulation in fishes. This study investigated the expression of Pgr in zebrafish ovarian follicles throughout development as well as putative downstream targets of Pgr by searching the promoter regions of selected genes for specific DNA sequences to which Pgr binds and acts as a transcription factor. Expression of Pgr mRNA increases dramatically as follicles grow and mature. In silico analysis of selected genes linked to ovulation showed that the prostaglandin receptors ptger4a and ptger4b contained the progesterone responsive element (PRE) GRCCGGA in their promoter regions. Studies using full-grown follicles incubated in vitro revealed that ptger4b was upregulated in response to 17,20β-P. Our studies also showed that the expression of phospholipase A2 (PLA2G4A) mRNA and protein, a key enzyme in prostaglandin synthesis, was upregulated in response to 17,20β-P treatment. pla2g4a was not found to contain a PRE, indicating that it is regulated indirectly by 17,20β-P or that it may contain an as-of-yet unidentified PRE in its promoter region. Collectively, these studies provide further evidence of the importance of Pgr during the periovulatory periods through its involvement in prostaglandin production and function by controlling expression of PLA2G4A and the receptor EP4b and that these genes appear to be regulated through the actions of 17,20β-P.

Chronic Exposure to Two Gestagens Differentially Alters Morphology and Gene Expression in Silurana tropicalis

Gestagens are active ingredients in human and veterinary drugs with progestogenic activity. Two gestagens-progesterone (P4), and the synthetic P4 analogue, melengestrol acetate (MGA)-are approved for use in beef cattle agriculture in North America. Both P4 and MGA have been measured in surface water receiving runoff from animal agricultural operations. This project aimed to assess the morphometric and molecular consequences of chronic exposures to P4, MGA, and their mixture during Western clawed frog metamorphosis. Chronic exposure (from embryo to metamorphosis) to MGA (1.7 µg/L) or P4 + MGA (0.22 µg/L P4 + 1.5 µg/L MGA) caused a considerable dysregulation of metamorphic timing, as evidenced by an inhibition of growth, narrower head, and lack of forelimb emergence in all animals. Molecular analysis revealed that chronic exposure to the mixture induced an additive upregulation of neurosteroid-related (GABA_A receptor subunit α6 (gabra6) and steroid 5-alpha reductase 1 (srd5α1) gene expression in brain tissue. Chronic P4 exposure (0.26 µg/L P4) induced a significant upregulation of the expression hypothalamic-pituitary-gonadal (HPG)-related genes (ipgr, erα) in the gonadal mesonephros complex (GMC). Our data suggest that exposure to P4, MGA, and their mixture induces multiple endocrine responses and adverse effects in larval Western clawed frogs. This study helps to better our understanding of the consequences of chronic gestagen exposure and suggests that the implications and risk of high gestagen use in beef cattle feeding operations may extend to the aquatic environment.

Roles of melatonin in the teleost ovary: A review of the current status

Melatonin, the neurohormone mainly synthesized in and secreted from the pineal gland of vertebrates following a circadian rhythm, is an important factor regulating various physiological processes, including reproduction. Recent data indicate that melatonin is also synthesized in the ovary and that it acts directly at the level of the ovary to modulate ovarian physiology. In some teleosts, melatonin is reported to affect ovarian steroidogenesis. The direct action of melatonin on the ovary could be a possible factor promoting oocyte maturation in teleosts. A role for melatonin in follicle rupture during ovulation in the teleost medaka has recently emerged. In addition, melatonin is suggested to affect oocyte maturation by its antioxidant activity. However, the molecular mechanisms underlying these direct effects of melatonin are largely unknown.

Human and Zebrafish Nuclear Progesterone Receptors Are Differently Activated by Manifold Progestins

The environmental risk of natural and synthetic ligands of the nuclear progesterone receptor (nPR) has been pointed out, however there is still a lack of mechanistic information regarding their ability to interact with nuclear PR in aquatic species. To identify possible interspecies differences, we assessed in vitro the ability of manifold progestins to transactivate zebrafish (zf) and human (h) PRs, using two established reporter cell lines, U2OS-zfPR and HELN-hPR, respectively. Reference ligands highlighted some differences between the two receptors. The reference human agonist ligands promegestone and progesterone induced luciferase activity in both cell lines in a concentration-dependent manner, whereas the natural zebrafish progestin 17α,20β-dihydroxy-4-pregnen-3-one activated zfPR but not hPR. The potent human PR antagonist mifepristone (RU486) blocked PR-induced luciferase in both cell models but with different potencies. In addition, a set of 22 synthetic progestins were screened on the two cell lines. Interestingly, all of the tested compounds activated hPR in the HELN-hPR cell line, whereas the majority of them acted as zfPR antagonists in U2OS-zfPR. Such zfPR-specific response was further confirmed in zebrafish liver cells. This study provides novel information regarding the activity of a large set of progestins on human and zebrafish PR and highlights major interspecies differences in their activity, which may result in differential effects of progestins between fish and humans.

An agonist for membrane progestin receptor (mPR) induces oocyte maturation and ovulation in zebrafish in vivo

The maturation and ovulation of fish oocytes are well-characterized biological processes induced by progestins via coordination of nongenomic actions and genomic actions. Previously, we established a procedure that enables the induction of oocyte maturation and ovulation in live zebrafish by simple administration of the natural teleost maturation-inducing hormone 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20β-DHP) into the surrounding water. By this in vivo assay, the potencies of chemicals in inducing or preventing oocyte maturation and ovulation can be evaluated. The potencies of compounds in inducing ovulation of zebrafish oocytes also can be evaluated in vivo with improved in vitro assays. Here, we attempted to evaluate the effect of Org OD 02-0 (Org OD 02), a selective agonist for membrane progestin receptor (mPR), on fish oocyte maturation and ovulation with in vitro and in vivo assays. As reported previously, Org OD 02 triggered oocyte maturation in vitro. The same Org OD 02 triggered oocyte maturation within several hours in vivo. Surprisingly, Org OD 02 even induced ovulation both in in vivo and in vitro. Eggs from Org OD 02-induced ovulation could be fertilized by artificial insemination. The juveniles developed normally. These results indicated that Org OD 02 triggered physiological ovulation in live zebrafish. In summary, we have demonstrated the effect of Org OD 02 on fish oocyte maturation and ovulation in vitro and in vivo. The results suggested that Org OD 02 acted as an agonist not only of mPR but also of nuclear progesterone receptor (nPR).

Norethindrone alters mating behaviors, ovary histology, hormone production and transcriptional expression of steroidogenic genes in zebrafish (Danio rerio)

The impact of progestins (i.e. synthetic forms of progesterone) on aquatic organisms has drawn increasing attention due to their widespread occurrence in the aquatic environments and potential effects on the endocrine system of fish. In this study, the effects of norethindrone (NET, a progestin) on the reproductive behavior, sex hormone production and transcriptional expressions were evaluated by exposing female zebrafish to NET at 0, 3.1, 36.2 and 398.6 ng L^-1 for 60 days. Results showed that NET impaired the mating behaviors of female at 36.2 and 398.6 ng L^-1 exhibited by males and increased the frequency of atretic follicular cells in the ovary exposed to NET at 398.6 ng L^-1. As for sex hormones, plasma testosterone concentration in zebrafish increased, while estradiol concentration decreased. Up-regulation of genes (Npr, Mpra, Mprβ, Fshβ, Lβ, Tshb, Nis and Dio2) was detected in the brain of fish exposed to NET at 398.6 ng L^-1. The transcriptional levels of genes (Esr1, Vtg1, Ar, Cyp19a, Cyp11b and Ptgs2) were generally inhibited in the ovary of zebrafish by NET at 398.6 ng L^-1. Moreover, the transcripts of genes (Vtg1, Esr1, Ar and Pgr) in the liver were reduced by NET at 36.2 and 398.6 ng L^-1. Our findings suggest that NET can potentially diminish the of fish populations not only by damaging their reproductive organs, but also by altering their mating behavior through the changes in the expressions of genes responsible for the production of sex hormones.

Climate change impacts on fish reproduction are mediated at multiple levels of the brain-pituitary-gonad axis

Anthropogenic emissions of carbon dioxide in the atmosphere have generated rapid variations in atmospheric composition which drives major climate changes. Climate change related effects include changes in physico-chemical proprieties of sea and freshwater, such as variations in water temperature, salinity, pH/pCO₂ and oxygen content, which can impact fish critical physiological functions including reproduction. In this context, the main aim of the present review is to discuss how climate change related effects (variation in water temperature and salinity, increases in duration and frequency of hypoxia events, water acidification) would impact reproduction by affecting the neuroendocrine axis (brain-pituitary-gonad axis). Variations in temperature and photoperiod regimes are known to strongly affect sex differentiation and the timing and phenology of spawning period in several fish species. Temperature mainly acts at the level of gonad by interfering with steroidogenesis, (notably on gonadal aromatase activity) and gametogenesis. Temperature is also directly involved in the quality of released gametes and embryos development. Changes in salinity or water acidification are especially associated with reduction of sperm quality and reproductive output. Hypoxia events are able to interact with gonad steroidogenesis by acting on the steroids precursor cholesterol availability or directly on aromatase action, with an impact on the quality of gametes and reproductive success. Climate change related effects on water parameters likely influence also the reproductive behavior of fish. Although the precise mechanisms underlying the regulation of these effects are not always understood, in this review we discuss different hypothesis and propose future research perspectives.

Zebrafish as a model for studying ovarian development: Recent advances from targeted gene knockout studies

Ovarian development is a complex process controlled by precise coordination of multiple factors. The targeted gene knockout technique is a powerful tool to study the functions of these factors. The successful application of this technique in mice in the past three decades has significantly enhanced our understanding on the molecular mechanism of ovarian development. Recently, with the advent of genome editing techniques, targeted gene knockout research can be carried out in many species. Zebrafish has emerged as an excellent model system to study the control of ovarian development. Dozens of genes related to ovarian development have been knocked out in zebrafish in recent years. Much new information and perspectives on the molecular mechanism of ovarian development have been obtained from these mutant zebrafish. Some findings have challenged conventional views. Several genes have been identified for the first time in vertebrates to control ovarian development. Focusing on ovarian development, the purpose of this review is to briefly summarize recent findings using these gene knockout zebrafish models, and compare these findings with mammalian models. These established mutants and rapid development of gene knockout techniques have prompted zebrafish as an ideal animal model for studying ovarian development.

Investigating the role of prostaglandin receptor isoform EP4b in zebrafish ovulation

Prostaglandins (PGs) are a class of fatty acid-derived hormones that play an essential role in the regulation of ovulation of teleosts. This study investigated the various isoforms of ovarian PG receptors in the zebrafish ovary and their role in ovulation. Using real time qPCR, six PG receptor isoforms (ptger1a, ptger1b, ptger2a, ptger4a, ptger4b, and ptgfr) were shown to be expressed in the ovary. Only the PG receptor isoform ptger4b was upregulated at the time of ovulation in vivo, or following treatment in vivo with Ovaprim, which contains a gonadotropin releasing hormone analogue and a dopamine receptor antagonist and stimulates ovulation. Treatment of full-grown follicles with the maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP) in vitro also induced expression of EP4b mRNA. Females ovulate in vivo after injection with Ovaprim, or injection with Ovaprim and inhibitors of EP1 (ONO-8130) or EP2 (TG4-155) function; they do not ovulate when injected with Ovaprim and an EP4 inhibitor (GW237368x). These findings suggest that the EP4 receptor, in particular the EP4b isoform, is essential for ovulation.

Igf3 serves as a mediator of luteinizing hormone in zebrafish ovulation

Both oocyte maturation and ovulation is triggered by the luteinizing hormone (LH) surge in vertebrates, but exactly how these processes are regulated by LH remains to be fully elucidated. Previously, we found that Igf3, a fish-specific member of the igf family predominantly expressed in the gonads, could mediate the action of LH on oocyte maturation in zebrafish. Here, we further reveal the importance of Igf3 in mediating the action of LH on ovulation in zebrafish. All the four igf gene family members are expressed in the zebrafish ovary but only the igf3 transcript level is increased in hCG-induced ovulation in vivo. The expression of Igf3 protein in the follicles is also increased during ovulation. The actions of hCG on the expression of ovulatory enzymes and on ovulation itself could be largely mimicked by the recombinant zebrafish Igf3 protein. Intriguingly, the phosphorylation of Igf1r, the receptor for Igf3, could be activated by hCG in the follicular cells during ovulation. And inhibition of Igf3 signaling by Igf1r inhibitors and Igf3 antiserum could significantly attenuate the hCG-induced ovulation. Collectively, all these data support the notion that Igf3 serves as a mediator of LH action in zebrafish ovulation.

Transcriptomic Analysis Revealed the Regulatory Mechanisms of Oocyte Maturation and Hydration in Orange-Spotted Grouper (Epinephelus coioides)

Oocyte maturation and hydration are regulated by a complex interplay of various hormones and local factors. We have investigated the morphological changes of follicles and serum steroid levels during the HCG (human choionic gonadotophin)-induced oocyte maturation in the orange-spotted grouper. For the first time, a large-scale transcriptomic analysis of follicles during the maturation has been conducted in a fish species which produce pelagic oocytes. Eight cDNA libraries of follicle samples, from full-grown immature follicles to mature follicles, were constructed. A total of 402,530,284 high-quality clean reads were obtained after filtering, 79.66% of which perfectly mapped to the orange-spotted grouper genome. Real-time PCR results of 12 representative genes related to oocyte maturation and hydration verified the reliability of the RNA-seq data. A large number of genes related to oocyte maturation and hydration were identified in the transcriptome dataset. And the transcriptomic analysis revealed the dynamic changes of the steroid synthesis pathway and the pathway of hydration during oocyte maturation. The present study will facilitate future study on the oocyte maturation and hydration in the orange-spotted grouper and other marine pelagic egg spawner.

Fertility impairment with defective spermatogenesis and steroidogenesis in male zebrafish lacking androgen receptor

The pivotal role of androgen receptor (AR) in regulating male fertility has attracted much research attention in the past two decades. Previous studies have shown that total AR knockout would lead to incomplete spermatogenesis and lowered serum testosterone levels in mice, resulting in azoospermia and infertility. However, the precise physiological role of ar in controlling fertility of male fish is still poorly understood. In this study, we have established an ar knockout zebrafish line by transcription activator-like effectors nucleases. Homozygous ar mutant male fish with smaller testis size were found to be infertile when tested by natural mating. Intriguingly, a small amount of mature spermatozoa was observed in the ar mutant fish. These mature spermatozoa could fertilize healthy oocytes, albeit with a lower fertilization rate, by in vitro fertilization. Moreover, the expression levels of most steroidogenic genes in the testes were significantly elevated in the ar mutants. In contrast, the levels of estradiol and 11-ketotestosterone (11-KT) were significantly decreased in the ar mutants, indicating that steroidogenesis was defective in the mutants. Furthermore, the protein level of LHβ in the serum decreased markedly in the ar mutants when compared with wild-type fish, probably due to the positive feedback from the diminished steroid hormone levels.

Abnormal expressions of ADAMTS-1, ADAMTS-9 and progesterone receptors are associated with lower oocyte maturation in women with polycystic ovary syndrome

PURPOSE

ADAMTS-1 and 9 play a crucial role in the ovulation and their altered levels may play a role in the pathogenesis of polycystic ovary syndrome (PCOS). The aim of this study was to assess ADAMTS-1 and 9 expression and their correlation with the oocyte quality and maturity in the cumulus cells (CCs) of PCOS patients and normovulatory women during an IVF procedure.

METHODS

Expression of ADAMTS-1 and 9 and progesterone receptors (PRs) in the CCs containing MII and germinal vesicle (GV) oocytes of 37 PCOS patients and 37 women with normal ovulatory function who underwent IVF treatment was evaluated using qRT-PCR. Moreover, correlation between ADAMTS-1 and 9 expression and oocyte quality were also investigated.

RESULTS

mRNA expression levels of ADAMTS-1 and ADAMTS-9 were significantly reduced in the women with PCOS compared to the normovulatory women. ADAMTS-1 and ADAMTS-9 mRNA expression levels in the CCs showed a considerable correlation. Lower expression levels of ADAMTS-1 and ADAMTS-9 in PCOS patients were strongly correlated with diminished oocyte maturation. There was a remarkable association between ADAMTS-1 and ADAMTS-9 mRNA expression levels and oocyte quality. PRs (PRA and PRB) were dramatically decreased in PCOS patients when compared with the control group.

CONCLUSIONS

The results of the present study indicated that ADAMTS-1 and ADAMTS-9 as well as PRs are downregulated in the human CCs in PCOS patients, which could be associated with impaired oocyte maturation and may result in a lower oocyte recovery and oocyte maturity rates, as well as lower fertilization rate.

Candidate gene identification of ovulation-inducing genes by RNA sequencing with an in vivo assay in zebrafish

We previously reported the microarray-based selection of three ovulation-related genes in zebrafish. We used a different selection method in this study, RNA sequencing analysis. An additional eight up-regulated candidates were found as specifically up-regulated genes in ovulation-induced samples. Changes in gene expression were confirmed by qPCR analysis. Furthermore, up-regulation prior to ovulation during natural spawning was verified in samples from natural pairing. Gene knock-out zebrafish strains of one of the candidates, the starmaker gene (stm), were established by CRISPR genome editing techniques. Unexpectedly, homozygous mutants were fertile and could spawn eggs. However, a high percentage of unfertilized eggs and abnormal embryos were produced from these homozygous females. The results suggest that the stm gene is necessary for fertilization. In this study, we selected additional ovulation-inducing candidate genes, and a novel function of the stm gene was investigated.

Steroid Transport, Local Synthesis, and Signaling within the Brain: Roles in Neurogenesis, Neuroprotection, and Sexual Behaviors

Sex steroid hormones are synthesized from cholesterol and exert pleiotropic effects notably in the central nervous system. Pioneering studies from Baulieu and colleagues have suggested that steroids are also locally-synthesized in the brain. Such steroids, called neurosteroids, can rapidly modulate neuronal excitability and functions, brain plasticity, and behavior. Accumulating data obtained on a wide variety of species demonstrate that neurosteroidogenesis is an evolutionary conserved feature across fish, birds, and mammals. In this review, we will first document neurosteroidogenesis and steroid signaling for estrogens, progestagens, and androgens in the brain of teleost fish, birds, and mammals. We will next consider the effects of sex steroids in homeostatic and regenerative neurogenesis, in neuroprotection, and in sexual behaviors. In a last part, we will discuss the transport of steroids and lipoproteins from the periphery within the brain (and vice-versa) and document their effects on the blood-brain barrier (BBB) permeability and on neuroprotection. We will emphasize the potential interaction between lipoproteins and sex steroids, addressing the beneficial effects of steroids and lipoproteins, particularly HDL-cholesterol, against the breakdown of the BBB reported to occur during brain ischemic stroke. We will consequently highlight the potential anti-inflammatory, anti-oxidant, and neuroprotective properties of sex steroid and lipoproteins, these latest improving cholesterol and steroid ester transport within the brain after insults.

The Primodos components Norethisterone acetate and Ethinyl estradiol induce developmental abnormalities in zebrafish embryos

Primodos was a hormone pregnancy test used between 1958-1978 that has been implicated with causing a range of birth defects ever since. Though Primodos is no longer used, it's components, Norethisterone acetate and Ethinyl estradiol, are used in other medications today including treatments for endometriosis and contraceptives. However, whether Primodos caused birth defects or not remains controversial, and has been little investigated. Here we used the developing zebrafish embryo, a human cell-line and mouse retinal explants to investigate the actions of the components of Primodos upon embryonic and tissue development. We show that Norethisterone acetate and Ethinyl estradiol cause embryonic damage in a dose and time responsive manner. The damage occurs rapidly after drug exposure, affecting multiple organ systems. Moreover, we found that the Norethisterone acetate and Ethinyl estradiol mixture can affect nerve outgrowth and blood vessel patterning directly and accumulates in the forming embryo for at least 24 hrs. These data demonstrate that Norethisterone acetate and Ethinyl estradiol are potentially teratogenic, depending on dose and embryonic stage of development in the zebrafish. Further work in mammalian model species are now required to build on these findings and determine if placental embryos also are affected by synthetic sex hormones and their mechanisms of action.

Prostaglandins in teleost ovulation: A review of the roles with a view to comparison with prostaglandins in mammalian ovulation

Prostaglandins are well known to be central regulators of vertebrate ovulation. Studies addressing the role of prostaglandins in mammalian ovulation have established that they are involved in the processes of oocyte maturation and cumulus oocyte complex expansion. In contrast, despite the first indication of the role of prostaglandins in teleost ovulation appearing 40 years ago, the mechanistic background of their role has long been unknown. However, studies conducted on medaka over the past decade have provided valuable information. Emerging evidence indicates an indispensable role of prostaglandin E₂ and its receptor subtype Ptger4b in the process of follicle rupture. In this review, we summarize studies addressing the role of prostaglandins in teleost ovulation and describe recent advances. To help understand differences from and similarities to ovulation in mammalian species, the findings on the roles of prostaglandins in mammalian ovulation are discussed in parallel.

Genome editing in fishes and their applications

There have been revolutionary progresses in genome engineering in the past few years. The newly-emerged genome editing technologies including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN) and clustered regularly interspaced short palindromic repeats associated with Cas9 (CRISPR/Cas9) have enabled biological scientists to perform efficient and precise targeted genome editing in different species. Fish represent the largest group of vertebrates with many species having values for both scientific research and aquaculture industry. Genome editing technologies have found extensive applications in different fish species for basic functional studies as well asapplied research in such fields as disease modeling and aquaculture. This mini-review focuses on recent advancements and applications of the new generation of genome editing technologies in fish species, with particular emphasis on their applications in understanding reproductive functions because the reproductive axis has been most systematically and best studied among others and its function has been difficult to address with reverse genetics approach.

Mettl3 Mutation Disrupts Gamete Maturation and Reduces Fertility in Zebrafish

N⁶-methyladenosine (m⁶A), catalyzed by Mettl3 methyltransferase, is a highly conserved epigenetic modification in eukaryotic messenger RNA (mRNA). Previous studies have implicated m⁶A modification in multiple biological processes, but the in vivo function of m⁶A has been difficult to study, because mettl3 mutants are embryonic lethal in both mammals and plants. In this study, we have used transcription activator-like effector nucleases and generated viable zygotic mettl3 mutant, Zmettl3^m/m , in zebrafish. We find that the oocytes in Zmettl3^m/m adult females are stalled in early development and the ratio of full-grown stage (FG) follicles is significantly lower than that of wild type. Human chorionic gonadotropin-induced ovarian germinal vesicle breakdown in vitro and the numbers of eggs ovulated in vivo are both decreased as well, while the defects of oocyte maturation can be rescued by sex hormone in vitro and in vivo In Zmettl3^m/m adult males, we find defects in sperm maturation and sperm motility is significantly reduced. Further study shows that 11-ketotestosterone (11-KT) and 17β-estradiol (E2) levels are significantly decreased in Zmettl3^m/m , and defective gamete maturation is accompanied by decreased overall m⁶A modification levels and disrupted expression of genes critical for sex hormone synthesis and gonadotropin signaling in Zmettl3^m/m Thus, our study provides the first in vivo evidence that loss of Mettl3 leads to failed gamete maturation and significantly reduced fertility in zebrafish. Mettl3 and m⁶A modifications are essential for optimal reproduction in vertebrates.

New Insights Into the Role of Estrogens in Male Fertility Based on Findings in Aromatase-Deficient Zebrafish

It has been demonstrated that estrogens are indispensable for male fertility in mammals. Aromatase (encoded by CYP19) catalyzes the final step of estradiol biosynthesis. However, less is known about the role of aromatase in male fertility in nonmammalian species. Fish aromatase is encoded by two separate genes: the gonad-specific cyp19a1a and the brain-specific cyp19a1b. In a recent study, we used transcription activatorlike effector nucleases to systematically generate cyp19a1a and cyp19a1b mutant lines and a cyp19a1a;cyp19a1b double-mutant line in zebrafish and demonstrated that cyp19a1a was indispensable for sex differentiation. In this study, we focused on male fertility in these aromatase-deficient zebrafish. Our results showed that all aromatase-deficient male fish had normal fertility even at 1 year after fertilization. Interestingly, we observed more spermatozoa in the cyp19a1a and double-mutant males than in the wild-type and cyp19a1b mutant males. The whole-body androgen levels, follicle-stimulating hormone β and luteinizing hormone β protein levels in the pituitary, and transcript levels of genes known to be involved in spermatogenesis and steroidogenesis in the testes were significantly higher in the cyp19a1a mutant and aromatase double-mutant males than in the wild-type and cyp19a1b mutant males. These results might explain why more spermatozoa were observed in these fish. Collectively, our findings indicate that estrogens are not needed to achieve and maintain normal fertility in male zebrafish. This finding challenges the traditional view that estrogens are indispensable for male fertility.

Targeted Disruption of Aromatase Reveals Dual Functions of cyp19a1a During Sex Differentiation in Zebrafish

Aromatase (encoded by the cyp19a1a and cyp19a1b genes) plays a central role in sex differentiation in fish, but its precise roles during sex differentiation are still largely unknown. Here, we systematically generated cyp19a1a and cyp19a1b mutant lines as well as a cyp19a1a;cyp19a1b double mutant line in zebrafish using transcription activatorlike effector nucleases. Our results showed that cyp19a1a mutants and cyp19a1a;cyp19a1b double mutants, but not cyp19a1b mutants, had impaired sex differentiation, and all cyp19a1a mutants and cyp19a1a;cyp19a1b double mutants were males. During sex differentiation, the ovary-like gonads were not observed and the male sex differentiation program was delayed in the cyp19a1a-null fish, and these phenotypes could be partially rescued by 17β-estradiol treatment. Gene expression analysis indicated that male and female sex differentiation-related genes were significantly decreased in the cyp19a1a mutant. Collectively, our results revealed dual functions of the cyp19a1a gene during sex differentiation: cyp19a1a is not only indispensable for female sex differentiation but also required for male sex differentiation.

LH signaling induced ptgs2a expression is required for ovulation in zebrafish

It is well known that ovulation is induced by luteinizing hormone (LH) surge. However, the down-stream factors that mediating LH surge induced ovulation are less clear. The cyclooxygenases (also known as PTGS) as key enzymes for prostaglandins synthesis appear to be important for ovulation in mammals, but their functional roles and molecular mechanism in regulation of fish ovulation are largely unexplored. In this study, we have systematically investigated the expression, regulation and functional roles of cox genes during zebrafish ovulation. Three types of cox genes including ptgs1, ptgs2a and ptgs2b have been identified in zebrafish. The ptgs2a was dominantly expressed in the ovary with a maximal level at the maturation stage of the follicles. In addition, the ptgs2a expression is up-regulated by LH signaling in vitro and in vivo. Moreover, co-injection of a selective Ptgs2 inhibitor and non-selective Ptgs inhibitor with hCG could significantly block the stimulatory effect of hCG induced ovulation in vivo. Collectively, our findings indicate that LH signaling induced ptgs2a expression is required for ovulation in zebrafish.