Cloning of a second form of activin-betaA cDNA and regulation of activin-betaA subunits and activin type II receptor mRNA expression by gonadotropin in the zebrafish ovary

Optimizing spinal cord injury in zebrafish larvae: effects of age on the injury response

Zebrafish are an increasingly popular model to study spinal cord injury (SCI) regeneration. The transparency of larval zebrafish makes them ideal to study cellular processes in real time. Standardized approaches, including age of injury, are not readily available making comparisons of the results with other models challenging. In this study, we systematically examined the response to spinal cord transection of larval zebrafish at three different ages (3-7 days post fertilization or dpf) to determine whether the developmental complexity of the central nervous system affects the overall response to SCI. We then used imaging and behavioral analysis to evaluate whether differences existed based on the age of injury. All ages of larval zebrafish upregulated the required genes for glial bridge formation, ctgfa and gfap, at the site of injury, consistent with studies from adult zebrafish. Though all larval ages upregulated factors required to promote glial bridging, young larval zebrafish (3 dpf) were better able to regenerate axons independent of the glial bridge, unlike older zebrafish (7 dpf). Consistent with this data, locomotor experiments demonstrated that some swimming behavior occurs independent of glial bridge formation, further highlighting the need for standardization of this model and recovery assays. Overall, we found subtle cellular differences based on the age of transection in zebrafish, underlining the importance of considering age when designing experiments aimed at understanding regeneration.

Genetic analysis of activin/inhibin β subunits in zebrafish development and reproduction

Activin and inhibin are both dimeric proteins sharing the same β subunits that belong to the TGF-β superfamily. They are well known for stimulating and inhibiting pituitary FSH secretion, respectively, in mammals. In addition, activin also acts as a mesoderm-inducing factor in frogs. However, their functions in development and reproduction of other species are poorly defined. In this study, we disrupted all three activin/inhibin β subunits (βAa, inhbaa; βAb, inhbab; and βB, inhbb) in zebrafish using CRISPR/Cas9. The loss of βAa/b but not βB led to a high mortality rate in the post-hatching stage. Surprisingly, the expression of fshb but not lhb in the pituitary increased in the female βA mutant together with aromatase (cyp19a1a) in the ovary. The single mutant of βAa/b showed normal folliculogenesis in young females; however, their double mutant (inhbaa-/-;inhbab-/-) showed delayed follicle activation, granulosa cell hypertrophy, stromal cell accumulation and tissue fibrosis. The ovary of inhbaa-/- deteriorated progressively after 180 dpf with reduced fecundity and the folliculogenesis ceased completely around 540 dpf. In addition, tumor- or cyst-like tissues started to appear in the inhbaa-/- ovary after about one year. In contrast to females, activin βAa/b mutant males showed normal spermatogenesis and fertility. As for activin βB subunit, the inhbb-/- mutant exhibited normal folliculogenesis, spermatogenesis and fertility in both sexes; however, the fecundity of mutant females decreased dramatically at 270 dpf with accumulation of early follicles. In summary, the activin-inhibin system plays an indispensable role in fish reproduction, in particular folliculogenesis and ovarian homeostasis.

Activin receptor type IIB in rohu (Labeo rohita): molecular characterization, tissue distribution and immunohistochemical localization during different stages of gonadal maturation

Activin receptor type IIB (ActRIIB) is a transmembrane serine/threonine kinase receptor which plays a pivotal role in regulating the reproduction in vertebrates including teleost. Earlier studies have documented its importance in governing gonadal maturation in higher vertebrates. However, reports on the regulation of fish reproductive system by ActRIIB gene are still limited. Here, we report the identification and characterization of ActRIIB cDNA of Labeo rohita, a commercially important fish species of the Indian subcontinent. The full-length gene encoding rohu ActRIIB was cloned and found to be of 1674 bp in length. Functional similarities were evident from evolutionary analysis across vertebrates. Real-time PCR to measure the expression of ActRIIB transcript in rohu revealed significant mRNA levels in gonads followed by non-reproductive tissues, including the brain, pituitary and muscle. With respect to different gonadal maturation stages, predominant expression of ActRIIB mRNA was observed during the pre-spawning phase of both sexes. To further delineate its role in rohu reproduction, a recombinant protein of the extracellular domain of ActRIIB (rECD-ActRIIB) was produced, and polyclonal antibody is raised against the protein for its immuno-localization studies during different gonadal maturation stages. Strong immunoreactivity was noticed in the pre-vitellogenic oocytes which decreased dramatically in the fully mature oocytes. Similarly, the strong and intense immunoreactivity was found in the spermatids and spermatocytes of the immature testis, and eventually the intensity reduced with the progression of the maturation stage. These results provide the first evidence of the presence of ActRIIB in rohu gonadal tissues. Taken together, our observations lay the groundwork for further understanding and investigating on the potential role of ActRIIB in fish reproduction system in the event of gonadal maturation.

Nodal regulates ovarian functions in zebrafish

Nodal, a member of the transforming growth factor-β (TGF-β) superfamily, plays critical roles during embryo development. Several studies suggest that Nodal also regulates reproduction. The objective of this study was to investigate if Nodal is expressed in zebrafish ovary and if it is involved in the regulation of ovarian functions. Using real-time PCR, we detected two Nodal homologs, nodal-related (ndr)1, and ndr2 in zebrafish ovarian follicles. We further compared the mRNA levels of ndr1, ndr2, and their receptors between maturational incompetent early vitellogenic follicles (stage IIIa) and mid- to late-vitellogenic follicles (stage IIIb) which are capable of undergoing maturation when they are induced by hormones. We found that mRNAs for ndr1 and ndr2, as well as a type I receptor, acvr1ba, were significantly increased in follicular cells isolated from stage IIIb follicles. In primary cultures of ovarian follicular cells, treatment with recombinant human Nodal inhibited cell proliferation. On the other hand, Nodal increased the mRNA levels of two steroidogenic enzymes hsd3b2 and cyp17a1, as well as paqr8, which encodes the membrane progestin receptor-β (mPR-β). Conversely, knockdown of ndr1 and ndr2 using siRNAs decreased the mRNA levels of hsd3b2, cyp17a1, and paqr8. Finally, treatment of Nodal significantly induced oocyte maturation. Taken together, these findings suggest that Nodal exerts multiple effects on zebrafish ovary to regulate follicle growth, steroidogenesis, and oocyte maturation.

Expression and regulation of Smad2 by gonadotropins in the protogynous hermaphroditic ricefield eel (Monopterus albus)

Smad2, a receptor-activated Smad, plays a critical role in regulating gametogenesis. In this study, a smad2 homologue was identified and sequenced from ricefield eel ovary cDNA, and its mRNA and protein expression levels were analysed during oocyte development. The cDNA sequence of ricefield eel smad2 consisted of 1863 bp encoding a 467-amino acid protein that had high sequence homology with Smad proteins in other teleosts, especially in Poeciliopsis prolifica. The results of real-time quantitative PCR (RT-qPCR) analysis revealed that smad2 is expressed in the ovary during gonad development, increased continuously until the early vitellogenic stage in the ovaries, and then decreased with ovary maturation. Smad2 protein immunoreactivity was localized in the cytoplasm of follicular cells, oogonia, and primary growth stage oocytes. In vitro experiments revealed that follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) promoted smad2 expression in ovary tissue in a time- and dose-dependent manner, respectively. In summary, Smad2 plays a potentially vital role in ricefield eel ovary development.

TETs Regulate Proepicardial Cell Migration through Extracellular Matrix Organization during Zebrafish Cardiogenesis

Ten-eleven translocation (Tet) enzymes (Tet1/2/3) mediate 5-methylcytosine (5mC) hydroxylation, which can facilitate DNA demethylation and thereby impact gene expression. Studied mostly for how mutant isoforms impact cancer, the normal roles for Tet enzymes during organogenesis are largely unknown. By analyzing compound mutant zebrafish, we discovered a requirement for Tet2/3 activity in the embryonic heart for recruitment of epicardial progenitors, associated with development of the atrial-ventricular canal (AVC). Through a combination of methylation, hydroxymethylation, and transcript profiling, the genes encoding the activin A subunit Inhbaa (in endocardium) and Sox9b (in myocardium) were implicated as demethylation targets of Tet2/3 and critical for organization of AVC-localized extracellular matrix (ECM), facilitating migration of epicardial progenitors onto the developing heart tube. This study elucidates essential DNA demethylation modifications that govern gene expression changes during cardiac development with striking temporal and lineage specificities, highlighting complex interactions in multiple cell populations during development of the vertebrate heart.

Lan et al. show that zebrafish larvae mutant for tet2 and tet3 fail to demethylate genes encoding Inhbaa (in endocardium) and Sox9b (in myocardium), leading to defects in ECM needed to form valves and to recruit epicardial progenitors onto the heart tube.

Identification of Novel MicroRNAs and Characterization of MicroRNA Expression Profiles in Zebrafish Ovarian Follicular Cells

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression primarily at the post-transcriptional levels and thereby play important roles in regulating many physiological and developmental processes. Oocyte maturation in fish is induced by hormones produced from the hypothalamus, pituitary, and ovary. Gonadotropin-releasing hormone (GnRH) stimulates the secretion of luteinizing hormone (LH), which in turn, induces the secretion of maturation-inducing hormone (MIH) from the ovary. It is documented that small early vitellogenic (or stage IIIa) follicles are unable to undergo oocyte maturation whereas oocytes in mid- to late vitellogenic (stage IIIb) follicles can be induced by LH and MIH to become mature. To determine whether miRNAs may be involved in the growth and acquisition of maturational competency of ovarian follicles, we determined the miRNA expression profiles in follicular cells collected from stage IIIa and IIIb follicles using next-generation sequencing. It was found that miRNAs are abundantly expressed in the follicular cells from both stages IIIa and IIIb follicles. Furthermore, bioinformatics analysis revealed the presence of 214 known, 31 conserved novel and 44 novel miRNAs in zebrafish vitellogenic ovarian follicular cells. Most mature miRNAs in follicular cells were found to be in the length of 22 nucleotides. Differential expression analysis revealed that 11 miRNAs were significantly up-regulated, and 13 miRNAs were significantly down-regulated in the stage IIIb follicular cells as compared with stage IIIa follicular cells. The expression of four of the significantly regulated miRNAs, dre-miR-22a-3p, dre-miR-16a, dre-miR-181a-3p, and dre-miR-29a, was validated by real-time PCR. Finally, gene enrichment and pathway analyses of the predicted targets of the significantly regulated miRNAs supported the involvement of several key signaling pathways in regulating ovarian function, including oocyte maturation. Taken together, this study identifies novel zebrafish miRNAs and characterizes miRNA expression profiles in somatic cells within the zebrafish ovarian follicles. The differential expression of miRNAs between stage IIIa and IIIb follicular cells suggests that these miRNAs are important regulators of zebrafish ovarian follicle development and/or oocyte maturation.

Exposure to tris(1,3-dichloro-2-propyl) phosphate for Two generations decreases fecundity of zebrafish at environmentally relevant concentrations

Previous studies reported that exposure to environmentally relevant concentrations of TDCIPP significantly decreased the number of cumulative eggs in zebrafish, but effects on the quantity of eggs and sperms remained unknown. Therefore, in this study, effects of TDCIPP on yolk diameter, surface morphology of eggs, sperm density and total motility were evaluated. First generation (F0) zebrafish larvae (Danio rerio) were exposed to 0, 50, 500 or 5000 ng/L tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) from 14 days post fertilization (dpf) to 120 dpf. The F0 generation of zebrafish were paired and F1 generation of embryos were collected and continuously exposed to the same concentrations of TDCIPP until 150 dpf. TDCIPP bioconcentration in the whole body as well as effects on survival and fecundity were evaluated in F1 generation. Exposure to TDCIPP resulted in an accumulation of the chemical and decreased survival of F1 generation of zebrafish. TDCIPP decreased cumulative production and changed surface morphology of eggs in females. In males, TDCIPP decreased total motility of sperm but did not affect sperm density. These effects on quality of egg and sperm might be responsible for the decreased hatching rates observed in cross mating experiments. Furthermore, TDCIPP exposure resulted in down-regulated gene expression related to gonadal development and maturation of germ cells in females or/and males, and the down-regulation was correlated to decreased fecundity. Taken together, the results suggested that exposure to TDCIPP could decrease the quantity of eggs and sperms by down-regulating the expression of genes related to gonadal development and maturation of germ cells in zebrafish.

Developmental Toxicity of Diethylnitrosamine in Zebrafish Embryos/Juveniles Related to Excessive Oxidative Stress

Diethylnitrosamine (DEN) is present in food, water, and daily supplies and is regarded as a toxicant of carcinogenicity. The developmental toxicity of DEN has been rarely reported as yet. In this study, zebrafish were exposed to different concentrations of DEN at 6 h post-fertilization (hpf) to access embryonic toxicity of the compound. The results show that DEN resulted in negative effects of hatching rate, heartbeat, body length, and spontaneous movement. Deformities, including notochord malformation, pericardium edema, embryonic membrane turbidity, tail hypoplasia, yolk sac deformity, and growth retardation, happened during exposure period. Moreover, production of reactive oxygen species (ROS) significantly increased after DEN treatment. Then, alterations of the expression level of oxidative stress-related genes were observed in our results. To our knowledge, this is the first study concerning the effect of DEN on zebrafish. And from the information of our research, we speculated that development toxicity of DEN should be related to the excessive oxidative stress.

Activin/follistatin system in grass carp pituitary cells: - Regulation by local release of growth hormone and luteinizing hormone and its functional role in growth hormone synthesis and secretion

Gonadotrophin regulation by activin/follistatin system is well-documented, but the corresponding effect on growth hormone (GH) has not been fully characterized and with little information available in lower vertebrates, especially in fish models. In grass carp, local interactions of GH and luteinizing hormone (LH) can induce GH release and gene expression at pituitary level via autocrine/paracrine mechanisms. To shed light on the role of activin/follistatin system in GH regulation by local actions of GH and LH, grass carp activin βA and βB were cloned, shown to be single-copy genes expressed in the pituitary, and confirmed to encode activin proteins capable of transactivating promoter with activin-responsive elements. In grass carp pituitary cells, activin A and B were effective in reducing GH secretion and GH cell content with concurrent drop in GH mRNA level whereas the opposite was true for follistatin, the activin-binding protein known to neutralize the effects of endogenous activin. Treatment with activin A and B not only could suppress basal but also inhibit GH mRNA expression induced by GH and human chorionic gonadotropin (hCG), a functional analogue of LH in fish model. Apparently, down-regulation of GH mRNA by activin was mediated by reducing GH transcript stability with concurrent inhibition on GH promoter activity via the SMAD pathway. In reciprocal experiments, GH treatment was found to up-regulate activin βA, activin βB and follistatin mRNA levels in carp pituitary cells but the opposite was noted by removing endogenous GH with GH antiserum. Interestingly, parallel treatment with hCG could also inhibit basal as well as GH-induced activin βA, activin βB and follistatin gene expression. These results, as a whole, indicate that the pituitary activin/follistatin system can serve as a regulatory target for local interactions of GH and LH and contribute to GH regulation by autocrine/paracrine mechanisms in the carp pituitary.

Quizalofop-P-ethyl exposure increases estrogen axis activity in male and slightly decreases estrogen axis activity in female zebrafish (Danio rerio)

The herbicide Quizalofop-P-ethyl (QpE) exerts toxic effects in fish, but limited information is currently available on its effects on the endocrine system. In the current study, adult zebrafish (Danio rerio) were exposed to different concentrations (0, 2, 20, 200μg/L) of QpE for 30days. In males, QpE exposure significantly increased plasma estradiol (E2) and vitellogenin (VTG) levels, concomitant with up-regulation of hepatic esr1 and vtg gene expression. In females, plasma sex hormone levels and VTG concentrations were not altered significantly, but an increased expression of hepatic esr1 in addition to decreased expression of hepatic vtg, esr2a and esr2b was observed. Marked histological lesions were also observed in the gonads of both males and females. Moreover, QpE exposure significantly increased transcriptional profiles of some genes in the HPG axis and liver in males, while the majority of these genes were down-regulated in females. Docking studies showed QpE forming stable interactions with the ligand-binding domain (LBD) of zebrafish ESR1 and ESR2a, suggesting QpE may bind to estrogen receptors (ESRs). This study for the first time reveals QpE as an endocrine-disrupting chemical (EDC) disrupting the zebrafish endocrine system in a sex-specific manner, whereby it increases estrogen axis activity in males and slightly decreases estrogen axis activity in females, which may be accounted for by QpE regulating steroidogenesis and/or activating ESR(s).

Neurokinin B Exerts Direct Effects on the Ovary to Stimulate Estradiol Production

Neurokinin B (NKB) and its receptor, NK3R, play critical roles in reproduction by regulating the secretion of the hypothalamic GnRH. NKB and NK3R genes are also expressed in the ovary; however, their physiological roles within the ovary are unknown. The aim of this study was to determine whether NKB acts directly on the ovary to regulate reproduction. Injection of NKB into zebrafish accelerated follicle development, increased the mRNA levels of cyp11a1 and cyp19a1, and enhanced estradiol production. Similarly, NKB induced cyp11a1 and cyp19a1 expression in primary cultures of zebrafish follicular cells and stimulated estradiol production from cultured follicles. Furthermore, NKB activates cAMP response element-binding protein and ERK, and ERK inhibitors abolished the effect of NKB on cyp11a1, whereas protein kinase A and calmodulin-dependent protein kinase II inhibitors that blocked the activation of cAMP response element-binding protein, attenuated the effect of NKB on cyp19a1 expression. In a human granulosa cell line, COV434, a NKB agonist, senktide, also increased CYP11A1 and CYP19A1 mRNA levels and enhanced aromatase protein levels and activities. Small interfering RNA-mediated knockdown of NK3R reduced senktide-induced CYP11A1 and CYP19A1 mRNA levels. Finally, we found that NK3R mRNA was strongly down-regulated in granulosa cells obtained from polycystic ovary syndrome (PCOS) patients when compared with non-PCOS subjects. Taken together, our findings establish a direct action of NKB to induce ovarian estrogen production and raise the possibility that defective signaling of this pathway may contribute to the development of PCOS.

Molecular characterization of Activin Receptor Type IIA and its expression during gonadal maturation and growth stages in rohu carp

Activin receptor type IIA (ActRIIA), a transmembrane serine/threonine kinase receptor is an important regulator of physiological traits, viz., reproduction and body growth in vertebrates including teleosts. However, existing knowledge of its role in regulating fish physiology is limited. To address this, we have cloned and characterized the ActRIIA cDNA of Labeo rohita (rohu), an economically important fish species of the Indian subcontinent. Comparative expression profiling of the receptor gene at various reproductive and growth stages supports to its role in promoting oocyte maturation, spermatogenesis and skeletal muscle development via interaction with multiple ligands of transforming growth factor-β (TGF-β) family. The full-length cDNA of rohu ActRIIA was found to be of 1587bp length encoding 528 amino acids. The three-dimensional structure of the intracellular kinase domain of rohu ActRIIA has also been predicted. Phylogenetic relationship studies showed that the gene is evolutionarily conserved across the vertebrate lineage implicating that the functioning of the receptor is more or less similar in vertebrates. Taken together, these findings could be an initial step towards the use of ActRIIA as a potential candidate gene marker for understanding the complex regulatory mechanism of fish reproduction and growth.

Developmental exposure to the organophosphorus flame retardant tris(1,3-dichloro-2-propyl) phosphate: estrogenic activity, endocrine disruption and reproductive effects on zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate flame retardant that is detectable in the environment and biota, prompting concern over its risk to wildlife and human health. Our objective was to investigate whether long-term exposure to low concentrations of TDCPP can affect fish reproduction. Zebrafish embryos were exposed to low concentrations (0, 4, 20 and 100μg/L) of TDCPP from 2h post-fertilization until sexual maturation. Exposure to TDCPP significantly increased plasma estradiol and testosterone levels in females, but had no effect in males. TDCPP exposure also caused a significant reduction in fecundity as indicated by decreased egg production. Real-time PCR was performed to examine selected genes in the hypothalamic-pituitary-gonadal (HPG) axis and liver. Principle component analysis (PCA) showed that sex hormone levels and fecundity were related to the mRNA level of several genes in the HPG axis. Furthermore, hepatic vitellogenin (vtg1 and vtg3) expression was upregulated in both females and males, suggesting TDCPP has estrogenic activity. Histological examination revealed promotion of oocyte maturation in the females, but retardation of spermiation in males. Reduced egg quality (e.g., egg diameter) and increased malformation rates were observed in the F1 generation. Chemical analysis showed significant levels of TDCPP and its metabolite bis(1,3-dichloro-2-propyl) phosphate in the gonads of males and females. In conclusion, long-term exposure to low concentrations of TDCPP impairs fish reproduction.

IGFs mediate the action of LH on oocyte maturation in zebrafish

LH signaling is required for oocyte maturation in fish and other vertebrates. However, the downstream factors mediating LH signaling are largely unexplored in fish. In this study, we investigated whether IGFs could mediate LH action on oocyte maturation in zebrafish. Our results show that all igfs, including igf1, igf2a, igf2b, and igf3, are dynamically expressed during folliculogenesis, with the expression of igf3 reaching its maximal level in full grown stage follicles. The expression of igfs is regulated by LH through a cAMP pathway in intact follicles as well as in primary cultured follicular cells, with igf3 expression being the most sensitive to human chorionic gonadotropin (hCG) treatment. Moreover, recombinant zebrafish IGF-2a, IGF-2b, and IGF-3 proteins significantly enhanced oocyte maturation via IGF-1 receptors (IGF-1rs), with IGF-3 exhibiting the most potent stimulatory action on oocyte maturation. Furthermore, we have demonstrated that IGF-3 or hCG treatment could stimulate IGF-1rs phosphorylation, and hCG-induced oocyte maturation could be attenuated by IGF-1r inhibitors as well as by an anti-IGF-3 antiserum in vitro and in vivo, indicating that the IGF system especially IGF-3 plays a crucial role in mediating LH action on oocyte maturation. In addition, igf3 expression is significantly attenuated in LH β-subunit (lhb) mutant zebrafish and treatment with recombinant IGF-3 could partially rescue the oocyte maturation defects of the lhb mutants in vitro and in vivo. Collectively, our results clearly demonstrated that IGFs, particularly the gonad-specific IGF-3, act as important mediators of LH action on oocyte maturation in zebrafish.

A mixture of the novel brominated flame retardants TBPH and TBB affects fecundity and transcript profiles of the HPGL-axis in Japanese medaka

The novel brominated flame retardants (NBFRs), bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) and 2-ethylhexyl-2,3,4,5 tetrabromobenzoate (TBB) are components of the flame retardant mixture Firemaster 550 and both TBPH and TBB have recently been listed as high production volume chemicals by the US EPA. These NBFRs have been detected in several environmental matrices but very little is known about their toxic effects or potencies. Results of in vitro assays demonstrated potentials of these NBFRs to modulate endocrine function through interactions with estrogen (ER) and androgen receptors (AR) and via alterations to synthesis of 17-β-estradiol (E2) and testosterone (T), but in vivo effects of these chemicals on organisms are not known. Therefore a 21-day short term fish fecundity assay with Japanese medaka (Oryzias latipes) was conducted to investigate if these NBFRs affect endocrine function in vivo. Medaka were fed a diet containing either 1422 TBPH:1474 TBB or 138:144 μg/g food, wet weight (w/w). Cumulative production of eggs was used as a measure of fecundity and abundances of transcripts of 34 genes along the hypothalamus-pituitary-gonadal-liver (HPGL) axis were quantified to determine mechanisms of observed effects. Cumulative fecundity was impaired by 32% in medaka exposed to the greatest dose of the mixture of TBPH/TBB. A pattern of global down-regulation of gene transcription at all levels of the HPGL axis was observed, but effects were sex-specific. In female medaka the abundance of transcripts of ERβ was lesser in livers, while abundances of transcripts of VTG II and CHG H were greater. In male medaka, abundances of transcripts of ERα, ERβ, and ARα were lesser in gonads and abundances of transcripts of ERβ and ARα were lesser in brain. Abundances of transcripts of genes encoding proteins for synthesis of cholesterol (HMGR), transport of cholesterol (HDLR), and sex hormone steroidogenesis (CYP 17 and 3β-HSD) were significantly lesser in male medaka, which might have implications for concentrations of sex hormones. The results of this study demonstrate that exposure to components of the flame retardant mixture Firemaster(®) 550 has the potential to impair the reproductive axis of fishes.

Luteinizing hormone receptor (lhcgr) as a marker gene for characterizing estrogenic endocrine-disrupting chemicals in zebrafish ovarian follicle cells

The adverse effects of endocrine-disrupting chemicals (EDCs) have been well documented; however, the action mechanisms of many EDCs remain elusive and controversial. Furthermore, the highly diversified chemical structures and low environmental concentrations of EDCs present a major challenge to their chemical detection. Clearly, there is an urgent need for simple and reliable bioassays to detect EDCs in the environment and unravel their action mechanisms. We have recently identified luteinizing hormone receptor (lhcgr) as a robust estradiol (E2)-responsive gene in cultured zebrafish ovarian follicle cells. The expression of lhcgr exhibited a distinct biphasic response to E2 over a 24-h time-course treatment, making this a unique system for characterizing estrogenic EDCs. This study was undertaken to validate this platform by testing a wide range of EDCs, including 17α-ethinylestradiol (EE2), diethylstilbestrol (DES), bisphenol A (BPA), genistein (GEN), 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'-DDT), vinclozolin (VIN), bis(2-ethylhexyl) phthalate (DEHP), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Diethylstilbestrol (DES), EE2 and o,p'-DDT mimicked E2 and induced a biphasic expression of lhcgr while BPA and GEN stimulated a monophasic expression in the 24-h time-course. In contrast, BDE-47, DEHP and VIN had no effect, whereas TCDD decreased lhcgr expression. Dose-response experiment showed that E2, EE2 and DES had the highest potency, which was followed by GEN, BPA and o,p'-DDT. The effects of estrogenic EDCs were further confirmed by their potentiation of hCG-induced activin βA2 subunit (inhbab) expression. In conclusion, the present study showed that the expression of lhcgr in cultured zebrafish follicle cells and its biphasic response to estrogens provide a unique in vitro platform for screening and categorizing estrogenic substances and deciphering their action mechanisms.

Expression and regulation of miR-17a and miR-430b in zebrafish ovarian follicles

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate gene expression and control many developmental and physiological processes. Oocyte maturation in fish is mainly regulated by luteinizing hormone (LH) and maturation-inducing hormone (MIH). In addition, growth factors, including members of the transforming growth factor β (TGF-β) superfamily, have also been shown to play important roles in regulating oocyte maturation. In this study, we determined the expression and regulation of two miRNAs, miR-17a and miR-430b, which potentially target signalling molecules in the TGF-β pathway, in zebrafish ovarian follicles. Using real-time PCR, we observed that miR-17a and miR-430b levels in follicular cells were significantly lower in late vitellogenic and full grown follicles than in early vitellogenic follicles. Treatment with a LH analog, human chorionic gonadotropin, significantly down-regulated miR-17a and miR-430b expression in follicular cells but had no effect on their expression in oocytes. Forskolin also inhibited follicular cell miR-430b expression; however, no significant changes in miR-17a levels were observed after Forskolin treatment. Finally, MIH did not affect the expression of these miRNAs either in follicular cells or oocytes at the time points tested. These findings suggest that miR-17a and miR-430b may be involved in the regulation of follicle development and oocyte maturation in zebrafish.

Human chorionic gonadotropin (hCG) induces MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells independent of EGF/EGFR pathway

In mammals, human chorionic gonadotropin (hCG), a luteinizing hormone (LH) analogue, induces MAPK3/1 phosphorylation in the granulosa cells and this event is largely dependent on epidermal growth factor receptor (EGFR) activity. However, whether this mechanism also works in other vertebrates such as fish remains unknown. Here, we showed that treatment of cultured zebrafish ovarian follicle cells with hCG also resulted in MAPK3/1 phosphorylation without affecting the total protein level of MAPK3/1. The phosphorylation level peaked at 5 min and then declined to the basal level after 40 min of hCG treatment. Further experiment showed that H89 (a PKA inhibitor) could abolish hCG-stimulated MAPK3/1 phosphorylation, but had no effect on EGF-induced phosphorylation, suggesting a mediating role for cAMP/PKA in hCG activation of MAPK3/1. On the other hand, AG1478 (an EGFR inhibitor) completely blocked EGF-stimulated MAPK3/1 phosphorylation, but had no effect on the hCG-induced MAPK3/1 phosphorylation. These data indicate that similar to its action in mammals, hCG/LH also stimulated MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells; however, unlike the situation in the mammalian ovary, the hCG-stimulated MAPK3/1 phosphorylation in cultured zebrafish ovarian follicle cells was independent of EGFR.

Differential regulation of gonadotropin receptors (fshr and lhcgr) by epidermal growth factor (EGF) in the zebrafish ovary

Epidermal growth factor (egf) is expressed in the zebrafish oocyte whereas its receptor EGF receptor (egfr) is expressed in the somatic follicle layer, strongly suggesting a role for Egf in the intrafollicular paracrine communication that mediates an oocyte-to-follicle cell signaling pathway. However, the exact function of Egf in the follicle remains largely unknown. The present study aimed to explore the possible role of Egf in regulating gonadotropin receptors (fshr and lhcgr) in cultured zebrafish follicle cells. EGF down-regulated lhcgr expression dose-dependently in a biphasic manner with significant effect observed at 1.5 and 24 h. The effect was mediated via Egfr on the follicle cells. On the contrary, EGF also tended to decrease fshr expression at 1.5 h but it appeared to up-regulate fshr at 24 h. The EGF suppression of lhcgr expression was functionally relevant as pre-exposure to EGF reduced the follicle cell responsiveness to LH/hCG. We have recently reported that estradiol (E2) strongly stimulated lhcgr expression in the zebrafish ovary. In the current study, we further demonstrated that EGF and other EGF family members, heparin-binding EGF-like growth factor (HBEGF), transforming growth factor α (TGFα) and betacellulin (BTC), all reduced basal and E2-induced lhcgr expression. This study provides evidence for a potential paracrine role of Egf and its related peptides in the zebrafish follicle. The oocyte-derived EGF family ligands may actively control the process of follicle growth and maturation by differentially controlling the expression of fshr and lhcgr in the follicle cells in a paracrine manner.

Epidermal growth factor differentially regulates activin subunits in the zebrafish ovarian follicle cells via diverse signaling pathways

Epidermal growth factor (EGF) promotes oocyte maturation in the zebrafish and its effect is mediated via the activin system. However, the mechanisms by which EGF regulates activin subunits in the follicle cells remain unknown. The present study demonstrated that EGF controlled expression of three activin subunits (inhbaa, inhbab and inhbb) in the follicle cells via diverse signaling pathways. The expression of inhbaa and inhbb was often co-regulated via similar pathways. Suppression of MAPK3/1, p38 MAPK, PKC and PKA each blocked or partially reduced the stimulatory effects of EGF on the expression of inhbaa and inhbb while up-regulated that of inhbab. Conversely, inhibition of PI3K did not have any effect on the expression of inhbaa and inhbb but significantly suppressed the stimulatory effect of EGF on inhbab. In summary, EGF action in the zebrafish ovary involves activin system and its regulation of activin subunits is mediated by diverse signaling pathways downstream of EGFR.

Probiotics can induce follicle maturational competence: the Danio rerio case

In the present study, the effects of the probiotic Lactobacillus rhamnosus IMC 501 on the acquisition of oocyte maturational competence was examined in zebrafish (Danio rerio). L. rhamnosus administration induced the responsiveness of incompetent follicles (stage IIIa) to 17,20-dihydroxy-4-pregnen-3-one and their in vitro maturation. Acquisition of competence by the stage IIIa follicles was further validated by changes of lhr, mprb, inhbaa (activin betaA1), tgfb1, and gdf9 gene expression, which have recently emerged as key regulators of oocyte acquisition of maturational competence, and pou5f1 gene expression, which in other models has been shown to govern the establishment of developmental competence of oocytes. In addition, a DNA microarray experiment was conducted using the same follicles, and with relative gene ontology (GO) data analysis, the molecular effects of probiotic administration emerged. Molecular analysis using PCR-DGGE (denaturing gradient gel electrophoresis) approach, providing information about only the most abundant bacterial members of the microbial community, revealed that the probiotic was able to populate the gastrointestinal tract and modulate the microbial communities, causing a clear shift in them and specifically enhancing the presence of the lactic acid bacteria Streptococcus thermophilus. At the same time, PCR-DGGE analysis revealed that the probiotic was not directly associated with the ovaries. Finally, the effects of probiotic treatment on zebrafish follicle development were also analyzed by FPA (focal plane array) Fourier transform-infrared (FT-IR) imaging, a technique that provides the overall biochemical composition of samples. Changes were found above all in stage IIIa follicles from probiotic-exposed females; the modifications, observed in protein secondary structures as well as in hydration and in bands related to phosphate moieties, allowed us to hypothesize that probiotics act at this follicle stage, affecting the maturation phase.

The role and mechanism of action of activin A in neurite outgrowth of chicken embryonic dorsal root ganglia

Activin A, a member of the transforming growth factor β (TGFβ) superfamily, plays an essential role in neuron survival as a neurotrophic and neuroprotective factor in the central nervous system. However, the effects and mechanisms of action of activin A on the neurite outgrowth of dorsal root ganglia (DRG) remain unclear. In the present study, we found that activin A is expressed in DRG collected from chicken embryos on embryonic day 8 (E8). Moreover, activin A induced neurite outgrowth of the primary cultured DRG and maintained the survival of monolayer-cultured DRG neurons throughout the observation period of ten days. Follistatin (FS), an activin-binding protein, significantly inhibited activin A-induced neurite outgrowth of DRG, but failed to influence the effect of nerve growth factor (NGF) on DRG neurite outgrowth. Furthermore, the results showed that activin A significantly upregulated mRNA expression of activin receptor type IIA (ActRIIA) and calcitonin gene-related peptide (CGRP) in DRG, and stimulated serotonin (5-HT) production from DRG, indicating that activin A might induce DRG neurite outgrowth by promoting CGRP expression and stimulating 5-HT release. These data suggest that activin A plays an important role in the development of DRG in an autocrine or paracrine manner.

Pituitary gonadotropins FSH and LH are oppositely regulated by the activin/follistatin system in a basal teleost, the eel

European eels are blocked at a prepubertal silver stage due to a deficient production of pituitary gonadotropins. We investigated the potential role of activin/follistatin system in the control of eel gonadotropins. Through the development of qPCR assays for European eel activin β(B) and follistatin, we first analyzed the tissue distribution of the expression of these two genes. Both activin β(B) and follistatin are expressed in the brain, pituitary and gonads. In addition, a striking expression of both transcripts was also found in the retina and in adipose tissue. The effects of recombinant human activins and follistatin on eel gonadotropin gene expression were studied using primary cultures of eel pituitary cells. Activins A and B strongly stimulated FSHβ subunit expression in a time- and dose-dependent manner. In contrast, activin reduced LHβ expression, an inhibitory effect which was highlighted in the presence of testosterone, a known activator of eel LHβ expression. No effect of activin was observed on other pituitary hormones. Follistatin antagonized both the stimulatory and inhibitory effects of activin on FSHβ and LHβ expression, respectively. Activin is the first major stimulator of FSH expression evidenced in the eel. These results in a basal teleost further support the ancient origin and strong conservation of the activin/follistatin system in the control of FSH in vertebrates. In contrast, the opposite regulation of FSH and LH may have emerged in the teleost lineage.

Differential regulation of gonadotropin receptors (fshr and lhcgr) by estradiol in the zebrafish ovary involves nuclear estrogen receptors that are likely located on the plasma membrane

FSH and LH are gonadotropins (GTH) that control all major events of gonadal function. FSH and LH signal through their cognate receptors, FSH receptor and LH/choriogonadotropin receptor, respectively, across vertebrates. Compared with the information in mammals, very little is known about these receptors in fish, especially the regulation of their expression. In female zebrafish, fshr and lhcgr exhibit significant temporal difference in expression, with fshr increasing first when the follicles are activated to enter the vitellogenic growth phase and lhcgr lagging behind. This raises an interesting question on the differential regulation of these two GTH receptors (GTHR) during folliculogenesis. Using a primary follicle cell culture, the present study demonstrated that 17β-estradiol (E2), but not testosterone, was a potent endocrine hormone that differentially regulated the expression of fshr and lhcgr. Although E2 stimulated both receptors, its effect on the steady-state level of lhcgr mRNA was much higher (>8-fold up-regulation) than that of fshr (∼0.5-fold increase). E2 likely acted at the transcription level via its nuclear estrogen receptors (ERα and ERβ), because ICI 182,780 could abolish its effects. However, our evidence suggested that these receptors might be localized on the plasma membrane, because β-estradiol 6-(O-carboxy methyl)oxime:BSA could fully mimic the effects of E2. Demonstrating that E2 is likely one of the differentiating factors for the distinct expression of the two GTHR in the zebrafish ovary, this study sheds important light on the functions of the two GTH and their receptors in fish as well as the conservation and diverse aspects of GTHR regulation across vertebrates.

The maturation-inducing hormone 17alpha,20beta-dihydroxy-4-pregnen-3-one regulates gene expression of inhibin betaA and bambi (bone morphogenetic protein and activin-membrane-bound inhibitor) in the rainbow trout ovary

Transforming growth factor-beta (TGFbeta) superfamily members are important paracrine and autocrine regulators of ovarian development and steroidogenesis in mammals and birds, but their reproductive roles in fish are not well understood. The activin system, Tgfb, and bone morphogenetic protein 15 (Bmp15) participate in the regulation of follicle maturation in some fish species. In addition, transcript levels of TGFbeta superfamily members and their inhibitor, bambi (bmp and activin-membrane-bound inhibitor), change in the rainbow trout (Oncorhynchus mykiss) ovary during reproductive development including the transition from vitellogenesis to follicle maturation. The objective of the present study was to determine if the maturation-inducing hormone (MIH) in trout, 17alpha,20beta-dihydroxy-4-pregnen-3-one, regulates gene expression of TGFbeta superfamily members and their inhibitors. Transcript levels of inhibin beta(A) subunit (inhba) were increased and bambi decreased in isolated follicles incubated overnight without hormones compared to abundance in freshly excised tissues from the same fish, suggesting systemic factors influenced transcript abundance. Incubation with MIH decreased inhba and increased bambi expression in a dose-dependant manner and MIH was the most potent steroid examined. The transcripts' responses to incubation with and without MIH were observed in maturationally competent follicles, which are follicles competent to resume meiosis in response to MIH, and incompetent follicles, although the responses to MIH were greater in competent follicles. In summary, MIH regulates inhba and bambi expression in a stage specific manner supporting a role for MIH regulation of the TGFbeta superfamily system and participation of the TGFbeta superfamily system in the regulation of follicle maturation in rainbow trout.

Molecular cloning of activin type I and type II receptors and differential regulation of their expression by activin in grass carp pituitary cells

Activins, like other members of the transforming growth factor-beta superfamily, signal via two structurally related transmembrane serine/threonine kinase receptors classified as types II and I. Two cDNAs encoding activin type IIB receptor (ActRIIB) and activin type IB receptor (ActRIB) were cloned and characterized from grass carp. The deduced ActRIIB protein of 510 amino acids shared 79-90% identity with those in other vertebrates, while the predicted ActRIB protein of 505 amino acids exhibited high sequence identity (80-96%) to its counterparts in human, rat, mouse, frog, and zebrafish. Comparative analysis showed that both receptors contained the conserved amino acid residues required for ligand binding, and comprised the characteristic regions of an extracellular ligand binding domain, a single transmembrane region, and an intracellular serine/threonine kinase domain. Real-time PCR analysis revealed that both ActRIIB and ActRIB transcripts were ubiquitously expressed in all tissues examined, in particular with high expression levels in extra-gonadal tissues, including pituitary, brain, and liver. Using a static incubation approach, the feedback effects of exogenous activin on ActRIIB and ActRIB mRNA expression were examined at the pituitary level. Activin significantly stimulated ActRIB mRNA expression in a time- and dose-dependent manner, but had no effect on ActRIIB mRNA levels. These findings support the notion that activin receptors may serve as a local regulatory point involving in pituitary function of activin in fish.

Endocrine/paracrine control of zebrafish ovarian development

Ovarian differentiation and the processes of follicle development, oocyte maturation and ovulation are complex events, requiring the coordinated action of regulatory molecules. In zebrafish, ovarian development is initiated at 10 days after hatching and fish become sexually mature at 3 months. Adult zebrafish have asynchronous ovaries, which contain follicles of all stages of development. Eggs are spawned daily under proper environmental conditions in a population of zebrafish, with individual females spawning irregularly every 4-7 days in mixed sex conditions. Maximal embryo viability is achieved when sexually isolated females are bred in 10-day intervals [Niimi, A.J., LaHam, Q.N., 1974. Influence of breeding time interval on egg number, mortality, and hatching of the zebra fish Brachydanio verio. Can. J. Zool. 52, 515-517]. Similar to other vertebrates, hormones from the hypothalamus-pituitary-gonadal axis play important roles in regulating follicle development. Follicle stimulating hormone (FSH) stimulates estradiol production, which in turn, promotes viteollogenesis. Luteinizing hormone (LH) stimulates the production of 17,20beta-dihydroxy-4-pregnen-3-one (17,20betaP) or maturation inducing hormone (MIH) which acts through membrane progestin receptors to activate maturation promoting factor, leading to oocyte maturation. Recent studies in zebrafish have also provided novel insights into the functions of ovary-derived growth factors in follicle development and oocyte maturation. The present review summarizes the current knowledge on how endocrine and paracrine factors regulate ovarian development in zebrafish. Special emphasis is placed on how follicle development and oocyte maturation in adult females is regulated by gonadotropins, ovarian steroids and growth factors produced by the ovary.

Regulation of membrane progestin receptors in the zebrafish ovary by gonadotropin, activin, TGF-beta and BMP-15

Progestin hormones are vital for inducing oocyte maturation in fish by binding to membrane progestin receptors (mPRs). The aim of this study was to examine the expression and regulation of mPRalpha and mPRbeta in zebrafish follicles. First, defolliculated fully grown oocytes were subjected to immunofluorescent staining using anti-mPRalpha and mPRbeta antibodies, and their expression on the oocyte membrane was confirmed. Second, total protein was collected from zebrafish follicles and Western blotting revealed that the level of mPRalpha and mPRbeta increased with follicle development. We have previously shown that several members of the transforming growth factor-beta (TGF-beta) superfamily, including TGF-beta1, activin-A, and bone morphogenetic protein (BMP)-15, regulate oocyte maturation in zebrafish. Therefore, the third major focus of this study was to test if these growth factors, as well as gonadotropins, regulate the expression of mPRs. Overexpression of BMP-15 significantly reduced, while knockdown of BMP-15 increased, mPRbeta levels. However, mPRalpha expression level remained unchanged with BMP-15 overexpression or knockdown. Treatment of follicles with human chorionic gonadotropin (hCG) resulted in an increased in mPRbeta, but not mPRalpha, expression levels. Activin-A induced the expression of mPRalpha and mPRbeta in a dose- and time-dependent manner. On the other hand, TGF-beta1 treatment suppressed the expression of mPRbeta, but not mPRalpha. Taken together, these findings further support the role of mPRs in oocyte maturation and suggest that gonadotropins, BMP-15, activin-A, and TGF-beta1 exert their regulatory effects on oocyte maturation in part by regulating mPR expression.

Expression and localization of activin receptor-interacting protein 2 in mouse tissues

Activin plays important roles in reproductive tissues as a stimulator of follicle-stimulating hormone (FSH) secretion. Activin receptor-interacting protein 2 (ARIP2) has been recently identified in mouse tissues as a regulatory protein of activin signal transduction. However, the localization and function of ARIP2 are not well characterized. In this study, we found that ARIP2 mRNA and protein were widely expressed in mouse tissues by reverse transcription-PCR (RT-PCR) and Western blotting. The immunoreactivities of ARIP2 were mainly localized at myocardial cells of heart, Leydig cells in testis, macrophages and epithelial cells of bronchus in lung, renal tubule and collecting tubule, pancreatic islet, adrenal gland, adenohypophysis and hypothalamus by immunohistochemical staining. Furthermore, ARIP2 overexpression down-regulated signal transduction induced by activin A in pituitary gonadotroph LbetaT2 cells and inhibited FSH secretion from primary cultured anterior pituitary cells induced by activin A. These findings suggest that ARIP2 is widely distributed in various tissues and may be a negative regulator of activin action in pituitary cells.

Time-dependent transcriptional profiles of genes of the hypothalamic-pituitary-gonadal axis in medaka (Oryzias latipes) exposed to fadrozole and 17beta-trenbolone

Both the anabolic androgen 17beta-trenbolone (TRB) and the aromatase inhibitor fadrozole (FAD) can cause decreased plasma concentrations of estrogen (E2) and reduce fecundity of fish. However, the underlying mechanisms and the molecular pathways involved are largely unknown. The present study was designed to assess time-dependent effects of FAD and TRB on the transcriptional responses of the hypothalamic-pituitary-gonadal (HPG) axis of Japanese medaka (Oryzias latipes). Fourteen-week-old Japanese medaka were exposed to 50 microg FAD/L or 2 microg TRB/L in a 7-d static renewal test, and the expression profiles of 36 HPG axis genes were measured by means of a medaka HPG real-time reverse-transcription polymerase chain reaction array after 8 h, 32 h, or 7 d of exposure. Exposure to TRB or FAD caused lesser fecundity of Japanese medaka and down-regulated transcription of vitellogenin and choriogenin (CHG) gene expression in the liver of females. Exposure to FAD for 8 h resulted in an 8-fold and 71-fold down-regulation of expression of estrogen receptor alpha and choriogenin L (CHG L), respectively, in female liver. 17beta-Trenbolone caused similar down-regulation of these genes, but the effects were not observed until 32 h of exposure. These results support the hypothesis that FAD reduces plasma E2 more quickly by inhibiting aromatase enzyme activity than does TRB, which inhibits the production of the E2 precursor testosterone. Exposure to FAD and TRB resulted in rapid (after 8 h) down-regulation of luteinizing hormone receptor and low-density-lipoprotein receptor in the testis to compensate for excessive androgen levels. Overall, the molecular responses observed in the present study differentiate the mechanisms of the reduced fecundity by TRB and FAD.

Characterization of housekeeping genes in zebrafish: male-female differences and effects of tissue type, developmental stage and chemical treatment

BACKGROUND

Research using the zebrafish model has experienced a rapid growth in recent years. Although real-time reverse transcription PCR (QPCR), normalized to an internal reference ("housekeeping") gene, is a frequently used method for quantifying gene expression changes in zebrafish, many commonly used housekeeping genes are known to vary with experimental conditions. To identify housekeeping genes that are stably expressed under different experimental conditions, and thus suitable as normalizers for QPCR in zebrafish, the present study evaluated the expression of eight commonly used housekeeping genes as a function of stage and hormone/toxicant exposure during development, and by tissue type and sex in adult fish.

RESULTS

QPCR analysis was used to quantify mRNA levels of bactin1, tubulin alpha 1(tuba1), glyceraldehyde-3-phosphate dehydrogenase (gapdh), glucose-6-phosphate dehydrogenase (g6pd), TATA-box binding protein (tbp), beta-2-microglobulin (b2m), elongation factor 1 alpha (elfa), and 18s ribosomal RNA (18s) during development (2 - 120 hr postfertilization, hpf); in different tissue types (brain, eye, liver, heart, muscle, gonads) of adult males and females; and after treatment of embryos/larvae (24 - 96 hpf) with commonly used vehicles for administration and agents that represent known environmental endocrine disruptors. All genes were found to have some degree of variability under the conditions tested here. Rank ordering of expression stability using geNorm analysis identified 18s, b2m, and elfa as most stable during development and across tissue types, while gapdh, tuba1, and tpb were the most variable. Following chemical treatment, tuba1, bactin1, and elfa were the most stably expressed whereas tbp, 18s, and b2m were the least stable. Data also revealed sex differences that are gene- and tissue-specific, and treatment effects that are gene-, vehicle- and ligand-specific. When the accuracy of QPCR analysis was tested using different reference genes to measure suppression of cyp19a1b by an estrogen receptor antagonist and induction of cyp1a by an arylhydrocarbon receptor agonist, the direction and magnitude of effects with stable and unstable genes differed.

CONCLUSION

This study provides data that can be expected to aid zebrafish researchers in their initial choice of housekeeping genes for future studies, but underlines the importance of further validating housekeeping genes for each new experimental paradigm and fish species.

Role of activin, transforming growth factor-beta and bone morphogenetic protein 15 in regulating zebrafish oocyte maturation

The transforming growth factor-beta (TGF-beta) superfamily is a large group of peptide growth and differentiation factors that have important functions in many physiological processes, including reproduction. We previously reported that several members of the TGF-beta superfamily, including activin-A, bone morphogenetic protein-15 (BMP-15) and TGF-beta1, regulate oocyte maturation in zebrafish. The aim of this study was to further examine the functions and mechanisms of these growth factors in regulating zebrafish oocyte maturation. First, the interaction among three regulators was examined. Overexpression of BMP-15 reduced the effect of activin-A on oocyte maturation. Inhibition of BMP-15 function or expression increased oocyte maturation but had no additive effect with activin-A. TGF-beta1 suppressed activin-A-, as well as BMP-15 antiserum-induced oocyte maturation. Second, the role of Smad 2, an intracellular mediator of activin and TGF-beta, in oocyte maturation was investigated. Western blot analysis revealed that both activin-A and TGF-beta1 activate Smad2 in zebrafish follicles. Injection of morpholino antisense olignucleotides against Smad2 into oocytes reduced Smad2 expression and completely blocked activin-A-induced oocyte maturation. Knockdown of Smad 2 also significantly decreased basal and hCG-induced oocyte maturation. These findings suggest that activin-A, TGF-beta1, and BMP-15 may target common gene(s) to regulate oocyte maturation and demonstrate that Smad2 plays an important role in oocyte maturation.

Responses of the medaka HPG axis PCR array and reproduction to prochloraz and ketoconazole

Effects of two model imidazole-type fungicides, prochloraz (PCZ) and ketoconazole (KTC), on the hypothalamic-pituitary-gonadal (HPG) axis of the Japanese medaka (Oryzias latipe) [corrected] were examined by use of real time PCR (RT-PCR) array. Fourteen-week-old Japanese medaka were exposed for seven days to concentrations of PCZ or KTC from 3.0 to 300 microg/L Exposure [corrected] to KTC or PCZ caused significant reduction of fecundity of Japanese medaka and down-regulated expression of estrogen receptor (ER)-alpha and egg precursors in livers of males and females. However, PCZ was more potent than KTC both in modulating transcription and causing lesser fecundity. Exposure to nominal 30 microg PCZ/L resulted in 50% less fecundity and significant down-regulation of vitellogenin II expression, but KTC did not cause such effects at this concentration. Exposure to PCZ caused a compensatory upregulation in cytochrome P450 c17alphahydroxylase, 17,20-lyase (CYP17) and aromatase (CYP19) expression in the ovary, while KTC did not. Furthermore, the ecologically relevant end point, fecundity was log-log related to mRNA level of six genes in livers of females.

Role of inhibin and activin in the modulation of gonadotropin- and steroid-induced oocyte maturation in the teleost Fundulus heteroclitus

BACKGROUND

Activin and inhibin are glycoproteins structurally related to the transforming growth factor-beta superfamily. These peptides were first described as factors that regulate the follicle-stimulating hormone (FSH) at the pituitary level. The possible role of inhibin and activin, at the ovarian level, in mediating the stimulatory actions of a Fundulus pituitary extract (FPE) and 17alpha,20beta-dihydroprogesterone (DHP) on oocyte maturation was investigated in this study.

METHODS

In vitro culture of ovarian follicles and induction of oocyte maturation were carried out in 75% Leibovitz L-15 medium. Follicles or denuded oocytes were exposed to FPE, inhibin, activin, ethanol vehicle (control group), or DHP. The competence of the follicles or denuded oocytes to respond to the hormones was assessed by scoring germinal vesicle breakdown (GVBD) used as an indication of the reinitiation of meiosis or oocyte maturation. DHP level was measured by radioimmunoassay.

RESULTS

Addition of FPE promoted the synthesis of DHP by the granulose cells of fully grown ovarian follicles and thus stimulated GVBD in the oocyte. Presence of porcine inhibin did not hinder the synthesis of DHP stimulated by FPE, although it did inhibit the subsequent GVBD in a dose-dependent manner, suggesting that the action of inhibin was at the oocyte level. Similarly to the findings with FPE, inhibin also blocked the DHP-induced GVBD in intact follicles, as well as the spontaneous and steroid-induced GVBD of denuded oocyte. Inhibin straightforwardly blocked the response to a low dose of DHP throughout the culture period, while higher doses of the steroid appeared to overcome the inhibitory effect especially at later times. In contrast to inhibin, recombinant human activin A significantly enhanced DHP-induced GVBD in a dose-dependent manner after 48 hr, although activin alone was not able to induce GVBD without the presence of the steroid.

CONCLUSION

Taking together with our previous studies that demonstrate the presence of activin/inhibin subunits in the ovary of F. heteroclitus, these in vitro findings indicate that inhibin and activin are local regulators in the teleost ovary and have opposing effects in modulating oocyte maturation.

Environmental and genetic modifiers of squint penetrance during zebrafish embryogenesis

The Nodal-related subgroup of the TGFbeta superfamily of secreted cytokines regulates the specification of the mesodermal and endodermal germ layers during gastrulation. Two Nodal-related proteins - Squint (Sqt) and Cyclops (Cyc) - are expressed during germ-layer specification in zebrafish. Genetic sqt mutant phenotypes have defined a variable requirement for zygotic Sqt, but not for maternal Sqt, in midline mesendoderm development. However a comparison of phenotypes arising from oocytes or zygotes injected with Sqt antisense morpholinos has suggested a novel requirement for maternal Sqt in dorsal specification. In this study we examined maternal-zygotic mutants for each of two sqt alleles and we also compared phenotypes of closely related zygotic and maternal-zygotic sqt mutants. Each of these approaches indicated there is no general requirement for maternal Sqt. To better understand the dispensability of maternal and zygotic Sqt, we sought out developmental contexts that more rigorously demand intact Sqt signalling. We found that sqt penetrance is influenced by genetic modifiers, by environmental temperature, by levels of residual Activin-like activity and by Heat-Shock Protein 90 (HSP90) activity. Therefore, Sqt may confer an evolutionary advantage by protecting early-stage embryos against detrimental interacting alleles and environmental challenges.

Expression of activin and inhibin subunits, receptors and binding proteins in human adrenocortical neoplasms

OBJECTIVE

The growth and differentiation factors activin and inhibin can affect tumour formation and steroid production in the adrenal cortex. These factors bind to type I (Alk-4), type II (ActRIIA, ActRIIB) and type III (betaglycan) receptors or to the activin-binding protein follistatin. Expression of these activin-related mRNAs was measured in different types of adrenocortical tissues and tumours to study the relationship with tumorigenesis.

DESIGN

Quantitative expression of activin-related mRNAs was investigated in patient adrenocortical samples.

PATIENTS

Twenty-eight human adrenocortical samples from normal and hyperplastic adrenals and from adrenocortical adenomas and carcinomas were collected after surgery for study purposes.

MEASUREMENTS

Using quantitative reverse transcription polymerase chain reaction (RT-PCR), we investigated the expression of inhibin alpha-, betaA- and betaB-subunits, follistatin, betaglycan, ActRIIA, ActRIIB and Alk-4 in the adrenocortical tissues. The expression of cytochrome P450c17 (CYP17) mRNA was also measured to investigate its association with inhibin and activin subunit expression.

RESULTS

All genes studied were expressed in all tissues, with the exception of the inhibin alpha-subunit in one hyperplastic adrenal and three adrenocortical carcinomas. Expression of inhibin betaA-subunit, follistatin, betaglycan, ActRIIA, ActRIIB and CYP17 differed between nontumorous adrenals and carcinomas.

CONCLUSIONS

These differences, together with correlation analysis, indicate parallel regulation of the expression of CYP17, the inhibin alpha-subunit, ActRIIA, ActRIIB, betaglycan and follistatin. We conclude that the expression of activin and inhibin subunits, receptors and binding proteins is affected by tumour formation in the adrenal gland and may play a role in tumorigenesis.

Bone morphogenetic protein-15 in the zebrafish ovary: complementary deoxyribonucleic acid cloning, genomic organization, tissue distribution, and role in oocyte maturation

Bone morphogenetic protein-15 (BMP-15) is a member of the TGFbeta family known to regulate ovarian functions in mammals. The structure and function of BMP-15 in lower vertebrates are less known. In this study, we cloned the zebrafish BMP-15 (zfBMP-15) cDNA and depicted its genomic organization. The zfBMP-15 cDNA encodes a protein of 384 amino acids. The mature protein has 46-51% sequence identities to fugu, chicken, and mammalian BMP-15. It also shares 38-46% homology with growth and differentiation factor-9 in fishes, chicken, and mammals. Phylogenetic analysis further confirms that the zfBMP-15 is most closely related to BMP-15 from other species, whereas the growth and differentiation factor-9 peptides from fish to mammals form a distinct branch. Comparison of zfBMP-15 cDNA with zebrafish genome database revealed that zfBMP-15 is encoded by a gene with two exons and one intron, located on chromosome 6. BMP-15 mRNA is expressed in the ovary and testis and, to a lesser extent, brain, liver, gut, heart, and muscle. Real-time PCR revealed that BMP-15 is expressed in follicles at all stages of development with no significant changes over the course of folliculogenesis. Using in situ hybridization and immunocytochemistry, we detected BMP-15 in both oocytes and follicular cells. Incubation of follicles with antiserum against zfBMP15 increased oocyte maturation, whereas incubation with recombinant human BMP-15 suppressed human chorionic gonadotropin-induced oocyte maturation. These findings suggest that BMP-15 plays a role in regulating gonadal functions in fish, in particular oocyte maturation.