In vitro ovulation, prostaglandin synthesis, and proteolysis in isolated ovarian components of yellow perch (Perca flavescens): effects of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one and phorbol ester

Significance of fatty acids in fish broodstock nutrition

The nutritional status of broodstock profoundly affects their reproductive performance and offspring survival. Studies on lipids and essential fatty acids in broodstock diets highlight their importance in cell structure, fecundity, fertilization, egg and larval quality, and providing metabolic energy for reproduction. Long-chain polyunsaturated fatty acids (Lc-PUFA) like DHA (22:6 n-3) and EPA (20:5 n-3) are vital for egg and larval development, while arachidonic acid (ARA) produces eicosanoids essential for reproduction. The fatty acid requirements vary by habitat; freshwater fish typically lack ∆12 and ∆15 desaturase enzymes to convert oleic acid into vital polyunsaturated fatty acids like linoleic and linolenic acids but can synthesize linoleic (18:2 n-6) and linolenic (18:3 n-3) into Lc-PUFAs such as EPA, DHA, and ARA through desaturation and elongation, whereas marine teleost cannot. Hence, broodstock feed fatty acid composition must be tailored by incorporating ingredients with a specific fatty acid composition to enhance reproductive performance. This review provides updated information on fatty acid supplementation in broodstock diets to improve reproductive outcomes in commercially important finfish, offering valuable insights for researchers, academicians, hatchery owners, and fish farmers to produce better-quality seeds.

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.

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.

Constant darkness negatively affects the outcome of hormonally induced reproduction in cultured Eurasian perch females

This study aimed to assess the effect of constant darkness applied to fish during controlled breeding on reproductive traits in domesticated females of Eurasian perch. Based on the assumption that keeping fish in constant darkness during the reproduction operation may reduce stress, suspected to be responsible for variable spawning effectiveness in this species. Two conditions were assessed (16 h light per day [group 16L] and constant darkness [group 0L], two tank replicates per condition). The reproductive protocol involved a 7-day-long adaptation period for group 0L where photoperiod was reduced by 2.3 h a day down to constant darkness. After the adaptation period, two hormone injections (salmon gonadoliberin analogue) were applied to both groups: priming (10 µg/kg) and resolving (25 µg/kg) with a 7-day interval between them. During the study, morphometric indices were recorded and blood, brain, and pituitary samples were collected to assess stress markers and determine hypothalamic-pituitary-gonadal axis functioning via measuring blood plasma hormones, as well as gonadoliberin and gonadotropins (luteinising hormone [LH] and follicle-stimulating hormone [FSH]) transcript abundance (n = 7 for each group at each sampling point). In addition, kinetics of the final oocyte maturation (FOM) process, ovulation rate, and egg quality of each group was monitored (n = 12 for each group). The results indicated that there were no differences in terms of morphometry, FOM kinetics, and most stress indices between groups throughout the experiment, except haematocrit, which increased immediately following the acclimation period in fish kept in darkness. Constant darkness negatively affected plasma levels of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) and LH transcript expression at the time of the second hormone injection. This indicated that exposure to constant darkness negatively affected priming of the hormonal dose applied, resulted in the disruption of ovulation, and reduced ovulation rates (50%) for group 0L, as compared to 16L (91%). The findings of this study clearly indicate that constant darkness may have significant deleterious effects on reproductive traits throughout out-of-season induced, hormonally supported, controlled reproduction. Therefore, we advise against the use of constant darkness when managing broodstock reproduction in domesticated Eurasian perch.

Dydrogesterone exposure induces zebrafish ovulation but leads to oocytes over-ripening: An integrated histological and metabolomics study

Dydrogesterone (DDG) is a synthetic progestin widely used in numerous gynecological diseases. DDG has been shown to disturb fish reproduction, however, the mechanism is still unclear. Here we studied the histological changes and differences of metabolome between exposed and control fish gonads after exposure of zebrafish (Danio rerio) embryos to 2.8, 27.6, and 289.8 ng/L DDG until sexual maturity for a total of 140 days. Dydrogesterone exposure led to male-biased zebrafish sex ratios. Histological examination revealed that DDG induced postovulatory follicles and atretic follicles in the ovary of the female fish. Postovulatory follicles indicated the occurrence of ovulation. DDG also increased spermatids and spermatozoa in the male fish testis, suggesting promotion of spermatogenesis. Ovarian metabolome showed that DDG increased the concentrations of free amino acids, urea, putrescine, free fatty acids, acylcarnitines, lysophospholipids, and other metabolites catabolized from phospholipids. Most of these metabolites are biodegradation products of proteins and lipids, suggesting the existence of ovulated oocytes over-ripening. Further, DDG upregulated arachidonic acid (AA) and its 5‑lipoxygenase (5-LOX) metabolites 5‑oxo‑6,8,11,14‑eicosatetraenoic acid (5-oxo-ETE) in the ovary, which could lead to suppression of AA cyclooxygenase (COX) metabolite prostaglandin F2α (PGF2α). It is believed that AA induced oocyte maturation, while 5-oxo-ETE and related metabolites in purinergic signaling promoted ovulation. Whereas, the suppression of PGF2α production might block spawning and damaged follicular tissue digestion, which explained the oocytes over-ripening and atretic follicles in the treated ovary. Overall, our results suggested that DDG exposure induced zebrafish oocyte maturation and ovulation but led to oocytes over-ripening via the AA metabolic pathway and purinergic signaling.

Prostaglandin affects in vitro ovulation and 17α, 20β-Dihydroxy- 4-pregnen-3-one production in longchin goby, Chasmichthys dolichognathus oocytes

This study focused on the association of prostaglandins and a progestin, 17α, 20β-dihydroxy-4-pregnen-3-one (17α20βP) during the ovulation process in longchin goby, Chasmichthys dolichognathus. We performed several in vitro experiments using 850–920 μm diameter oocytes which were at the migratory nucleus stage. With the 890–920 μm diameter oocytes, no significant difference in ovulation was observed in any of the prostaglandins (PGE1, PGE2, and PGF2α) treated groups although PGE2 and PGF2α at concentrations of 50 ng/mL increased ovulation slightly compared with controls; however, 17α20βP production was stimulated with PGE1 alone at low concentrations (5 ng/mL). In 850 μm diameter oocytes, PGF2α at concentrations of 50 and 500 ng/ml resulted in a significant increase in ovulation. 17α20βP (50 ng/ml) alone had no observable effect on ovulation, but in the combined of PGF2α 50 or 500 ng/ml it caused the greatest effect on ovulation. The sensitivity of oocytes to the induction of ovulation varies between 850 and 890–920 μm, it appeared to vary depending on the migration status of nucleus. These results suggest that PGF2α (or combined of 17α20βP) was more potent in inducing ovulation of the longchin goby.

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.

The role of eicosanoids in 17α, 20β-dihydroxy-4-pregnen-3-one-induced ovulation and spawning in Danio rerio

This study employed a hormone bioassay to characterize the eicosanoids involved in zebrafish ovulation and spawning, in particular the prostaglandin (PG) products of cyclooxygenase (COX) metabolism and the leukotriene (LT) products of lipoxygenase (LOX) metabolism. Exposure to the teleost progestogen 17α, 20β-dihydroxy-4-pregnen-3-one (17,20βP) induced ovulation, but not spawning, in solitary females and both ovulation and spawning in male-female pairs. Transcription of the eicosanoid-synthesizing enzymes cytosolic phospholipase A2 (cPLA(2)) and COX-2 increased and LTC(4) synthase decreased in peri-ovulatory ovaries of 17,20βP-exposed fish. Ovarian PGF(2α) levels increased post-spawning in 17,20βP-exposed fish, but there was no difference in LTB(4) or LTC(4). Pre-exposure to cPLA(2) or LOX inhibitors reduced 17,20βP-induced ovulation rates, while a COX inhibitor had no effect on ovulation or spawning. Collectively, these findings suggest that eicosanoids, in particular LOX metabolites, mediate 17,20βP-induced ovulation in zebrafish. COX metabolites also appear to be involved in ovulation and spawning but their role remains undefined.

Role of catecholestrogens on ovarian prostaglandin secretion in vitro in the catfish Heteropneustes fossilis and possible mechanism of regulation

Seasonal, periovulatory and 2-hydroxyestradiol-17β (2-OHE(2))-induced changes on ovarian prostaglandin (PG) E(2) and F(2α) were investigated under in vivo or in vitro in the female catfish Heteropneustes fossilis. Both PGE(2) and PGF(2α) increased significantly during ovarian recrudescence with the peak levels in spawning phase. The PGs showed periovulatory changes with the peak levels at 16 h after the hCG treatment. Incubation of postvitellogenic ovary fragments with estradiol-17β (E(2)), 2-OHE(2) or 2-methoxyE(2) produced concentration-dependent increases in PG levels; 2-OHE(2) was more effective. In order to identify the receptor mechanism involved in the 2-OHE(2)-induced PG stimulation, the ovarian pieces were incubated with phentolamine (an α-adrenergic antagonist), propranolol (a β-adrenergic antagonist) or tamoxifen (an estrogen receptor blocker) alone or in combination with 2-OHE(2). The incubation of the tissues with the receptor blockers alone did not produce any significant effect on basal PG levels. However, co- and pre-incubation of the tissues with the blockers resulted in inhibition of the stimulatory effect of 2-OHE(2) on the PGs. Phentolamine was more effective than propranolol. The signal transduction pathway(s) involved in the 2-OHE(2)-induced PG secretion was investigated. The incubation of the ovarian pieces with 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor), chelerythrine (a protein kinase C inhibitor) and PD098059 (a mitogen-activated protein kinase inhibitor) significantly lowered the basal secretion of PGF(2α) and PGE(2). In contrast, H89 (a protein kinase A inhibitor) increased the basal secretion of PGs at 1 and 5 μM concentration and decreased it at 10 μM concentration. The co- or pre-incubation with IBMX, H89, chelerythrine and PD098059 significantly inhibited the stimulatory effect of 2-OHE(2) on PGF(2α) and PGE(2) levels. The inhibition was higher in the pre-incubation groups. Chelerythrine was the most effective followed by PD098059, IBMX and H89. The results suggest that 2-OHE(2) may employ both adrenergic and estrogen receptors, or a novel receptor mechanism having properties of both adrenergic and estrogen receptors.

Identification of new participants in the rainbow trout (Oncorhynchus mykiss) oocyte maturation and ovulation processes using cDNA microarrays

BACKGROUND

The hormonal control of oocyte maturation and ovulation as well as the molecular mechanisms of nuclear maturation have been thoroughly studied in fish. In contrast, the other molecular events occurring in the ovary during post-vitellogenesis have received far less attention.

METHODS

Nylon microarrays displaying 9152 rainbow trout cDNAs were hybridized using RNA samples originating from ovarian tissue collected during late vitellogenesis, post-vitellogenesis and oocyte maturation. Differentially expressed genes were identified using a statistical analysis. A supervised clustering analysis was performed using only differentially expressed genes in order to identify gene clusters exhibiting similar expression profiles. In addition, specific genes were selected and their preovulatory ovarian expression was analyzed using real-time PCR.

RESULTS

From the statistical analysis, 310 differentially expressed genes were identified. Among those genes, 90 were up-regulated at the time of oocyte maturation while 220 exhibited an opposite pattern. After clustering analysis, 90 clones belonging to 3 gene clusters exhibiting the most remarkable expression patterns were kept for further analysis. Using real-time PCR analysis, we observed a strong up-regulation of ion and water transport genes such as aquaporin 4 (aqp4) and pendrin (slc26). In addition, a dramatic up-regulation of vasotocin (avt) gene was observed. Furthermore, angiotensin-converting-enzyme 2 (ace2), coagulation factor V (cf5), adam 22, and the chemokine cxcl14 genes exhibited a sharp up-regulation at the time of oocyte maturation. Finally, ovarian aromatase (cyp19a1) exhibited a dramatic down-regulation over the post-vitellogenic period while a down-regulation of Cytidine monophosphate-N-acetylneuraminic acid hydroxylase (cmah) was observed at the time of oocyte maturation.

CONCLUSION

We showed the over or under expression of more that 300 genes, most of them being previously unstudied or unknown in the fish preovulatory ovary. Our data confirmed the down-regulation of estrogen synthesis genes during the preovulatory period. In addition, the strong up-regulation of aqp4 and slc26 genes prior to ovulation suggests their participation in the oocyte hydration process occurring at that time. Furthermore, among the most up-regulated clones, several genes such as cxcl14, ace2, adam22, cf5 have pro-inflammatory, vasodilatory, proteolytics and coagulatory functions. The identity and expression patterns of those genes support the theory comparing ovulation to an inflammatory-like reaction.

Effects of external pH on hormonally regulated ovarian follicle maturation and ovulation in Atlantic croaker

In vitro studies of ovarian follicle maturation and ovulation in teleost fishes typically are conducted within a narrow range (7.5-7.8) of constant external (medium) pH, although there is evidence that pH can influence ovulation. Therefore, this study with Atlantic croaker investigated the effects of external pH on hormonally regulated in vitro maturation and ovulation as well as changes in the pH of ovarian fluid during in vivo maturation and ovulation. For the in vitro experiments, follicles were first incubated with human chorionic gonadotropin (hCG) to induce maturational and ovulatory competencies, and then with maturation-inducing hormone (MIH) to induce completion of maturation and ovulation. At a constant external pH within the range of 7.0-8.2, the lower pH levels (7.0-7.3) generally inhibited or slowed down hormonally induced maturation and ovulation whereas higher pH (7.6-8.2) facilitated these processes. When ovarian follicles were incubated at a constant pH of 7.6 during the priming incubation with hCG, changing the external pH during the incubation with MIH had relatively little effect on oocyte maturation or ovulation. Thus, the inhibitory effect of constant low levels of external pH (7.0-7.3) on maturation and ovulation may be primarily due to disruptions in the gonadotropin-dependent acquisition of maturational and ovulatory competencies. The pH of ovarian fluid remained constant at 8.5 during in vivo ovarian follicle maturation and ovulation. Subsequent in vitro tests showed that external pH of 8.5 enhances hormonally induced maturation and ovulation relative to pH of 7.6. These observations suggest that attention should be paid to the pH of incubation media used in basic research and in biotechnological applications relying on in vitro maturation and ovulation in teleosts. Further, an understanding of the physiological significance of the enhancing effect of alkaline pH on maturation and ovulation will require determination of the intrafollicular pH around the oocyte during the periovulatory period.

Role of arachidonic acid and protein kinase C during maturation-inducing hormone-dependent meiotic resumption and ovulation in ovarian follicles of Atlantic croaker

The roles of arachidonic acid (AA) and protein kinase C (PKC) during in vitro maturation-inducing hormone (MIH)-dependent meiotic resumption (maturation) and ovulation were studied in ovarian follicles of Atlantic croaker (Micropogonias undulatus). The requirement for cyclooxygenase (COX) metabolites of AA was examined using a nonspecific COX inhibitor, indomethacin (IM), as well as two COX products, prostaglandin (PG) F(2alpha) and PGE(2), whereas the role of lipoxygenase (LOX) was investigated using a specific LOX inhibitor, nordihydroguaiaretic acid (NDGA). The involvement of PKC was examined using phorbol 12-myristate 13-acetate (PMA), a PKC activator, as well as GF109203X (GF), a specific inhibitor of PKC and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7), nonspecific inhibitor of protein kinases. Genomic mechanisms were examined with the transcription-inhibitor actinomycin D (ActD) and the functionality of heterologous (oocyte-granulosa) gap junctions (GJ) with a dye transfer assay. The AA (100 microM) and PGF(2alpha) (5 microM) did not induce maturation, and NDGA (10 microM) did not affect MIH-dependent maturation. However, IM (100 microM) partially inhibited MIH-dependent maturation. Conversely, AA and both PGs induced, and IM and NDGA inhibited, MIH-dependent ovulation in matured follicles. The PMA (1 microg/ml) did not induce maturation but caused ovulation in matured follicles, whereas PKC inhibitors (GF, 5 microM; H7, 50 microM) did not affect MIH-dependent maturation but inhibited MIH- and PMA-dependent ovulation. The PMA-dependent ovulation was inhibited by IM but not by NDGA. In addition, ActD (5 microM) blocked MIH-dependent, but not PMA-dependent, ovulation, and PGF(2alpha) restored MIH-dependent ovulation in ActD-blocked follicles. The AA and PGs did not induce, and GF did not inhibit, MIH-dependent heterologous GJ uncoupling. In conclusion, AA and PKC mediate MIH-dependent ovulation but not meiotic resumption or heterologous GJ uncoupling in croaker follicles, but a permissive role of COX products of AA during maturation is possible. A novel model of MIH-dependent ovulation is proposed in which 1). LOX and COX metabolites of AA are both required for ovulation, but at upstream and downstream sites of the pathway, respectively, relative to PKC, and 2). PKC is downstream of genomic activation.

A novel osteopontin-like protein is expressed in the trout ovary during ovulation

Using suppression subtraction hybridization between ovulatory and postovulatory trout ovaries, a down-regulated cDNA was obtained that presumably encodes a novel ovarian protein ('NOP'). NOP mRNA is present in the ovary during ovulation and down-regulated by 48 h postovulation, suggesting an important role for NOP during ovulation. Besides the ovary, NOP is also strongly expressed in the testis and at lower levels in the skin, gills, kidney and gastrointestinal tract. While the overall identity is not high, NOP shares several sequence similarities with mammalian and chicken osteopontins, including the percentage of aspartate, serine and alanine residues and the presence of a cell attachment motif.

Effects of polyunsaturated fatty acids and prostaglandins on oocyte maturation in a marine teleost, the European sea bass (Dicentrarchus labrax)

The effects of the polyunsaturated fatty acids (PUFAs), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and prostaglandins (PGs) on oocyte maturation were investigated in a marine teleost, the sea bass (Dicentrarchus labrax). Follicle-enclosed postvitellogenic, preovulatory oocytes were cultured in vitro and maturation was verified by assessing volume increase, lipid droplet coalescence, yolk clarification, and germinal vesicle migration and breakdown. Human chorionic gonadotropin was administered as the maturation-inducing gonadotropin (GTH) and was capable of inducing maturation in a time- and dose-dependent manner. Free AA induced maturation in a dose- and time-dependent manner and enhanced GTH-induced maturation, while EPA, DHA, and oleic acid were ineffective. Maturation induced by GTH was significantly suppressed by a phospholipase A(2) blocker, suggesting that mobilization of AA was involved in GTH-induced maturation. Moreover, EPA and DHA exhibited a significant, dose-dependent attenuation of GTH-induced maturation. Maturation induced by GTH was inhibited in the presence of a cyclooxygenase inhibitor, indomethacin, and this inhibition was reversed by addition of AA, PGE(2), or PGF(2alpha). PGE(2) and PGF(2alpha) alone were both effective stimulators of maturation, while PGE(1) and PGE(3) were ineffective. The effect of PUFAs on oocyte maturation in vitro were corroborated with studies in vivo. Oocytes were obtained from females fed a commercial, PUFA-enriched diet (RD) and maturational behavior was compared with oocytes from females fed a natural diet (ND) with a higher EPA content and n-3:n-6 ratio. Although no significant difference was observed in the rate of spontaneous oocyte maturation, a higher percentage of GTH-induced maturation and lower percentage of atresia were observed in RD oocytes. Moreover, while basal PGE production from oocytes from both groups was the same, RD oocytes produced significantly higher levels of PGE in the presence of hCG. The results from this study provide evidence for the participation of AA metabolism in GTH-induced oocyte maturation, and suggest that other PUFAs and PGs may play important roles in the induction of maturation in a marine teleost.

Cloning and characterization of prostaglandin endoperoxide synthase-1 and -2 from the brook trout ovary

Using a combination of reverse transcription-PCR and library screening, the cDNAs for prostaglandin endoperoxide synthase-1 (PGS-1) and 2 (PGS-2) were isolated from the brook trout ovary. The brook trout PGS-1 cDNA encodes for a 598 amino acid protein that is 69% identical to mammalian PGS-1. PGS-1 transcripts were observed in the ovary, spleen, gills, head kidney, trunk kidney, intestine, stomach, skin and heart. To our knowledge, this is the first characterization of a non-mammalian PGS-1 cDNA. The brook trout PGS-2 encodes for a 607 amino acid protein that is 69% identical to mammalian PGS-2 and was observed in the skin, gills, stomach and heart. PGS-2 transcripts were highly upregulated in the ovaries by the phorbol ester, phorbol-12-myristate-13-acetate, in combination with the calcium ionophore, A23187. However, PGS-2 was not observed in the ovary of brook trout undergoing natural oocyte maturation and ovulation.

A tumor necrosis factor decoy receptor homologue is up-regulated in the brook trout (Salvelinus fontinalis) ovary at the completion of ovulation

An up-regulated cDNA fragment was obtained from differential-display polymerase chain reaction of brook trout ovarian tissue stimulated by phorbol-12-myristate-13-acetate (PMA) and calcium ionophore A23187. Using this cDNA as a probe, a full-length cDNA of 2267 base pairs was obtained by screening a library of PMA/A23187-stimulated ovarian cDNA. The mRNA obtained presumably encodes for a 302-amino acid protein showing similarities with several members of the tumor necrosis factor (TNF) receptor superfamily. The protein contains several cysteine-rich domains characteristic of mammalian TNF receptor members and is most similar to human decoy receptor 3 and osteoprotegerin, two soluble decoy TNF receptors. Consequently, this TNF receptor homologue was tentatively named a trout decoy receptor (TDcR). On Northern blots of ovarian tissue, TDcR hybridized with a 2.2-kilobase transcript that was strongly up-regulated under phorbol ester stimulation. TDcR mRNA was localized in granulosa cells and was detected in the ovary during and after natural ovulation. Its expression was up-regulated at the end of ovulation and progressively down-regulated after 48 h postovulation. Among other trout tissues tested, the transcript was present only in the testis. To our knowledge this is the first description of a member of the TNF receptor family from a lower vertebrate and the first report of a decoy-like TNF receptor in the vertebrate ovary.

GTH I and GTH II secretion profiles during the reproductive cycle in female rainbow trout: relationship with pituitary responsiveness to GnRH-A stimulation

The recent purification of two gonadotropins, GTH I and GTH II, in teleost fish and the development of their specific radioimmunoassays using antibodies directed against their beta subunits have demonstrated that earlier assays for GTH II also measured GTH I. Most of the results on the gonadotropic control of reproduction in fish must thus be reinvestigated using specific assays for each gonadotropin. The present investigation examines changes in blood plasma levels of GTH I and GTH II during the annual reproductive cycle of rainbow trout in relation to the ability of gonadotropin-releasing hormone (GnRH) to stimulate in vivo GTH I and GTH II secretion, with focus on the periovulatory period. GTH I was detected from immature to postovulatory stages, with a significant increase at the onset of exogenous vitellogenesis, with GTH I levels rising from 7.83 +/- 3.37 to 16.87 +/- 4.52 ng/ml. GTH II remained very low until the end of the vitellogenesis. For both hormones, the most significant variations were measured during the periovulatory period. GTH II levels peaked on the day of maturation, but the increase was biphasic with a first peak arising 4 days prior to maturation. This evaluation of GTH II was preceded by a progressive and significant rise GTH I levels starting from 5.83 +/- 2.17 ng/ml 8 days before maturation and increasing to more than 10 ng/ml on the day of maturation. Thus, the GTH II maturation surge is not the only gonadotropic signal occurring before ovulation. The role of the preovulatory GTH I increase remains unknown. After ovulation the secretory profiles of the two hormones depended on the presence of absence of ovulated eggs in the body cavity. There was a major increase in GTH I levels starting 4 days after ovulation and egg stripping, reaching more than 25 ng/ml. Conversely, in these fish the GTH II levels gradually decreased. In the fish which kept their eggs in the body cavity the progress was reversed; 8 days after maturation, GTH II increased to levels similar to those measured prior to maturation; the presence of the eggs prevented an increase in GTH I. This seems to indicate that postovulatory regulation of GTH I and GTH II secretion might involve ovarian factors that act in an antagonistic fashion. The prevention of the increase in GTH I levels in the presence of eggs suggests that as long as eggs are present in the body cavity, the development of a new cycle of gametogenesis is not possible, since GTH I is the gonadotropin mainly involved in controlling this phenomena. GnRH cannot significantly stimulate GTH I secretion at any stage of gametogenesis, even when its levels increased after ovulation. Other factors antagonizing GnRH are involved. The well-known antagonistic effect of dopamine on the GnRH stimulated GTH II secretion is fish is not involved since the dopamine antagonist, pimozide, was ineffective in inducing a stimulatory action of GnRH on GTH I secretion. Although GnRH can stimulate GTH II secretion from mid-vitellogenesis, the response to GnRH was not correlated with GTH II in blood. These results suggest that GTH I and GTH II secretions are regulated by different mechanisms and different factors.

Characterization of a novel cDNA obtained through differential-display PCR of phorbol ester-stimulated ovarian tissue from the brook trout (Salvelinus fontinalis)

A cDNA (DRC1, differentially regulated clone 1) was obtained from differential-display polymerase chain reaction (PCR) of brook trout ovarian tissue stimulated with phorbol-12-myristate-13-acetate (PMA) and A23187. Using 5' RACE (rapid amplification of cDNA ends), two full-length clones were obtained from DRC1 that were 425 and 660 base pairs long and contained the same open reading frame. On Northern blots, DRC1 hybridized with two ovarian mRNAs of 0.45 and 0.7 kb that were significantly suppressed in the presence of PMA and/or A23187. The mRNAs were not observed in ovaries prior to the resumption of meiosis but were present during ovulation and 24 hr after ovulation. Of other trout tissues tested by Northern blotting, the expression of DRC1-related transcripts also was extremely high in the liver. Based on the full-length cDNAs obtained from RACE, these mRNAs presumably encode an 88-amino-acid protein (DRTP1, differentially regulated trout protein 1) that is homologous to a gene superfamily composed of snake venom neurotoxins, a CD59 complement regulatory protein, Ly-6 alloantigens, and a urokinase-type plasminogen activator receptor. To our knowledge, this is the first description of this type of cDNA from a nonmammalian source other than snake venom. In view of the sequence homology and tissue expression of DRTP1, a possible function of this protein may be to regulate the complement system in trout.

Effects of neurohypophyseal and adenohypophyseal hormones, steroids, eicosanoids, and extrafollicular tissue on ovulation in vitro of guppy (Poecilia reticulata) embryos

In the viviparous guppy, oocyte maturation is followed by intrafollicular fertilization and gestation. The fully developed embryos are ovulated at term just prior to parturition. Various agents were tested in vitro for their effects on ovulation of embryos in isolated follicles of the guppy. Arachidonic acid (10 and 100 microM), PGE2, PGF2 alpha, and 6-keto-PGF1 alpha (0.1 microgram/ml) induced ovulation, while PGE1, 15-keto-PGF2 alpha, leukotriene B4, 5-, 12-, and 15-HETEs (0.01 to 0.1 microgram/ml), cortisol, 11-deoxycortisol (25 and 250 ng/ml), estradiol-17 beta, testosterone, 17 alpha,20 beta-P, progesterone (5 and 50 ng/ml), isotocin, vasotocin (0.02 to 2 microgram/ml), and guppy pituitary extract (one and two glands per fish) did not. Extrafollicular (EF) ovarian tissue cocultured with isolated follicles induced ovulation, and the medium levels of PGE and PGF in such incubations were higher than those in the control. Indomethacin, the cyclooxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid and EF tissue, although it inhibited PGE and PGF production. NDGA, the lipoxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid or EF tissue. A combination of eicosanoids synthesized by follicles and EF tissue may be involved in the induction of ovulation. Dibutyryl cAMP inhibited ovulation induced by PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and EF tissue suggesting that a low level of cAMP may be associated with ovulation in the guppy.