Production of recombinant Japanese eel gonadotropins by baculovirus in silkworm larvae

Stable Production of a Tethered Recombinant Eel Luteinizing Hormone Analog with High Potency in CHO DG44 Cells

We produced a recombinant eel luteinizing hormone (rec-eel LH) analog with high potency in Chinese hamster ovary DG44 (CHO DG44) cells. The tethered eel LH mutant (LH-M), which had a linker comprising the equine chorionic gonadotropin (eLH/CG) β-subunit carboxyl-terminal peptide (CTP) region (amino acids 115 to 149), was inserted between the β-subunit and α-subunit of wild-type tethered eel LH (LH-wt). Monoclonal cells transfected with the tethered eel LH-wt and eel LH-M plasmids were isolated from five to nine clones of CHO DG44 cells, respectively. The secreted quantities abruptly increased on day 3, with peak levels of 5000-7500 ng/mL on day 9. The molecular weight of tethered rec-eel LH-wt was 32-36 kDa, while that of tethered rec-eel LH-M increased to approximately 38-44 kDa, indicating the detection of two bands. Treatment with the peptide N-glycanase F decreased the molecular weight by approximately 8 kDa. The oligosaccharides at the eCG β-subunit O-linked glycosylation sites were appropriately modified post-translation. The EC50 value and maximal responsiveness of eel LH-M increased by approximately 2.90- and 1.29-fold, respectively, indicating that the mutant exhibited more potent biological activity than eel LH-wt. Phosphorylated extracellular regulated kinase (pERK1/2) activation resulted in a sharp peak 5 min after agonist treatment, with a rapid decrease thereafter. These results indicate that the new tethered rec-eel LH analog had more potent activity in cAMP response than the tethered eel LH-wt in vitro. Taken together, this new eel LH analog can be produced in large quantities using a stable CHO DG44 cell system.

Production of Recombinant Single-Chain Eel Luteinizing Hormone and Follicle-Stimulating Hormone Analogs in Chinese Hamster Ovary Suspension Cell Culture

We produced rec-single chain eel luteinizing (rec-eel LH) and follicle-stimulating (rec- eel FSH) hormones displaying high biological activity in Chinese hamster ovary suspension (CHO-S) cells. We constructed several mutants, in which a linker, including an O-linked glycosylated carboxyl-terminal peptide (CTP) of an equine chorionic gonadotropin (eCG) β-subunit, was attached between the β- and α-subunit (LH-M and FSH-M) or in the N-terminal (C-LH and C-FSH) or C-terminal (LH-C and FSH-C) regions. The plasmids were transfected into CHO-S cells, and culture supernatants were collected. The secretion of mutants from the CHO-S cells was faster than that of eel LHβ/α-wt and FSHβ/α-wt proteins. The molecular weight of eel LHβ/α-wt and eel FSHβ/α-wt was 32-34 and 34-36 kDa, respectively, and that of LH-M and FSH-M was 40-43 and 42-45 kDa, respectively. Peptide-N-glycanase F-treatment markedly decreased the molecular weight by approximately 8-10 kDa. The EC50 value and the maximal responsiveness of the eel LH-M and eel FSH-M increased compared with the wild-type proteins. These results show that the CTP region plays a pivotal role in early secretion and signal transduction. We suggest that novel rec-eel LH and FSH proteins, exhibiting potent activity, could be produced in large quantities using a stable CHO cell system.

Recombinant Fsh and Lh therapy for spawning induction of previtellogenic and early spermatogenic arrested teleost, the flathead grey mullet (Mugil cephalus)

With the expansion and diversification of global aquaculture, efforts continue to develop new bio-technologies for assisted reproduction in species that present reproductive dysfunctions. Flathead grey mullet (Mugil cephalus) males held in intensive conditions in the Mediterranean region do not produce fluent milt and most females are arrested at previtellogenesis. The weekly injections of recombinant follicle stimulating hormone (rFsh) and luteinizing hormone (rLh) induced and completed vitellogenesis in treated females (n = 21), and treated males produced fluent sperm (n = 9). The application of a priming dose of 30 µg kg^-1 rLh and resolving dose of 40 mg kg^-1 Progesterone, or priming and resolving doses of 30 µg kg^-1 rLh, resulted in the induction of maturation, ovulation, and spontaneous spawns with a spawning success of the 85% (8 of 9 females) and 100% (n = 6), respectively. The eggs collected had 63 ± 21% fertilization with embryo development and 58 ± 23% hatching. In comparison, control individuals did not show advances in gonadal development and did not produce fluent sperm. The present results confirm the possibility of controlling oogenesis from previtellogenesis to the completion of maturation and fertilised tank spawning using exclusively rFsh and rLh in a teleost species.

C-terminal peptide (hCTP) of human chorionic gonadotropin enhances in vivo biological activity of recombinant Japanese eel follicle-stimulating hormone and luteinizing hormone produced in FreeStyle 293-F cell lines

Gonadotropins (Gths), follicle-stimulating hormone (Fsh), and luteinizing hormone (Lh) play central roles in the reproductive biology of vertebrates. In this study, recombinant single-chain Japanese eel Gths (rGth: rFsh and rLh), and recombinant chimeric Gths (rGth-hCTPs: rFsh-hCTP and rLh-hCTP; rGth-eCTPs: rFsh-eCTP and rLh-eCTP) with an extra O-glycosylation site (either a C-terminal peptide of human (hCTP) or equine (eCTP) chorionic gonadotropin), which are known to prolong the half-life of glycoprotein were produced in HEK293 cells and highly purified. Lectin blot analyses demonstrated that all these recombinant Gths contained N-glycans of the high mannose and complex types. In contrast, only rGth-hCTPs and rGth-eCTPs possessed highly sialylated O-linked oligosaccharides. Further analyses of glycans by liquid chromatography-mass spectrometry suggested that the species, amount, and degree of sialylation of N-glycans were comparable among recombinant Fshs and recombinant Lhs, while the amount of O-glycans with sialic acids in rGth-hCTPs was higher than that in the corresponding rGth-eCTPs. The serum levels of recombinant Gths in male eels significantly increased 12-24 h after a single injection of the Gths. The levels of rGth-hCTPs tended to be higher than those of the corresponding rGths and rGth-eCTPs throughout the experimental period, coinciding with the serum fluctuations of 11-ketotestosterone (11KT). The long-term treatment of male eels with these recombinant Gths also revealed the superiority of rGth-hCTPs in assisted reproduction; thus, the serum levels of 11KT and gonadosomatic indices in eels treated with rGth-hCTPs were higher than those in eels treated with the corresponding rGths and rGth-eCTPs. The induction of the entire process of spermatogenesis was only histologically observed in rGth-hCTPs-treated eels. These findings strongly suggest that hCTP enhances the in vivo biological activity of recombinant Japanese eel Gths due to the high abundance of O-linked glycans with sialylated antennae.

Generation and use of recombinant gonadotropins in fish

Understanding the differential roles of the pituitary gonadotropins Fsh and Lh in gonad maturation is crucial for a successful manipulation of the reproductive process in fish, and requires species-specific tools and appropriate active hormones. With the increasing availability of fish cDNAs coding for gonadotropin subunits, the production of recombinant hormones in heterologous systems has gradually substituted the approach of isolating native hormones. These recombinant hormones can be continually produced without depending on the fish as starting material and no cross-contamination with other pituitary glycoproteins is assured. Recombinant gonadotropins should be produced in eukaryotic cells, which have glycosylation capacity, but this post-translational modification varies greatly depending on the cell system, influencing hormone activity and stability. The production of recombinant gonadotropin beta-subunits to be used as antigens for antibody production has allowed the development of immunoassays for quantification of gonadotropins in some fish species. The administration in vivo of dimeric homologous recombinant gonadotropins has been used in basic studies and as a biotechnological approach to induce gametogenesis. In addition, gene-based therapies using somatic transfer of the gonadotropin genes have been tested as an alternative for hormone delivery in vivo. In summary, the use of homologous hormonal treatments can open new strategies in aquaculture to solve reproductive problems or develop out-of-season breeding programs.

Gonadal response of juvenile protogynous grouper (Epinephelus fuscoguttatus) to long-term recombinant follicle-stimulating hormone administration†

The role of follicle-stimulating hormone (FSH) in the gonadal development of protogynous hermaphroditic grouper (Epinephelus fuscoguttatus) was investigated. Recombinant giant grouper (E. lanceolatus) FSH (rggFSH) was produced in yeast. Its receptor-binding capacity and steroidogenic potency were confirmed in vitro. Weekly injections of rggFSH to juvenile tiger grouper for 8 weeks (100 μg/kg body weight, BW) resulted in significantly larger and more advanced oocytes (cortical alveolar stage vs primary growth stage in control). Sustained treatment with rggFSH (20 to 38 weeks at 200 μg/kg BW) resulted in significant reduction in gonad size, degeneration of oocytes, and proliferation of spermatogonial cells, indicative of female to male sex change. Gene expression analysis showed that, while initiating female to male sex change, the rggFSH significantly suppressed the steroidogenic genes cyp11b, cyp19a1a, and foxl2 which restrained the endogenous production of sex steroid hormones and thus prevented the differentiation of spermatogonial cells. Expression profile of sex markers dmrt1, amh, figla, and bmp15 suggests that the observed sex change was restricted at the initiation stage. Based on these results, we propose that the process of female to male sex change in the protogynous grouper is initiated by FSH, rather than sex steroids, and likely involves steroid-independent pathway. The cortical alveolar stage in oocyte development is the critical point after which FSH-induced sex change is possible in grouper.

Functional analysis of recombinant single-chain Japanese eel Fsh and Lh produced in FreeStyle 293-F cell lines: Binding specificities to their receptors and differential efficacy on testicular steroidogenesis

Pituitary gonadotropins, follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), play central roles in the control of gonadal development of vertebrates. In mammals, Fsh and Lh exclusively activate their respective cognate receptors: Fsh receptor (Fshr) in the Sertoli cell and Lh/choriogonadotropin receptor (Lhcgr) in the Leydig cell. In teleosts, the distinct functions of Fsh and Lh and information on cellular localization of their receptors are still poorly understood. Recently we established FreeStyle 293-F cell lines producing recombinant Japanese eel Fsh and Lh (reFsh and reLh), which form a single chain consisting of a common α-subunit and β-subunits. In this study, we conducted functional analyses of reFsh and reLh, focusing on the binding specificities to their receptors and effects on testicular steroidogenesis in vitro. Assays with gonadotropin receptors-expressing COS-7 cells indicated reFsh stimulated its cognate receptor, meanwhile reLh activated both receptors. Although results of in vitro incubations showed that reFsh and reLh induced testicular 11-ketotestosterone production in a dose and time-dependent manner by upregulating expression of steroidogenic enzymes, the effective doses of reLh were apparently lower and the effects of reLh emerged faster in comparison with reFsh. Results of quantitative real-time PCR using testicular cell fractions showed that fshr and lhcgr1 mRNA were detected both in Sertoli and Leydig cells. These analyses revealed that reFsh and reLh were biologically active and hence will be useful for future studies. Moreover, our data showed that both eel Fsh and Lh acted as steroidogenic hormones through their receptors in testicular somatic cells; however, Lh was more potent on androgen production, implying differential functions on spermatogenesis.

Development of specific enzyme-linked immunosorbent assay for yellowtail kingfish (Seriola lalandi) follicle stimulating hormone using recombinant gonadotropins

We developed a specific competitive enzyme-linked immunosorbent assay (ELISA) for yellowtail kingfish (Seriola lalandi) follicle stimulating hormone (FSH). We previously produced a full-length single chain recombinant yellowtail kingfish FSH using the Pichia pastoris expression system. We used the same method to produce the β subunit of the hormone, against which polyclonal antibodies were raised in rabbits. We first confirmed immunoreactivity of the polyclonal antibodies with the recombinant full length FSH and FSHβ as well as plasma and pituitary FSH of sexually immature and mature yellowtail kingfish by Western blot analysis. We then developed a precise and reproducible ELISA for yellowtail kingfish FSH and validated the assay in plasma and pituitary extracts. The intra- and inter-assay coefficients of variation was <2.2% and 10.2%, respectively. The sensitivity of the assay was 78 pg/ml. For further validation of the assay, we measured the plasma FSH in immature yellowtail kingfish treated with increasing doses (blank, 50, 100 and 150 µg/kg) of kisseptin2-10 peptide from a previous study. The dose response observed in treated females was not significant, however the increased plasma FSH levels coincided with the significantly higher estradiol levels we previously reported in the treated groups. We assessed the applicability of the assay in measuring circulating FSH in other species. We observed parallelism between the linearized FSH standard curve and displacement curves of serially diluted plasma from Atlantic bluefin tuna (Thunnus thynnus) and tilapia (Oreochromis niloticus). We also observed similar parallelism with full length recombinant giant grouper (Epinephelus lanceolatus) FSH. The ELISA we developed for yellowtail kingfish FSH will be useful in understanding the reproductive biology of the species as well as enhancing its aquaculture.

Site-specific roles of N-linked oligosaccharides in recombinant eel follicle-stimulating hormone for secretion and signal transduction

Eel follicle-stimulating hormone (eelFSH) is composed of a common α-subunit and a hormone specific β-subunit, both of which contain two N-linked carbohydrate residues. We characterized the biologically active single chains by fusing the α-subunit to the carboxyl terminal region of the eelFSH β-subunit. Expression vectors were constructed and the biological activity of the recombinant hormones (rec-hormones) was characterized using Chinese hamster ovary (CHO) K1 cells expressing the eelFSH receptor gene. Mutagenesis of the individual and double glycosylated sites was performed to determine the functions of the oligosaccharide chains on signal transduction. The absence of the Asn²² (eelFSHβΔ22/α) and Asn^5.22 (eelFSHβΔ5.22/α) N-linked oligosaccharide chain in the eelFSH β-subunit completely reduced the secretion level in the medium and cell lysate of CHO-K1 cells. The expression levels of eelFSHβ/α wild-type in CHO suspension (CHO-S) cells was approximately 4-fold higher in CHO-k1 cells. The molecular weight of rec-eelFSHβ/α wild-type by western blotting analysis was found to be 34 kDa. Mutants (β/αΔ56, β/αΔ79, and βΔ5/α) lacking single oligosaccharide sites showed molecular weights that were reduced by approximately 10%. The digestion of N-linked oligosaccharides using PNGaseF treatment showed that the molecular weights of all mutants were reduced to 27-kDa. The oligosaccharide chains in rec-eelFSHβ/α wild-type were modified to a molecular weight of approximately 7-10 kDa in CHO-K1 and CHO-S cells. Oligosaccharide site deletions at positions Asn⁵⁶ and Asn⁷⁹ on the α-subunit and Asn⁵ on the β-subunit were found to play an essential role in cAMP signal transduction through the eelFSH receptor. The EC₅₀ values of Asn⁵⁶ and Asn⁵ resulted in a significant decrease in potency to 64% and 53% of the wild type, respectively. Specifically, the removal of the carbohydrates at Asn⁷⁹ of the α-subunit (β/αΔ79) was drastically reduced to 53.8% of the wild-type levels in maximum response. These results have allowed for the identification of the site-specific roles of carbohydrate residues in eel FSH. Our data suggest that N-linked oligosaccharide chains play a pivotal role in biological activity through the eelFSH receptor as suggested in similar studies of other mammalian FSH hormones.

Involvement of Estrogen and Its Receptors in Morphological Changes in the Eyes of the Japanese Eel, Anguilla japonica, in the Process of Artificially-Induced Maturation

During the long migration from river habitats to the spawning ground, the Japanese eel undergoes sexual maturation. This spawning migration occurs concurrently with morphological changes, such as increases in eye size; however, the mechanisms by which sex steroids and their receptors influence these changes in peripheral tissues remain unclear. The aim of this study was to investigate changes in the eyes of female Japanese eels during sexual maturation, and our research focused on estrogen receptor (ER)α and ERβ transcripts. During ovarian development, the gonadosomatic index increased and yolk-laden oocytes developed rapidly. These changes occurred in conjunction with a steady increase in plasma levels of estradiol-17β (E₂). Concomitant increases in transcript levels of ERα and ERβ in eye, brain, pituitary, and ovary were also observed. Fluorescence in-situ hybridization analyses revealed that ERα and ERβ transcripts were present in the choriocapillary layer and photoreceptor layer of the eyes, and the analysis also revealed that their signals in these layers became stronger in mature females compared to those observed in immature females, suggesting that under the influence of gonadotropins, morphological changes in the eyes are regulated by E₂ through the activation of its receptors. In conclusion, E₂ plays a crucial role in physiological adaptations that occur in peripheral tissues during the spawning migration.

Medaka follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh): Developmental profiles of pituitary protein and gene expression levels

The two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) are of particular importance within the hypothalamic-pituitary-gonadal (HPG) axis of vertebrates. In the current study, we demonstrate the production and validation of Japanese medaka (Oryzias latipes) recombinant (md) gonadotropins Fshβ (mdFshβ), Lhβ (mdLhβ), Fshβα (mdFshβα), and Lhβα (mdLhβα) by Pichia pastoris, the generation of specific rabbit antibodies against their respective β subunits, and their use within the development and validation of competitive enzyme-linked immunosorbent assays (ELISAs) for quantification of medaka Fsh and Lh. mdFsh and mdLh were produced as single-chain polypeptides by linking the α subunit with mdFshβ or mdLhβ mature protein coding sequences to produce a "tethered" polypeptide with the β-chain at the N-terminal and the α-chain at the C-terminal. The specificity of the antibodies raised against mdFshβ and mdLhβ was determined by immunofluorescence (IF) for Fshβ and Lhβ on medaka pituitary tissue, while comparison with fluorescence in situ hybridization (FISH) for fshb and lhb mRNA was used for validation. Competitive ELISAs were developed using antibodies against mdFshβ or mdLhβ, and the tethered proteins mdFshβα or mdLhβα for standard curves. The standard curve for the Fsh ELISA ranged from 97.6 pg/ml to 50 ng/ml, and for the Lh ELISA from 12.21 pg/ml to 6.25 ng/ml. The sensitivity of the assays for Fsh and Lh was 44.7 and 70.8 pg/ml, respectively. A profile of pituitary protein levels of medaka Fsh and Lh comparing juveniles with adults showed significant increase of protein amount from juvenile group (body length from 12 mm to 16.5 mm) to adult group (body length from 21 mm to 26.5 mm) for both hormones in male medaka. Comparing these data to a developmental profile of pituitary mRNA expression of medaka fshb and lhb, the mRNA expression of lhb also increased during male maturation and a linear regression analysis revealed a significant increase of lhb expression with increased body length that proposes a linear model. However, fshb mRNA expression did not change significantly during male development and therefore was not correlated with body length. In summary, we have developed and validated homologous ELISA assays for medaka Fsh and Lh based on proteins produced in P. pastoris, assays that will be used to study the functions and regulations of Fsh and Lh in more detail.

Site specificity of eel luteinizing hormone N-linked oligosaccharides in signal transduction

Eel luteinizing hormone (eelLH) is composed of a common α-subunit and hormone specific β-subunit, both of which contain asparagine-linked carbohydrate residues, located at positions 56 and 79 on the α-subunit and position 10 on the β-subunit. The specific roles of the individual carbohydrate chains are poorly defined in eel. Thus, we characterized the biologically active single chains by fusing the α-subunit to the carboxyl terminal region of the eelLH β-subunit. Site-directed mutagenesis of the three N-linked glycosylation sites was performed to examine the function of individual glycosylation sites in secretion and signal transduction. The absence of the Asn⁷⁹N-linked sugar chain slightly reduced secretion in Chinese hamster ovary (CHO) cells. The expression of eelLHβ/α (wild-type) in CHO suspension cells was increased by approximately 2-fold higher than that of attached CHO cells. By western blotting analysis, the molecular weight of wild-type was found to be 32 kDa. Mutants (β/α△56, β/α△79, and β△10/α) of the oligosaccharide chain at a single site showed molecular weights that were reduced by approximately 10%. However, the double mutant (β/α△56.79) molecular weight was decreased by more than 20% compared to the wild-type. Enzymatic digestion of oligosaccharides using PNGaseF treatment showed that the molecular weights of all mutants, including wild-type, were reduced to 25 kDa. The results obtained in the absence of carbohydrates at Asn⁵⁶ of the α-subunit and at Asn¹⁰ of the β-subunit revealed their roles in signal transduction through the eelLH receptor. The EC₅₀ value of the cAMP response at Asn⁷⁹ of the α-subunit was increased by 5-fold, whereas the maximum response was dramatically reduced to 17.8% of wild-type levels. Specifically, removal of the carbohydrates at double mutant (β/α△56.79) is approximately 85% to wild-type levels in biopotency. These results revealed the site-specific roles of eelLH carbohydrate residues. Our data suggest that N-linked oligosaccharide chains play a pivotal role in biological activity through the eelLH receptor.

Characterization of carp gonadotropins: Structure, annual profile, and carp and zebrafish pituitary topographic organization

Two gonadotropins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), are important players in the hypothalamic-pituitary-gonadal axis of vertebrates. In the present work, we describe the construction of recombinant (r) common carp (Cyprinus carpio; c) FSH (rcFSH) and LH (rcLH) using the Pichia pastoris system, the generation of specific antibodies against their respective β subunits, and their use in the development and validation of specific ELISAs. We produced carp rLH and rFSH as single-chain polypeptides, wherein the GTH subunit α was joined with either cLHβ or cFSHβ mature protein-coding sequences to form a fusion gene that encodes a yoked polypeptide, in which the GTH β-subunit forms the N-terminal part and the α-subunit forms the C-terminal part. Competitive ELISAs were developed, using primary antibodies against rcLHβ or rcFSHβ, respectively, and rcLHβα or rcFSHβα for the standard curves. The standard curves for cLH paralleled those of pituitary extracts of the homologous fish and also those of other cyprinids species like the black carp (Mylopharyngodon piceus), goldfish (Carassius auratus), silver carp (Hypophthalmichthys molitrix), and grass carp (Ctenopharyngodon idella). We used the specific antibodies raised against cFSH and cLH to study the specific localization of the different GTH cells in the pituitary of carp and its taxonomic relative species - the zebrafish. Both FSH and LH cells are localized in the center of the proximal pars distalis enveloping both sides of the neurohypophysis. LH cells form a continuous population throughout the PPD, while FSH cells are more loosely distributed throughout the same area and form small aggregations. Marked annual changes were encountered in gonadosomatic index (GSI), follicle diameter, mRNA levels and protein levels of FSH and LH. From September to November, all fish had low GSI, and the ovary contained previtellogenic follicles. From December, the GSI level increased and remained high until March, the follicular diameter reached its maximum in January, where the ovary contained large fully grown follicles. Thereafter, spawning occurred through March and April and ended in May, and GSI level and follicle diameter increased again; and the ovary contained mid-vitellogenic follicles. LH pituitary content and mRNA levels were low at pre- and early vitellogenesis, increasing gradually during this process to reach a peak of LH mRNA levels in mid vitellogenic ovary and a peak of LH content in fully grown ovarian follicles. However, no significant change occurred in FSH pituitary content and mRNA levels in vitellogenic fish and in fish during final maturation stages. A dramatic difference was found in the total content of each gonadotropin in the pituitary, with higher LH than FSH. Moreover, follicle diameter was positively and significantly correlated with LH pituitary content and its transcript levels - but not with the pituitary content or mRNA levels of FSH. Taken together, these results indicate that in carp, LH alone is sufficient to regulate both vitellogenesis and final oocyte maturation while FSH may have another, yet undefined role.

Electrotransfer of single-chain LH gene into skeletal muscle induces early ovarian development of orange-spotted grouper (Epinephelus coioides)

Luteinizing hormone (LH) plays important roles in regulating steroidogenesis and reproductive development of vertebrates. In the present paper, we study function of LH on early ovarian development of orange-spotted grouper by electrotransfer of single-chain LH gene into skeletal muscle for the first time. Short-term and long-term injection experiments were performed in this work, respectively. For short-term injection experiments, fish received one electrotransfer with the plasmid in skeletal muscle, then blood and muscle around the injected area were sampled 1, 3, 5 and 7 days after the injection, mRNA expression levels of LH gene relative to 18S were determined by quantitative real-time PCR (RT-PCR) assays and serum 17β-estradiol (E2) levels were quantified by ELISA method. The results showed that levels of mRNA of LH gene in muscle and serum E2 level increased from 1 day to 7 days after the injection. For long-term injection experiments, fish received electrotransfer with the plasmid 4 times at weekly intervals in skeletal muscle. 48 h after the last injection, blood, gonad and hypothalamus samples were collected. Transcripts of cyp19a1a, cyp19a1b and gnrh1 genes and levels of serum E2 were separately analyzed by RT-PCR assays and ELISA method, and ovarian tissues were made of paraffin sections and stained by hematoxylin-eosin by method and observed by optical microscopy. The results suggested that long-term injection of LH gene into muscle upregulated transcripts of cyp19a1a and cyp19a1b and downregulated that of gnrh1, and stimulated E2 production and early-stage oogenesis. Moreover, statistical data showed that 9 of 10 ovaries of injected fish with LH gene began to develop after the long-term experiments. These data suggest that single-chain LH gene introduced into skeletal muscle via electrotransfer can be expressed and induce the early ovarian development of juvenile orange-spotted grouper. This work contributes to solve reproductive dysfunctions associated with low hormone levels of teleosts, further it may represent the demonstration at regulation of LH on early ovarian development of orange-spotted grouper to a certain extent.

Signal Transduction of Eel Luteinizing Hormone Receptor (eelLHR) and Follicle Stimulating Hormone Receptor (eelFSHR) by Recombinant Equine Chorionic Gonadotropin (rec-eCG) and Native eCG

Previous studies showed that recombinant equine chorionic gonadotropin (rec-eCGβ/α) exhibits both follicle-stimulating hormone (FSH) and luteinizing hormone (LH)-like activities in rat LHR- and FSHR-expressing cells. In this study, we analyzed signal transduction by eelFSHR and eelLHR upon stimulation with rec-eCGβ/α and native eCG. The cyclic adenosine monophosphate (cAMP) stimulation in CHO-K1 cells expressing eelLHR was determined upon exposure to different doses (0-1,450 ng/mL) of rec-eCGβ/α and native eCG. The EC₅₀ values of rec-eCGβ/α and native eCG were 172.4 and 786.6 ng/mL, respectively. The activity of rec-eCGβ/α was higher than that of native eCG. However, signal transduction in the CHO PathHunter Parental cells expressing eelFSHR was not enhanced by stimulation with both agonist rec-eCGβ/α and native eCG. We concluded that rec-eCGβ/α and native eCG were completely active in cells expressing eelLHR, similar to the activity in the mammalian cells expressing LHRs. However, rec-eCGβ/α and native eCG did not invoke any signaling response in the cells expressing eelFSHR. These results suggest that eCG has a potent activity in cells expressing eelLHR. Thus, we also suggest that rec-eCGβ/α can induce eel maturation by administering gonadotropic reagents (LH), such as salmon pituitary extract.

Toward developing recombinant gonadotropin-based hormone therapies for increasing fertility in the flatfish Senegalese sole

Captive flatfishes, such as the Senegalese sole, typically produce very low volumes of sperm. This situation is particularly prevalent in the first generation (F1) of reared sole males, which limits the development of artificial fertilization methods and the implementation of selective breeding programs. In this study, we investigated whether combined treatments with homologous recombinant follicle-stimulating (rFsh) and luteinizing (rLh) hormones, produced in a mammalian host system, could stimulate spermatogenesis and enhance sperm production in Senegalese sole F1 males. In an initial autumn/winter experiment, weekly intramuscular injections with increasing doses of rFsh over 9 weeks resulted in the stimulation of gonad weight, androgen release, germ cell proliferation and entry into meiosis, and the expression of different spermatogenesis-related genes, whereas a subsequent single rLh injection potentiated spermatozoa differentiation. In a second late winter/spring trial corresponding to the sole’s natural prespawning and spawning periods, we tested the effect of repeated rLh injections on the amount and quality of sperm produced by males previously treated with rFsh for 4, 6, 8 or 10 weeks. These latter results showed that the combination of rFsh and rLh treatments could increase sperm production up to 7 times, and slightly improve the motility of the spermatozoa, although a high variability in the response was found. However, sustained administration of rFsh during spawning markedly diminished Leydig cell survival and the steroidogenic potential of the testis. These data suggest that in vivo application of rFsh and rLh is effective at stimulating spermatogenesis and sperm production in Senegalese sole F1 males, setting the basis for the future establishment of recombinant gonadotropin-based hormone therapies to ameliorate reproductive dysfunctions of this species.

In-vitro and in-vivo biological activity of recombinant yellowtail kingfish (Seriola lalandi) follicle stimulating hormone

Biologically active recombinant yellowtail kingfish follicle stimulating hormone (rytkFsh) was produced in yeast Pichia pastoris and its biological activity was demonstrated by both in-vitro and in-vivo bioassays. Incubation of ovarian and testicular fragments with the recombinant hormone stimulated E₂ and 11-KT secretion, respectively. In-vivo trial in immature female YTK resulted in a significant increase of plasma E₂ levels and development of oocytes. In males at the early stages of puberty, advancement of spermatogenesis was observed, however plasma 11-KT levels were reduced when administered with rytkFsh.

Gonadotropins in the Russian Sturgeon: Their Role in Steroid Secretion and the Effect of Hormonal Treatment on Their Secretion

In the reproduction process of male and female fish, pituitary derived gonadotropins (GTHs) play a key role. To be able to specifically investigate certain functions of Luteinizing (LH) and Follicle stimulating hormone (FSH) in Russian sturgeon (Acipenser gueldenstaedtii; st), we produced recombinant variants of the hormones using the yeast Pichia pastoris as a protein production system. We accomplished to create in vitro biologically active heterodimeric glycoproteins consisting of two associated α- and β-subunits in sufficient quantities. Three dimensional modelling of both GTHs was conducted in order to study the differences between the two GTHs. Antibodies were produced against the unique β-subunit of each of the GTHs, in order to be used for immunohistochemical analysis and to develop an ELISA for blood and pituitary hormone quantification. This detection technique revealed the specific localization of the LH and FSH cells in the sturgeon pituitary and pointed out that both cell types are present in substantially higher numbers in mature males and females, compared to immature fish. With the newly attained option to prevent cross-contamination when investigating on the effects of GTH administration, we compared the steroidogeneic response (estradiol and 11-Keto testosterone (11-KT) in female and males, respectively) of recombinant stLH, stFSH, and carp pituitary extract in male and female sturgeon gonads at different developmental stages. Finally, we injected commercially available gonadotropin releasing hormones analog (GnRH) to mature females, and found a moderate effect on the development of ovarian follicles. Application of only testosterone (T) resulted in a significant increase in circulating levels of 11-KT whereas the combination of GnRH + T did not affect steroid levels at all. The response pattern for estradiol demonstrated a similar situation. FSH levels showed significant increases when GnRH + T was administered, while no changes were present in LH levels.

Production and characterization of monoclonal antibodies against recombinant tethered follicle-stimulating hormone from Japanese eel Anguilla japonica

We prepared monoclonal antibodies (mAbs) against a recombinant tethered follicle-stimulating hormone (rec-FSH) from Japanese eel Anguilla japonica that was produced in Escherichia coli. Positive hybridomas (clones eFA-C5, eFA-C10, eFA-C11, eFA-C12, eFA-C13, and eFB-C14) were selected by using the eel FSH antigen in ELISA, and anti-eel FSH mAbs were purified from culture supernatants by performing affinity chromatography. Three of the 6mAbs were characterized and their isotypes were identified as IgG2b (eFA-C5 and eFA-C11) and IgG1 (eFB-C14). In western blotting assays, the mAbs recognized the antigen as a 24.3-kDa band, and further detected bands of 34 and 32kDa in the supernatants of CHO cells transfected with cDNA encoding tethered eel FSHβ/α and LHβ/α, respectively. PNase F-mediated deglycosylation of the recombinant proteins resulted in a drastic reduction in their molecular weight, to 7-9kDa. The mAbs eFA-C5 and eFA-C11 recognized the eel FSHα-subunit that is commonly encoded among glycoprotein hormones, whereas eFB-C14 recognized the eel FSHβ-subunit, and immunohistochemical analysis revealed that the staining by these mAbs was specifically localized in the eel pituitary. We also established an ELISA system for detecting rec-tethered FSHβ/α and LHβ/α produced from CHO cell lines. Measurement of biological activities in vitro revealed that only weak activity of rec-FSHβ/α was detected. The activity of rec-LHβ/α was found to be increased in a dose-dependent manner for eel oocyte maturation.

Development of a flatfish-specific enzyme-linked immunosorbent assay for Fsh using a recombinant chimeric gonadotropin

In flatfishes with asynchronous and semicystic spermatogenesis, such as the Senegalese sole (Solea senegalensis), the specific roles of the pituitary gonadotropins during germ cell development, particularly of the follicle-stimulating hormone (Fsh), are still largely unknown in part due to the lack of homologous immunoassays for this hormone. In this study, an enzyme-linked immunosorbent assay (ELISA) for Senegalese sole Fsh was developed by generating a rabbit antiserum against a recombinant chimeric single-chain Fsh molecule (rFsh-C) produced by the yeast Pichia pastoris. The rFsh-C N- and C-termini were formed by the mature sole Fsh β subunit (Fshβ) and the chicken glycoprotein hormone common α subunit (CGA), respectively. Depletion of the antiserum to remove anti-CGA antibodies further enriched the sole Fshβ-specific antibodies, which were used to develop the ELISA using the rFsh-C for the standard curve. The sensitivity of the assay was 10 and 50 pg/ml for Fsh measurement in plasma and pituitary, respectively, and the cross-reactivity with a homologous recombinant single-chain luteinizing hormone was 1%. The standard curve for rFsh-C paralleled those of serially diluted plasma and pituitary extracts of other flatfishes, such as the Atlantic halibut, common sole and turbot. In Senegalese sole males, the highest plasma Fsh levels were found during early spermatogenesis but declined during enhanced spermiation, as found in teleosts with cystic spermatogenesis. In pubertal males, however, the circulating Fsh levels were as high as in adult spermiating fish, but interestingly the Fsh receptor in the developing testis containing only spermatogonia was expressed in Leydig cells but not in the primordial Sertoli cells. These results indicate that a recombinant chimeric Fsh can be used to generate specific antibodies against the Fshβ subunit and to develop a highly sensitive ELISA for Fsh measurements in diverse flatfishes.

Production and characterization of recombinant Manchurian trout thyrotropin

Thyrotropin (thyroid-stimulating hormone, TSH), a heterodimeric glycoprotein hormone produced in the pituitary, stimulates the thyroid gland and release of thyroid hormones. In contrast to a well-known efficacy of recombinant mammalian TSHs, there is no report about the production of teleost recombinant TSH and its biological activity. In this study, we report the production of a single-chain recombinant TSH (mtTSH) of Manchurian trout (Brachymystax lenok), by baculovirus in silkworm (Bombyx mori) larvae. The mtTSH was produced in silkworm larvae and characterized as a form of N-linked glycosylation. The cAMP signaling system in transiently transfected COS-7 cells revealed that the mtTSH was recognized by their cognate receptors, salmon TSHα and TSHβ receptors, but not LH receptor. The thyrotropic potency of the mtTSH was examined by rainbow trout basibranchial tissues containing thyroid follicles. The height of follicle epithelial cells was significantly increased by treatments of mtTSH in vivo and in vitro. In conclusion, the present study suggests that the mtTSH produced by baculovirus-silkworm larvae is a biologically active recombinant TSH.

Experimental and computational study of inter- and intra- species specificity of gonadotropins for various gonadotropin receptors

The gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and their receptors play critical roles in vertebrate reproduction. In order to study intra- and interspecies ligand promiscuity of gonadotropins, COS-7 cells were transiently transfected with one of the gonadotropin receptor genes, FSHR or LHR, and tested for activation by gonadotropins from representative fish orders: Aquilliformes (eel; e), Salmoniformes (trout; tr), and Perciformes (tilapia; ta), and of mammalian origin: porcine (p), bovine (b) and human (h). The study reveals complex relations between the gonadotropin hormones and their receptors. Each gonadotropin activated its own cognate receptor. However, taLHR was also activated by hCG and eLHR was activated by hFSH, hCG, and trFSH. For FSHR, the only cross-reactivity detected was for hFSHR, which was activated by pFSH and bFSH. These findings are of great interest and applicability in the context of activation of various GTHRs by their ligands and by ligands from other vertebrates. Analysis of the three-dimensional models of the structures highlights the importance of residues outside of the currently established hormone-receptor interface region. In addition, the interface residues in taFSHR and the effect of exon duplication, which causes an insert in the LRR domain, are suggested to affect the interaction and binding of taFSH.

Follicle-stimulating hormone and luteinizing hormone mediate the androgenic pathway in Leydig cells of an evolutionary advanced teleost

The endocrine pathways controlling vertebrate spermatogenesis are well established in mammals where the pituitary gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) exclusively activate the FSH receptor (FSHR) in Sertoli cells and the LH/choriogonadotropin receptor (LHCGR) in Leydig cells, respectively. In some teleosts, however, it has been shown that Lh can cross-activate the Fshra ortholog, and that Leydig cells coexpress the Lhcgrba and Fshra paralogs, thus mediating the androgenic function of Fsh in the testis. Here, we investigated whether these proposed mechanisms are conserved in an evolutionary advanced pleuronectiform teleost, the Senegalese sole (Solea senegalensis). Transactivation assays using sole Fshra- and Lhcgrba-expressing cells and homologous single-chain recombinant gonadotropins (rFsh and rLh) showed that rFsh exclusively activated Fshra, whereas rLh stimulated both Lhcgrba and Fshra. The latter cross-activation of Fshra by rLh occurred with an EC(50) 4-fold higher than for rFsh. Both recombinant gonadotropins elicited a significant androgen release response in vitro and in vivo, which was blocked by protein kinase A (PKA) and 3beta-hydroxysteroid dehydrogenase inhibitors, suggesting that activation of steroidogenesis through the cAMP/PKA pathway is the major route for both Lh- and Fsh-stimulated androgen secretion. Combined in situ hybridization and immunocytochemistry using cell-specific molecular markers and antibodies specifically raised against sole Fshra and Lhcgrba demonstrated that both receptors are expressed in Leydig cells, whereas Sertoli cells only express Fshra. These data suggest that Fsh-mediated androgen production through the activation of cognate receptors in Leydig cells is a conserved pathway in Senegalese sole.

Steroidogenic response of carp ovaries to piscine FSH and LH depends on the reproductive phase

The gonadotropins (GTHs) follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are the key regulators of reproduction. We determined the competence of heterologous recombinant GTHs at eliciting steroid secretion from carp ovaries at different reproductive stages. We collected carp ovaries at: early, mid and end vitellogenesis, when most of the oocytes still contained a germinal vesicle (GV) at a central stage, and mature ovaries with a migrating GV. Plasma estradiol (E2) levels at early vitellogenesis were high and decreased thereafter. Basal secretion levels of E2 increased with oocyte diameter and GSI value, whereas 17α,20β-dihydroxy-4-pregnen-3-one (DHP) was detected only in females with mature follicles. Carp ovary fragments were exposed to recombinant fish GTHs belonging to different teleost orders: Japanese eel (Anguilla japonica, Anguilliformes), Manchurian trout (Brachymystax lenok, Salmoniformes), and Nile tilapia (Oreochromis niloticus); to mammalian GTHs (pFSH and hCG), or to carp and tilapia pituitary extract (CPE and TPE, respectively). All of the recombinant GTHs tested stimulated steroid secretion. However, the steroid secretion differed according to the type of GTH and the developmental state of the ovary. CPE increased the secretion of both E2 and DHP at almost all stages of ovarian maturity. In mature ovarian fragments, DHP secretion was higher in response to recombinant LHs (eel and tilapia) than to recombinant FSH. Early- and mid-vitellogenic ovaries showed no secretion of DHP and high secretion of E2 in response to all recombinant GTHs tested. This is in line with the hypothesis that LH regulates the final stages of maturation, when the involvement of FSH is marginal. These results may contribute to understanding the mechanisms that determine differential activation of steroid secretion and specificity in fish.