Production of recombinant orange-spotted grouper (Epinephelus coioides) luteinizing hormone in insect cells by the baculovirus expression system and its biological effect

Identification and functional characterization of gonadotropin -releasing hormone in pompano (Trachinotus ovatus)

Gonadotropin-releasing hormone (GnRH) is an important neuropeptide in the reproductive system. Although GnRH analogues have been used to artificially spawn pompano (Trachinotus sp.), the native forms of GnRH have not been described in this species. In this study three GnRH subtypes [sea bream GnRH (sbGnRH), chicken GnRH-Ⅱ (cGnRH-Ⅱ) and salmon GnRH (sGnRH)] were identified in pompano (Trachinotus ovatus). cgnrh-Ⅱ and sgnrh were mainly expressed in the brain of male and female fish, showing a tissue-specific expression pattern, while sbgnrh was expressed at different transcriptional levels in all tested tissues. In vivo injection experiment showed that sbGnRH significantly increased fsh and lh genes expression in a dose-dependent manner, but a high concentration of sbGnRH could desensitize the expression of lh. High concentrations of cGnRH-Ⅱ and sGnRH could induce the expression of fsh and lh. In addition, the results of in vitro incubation experiments showed that the high concentration of sbGnRH peptide could induce the expression of fsh and lh, while cGnRH-Ⅱ and sGnRH peptides could only induce the expression of fsh. 17β-estradiol (E₂) and 17α-methyltestosterone (MT) significantly inhibited sbgnrh mRNA expression in a dose-dependent manner, but did not affect the expression of cgnrh-Ⅱ and sgnrh mRNA. sbGnRH is the main GnRH subtype in pompano. E₂ and MT can play a negative role in the regulation of sbgnrh. This study provides a theoretical basis for the reproductive endocrinology of pompano.

Direct and Indirect Effects of Sex Steroids on Gonadotrope Cell Plasticity in the Teleost Fish Pituitary

The pituitary gland controls many important physiological processes in vertebrates, including growth, homeostasis, and reproduction. As in mammals, the teleost pituitary exhibits a high degree of plasticity. This plasticity permits changes in hormone production and secretion necessary to meet the fluctuating demands over the life of an animal. Pituitary plasticity is achieved at both cellular and population levels. At the cellular level, hormone synthesis and release can be regulated via changes in cell composition to modulate both sensitivity and response to different signals. At the cell population level, the number of cells producing a given hormone can change due to proliferation, differentiation of progenitor cells, or transdifferentiation of specific cell types. Gonadotropes, which play an important role in the control of reproduction, have been intensively investigated during the last decades and found to display plasticity. To ensure appropriate endocrine function, gonadotropes rely on external and internal signals integrated at the brain level or by the gonadotropes themselves. One important group of internal signals is the sex steroids, produced mainly by the gonadal steroidogenic cells. Sex steroids have been shown to exert complex effects on the teleost pituitary, with differential effects depending on the species investigated, physiological status or sex of the animal, and dose or method of administration. This review summarizes current knowledge of the effects of sex steroids (androgens and estrogens) on gonadotrope cell plasticity in teleost anterior pituitary, discriminating direct from indirect effects.

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.

Identification, functional characterization, and estrogen regulation on gonadotropin-releasing hormone in the spotted scat, Scatophagus argus

Gonadotropin-releasing hormone (GnRH) is a key neuropeptide of the reproductive system. However, little is known about the role of GnRH in the spotted scat (Scatophagus argus). Here, three GnRH subtypes (cGnRH-II, sGnRH, and sbGnRH) were identified in the spotted scat. cGnRH-II and sGnRH were only expressed in the brains and gonads of both male and female fish, exhibiting a tissue-specific expression pattern, while sbGnRH was expressed at different transcription levels in all examined tissues. During ovarian maturation, hypothalamus-associated sbGnRH was upregulated, while the expression of sGnRH was variable and cGnRH-II first increased and then decreased. In vivo experiments showed that sbGnRH significantly promoted the expression of fsh and lh genes in a dose-dependent manner and exhibited a desensitization effect on lh expression at high concentrations. For sGnRH and cGnRH-II, only high concentrations could induce fsh and lh expression. Furthermore, treatment with highly concentrated sbGnRH peptide also induced fsh and lh expression, whereas the sGnRH and cGnRH-II peptides only induced fsh expression in vitro. 17β-Estradiol (E₂) significantly inhibited the expression of sbGnRH mRNA in a dose-dependent manner and did not impact sGnRH and cGnRH-II mRNA levels in vivo or in vitro. The inhibitory effect of E₂ on sbGnRH expression was attenuated by the estrogen receptor (ER) broad-spectrum antagonist (fulvestrant) and the ERα-specific antagonist (methyl-piperidinopyrazole), respectively, implying that the feedback regulation on sbGnRH is mediated via ERα. This study provides a theoretical basis for the reproductive endocrinology of the spotted scat by studying GnRH.

Development of a giant grouper Luteinizing Hormone (LH) Enzyme-Linked Immunosorbent Assay (ELISA) and its use towards understanding sexual development in grouper

A recombinant giant grouper Luteinizing Hormone (LH) consisting of tethered beta and alpha subunits was produced in a yeast expression system. The giant grouper LH β-subunit was also produced and administered to rabbits for antibody development. The recombinant LH and its antibody were used to develop an Enzyme Linked Immunosorbent Assay (ELISA). This ELISA enabled detection of plasma LH levels in groupers at a sensitivity between 391 pg/ml and 200 ng/ml. Different species of grouper were assayed with this ELISA in conjunction with gonadal histology and body condition data to identify links between circulating LH levels and sexual development. We found that circulating levels of LH decreased when oocytes began to degenerate, and sex-transition gonadal characteristics were apparent when LH levels decreased further. When circulating LH levels were related to body condition (body weight/ body length), transitioning-stage fish had relatively high body condition but low plasma LH levels. This observation was similar across multiple grouper species and indicates that plasma LH levels combined with body condition may be a marker for early male identification in the protogynous hermaphrodite groupers.

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.

New Insights Into the Role of Follicle-Stimulating Hormone in Sex Differentiation of the Protogynous Orange-Spotted Grouper, Epinephelus coioides

Follicle-stimulating hormone (FSH) signaling is considered to be essential for early gametogenesis in teleosts, but its functional roles during sex differentiation are largely unknown. In this study, we investigated the effects of long-term and short-term FSH injection on sex differentiation in the protogynous orange-spotted grouper (Epinephelus coioides). Long-term FSH treatment initially promoted the formation of ovaries but subsequently induced a male fate. The expression of female pathway genes was initially increased but then decreased, whereas the expression of male pathway genes was up-regulated only during long-term FSH treatment. The genes related to the synthesis of sex steroid hormones, as well as serum 11-ketotestosterone and estradiol, were also up-regulated during long-term FSH treatment. Short-term FSH treatment activated genes in the female pathway (especially cyp19a1a) at low doses but caused inhibition at high doses. Genes in the male pathway were up-regulated by high concentrations of FSH over the short term. Finally, we found that low, but not high, concentrations of FSH treatment activated cyp19a1a promoter activities in human embryonic kidney (HEK) 293 cells. Overall, our data suggested that FSH may induce ovarian differentiation or a change to a male sex fate in the protogynous orange-spotted grouper, and that these processes occurred in an FSH concentration-dependent manner.

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.

Biologically active recombinant carp LH as a spawning-inducing agent for carp

Currently, spawning is induced in carp species by carp pituitary extract (CPE) and a combination of synthetic agonist of GnRH combined with a dopamine antagonist. The main goal of this study was the production of recombinant gonadotropins (GtHs) on a large scale to serve as an alternative to currently used agents. We produced carp (c) recombinant (r) Lh as a single chain in the methylotrophic yeast Pichia pastoris Lha subunit was joined with Lhb subunit with a flexible linker of three glycine-serine repeats and six Histidines to form a mature protein, the β-subunit formed the N-terminal part and the α-subunit formed the C-terminal part. The ability of the rcLh to elicit biological response was tested by in vivo stimulation of estradiol (E2) and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) and by its in vivo potency to induce ovulation and spawning induction. rcLh tested in this work significantly enhanced both E2 and DHP secretion in a dose-dependent manner similar to the results obtained with CPE. E2 levels showed a moderate rise following the priming injection and a subsequent decrease during the rest of the trial. DHP levels were only increased after the resolving injection, approximately 5 h before spawning. At the highest dose of rcLh (350 µg/kg BW), the recombinant protein was more efficient than CPE in terms of both spawning success and fertilization rate. It is shown here that rcLh can elicit the secretion of DHP in vivo and actually trigger spawning. These novel findings introduce the potential of utilizing recombinant gonadotropins in aquaculture.

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.

Production of recombinant orange-spotted grouper (Epinephelus coioides) follicle-stimulating hormone (FSH) in single-chain form and dimer form by Pichia pastoris and their biological activities

FSH is a key regulator of steroidogenesis and gonadal growth in teleosts. However, function of FSH is elusive in grouper due to the lack of purified and native FSH. In the present study, we reported production of bioactive orange-spotted grouper (Epinephelus coioides) FSH in dimer form and single-chain form by Pichia pastoris. Dimer form of recombinant grouper FSH (rgFSHba) was accomplished by co-expressing mature FSHb-subunit and a-subunit genes. Fusion of mature FSHb-subunit and a-subunit genes together linking with a polypeptide (4×(Gly-Ser)-Gly-Thr) gene generated single-chain form of recombinant grouper FSH (rgFSHb-a). Recombinant grouper common α-subunit (rgCga) and FSHb-subunit (rgFSHb) were also separately produced. Recombinant proteins were verified by Western blot and mass spectrometry assays, and characterized by deglycosylation analysis. Deglycosylation assay suggested that glycosylation of recombinant FSH mainly occurred on common a-subunit. Bioactivities of recombinant proteins were initially evaluated by activating grouper FSH receptor, and further demonstrated by incubating ovarian fragments of adult grouper and intraperitoneal injection in juvenile female grouper. Two forms of recombinant FSH presented similar biological activities of activating FSH receptor and stimulating in vitro testosterone (T) and estradiol-17β (E2) secretion, though the dimer form functioned slightly weaker than the single-chain form. However, injections of rgFSHb-a or rgFSHba could significantly increase serum T and E2 levels, induce early ovarian development, reduce hypothalamic gnrh1 mRNA level, and increase hypothalamic cyp19a1b mRNA level. Data in this study suggested that recombinant gonadotropin could be produced in dimer form or single-chain form by P. pastoris, and FSH could regulate steroidogenesis and early ovarian development in juvenile grouper.

Isolation and characterization of cyp19a1a and cyp19a1b promoters in the protogynous hermaphrodite orange-spotted grouper (Epinephelus coioides)

Aromatase (CYP19A1) catalyzes the conversion of androgens to estrogens. In teleosts, duplicated copies of cyp19a1 genes, namely cyp19a1a and cyp19a1b, were identified, however, the transcriptional regulation of these two genes remains poorly understood. In the present study, the 5'-flanking regions of the orange-spotted grouper cyp19a1a (gcyp19a1a) and cyp19a1b (gcyp19a1b) genes were isolated and characterized. The proximal promoter regions of both genes were relatively conserved when compared to those of the other teleosts. Notably, a conserved FOXO transcriptional factor binding site was firstly reported in the proximal promoter of gcyp19a1a, and deletion of the region (-112 to -60) containing this site significantly decreased the promoter activities. The deletion of the region (-246 to -112) containing the two conserved FTZ-F1 sites also dramatically decreased the transcriptional activities of gcyp19a1a promoter, and both two FTZ-F1 sites were shown to be stimulatory cis-acting elements. A FTZ-F1 homologue isolated from ricefield eel (eFTZ-F1) up-regulated gcyp19a1a promoter activities possibly via the FTZ-F1 sites, however, a previously identified orange-spotted grouper FTZ-F1 homologue (gFTZ-F1) did not activate the transcription of gcyp19a1a promoter unexpectedly. As to gcyp19a1b promoter, all the deletion constructs did not show good promoter activities in either TM4 or U251-MG cells. Estradiol (100nM) up-regulated gcyp19a1b promoter activities by about 13- and 36-fold in TM4 and U251-MG cells, respectively, via the conserved ERE motif, but did not stimulate gcyp19a1a promoter activities. These results are helpful to further elucidate the regulatory mechanisms of cyp19a1a and cyp19a1b expression in the orange-spotted grouper as well as other teleosts.

Molecular cloning and functional analysis of the zebrafish luteinizing hormone beta subunit (LH<beta>) promoter

The luteinizing hormone (LH) plays important roles in vertebrate reproduction. In the present study, we cloned and characterized the zebrafish (Danio rerio) LH<beta> subunit gene structure and promoter region. Analysis of 3.0 kb (LH3.4K~5'UTR) of the LH<beta> subunit proximal promoter region displayed maximal promoter activity in a tilapia ovary cell line (TO2 cells) after treatment with gonadotropin-releasing hormone (GnRH). Transient expression experiments with a 5'-deletion revealed at least 10 regulatory regions in the zebrafish LH<beta> subunit gene. Compared to the molecular mechanisms of other vertebrates, GnRH treatment led to the activation of zebrafish LH<beta> subunit gene transcription in ovary cells. We demonstrated that LH<beta> subunit gene transcription increased with 6 h of treatment with GnRH but was repressed by protein kinase C, mitogen-activated protein kinase, and calcium in the TO2 cell line. To study promoter-specific expression, we constructed an LH<beta> subunit (LH3.4k~5'UTR) promoter region-driven green fluorescent protein (GFP), and the results indicated that LH<beta> promoter-driven GFP transcripts appeared in the pituitary gland. For the gene knockdown study, we targeted knockdown of the LH<beta> subunit gene by two antisense morpholino oligonucleotides that resulted in serious abnormalities and death during zebrafish embryogenesis. These results suggest that the LH plays important roles in reproduction and general embryonic development in zebrafish.

Production of recombinant Japanese eel gonadotropins by baculovirus in silkworm larvae

Recombinant follicle-stimulating hormone (reFSH) and luteinizing hormone (reLH) of the Japanese eel Anguilla japonica were produced by baculovirus in silkworm Bombyx mori larvae. cDNAs encoding Japanese eel gonadotropin subunits (i.e., FSH beta, LH beta, and common alpha) were introduced into the baculovirus, which was infected into silkworm larvae after propagation of the recombinant virus in B. mori culture cells. A 100ml solution of pooled hemolymph from silkworm larvae containing reFSH or reLH were obtained from approximately 250 infected larvae. Ten milliliters of hemolymph were applied to Ni-affinity choromatography, and 5.6 and 3.5mg of partially purified reFSH and reLH were obtained, respectively. Using Western blot analysis concentrations of reFSH and reLH in the original hemolymph was estimated to be 2.2 and 1.1mg/ml, respectively. Biological activities of reFSH and reLH were assessed in vitro and in vivo. Purified reFSH and reLH induced eel oocyte maturation in vitro, and administration of hemolymph containing reFSH or reLH induced spermatogenesis in vivo in sexually immature Japanese eel. The present study indicates that a baculovirus-silkworm system could produce large amounts of biologically active recombinant fish gonadotropins for use in investigations in reproductive endocrinology and/or aquaculture of fish.

Expression of recombinant zebrafish follicle-stimulating hormone (FSH) in methylotropic yeast Pichia pastoris

Pituitary gonadotropin follicle-stimulating hormone (FSH) was identified in fish two decades ago, but its functional importance in fish reproduction remains poorly defined, especially in non-salmonid species. This gap in our knowledge is partially due to the lack of the hormone in pure form in most of the species studied. We describe here the production of two different forms of biologically active recombinant zebrafish FSH (zfFSH and zfFSH(HIS)) using methylotrophic yeast, Pichia pastoris, as the bioreactor. One form (zfFSH) was produced as the molecule closer to the native form, with the two subunits (Cga and Fshb) expressed separately under different promoters. The other form (zfFSH(HIS)) was produced as a single polypeptide, with the cDNAs for the two subunits joined to form a fusion gene that contained a 6X His tag as part of the linker between the two subunits. The culture conditions were optimized for pH and incubation time for maximal production of the proteins. Using a zebrafish FSH receptor (Fshr)-based reporter gene assay, we tested and compared the biological activities of the two forms of recombinant zebrafish FSH. Our results provide useful information for the future production of recombinant gonadotropins in other fish species.

Molecular mechanisms underlying sex change in hermaphroditic groupers

Groupers are widely distributed throughout the tropical and subtropical waters of the world and are regarded as a favourite marine food fish. However, their large-scale aquaculture has been hindered by the rarity of natural males. Being protogynous hermaphrodites, groupers have been considered as study model for development and reproduction, especially for sex determination or sex differentiation, owing to the advantage that grouper gonad development undergoes transition from ovary to intersexual gonad and then to testis, and primordial germ cells and different stages of gametic cells during oogenesis and spermatogenesis are synchronously observed in the transitional gonads. Recently, a series of genes related to the reproduction regulation or sex differentiation have been identified in the groupers, mainly by researchers in China. One important finding was that the grouper gene, doublesex/male abnormal 3-related transcription factor 1 (DMRT1), is not only differentially expressed in gonads at different stages, but that it is also restricted to specific stages and specific cells of spermatogenesis. Grouper DMRT1 protein exists only in spermatogonia, primary spermatocytes and secondary spermatocytes, but not in the supporting Sertoli cells. Moreover, no introns were found in the grouper DMRT1, and no duplicated DMRT1 genes were detected. The finding implies that the intronless DMRT1 that is able to undergo rapid transcriptional turnover might be a significant gene for stimulating spermatogenesis in the protogynous hermaphroditic gonad. Additionally, we have found that grouper expression of sex-determining region Y-related high-mobility group-box gene 3 (SOX3) is a significant time point for enterable gametogenesis of primordial germ cells, because SOX3 is obviously expressed and localized in primordial germ cells. As SOX3 continues to express, the SOX3-positive primordial germ cells develop toward oogonia and then oocytes, whereas, when SOX3 expression is ceased, the SOX3-positive primordial germ cells develop toward spermatogonia. Therefore, we suggest that SOX3, as a transcription factor, might have more important roles in oogenesis than in spermatogenesis. Based on the findings, a hypothetic molecular mechanism underlying sex change is proposed in the hermaphroditic groupers, and some candidate genes related to the grouper sex change are also suggested for further research.

Powerful workhorses for antimicrobial peptide expression and characterization

Discovery of antimicrobial peptides (AMP) is to a large extent based on screening of fractions of natural samples in bacterial growth inhibition assays. However, the use of bacteria is not limited to screening for antimicrobial substances. In later steps, bioengineered "bugs" can be applied to both production and characterization of AMPs. Here we describe the idea to use genetically modified Escherichia coli strains for both these purposes. This approach allowed us to investigate SpStrongylocins 1 and 2 from the purple sea urchin Strongylocentrotus purpuratus only based on sequence information from a cDNA library and without previous direct isolation or chemical synthesis of these peptides. The recombinant peptides are proved active against all bacterial strains tested. An assay based on a recombinant E. coli sensor strain expressing insect luciferase, revealed that SpStrongylocins are not interfering with membrane integrity and are therefore likely to have intracellular targets.

Perspectives on fish gonadotropins and their receptors

Teleosts lack a hypophyseal portal system and hence neurohormones are carried by nerve fibers from the preoptic region to the pituitary. The various cell types in the teleost pituitary are organized in discrete domains. Fish possess two gonadotropins (GtH) similar to FSH and LH in other vertebrates; they are heterodimeric hormones that consist of a common alpha subunit non-covalently associated with a hormone-specific beta subunit. In recent years the availability of molecular cloning techniques allowed the isolation of the genes coding for the GtH subunits in 56 fish species representing at least 14 teleost orders. Advanced molecular engineering provides the technology to produce recombinant GtHs from isolated cDNAs. Various expression systems have been used for the production of recombinant proteins. Recombinant fish GtHs were produced for carp, seabream, channel and African catfish, goldfish, eel, tilapia, zebrafish, Manchurian trout and Orange-spotted grouper. The hypothalamus in fishes exerts its regulation on the release of the GtHs via several neurohormones such as GnRH, dopamine, GABA, PACAP, IGF-I, norepinephrine, NPY, kisspeptin, leptin and ghrelin. In addition, gonadal steroids and peptides exert their effects on the gonadotropins either directly or via the hypothalamus. All these are discussed in detail in this review. In mammals, the biological activities of FSH and LH are directed to different gonadal target cells through the cell-specific expression of the FSH receptor (FSHR) and LH receptor (LHR), respectively, and the interaction between each gonadotropin-receptor couple is highly selective. In contrast, the bioactivity of fish gonadotropins seems to be less specific as a result of promiscuous hormone-receptor interactions, while FSHR expression in Leydig cells explains the strong steroidogenic activity of FSH in certain fish species.

Regulation of preprosomatostatin 1 (PSS1) gene expression by 17beta-estradiol and identification of the PSS1 promoter region in orange-spotted grouper (Epinephelus coioides)

In the present paper the effects of 17beta-estradiol on the expression of the preprosomatostatin 1 (PSS1) in the orange-spotted grouper hypothalamus and ovary were investigated. Results from in vivo of intraperitoneal injection and in vitro static cultures showed that estradiol increased the mRNA expression of PSS1 gene in both hypothalamus and ovary. To investigate the molecular basis of the estrogen regulation on PSS1 gene expression, we cloned the upstream region of 848bp from the translation initiation codon of the grouper PSS1 gene. The TATA-box and putative transcription factor binding sites were identified using computer analysis. Transient transfections with promoter-luciferase reporter constructs together with hER expression vector were carried out in MCF-7 cell line. The results suggest that the region from -848 to -373bp, containing five putative ERE half sites, may contribute to the promoter activity induced by estradiol. These results represent the first demonstration at the molecular level of the regulation of PSS1 gene by 17beta-estradiol in fish.

Japanese eel follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh): production of biologically active recombinant Fsh and Lh by Drosophila S2 cells and their differential actions on the reproductive biology

Two gonadotropins (Gths), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), control gonadal steroidogenesis and gametogenesis in vertebrates, including teleost fish. Here, we report on the production of biologically active recombinant Fsh (rec-Fsh) and Lh (rec-Lh) in Japanese eel using Drosophila S2 cells. The three subunits composing Gths, i.e., glycoprotein hormone, alpha polypeptide (Cga), follicle-stimulating hormone, beta polypeptide (Fshb), and luteinizing hormone, beta polypeptide (Lhb), were at first independently produced and were proven to be glycosylated and secreted as the mature peptides. Each beta subunit, along with its Cga, was simultaneously coexpressed to produce heterodimeric rec-Fsh and rec-Lh that were subsequently highly purified. The biological activity of rec-Gths was demonstrated in various in vitro assays. The rec-Gths differentially activated their receptors, which resulted in an increase in 11-ketotestosterone (11KT) secretion, a differential alteration of gene expression of steroidogenic enzymes in immature testis, and the induction of the complete process of spermatogenesis in vitro. The data strongly suggest that Fsh and Lh differentially play important roles in the reproductive physiology of the Japanese eel. By contrast, these rec-Gths exhibited little activity in the gonad when administered in vivo. This difference between in vitro and in vivo bioactivity is probably due to the qualitative nature of glycosylation in S2 cells, which resulted in degradation of the recombinant protein in vivo. These differences in the carbohydrate moieties need to be elucidated and ameliorated.