Quantification of gonadotropin subunits GPalpha, FSHbeta, and LHbeta mRNA expression from Atlantic cod (Gadus morhua) throughout a reproductive cycle

Gonadotropins and Sex Steroid Hormones in Captive-Reared Small Yellow Croaker (Larimichthys polyactis) and Their Role in Female Reproductive Dysfunction

The seed production of small yellow croaker (SYC) is constrained by reproductive dysfunction in captive-reared females. Reproductive dysfunction is closely linked to endocrine reproductive mechanisms. To better understand the reproductive dysfunction in captive broodstock, functional characterization of gonadotropins (GtHs: follicle stimulating hormone β subunit, fshβ; luteinizing hormone β subunit, lhβ; and glycoprotein α subunit, gpα) and sex steroids (17β-estradiol, E2; testosterone, T; progesterone; P) was performed using qRT-PCR, ELISA, in vivo, and in-vitro assay. The pituitary GtHs and gonadal steroids levels were significantly higher in ripen fish of both sexes. However, changes in lhβ and E2 levels in females were not significant in the developing and ripen stages. Furthermore, GtHs and steroids levels were lower in females compared to males throughout the reproductive cycle. In vivo administration of gonadotropin releasing hormone analogue (GnRHa) significantly increased the expression of GtHs in both dose- and time-related manners. The lower and higher doses of GnRHa led to successful spawning in male and female SYC, respectively. Sex steroids in vitro significantly inhibited the expression of lhβ in female SYC. Overall, GtHs were shown to play a vital role in final gonadal maturation, while steroids promoted negative feedback in the regulation of pituitary GtHs. Lower levels of GtHs and steroids might be key components in the reproductive dysfunction of captive-reared female SYC.

Transcription pattern of reproduction relevant genes along the brain-pituitary-gonad axis of female, male and intersex thicklip grey mullets, Chelon labrosus, from a polluted harbor

The reproductive cycle of teleost fishes is regulated by the brain-pituitary-gonad (BPG) axis. The transcription profile of genes involved in the reproduction signalling in the BPG-axis differs in females and males during the gametogenic cycle. Impacts of endocrine disrupting chemicals on these signalling pathways in fish are known, but the participation of the BPG-axis in the development of the intersex condition is not well understood. Intersex thicklip grey mullets (Chelon labrosus) have been identified in several estuaries from the SE Bay of Biscay, revealing the presence of feminizing contaminants in the area. In previous studies, transcription patterns of genes related with steroidogenesis and gamete growth have been shown to differ among female, male and intersex mullets. However, many components of the reproduction control have not been studied yet. The aim of this study was to assess the transcription levels of target BPG-axis genes in female, male and intersex mullets captured in the polluted harbour of Pasaia, during their gametogenic cycle. After histologically examining the gonads, the transcription levels of previously sequenced target genes were measured by qPCR: kiss2, gpr54 and gnrh1 in brain, fshβ and lhβ in pituitary and fshr and lhr in gonads. In both females and males, brain genes were most transcribed in early gametogenesis, proving their relevance in the onset of both oogenesis and spermatogenesis. Pituitary gonadotropins in females showed upregulation as oogenesis progressed, reaching the highest transcription levels at vitellogenic stage, while in males transcript levels were constant during spermatogenesis. Transcription levels of gonadotropin receptors showed different patterns in ovaries and testes, suggesting differing function in relation to gametogenesis and maturation. Intersex mullets showed transcription levels of brain target genes similar to those observed in females at cortical alveoli stage and to those in mid spermatogenic males. In intersex testes the transcription pattern of gonadotropin receptor fshr was downregulated in comparison to non-intersex testes.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Molecular cloning and characterization of pirarucu (Arapaima gigas) follicle-stimulating hormone and luteinizing hormone β-subunit cDNAs

The common gonadotrophic hormone α-subunit (GTHα) has been previously isolated by our research group from A. gigas pituitaries; in the present work the cDNA sequences encoding FSHβ and LHβ subunits have also been isolated from the same species of fish. The FSH β-subunit consists of 126 amino acids with a putative 18 amino acid signal peptide and a 108 amino acid mature peptide, while the LH β-subunit consists of 141 amino acids with a putative 24 amino acid amino acid signal peptide and a 117 amino acid mature peptide. The highest identity, based on the amino acid sequences, was found with the order of Anguilliformes (61%) for FSHβ and of Cypriniformes (76%) for LHβ, followed by Siluriformes, 53% for FSHβ and 75% for LHβ. Interestingly, the identity with the corresponding human amino acid sequences was still remarkable: 45.1% for FSHβ and 51.4% for LHβ. Three dimensional models of ag-FSH and ag-LH, generated by using the crystal structures of h-FSH and h-LH as the respective templates and carried out via comparative modeling and molecular dynamics simulations, suggested the presence of the so-called "seat-belt", favored by a disulfide bond formed between the 3rd and 12th cysteine in both β-subunits. The sequences found will be used for the biotechnological synthesis of A. gigas gonadotrophic hormones (ag-FSH and ag-LH). In a first approach, to ascertain that the cloned transcripts allow the expression of the heterodimeric hormones, ag-FSH has been synthesized in human embryonic kidney 293 (HEK293) cells, preliminarily purified and characterized.

Sex steroids differentially regulate fshb, lhb and gnrhr expression in Atlantic cod (Gadus morhua)

Depending on the stage of gonad maturation, as well as other factors, gonadal steroids can exert either a positive or negative feedback at the brain and pituitary level. While this has been demonstrated in many teleost species, little is known about the nature of steroid feedback in Gadiform fish. Using an optimized in vitro model system of the Atlantic cod pituitary, the present study investigated the potential effects of two physiologically relevant doses of estradiol, testosterone (TS) or dihydrotestosterone (DHTS) on cell viability and gene expression of gonadotropin subunits (fshb/lhb) and two suggested reproduction-relevant gonadotropin-releasing hormone receptors (gnrhr1b/gnrhr2a) during three stages of sexual maturity. In general, all steroids stimulated cell viability in terms of metabolic activity and membrane integrity. Furthermore, all steroids affected fshb expression, with the effect depending on both the specific steroid, dose and maturity status. Conversely, only DHTS exposure affected lhb levels, and this occurred only during the spawning season. Using single-cell qPCR, co-transcription of gnrhr1b and gnrhr2a was confirmed to both fshb- and lhb- expressing gonadotropes, with gnrhr2a being the most prominently expressed isoform. While steroid exposure had no effect on gnrhr1b expression, all steroids affected gnrhr2a transcript levels in at least one maturity stage. These and previous results from our group point to Gnrhr2a as the main modulator of gonadotropin regulation in cod and that regulation of its gene expression level might function as a direct mechanism for steroid feedback at the pituitary level.

Gonadotropin characterization, localization and expression in the European hake (Merluccius merluccius)

In vertebrates, the regulation of gametogenesis is under the control of gonadotropins (Gth), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). In fish, the physiological role of Gths is not fully understood, especially in species with asynchronous ovarian development. To elucidate the role of Gths in species with asynchronous ovary, we studied European hake (Merluccius merluccius) during the reproductive season. For this aim, we first cloned and sequenced both hormones. Then, we characterized their amino acid sequence and performed phylogenetic analyses to verify the relationship to their orthologues in other species. In addition, the quantification of gene expression during their natural reproductive season was analyzed in wild-caught female hake. Our results revealed that fshb peaked during the vitellogenic phase, remaining high until spawning. This is in contrast to the situation in species with synchronous ovary. lhb, on the other hand, peaked during maturation as it is also common in species with synchronous ovarian development. Finally, combining double-labeling fluorescent in situ hybridization (FISH) for Gth mRNAs with immunofluorescence for Lh protein, we evidenced the specific expression of fshb and lhb in different cells within the proximal pars distalis (PPD) of the pituitary. In addition to gonadotrope cells specific to expression of either fshb or lhb, some cells showed co-expression of both genes. This suggests either that gonadotropes with co-expression are not yet specified or they could have a plasticity that permits changes from one cell phenotype to another during certain life stages and in turn during different physiological states.

Influence of tidal cycles on the endocrine control of reproductive activity in common snook (Centropomus undecimalis)

The aim of our study was to confirm the role of tidal pattern on the coordination of oocyte maturation and spawning in common snook Centropomus undecimalis. To do so, we studied oocyte maturation during the spawning season in relation to the tidal pattern in both males and females by means of histology and hormonal profiling along the pituitary-gonadal axis. Plasma LH levels, as well as transcript levels of gonadotropin genes (fshβ and lhβ) from the pituitaries of sexually mature male and female common snook were analyzed using a heterologous ELISA and quantitative RT-PCR, respectively. The fshβ and lhβ cDNAs were isolated and phylogenetic analysis of the deduced amino acid sequences revealed strong identity with other teleosts (75-90%). A strong link was found between tide and follicular development irrespective of the time of the day: female snook sampled on the rising tide were all found to have oocytes in the Secondary Growth Stage whereas females sampled at high tide or on the falling tide had oocytes in the later stages of maturation and ovulation. In addition, LH plasma and mRNA levels of fshβ and lhβ increased during the later stages of vitellogenesis peaking at ovulation in females. Plasma estradiol and testosterone significantly increased in late vitellogenesis (Secondary Growth Stage) and oocyte maturation (Eccentric Germinal Vesicle Step) respectively. Among male common snook sampled, no correlation was identified between tide and gonadal development. In addition, lhβ mRNA expression in males peaked at the mid germinal epithelium stage as for testosterone and 11-KT in the blood while fshβ expression and plasma LH levels peaked at late germinal epithelium stage. This study confirms the role played by tidal cycle on the entrainment of the later stages of oogenesis of common snook and provides a better understanding of the link between environmental and endocrine control of reproduction in this species.

Molecular characterization of three gonadotropin subunits and their expression patterns during ovarian maturation in Cynoglossus semilaevis

The endocrine regulation of reproduction in a multiple spawning flatfish with an ovary of asynchronous development remains largely unknown. The objectives of this study were to monitor changes in mRNA expression patterns of three gonadotropin hormone (GTH) subunits (FSHβ, LHβ and CGα) and plasma GTH levels during ovarian maturation of half-smooth tongue sole Cynoglossus semilaevis. Cloning and sequence analysis revealed that the cDNAs of FSHβ, LHβ and CGα were 541, 670 and 685 bp in length, and encode for peptides of 130, 158 and 127 amino acids, respectively. The number of cysteine residues and potential N-linked glycosylation sites of the flatfish GTHs were conserved among teleosts. However, the primary structure of GTHs in Pleuronectiformes appeared to be highly divergent. The FSHβ transcriptional level in the pituitary remained high during the vitellogenic stage while plasma levels of FSH peaked and oocyte development was stimulated. The LHβ expression in the pituitary and ovary reached the maximum level during oocyte maturation stages when the plasma levels of LH peaked. The brain GTHs were expressed at the different ovarian stages. These results suggested that FSH and LH may simultaneously regulate ovarian development and maturation through the brain-pituitary-ovary axis endocrine system in tongue sole.

Electrophysiological differences between fshb- and lhb-expressing gonadotropes in primary culture

Synthesis and release of FSH and LH are differentially regulated by GnRH, but the mechanisms by which this regulation is achieved are not well understood. Teleost fish are powerful models for studying this differential regulation because they have distinct pituitary cells producing either FSH or LH. By using pituitary cultures from Atlantic cod (Gadus morhua), we were able to investigate and compare the electrophysiological properties of fshb- and lhb-expressing cells, identified by single-cell quantitative PCR after recording. Both cell types fired action potentials spontaneously. The relative number of excitable cells was dependent on reproductive season but varied in opposing directions according to season in the 2 cell types. Excitable and quiescent gonadotropes displayed different ion channel repertoires. The dynamics of outward currents and GnRH-induced membrane responses differed between fshb- and lhb-expressing cells, whereas GnRH-induced cytosolic Ca²⁺ responses were similar. Expression of Ca²⁺-activated K⁺ channels also differed with cell type and showed seasonal variation when measured in whole pituitary. The differential presence of these channels corresponds to the differences observed in membrane response to GnRH. We speculate that differences in ion channel expression levels may be involved in seasonal regulation of hormone secretion as well as the differential response to GnRH in LH- and FSH-producing gonadotropes, through differences in excitability and Ca²⁺ influx.

Isolation of the pituitary gonadotrophic α-subunit hormone of the giant amazonian fish: pirarucu (Arapaima gigas)

The cDNAs of the α-subunit of the pituitary gonadotrophic hormones (GTHα) of fish of the order Osteoglossiformes or the superorder Osteoglossomorpha have never been sequenced. For a better understanding the phylogenetic diversity and evolution of PGHα in fish and for future biotechnological synthesis of the gonadotrophic hormones (ag-FSH and ag-LH), of Arapaima gigas, one of the largest freshwater fishes of the world, its GTHα cDNA was synthesized by reverse transcriptase and the polymerase chain reaction starting from total pituitary RNA. The ag-GTHα-subunit was found to be encoded by 348 bp, corresponding to a protein of 115 amino acids, with a putative signal peptide of 24 amino acids and a mature peptide of 91 amino acids. Ten cysteine residues, responsible for forming 5 disulfide linkages, 2 putative N-linked glycosylation sites and 3 proline residues, were found to be conserved on the basis of the known sequences of vertebrate gonadotrophic hormones. Phylogenetic analysis, based on the amino acid sequences of 38 GTHα-subunits, revealed the highest identity of A. gigas with members of the Acipenseriformes, Anguilliformes, Siluriformes and Cypriniformes (87.1-89.5 %) and the lowest with Gadiformes and Cyprinodontiformes (55.0 %). The obtained phylogenetic tree agrees with previous analysis of teleostei, since A. gigas, of the order of Osteoglossiformes, appears as the sister group of Clupeocephala, while Elopomorpha forms the most basal group of all other teleosts.

Differential regulation of GnRH ligand and receptor genes in the brain and pituitary of Atlantic cod exposed to different photoperiod

The onset of puberty and reproduction are tightly controlled by extrinsic and intrinsic inputs combined with genetically determined biological blueprints. Environmental inputs are then mediated by the brain-pituitary-gonad endocrine axis resulting in a unified output. In fish, one of the primary factors controlling the timing of sexual maturation is light, although how these signals are mediated in the brain and pituitary is not well understood. We therefore aimed to elucidate the molecular basis of the control of reproduction during the first spawning season in two year old female Atlantic cod. To this end, we measured GnRH and GnRH-R variant gene expression in brains and pituitaries collected from cod kept under four different photoperiod regimes: natural light (NL), continuous light (LL) and combined treatment of NL-LL and LL-NL. LL inhibited sexual development and spawning and LL-NL delayed sexual development and spawning. LL inhibited the spawning-related increase in brain GnRH3 and pituitary GnRH-R2a gene expression found under NL conditions, and the expression of these genes were delayed in concert with spawning of LL-NL cod. This study indicates that regulation of brain GnRH3 and pituitary GnRH-R2a genes likely mediates photoperiod induced changes in cod gonadal maturation.

Identification of ovarian gene expression patterns during vitellogenesis in Atlantic cod (Gadus morhua)

Follicular maturational competence and ovulatory competence in teleost fish refer to the ability of the ovarian follicle to undergo final oocyte maturation and ovulation, respectively, in response to gonadotropin stimulation and other external cues. Some gene products related to competence acquisition are likely synthesized during vitellogenic growth, as these follicles gain in vivo responsiveness to exogenous gonadotropin stimulation and can be induced to undergo maturation and ovulation. In Atlantic cod (Gadus morhua), gonadotropin responsiveness has been shown to be oocyte size-dependent, and only ovaries containing late-stage vitellogenic follicles can be induced to ovulate. The purpose of the present study was to compare gene expression patterns between mid (unresponsive) and late (responsive) vitellogenic ovaries to identify genes involved in gonadotropin responsiveness and the acquisition of maturational and ovulatory competencies. Representational difference analysis was conducted in two reciprocal comparisons using intact ovarian fragments and follicle wall-enriched tissues, and genes of interest were used in real time quantitative PCR to confirm differential expression. Few differences were detected in intact ovarian fragments, but type IV ice-structuring protein and gephyrin were upregulated later in development and may be involved in lipid and sulfur metabolism, respectively. Candidate gene assays for luteinizing hormone receptor and aromatase also exhibited significant upregulation during vitellogenesis. Many genes were differentially expressed in follicle wall-enriched tissues, including endocrine maturational regulators and smooth muscle genes. Overall, maturational and ovulatory competencies during vitellogenesis in Atlantic cod are associated with up- and downregulation of many genes involved in lipid metabolism, endocrine regulation, and ovulatory preparation.

Low-dose exposure to alkylphenols adversely affects the sexual development of Atlantic cod (Gadus morhua): acceleration of the onset of puberty and delayed seasonal gonad development in mature female cod

Produced water (PW), a by-product of the oil-production process, contains large amount of alkylphenols (APs) and other harmful oil compounds. In the last 20 years, there have been increasing concerns regarding the environmental impact of large increases in the amounts of PW released into the North Sea. We have previously shown that low levels of APs can induce disruption of the endocrine and reproductive systems of Atlantic cod (Gadus morhua). The aims of this follow-up study were to: (i) identify the lowest observable effect concentration of APs; (ii) study the effects of exposure to real PW, obtained from a North Sea oil-production platform; and (iii) study the biological mechanism of endocrine disruption in female cod. Fish were fed with feed paste containing several concentrations of four different APs (4-tert-butylphenol, 4-n-pentylphenol, 4-n-hexylphenol and 4-n-heptylphenol) or real PW for 20 weeks throughout the normal period of vitellogenesis in Atlantic cod from October to January. Male and female cod, exposed to AP and PW, were compared to unexposed fish and to fish fed paste containing 17β-oestradiol (E(2)). Approximately 60% of the females and 96% of the males in the unexposed groups were mature at the end of the experiment. Our results show that exposure to APs and E(2) have different effects depending on the developmental stage of the fish. We observed that juvenile females are advanced into puberty and maturation, while gonad development was delayed in both maturing females and males. The AP-exposed groups contained increased numbers of mature females, and significant differences between the untreated group and the AP-treated groups were seen down to a dose of 4 μg AP/kg body weight. In the high-dose AP and the E(2) exposed groups, all females matured and no juveniles were seen. These results suggest that AP-exposure can affect the timing of the onset of puberty in fish even at extremely low concentrations. Importantly, similar effects were not seen in the fish that were exposed to real PW.

Four gonadotropin releasing hormone receptor genes in Atlantic cod are differentially expressed in the brain and pituitary during puberty

Gonadotropin releasing hormones (GnRH) are an important part of the brain-pituitary-gonad axis in vertebrates. GnRH binding to its receptors (GnRH-R) stimulates synthesis and release of gonadotropins in the pituitary. GnRH-Rs also mediate other processes in the central nervous system such as reproductive behavior and neuromodulation. As many as five GnRH-R genes have been identified in two teleost fish species, but the function and phylogenetic relationship of these receptors is not fully understood. To gain a better understanding of the functional relationship between multiple GnRH-Rs in an important aquaculture species, the Atlantic cod (Gadus morhua), we identified four GnRH-Rs (gmGnRH-R) by RT-PCR, followed by full-length cloning and sequencing. The deduced amino acid sequences were used for phylogenetic analysis to identify conserved functional motifs and to clarify the relationship of gmGnRH-Rs with other vertebrate GnRH-Rs. The function of GnRH-R variants was investigated by quantitative PCR gene expression analysis in the brain and pituitary of female cod during a full reproductive cycle and in various peripheral tissues in sexually mature fish. Phylogenetic analysis revealed two types of teleost GnRH-Rs: Type I including gmGnRH-R1b and Type II including gmGnRH-R2a, gmGnRH-R2b and gmGnRH-R2c. All four gmGnRH-Rs are expressed in the brain, and gmGnRH-R1b, gmGnRH-R2a and gmGnRH-R2c are expressed in the pituitary. The only GnRH-R differentially expressed in the pituitary during the reproductive cycle is gmGnRH-R2a such that its expression is significantly increased during spawning. These data suggest that gmGnRH-R2a is the most likely candidate to mediate the hypophysiotropic function of GnRH in Atlantic cod.

Pituitary gonadotropin and testicular gonadotropin receptor expression in Atlantic cod (Gadusmorhua L.) during the first reproductive season: Effects of photoperiod modulation

Pituitary mRNA levels of gonadotropin β-subunits and of their cognate receptors in the testis were studied during puberty in Atlantic cod under normal and experimental photoperiod conditions that suppressed, delayed or accelerated testis maturation. Results are discussed in context with changes in testicular histology and plasma androgen levels, considered as end points of gonadotropic regulation. Up-regulation of fshb was closely associated with the onset of puberty, decreased when spermatogenesis was completed and reached minimum levels after spawning. These results demonstrate, for the first time using an experimental approach, that activation of Fsh-dependent signaling is associated with spermatogonial proliferation and formation of spermatogenic cysts. Changes in fshr expression were less prominent and could be explained by changes in the cellular composition and RNA content of cod testis tissue. At more advanced stages of development (spermiogenesis, spermiation and spawning), lhb and, one month later, lhcgr transcript levels increased and reached peak values in spawning fish, in a positive feedback loop involving plasma androgens and Lh/Lhcgr-dependent signaling. This loop was broken by a loss of lhb expression at the end of the spawning season. Continuous light (LL) from summer solstice, ~8 months prior to spawning, suppressed the start of testis maturation and the changes in gonadotropin and receptor mRNA levels, while LL from winter solstice initially up-regulated lhb and lhcgr expression, before resulting in a precocious termination of the spawning season and low expression of all four genes. Our studies provide experimental evidence for a clear functional discrimination of cod gonadotropins.

Identification and gene expression analysis of three GnRH genes in female Atlantic cod during puberty provides insight into GnRH variant gene loss in fish

Gonadotropin releasing hormone (GnRH) is a key regulator of sexual development and reproduction in vertebrates. Fish have either two or three pre-pro-GnRH genes, encoding structurally distinct peptides. We identified three pre-pro-GnRH genes in Atlantic cod (Gadus morhua, gmGnRH) using RT-PCR, RACE-PCR and BAC DNA library clone sequencing based on synteny searching. Gene identity was confirmed by sequence alignment and subsequent phylogenetic analysis. The expression of these genes was measured by quantitative PCR in the brain and pituitary of female cod throughout their reproductive cycle and in peripheral tissues. All three gmGnRH genes have highly conserved deduced decapeptide sequences, but sequence and phylogenetic data for gmGnRH1 suggest that this is a pseudogene. gmGnRH1 shares low identity with all fish GnRH variants and grouped with the GnRH3 clade. Although gmGnRH1 is a putative pseudogene, it is transcribed in multiple tissues but at low levels in the brain, indicating the loss of conserved hypophysiotrophic function. Phylogenetic analysis reveals that gmGnRH2 and gmGnRH3 variants are located in variant-specific clades. Both gmGnRH2 and gmGnRH3 transcripts are most abundant in the brain, with lower expression in pituitaries and ovaries. Brain gmGnRH3 gene expression increases in spawning fish and is expressed in the pituitary during puberty. Brain gmGnRH2 transcripts are highly expressed relative to gmGnRH3 before and during spawning. Sequence and expression data suggest that gmGnRH1 is a pseudogene and that gmGnRH3 is likely the hypophysiotrophic form of GnRH in Atlantic cod.

Relationships between the transcriptome and physiological indicators of reproduction in female rainbow trout over an annual cycle

Normal transcriptomic patterns along the brain-pituitary-gonad-liver (BPGL) axis should be better characterized if endocrine-disrupting compound-induced changes in gene expression are to be understood. Female rainbow trout were studied over a complete year-long reproductive cycle. Tissue samples from pituitary, ovary, and liver were collected for microarray analysis using the 16K Genomic Research on Atlantic Salmon Project (GRASP) microarray and for quantitative polymerase chain reaction measures of estrogen receptor (ER) isoform messenger RNA (mRNA) levels. Plasma was collected to determine levels of circulating estradiol-17β (E2), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). As an a priori hypothesis, changes in gene expression were correlated to either circulating levels of E2, FSH, and LH, or ER mRNAs quantified by quantitative polymerase chain reaction. In the liver, most transcriptomic patterns correlated to levels of either E2, LH, or ERs. Fewer ovarian transcripts could be correlated to levels of E2, ERα, or FSH. No significant associations were obvious in the pituitary. As a post hoc hypothesis, changes in transcript abundance were compared with microarray features with known roles in gonadal maturation. Many altered transcripts in the ovary correlated to transcript levels of estradiol 17-beta-dehydrogenase 8 or 17 B HSD12, or to glycoprotein alpha chain 1 or 2. In the pituitary, genes involved with the growth axis (e.g., growth hormone, insulin-related growth factor binding protein) correlated with the most transcripts. These results suggest that transcriptional networks along the BPGL axis may be regulated by factors other than circulating steroid hormones.

Plasticity of the reproductive axis caused by social status change in an african cichlid fish: I. Pituitary gonadotropins

Social position in a dominance hierarchy is often tightly coupled with fertility. Consequently, an animal that can recognize and rapidly take advantage of an opportunity to rise in rank will have a reproductive advantage. Reproduction in all vertebrates is controlled by the brain-pituitary-gonad axis, and in males of the African cichlid fish Astatotilapia burtoni, GnRH1 neurons at the apex of this axis are under social control. However, little is known about how quickly social information is transformed into functional reproductive change, or about how socially controlled changes in GnRH1 neurons influence downstream actions of the brain-pituitary-gonad axis. We created an opportunity for reproductively suppressed males to ascend in status and then measured how quickly the perception of this opportunity caused changes in mRNA and protein levels of the pituitary gonadotropins. mRNA levels of the β-subunits of LH and FSH rose rapidly in the pituitary 30 min after suppressed males perceived an opportunity to ascend. In contrast, mRNA levels of GnRH receptor-1 remained unchanged during social transition but were higher in stable dominant compared with subordinate males. In the circulation, levels of both LH and FSH were also quickly elevated. There was a positive correlation between mRNA in the pituitary and circulating protein levels for LH and FSH, and both gonadotropins were positively correlated with plasma 11-ketotestosterone. Our results show that the pituitary is stimulated extremely rapidly after perception of social opportunity, probably to allow suppressed males to quickly achieve reproductive success in a dynamic social environment.

Single-cell qPCR on dispersed primary pituitary cells -an optimized protocol

Background

The incidence of false positives is a potential problem in single-cell PCR experiments. This paper describes an optimized protocol for single-cell qPCR measurements in primary pituitary cell cultures following patch-clamp recordings. Two different cell harvesting methods were assessed using both the GH₄ prolactin producing cell line from rat, and primary cell culture from fish pituitaries.

Results

Harvesting whole cells followed by cell lysis and qPCR performed satisfactory on the GH₄ cell line. However, harvesting of whole cells from primary pituitary cultures regularly produced false positives, probably due to RNA leakage from cells ruptured during the dispersion of the pituitary cells. To reduce RNA contamination affecting the results, we optimized the conditions by harvesting only the cytosol through a patch pipette, subsequent to electrophysiological experiments. Two important factors proved crucial for reliable harvesting. First, silanizing the patch pipette glass prevented foreign extracellular RNA from attaching to charged residues on the glass surface. Second, substituting the commonly used perforating antibiotic amphotericin B with β-escin allowed efficient cytosol harvest without loosing the giga seal. Importantly, the two harvesting protocols revealed no difference in RNA isolation efficiency.

Conclusion

Depending on the cell type and preparation, validation of the harvesting technique is extremely important as contaminations may give false positives. Here we present an optimized protocol allowing secure harvesting of RNA from single cells in primary pituitary cell culture following perforated whole cell patch clamp experiments.

Timing of the maturation transition in haddock Melanogrammus aeglefinus

The timing of maturation in haddock Melanogrammus aeglefinus was examined using changes in gonad development, follicle stimulating hormone β (FSH-β) transcript expression profile, growth and condition of 1 year old females held under a common environment between the summer and winter solstices. The circumnuclear ring, cortical alveolus and vitellogenic oocyte stages were first observed in August, October and November, respectively. FSH-β transcript levels did not change significantly until September but increased markedly thereafter in maturing fish. A combined analysis of the mean oocyte diameter of the leading cohort, histological staging and FSH-β transcript profile provided evidence of a commitment to maturation by October or November. Contrary to that previously proposed for gadoid species, histological analysis of field-caught immature M. aeglefinus during the spawning season indicated that cortical alveolar, rather than circumnuclear ring, stage oocytes provided definitive evidence of maturation. A decrease in relative liver size following the summer solstice suggested a possible link between energy status and maturation.