Regulation of steroid production and key genes in catfish Heteropneustes fossilis using recombinant gonadotropins.

The two gonadotropins, FSH and LH, stimulate growth and development of the gonads through gonadal biosynthesis of steroid hormones and growth factors. To date, cDNA sequences encoding gonadotropin subunits have been isolated and characterized from a large number of fish species. Recently, we successfully cloned and characterized gonadotropins (LHß, FSHß, and GPα) from the pituitary glands of the catfish, Heteropneustes fossilis. In the present study, we describe herein the production of recombinant stinging catfish, H. fossilis (hf) FSH (rhfFSH) and LH (rhfLH) using the methylotrophic yeast P. pastoris expression system. We further explored the hypothesis that the recombinant gonadotropins can modulate the hypothalamus-pituitary-ovarian (HPO) axis genes (avt, it, gnrh2, kiss2, and cyp19a1a) and regulate their transcriptional profile and steroid levels in relation to their annual developmental stage during preparatory and pre-spawning phases under in-vitro conditions. We found that the different concentrations of recombinant rhfFSH and rhfLH significantly stimulated E2 levels in the preparatory and prespawning season, and also upregulated gonadal aromatase gene expression in a dose dependent manner. Our results demonstrate that the yeast expression system produced biologically active recombinant catfish gonadotropins, enabling the study of their function in the catfish.

Presence of GnRH3 in sturgeon and the roles of GnRH1 and GnRH2 on the regulation of LH/FSH in mature female sterlet Acipenser ruthenus in vitro.

Three forms of gonadotropin-releasing hormones (GnRHs), ArGnRH1, ArGnRH2, and ArGnRH3, were identified in sterlet. Compared with their orthologue, ArGnRH1 and ArGnRH2 have conserved core decapeptide but show low identity in the signal peptide and the rest of the sequences. The existence of the GnRH3 paralogue of sturgeon was predicted for the first time with TBLASTN by using the amino acid sequences of catshark and whale shark GnRH3 precursor as queries against the whole genome and transcript data of sterlet. The predicted ArGnRH3 cDNA sequence was composed of three exons containing all the elements of the GnRH family. The successful molecular cloning of GnRH3 from sterlets verified its expression in the brain of sturgeons. The analysis of the ArGnRH3 amino acid sequence revealed a completely conserved decapeptide sequence that shows 100% identity with the sequence of teleosts and differs in one amino acid with that of the cartilaginous fish (catshark and whale shark) at the 5th position. The structure of the phylogenetic tree showed that a total of 52 vertebrate GnRH sequences were clustered into three main clades corresponding to GnRH1, GnRH2, and GnRH3. The ArGnRH3 sequence is the oldest GnRH3 identified in teleosts. The tissue distribution analysis showed that ArGnRH1 was expressed in all the 13 examined tissues of females and in most of the tested tissues of male fish, with the highest expression in the pituitary and hypothalamus. ArGnRH2 is only expressed in the pituitary, hypothalamus, and gonads of both female and male sterlets. ArGnRH3 mRNA could be detected in the pituitary, hypothalamus, and gonad in both female and male fish. It is also present in the spleen, head kidney, and gill in female fish and in kidney and heart in male fish. However, the ArGnRH3 only showed weak expression in all the positive tissues. ArGnRH1 and ArGnRH2 active decapeptides were synthesized to investigate their roles on the regulation of LH/FSH using a mixed brain cell line from a sexually mature female sterlet. The results showed that ArGnRH1 and ArGnRH2 exerted different effects on the gene expression and release of gonadotropins. ArGnRH1 promoted the expression of fshß significantly around 48 h, and the expression was suppressed when the treatment time was extended to 72 h. ArGnRH1 had no significant effects on the level of either mRNA or secreted lh in any of the tested treatment length or concentrations. Moreover, ArGnRH1 did not stimulate the activity of gonadotropins in the maturation stage of female sturgeons. ArGnRH2 promoted the expression of fshß at 24 h and 48 h and increased mRNA level of lhß at 6 h and 48 h, accompanied by the significant secretion of LH at 72 h, although the high mRNA level of fsh did not correlate with the secretion of FSH in ArGnRH2-treated groups. In conclusion, ArGnRH2 plays an important role in the maturation stage of female sterlets. Therefore, ArGnRH2 has the potential to induce ovulation and spermiation in sturgeons.

Cloning of gonadotropin Gph-alpha, FSH-beta and LH-beta subunits and seasonal profiles of steroid hormones in wild-caught Nile perch, Lates niloticus.

The Nile perch (np; Lates niloticus) is a freshwater teleost species with a potential for aquaculture in freshwater surroundings. However, wild-caught breeders have persistently failed to spawn spontaneously in captivity. Cloning of the gonadotropin subunits and analysing seasonal variation in reproductive hormone levels for a 1-year period were done to gain knowledge on the physiological basis underlying the reproductive biology of np. The ß-follicle-stimulating hormone (FSH-ß) and ß-luteinizing hormone (LH-ß) subunits and their common α-glycoprotein (Gph-α) subunit were cloned using 3' and 5' RACE-PCR. The nucleotide sequences of the npgph-α, npfsh-ß, and nplh-ß subunits were 664, 580 and 675 nucleotides in length, encoding peptides of 124, 120 and 148 amino acids, respectively. The deduced amino acid sequence of each mature subunit showed high similarity with its counterparts in other teleost. Sequence analysis showed that npFSH-ß is more similar to higher vertebrate FSH-ßs than to higher vertebrate LH-ßs. Heterologous immunoassay was calibrated to analyse pituitary LH levels. While the LH immunoassay showed parallelism of npLH with that of tilapia (ta), no parallelism for FSH was found. Levels of pituitary LH were higher in females at gonadal stages of vitellogenic oocytes, mature secondary oocytes and mature tertiary oocytes with migrating nucleus than in pre-vitellogenic oocytes and early and late perinucleolus oocytes. Using competitive steroid ELISA, variations in the levels of the steroid hormones 11-ketotestosterone (11-KT) in males and E2 in females were characterized in relation to month and reproductive index of Nile perch. Our findings show that in females, gonadosomatic index and plasma E2 were highly correlated (R2 = 0.699, n = 172) and peaked from September to November while in males, the gonadosomatic index and plasma 11-KT peaked from October to November. In female fish, both steroid hormones were detected in the plasma but greatly varied in concentrations. E2 in particular, increased with the developmental stage of the gonads. The levels of steroid hormones, E2 and 11-KT in females and males respectively increased with fish size (total lengths) and suggest that females mature at a body length of 40-59 cm than their counter part males that mature at a total length of 60-70 cm. Taken together, we describe seasonal endocrine differences in wild-caught adult Nile perch which could potentially be exploited to manipulate the reproductive axis in cultured breeders.

In silico analysis of kiss2, expression studies and protein-protein interaction with gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHß) in Heteropneustes fossilis.

Kisspeptins, encoded by the kiss genes, are neuropeptides that regulate the onset of puberty, maturation of gonads, and fertility in higher vertebrates including fishes. The gene ontology suggests that kisspeptin plays an important role not only in reproduction but also in cell signaling, immune response and metabolic processes, and to decipher protein-protein interactions, computational approach has been favored. The present investigation focuses on the detailed structural analysis and molecular docking of kiss2 gene using in silico tools. A putative kiss2 protein of 113 amino acids was encoded by an open reading frame of 342 bp kiss2 gene. The protein is of 13.12 kDa with isoelectric point of 9.45. The secondary structure of the protein indicates more than 50% random coils, followed by 34% of alpha helix and 13% extended strand. The protein was found to be extracellular and secretory in nature. Since, protein-protein interactions play a very crucial role in every cellular process and due to unavailability of crystal structure of our protein of interest in fishes computational approach has been employed. The 3D PDB modeling and the molecular docking of kiss2, Gonadotropin-releasing hormone 2 (GnRH2) and luteinizing hormone beta (LHß) proteins in fishes have been demonstrated applying protein-docking approach. Molecular interactions of kiss2 protein were the highest with kisspeptin receptor 2 and lowest for the neuropeptide FF-amide peptide precursor protein. Expression of kiss2 transcripts, mainly in the brain and ovary of H. fossilis, supports its hypothalamic-pituitary-gonadal axis signaling and reproductive function. Further, changes in expression patterns of kiss2 mRNA during different developmental stages, indicate its potential role in embryonic development also. The present study conclusively reveals interaction of kiss2 with other neuropeptides. Prediction of binding structures and identification of key residues in protein-protein interaction illustrate direct interaction among these proteins, playing a cardinal role in neuroendocrine regulation of reproduction in catfish. Communicated by Ramaswamy H. Sarma.

Single molecule characterization of the binding kinetics of a transcription factor and its modulation by DNA sequence and methylation.

The interaction of transcription factors with their response elements in DNA is emerging as a highly complex process, whose characterization requires measuring the full distribution of binding and dissociation times in a well-controlled assay. Here, we present a single-molecule assay that exploits the thermal fluctuations of a DNA hairpin to detect the association and dissociation of individual, unlabeled transcription factors. We demonstrate this new approach by following the binding of Egr1 to its consensus motif and the three binding sites found in the promoter of the Lhb gene, and find that both association and dissociation are modulated by the 9 bp core motif and the sequences around it. In addition, CpG methylation modulates the dissociation kinetics in a sequence and position-dependent manner, which can both stabilize or destabilize the complex. Together, our findings show how variations in sequence and methylation patterns synergistically extend the spectrum of a protein's binding properties, and demonstrate how the proposed approach can provide new insights on the function of transcription factors.

Expression of genes that regulate follicle development and maturation during ovarian stimulation in poor responders.

RESEARCH QUESTION: Sex hormone-binding globulin (SHBG), androgen receptor (AR), LH beta polypeptide (LHB), progesterone receptor membrane component 1 (PGRMC1) and progesterone receptor membrane component 2 (PGRMC2) regulate follicle development and maturation. Their mRNA expression was assessed in peripheral blood mononuclear cells (PBMC) of normal and poor responders, during ovarian stimulation. DESIGN: Fifty-two normal responders and 15 poor responders according to the Bologna criteria were enrolled for IVF and intracytoplasmic sperm injection and stimulated with 200 IU of follitrophin alpha and gonadotrophin-releasing hormone antagonist. HCG was administered for final oocyte maturation. On days 1, 6 and 10 of stimulation, blood samples were obtained, serum hormone levels were measured, RNA was extracted from PBMC and real-time polymerase chain reaction was carried out to identify the mRNA levels. Relative mRNA expression of each gene was calculated by the comparative 2-DDCt method. RESULTS: Differences between mRNA levels of each gene on the same time point between the two groups were not significant. PGRMC1 and PGRMC2 mRNA levels were downregulated, adjusted for ovarian response and age. Positive correlations between PGRMC1 and AR (standardized beta = 0.890, P < 0.001) from day 1 to 6 and PGRMC1 and LHB (standardized beta = 0.806, P < 0.001) from day 1 to 10 were found in poor responders. PGRMC1 and PGRMC2 were positively correlated on days 6 and 10 in normal responders. CONCLUSIONS: PGRMC1 and PGRMC2 mRNA are significantly decreased during ovarian stimulation, with some potential differences between normal and poor responders.

Kisspeptin2 regulates hormone expression in female zebrafish (Danio rerio) pituitary.

Kisspeptin2 is a neuropeptide widely found in the brain and multiple peripheral tissues in the zebrafish. The pituitary is the center of synthesis and secretes various endocrine hormones. However, Kiss2 innervation in the zebrafish pituitary is unknown. In this study, the organization of Kiss2 cells and structures in the zebrafish pituitary by promoter-driving mCherry-labeling Kiss2 neurons were investigated. Kiss2 neurons in the hypothalamus do not project into the pituitary. Kiss2 cells are found in the female pituitary. Unidentified Kiss2 cells and extensions are located in the proximal pars distalis (PPD), similar to the distribution of Gnrh3 fibers. Kiss2 structures reside alongside Gnrh3 fibers. No Kiss2 structures are found in the male pituitary. The transcriptional expression of the kisspeptin receptor kiss1rb is detected in both female and male pituitaries. In situ hybridization shows that kiss1rb-positive cells are located in the PPD and pars intermedia (PI). In vitro Kiss2-10 treatment stimulates Akt and Erk phosphorylation and significantly induces lhß, fshß, and prl1 mRNA expression in the female pituitary. The results in this study suggest that Kiss2 and Kiss1rb may form an independent paracrine or autocrine system in the female zebrafish pituitary. Kiss2 and Kiss1rb signaling regulates the expression of pituitary hormones.

Gpr120 mRNA expression in gonadotropes in the mouse pituitary gland is regulated by free fatty acids.

GPR120 is a long-chain fatty acid (LCFA) receptor that is specifically expressed in gonadotropes in the anterior pituitary gland in mice. The aim of this study was to investigate whether GPR120 is activated by free fatty acids in the pituitary of mice and mouse immortalized gonadotrope LßT2 cells. First, the effects of palmitate on GPR120, gonadotropic hormone b-subunits, and GnRH-receptor expression in gonadotropes were investigated in vitro. We observed palmitate-induced an increase in Gpr120 mRNA expression and a decrease in follicle-stimulating hormone b-subunit (Fshb) expression in LßT2 cells. Furthermore, palmitate exposure caused the phosphorylation of ERK1/2 in LßT2 cells, but no significant changes were observed in the expression levels of luteinizing hormone b-subunit (Lhb) and gonadotropin releasing hormone-receptor (Gnrh-r) mRNA and number of GPR120 immunoreactive cells. Next, diurnal variation in Gpr120 mRNA expression in the male mouse pituitary gland was investigated using ad libitum and night-time restricted feeding (active phase from 1900 to 0700 h) treatments. In ad libitum feeding group mice, Gpr120 mRNA expression at 1700 h was transiently higher than that measured at other times, and the peak blood non-esterified fatty acid (NEFA) levels were observed from 1300 to 1500 h. These results were not observed in night-time-restricted feeding group mice. These results suggest that GPR120 is activated by LCFAs to regulate follicle stimulating hormone (FSH) synthesis in the mouse gonadotropes.

Colocalization of GPR120 and anterior pituitary hormone-producing cells in female Japanese Black cattle.

Negative energy balance in domestic animals suppresses their reproductive function. These animals commonly use long-chain fatty acids (LCFAs) from adipocytes as an energy source under states of malnutrition. The G-protein coupled receptor, GPR120, is a specific receptor for LCFAs, but its role in reproductive function remains unknown in domestic animals. The purpose of this study was to examine whether GPR120 is involved in the reproductive system of cattle. GPR120 mRNA expression was evaluated in brain, pituitary, and ovarian tissue samples by RT-PCR. GPR120 gene expression was detected with high intensity only in the anterior pituitary sample, and GPR120-immunoreactive cells were found in the anterior pituitary gland. Double immunohistochemistry of GPR120 in the anterior pituitary hormone-producing cells, such as gonadotropes, thyrotropes, lactotropes, somatotropes, and corticotropes, was performed to clarify the distribution of GPR120 in the anterior pituitary gland of ovariectomized heifers. Luteinizing hormone ß subunit (LHß)- and follicle-stimulating hormone ß subunit (FSHß)-immunoreactive cells demonstrated GPR120 immunoreactivity at 80.7% and 85.9%, respectively. Thyrotropes, lactotropes, somatotropes, and corticotropes coexpressed GPR120 at 21.1%, 5.4%, 13.6%, and 14.5%, respectively. In conclusion, the present study suggests that GPR120 in the anterior pituitary gland might mediate LCFA signaling to regulate gonadotrope functions, such as hormone secretion or production, in cattle.

Short-term but not long-term high-fat diet induces an increase in gene expression of gonadotropic hormones and GPR120 in the male mouse pituitary gland.

High-fat diet (HFD) is associated with the regulation of reproductive functions. This study aimed to investigate the effects of short-term HFD on the mRNA expression levels of follicle-stimulating hormone ß subunit (FSHß), luteinizing hormone ß subunit (LHß), gonadotropin-releasing hormone receptor, and long-chain fatty acid receptor, GPR120, in the matured male mouse pituitary gland. Adult male mice were fed either control chow or HFD for 1, 2, 5, 10, 30 and 150 days. Fshb and Gpr120 mRNA expression levels in the pituitary glands were significantly increased during 2 to 30 days of HFD feeding. Gnrh-r mRNA in the 30 days HFD fed group and body weight in the 30 and 150 days HFD fed groups were higher than control. However, there were no significant differences in plasma non-esterified fatty acids or glucose levels during the 150 days of HFD feeding. These results suggest that male mice feeding a short-term HFD induces FSHß synthesis and GPR120 expression in their pituitary gonadotropes.

AMP-activated protein kinase activation reduces the transcriptional activity of the murine luteinizing hormone ß-subunit gene.

Malnutrition is one of the factors that induces reproductive disorders. However, the underlying biological processes are unclear. AMP-activated protein kinase (AMPK) is an enzyme that plays crucial role as a cellular energy sensor. In the present study, we examined the effects of AMPK activation on the transcription of the murine gonadotropin subunit genes Cga, Lhb, and Fshb, and the gonadotropin-releasing hormone receptor Gnrh-r. Real-time PCR and transcription assay using LßT2 cells demonstrated that 5-amino-imidazole carboxamide riboside (AICAR), a cell-permeable AMP analog, repressed the expression of Lhb. Next, we examined deletion mutants of the upstream region of Lhb and found that the upstream regulatory region of Lhb (-2527 to -2198 b) was responsible for the repression by AICAR. Furthermore, putative transcription factors (SP1, STAT5a, and TEF) that might mediate transcriptional control of the Lhb repression induced by AICAR were identified. In addition, it was confirmed that both AICAR and a competitive inhibitor of glucose metabolism, 2-deoxy-D-glucose, induced AMPK phosphorylation in LßT2 cells. Therefore, the upstream region of Lhb is one of the target sites for glucoprivation inducing AMPK activation. In addition, AMPK plays a role in repressing Lhb expression through the distal -2527 to -2198 b region.

Nr5a1b promotes and Nr5a2 inhibits transcription of lhb in the orange-spotted grouper, Epinephelus coioides†.

Nr5a1 (Sf-1) up-regulates lhb expression across vertebrates; however, its regulatory roles on fshb remain to be defined. Moreover, the involvement of Nr5a2 in the regulation of gonadotropin expression is not clear either. In the present study, the involvement of Nr5a1b (a homologue of Nr5a1) and Nr5a2 in the regulation of lhb and fshb expression in the orange-spotted grouper was examined. Dual fluorescent immunohistochemistry using homologous antisera showed that in the pituitary of orange-spotted groupers, Lh cells contain both immunoreactive Nr5a1b and Nr5a2 signals, whereas Fsh cells contain neither of them. In LßT2 cells, Nr5a1b up-regulated basal activities of lhb and fshb promoters possibly via Nr5a sites, and synergistically (on lhb promoter) or additively (on fshb promoter) with forskolin. Surprisingly, Nr5a2 inhibited basal activities of lhb promoter possibly via Nr5a sites and attenuated the stimulatory effects of both forskolin and Nr5a1b. In contrast, Nr5a2 had no effects on fshb promoter. Chromatin immunoprecipitation analysis showed that both Nr5a1b and Nr5a2 bound to lhb promoter, but not fshb promoter in the pituitary of the orange-spotted grouper. The abundance of Nr5a1b bound to lhb promoter was significantly higher at the vitellogenic stage than the pre-vitellogenic stage, whereas that of Nr5a2 exhibited an opposite trend. Taken together, data of the present study demonstrated antagonistic effects of Nr5a1b and Nr5a2 on lhb transcription in the orange-spotted grouper and revealed novel regulatory mechanisms of differential expression of lhb and fshb genes through Nr5a homologues in vertebrates.

Thermal manipulation and GnRHa therapy applied to the reproduction of lambari-do-rabo-amarelo, Astyanax altiparanae females (Characiformes: Characidae) during the non-breeding season.

Lambari-do-rabo-amarelo Astyanax altiparanae in the wild reproduce during spring and summer, but females undergo vitellogenesis throughout the year, including the non-spawning winter period when water temperatures are low. The present study investigated the physiological role of temperature modulation on the hypothalamus-pituitary-gonads axis of lambari during winter, as well as the effects of gonadotropin releasing hormone agonist (GnRHa) therapy. Captive females were exposed to two different temperatures (20 °C and 27 °C) and were injected weekly with GnRHa for 21 days during winter (Control, CTR; Low dose; LD and high dose of GnRHa, HD). At the end of the 21-days period gonadosomatic index (GSI), oocyte stage of development and theoretical fecundity were evaluated, together with plasma levels of 17ß-estradiol (E2). Gene expression of the two pituitary gonadotropins follicle-stimulating hormone (fshß) and luteinizing hormone (lhß), as well as hepatic vitellogenin-A (vtgA) expression were also analyzed. At the end of the experimental period, females from the six different experimental conditions were induced to spawn using human chorionic gonadotropin (hCG). Spawning performance parameters and plasma levels of the maturation inducing steroid (MIS) were analyzed. Gene expression of fshß did not change with temperature manipulation, but females exposed to 27 °C and supplemented with a HD of GnRHa exhibited an increased fshß gene expression, associated with higher E2 levels. The higher water temperature alone was able to increase E2 levels. At both water temperatures GnRHa injections induced a decrease in E2 levels. GnRHa injected females had a lower vtgA gene expression levels at 20 °C. Even with differences in the gene expression of gonadotropins among the various temperature/GnRHa treatments, GSI and oocyte diameter did not change, but GnRHa enhanced the number of vitellogenic oocytes at 20 °C. The reproductive performance of lambari induced to spawn with hCG was better after the combined treatment with GnRHa and summer temperature.

Photoperiodic regulation of plasma gonadotropin levels in previtellogenic greater amberjack (Seriola dumerili).

In Seriola species, exposure to a long photoperiod regime is known to induce ovarian development. This study examined photoperiodic effects on pituitary gene expression and plasma levels of follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) in previtellogenic greater amberjack (Seriola dumerili). The fish were exposed to short (8L:16D) or long (18L:6D) photoperiod. The water temperature was maintained at 22 °C. Compared with the short-photoperiod group, plasma Fsh levels were higher on days 10 and 30 in the long-photoperiod group, but plasma Lh levels did not significantly differ. On day 30, pituitary Fsh- and Lh-ß subunit gene expressions were also higher in the long-photoperiod group than the short-photoperiod group, whereas α-subunit gene expressions were higher on days 20 and 30. Throughout the experiment, average gonadosomatic index and plasma E2 levels did not significantly differ between the two groups. This study clearly demonstrated that a long photoperiod induced Fsh release in the previtellogenic fish followed by upregulation of pituitary Fsh and Lh subunit gene expressions. An increase in plasma Fsh levels may be a key factor that mediates the photoperiodic effect on the initiation of ovarian development.

Bu-shen-zhu-yun decoction promotes synthesis and secretion of FSHß and LHß in anterior pituitary cells in vitro.

Luteal phase defects (LPD) are an important etiology of infertility which has increased in recent years. Studies have shown that bu-shen-zhu-yun decoction (BSZY-D) can lower the expression of estrogen receptor and progesterone receptor, in rats endometrium of embryonic implantation period, which upregulated by mifepristone, and improve uterine receptivity. The aim of present study was to determine the effect of BSZY-D on the synthesis and secretion of gonadotropic hormones in the anterior pituitary cells of rats. Rats were treated with saline (control) or BSZY-D two times/day for three estrous cycles by gavage. The cerebrospinal fluid (CSF) were collected for further cell treatment. The components in BSZY-D, serum and CSF were analysed by High Performance Liquid Chromatography (HPLC). Cells were either pretreated with normal CSF or BSZY-D/CSF before being stimulated with or without cetrorelix. The mRNA and proteins levels of receptors, hormones, and transcription factors were detected by RT-PCR, western blot analysis and immunostaining. We show that non-toxic concentrations of cetrorelix, a GnRH antagonist, can reduce the mRNA and protein levels of GnRHR, LH, and FSH. This effect could be reversed by the addition of BSZY-D/CSF. We also show decreased mRNA and protein expression of transcription factors, such as CREB, and Egr-1 and secretory vescicles, including SNAP-25 and Munc-18 upon treatment with cetrorelix could be reversed post co-treatment with BSZY-D/CSF. These results indicate that BSZY-D/CSF treatment led to increased levels of GnRHR, transcription factors, and secretory vesicles leading to increased secretion of FSH and LH. Thus, BSZY-D presents a promising candidate to treat luteal phase defects and infertility.

Reproductive stage- and sex-dependant effects of neurohypophyseal nonapeptides on gonadotropin subunit mRNA expression in the catfish Heteropneustes fossilis: An in vitro study.

In the present study, in vitro effects of synthetic vasotocin (VT), isotocin (4Ser, 8Ile- oxytocin; ITb) and the recently cloned IT gene paralog product (8Val-Isotocin, ITa) were studied on the expression of pituitary gonadotropin (GtH) subunit mRNA levels. In male pituitaries of early (preparatory phase) and late (prespawning phase) recrudescing catfish, Heteropneustes fossilis, VT (10 nM, 100 nM and 1000 nM) stimulated fshß expression dose-dependently. But in females, the dose-dependent effect was found only in the preparatory phase. In males, VT stimulated lhß expression only at higher doses. In females, VT produced a significant dose-dependent increase of the lhß expression only in the prespawning phase. VT stimulated the expression of gpα, dose-dependently in the preparatory phase in males and in the prespawning phase in females. The incubation of the pituitaries with ITb did not alter the fshß expression in either sex in both preparatory and prespawning phases. In males, ITb stimulated the expression of lhß and gpα only at the highest concentration (1000 nM) in both phases. In females, ITb stimulated both lhß and gpα expression only at 1000 nM in the preparatory phase and dose-dependently in the prespawning phase. The incubation of the pituitaries with ITa produced effects similar to ITb on the expression of fshß, lhß, and gpα. The results show that the basic peptide VT modulates both fshß and lhß expressions, which are influenced by the sex and reproductive stage. The neutral peptide ITA/ITb exerts an insignificant effect on the fshß expression regardless of sex or season. Both VT and ITa/ITb elicit a significant effect on the lhß expression in late recrudescent phase especially in females.

Neurokinin B signaling in hermaphroditic species, a study of the orange-spotted grouper (Epinephelus coioides).

Neurokinin B (NKB) plays important roles in the mammalian reproductive axis by modulating the release of gonadotropin-releasing hormone (GnRH) and gonadotropins. In the present study, the tac3 cDNA was cloned from a hermaphroditic species, the orange-spotted grouper. Sequence analysis showed that the grouper Tac3 precursor encoded two tachykinin peptides, NKB and NKB-related peptide (NKBRP). Expression analysis in different tissues revealed that tac3 mRNA was highly expressed in the brain of the orange-spotted grouper. In situ hybridization further revealed that it was localized in some hypothalamic nuclei associated with reproductive regulation. During ovarian development, an increase of tac3 expression in the hypothalamus was observed at vitellogenesis stage. Intraperitoneal administration of NKB could increase the gnrh1 and lhß mRNA levels, and enhance the serum estrogen levels, but did not significantly influence lhß expression in cultured pituitary cells, indicating that NKB does not directly exert its actions on the pituitary gland. However, it was found that NKBRP had no effect on the expression of two gnrhs and two gths in vivo and in vitro. Effects of sex steroids on tac3 expression were further investigated. During the 17-methyltestosterone-induced sex change in the orange-spotted grouper, hypothalamic tac3 expression showed no significant change. Interestingly, ovariectomy greatly stimulated tac3 expression, while the 17ß-estradiol treatment reversed this effect. In general, our data highly indicated that NKB signaling could activate the reproductive axis in the orange-spotted grouper. Our study is the first description of the NKB signaling in the hermaphroditic species.

Molecular identification of the Dyn/Kor system and its potential role in the reproductive axis of goldfish.

To ascertain the significance of the dynorphin/kappa-opioid receptor (Dyn/Kor) system in fish reproduction, prodynorphin (pdyn) cDNA was cloned from goldfish. Two Dyn peptides (DynA and DynB) are present in the goldfish prodynorphin precursor. Both DynA and DynB are biologically active as they are able to functionally interact with the goldfish Kor expressed in cultured eukaryotic cells to suppress forskolin-induced CRE promoter activity. RT-PCR analysis showed that pdyn is widely expressed in brain regions, with the highest expression in hypothalamus. During ovarian development, hypothalamic pdyn and kor mRNA levels are lower in the early vitellogenic stage. Then the biological effects of Dyn peptides on salmon gonadotropin releasing hormone (sgnrh), luteinizing hormone beta (lhb) and follicle stimulating hormone beta (fshb) mRNA synthesis were further investigated in goldfish. Intraperitoneal injections of DynA and DynB significantly reduced hypothalamic sgnrh and pituitary lhb and fshb mRNA levels in male goldfish, but these two peptides only down-regulated sgnrh and lhb mRNA expression in female goldfish. In vitro studies revealed that DynA also decreased lhb mRNA levels in primary cultures of pituitary cells, indicating that this peptide can exert its actions at the pituitary level. Our findings suggest that the Dyn/Kor system plays a negative role in regulating the reproductive axis in goldfish.

Estrogen directly stimulates LHb expression at the pituitary level during puberty in female zebrafish.

The LHb expression is up-regulated during puberty in female zebrafish. However, the molecular mechanism underlying how LHb expression is regulated during puberty remains largely unknown. In this study, we found that the mRNA expression levels of lhb, fshb and cyp19a1b were up-regulated along with the puberty onset in zebrafish. Among the three nuclear estrogen receptors (nERs), the esr2b is the only type whose expression is significantly up-regulated during puberty onset in the pituitary. However, in situ hybridization results revealed that lhb mRNA was colocalized with esr1 and esr2a but not esr2b. Exposure to estradiol (E2) significantly stimulates LHb expression in both wild-type and kiss1-/-;kiss2-/-;gnrh3-/- triple knockout pubertal zebrafish. Moreover, exposure of cultured pituitary cells to E2 increased the LHb expression, indicating that the estrogenic effect on LHb expression could be acted at the pituitary level. Finally, we cloned and analyzed the promoter of lhb by luciferase assay. Our results indicated that the E2 responsive regions of lhb promoter for ERα and ERß2 are identical, suggesting that ERα and ERß2 could bind to the same half ERE region of the promoter of lhb, exhibiting a classical ERE-dependent pathway. In summary, we demonstrate that E2 could directly act on the pituitary level to stimulate LHb transcription during puberty in zebrafish.

Fertility impairment with defective spermatogenesis and steroidogenesis in male zebrafish lacking androgen receptor.

The pivotal role of androgen receptor (AR) in regulating male fertility has attracted much research attention in the past two decades. Previous studies have shown that total AR knockout would lead to incomplete spermatogenesis and lowered serum testosterone levels in mice, resulting in azoospermia and infertility. However, the precise physiological role of ar in controlling fertility of male fish is still poorly understood. In this study, we have established an ar knockout zebrafish line by transcription activator-like effectors nucleases. Homozygous ar mutant male fish with smaller testis size were found to be infertile when tested by natural mating. Intriguingly, a small amount of mature spermatozoa was observed in the ar mutant fish. These mature spermatozoa could fertilize healthy oocytes, albeit with a lower fertilization rate, by in vitro fertilization. Moreover, the expression levels of most steroidogenic genes in the testes were significantly elevated in the ar mutants. In contrast, the levels of estradiol and 11-ketotestosterone (11-KT) were significantly decreased in the ar mutants, indicating that steroidogenesis was defective in the mutants. Furthermore, the protein level of LHß in the serum decreased markedly in the ar mutants when compared with wild-type fish, probably due to the positive feedback from the diminished steroid hormone levels.