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

In vivo effect of recombinant Fsh and Lh administered to meagre (Argyrosomus regius) at the initial stages of sex differentiation

Recombinant gonadotropins, follicle stimulating (rFsh) and luteinizing hormone (rLh), offer the potential to induce gametogenesis in prepubertal fish. This study aimed to determine the in vivo effect of the administration of Argyrosomus regius rFsh and rLh on the reproductive development of prepubertal meagre juveniles at the initial stages of sexual differentiation. Juvenile meagre, 9-months old with mean weight of 219 ± 3.9 g (mean ± SEM) were randomly distributed into nine groups (n = 8 per group). Experimental groups were treated weekly with an acute injection of either rFsh or rLh. Control groups were injected with saline solution. In a 3-week experiment, different groups were administered with different doses 6, 12 or 18 µg kg-1 of rFsh or rLh or saline solution. In a 6-week experiment a group was administered with 12 µg kg-1 of rFsh and a second group with saline solution. The fish were held in a single 10 m3 tank with natural photoperiod (Feb. - March) and temperature 16.1 ± 0.4 °C. At the start of the experiment (n = 8) and at the end of the 3-week experiment, fish were blood sampled and sacrificed. Blood was analysed for 17β-estradiol (E2) and 11-ketotestosterone (11-KT). Gonads and liver were dissected and weighed. Gonads were fixed in Bouińs solution and processed for histological analysis. Juvenile meagre at the start of the experiment were in the initial stages of sexual differentiation, indicated by the presence of the ovarian cavity or testes duct that was surrounded by undifferentiated embryonic germ stem cells and somatic cells. At the end of the 3-week experiment, there was no significant difference in gonadosomatic index (GSI) amongst control (initial and saline treated) and the experimental groups. After three weeks of application of rFsh, rLh or saline all fish presented a similar gonadal structure as at the start of the experiment. However, the incidence of sporadic developing germ cells (principally spermatogonia, spermatocytes, spermatids, but also perinucleolar stage oocytes) generally increased in rGth treated meagre. A mean of 44 % of meagre treated with rFsh or rLh presented sporadic isolated developing germ cells, mainly male cells. Plasma steroid levels of E2 decreased significantly from the start of the experiments to the end. At the end of the experiments there were no differences in plasma E2 amongst Control fish and rGth treated fish. Plasma 11-KT showed no change from the start of the experiment to week 3. However, a significant increase was observed in a proportion of the rFsh group after six weeks of treatment compared to the start of the experiment and the saline control group on week 6. The application of rFsh or rLh to meagre at the initial stages of sex differentiation did not stimulate steroid production until week six (11-KT) and had a limited, but evident effect on the development of sporadic isolated germ cells. However, we conclude that rGth, rFsh or rLh did not stimulate large developmental changes in sexually undifferentiated meagre gonads.

Establishment of cell-lines stably expressing recombinant Japanese eel follicle-stimulating hormone and luteinizing hormone using CHO-DG44 cells: fully induced ovarian development at different modes

The gonadotropins (Gth), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), play central roles in gametogenesis in vertebrates. However, available information on their differential actions in teleost, especially in vivo, is insufficient. In this study, we established stable CHO-DG44 cell lines expressing long-lasting recombinant Japanese eel Fsh and Lh with extra O-glycosylation sites (Fsh-hCTP and Lh-hCTP), which were produced in abundance. Immature female eels received weekly intraperitoneal injections of Gths. Fsh-hCTP induced the entire ovarian development by 8 weeks from the beginning of injection; thus, the ovaries of most fish were at the migratory nucleus stage while the same stage was observed in eels after 4 weeks in the Lh-hCTP-treated group. In contrast, all pretreated and saline-injected eels were in the pre-vitellogenic stage. Gonadosomatic indices in the Fsh-hCTP-treated group were significantly higher than those in the Lh-hCTP group at the migratory nucleus stage because of the significantly higher frequency of advanced ovarian follicles. Ovarian mRNA levels of genes related to E2 production (cyp11a1, cyp17a1, cyp19a1, hsd3b, fshr, and lhr) were measured using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). All genes were induced by both Fsh-hCTP and Lh-hCTP, with a peak at either the mid- or late vitellogenic stages. Transcript abundance of cyp19a1 and fshr in the Lh-hCTP group were significantly higher than those in the Fsh-hCTP group, whereas no difference in the expression of other genes was observed between the groups. Fluctuations in serum levels of sex steroid hormones (estradiol-17β, 11-ketotestosterone, and testosterone) in female eels were comparable in the Fsh-hCTP and Lh-hCTP groups, thus increasing toward the maturational phase. Furthermore, the fecundity of the eels induced to mature by Fsh-hCTP was significantly higher than that induced by Lh-hCTP. These findings indicate that Fsh and Lh can induce ovarian development in distinctively different modes in the Japanese eel.

Neurohypophysial and paracrine vasopressinergic signaling regulates aquaporin trafficking to hydrate marine teleost oocytes

The dual aquaporin (Aqp1ab1/Aqp1ab2)-mediated hydration of marine teleost eggs, which occurs during oocyte meiosis resumption (maturation), is considered a key adaptation underpinning their evolutionary success in the oceans. However, the endocrine signals controlling this mechanism are almost unknown. Here, we investigated whether the nonapeptides arginine vasopressin (Avp, formerly vasotocin) and oxytocin (Oxt, formerly isotocin) are involved in marine teleost oocyte hydration using the gilthead seabream (Sparus aurata) as a model. We show that concomitant with an increased systemic production of Avp and Oxt, the nonapeptides are also produced and accumulated locally in the ovarian follicles during oocyte maturation and hydration. Functional characterization of representative Avp and Oxt receptor subtypes indicates that Avpr1aa and Oxtrb, expressed in the postvitellogenic oocyte, activate phospholipase C and protein kinase C pathways, while Avpr2aa, which is highly expressed in the oocyte and in the follicular theca and granulosa cells, activates the cAMP-protein kinase A (PKA) cascade. Using ex vivo, in vitro and mutagenesis approaches, we determined that Avpr2aa plays a major role in the PKA-mediated phosphorylation of the aquaporin subdomains driving membrane insertion of Aqp1ab2 in the theca and granulosa cells, and of Aqp1ab1 and Aqp1ab2 in the distal and proximal regions of the oocyte microvilli, respectively. The data further indicate that luteinizing hormone, which surges during oocyte maturation, induces the synthesis of Avp in the granulosa cells via progestin production and the nuclear progestin receptor. Collectively, our data suggest that both the neurohypophysial and paracrine vasopressinergic systems integrate to differentially regulate the trafficking of the Aqp1ab-type paralogs via a common Avp-Avpr2aa-PKA pathway to avoid competitive occupancy of the same plasma membrane space and maximize water influx during oocyte hydration.

Male germ cell proliferation and apoptosis in sexually immature meagre Argyrosomus regius (Asso, 1801) treated with recombinant follicle stimulating hormone

The meagre Argyrosomus regius (Asso, 1801) is a marine fish species that has an increasing aquaculture production in Europe. Lowering the age at maturity of hatchery-produced juveniles would support meagre aquaculture by reducing time between generations in selective breeding programs and reducing industrial costs for broodstock maintenance. The aim of this work was to assess the effects of a treatment with recombinant follicle stimulating hormone (rFsh), produced in ovarian cells of Chinese hamsters, on male germ cell proliferation and apoptosis in sexually immature meagre. The rFsh-treated fish had higher gonadosomatic index, larger seminiferous tubules, more abundant luminal spermatozoa, a lower density of anti-PCNA positive single A spermatogonia, a higher density of anti-PCNA positive spermatocysts and a lower incidence of germ cell apoptosis than control groups. The present study demonstrated the effectiveness of the produced rFsh in stimulating testis development and spermatogenesis in pre-pubertal meagre. Moreover, the rFsh treatment proved to be highly efficient in removing the apoptotic block of spermatogenesis observed in juvenile meagre, allowing spermatogonial survival and progress towards meiosis. The administration of rFsh did not stimulate spermatogonial self-renewal, a process whose control still needs to be elucidated.

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

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

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

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

Low sperm to egg ratio required for successful in vitro fertilization in a pair-spawning teleost, Senegalese sole (Solea senegalensis)

Cultured Senegalese sole (Solea senegalensis) breeders fail to spawn fertilized eggs. The implantation of large-scale in vitro fertilization protocols, to solve this problem, has been frustrated by low production of poor quality sperm. Cultured females were induced to ovulate with a 5 µg kg^-1 single injection of gonadotropin-releasing hormone agonist (GnRHa) and viable eggs (82.6 ± 9.2% fertilization) were stripped 41:57 ± 1:46 h after the injection. Sperm was collected from cultured males, diluted in modified Leibovitz and used fresh to fertilize the eggs. Males were not treated with hormones. A nonlinear regression, an exponential rise to a maximum (R = 0.93, p < 0.0001) described the number of motile spermatozoa required to fertilize a viable egg and 1617 motile spermatozoa were sufficient to fertilize 99 ± 12% (±95% CI) of viable eggs. Similar, spermatozoa egg^-1 ratios of 592 ± 611 motile spermatozoa egg^-1 were used in large-scale in vitro fertilizations (190 512 ± 38 471 eggs). The sperm from a single male (145 ± 50 µl or 8.0 ± 6.8 × 10⁸ spermatozoa) was used to fertilize the eggs. The mean hatching rate was 70 ± 14% to provide 131 540 ± 34 448 larvae per fertilization. The viability of unfertilized eggs stored at room temperature decreased gradually, and the sooner eggs were fertilized after stripping, the higher the viability of the eggs. The collection of sperm directly into a syringe containing modified Leibovitz significantly increased the percentage of motile spermatozoa (33.4 ± 12.2%) compared with other collection methods. The spz egg^-1 ratios for Senegalese sole were at the lower end of ratios required for fish. Senegalese sole have a pair-spawning reproductive behaviour characterized by gamete fertilization in close proximity with no sperm competition. The provision of a large-scale in vitro fertilization protocol (200 µl of sperm per 100 ml of eggs) will enable the industry to operate sustainably and implement breeding programmes to improve production.

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.

Kisspeptin Influences the Reproductive Axis and Circulating Levels of microRNAs in Senegalese Sole

Kisspeptin regulates puberty and reproduction onset, acting upstream of the brain–pituitary–gonad (HPG) axis. This study aimed to test a kisspeptin-based hormonal therapy on cultured Senegalese sole (G1) breeders, known to have reproductive dysfunctions. A single intramuscular injection of KISS2-10 decapeptide (250 µg/kg) was tested in females and males during the reproductive season, and gonad maturation, sperm motility, plasma levels of gonadotropins (Fsh and Lh) and sex steroids (11-ketotestosterone, testosterone and estradiol), as well as changes in small non-coding RNAs (sncRNAs) in plasma, were investigated. Fsh, Lh, and testosterone levels increased after kisspeptin injection in both sexes, while sperm analysis did not show differences between groups. Let7e, miR-199a-3p and miR-100-5p were differentially expressed in females, while miR-1-3p miRNA was up-regulated in kisspeptin-treated males. In silico prediction of mRNAs targeted by miRNAs revealed that kisspeptin treatment might affect paracellular transporters, regulate structural and functional polarity of cells, neural networks and intracellular trafficking in Senegalese sole females; also, DNA methylation and sphingolipid metabolism might be altered in kisspeptin-treated males. Results demonstrated that kisspeptin stimulated gonadotropin and testosterone secretion in both sexes and induced an unanticipated alteration of plasma miRNAs, opening new research venues to understand how this neuropeptide impacts in fish HPG axis.

Male reproductive dysfunction in Solea senegalensis: new insights into an unsolved question

Senegalese sole (Solea senegalensis) is a species with a high commercial value that exhibits a reproductive dysfunction in males born and raised in captivity (F1) that hinders their sustainable culture. The present study evaluates the sperm quality and dopaminergic pathway of males born in the wild environment and of F1 males. Traditional sperm analyses were performed, finding only significant differences in curvilinear velocity (VCL) and no significant differences in viability and total motility. No differences in global sperm methylation were observed either in spermatozoa or brain between the two groups (F1 and wild-born males). However, our results point to a different sperm molecular signature between wild fish and fish born in captivity, specifically the differential expression in miR-let7-d and miR-200a-5p between these two groups. miR-let7-d has been correlated with spermatogenesis and sex preferences, whereas the miR-200 family is implied in target innervation of dopaminergic neurons in zebrafish. When we analysed the dopaminergic pathway, no differences were found in terms of different mRNA expression of dopaminergic markers. However, some differences were detected in terms of tyrosine hydroxylase protein expression by western blot analysis, thus suggesting an altered post-transcriptional regulation in F1 males. The results of this study suggest that an altered sperm miRNA signature in F1 males could be one possible mode of transmission of reproductive dysfunction to the progeny.

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

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

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

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

Characterization of Sexual Trait Development in cyp17a1-Deficient Zebrafish

Cytochrome P450 (Cyp)17A1 has both 17α-hydroxylase and 17,20-lyase activities, which are involved in the steroidogenic pathway that produces androgens and estrogens. Previously, a phenotype of all-male cyp17a1-deficient zebrafish generated by transcription activatorlike effector nuclease has been reported. In the current study, the mechanisms relating to Cyp17a1 that are involved in the development of sexual traits, especially gonadal differentiation and testicular development, were characterized. We found that the cyp17a1-deficient fish at 3 months postfertilization (mpf) were all fertile males with normal testis and spermatogenesis but compromised male-typical mating behaviors and secondary sex characters (SSCs), including breeding tubercles, body pigmentation, and anal fin coloration. These results demonstrate that spermatogenesis and testicular development are not as susceptible to androgen deficiency compared with the formation of male-typical SSCs and mating behaviors in zebrafish. The differentiation of the juvenile ovary into the mature ovary failed during the critical sexual differentiation stage. This all-male phenotype of the cyp17a1-deficient fish could be restored with testosterone or estradiol treatment. For testicular development in cyp17a1-deficient fish, a gradually increasing number of spermatozoa and testis hypertrophy from 3 to 6 mpf were observed, accompanied by constitutively upregulated pituitary gonadotropin FSH subunit β (fshβ). The hypertrophic testis and enhanced spermatogenesis in the cyp17a1-deficient fish at 6 mpf could be effectively rescued by fshβ depletion. These results confirm that adequate estrogen is essential for maintaining ovarian differentiation, and they provide new insight into the role of FSHβ in male testicular development and spermatogenesis.

In silico analysis, temporal expression and gonadotropic regulation of receptors for follicle-stimulating hormone and luteinizing hormone in testis of spotted snakehead Channa punctata

This study in spotted snakehead Channa punctata was aimed to develop a comprehensive understanding of testicular gonadotropin receptors, from their sequence characterization, temporal expression to gonadotropic regulation, in seasonally breeding teleosts. A single form of follicle-stimulating hormone receptor (cpfshra) and luteinizing hormone/choriogonadotropin receptor (cplhcgr), was identified from testicular transcriptome data of C. punctata. Although deduced full-length protein sequence for cpFshra (694 amino acids) and cpLhcgr (691 amino acids) showed homology with their counterparts of other vertebrates, multiple insertion-deletion-substitution of residues suggest marked alterations in their structure and ligand specificity. The absolute quantification of testicular cpfshra and cplhcgr was estimated along the reproductive cycle following real-time PCR. The temporal expression profile showed highest testicular expression of both the gonadotropin receptors during resting phase. Their expression progressively decreased during preparatory and spawning phases concomitant with spermatogonial proliferation and differentiation and spermiogenesis. However, levels of cpfshra and cplhcgr sharply increased during post-spawning when seminiferous lobules were largely devoid of germ cells. To explore gonadotropic regulation of testicular cpfshra and cplhcgr, one group of fish of resting phase was administered with single dose of human chorionic gonadotropin (hCG; 5,000 IU/kg body mass) on day 0 and sacrificed on day 3 and day 5, while another group receiving two injections of hCG (day 0 and day 7) was sacrificed on day 14. The expression pattern of testicular gonadotropin receptors in hCG-treated fish sacrificed after 3, 5 and 14 days was similar to that of preparatory, spawning and postspawning phases, respectively. Likewise, testicular histology of hCG-treated fish sacrificed on day 3, day 5 and day 14 was comparable with that of preparatory, early spawning and late spawning phases, respectively. In light of the fact that gonadotropin receptors are largely expressed on somatic cells, an apparent decrease in testicular cpfshra and cplhcgr levels during preparatory and spawning phases or after 3 and 5 days from first hCG injection might not be due to downregulation of their expression. Rather, this could be due to dilution of somatic cell mRNA by large amount of germ cell mRNA. To verify this assumption, effect of hCG on plasma level of androgens was investigated employing enzyme-linked immunosorbent assay. A marked increase in plasma level of testosterone and 11-ketotestosterone was observed after hCG treatment in C. punctata. This would have been possible only when hCG upregulated the expression of testicular gonadotropin receptors.

New Insights Into the Role of Estrogens in Male Fertility Based on Findings in Aromatase-Deficient Zebrafish

It has been demonstrated that estrogens are indispensable for male fertility in mammals. Aromatase (encoded by CYP19) catalyzes the final step of estradiol biosynthesis. However, less is known about the role of aromatase in male fertility in nonmammalian species. Fish aromatase is encoded by two separate genes: the gonad-specific cyp19a1a and the brain-specific cyp19a1b. In a recent study, we used transcription activatorlike effector nucleases to systematically generate cyp19a1a and cyp19a1b mutant lines and a cyp19a1a;cyp19a1b double-mutant line in zebrafish and demonstrated that cyp19a1a was indispensable for sex differentiation. In this study, we focused on male fertility in these aromatase-deficient zebrafish. Our results showed that all aromatase-deficient male fish had normal fertility even at 1 year after fertilization. Interestingly, we observed more spermatozoa in the cyp19a1a and double-mutant males than in the wild-type and cyp19a1b mutant males. The whole-body androgen levels, follicle-stimulating hormone β and luteinizing hormone β protein levels in the pituitary, and transcript levels of genes known to be involved in spermatogenesis and steroidogenesis in the testes were significantly higher in the cyp19a1a mutant and aromatase double-mutant males than in the wild-type and cyp19a1b mutant males. These results might explain why more spermatozoa were observed in these fish. Collectively, our findings indicate that estrogens are not needed to achieve and maintain normal fertility in male zebrafish. This finding challenges the traditional view that estrogens are indispensable for male fertility.