Estradiol-induced mitogen-activated protein kinase (extracellular signal-regulated kinase 1 and 2) activity in the frog (Rana esculenta) testis

Differentiation of neonate mouse spermatogonia on two-dimensional and three-dimensional culture systems supplemented with d-Serine and Dizocilpine (MK-801)

N-methyl-d-aspartate (NMDA) modulates the spermatogenesis process through stimulating the steroid hormone biosynthesis. The aim of this study was to evaluate the effects of NMDA receptors agonists (d-Serine) and antagonists (MK801) on spermatogonia differentiation on decellularization testicular matrix (DTM) hydrogel scaffold. Four treatment groups were planned: 2D + D-Serine, 3D + D-Serine, 2D + MK801, and 3D + MK801. Results showed that cell viability was significantly decreased after 48 h in the 3D + D-Serine group and after 24 and 48 h in the 3D + MK801 group compared to the controls. The spermatogonia proliferation after two, four, and eight weeks was significantly increased in the 3D + D-Serine culture, while it was significantly reduced in the 2D + MK801 and 3D + MK801 groups after four and eight weeks. Real-time PCR results demonstrated that pre-meiotic gene (Plzf) expression was significantly increased only in the 3D + D-Serine culture compared to the control groups after four weeks of culture. The meiotic gene (Sycp3) expression was significantly increased in the 2D + D-Serine and 3D + D-Serine compared to the 2D controls after four and eight weeks. The post-meiotic gene (Tnp1) level in the 3D + D-Serine was significantly higher than the other groups. Flow-cytometry results indicated that the protein expression of Plzf (after four and eight weeks), Sycp3 (after eight weeks), and Tnp1 (after eight weeks) in the d-Serine-treated groups was significantly increased compared with the 2D control groups. There were not any significant changes in the gene expression of spermatogenic-related markers in MK801 culture media. However, a significant decrease in the protein levels of Plzf after eight weeks and Sycp3 after four and eight weeks was observed. In conclusion, the addition of NMDARs agonists (d-Serine) could be used to regulate the differentiation of spermatogonia in the 3D culture system.

d-aspartate and N-methyl-d-aspartate promote proliferative activity in mouse spermatocyte GC-2 cells

D-Aspartate (D-Asp) and its methylated form N-methyl-d-aspartate (NMDA) promote spermatogenesis by stimulating the biosynthesis of sex steroid hormones. d-Asp also induces spermatogonia proliferation directly by activating the ERK/Aurora B pathway. In the present study, a mouse spermatocyte-derived cell line (GC-2) which represents a stage between preleptotene spermatocyte and round spermatids was exposed to 200 μM d-Asp or 50 μM NMDA for 30 min, 2 h, and 4 h to explore the influence of these amino acids on cell proliferation and mitochondrial activities occurring during this process. By Western blotting analyses, the expressions of AMPAR (GluA1-GluA2/3 subunits), cell proliferation as well as mitochondria functionality markers were determined at different incubation times. The results revealed that d-Asp or NMDA stimulate proliferation and meiosis in the GC-2 cells via the AMPAR/ERK/Akt pathway, which led to increased levels of the PCNA, p-H3, and SYCP3 proteins. The effects of d-Asp and NMDA on the mitochondrial functionality of the GC-2 cells strongly suggested an active role of these amino acids in germ cell maturation. In both d-Asp- and NMDA-treated GC-2 cells mitochondrial biogenesis as well as mitochondrial fusion are increased while mitochondria fission is inhibited. Finally, the findings showed that NMDA significantly increased the expressions of the CII, CIII, CIV, and CV complexes of oxidative phosphorylation system (OXPHOS), whereas d-Asp induced a significant increase in the expressions only of the CIV and CV complexes. The present study provides novel insights into the mechanisms underlying the role of d-Asp and NMDA in promoting spermatogenesis.

Proliferative and Apoptotic Pathways in the Testis of Quail Coturnix coturnix during the Seasonal Reproductive Cycle

Simple Summary

The quail Coturnix coturnix exhibits an annual cycle of testis size, sexual steroid production, and spermatogenesis. The testicular levels of both 17β-estradiol (E₂) and androgens are higher during the reproductive period compared to the non-reproductive period, suggesting that estrogens act in synergy with the androgens for the initiation of spermatogenesis. Therefore, the present study aimed to investigate the estrogen responsive system in quail testis in relation to the reproduction seasons, with a focus on the molecular pathways activated in both active and regressive quail testes. The results indicated that estrogens participated in the activation of mitotic and meiotic events during the reproductive period by activating the ERK1/2 and Akt-1 pathways. In the non-reproductive period, when the E₂/ERα levels are low, ERK1/2 and Akt-1 pathways remain inactive and apoptotic events occur. Our results suggest that the activation or inhibition of these molecular pathways plays a crucial role in the physiological switch “on/off” of the testicular activity in male quail during the seasonal reproductive cycle.

Abstract

The quail Coturnix coturnix is a seasonal breeding species, with the annual reproductive cycle of its testes comprising an activation phase and a regression phase. Our previous results have proven that the testicular levels of both 17β-estradiol (E₂) and androgens are higher during the reproductive period compared to the non-reproductive period, which led us to hypothesize that estrogens and androgens may act synergistically to initiate spermatogenesis. The present study was, therefore, aimed to investigate the estrogen responsive system in quail testis in relation to the reproduction seasonality, with a focus on the molecular pathways elicited in both active and regressive quail testes. Western blotting and immunohistochemistry analysis revealed that the expression of ERα, which is the predominant form of estrogen receptors in quail testis, was correlated with E₂ concentration, suggesting that increased levels of E₂-induced ERα could play a key role in the resumption of spermatogenesis during the reproductive period, when both PCNA and SYCP3, the mitotic and meiotic markers, respectively, were also increased. In the reproductive period we also found the activation of the ERK1/2 and Akt-1 kinase pathways and an increase in second messengers cAMP and cGMP levels. In the non-reproductive phase, when the E2/ERα levels were low, the inactivation of ERK1/2 and Akt-1 pathways favored apoptotic events due to an increase in the levels of Bax and cytochrome C, with a consequent regression of the gonad.

miRNAs and Biomarkers in Testicular Germ Cell Tumors: An Update

Testicular germ cell tumors (TGCTs) are the leading form of solid cancer and death affecting males between the ages of 20 and 40. Today, their surgical resection and chemotherapy are the treatments of first choice, even if sometimes this is not enough to save the lives of patients with TGCT. As seen for several tumors, the deregulation of microRNAs (miRNAs) is also a key feature in TGCTs. miRNAs are small molecules of RNA with biological activity that are released into biological fluids by testicular cancer cells. Their presence, therefore, can be detected and monitored by considering miRNAs as diagnostic and prognostic markers for TGCTs. The purpose of this review is to collect all the studies executed on miRNAs that have a potential role as biomarkers for testicular tumors.

Celebrating 50+ years of research on the reproductive biology and endocrinology of the green frog: An overview

This issue is dedicated to the late Professor Giovanni Chieffi, and this article is an overview of the research on Comparative Endocrinology of reproduction using Rana esculenta (alias Pelophylax esculentus) as a model system. Starting from the early 1970s till today, a large quantity of work have been conducted both in the fields of experimental endocrinology and in the definition of the diffuse neuroendocrine system, with a major focus on the increasing role of regulatory peptides. The various aspects investigated concerned the histological descriptions of principal endocrine glands of the hypothalamic-pituitary-gonadal (HPG) axis, the localization and distribution in the HPG of several different substances (i.e. neurosteroids, hypothalamic peptide hormones, pituitary gonadotropins, gonadal sex steroids, and other molecules), the determination of sex hormone concentrations in both serum and tissues, the hormone manipulations, as well as the gene and protein expression of steroidogenic enzymes and their respective receptors. All together these researches, often conducted considering different periods of the annual reproductive cycle of the green frog, allowed to understand the mechanism of cascade control/regulation of the HPG axis of R. esculenta, characterizing the role of different hormones in the two sexes, and testing the hypotheses about the function of single hormones in different target organs. It becomes evident from the review that, in their simplest form, several features of this species are specular as compared to those of other vertebrate species and that reproduction in this frog species is either under endogenous multi-hormonal control or by a wide array of different factors. Our excursus of this research, spanning almost five decades, shows that R. esculenta has been intensively and successfully used as an animal model in reproductive endocrinology as well as several field studies such as those involving environmental concerns that focus on the effects of endocrine disruptors and other environmental contaminants.

Role of GPER-Mediated Signaling in Testicular Functions and Tumorigenesis

Estrogen signaling plays important roles in testicular functions and tumorigenesis. Fifteen years ago, it was discovered that a member of the G protein-coupled receptor family, GPR30, which binds also with high affinity to estradiol and is responsible, in part, for the rapid non-genomic actions of estrogens. GPR30, renamed as GPER, was detected in several tissues including germ cells (spermatogonia, spermatocytes, spermatids) and somatic cells (Sertoli and Leydig cells). In our previous review published in 2014, we summarized studies that evidenced a role of GPER signaling in mediating estrogen action during spermatogenesis and testis development. In addition, we evidenced that GPER seems to be involved in modulating estrogen-dependent testicular cancer cell growth; however, the effects on cell survival and proliferation depend on specific cell type. In this review, we update the knowledge obtained in the last years on GPER roles in regulating physiological functions of testicular cells and its involvement in neoplastic transformation of both germ and somatic cells. In particular, we will focus our attention on crosstalk among GPER signaling, classical estrogen receptors and other nuclear receptors involved in testis physiology regulation.

An up-date on novel molecular targets in testicular germ cell tumors subtypes

Testicular germ cell tumors (TGCTs) are the most frequent solid malignant tumors in men 20-34 years of age and the most frequent cause of death from solid tumors in this age group. In addition, the incidence of these tumors has significantly increased over the last few decades. Testicular germ cell tumors are classified into seminoma and nonseminoma germ cell tumors (NSGCTs). NSGCTs can be further divided into embryonal carcinoma, Teratoma, yolk sac tumor, and choriocarcinoma. There are noteworthy differences about therapy and prognosis of seminomas and nonseminoma germ cell tumors, even though both share characteristics of the primordial germ cells (PGCs). Many discovered biomarkers including HMGA1, GPR30, Aurora-B, estrogen receptor β, and others have given further advantage to discriminate between histological subgroups and could represent useful molecular therapeutic targets.

New Anti-Cancer Strategies in Testicular Germ Cell Tumors

Methods:

Bibliographic data from peer-reviewed research, patent and clinical trial literature, and around eighty papers and patents have been included in this review.

Results:

Our study reveals that several biomarkers are usefully utilized to discriminate among different histotypes. Moreover, we found new patents regarding testicular germ cell tumor treatments such as the expression of claudin 6, monoclonal antibody (Brentuximab Vedotin), immune checkpoint blockade (ICB) with the FDA-approved drugs pembrolizumab and nivolumab or the oncolytic virus Pelareorep, the combination of selective inhibitors of Aurora kinase.

Conclusion:

Finally, the pathogenesis of testicular germ cell tumor needs to be deeply understood so that it will improve data on stem cells, tumorigenesis and disease tumor management by more selective treatment.

Estradiol and reproduction in the South American toad Rhinella arenarum (Amphibian, Anura)

Rhinella arenarum is a South American toad with wide geographic distribution. Testes of this toad produce high amount of androgens during the non reproductive season and shift steroid synthesis from androgens to 5α-pregnanedione during the breeding. In addition, plasma estradiol (E₂) in males of this species shows seasonal variations but, since testes of R. arenarum do not express aromatase, the source of plasma E₂ remained unknown for several years. However, the Bidder's organ (BO), a structure located at one pole of each testis, is proposed to be the main source of E₂ in male's toads since it expresses several steroidogenic enzymes and is able to produce E₂ from endogenous substrates throughout the year. In addition, there were significant correlations between plasma E₂ and total activity of BO aromatase, and between plasma E₂ and the amount of hormone produced by the BO in vitro. In the toad, apoptosis induced by in vitro treatment with E₂ was mostly detected in spermatocytes during the breeding and in spermatids during the post-reproductive season, suggesting that this steroid has an important role in controlling spermatogenesis. However, in vitro treatment with E₂ had no effect on proliferation. This evidence suggests that the mechanism of action of E₂ on amphibian spermatogenesis is complex and more studies are necessary to fully understand the role of estrogens regulating the balance between cellular proliferation and apoptosis. In addition, in R. arenarum in vitro studies suggested that E₂ has no effect on CypP450c17 protein levels or enzymatic activity, while it reduces 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD/I) activity during the post reproductive season. As well, E₂ regulates FSHβ mRNA expression all over the year suggesting a down regulation process carried out by this steroid. The effect on LHβ mRNA is dual, since during the reproductive season estradiol increases the expression of LHβ mRNA while in the non-reproductive season it has no effect. In conclusion, the effect of E₂ on gonadotropins and testicular function is complex, not clearly understood and probably varies depending on the species. The aim of the current article is to review evidence on reproductive endocrinology and on the role of estradiol regulating reproduction in amphibians, with emphasis on the South American species Rhinella arenarum.

A comparative review on estrogen receptors in the reproductive male tract of non mammalian vertebrates

Estrogen receptors alpha (ERα) and beta (ERβ) are transcription factors known to be involved in the regulation of many complex physiological processes in mammals. They are expressed primarily in the reproductive tract of all vertebrates females, thus indicating important and conserved functions in female reproductive success. ERs are also present in physiological different tissues as bone, brain, liver, skin and adipose tissues, in both females and males. In the latter, ERs have been found also in the genital tract, supporting the findings of a complex role for estrogen in spermatogenesis and, more generally, in male reproduction. This review provides an overview and update on ERα and ERβ expression and synthesis in male reproductive tract of non-mammalian vertebrates, with focus on their role in germ cells proliferation, maturation and survival. Data from studies on fish, amphibians, reptiles and birds were collated and common or species-specific distribution highlighted. The widespread distribution of estrogen receptors in testicular cells and ducts of all vertebrates so far investigated suggests that whatever are the roles that estrogens may exert on these structures, they are phylogenetically conserved and are possibly related to the physiological support given to achieve male reproductive success.

Estrogen-induced inhibition of spermatogenesis in zebrafish is largely reversed by androgen

The hormonal regulation of spermatogenesis involves both gonadotropins and steroid hormones. Long-term in vivo exposure of adult zebrafish to estrogen impaired spermatogenesis associated with an androgen insufficiency, possibly induced by inhibiting gonadotropin release. Using this experimental model, we investigated if androgen treatment could enhance spermatogenesis, while maintaining the inhibition of gonadotropin release through continued estrogen exposure. Moreover, we also exposed animals to androgen alone, in order to examine androgen effects in the absence of estrogen-induced gonadotropin inhibition. Estrogen exposure depleted type B spermatogonia, meiotic and postmeiotic germ cells from the adult testis, but promoted the proliferation of type A undifferentiated spermatogonia, which accumulated in the testis. This change in germ cell composition was accompanied by reduced mRNA levels of those growth factors (e.g. insl3 and igf3) expressed by testicular somatic cells and known to stimulate spermatogonial differentiation in zebrafish. Additional androgen (11-ketoandrostenedione, which is converted to 11-ketotestosterone) treatment in vivo reversed most of the effects of estrogen exposure on spermatogenesis while insl3 and igf3 transcript levels remained suppressed. When androgen treatment was given alone, it promoted the production of haploid cells at the expense of spermatogonia, and increased transcript levels of some growth factor and hormone receptor genes, but not those of insl3 or igf3 We conclude that estrogen exposure efficiently inhibits spermatogenesis because it induces androgen insufficiency and suppresses gonadotropin-regulated growth factors known to stimulate germ cell differentiation. Moreover, our results suggest that androgens and the growth factors Insl3 and Igf3 stimulate spermatogenesis via independent pathways.

Of Oestrogens and Sperm: A Review of the Roles of Oestrogens and Oestrogen Receptors in Male Reproduction

The crucial role that oestrogens play in male reproduction has been generally accepted; however, the exact mechanism of their action is not entirely clear and there is still much more to be clarified. The oestrogen response is mediated through oestrogen receptors, as well as classical oestrogen receptors’ variants, and their specific co-expression plays a critical role. The importance of oestrogen signalling in male fertility is indicated by the adverse effects of selected oestrogen-like compounds, and their interaction with oestrogen receptors was proven to cause pathologies. The aims of this review are to summarise the current knowledge on oestrogen signalling during spermatogenesis and sperm maturation and discuss the available information on oestrogen receptors and their splice variants. An overview is given of species-specific differences including in humans, along with a detailed summary of the methodology outcome, including all the genetically manipulated models available to date. This review provides coherent information on the recently discovered mechanisms of oestrogens’ and oestrogen receptors’ effects and action in both testicular somatic and germ cells, as well as in mature sperm, available for mammals, including humans.

Effect of estradiol on apoptosis, proliferation and steroidogenic enzymes in the testes of the toad Rhinella arenarum (Amphibia, Anura)

Estrogens inhibit androgen production and this negative action on amphibian steroidogenesis could be related to the regulation of steroidogenic enzymes. Estrogens are also involved in the regulation of amphibian spermatogenesis by controlling testicular apoptosis and spermatogonial proliferation. The Bidder's organ (BO) is a structure characteristic from the Bufonidae family and in adult males of Rhinella arenarum it is one of the main sources of plasma estradiol (E2). The purpose of this study is to analyze the effect of E2 on testicular steroidogenic enzymes, apoptosis and proliferation in the toad R. arenarum. For this purpose, testicular fragments were treated during 24h with or without 2 or 20nM of E2. After treatments, the activities of cytochrome P450 17α-hydroxylase-C17-20 lyase (CypP450c17) and 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD/I) were measured by the transformation of radioactive substrates into products, and CypP450c17 expression was determined by Western blot analysis. Apoptosis in testicular sections was detected with a commercial fluorescent kit based on TUNEL method, and proliferation was evaluated by BrdU incorporation. Results indicate that E2 has no effect on CypP450c17 protein levels or enzymatic activity, while it reduces 3β-HSD/I activity during the post reproductive season. Furthermore, although E2 has no effect on apoptosis during the pre and the post reproductive seasons, it stimulates testicular apoptosis during the reproductive season, mostly in spermatocytes. Finally, E2 has no effect on testicular proliferation all year long. Taken together, these results suggest that E2 is involved in the regulation of testicular steroidogenesis and spermatogenesis.

High levels of GPR30 protein in human testicular carcinoma in situ and seminomas correlate with low levels of estrogen receptor-beta and indicate a switch in estrogen responsiveness

The G protein-coupled estrogen receptor (GPR30) is suggested to be involved in non-nuclear estrogen signalling and is expressed in a variety of hormone dependent cancer entities. It is well established that oestrogens are involved in pathological germ cell proliferation including testicular germ cell tumours. This study was performed to further elucidate the role of this receptor and the possible correlation with the estrogen receptor β in human testicular carcinoma in situ (CIS), seminomas and in GC1 and TCam-2 germ cell lines; in addition, a Tissue Micro-Array was built using the most representative areas from 25 cases of human testicular seminomas and 20 cases of CIS. The expression of ERβ and GPR30 were observed by using Western blot analysis in combination with immunocytochemistry and immunofluorescence analyses. Here, we show that down regulation of ERβ associates with GPR30 over-expression both in human testicular CIS and seminomas. In addition, we show that 17β-oestradiol induces the ERK1/2 activation and increases c-Fos expression through GPR30 associated with ERβ down-regulation in TCam-2 cell line. The present results suggest that exposure to oestrogens or oestrogen-mimics, in some as of yet undefined manner, diminishes the ERβ-mediated growth restraint in CIS and in human testicular seminoma, probably due to ERβ down-regulation associated to GPR30 increased expression indicating that GPR30 could be a potential therapeutic target to design specific inhibitors.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Recent advances in molecular and cell biology of testicular germ-cell tumors

Testicular germ-cell tumors (TGCTs) are the most frequent solid malignant tumors in men 20-40 years of age and the most frequent cause of death from solid tumors in this age group. TGCTs comprise two major histologic groups: seminomas and nonseminomas germ-cell tumors (NSGCTs). NSGCTs can be further divided into embryonal, carcinoma, Teratoma, yolk sac tumor, and choriocarcinoma. Seminomas and NSGCTs present significant differences in clinical features, therapy, and prognosis, and both show characteristics of the primordial germ cells. Many discovered biomarkers including OCT3/4, SOX2, SOX17, HMGA1, Nek2, GPR30, Aurora-B, estrogen receptor β, and others have given further advantages to discriminate between histological subgroups and could represent useful novel molecular targets for antineoplastic strategies. More insight into the pathogenesis of TGCTs is likely to improve disease management not only to better treatment of these tumors but also to a better understanding of stem cells and oncogenesis.

Role of estrogen receptors and g protein-coupled estrogen receptor in regulation of hypothalamus-pituitary-testis axis and spermatogenesis

Male reproductive function is under the control of both gonadotropins and androgens through a negative feedback loop that involves the hypothalamus, pituitary, and testis known as hypothalamus-pituitary-gonadal axis (HPG). Indeed, estrogens also play an important role in regulating HPG axis but the study on relative contribution to the inhibition of gonadotropins secretion exerted by the amount of estrogens produced within the hypothalamus and/or the pituitary or by the amount of circulating estrogens is still ongoing. Moreover, it is known that the maintenance of spermatogenesis is controlled by gonadotropins and testosterone, the effects of which are modulated by a complex network of locally produced factors, including estrogens. Physiological effects of estrogens are mediated by the classical nuclear estrogen receptor alpha and estrogen receptor beta, which mediate both genomic and rapid signaling events. In addition, estrogens induce rapid non-genomic responses through a membrane-associated G protein-coupled estrogen receptor (GPER). Ours and other studies reported that, in the testis, GPER is expressed in both normal germ cells and somatic cells and it is involved in mediating the estrogen action in spermatogenesis controlling proliferative and/or apoptotic events. Interestingly, GPER expression has been revealed also in the hypothalamus and pituitary. However, its role in mediating estrogen rapid actions in this context is under investigation. Recent studies indicate that GPER is involved in modulating gonadotropin-releasing hormone (GnRH) release as well as gonadotropins secretion. In this review, we will summarize the current knowledge concerning the role of estrogen/estrogen receptors molecular pathways in regulating GnRH, follicle-stimulating hormone, and luteinizing hormone release at the hypothalamic and pituitary levels in males as well as in controlling specific testicular functions such as spermatogenesis, focusing our attention mainly on estrogen signaling mediated by GPER.

GPER Signaling in Spermatogenesis and Testicular Tumors

Estrogens play important roles in the regulation of testis development and spermatogenesis. Moreover, several evidences suggest that estrogen signaling can be involved in testicular tumorigenesis. The physiological effects of estrogen are mediated by the classical nuclear estrogen receptors ESR1 and 2, which regulate both genomic and rapid signaling events. In the recent years, a member of the seven-transmembrane G protein-coupled receptor family, GPR30 (GPER), has been identified to promote estrogen action in target cells including testicular cells. Ours and other studies reported that GPER is expressed in normal germ cells (spermatogonia, spermatocytes, spermatids), somatic cells (Sertoli and Leydig cells), and it is also involved in mediating estrogen action during spermatogenesis and testis development. In addition, GPER seems to be involved in modulating estrogen-dependent testicular cancer cell growth. However, in this context, the effects of GPER stimulation on cell survival and proliferation appear to be cell type specific. This review summarizes the current knowledge on the functions regulated by estrogens and mediated by GPER in normal and tumor testicular cells.

Molecular biomarkers as potential targets for therapeutic strategies in human testicular germ cell tumors: an overview

Testicular germ cell tumors (TGCTs), the most common malignancy in males between 15 and 34 years of age and the most frequent cause of death from solid tumors in this age group. TGCTs can be subdivided into seminoma and non-seminoma germ cell tumors (NSGCTs), including embryonal cell carcinoma, choriocarcinoma, yolk sac tumor, and teratoma. Seminomas and NSGCTs do not only present distinctive clinical features, but they also show significant differences as far as therapy and prognosis are concerned. Seminomas are highly sensitive to both radiation and chemotherapy, with a good prognosis, non-seminomas are sensitive to platinum-based combination chemotherapy and are less susceptible to radiation, with the exception of teratomas. The different therapeutic outcome might be explained by inherent properties of the cells from which testicular neoplasia originate. The unique treatment sensitivity of TGCTs is unexplained so far, but it is likely to be related to intrinsic molecular characteristics of the PGCs/gonocytes, from which these tumors originate. Many discovered bio-markers including OCT3/4, SOX2, SOX17, HMGA1, HMGA2, PATZ1, GPR30, Aurora B, estrogen receptor β, and others have given further advantages to discriminate between histological subgroups. In addition, therapeutic approaches for the treatment of TGCTs have been proposed: humanized antibodies against receptors/surface molecules on cancer cells, inhibitors of serine-threonine, and tyrosine kinases, and others. The mini-review will be an overview on the molecular alterations identified in TGCTs and on novel targeted antineoplastic strategies that might help to treat chemotherapy resistant TGCTs.

Characterization and seasonal changes in LHβ and FSHβ mRNA of Rhinella arenarum (Amphibia, Anura)

In anurans, two types of gonadotropins were described in several species of Ranidae and Pipidae families but only in one of the Bufonidae family. Rhinella arenarum is a bufonid that have the lowest concentration of plasma androgens during the breeding. The objective of this paper was to characterize the cDNA sequence of β subunit of LH and FSH from toad pituitary and study seasonal variation in gonadotropins mRNA using quantitative real-time RT-PCR. The LHβ cDNA is a 636 bp sequence containing an open reading frame (ORF), 45 bp of 5'-untranslated region (UTR) and 174 bp of 3'-UTR. The ORF encodes for a signal peptide of 26 amino acids and a mature protein of 113 amino acids with one N-glycosylation site at the 34th position. The FSHβ cDNA sequence is a 535 bp fragment containing an ORF, 8 bp of 5'-UTR and 152 bp of 3'-UTR. The ORF encodes for a signal peptide of 20 amino acids and a mature protein of 104 amino acids with two N-glycosylation sites at 25th and 42nd positions. Multiple alignments of aminoacid deduced sequences of LHβ and FSHβ (teleosts, amphibians, birds, mammals) showed that all the tetrapods studied conserve 12 cysteins and one (LH) or two (FSH) N-Glycosylation sites. LHβ is closer to teleosts than to mammals and birds while FSHβ is closer to mammals. The analysis of seasonal changes in LHβ and FSHβ mRNA indicates that transcript levels have seasonal variations and that the profile of androgens is opposite to that of the gonadotropins mRNA.

Immunoexpression of aromatase and estrogen receptors β in stem spermatogonia of bullfrogs indicates a role of estrogen in the seasonal spermatogonial mitotic activity

Bullfrog stem spermatogonia, also named primordial germ cells (PGCs), show strong testosterone immunolabeling in winter, but no or weak testosterone immunoexpression in summer. Thus, the role of testosterone in these cells needs to be clarified. In this study, we proposed to evaluate whether PGCs express aromatase and estrogen receptors, and verify a possible role of estrogen in PGCs seasonal proliferation. Testes of male adult bullfrogs, collected in winter (WG) and summer (SG), were fixed and embedded in historesin, for quantitative analysis, or paraffin for immunohistochemistry (IHC). The number of haematoxylin/eosin stained PGCs/lobular area was obtained. Proliferating cell nuclear antigen (PCNA), aromatase, estrogen receptor β (ERβ) and PCNA/ERβ double immunolabeling were detected by IHC. The number of PCNA-positive PGCs and the histological score (HSCORE) of aromatase and ERβ immunolabeled PGCs were obtained. Although the number of PGCs increased significantly in WG, a high number of PCNA-positive PGCs was observed in summer. Moreover, aromatase and ERβ HSCORE was higher in SG than WG. The results indicate that PGCs express a seasonal proliferative activity; the low mitotic activity in winter is related to the maximal limit of germ cells which can be supported in the large lobules. In SG, the increased ERβ and aromatase HSCORE suggests that testosterone is converted into estrogen from winter to summer. Moreover, the parallelism between the high PGCs mitotic activity and ERβ immunoexpression suggest a participation of estrogen in the control of the PGCs seasonal proliferative activity which guarantee the formation of new germ cysts from summer to next autumn.

Anchoring ethinylestradiol induced gene expression changes with testicular morphology and reproductive function in the medaka

Environmental estrogens are ubiquitous in the environment and can cause detrimental effects on male reproduction. In fish, a multitude of effects from environmental estrogens have been observed including altered courting behavior and fertility, sex reversal, and gonadal histopathology. However, few studies in fish assess the impacts of estrogenic exposure on a physiological endpoint, such as reproduction, as well as the associated morphologic response and underlying global gene expression changes. This study assessed the implications of a 14 day sub-chronic exposure of ethinylestradiol (EE2; 1.0 or 10.0 µg/L EE2) on male medaka fertility, testicular histology and testicular gene expression. The findings demonstrate that a 14 day exposure to EE2 induced impaired male reproductive capacity and time- and dose-dependent alterations in testicular morphology and gene expression. The average fertilization rate/day following the exposure for control, 1.0 and 10.0 µg/L EE2 was 91.3% (±4.4), 62.8% (±8.3) and 28.8% (±5.8), respectively. The testicular morphologic alterations included increased germ cell apoptosis, decreased germinal epithelium and thickening of the interstitium. These changes were highly associated with testicular gene expression changes using a medaka-specific microarray. A pathway analysis of the differentially expressed genes emphasized genes and pathways associated with apoptosis, cell cycle and proliferation, collagen production/extracellular matrix organization, hormone signaling, male reproduction and protein ubiquitination among others. These findings highlight the importance of anchoring global gonadal gene expression changes with morphology and ultimately with tissue/organ function.

Recent advances in the biology of germ cell tumors: implications for the diagnosis and treatment

Testicular germ cell tumors (TGCT), are the most frequent solid malignant tumors in men 20-40 yr of age, and the most frequent cause of death from solid tumors in this age group. TGCT can be subdivided into seminoma and nonseminoma germ cell tumors (NSGCT), including embryonal cell carcinoma, choriocarcinoma, yolk sac tumor, and teratoma. Seminomas and NSGCT do not only present distinctive clinical features, but they also show significant differences as far as therapy and prognosis are concerned. Many novel markers have given further advantages to discriminate between histological subgroups. In addition, therapeutic approaches for the treatment of TGCT have been proposed: humanized antibodies against receptors/surface molecules on cancer cells, inhibitors of serine-threonine, and tyrosine kinases, and others. The review will focus on the recent advances in the research of molecular alterations identified in TGCT and on novel targeted anti-neoplastic strategies that might help to treat chemotherapy-resistant TGCT.

Induced synthesis of P450 aromatase and 17β-estradiol by D-aspartate in frog brain

D-Aspartic acid is an endogenous amino acid occurring in the endocrine glands as well as in the nervous system of various animal phyla. Our previous studies have provided evidence that D-aspartate plays a role in the induction of estradiol synthesis in gonads. Recently, we have also demonstrated that D-aspartic acid induces P450 aromatase mRNA expression in the frog (Pelophylax esculentus) testis. P450 aromatase is the key enzyme in the estrogen synthetic pathway and irreversibly converts testosterone into 17β-estradiol. In this study, we firstly investigated the immunolocalisation of P450 aromatase in the brain of P. esculentus, which has never previously been described in amphibians. Therefore, to test the hypothesis that d-aspartate mediates a local synthesis of P450 aromatase in the frog brain, we administered D-aspartate in vivo to male frogs and then assessed brain aromatase expression, sex hormone levels and sex hormone receptor expression. We found that D-aspartate enhances brain aromatase expression (mRNA and protein) through the CREB pathway. Then, P450 aromatase induces 17β-estradiol production from testosterone, with a consequent increase of its receptor. Therefore, the regulation of d-aspartate-mediated P450 aromatase expression could be an important step in the control of neuroendocrine regulation of the reproductive axis. Accordingly, we found that the sites of P450 aromatase immunoreactivity in the frog brain correspond to the areas known to be involved in neurosteroid synthesis.

The novel estrogen receptor, G protein-coupled receptor 30, mediates the proliferative effects induced by 17beta-estradiol on mouse spermatogonial GC-1 cell line

Many studies have indicated that estrogens could have a role in the regulation of testicular function. However, it remains uncertain whether estrogens are able to directly activate signaling pathways in male germ cells. Estrogens are synthesized by the enzyme aromatase and classically act by binding to estrogen receptors (ERs)-alpha and ERbeta. Knockout mice for both receptor isoforms exhibit a testicular phenotype that is less severe than aromatase knockout mice, suggesting the existence of an estrogen-binding receptor that may compensate for the lack of ERs. Recently studies using estrogen-sensitive tumor cell lines have demonstrated that the G-protein-coupled receptor (GPR)-30 binds and mediates estrogen action through the activation of the epidermal growth factor receptor (EGFR)/ERK/fos transduction pathway. The present study investigated the ability of 17beta-estradiol (E2) to activate this pathway in the mouse spermatogonial cell line (GC-1). Using the GC-1 cell line as a model system, we demonstrated that GC-1 cells express GPR30 and ERalpha but not ERbeta. E2, the selective GPR30 agonist G1, and the selective ERalpha agonist 4,4',4''-(4-propyl-[1H]pyrazole-1,3,5-triyl) trisphenol activated the rapid ERK1/2-fos signaling cascade. This response was abrogated by the EGFR inhibitor AG1478, ERK inhibitor PD98059 and ER inhibitor ICI 182780, or by silencing GPR30 expression. Moreover, E2 and G1 up-regulated cyclin D1 expression and GC-1 cell proliferation. Our results indicate for the first time that estrogens, through a cross talk between GPR30 and ERalpha, activate the rapid EGFR/ERK/fos pathway, which in turn stimulate mouse GC-1 cell proliferation. Further studies to elucidate the involvement of rapid estrogen signaling pathways in the regulation of male fertility are warranted.

Endocannabinoid System in Frog and Rodent Testis: Type-1 Cannabinoid Receptor and Fatty Acid Amide Hydrolase Activity in Male Germ Cells1

N-arachidonoylethanolamide (anandamide [AEA]) is the main endocannabinoid described to date in the testis. It exerts its effects through the activation of G-protein coupled cannabinoid receptors (CNR). However, the activity of AEA in controlling male reproduction is still poorly known. Here we provide direct evidence on the presence of the "endocannabinoid system," constituted by type-1 cannabinoid receptor (CNR1) and fatty acid amide hydrolase (FAAH), in the frog Rana esculenta testis demonstrating its expression in tubular compartment. In fact, during the annual reproductive cycle, both proteins increase in September, when the appearance of spermatids (SPT) occurs. Immunocytochemistry confirms their localization in germ cells and, in particular, in elongated SPT. Signals are still present in spermatozoa (SPZ), as demonstrated by Western blot analysis. Furthermore, the activation of CNR1 reduces sperm motility. Comparative research, carried out using mouse and rat SPZ, definitely indicates that the endocannabinoid system operates in SPZ of phylogenetically distant species. A conserved physiological role of endocannabinoid system in controlling the inhibition of sperm motility is suggested.

Estrogen-induced Akt-1 activity in the lizard (Podarcis s. sicula) testis

There are always more evidences indicating that 17beta-estradiol (E2) is to be necessary for normal male fertility. Here we report the expression of the most ubiquitously expressed member of the akt family of genes, akt1, in the lizard (Podarcis s. sicula) testis. We have used a nonmammalian vertebrate model (the lizard P. s. sicula) to investigate the regulation of the serine/threonine kinase Akt activity, implicated in the control of cell proliferation, survival, and metabolism, in the testis during the annual sexual cycle and to study whether E2 exerts a role in the spermatogenesis through Akt-1 activity. Immunocytochemistry analysis show that Akt-1 proteins are present in the spermatogonia (SPG), and spermatocytes (SPC), and spermatids (SPT). The annual E2 profile shows a progressive increase during the active spermatogenesis (from April to June) and a peak in the month of August (spermatogonial mitosis). In parallel, Akt-1 (molecular weight 60 kDa) are highly phosphorylated during the period of active spermatogenesis and in post-refractory period (August) compared with the winter stasis (from November to March). Present results demonstrate that E2 treatment induces the activation of Akt-1, and this effect is counteracted by the anti-estrogen ICI 182-780.

Alteration of the hypothalamic-pituitary-gonadal axis in estrogen- and androgen-treated adult male leopard frog, Rana pipiens

BACKGROUND

Gonadal steroids, in particular 5 alpha-dihydrotestosterone (DHT) and 17 beta-estradiol (E2), have been shown to feed back on the hypothalamic-pituitary-gonadal (HPG) axis of the ranid frog. However, questions still remain on how DHT and E2 impact two of the less-studied components of the ranid HPG axis, the hypothalamus and the gonad, and if the feedback effects are consistently negative. Thus, the goal of the study was to examine the effects of DHT and E2 upon the HPG axis of the gonadally-intact, sexually mature male leopard frogs, Rana pipiens.

METHODS

R. pipiens were implanted with silastic capsules containing either cholesterol (Ch, a control), DHT, or E2 for 10 or 30 days. At each time point, steroid-induced changes in hypothalamic GnRH and pituitary LH concentrations, circulating luteinizing hormone (LH), and testicular histology were examined.

RESULTS

Frogs implanted with DHT or E2 for 10 days did not show significant alterations in the HPG axis. In contrast, frogs implanted with hormones for 30 days had significantly lower circulating LH (for both DHT and E2), decreased pituitary LH concentration (for E2 only), and disrupted spermatogenesis (for both DHT and E2). The disruption of spermatogenesis was qualitatively similar between DHT and E2, although the effects of E2 were consistently more potent. In both DHT and E2-treated animals, a marked loss of all pre-meiotic germ cells was observed, although the loss of secondary spermatogonia appeared to be the primary cause of disrupted spermatogenesis. Unexpectedly, the presence of post-meiotic germ cells was either unaffected or enhanced by DHT or E2 treatment.

CONCLUSIONS

Overall, these results showed that both DHT and E2 inhibited circulating LH and disrupted spermatogenesis progressively in a time-dependent manner, with the longer duration of treatment producing the more pronounced effects. Further, the feedback effects exerted by both steroid hormones upon the HPG axis were largely negative, although the possibility exists for a stimulatory effect upon the post-meiotic germ cells.

Changes in JNK1 activity in the frog (Rana esculenta) testis

Several lines of evidences support a key role of mitogen-activated protein kinases (MAPK) in male fertility. It has been used as a non-mammalian vertebrate model, the frog Rana esculenta, to investigate the regulation of Jun amino-terminal kinase 1 (JNK1) activity in the testis in two different periods of the annual reproductive cycle: winter stasis and breeding season. JNK1 protein was localized by immunohistochemistry in the cytoplasm and nucleus of spermatogonia (SPG) and spermatocytes (SPC) during all the year. Immunoprecipitation analysis of JNK1 clearly shows that this isoform presents a strong phosphorylation status (thr183/Tyr185) in the breeding period, in contrast with only very low activity during the winter stasis. Simultaneously, during the breeding period c-Jun protein is highly phosphorylated on Ser-63. These data suggest that the increase of JNK1 activity, with strong c-Jun phosphorylation (Ser-63) during the breeding period, could be the signal of increasing transcriptional activity in the frog testis.

Environmental influence on testicular MAP kinase (ERK1) activity in the frog Rana esculenta

Recent studies suggest a role for ERK1 in the regulation of spermatogonial proliferation. In this report the frog Rana esculenta, a seasonal breeder, was used as a model to study the possible effect on ERK1 of photoperiod and temperature. Adult male R. esculenta were subjected to several combinations of light and temperature at different times of the year to elucidate the regulation of ERK1 testicular activity in the spermatogonial proliferation by these environmental factors.

Western blot analysis shows that under controlled experimental conditions an increase of temperature and photoperiod in November, characterized by a decrease in primary spermatogonial mitosis, induces ERK1 activity and spermatogonial proliferation, as confirmed using the proliferating cellular nuclear antigen (PCNA) as an early molecular marker. In contrast, a decrease in temperature and photoperiod in March, with an increase of primary spermatogonial mitosis, impairs ERK1 activity and spermatogonial proliferation.

In conclusion, our data clearly show for the first time in a non-mammalian vertebrate that the temperature and the photoperiod exert a role in the spermatogonial proliferation via ERK1 activity.

Effects of steroid hormones on spermatogenesis and GnRH release in male Leopard frogs, Rana pipiens

Several lines of evidence suggest reproduction in the ranid frogs is potently regulated by the gonadal steroids, in particular 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E(2)), and a non-gonadal steroid, the stress hormone corticosterone (Cort). Little is known about how these steroid hormones act upon the GnRH system to regulate the downstream reproductive events. We address these gaps in our knowledge by investigating the effects of Cort, E(2), and DHT administration on the in vitro release of GnRH and on the spermatogenesis of adult male leopard frog, Rana pipiens. R. pipiens were implanted for 20 days with silastic capsules containing cholesterol (Ch; control), Cort, E(2), or DHT. Upon sacrifice, acute hypothalamic explants were cultured and measured for GnRH release, and testes processed for histological analysis. Although only E(2) implant significantly reduced the gonadosomatic index, all three steroid hormones altered spermatogenesis. Cort modestly but significantly reduced the presence of spermatids. The effects of E(2) and DHT were both stimulatory and inhibitory, depending on the stage of spermatogenesis. None of the steroid hormones altered baseline GnRH release. Interestingly, only E(2) significantly stimulated veratridine-induced GnRH release, suggesting E(2) treatment increased the releasable pool of GnRH and/or enhance the excitability of GnRH neurons. In sum, this is the first study to report the direct measurement of GnRH secretion in a poikilothermic tetrapod. Our results revealed potent but sometimes paradoxical effects of steroid hormones, especially E(2), on the reproductive regulation of the male R. pipiens.

Dietary diethylstilbestrol but not genistein adversely affects rat testicular development

Isoflavones, including genistein, contribute to the health benefits of a soy diet. However, the estrogenic activity of genistein suggests that there may be adverse effects on reproductive tract development. We investigated the potential of exposure to genistein (250 and 1000 mg/kg diet) and the synthetic estrogen and known male reproductive toxicant, diethylstilbestrol (DES, 75 micro g/kg diet) from d 21 to d 35 to alter rat testicular development. These dietary genistein concentrations resulted in serum concentrations that approximate or exceed concentrations in Asian men on a soy-containing diet. DES exposure reduced testicular weights, altered morphology and increased apoptosis in the seminiferous tubules. The effects of DES were accompanied by a reduction in androgen receptor (AR) protein concentrations, predominantly localized to Sertoli cells. Increased expression and immunostaining for the epidermal growth factor receptor (EGFR) and its downstream extracellular signal-regulated kinases (ERK) 1 and 2 in spermatagonia and spermatocytes were also observed. Immunohistochemical analysis of serial sections demonstrated that greater EGFR expression correlated with increased cellular proliferation, rather than apoptosis, and reflected impaired testicular development in DES-treated rats. Genistein in the diet did not significantly alter testicular weights, morphology, AR, EGFR and ERK expression or apoptosis. However, the higher concentration significantly reduced testicular aromatase activity, an effect that may contribute to reduced estrogen concentrations and suppression of prostate cancer development. These data suggest that exposure to genistein in the diet at concentrations that result in serum concentrations at the upper limit of humans consuming soy products does not adversely affect testicular development, but may provide health benefits.

In vitro hCG and human recombinant FSH actions on testicular steroidogenesis in the toad Bufo arenarum

In order to study the regulation of testicular steroidogenesis in the toad Bufo arenarum, the effect of gonadotropins (hCG and hrFSH) on steroidogenic enzymes was determined using an in vitro system. 3beta-Hydroxysteroid dehydrogenase/isomerase activity was not affected by any of the gonadotropins, at any of the concentrations used. In contrast, 5alpha-reductase activity was strongly reduced by both hCG and hrFSH. Human chorionic gonadotropin inhibited the activity of cytochrome P450 17alpha-hydroxylase-C(17-20) lyase (P450(c17)), only at the highest concentration used, while hrFSH strongly reduced P450(c17) activity at all the doses assayed. In conclusion, these data suggest that LH (hCG) and FSH regulate steroidogenic enzymes such as 5alphaRed and P450(c17). The results also suggest that FSH could be involved in the regulation of the change in steroidogenesis undergone by the testis during the breeding season. In turn, the inhibition of P450(c17) activity could result in a reduction of androgen production and an increment of C21 steroids.

The amphibian testis as model to study germ cell progression during spermatogenesis

Testicular morphology of vertebrate testis indicates requirement of local control. In urodeles, the testis is organized in lobes of increasing maturity throughout the cephalocaudal axis. The anuran testis is organized in tubules. Spermatogenesis occurs in cysts composed by Sertoli cells enveloping germ cells at synchronous stages. Moreover, in numerous species germ cell progression lasts a year which defines the sexual cycle. Due to the above quoted features, research on factors regulating germ cell progression in amphibians may reach greater insight as compared with mammalian animal models. In particular, studies on endocrine and paracrine/autocrine factors involved in the regulation of germ cell functions reveal that fos activation and a J protein, previously specifically found in mouse testis, exert an important role in spermatogonial proliferation and maturation of post-meiotic stages, respectively.