17 beta-estradiol induces spermatogonial proliferation through mitogen-activated protein kinase (extracellular signal-regulated kinase 1/2) activity in the lizard (Podarcis s. sicula)

Seasonal spermatogenesis in the red-eared slider (Trachemys scripta elegans): The roles of GnRH, actin cytoskeleton, and MAPK

Reproduction is the key to the ecological invasion of alien species. As an invasive species, the characteristic and regularity of red-eared slider (Trachemys scripta elegans) spermatogenesis is an index for evaluating reproduction and ecological adaptation. Here, we investigated the characteristics of spermatogenesis i.e., the gonadosomatic index (GSI), plasma reproductive hormone levels, and the histological structure of testes by HE and TUNEL staining, and then RNA-Seq in T. s. elegans. The histomorphological evidence confirmed that seasonal spermatogenesis in T. s. elegans has four successive phases: quiescence (December-May of the following year), early-stage (June-July), mid-stage (August-September), and late-stage (October-November). In contrast to 17β-estradiol, testosterone levels were higher during quiescence (breeding season) compared to mid-stage (non-breeding season). Based on RNA-seq transcriptional analysis, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were used to analyze the testis in the quiescent and mid-stage. Our study found that circannual spermatogenesis is regulated by interactive networks including gonadotropin-releasing hormone (GnRH) secretion, regulation of actin cytoskeleton, and MAPK signaling pathways. Moreover, the number of genes associated with proliferation and differentiation (srf, nr4a1), cell cycle (ppard, ccnb2), and apoptosis (xiap) were up-regulated in the mid-stage. With the maximum energy saving, this seasonal pattern of T. s. elegans determines optimal reproductive success and thus adapts better to the environment. These results provide the basis for the invasion mechanism of T. s. elegans and lay the foundation for deeper insight into the molecular mechanism of seasonal spermatogenesis in reptiles.

The Italian Wall Lizard Podarcis siculus as a Biological Model for Research in Male Reproductive Toxicology

Spermatogenesis is a genetically driven differentiation process that occurs in the testis and leads to the formation of spermatozoa. This process is extensively studied in several experimental models, particularly in vertebrates that share the morphological structure and functionality of the mammalian testis. Although reptiles are not generally considered biological models, the lizard Podarcis siculus has represented a suitable organism for the study of spermatogenesis over the years. In this lizard, the process of spermatogenesis is regulated by the interaction between systemic factors such as gonadotropins and local factors, i.e., molecules produced by the somatic and germinal cells of the testis. Many exogenous substances are able to alter the production of these regulative factors, thus altering the course of spermatogenesis, and P. siculus has proven to be an excellent model for studying the effects of various endogenous or exogenous substances on mechanisms underlying spermatogenesis. This review summarizes the available data on the effects of different substances on the control of spermatogenesis, highlighting the induced morphological and molecular alterations. Overall, the data show that sex hormone levels as well as the final stages of spermatogenesis are most affected by an imbalance of endogenous compounds or contamination by environmental pollutants. This is helpful for the male individual, since the damage, not affecting the spermatogonial stem cells, can be considered transient and not irreversible.

Growth and gonadal development retardations after long-term exposure to estradiol in little yellow croaker, Larimichthys polyactis

Endocrine disrupting chemicals (EDCs) including 17β-estradiol (E2) are widely distributed in the aquatic environment and are known to negatively affect the reproductive system of many animals, including fish. EDCs leading to feminization, altered sex ratio and reduced fecundity, it is possibly posing potential risks to the ecosystems. To investigate the potentially toxic effects of E2 exposure on little yellow croaker (Larimichthys polyactis, L. poliactis) who have a unique gonadal development pattern that males undergo a hermaphroditic stage. An experiment was set up where L. poliactis were maintained in tanks and exposed to E2 concentrations of 10 μg/L or no E2 exposure (the ethanol and control groups) from 30 to 90 days post-hatching (dph). After exposure, the E2 withdrawal and continual cultured to 150 and 365 dph. The morphological and histological analyses were used to compare the changes in the fish body and gonad under E2 exposure. The results showed that E2 exposure caused three major phenotypes at 30 and 60 days after treatment (dat), including ovary, ovotestis and gonadal development retardation compared with the control groups. The average ratio of these three phenotypes is 60.6%, 11.97% and 27.43%, respectively. The body length and weight of E2 exposure groups were repressed during the E2 exposure period, while it can recover after E2 withdrawal. However, the gonadal development (Gonadosomatic Index) of E2 exposure groups testis were retarded at 60 dat and doesn't recover until 365 dph. The sex determination/differentiation-related genes erα, erβI, erβII, fshβ and cyp11b2 were significantly decreased in E2-exposure male fish. This research highlights the E2 leads to feminization, disrupts testis maturation and spermatogenesis, this effect persisted into the stage of sexual maturity. Collectively, our findings provide insights into the molecular mechanisms underlying E2 disturbance of a marine economic fish reproduction.

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.

Alkyphenol Exposure Alters Steroidogenesis in Male Lizard Podarcis siculus

BACKGROUND

Nonylphenol (NP) and Octylphenol (OP) are persistent and non-biodegradable environmental contaminants classified as endocrine disruptor chemicals (EDCs). These compounds are widely used in several industrial applications and present estrogen-like properties, which have extensively been studied in aquatic organisms. The present study aimed to verify the interference of these compounds alone, and in mixture, on the reproductive cycle of the male terrestrial vertebrate Podarcis siculus, focusing mainly on the steroidogenesis process.

METHODS

Male lizards have been treated with different injections of both NP and OP alone and in mixture, and evaluation has been carried out using a histological approach.

RESULTS

Results obtained showed that both substances are able to alter both testis histology and localization of key steroidogenic enzymes, such as 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β- hydroxysteroid dehydrogenase (17β-HSD) and P450 aromatase. Moreover, OP exerts a preponderant effect, and the P450 aromatase represents the major target of both chemicals.

CONCLUSIONS

In conclusion, NP and OP inhibit steroidogenesis, which in turn may reduce the reproductive capacity of the specimens.

Spermatogenesis and regulatory factors in the wall lizard Podarcis sicula

Spermatogenesis is an extraordinarily complex process, regulated by several factors, which leads to the differentiation of spermatogonia into spermatozoa. Among vertebrates, several reports have been focused on the lizard Podarcis sicula, a seasonal breeder and a good model for the study of reproductive processes. The goal of this review is to resume all the available data about systemic and above all local control factors involved in the control of P. sicula testicular activity. During the seasonal reproductive cycle, the variation of the expression levels of these factors determines significant variations that induce the activation or blocking of spermatogenesis. The data supplied in this review, in addition to analyze the current literature regarding the main actors of Podarcis sicula spermatogenesis, will hopefully provide a basic model that can be used for further studies on the intratesticular interaction between molecular factors that control spermatogenesis.

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.

Agonist and antagonist NMDA receptor effect on cell fate during germ cell differentiation and regulate apoptotic process in 3D organ culture

In this work, agonist and antagonist N-methyl-D-aspartate (NMDA) receptor activation effect on cell fate during germ cell differentiation and regulate apoptotic process in 3D organ culture were studied. Afterwards, the effect of D-serine, retinoic acid (RA) and MK801 on spermatogenesis development was investigated. The animals were injected a single dose (40 mg/kg, intraperitoneal) of busulfan. After confirming the model, ten 5-day-old NMRI mice were used as spermatogonial stem cells (SSCs) transplantation donors. The SSCs were confirmed by detecting the promyelocytic leukaemia zinc finger (PLZF) protein. Then, tissue culture of the azoospermia model which had received SSCs was performed in various conditions (seven groups). The apoptosis markers levels of cells were significantly decreased in differentiation media containing RA and serine. In contrast, the expression of apoptotic markers including caspase 3, caspase 9 and Bax was increased in the presence of MK801. In conclusion, a new in vitro system capable of producing mature spermatozoa was developed that would be useful for investigating the medicinal effects of agents on the male reproductive system. Also, a comparison of spermatogenesis development in different media revealed that the presence of D-serine and RA (retinoic acid) in the culture medium has a positive effect on spermatogenesis.

AMPA receptor expression in mouse testis and spermatogonial GC-1 cells: A study on its regulation by excitatory amino acids

Excitatory amino acids (EAAs) are found present in the nervous and reproductive systems of animals. Numerous studies have demonstrated a regulatory role for Glutamate (Glu), d-aspartate ( d-Asp) and N-methyl- d-aspartate (NMDA) in the control of spermatogenesis. EAAs are able to stimulate the Glutamate receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Here in, we assess expression of the main AMPAR subunits, GluA1 and GluA2/3, in the mouse testis and in spermatogonial GC-1 cells. The results showed that both GluA1 and GluA2/3 were localized in mouse testis prevalently in spermatogonia. The subunit GluA2/3 was more highly expressed compared with GluA1 in both the testis and the GC-1 cells. Subsequently, GC-1 cells were incubated with medium containing l-Glu, d-Glu, d-Asp or NMDA to determine GluA1 and GluA2/3 expressions. At 30 minutes and 2 hours of incubation, EAA-treated GC-1 cells showed significantly higher expression levels of both GluA1 and GluA2/3. Furthermore, p-extracellular signal-regulated kinase (ERK), p-Akt, proliferating cell nuclear antigen (PCNA), and Aurora B expressions were assayed in l-Glu-, d-Glu-, and NMDA-treated GC-1 cells. At 30 minutes and 2 hours of incubation, treated GC-1 cells showed significantly higher expression levels of p-ERK and p-Akt. A consequent increase of PCNA and Aurora B expressions was induced by l-Glu and NMDA, but not by d-Glu. Our study demonstrates a direct effect of the EAAs on spermatogonial activity. In addition, the increased protein expression levels of GluA1 and GluA2/3 in EAA-treated GC-1 cells suggest that EAAs could activate ERK and Akt pathways through the AMPAR. Finally, the increased PCNA and Aurora B levels may imply an enhanced proliferative activity.

Seasonal and pharmaceutical-induced changes in selenoprotein glutathione peroxidase 4 activity in the reproductive dynamics of the soil biosentinel Podarcis sicula (Chordata: Reptilia)

There is rising concern for the interaction of environmental contaminants with brain transcriptome and the potential effect on reproductive processes. The present study sought to determine selenoprotein glutathione peroxidase 4 (gpx4) transcriptional activity in the brain and testis of the soil biosentinel, Podarcis sicula, through the main phases of the reproductive cycle and whether pharmaceuticals exert an endocrine disruption. Based on gpx4 cloned amminoacids sequence (GenBank AEX09236.1.), we used a bioinformatic approach to assess the structural role. Specifically, we detected seasonally the reactive oxygen species (ROS) level using electron spin resonance spectroscopy and gpx4 transcriptional activity using quantitative real-time polymerase chain reaction. In addition, the impact of pharmaceuticals was assessed after 21-days of treatment with ICI 182,780 and human chorionic gonadotropin administration in mating and winter stasis, respectively. Bioinformatic data shows the gpx4 proteic activity and a phylogenetic profile. ROS contents in lizard brain are significantly less than in testis and display higher levels after treatments. Brain gpx4 expression gives statistically significant seasonal differences, opposite trends in testis and altered expression in both tissues, with evidence of testis morphological and DNA disruption. Taken together, these results provide direct evidence that gpx4 in P. sicula plays a seasonal regulatory role and may be a reliable biomarker for reproductive health toxicity screening.

Long-term exposure of xenoestrogens with environmental relevant concentrations disrupted spermatogenesis of zebrafish through altering sex hormone balance, stimulating germ cell proliferation, meiosis and enhancing apoptosis

Environmental estrogens are capable of interfering with the spermatogenesis and fertility of fish. However in natural waters, these chemicals are more likely to occur as a combination rather than a single stressor. Whether and how the mixture of xenoestrogens with environmental relevant concentrations may affect fish spermatogenesis remains largely unknown. In this study, male zebrafish adults were administered to 17alpha-ethinylestradiol (EE2) and a mixture of xenoestrogens (Mix (E2, EE2, DES, 4-t-OP, 4-NP and BPA)), with the estrogenic potency equivalent to EE2. After a 60-day exposures, elevated mRNA levels of vitellogenin 1 (vtg1) and estrogen receptor 1 (esr1) in the liver of fish in both treated groups were observed. Moreover, the plasma level of E2 declined significantly in the Mix group and the ratio of 11-KT/E2 was significantly elevated in both treated groups. Consistently, the mRNA level of P450 side-chain cleavage (scc) in the EE2 group and ovarian type aromatase (cyp19a1a) in the Mix group was significantly suppressed. In addition, decreased gonadosomatic index and sperm count in the fish of Mix group were present. Furthermore, increased number of the proliferating germ cells (such as spermatogonia and spermatocytes) was observed in the fish of both groups, suggesting a stimulated germ cell proliferation and meiosis. Accordingly, both exposures significantly up-regulated the mRNA levels of genes in mitosis (cyclinb1) and meiosis (cyp26a1 in EE2 group, aldh1a2, cyp26a1, sycp3 and spo11 in Mix). In addition, decreased number of spermatozoa and increased number of TUNEL-positive signals were present in the testis of fish in the Mix group, indicating an enhanced apoptosis. Further analyses demonstrated the significant elevated expressions of tnfrsf1a and the ratio of tnfrsf1a/tnfrsf1b in the Mix group, suggesting an elevated apoptosis in the testis of fish in the Mix group via extrinsic pathway. The present study greatly extends our understanding of the underlying mechanisms of the reproductive toxicity of xenoestrogens on fish.

Comparative Effects of Estrogen and Phytoestrogen, Genistein on Testicular Activities of Streptozotocin-Induced Type 2 Diabetic Mice

The aim of this study was to compare the effect of synthetic estrogen (E2) with a phytoestrogen and genistein in ameliorating type 2 diabetes mellitus (T2D)-mediated testicular dysfunction in mice. The streptozotocin (STZ)-induced type 2 diabetic mice were treated exogenously with either E2 or genistein for 2 durations and compared their effects on testicular activities, serum glucose, and insulin level. Type 2 diabetic mice treated with E2 for only short term (14 days) improved regressive changes in the testicular histology by increasing testosterone synthesis and improving insulin sensitivity, whereas those treated for longer duration (28 days) failed to improve testicular dysfunctions. On the other hand, genistein treated for both short- and long term was useful in improving T2D-induced adverse effects on testicular functions. This study further suggests that treatment with genistein improves spermatogenesis in type 2 diabetic mice by increasing insulin-induced formation of lactate and antioxidative enzymes, which contributes to prevent germ cell apoptosis. Thus, genistein can be used to ameliorate T2D-induced testicular dysfunction.

Testicular steroidogenic enzymes in the lizard Podarcis sicula during the spermatogenic cycle

Steroidogenic Acute Regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD), 5α-Reductase (5α-Red), P450 aromatase are key enzymes involved in steroidogenesis. Recently, we showed the expression and the localization of P450 aromatase in Podarcis sicula testis during the different phases of the reproductive cycle, showing its involvement in the control of steroidogenesis, particularly in 17β-estradiol synthesis. Now, we have investigated the presence and distribution of the other enzymes involved in steroidogenesis, i.e. StAR, 3β-HSD, 17β-HSD and 5α-Red, during three significant periods of the reproductive cycle: summer stasis (July-August), autumnal resumption (November) and reproductive period (May-June). We demonstrated for the first time that all these enzymes are always present in somatic cells (Leydig and Sertoli) and germ cells (spermatogonia, spermatocytes I and II, spermatids and spermatozoa) of Podarcis testis, mainly in spermatids and spermatozoa. The present results strongly suggest that in Podarcis testis both somatic and germ cells could be involved in local sex hormone synthesis and that 5α-Red and P450 could carry out a pivot role.

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.

Response to gonadotropin-releasing hormone challenge: Seasonal variation in steroid production in a viviparous lizard, Tiliqua nigrolutea

The hypothalamic-pituitary-gonadal axis plays a central role in the regulation of gamete maturation, sex steroid production and the stimulation of reproductive behaviours in vertebrates. In seasonal breeders, the timely activation and deactivation of this control system is important to ensure successful reproduction: this process is not well understood in species which breed irregularly. Males of the viviparous blotched blue-tongued lizard, Tiliqua nigrolutea, breed annually, while females display a multiennial cycle. We investigated seasonal variation in hypothalamic-pituitary-gonadal axis responsiveness in both sexes of T. nigrolutea. We measured changes in plasma concentrations of testosterone and estrogen in response to a single intraperitoneal injection of a GnRH agonist, chicken-II LH-RH, at three reproductively distinct times of year. Plasma testosterone concentrations in males were significantly increased during gonadal quiescence, but not initial or final spermatogenesis. There was no estrogen response in males at any time of year. Conversely, in females, there was an increase in plasma testosterone, but not estrogen, concentration, in reproductively quiescent females several months in advance of a successful pregnancy. These results indicate clear variation in HPG axis activity with sex, season and reproductive condition in this seasonally breeding viviparous lizard. This study opens the way for further investigation into the mechanisms by which internal (body condition) and external seasonal cues (temperature and photoperiod) are coordinated to regulate reproduction in irregularly-breeding reptiles.

Effect of Letrozole, a selective aromatase inhibitor, on testicular activities in adult mice: Both in vivo and in vitro study

The aim of present study was to evaluate the significance of estradiol (E2) in testicular activities and to find out the mechanism by which E2 regulates spermatogenesis in mice. To achieve this, both in vivo and in vitro effect of Letrozole on testis of adult mice was investigated. Letrozole-induced changes in testicular histology, cell proliferation (proliferating cell nuclear antigen; PCNA), cell survival (B cell lymphoma factor-2; Bcl2), apoptotic (cysteine-aspartic proteases; caspase-3), steroidogenic (side chain cleavage; SCC, 3β-hydroxy steroid dehydrogenase enzyme; 3β HSD, steroidogenic acute regulatory protein; StAR, aromatase and luteinizing hormone receptor; LH-R) markers, glucose level, and rate of expression of glucose transporter (GLUT) 8 and insulin receptor (IR) proteins in the testis along with changes in serum E2 and testosterone (T) levels were evaluated. Letrozole acts on testis and caused significant decrease in E2 synthesis, but increase in testosterone level and showed regressive changes in the spermatogenesis. Letrozole-induced changes in various testicular markers were compared with the changes in serum E2 level. The correlation study showed that decreased circulating E2 level may be responsible for decreased insulin receptor (IR) level in the testis. The decreased effects of insulin inhibited the glucose transport in the testis by suppressing GLUT8. The decreased level of testicular glucose may produce less lactate as energy support to developing germ cells consequently resulting in decreased cell proliferation and cell survival, but increased apoptosis. Thus, Letrozole suppresses spermatogenesis by reducing insulin sensitivity and glucose transport in the testis, but significantly increased testosterone level by promoting gonadotrophin release by decreased E2.

Effects of Elevated β-Estradiol Levels on the Functional Morphology of the Testis - New Insights

Elevated estradiol levels are correlated with male infertility. Causes of hyperestrogenism include diseases of the adrenal cortex, testis or medications affecting the hypothalamus-pituitary-gonadal axis. The aim of our study was to elucidate the effects of estradiol treatment on testicular cellular morphology and function, with reference to the treatment regimen received. Testes samples (n = 9) were obtained post-orchiectomy from male-to-female transsexuals within the age range of 26–52 years. Each patient had a minimum of 1–6 years estradiol treatment. For comparison, additional samples were obtained from microscopically unaltered testicular tissue surrounding tumors (n = 7). The tissues obtained were investigated by stereomicroscopy, histochemistry, scanning electron microscopy (SEM) and immunohistochemistry. Our studies revealed that estradiol treatment significantly decreased the diameter of the seminiferous tubules (p < 0.05) and induced fatty degeneration in the surrounding connective tissue. An increase in collagen fiber synthesis in the extracellular matrix (ECM) surrounding the seminiferous tubules was also induced. Spermatogenesis was impaired resulting in mainly spermatogonia being present. Sertoli cells revealed diminished expression of estrogen receptor alpha (ERα). Both Sertoli and Leydig cells showed morphological alterations and glycoprotein accumulations. These results demonstrate that increased estradiol levels drastically impact the human testis.

P450 aromatase: a key enzyme in the spermatogenesis of the Italian wall lizard, Podarcis sicula

P450 aromatase is a key enzyme in steroidogenesis involved in the conversion of testosterone into 17β-estradiol. We investigated the localization and the expression of P450 aromatase in Podarcis sicula testes during the different phases of the reproductive cycle: summer stasis (July–August), early autumnal resumption (September), middle autumnal resumption (October–November), winter stasis (December–February), spring resumption (March–April) and the reproductive period (May–June). Using immunohistochemistry, we demonstrated that the P450 aromatase is always present in somatic and germ cells of P. sicula testis, particularly in spermatids and spermatozoa, except in early autumnal resumption, when P450 aromatase is evident only within Leydig cells. Using real-time PCR and semi-quantitative blot investigations, we also demonstrated that both mRNA and protein were expressed in all phases, with two peaks of expression occurring in summer and in winter stasis. These highest levels of P450 aromatase are in line with the increase of 17β-estradiol, responsible for the spermatogenesis block typical of this species. Differently, in autumnal resumption, the level of P450 aromatase dramatically decreased, along with 17β-estradiol levels, and testosterone titres increased, responsible for the subsequent renewal of spermatogenesis not followed by spermiation. In spring resumption and in the reproductive period we found intermediate P450 aromatase amounts, low levels of 17β-estradiol and the highest testosterone levels determining the resumption of spermatogenesis needed for reproduction. Our results, the first collected in a non-mammalian vertebrate, indicate a role of P450 aromatase in the control of steroidogenesis and spermatogenesis, particularly in spermiogenesis.

Molecular Mechanisms Elicited by d-Aspartate in Leydig Cells and Spermatogonia

A bulk of evidence suggests that d-aspartate (d-Asp) regulates steroidogenesis and spermatogenesis in vertebrate testes. This review article focuses on intracellular signaling mechanisms elicited by d-Asp possibly via binding to the N-methyl-d-aspartate receptor (NMDAR) in both Leydig cells, and spermatogonia. In Leydig cells, the amino acid upregulates androgen production by eliciting the adenylate cyclase-cAMP and/or mitogen-activated protein kinase (MAPK) pathways. d-Asp treatment enhances gene and protein expression of enzymes involved in the steroidogenic cascade. d-Asp also directly affects spermatogonial mitotic activity. In spermatogonial GC-1 cells, d-Asp induces phosphorylation of MAPK and AKT serine-threonine kinase proteins, and stimulates expression of proliferating cell nuclear antigen (PCNA) and aurora kinase B (AURKB). Further stimulation of spermatogonial GC-1 cell proliferation might come from estradiol/estrogen receptor β (ESR2) interaction. d-Asp modulates androgen and estrogen levels as well as the expression of their receptors in the rat epididymis by acting on mRNA levels of Srd5a1 and Cyp19a1 enzymes, hence suggesting involvement in spermatozoa maturation.

D-Aspartate Induces Proliferative Pathways in Spermatogonial GC-1 Cells

D-aspartate (D-Asp) is an endogenous amino acid present in vertebrate tissues, with particularly high levels in the testis. In vivo studies indicate that D-Asp indirectly stimulates spermatogenesis through the hypothalamic-pituitary-gonadal axis. Moreover, in vitro studies have demonstrated that D-Asp up-regulates testosterone production in Leydig cells by enhancing expression of the steroidogenic acute regulatory protein. In this study, a cell line derived from immortalized type-B mouse spermatogonia retaining markers of mitotic germ cells (GC-1) was employed to explore more direct involvement of D-Asp in spermatogenesis. Activity and protein expression of markers of cell proliferation were determined at intervals during incubation in D-Asp-containing medium. D-Asp induced phosphorylation of ERK and Akt proteins, stimulated expression of PCNA and Aurora B, and enhanced mRNA synthesis and protein expression of P450 aromatase and protein expression of Estrogen Receptor β (ERβ). These results are the first demonstration of a direct effect of D-Asp on spermatogonial mitotic activity. Considering that spermatogonia express the NR1 subunit of the N-Methyl-D-Aspartic Acid receptor (NMDAR), we suggest that their response to D-Asp depends on NMDAR-mediated activation of the ERK and Akt pathways and is further enhanced by activation of the P450 aromatase/ERβ pathway.

Di-n-butyl phthalate causes estrogenic effects in adult male Murray rainbowfish (Melanotaenia fluviatilis)

Phthalic acid esters (PAEs) are a class of synthetic industrial chemicals commonly found in the aquatic environment worldwide. PAEs have been recognised as anti-androgens in male mammals but little is known about their endocrine disrupting effects in fish. This study investigated the effects of 7-day exposures to nominal (measured) concentrations of 125 (62), 250 (140), 500 (230) and 1,000 (383) μg/L of di-n-butyl phthalate (DnBP) on the biomarkers of reproduction in adult male Murray River rainbowfish (Melanotaenia fluviatilis) using molecular, biochemical and histological endpoints. None of the tested concentrations of DnBP had any effect on survival or the vital body indices of the fish. The sizes of spermatogonia, Type A and B spermatocytes and spermatids were significantly smaller relative to the controls after treatment with DnBP. This was accompanied by a significant increase in the proportion of spermatogonia in fish treated with 250-1,000 μg/L of DnBP in comparison to the unexposed fish. At the end of the exposure period, the expressions of the transcripts for the androgen receptors α and β were significantly elevated in the livers of the fish treated with 500 and 1,000 μg/L of DnBP. In addition, there was also an increase in the circulating concentrations of vitellogenin in the plasma in the higher treatment groups. An induction in the activity of aromatase was noted in the brains of 1,000 μg/L DnBP-treated fish. This was accompanied by an increase in the hepatic expression of the genes (here and later, whenever the phrase gene expression is used as a synonym for gene transcription although it is acknowledged that it is also regulated, e.g., by translation, mRNA stability and protein stability) encoding for the oestrogen receptors α and β and choriogenin L. Collectively, an increase in the proportion of spermatogonia in the testes, the upregulation of the genes for the oestrogen receptors and choriogenin in the liver, an induction in the brain aromatase activity and the increase in the circulating levels of plasma vitellogenin suggest that continuous exposures for 7 days to sub-acute concentrations of DnBP can adversely affect the reproductive health of the male Murray rainbowfish by an estrogenic mode of action.

Variations of estradiol-17β and testosterone levels correlated with gametogenesis in the gonad of Zhikong scallop (Chlamys farreri) during annual reproductive cycle

To assess the potential roles of sex steroids in modulating reproductive processes in the Zhikong scallop (Chlamys farreri (Jones and Preston, 1904)), variations in estradiol-17β (E2) and testosterone (T) levels in gonads were examined monthly from January to December 2012 by enzyme-linked immunosorbent assay (ELISA). The mean concentrations of E2 and T in gonads ranged from 75.07 to 666.24 pg/g and from 91.09 to 506.28 pg/g, respectively. Concentrations of E2 were significantly higher in ovaries than in testes, while T concentrations were higher in testes than in ovaries during gametogenesis. Concentrations of E2 in females and T in males increased with development and maturation of gonad, attained the highest value before spawning, and decreased rapidly after spawning. A positive correlation between E2 levels and oocyte diameters (r = 0.743, P < 0.05, n = 25) was observed, suggesting that E2 may play a role in oogenesis. These findings indicate that E2 and T, which are highly correlated with the reproductive cycle, may play an important role in sex determination, sex differentiation, gametogenesis, and spawning in C. farreri.

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.

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.

Role of estrogen in the regulation of spermatogenesis in the Indian wall lizard Hemidactylus flaviviridis

The role of estrogen in the Indian wall lizard, Hemidactylus flaviviridis during PMSG induced spermatogenesis in the regression phase and during normal spermatogenesis in the active breeding phase was investigated. Blood hormone levels demonstrated a high testosterone to estrogen ratio in the breeding and vice verse during the regressed phase. PMSG treatment (30 IU in 100 μl saline/lizard/alternate day for 30 days) during the regressed phase stimulated spermatogenesis which was associated with a significant (p<0.001) rise in plasma testosterone levels. Complete spermatogenesis with sperms was resolved in many tubular sections. However, co-administration of PMSG plus estrogen in high doses (2 μg of estradiol benzoate/alternate day) for the same period not only curtailed germ cell proliferation significantly but also induced apoptosis in germ cells. There was no significant reduction in testicular weight but sperms were found completely absent in all the tubules. Decline in the plasma testosterone was more pronounced in high compared to low estrogen treated groups. Further, low estrogen administration had little effect either on raising the plasma levels of estrogen or subsequently on spermatogenesis which was identically observed in the breeding phase too. Estrogen intervention (2 μg) in the breeding phase also profoundly suppressed spermatogenesis leading to a severe depletion in germ cells. Simultaneously, there was a significant rise in germ cell apoptosis which was associated with an up-regulation of extrinsic (caspase 8, Fas, FasL) and intrinsic (caspase 9, Bax, Bcl2) markers in these cells. Taken together, the above data indicate that the estrogen plays a key role in regulating spermatogenesis in the wall lizard retarding it during testicular quiescence and eliminating germ cells through apoptosis during the active breeding phase.

Occurrence and cellular distribution of estrogen receptors ERα and ERβ in the testis and epididymal region of roosters

Estrogen signaling is required for the maintenance of male reproductive function and is mediated by the estrogen receptors ERα and ERβ. These receptors are widely distributed in mammalian reproductive tissues, but information is limited in non-mammalian species including birds. The aim of this study was to investigate the occurrence and cellular distribution of ERα and ERβ in the testis and epididymal region of roosters. The results showed for the first time that ERβ was the predominant receptor detected in the testis, being expressed in the somatic and some germ cells. Within the epididymal region, ERβ was strongly expressed in all segments, whereas the most intense reaction for ERα was found in the distal efferent ductules. The differential expression of ERα and ERβ within the rooster testis and epididymal region suggests that these organs may be a target for different actions of estrogen.

Spermatogenesis in fish

Spermatogenesis is a developmental process during which a small number of diploid spermatogonial stem cells produce a large number of highly differentiated spermatozoa carrying a haploid, recombined genome. We characterise morphologically the different germ cell stages with particular attention for the spermatogonial generations, including the stem cells and their specific capacity to colonise a recipient's testis after transplantation. We propose a nomenclature for fish germ cells to improve the comparability among different teleost fish but also to higher vertebrates. Survival and development of germ cells depends on their continuous and close contact to Sertoli cells, and we review their multiple roles in the cystic mode of spermatogenesis seen in fish. We then discuss gene expression patterns associated with testis maturation. The endocrine system of vertebrates has evolved as master control system over spermatogenesis. In fish, both pituitary gonadotropins LH and FSH stimulate gonadal sex steroid hormone production directly by activating Leydig cells. Information is reviewed on the effects of progestin, androgens, and estrogens on global testicular gene expression patterns (microarray analysis), and on the molecular mechanisms by which steroids regulate specific candidate genes (identified by subtractive hybridization approaches) during early stages of testis maturation. Moreover, progestin and androgen effects on spermiation and milt hydration are discussed. Sex steroids mainly act via receptors expressed by Sertoli cells. One type of response is that Sertoli cells change growth factor expression, which subsequently modulates germ cell proliferation/differentiation via mechanisms yet to be characterised. Finally, we review data on germ cell autonomous processes, mainly derived from loss-of-function mutant fish lines, before identifying a number of focus areas for future research activities.

The role of Mitogen activated protein kinase (MAPK) in sperm functions

The generation of mature spermatozoa in the epididymis includes the activation of the MAPK cascade in a complex manner. MAPKs are thought to be involved in the regulation of transcription and ectoplasmic specialization (ES) in the testis. MAPKs also regulate mature spermatozoa flagellar motility, hyperactivation and the acrosome reaction. Here we review the current data regarding the functions of MAPKs in spermatogenesis and in mature spermatozoa.

The Italian wall lizard (Podarcis sicula) as a bioindicator of oil field activity

The aim of this study was to develop and to validate a methodology based on biomarker responses and residue analysis on the terrestrial lizard Podarcis sicula to assess the ecotoxicological effects associated with on-shore oil extraction. The oil treatment plant investigated is located in Val d'Agri (southern Italy). Italian wall lizards were sampled on four stations along a transect determined on the basis of prevailing winds downwind of the oil plant. Cytochrome P450 1A1 activities (EROD and BPMO), AChE activity, PAH bile metabolites and contaminant levels (PAHs and trace elements) were measured. Major results in the evaluation of toxicological impact of oil field activity in the Italian wall lizards were obtained for Cd, Hg, total and carcinogenic PAH levels, and PAH metabolites in bile. Results obtained validate, for the first time, P. sicula as a terrestrial bioindicator for the assessment of the toxicological impact of on-shore extraction activity.

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.

Effects of sex, age, and season on plasma steroids in free-ranging Texas horned lizards (Phrynosoma cornutum)

The Texas horned lizard (Phrynosoma cornutum) is protected in several states due to its apparently declining numbers; information on its physiology is therefore of interest from both comparative endocrine and applied perspectives. We collected blood samples from free-ranging P. cornutum in Oklahoma from April to September 2005, spanning their complete active period. We determined plasma concentrations of the steroids, progesterone (P), testosterone (T), and corticosterone (CORT) by radioimmunoassay following chromatographic separation and 17beta-estradiol (E2) by direct radioimmunoassay. T concentrations in breeding males were significantly higher than in non-breeding males. P showed no significant seasonal variation within either sex. CORT was significantly higher during the egg-laying season compared to breeding and non-breeding seasons for adult females and it was marginally higher in breeding than in non-breeding males (P=0.055). CORT concentrations also significantly increased with handling in non-breeding males and egg-laying females. Perhaps most surprisingly, there were no significant sex differences in plasma concentrations of P and E2. Furthermore, with respect to seasonal differences, plasma E2 concentrations were significantly higher in breeding females than in egg-laying or non-breeding females, and they were significantly higher in breeding than in non-breeding males. During the non-breeding season, yearling males exhibited higher E2 concentrations than adult males; no other differences between the steroid concentrations of yearlings and adults were detected. In comparison to other vertebrates, the seasonal steroid profile of P. cornutum exhibited both expected and unexpected patterns, and our results illustrate the value of collecting such baseline data as a springboard for appropriate questions for future research.

Mitogen activated protein kinases (MAPKs) as regulators of spermatogenesis and spermatozoa functions

Spermatogenesis, culminating in the generation of mature motile spermatozoa, is a complex biological process that is regulated by cytokines and hormones of the male reproductive system. Spermatozoa must first undergo a series of biochemical processes termed capacitation, which is followed by acrosome reaction and egg fertilization. Here we review the role of mitogen-activated protein kinases (MAPK) cascades in spermatogenesis and spermatozoa functions.

17beta-estradiol stimulates proliferation of spermatogonia in experimental cryptorchid mice

AIM

To investigate whether estrogen stimulates the proliferation of spermatogonia or induces spermatogenesis in cryptorchid mice.

METHODS

Mice were surgically rendered cryptorchid, then treated with different doses of 17beta-estradiol (E2) s.c. once a day. Mice were killed at sexual maturity (45 days of age), and histological analysis and immunofluorescence were performed. Serum follicle stimulating hormone (FSH), estradiol, testosterone and luteinizing hormone (LH) were measured.

RESULTS

Low doses of E2 had no notable effect on spermatogonia, but at higher doses, E2 stimulated the proliferation of spermatogonia.

CONCLUSION

E2 has a dose-related mitogenic effect on spermatogonia.

Estrogen response system in the reproductive tract of the male turtle: an immunocytochemical study

Portions of the reproductive tract of the male (Trachemys scripta) turtle were examined by immunocytochemistry for evidence of the capacity to produce and respond to estrogen hormones (via the expression of P450 aromatase and estrogen receptors). Aromatase was detected in both the Sertoli and Leydig cells of the testis and was expressed at different levels during the spermatogenic cycle, being highest in the quiescent testis and lowest during germ cell meiosis. ERalpha was found in the Leydig cells surrounding the seminiferous tubules as well as in the epithelial cells of the excurrent canals (rete testis, efferent ductule, and epididymis). ERbeta immunoreactivity was found in both the spermatogonia and Sertoli cells in the testis, and in the epithelial cells of excurrent canals.

Winter profile of plasma sex steroid levels in free-living male western diamond-backed rattlesnakes, Crotalus atrox (Serpentes: Viperidae)

Recent field studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Arizona showed significant differences in the concentration of plasma sex steroids (testosterone, T; 5alpha-dihydrotestosterone, DHT; and 17beta-estradiol, E2) throughout the active season (March-October), and peak levels were coincident with the two mating periods (late summer and early spring). There is, however, no information on levels of sex steroids during winter. Similar to most snakes, hibernating individuals of C. atrox are typically inaccessible, but in southern Arizona, where environmental conditions are typically mild during winter, adult males frequently bask at or near the entrances of communal dens. Basking activity, therefore, offers a unique logistical opportunity to assess the complete annual profile of plasma sex steroid levels in males of a temperate reptile in nature. From November to February, we measured levels of plasma T, DHT, and E2 in adult male C. atrox that were located basking at communal dens. Additionally, cloacal, core body, and ambient air temperatures were obtained to investigate potential relationships between body temperatures and levels of sex steroids. Mean levels of T, DHT, and E2 were relatively high, and the concentration hierarchy was T>DHT>E2. Mean levels of T, DHT, and E2 showed no significant variation across the four months of sampling; however, E2 levels decreased progressively. In the annul cycle, sex steroid levels during winter were not basal when compared to values obtained during the active season. Mean cloacal temperatures of basking males were significantly higher than core body temperatures of non-basking males (inside dens) from November-December, and in February, which suggests that one function of winter basking is to elevate body temperatures. Steroid levels, nonetheless, were not significantly correlated with cloacal temperatures. We suggest that future field studies of male C. atrox should: (a) investigate sex steroid levels in non-basking individuals and (b) test whether elevated levels of sex steroids during winter facilitate the large increases that occur in early spring, which are coincident with the second mating season. Our findings on the reproductive biology of C. atrox and other viperids are discussed in the context of the associated-dissociated model of reproduction.

17β-Estradiol induces Akt-1 through estrogen receptor-β in the frog (Rana esculenta) male germ cells

Several lines of evidence support the key role of estrogens in male fertility. Here, we investigate the regulation of the serine/threonine kinase Akt-1 in the frog (Rana esculenta) testis during the annual sexual cycle and, whether 17β-estradiol (E2) exerts a role in the Akt-1 activity. Akt-1 has been shown to be the mediator of growth factor-dependent cell proliferation, survival, and metabolism in a variety of cell types.

First, we demonstrate by immunohistochemistry, the presence of estrogen receptor-β (ERβ), and Akt-1 in the spermatogonia (SPG), spermatocytes (SPC), and spermatids (SPT). Western-blot analysis revealed that ERβ isoform (molecular weight 55 kDa) was highly expressed in May (reproductive period) with respect to January and November (winter stasis); in parallel, Akt-1 (molecular weight 60 kDa) is highly phosphorylated (Ser-473) during the period of active spermatogenesis (May) compared with the winter stasis (January and November). In addition, in vitro experiments demonstrate that E2 treatment induces the activation of Akt-1, and this effect is counteracted by the anti-estrogen ICI 182–780. In conclusion, our data show that E2 induces Akt-1 phosphorylation (Ser-473) possibly via ERβ in frog (R. esculenta) male germ cells.

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.

Effects of endocrine-disrupting chemicals on expression of ubiquitin C-terminal hydrolase mRNA in testis and brain of the Japanese common goby

We investigated the effects of endocrine-disrupting chemicals (EDCs) on the expression of ubiquitin C-terminal hydrolase (UCH) mRNA in the testis and brain of the Japanese common goby, Acanthogobius flavimanus. The cDNA sequence of goby UCH contained an open reading frame encoding 220 amino acid residues (M(r)=24,223) with 51.3% overall sequence identity with human and mouse UCHL1. A competitive PCR assay was used to quantify the levels of UCH mRNA in the testis and brain of male gobies after exposure to bisphenol A, nonylphenol, or estradiol-17beta for 3 weeks. Exposure to estradiol-17beta at a nominal concentration of 100 ng/L induced significant increase in UCH mRNA levels in both testis and brain (P<0.05), whereas exposure to nonylphenol induced a significant decrease in UCH mRNA levels in the testis (P<0.01). These results suggest that EDCs can either positively or negatively regulate UCH mRNA levels.

Dose- and photoperiod-dependent effects of 17beta-estradiol and the anti-estrogen ICI 182,780 on testicular structure, acceleration of spermatogenesis, and aromatase immunoexpression in immature bank voles

It has been known that administration of estrogens or deficiency of estrogens can affect development and/or maintenance of male gonadal functions. These hormones are able to control germ cell development, and especially spermatid production and epididymis sperm maturation. The aim of the present study was to show the effects of 17beta-estradiol and a pure anti-estrogen, ICI 182,780, on the bank vole testis. Immature bank voles reared under either short or long light cycles were injected intraperitoneally with two doses of either 17beta-estradiol (0.1 and 10 microg/g body weight, respectively) or pure anti-estrogen ICI 182,780 (10 and 100 microg/g body weight, respectively) both dissolved in 20 microl sesame oil. Control groups (from both photoperiods) received 20 microl sesame oil only. The injections were performed twice a week during 2 weeks. Exposure to the low dose of estradiol induced acceleration of the onset of spermatogenesis. This was particularly apparent in voles kept under short light cycle conditions. On the other hand, when males were treated with a high dose of estradiol or ICI 182,780, disruption of testicular structure and tubular atrophy were observed. Increased apoptosis of germ cells was evident. It is concluded that bank voles as seasonally breeding animals are a useful model for studying the role of estrogens in structure and function of the testis.

Estrogen receptor beta-mediated inhibition of male germ cell line development in mice by endogenous estrogens during perinatal life

Epidemiological, clinical, and experimental studies have suggested that excessive exposure to estrogens during fetal/neonatal life can lead to reproductive disorders and sperm abnormalities in adulthood. However, it is unknown whether endogenous concentrations of estrogens affect the establishment of the male fetal germ cell lineage. We addressed this question by studying the testicular development of mice in which the estrogen receptor (ER) beta or the ERalpha gene was inactivated. The homozygous inactivation of ERbeta (ERbeta-/-) increased the number of gonocytes by 50% in 2- and 6-d-old neonates. The numbers of Sertoli and Leydig cells and the level of testicular testosterone production were unaffected, suggesting that estrogens act directly on the gonocytes. The increase in the number of gonocytes did not occur during fetal life but instead occurred just after birth, when gonocytes resumed mitosis and apoptosis. It seems to result from a decrease in the apoptosis rate evaluated by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method and cleaved caspase-3 immunohistochemical detection. Last, mice heterozygous for the ERbeta gene inactivation behaved similarly to their ERbeta-/- littermates in terms of the number of gonocytes, apoptosis, and mitosis, suggesting that these cells are highly sensitive to the binding of estrogens to ERbeta. ERalpha inactivation had no effect on the number of neonatal gonocytes and Sertoli cells. In conclusion, this study provides the first demonstration that endogenous estrogens can physiologically inhibit germ cell growth in the male. This finding may have important implications concerning the potential action of environmental estrogens.

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.

Does alligator testis produce estradiol? A comparison of ovarian and testicular aromatase

Testicular secretion of estradiol is necessary for normal spermatogenesis and male reproductive physiology in humans and rodents. The role of estradiol in nonmammalian vertebrates remains unknown, but elevated circulating estradiol has been reported in male lizards, alligators, and various bird species. We have been unable to detect circulating estradiol in male alligators; therefore, we reexamined the question of testicular production of estradiol in alligators using more rigorous assay procedures. A large pool of plasma from a male alligator was extracted and run through an HPLC column. Immunoreactive estradiol-like material eluted coincident with authentic estradiol. By using an ultrasensitive RIA and processing large volumes of male plasma (1000 microl), we were able to measure estradiol. Estradiol in male alligators ranged from 0.23 to 3.14 pg/ml, whereas estradiol in immature female alligators ranged from 14 to 66 pg/ml. Aromatase activity in microsomes from adult alligator ovarian tissue was 36.2 +/- 1.6 pmol mg-1 h-1, whereas activity in testicular microsomes ranged between 0.92 and 2.38 pmol mg-1 h-1. Ovarian aromatase activity was inhibited in a concentration-dependent fashion by Fadrozole, but the essentially background activity of testicular aromatase was not inhibited at any concentration of Fadrozole. Likewise, a comparison of alligator testicular and ovarian aromatase mRNA expression gave a similar result: the ovarian expression was 600-fold higher and brain tissue was 10-fold higher than that of the testis. Circulating estradiol in male alligators is probably of extragonadal origin, and the testis produces little if any of this steroid.