Estradiol concentration and the expression of estrogen receptors in the testes of the domestic goose (Anser anser f. domestica) during the annual reproductive cycle

Validation of enzyme immunoassays for quantifying sex steroid hormones in tropical screech owls (Megascops choliba)

Androgens and estrogens are steroid hormones that regulate reproductive processes in both males and females. Monitoring plasma levels of these steroids or their metabolites present in feces, offers diagnostic support for assessing the reproductive status of animals. Immunoassays are commonly used methods for quantifying these hormones, but their protocols require species-specific validation to ensure reliability. The objective of this study was to perform analytically and biologically validation of enzyme immunoassay (EIA) kits for measuring testosterone (T), estradiol (E2), faecal androgen metabolites (fAM), and faecal estrogenic metabolites (fEM) in the tropical screech owl (Megascops choliba). Serum and fecal samples were collected from six adult females and six males both before and during breeding season, with males' gonadal activity assessed using electroejaculation (EE). The parallelism test confirmed the immunogenic similarity of the antigens in the estradiol and testosterone standards and the antigens in the serum samples and fecal extracts of M. choliba. Additionally, the EIA kits displayed nearly 100% recovery rates, and showed coefficients of variation ranging from 8% to 14% at the intra-assay level and from 10% to 16% at the inter-assay level, underscoring result reliability and consistency. In males, the highest serum T and fAM levels were recorded concurrently with the presence of spermatozoa in samples collected via EE. Although females did not exhibit oviposition events, significantly higher E2 and fEM levels were observed in August compared to May, suggesting potential seasonal variations in estrogenic hormone production. Fecal androgen and estrogen levels were significantly different between sexes in August, with males having higher fAM and females having higher fEM levels. Overall, the immunoassays validated in this study were found to be efficient in diagnosing reproductive activity in owls.

Alterations in gonadotropin, prolactin, androgen and estrogen receptor and steroidogenesis-associated gene expression in gander testes in relation to the annual period

Physiological mechanisms of seasonal changes in testicular function in birds are not fully elucidated. The balance between androgens and estrogens and testis sensitivity for gonadotropin and gonadal steroids are still unclear. The aim of the study was to examine: (1) the changes in circulating and intra-testicular steroid hormone levels and their relationship; (2) the mRNA expression of testicular gonadotropin, prolactin (PRL), progesterone (P4), androgen, and estrogen receptors, and (3) key steroidogenesis processes-related genes with immunofluorescent localization of aromatase in gander testes during the annual period. Testes from ganders (n = 25) in the first reproduction season were obtained at five breeding stages, i.e., prebreeding (PrB), peak of reproduction (PR), postbreeding (PoB), nonbreeding (NB), and onset of reproduction (OR). Males were kept under breeding conditions. It was found that plasma P4 levels decreased at the PoB and NB stages, whereas intra-testicular P4 was the highest in the NB stage. Intra-testicular estradiol (E2) levels were higher at the PoB and NB stages than the other stages, whereas testosterone (T) levels showed a nearly opposite pattern. The plasma estradiol-to-testosterone ratios were higher at the PrB, PoB and NB stages compared to other stages. The transcript abundances for luteinizing hormone receptor (LHR), PRL receptor (PRLR), estrogen receptor alpha (ERα), and estrogen receptor beta (ERβ) also change in testicular tissue during the annual period. Moreover, StAR mRNA expression was upregulated at the PoB and NB stages, and CYP11A1 transcript level was the highest at the PoB stage. Stage-dependent changes in the CYP19A1 mRNA and aromatase protein levels with higher abundances of transcript at PoB and NB stages and protein at the NB stage were observed. Localization and immunofluorescent signal intensity for aromatase also differed in relation to the examined stages. It may be suggested that differential E2 levels, as well as aromatase expression and localization across annual stages are responsible for the seasonal activation/inactivation stages of testis spermatogenesis in domestic ganders. These data strongly suggest a role of aromatase in the control of gander steroidogenesis as changes in this enzyme level are associated with alternation in gonadal steroid hormones. In addition, joint action with others hormones, like PRL and LH, seems to be important in the final effect of seasonal reproduction potential.

The Effect of the Long-Term Calcipotriol/Betamethasone Dipropionate Local Therapy on Tissue Resident Memory Cells Markers in Psoriatic Eruptions

Background: The natural course of psoriasis is characterized by the long-term persistence of lesions and a predilection for relapse in the same area. It is caused by the inherence of TRM (tissue resident memory T cells) in apparently healthy skin. These cells are able to initiate an inflammatory cascade and induce relapse of the disease. These cells are characterized by high resistance to damaging factors and apoptosis, which determines their longevity. Aim: The aim of our study was to evaluate the presence of TRM in psoriatic plaques before, during and after 12 weeks of therapy in patients treated with topical calcipotriol and betamethasone dipropionate (Cal/BD) foam. Methods: TRM markers (CD4, CD8, CD103, CD69, CD49, CXCR6) and tissue expression of cytokines (IL-17A, IL-22) in the lesional psoriatic skin from 10 patients compared to 10 healthy skin samples were estimated by immunohistochemistry. Biopsy samples from the area of the same psoriatic plaque were collected three times: before the initiation of therapy, 4 and 12 weeks after its initiation. Results: The presence of TRM markers in the epidermis and dermis of psoriatic lesions was significantly higher when compared to the skin of control group patients. A reduction in the expression of the characteristic TRM markers (CD8, CD4, CD103, CD69, CXCR6, IL-17A and IL-22) was observed in the epidermis on week 12 of therapy, while a depletion in the expression of TRM in the dermis was demonstrated only in CD4 and IL-22. Conclusions: Topical treatment with Cal/BD foam significantly decreased the expression of TRM markers mainly in the epidermis, and to a lesser extent in the dermis, during the 12-week observation period. It probably results from a worse penetration of the drug into the dermis and the effect of the preparation mainly on the epidermis. The persistence of a high expression of TRM markers in the dermis may result in the rapid recurrence of lesions after discontinuation of topical treatment.

Stress and steroid interaction modulates expression of estrogen receptor alpha in the brain, pituitary, and testes of immature Gallus gallus domesticus

In nature, food availability stimulates hypothalamo-pituitary-gonadal (HPG) axis while its scarcity induces stress, which further stimulates hypothalamo-pituitary-adrenal (HPA) axis producing a detrimental effect on the avian reproductive physiology. The present experiment was designed to examine the interaction of stress like food restriction and estradiol on male reproductive physiology with special emphasis on estrogen receptor alpha (ERα) as these play crucial role in reproduction. To achieve this, 60 day old White Leghorn immature cockrels were taken and divided into four groups (n  =  8 per group). One group was provided with food and water ad libitum. Second group was food restricted (FR) for 9 h/day after 5 days, third and fourth were administered with estradiol benzoate (EB 0.5 mg/100g/day) for 12 days. Fourth group was FR for 9 h/day after 5 days of EB treatment till last day of experiment (EB + FR). Immunofluorescent localization of ERα was principally in the pre-optic area and paraventricular nuclei of hypothalamus and in anterior pituitary gland. ERα expression was highly reduced (from 40 AU to 20 AU) after FR in testis but it increased (50 AU) after EB administration, EB + FR reflects a diminishing pattern in the increment after EB. FR decreased plasma estradiol while EB increased it. Increased plasma corticosterone, hydrogen peroxide, malondialdehyde, and decreased anti-oxidant enzymes in brain and testis of all groups indicate oxidative stress in the HPG axis. The increased ERα after EB and a decrease with FR and EB + FR support their reproductive function. Estrogen and its receptor alpha are responsible for maintaining epithelial morphology but FR along with EB administration modulates the testicular development by significantly decreasing its size (p<.0001) and seminiferous tubules (p<.0001) and no sperm formation via highly reduced expression of ir-ERα in HPG axis. Our findings led us to conclude that stress like FR and estradiol induces testicular regression immature male chickens by modulating ir-ERα expression in the HPG axis thereby resulting in reduction in reproductive physiology.

Sex- and Developmental Stage-Related Differences in the Hepatic Transcriptome of Japanese Quail (Coturnix japonica) Exposed to 17β-Trenbolone

Endocrine-disrupting chemicals can cause transcriptomic changes that may disrupt biological processes associated with reproductive function including metabolism, transport, and cell growth. We investigated effects from in ovo and dietary exposure to 17β-trenbolone (at 0, 1, and 10 ppm) on the Japanese quail (Coturnix japonica) hepatic transcriptome. Our objectives were to identify differentially expressed hepatic genes, assess perturbations of biological pathways, and examine sex- and developmental stage-related differences. The number of significantly differentially expressed genes was higher in embryos than in adults. Male embryos exhibited greater differential gene expression than female embryos, whereas in adults, males and females exhibited similar numbers of differentially expressed genes (>2-fold). Vitellogenin and apovitellenin-1 were up-regulated in male adults exposed to 10 ppm 17β-trenbolone, and these birds also exhibited indications of immunomodulation. Functional grouping of differentially expressed genes identified processes including metabolism and transport of biomolecules, enzyme activity, and extracellular matrix interactions. Pathway enrichment analyses identified as perturbed peroxisome proliferator-activated receptor pathway, cardiac muscle contraction, gluconeogenesis, growth factor signaling, focal adhesion, and bile acid biosynthesis. One of the primary uses of 17β-trenbolone is that of a growth promoter, and these results identify effects on mechanistic pathways related to steroidogenesis, cell proliferation, differentiation, growth, and metabolism of lipids and proteins. Environ Toxicol Chem 2021;40:2559-2570. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Determination of Annual Plasma Hormone Levels Associated with Reproduction in Long-Day Breeding Domestic Geese

Simple Summary

In domestic birds, breeding practices and optimisation of the microenviroment and nutrition ensure egg production throughout the entire year. However, domestic geese experience an annual cycle of reproductive quiescence and recrudescence. Thus, patterns of reproductive hormones related to the initiation and termination of the breeding–laying period between the sexes seems to be especially important. This paper presents annual patterns of prolactin (PRL), triiodothyronine (T3), thyroxine (T4), testosterone (T), progesterone (P4), and estradiol (E2) in ganders and female geese. Long-day breeding Zatorska geese kept in controlled commercial conditions experienced periods with elevated plasma PRL levels in both sexes post-breeding and during the second half of the breeding–laying period. Increased plasma PRL levels by the end of the breeding–laying period were detected earlier in ganders than in female geese. Annual patterns of thyroid hormones (THs) were partially in agreement with existing theories on the specific role of THs in termination of breeding, which is permissive rather than causal. It may be suggested that ganders terminate their breeding–laying period one month earlier than female geese. These results may be useful in the manipulation of the endocrine axis to extend the duration of seasonal hatching egg production.

Abstract

This paper examines the dynamics of circulating hormone changes connected with reproduction in geese during the annual period related to gonad morphometry. One hundred geese were examined. The levels of prolactin (PRL), triiodothyronine (T3), thyroxine (T4), testosterone (T), progesterone (P4) and estradiol (E2) were estimated. In both sexes, PRL level patterns fit a quadratic trend with elevations in the post-breeding and the second half of the breeding–laying periods. During these periods, differences in the PRL level between sexes were noted. In ganders, increased PRL levels during the laying period occurred earlier compared to in female geese. Cubic trends for T and E2 in ganders and quadratic for T, P4, and E2 in female geese were observed. PRL was negatively correlated with T in both sexes and with P4 and E2 in female geese. A higher level of T3 and variation in T4 in ganders with a quartic trend in ganders vs. a quadratic in female geese were noted. Patterns of PRL, T, and E2 suggested that the breeding–laying period in ganders may be shorter than in female geese. These findings will be used to explore experimental manipulations of the endocrine axis to increase synchronisation of both sexes.

The Aromatase-Estrogen System in the Testes of Non-Mammalian Vertebrates

Estrogens are important physiological regulators of testicular activity in vertebrates. Estrogen levels depend on the activity of P450 aromatase, the enzyme responsible for the irreversible conversion of testosterone into 17β-estradiol. Therefore, P450 aromatase is the key player in the aromatase-estrogen system. The present review offers a comparative overview of P450 aromatase activity in male gonads of amphibians, reptiles, and birds, with a particular emphasis on the functions of the aromatase-estrogen system in these organisms during their developmental and adult stages. The aromatase-estrogen system appears to be crucial for the sex differentiation of gonads in vertebrates. Administration of aromatase inhibitors prior to sexual differentiation of gonads results in the development of males rather than females. In adults, both aromatase and estrogen receptors are expressed in somatic cells, Leydig and Sertoli cells, as well as germ cells, with certain differences among different species. In seasonal breeding species, the aromatase-estrogen system serves as an "on/off" switch for spermatogenesis. In some amphibian and reptilian species, increased estrogen levels in post-reproductive testes are responsible for blocking spermatogenesis, whereas, in some species of birds, estrogens function synergistically with testosterone to promote spermatogenesis. Recent evidence indicates that the production of the aromatase enzyme in excessive amounts reduces the reproductive performance in avian species of commercial interest. The use of aromatase inhibitors to improve fertility has yielded suitable positive results. Therefore, it appears that the role of the aromatase-estrogen system in regulating the testicular activity differs not only among the different classes of vertebrates but also among different species within the same class.

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.

Photoperiod dependent expression of estrogen receptor alpha in testes of Japanese quail: Involvement of Withania somnifera in apoptosis amelioration

Light plays important function in the regulation of reproduction in vertebrates including birds. The prolonged long day length exposure causes reproductively inactive state or photorefractoriness in many avian species including Japanese quail. Withania somnifera (WS) is a medicinal plant known to have beneficial effects on stress and infertility. The study investigates the physiological effect of WS on the light-induced stress in quail mediated by estrogen receptor alpha. Quails were exposed to long day length for three months and then transferred into intermediate day length to make them photorefractory (PR) while controls under natural day length. Administration of Withania somnifera root extract (WSRE) in PR quail induces estrogen and decreases corticosterone in male Japanese quail. Immunoreactivity of ERα decreased in testis of PR quail and increased after oral administration of WSRE compared to control. Expression of ir-Caspase-3 and ir-p53 in the testis increased in PR while decreased in PR + WS. Histologically, seminiferous tubules size decreased in PR whereas increased in PR + WS quails. Scanning electron microscopic study reveals sperms in clusters with proper head and tail in control. In PR quails sperms were few and distorted while WSRE improved the sperm morphology. From the study, it is concluded that during photorefractoriness gonadal regression occurs due to testicular apoptosis which causes stress. WSRE helps to overcome stress and improve reproductive performance via increase in expression of ir-ERα during PR condition. Further, the stress ameliorating effect of WSRE in reducing apoptosis mediated by ir-Caspase-3 and ir-p53 in the testes is clearly evident in Japanese quail.

Effect of estrogen and stress on estrogen receptor 1 in the HPG axis of immature male Gallus gallus domesticus: Involvement of anti-oxidant system

Estrogen plays a key role in the regulation of reproductive behavior and control of the neuroendocrine system in both males and females. However, excessive quantity of exogenous estrogen produces a deleterious effect on the male reproductive system. To elucidate the mechanism by which estrogen modulates its receptor alpha (ESR1) in immature chicken during stress the study has been undertaken. The experiment investigated the physiological changes in the abundance of ESR1 in brain, pituitary and testes of immature male chickens after stress like water restriction. Twenty four immature male chickens were randomly assigned into four groups. The control group was provided with food and water ad libitum, second was water restricted 9 h each day for seven days (WR), third was treated with estradiol benzoate (EB) and fourth group was treated with EB followed by water restriction during last seven days of treatment (EB + WR). EB was administered at a dose of 0.5 mg/100 g/day for 12 days. EB administration as well as WR increases both the H₂O₂ and Malondialdehyde levels indicating oxidative stress in brain as well as in testis. Plasma corticosterone significantly increased in all groups while estradiol significantly decreased after water restriction. ESR1 protein was detected by immuno-fluorescence predominantly in the pre-optic area of the hypothalamus, pituitary and testes after EB administration. EB administration increases ESR1 proteins abundantly in the Sertoli cells, Leydig cells, spermatogonia and spermatids while WR decreases it. The decline in ESR1 proteins after EB administration during stress appears to be mediated by interaction of estrogen with hypothalamo-pituitary-adrenal (HPA) axis. Therefore, the findings substantiate the fact that WR and EB treatment increase the stress and alter the anti-oxidant enzymes via its receptor ESR1 in the brain, pituitary and testis of immature chicks. Moreover, these findings highlight the effect of estradiol in male chicks causing stress which is disrupting the normal physiological feedback mechanism in hormone release and the expression of receptor ESR1 along the hypothalamo-pituitary-gonadal (HPG) axis.

Determination of testicular estrogen receptor alpha expression of male chickens (Gallus domesticus) with age

Background and Aim:

Estrogen activity, a central component of reproductive growth, is regulated by the receptor proteins, estrogen receptor alpha (ERα), and ER beta (ERβ) in chickens as in many other species. ERα expresses predominantly in gonads. Although the expression of ERα in embryonic gonads has been studied in detail, the expression of ERα in post-hatching male gonads has not been studied adequately. Therefore, the current research was conducted to determine the post-hatching changes in the expression of ERα in the left gonads of male chickens with age.

Materials and Methods:

Shaver Brown male chickens were raised and cared for according to the management guide and sacrificed at the intervals of 1, 4, and 8 weeks of age. The total RNA was extracted from the left gonads using the Trizol method and reverse transcribed using a pair of gene-specific primers. Following polymerase chain reaction amplification, the expression of ERα was quantified relative to the expression of the reference gene GAPDH.

Results:

The results showed that ERα expression significantly increases with age at p=0.0032. However, the increment of ERα expression from week 1 to week 4 was 2.04-fold and from week 4 to week 8 was 1.39-fold, with the later age reflecting a diminishing pattern in the increment.

Conclusion:

These results differentiate the post-hatching ERα expression of the left gonads of male chickens increase with age but with a diminishing gradient that may support their reproductive functions in later stages of life.

Drought leads to reproductive quiescence in smooth-billed anis: Phenotypic evidence for opportunistic breeding and reproductive readiness

Previous studies have suggested that the smooth-billed ani (Crotophaga ani, Linnaeus, 1758) breeds opportunistically following unpredictable rainfall in drought areas. To obtain proof of this phenomenon, the present study described and compared reproductive morphology and cell proliferation in the gonads of free-living smooth-billed anis during a wet season (April to June 2012) and the following dry season (July to September 2012) in a semiarid area using light and electron microscopy (transmission and scanning) and the AgNOR method. The morphological findings indicated distinct levels of reproductive activity related to seasonal changes. Morphological and morphometric analyses of the gonads confirmed intense gametogenic activity during the wet season, whereas gonadal involution occurred after rainfall ceased. The sizes of the testes and ovaries were significantly reduced compared to those in the wet season. The volumetric fraction of the seminiferous tubules in the testis decreased considerably, and no preovulatory follicles were detected in the ovary in the dry season. Moreover, the AgNOR count in the gonads revealed a significant decline in cell recruitment for gametogenesis after rainfall ceased. The histological findings indicated partial gonadal activation throughout the dry season. The analysis of the seminiferous epithelium confirmed the early testicular recrudescence phase, and sporadic postovulatory follicles indicated random ovulation during this time. The excurrent ducts and the oviduct also underwent remarkable involution in the dry season. Taken together, these findings confirm opportunistic breeding by smooth-billed anis in a semiarid habitat and suggest that gonadal recrudescence has been established as a reproductive strategy to cope with unexpected precipitation events.

Differences in aromatase expression and steroid hormone concentrations in the reproductive tissues of male domestic turkeys (Meleagris gallopavo) with white and yellow semen

1. To show hormonal differences between male turkeys with yellow semen syndrome (YSS) and white, normal semen (WNS), the expression of aromatase, oestrogen receptor α (ERα), and oestrogen receptor β (ERβ) as well as testosterone and oestradiol concentrations in YSS and WNS testes, epididymis, and ductus deferens were examined. 2. To measure gene expression levels of aromatase and oestrogen receptors (ERs), three complementary techniques (real-time PCR, Western blot, and immunohistochemistry) were used, whereas steroid hormone levels were determined radio-immunologically. 3. Upregulation of aromatase and ERα mRNAs in YSS testes (P < 0.05; P < 0.01), epididymis (P < 0.001; P < 0.001), and ductus deferens (P < 0.05; P < 0.01) compared to those of WNS tissues was detected. Significant increases in the levels of aromatase and ERα proteins were detected in YSS testes (P < 0.001; P < 0.05), epididymis (P < 0.001; P < 0.001), and ductus deferens (P < 0.001; P < 0.05). The expression of ERβ mRNA and protein level was upregulated in the testes (P < 0.05; P < 0.01) and epididymis (P < 0.001; P < 0.01) but not in ductus deferens where it was downregulated (P < 0.01; P < 0.01). Increased intensity of immunoreactive proteins in YSS versus WNS reproductive tissues corroborated gene expression results. 4. Testosterone concentration diminished in YSS epididymis (P < 0.05) and ductus deferens (P < 0.05), but not in the testes, remaining at high level (P < 0.05) compared to WNS values. Concomitantly, increased oestradiol concentration was found in YSS testes (P < 0.05) and epididymis (P < 0.05) but decreased in the ductus deferens (P < 0.05). 5. From the published literature, this study is the first to demonstrate the ability for androgen aromatisation in the turkey reproductive tissues and to show the cellular targets for locally produced oestrogens. The data suggested that the androgen/oestrogen ratio is a mechanistic basis for amplification of differences between turkeys with white and yellow semen and that these results can have a relevance in applied sciences to widen the knowledge on domestic bird reproduction.

Effect of Seasonal Change on Testicular Protein Expression in White Roman Geese

The purpose of this study was to investigate the change in protein expression in the testes of ganders at various breeding stages. A total of nine 3-year-old male White Roman ganders were used. The blood and testis samples were collected at the nonbreeding, sexual reactivation, and breeding stages for sex hormone analysis and proteomic analysis, respectively. The testicular weight and serum testosterone observed for ganders at the breeding stage were higher than those for ganders at nonbreeding and sexual reactivation stages (P < 0.05). There were 124 protein spots differentially expressed in the testes of ganders at various reproductive stages. A total of 107 protein spots of 74 proteins was identified through mass spectrometry. Most of the differentially expressed proteins were responsible for the molecular functions of protein binding (24%) and catalytic activity (16%). A functional pathway analysis suggested that proteins involved in steroidogenesis, metabolism, and spermatogenesis pathways changed in the White Roman geese at various reproductive stages. In conclusion, ganders at various reproductive stages exhibited different levels of testosterone and protein expression in the testes. The varied levels of the proteins might be essential and unique key factors in seasonal reproduction in ganders.

Estrogens in Male Physiology

Estrogens have historically been associated with female reproduction, but work over the last two decades established that estrogens and their main nuclear receptors (ESR1 and ESR2) and G protein-coupled estrogen receptor (GPER) also regulate male reproductive and nonreproductive organs. 17β-Estradiol (E2) is measureable in blood of men and males of other species, but in rete testis fluids, E2 reaches concentrations normally found only in females and in some species nanomolar concentrations of estrone sulfate are found in semen. Aromatase, which converts androgens to estrogens, is expressed in Leydig cells, seminiferous epithelium, and other male organs. Early studies showed E2 binding in numerous male tissues, and ESR1 and ESR2 each show unique distributions and actions in males. Exogenous estrogen treatment produced male reproductive pathologies in laboratory animals and men, especially during development, and studies with transgenic mice with compromised estrogen signaling demonstrated an E2 role in normal male physiology. Efferent ductules and epididymal functions are dependent on estrogen signaling through ESR1, whose loss impaired ion transport and water reabsorption, resulting in abnormal sperm. Loss of ESR1 or aromatase also produces effects on nonreproductive targets such as brain, adipose, skeletal muscle, bone, cardiovascular, and immune tissues. Expression of GPER is extensive in male tracts, suggesting a possible role for E2 signaling through this receptor in male reproduction. Recent evidence also indicates that membrane ESR1 has critical roles in male reproduction. Thus estrogens are important physiological regulators in males, and future studies may reveal additional roles for estrogen signaling in various target tissues.