Expression of Estrogen Receptors α and β in the Fetal Baboon Testisand Epididymis1

Seasonal variation of cell proliferation and apoptosis in the efferent ductules and epididymis of the Neotropical bat Artibeus lituratus (Chiroptera, Phyllostomidae)

The balance between cell proliferation and apoptosis is important for maintenance of male fertility, being influenced by a variety of stimuli including androgens and estrogens. However, studies concerning regulation of these processes along the male reproductive tract under physiological conditions are scarce. Therefore, in this study, we investigated the profile of cell proliferation and apoptosis in the efferent ductules and epididymis of the Neotropical bat Artibeus lituratus, a seasonal breeder that presents natural variation in components of the androgen and estrogen responsive systems along the circannual cycle. Low rates of cell proliferation and apoptosis were found in the efferent ductules and epididymis of A. lituratus during the reproductive period, as few epithelial cells were positive for MCM7 (proliferation marker) and cleaved caspase-3 or TUNEL (apoptosis markers). In contrast, during the regressive period, the rate of both proliferating and apoptotic cells was significantly higher in the epithelium lining the efferent ductules as well as throughout the epididymis. The increased proliferative activity at this phase was positively correlated with the expression of estrogen receptor alpha (ERα), whereas the variation in apoptosis appears to be unrelated to the local expression of androgen and estrogen receptors. Together, these data suggest that cell proliferation and apoptosis are differentially modulated in the efferent ductules and epididymis of A. lituratus during the annual reproductive cycle, and support the hypothesis that ERα may be important in preparing the male reproductive tract for sexual recrudescence.

Sex-specific expression of CTNNB1 in the gonadal morphogenesis of the chicken

BACKGROUND

Beta-catenin (CTNNB1), as a key transcriptional regulator in the WNT signal transduction cascade, plays a pivotal role in multiple biological functions such as embryonic development and homeostasis in adults. Although it has been suggested that CTNNB1 is required for gonad development and maintenance of ovarian function in mice, little is known about the expression and functional role of CTNNB1 in gonadal development and differentiation in the chicken reproductive system.

METHODS

To examine sex-specific, cell-specific and temporal expression of CTNNB1 mRNA and protein during gonadal development to maturation of reproductive organs, we collected left and right gonads apart from mesonephric kidney of chicken embryos on embryonic day (E) 6, E9, E14, E18, as well as testes, oviduct and ovaries from 12-week-old and adult chickens and performed quantitative PCR, in situ hybridization, and immunohistochemical analyses. In addition, localization of Sertoli cell markers such as anti-Müllerian hormone (AMH), estrogen receptor alpha (ESR1), cyclin D1 (CCND1) and N-cadherin (CDH2) during testicular development was evaluated.

RESULTS

Results of the present study showed that CTNNB1 mRNA and protein are expressed predominantly in the seminiferous cords on E6 to E14 in the male embryonic gonad, and are mainly localized to the medullary region of female embryonic gonads from E6 to E9. In addition, CTNNB1 mRNA and protein are abundant in the Sertoli cells in the testes and expressed predominantly in luminal epithelial cells of the oviduct, but not in the ovaries from 12-week-old and adult chickens. Concomitant with CTNNB1, AMH, ESR1, CCND1 and CDH2 were detected predominantly in the seminiferous cord of the medullary region of male gonads at E9 (after sex determination) and then maintained or decreased until hatching. Interestingly, AMH, ESR1, CCND1 and CDH2 were located in seminiferous tubules of the testes from 12-weeks-old chickens and ESR1, CCND1 and CDH2 were expressed predominantly in the Sertoli cells within seminiferous tubules of adult testes.

CONCLUSIONS

Collectively, these results revealed that CTNNB1 is present in gonads of both sexes during embryonic development and it may play essential roles in differentiation of Sertoli cells during formation of seminiferous tubules during development of the testes.

Seasonal variation in estrogen receptor ERα, but not ERβ, androgen receptor and aromatase, in the efferent ductules and epididymis of the big fruit-eating bat Artibeus lituratus

The efferent ductules (ED) are a major target for estrogens, which act via the estrogen receptors ERα (ESR1) and ERβ (ESR2). ERα has been found in the ED of all species studied so far. However, in the epididymis (EP), the expression of ERα is controversial, as is data about the occurrence of aromatase in the epithelium lining the excurrent ducts. Therefore, to further investigate this estrogen-responsive system, we used a seasonal breeder, the Neotropical bat, Artibeus lituratus, in which testicular expression of androgen (AR) and estrogen (ER) receptors vary with reproductive phase. The localization of aromatase, ERα, ERβ and AR in the ED and EP of A. lituratus was investigated. The results showed that aromatase, AR and ERβ were distributed throughout the excurrent ducts and did not vary during the annual reproductive cycle. Conversely, ERα was detected primarily in the ED epithelium, had marked seasonal variation and was increased during regression, especially in the EP epithelium. The results suggest that ERα may be involved in preparing the male genital tract for recrudescence. Together, the data obtained under natural conditions emphasize that specific segments of the excurrent ducts downstream of the testis are the primary targets for estrogen action via ERα, which is similar to previous findings in animals lacking functional ERα.

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.

Expression of P-450 aromatase, estrogen receptor α and β, and α-inhibin in the fetal baboon testis after estrogen suppression during the second half of gestation

Expression of the molecules that modulate the synthesis and action of estrogen in, or reflect function of, Sertoli cells was determined in the fetal testis of baboons in which estrogen levels were suppressed in the second half of gestation to determine whether this may account for the previously reported alteration in fetal testis germ cell development. P-450 aromatase, estrogen receptor (ER) β, and α-inhibin protein assessed by immunocytochemistry was abundantly expressed in Sertoli cells of the fetal baboon testis, but unaltered in baboons in which estrogen levels were suppressed by letrozole administration. Moreover, P-450 aromatase and ERα and β mRNA levels, assessed by real-time RT-PCR, were similar in germ/Sertoli cells and interstitial cells isolated from the fetal testis of untreated and letrozole-treated baboons. These results indicate that expression of the proteins that modulate the formation and action of estrogen in, and function of, Sertoli cells is not responsible for the changes in germ cell development in the fetal testis of estrogen-deprived baboons.

Application of laser-assisted microdissection for gene expression analysis of mammalian germ cells

Laser-assisted microdissection (LAM) is an important method to provide new significant insights into many embryological processes. To understand these processes, it is important to obtain specific populations of cells from complex tissue in an efficient and precise manner and to combine with many different molecular biological methods. During the last few years, the sophistication of the techniques of LAM has increased significantly and made the procedure easy to use. New micro-extraction protocols for DNA, RNA and proteins now allow broad downstream applications in the fields of genomics, transcriptomics and proteomics. In this review, we give a short overview of the application of LAM in combination with quantitative qPCR for the analysis of gene expression in mammalian germ cells.

Estrogen promotes germ cell and seminiferous tubule development in the baboon fetal testis

The foundation for development of the male reproduction system occurs in utero, but relatively little is known about the regulation of primate fetal testis maturation. Our laboratories have shown that estrogen regulates key aspects of the physiology of pregnancy and fetal development. Therefore, in the present study, we characterized and quantified germ cells and Sertoli cells in the fetal baboon testis in late normal gestation (i.e., Day 165; term is 184 days) and in baboons administered the aromatase inhibitor letrozole throughout the second half of gestation to assess the impact of endogenous estrogen on fetal testis development. In untreated baboons, the seminiferous cords were comprised of undifferentiated (i.e., type A) spermatogonia classified by their morphology as dark (Ad) or pale (Ap), gonocytes (precursors of type A spermatogonia), unidentified cells (UI), and Sertoli cells. In letrozole-treated baboons, serum estradiol levels were decreased by 95%. The number per milligram of fetal testis (x10(4)) of Ad spermatogonia (0.42 +/- 0.11) was 45% lower (P = 0.03), and that of gonocytes (0.58 +/- 0.06) and UI (0.45 +/- 0.12) was twofold greater (P < 0.01 and P = 0.06, respectively), than in untreated baboons. Moreover, in the seminiferous cords of estrogen-deprived baboons, the basement membrane appeared fragmented, the germ cells and Sertoli cells appeared disorganized, and vacuoles were present. We conclude that endogenous estrogen promotes fetal testis development and that the changes in the germ cell population in the estrogen-deprived baboon fetus may impair spermatogenesis and fertility in adulthood.

Application of laser-capture microdissection to analysis of gene expression in the testis

The isolation and molecular analysis of highly purified cell populations from complex, heterogeneous tissues has been a challenge for many years. Spermatogenesis in the testis is a particularly difficult process to study given the unique multiple cellular associations within the seminiferous epithelium, making the isolation of specific cell types difficult. Laser-capture microdissection (LCM) is a recently developed technique that enables the isolation of individual cell populations from complex tissues. This technology has enhanced our ability to directly examine gene expression in enriched testicular cell populations by routine methods of gene expression analysis, such as real-time RT-PCR, differential display, and gene microarrays. The application of LCM has however introduced methodological hurdles that have not been encountered with more conventional molecular analyses of whole tissue. In particular, tissue handling (i.e. fixation, storage, and staining), consumables (e.g. slide choice), staining reagents (conventional H&E vs. fluorescence), extraction methods, and downstream applications have all required re-optimisation to facilitate differential gene expression analysis using the small amounts of material obtained using LCM. This review will discuss three critical issues that are essential for successful procurement of cells from testicular tissue sections; tissue morphology, capture success, and maintenance of molecular integrity. The importance of these issues will be discussed with specific reference to the two most commonly used LCM systems; the Arcturus PixCell IIe and PALM systems. The rat testis will be used as a model, and emphasis will be placed on issues of tissue handling, processing, and staining methods, including the application of fluorescence techniques to assist in the identification of cells of interest for the purposes of mRNA expression analysis.

17beta-estradiol induces the translocation of the estrogen receptors ESR1 and ESR2 to the cell membrane, MAPK3/1 phosphorylation and proliferation of cultured immature rat Sertoli cells

The aim of the present study was to determine the mechanisms involved in estrogen actions in cultured rat Sertoli cells. RT-PCR detected transcripts for the estrogen receptors ESR1 and ESR2 in cultured immature Sertoli cells and in the testis of 15-, 28-, and 120-day-old rats. The expression of ESR1 and ESR2 was confirmed in Sertoli cells by immunofluorescence and Western blot. Immunohistochemistry with cryosections of testes from immature and adult rats revealed that ESR1 is present in Sertoli, Leydig, and some peritubular myoid cells, and ESR2 is present in multiple cell types, including germ cells. Treatment of Sertoli cells with 17beta-estradiol (E(2)) induced a translocation of ESR1 and ESR2 to the plasma membrane and a concomitant phosphorylation of MAPK3/1. Both effects reached a maximum after 10 min and were blocked by PP2, an inhibitor of the SRC family of protein tyrosine kinases, and by the antiestrogen ICI 182,780 (ICI). MAPK3/1 phosphorylation was also decreased in the presence of AG 1478, an inhibitor of the epidermal growth factor receptor (EGFR) kinase, and in the presence of MAP2K1/2 inhibitor UO126. Treatment with E(2) for 24 h increased the incorporation of [methyl-(3)H]thymidine, which was blocked by ICI. These results indicate that E(2) activates an SRC-mediated translocation of estrogen receptors to the plasma membrane, which results in the activation of EGFR and the mitogen-activated protein kinase signaling pathway. In addition, activation of ESR1 and/or ESR2 by E(2) is involved in proliferation of immature Sertoli cells. The estrogen actions in Sertoli cells might be a key step mediating cellular events important for spermatogenesis and fertility.

Laser-assisted microdissection (LAM) in developmental biology

The analysis of gene expression in developing organs is a valuable tool for the assessment of genetic fingerprints during the various stages of differentiation. Complex processes in developing tissues are particularly difficult to understand in terms of biochemical phenomena. Laser-assisted microdissection (LAM) allows the efficient and precise capture of cells or groups of cells from developing tissues in sufficient quantities and within the context of time and space to permit the subsequent molecular characterization of the targeted tissue. The technique development has dramatically increased the ease of isolating specific cells which, together with progress in tissue preparation and microextraction protocols, allows for broad-range down-stream applications in the fields of genomics, transcriptomics and proteomics. This review gives an overview of the LAM technology and its application in developmental biology.

Effects of ICI 182780 on estrogen receptor expression, fluid absorption and sperm motility in the epididymis of the bonnet monkey

Background

The importance of estrogen in regulation of fluid absorption and sperm maturation in the rodent epididymis has been established from studies on estrogen receptor-alpha knockout mice. However, functional studies on the role of estrogen in primate epididymis have been few. The main objective of this study was therefore to extend these observations and systematically analyze the presence and function of estrogen receptors in modulating the function of the primate epididymis, using the bonnet monkey (Macaca radiata) as a model system.

Methods

A steroidal estrogen receptor (ER) antagonist, ICI 182780 (ICI), was administered to adult male bonnet monkeys via mini-osmotic pumps for a duration of 30 to 180 days. The expression of key estrogen-regulated genes (ER-alpha, Na-K ATPase alpha-1 and Aquaporin-1) was examined at specific time points. Further, the effect of ICI in modulating fluid reabsorption in efferent ductules was monitored, and critical sperm-maturation parameters were also analyzed.

Results

Our studies in the bonnet monkey revealed that both ER-alpha and ER-beta were expressed in all the three regions of the epididymis. We observed an increase in ER-alpha mRNA and protein in the caput of ICI-treated monkeys. Steady state mRNA levels of the water-channel protein, Aquaporin-1, was significantly lower in the caput of ICI-treated monkeys compared to controls, whereas the mRNA levels of Na-K ATPase alpha-1 remained unchanged. In vitro incubation of efferent ductules with ICI resulted in two-fold increase in tubular diameter, indicating affected fluid reabsorption capacity. Furthermore, sperm from ICI-treated monkeys were immotile.

Conclusion

Taken together, our results point to an integral role for estrogen in modulating the functions of the bonnet monkey epididymis. This study also demonstrates possible differences in the epididymal physiology of rodents and non-human primates, and thus underscores the significance of reports such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.