Exclusive nuclear location of estrogen receptors in Squalus testis

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

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

Coordination of spermatogenic processes in the testis: lessons from cystic spermatogenesis

A common observation in the vertebrate testis is that new germ cell clones enter spermatogenesis proper before previously formed clones have completed their development. The extent to which the developmental advance of any given germ cell clone in any phase of spermatogenesis is dependent on that of neighboring clones and/or on the coordinating influence of associated Sertoli cells in the immediate vicinity or of others further away remains unclear. This review presents an overall synthesis of findings in an ancient vertebrate, the spiny dogfish shark and shows that, even at this phyletic level, the developmental advance of a given germ cell clone is the outcome of various processes emanating from its spatiotemporal relationship with (1) its own complement of Sertoli cells in the anatomically distinct spermatocyst and (2) Sertoli cells associated with other germ cell clones that lie upstream or downstream in the spermatogenic progression and that secrete, among others, androgen and estrogen destined for target sites upstream. Analysis of the protracted spermatogenic cycle shows the coordination in space and time of spermatogenic and steroidogenic events. Furthermore, the natural withdrawal of pituitary gonadotropin support in the dogfish causes a distinct and highly ordered gradient of apoptosis among the spermatogonial generations; this in turn is a major contributing factor to the cyclic nature of sperm production observed in this lower vertebrate. Because of the simplicity of their testicular organization, their cystic spermatogenesis and their phylogenetic position, cartilaginous fishes constitute a valid vertebrate reference system for comparative analysis with higher vertebrates.

Diversity and biological significance of sex hormone-binding globulin in fish, an evolutionary perspective

In fish, two different genes, shbga and shbgb, exist that encode for very different proteins. Shbga is the ortholog of mammalian Shbg and was found in all investigated teleosts. In contrast, Shbgb is highly divergent and appears to be a salmonid-specific protein. Here, we review existing data on fish Shbga and Shbgb that have been obtained in chondrichthyes and osteichtyes. Even though other significant expression sites exist, existing data indicate that Shbga is mainly expressed in liver and subsequently secreted into the blood as a homodimer. In contrast, Shbgb is mainly expressed in the ovary, probably secreted as a monomer, and could contribute to the regulation of local steroid action. Binding studies indicate a specialization of circulating Shbg during evolution towards the preferential binding of estradiol and testosterone in teleosts. In contrast, specific fish steroids such as 11-oxo-androgens and oocyte maturation-inducing steroids that are crucial for reproduction are poorly bound by either form of Shbg.

Surflan and oryzalin impair reproduction in the teleost medaka (Oryzias latipes)

We conducted studies to determine if the xenoestrogens Surflan and its active ingredient oryzalin, affect indices of reproductive fitness in medaka (Oryzias latipes). Oryzalin (0.5, 0.25mg/l) or Surflan (2.0 microl/l) and oryzalin (0.5mg/l) significantly increased the mean number of non-fertilized eggs produced by treated females paired with untreated males, or by untreated females paired with treated males. Oryzalin (1.0, 0.5, 0.25mg/l) and Surflan (3.8, 2.0, 1.0 microl/l) significantly affected the time to hatch of eggs from treated females paired with untreated males, and from untreated females paired with treated males. Surflan (3.8, 2.0, 1.0 microl/l) induced intersex lesions in 80-100% of males. Oryzalin-exposed males exhibited a significant increase in the incidence of necrotic spermatids and necrotic spermatogonia, while oryzalin-exposed females had significantly fewer immature oocytes and an increase in the occurrence of hyperplastic ovaries. Our results indicate that Surflan and oryzalin affect both reproduction and gonadal histology in male and female medaka.

Estrogen receptor-alpha protein localization in the testis of the rainbow trout (Oncorhynchus mykiss) during different stages of the reproductive cycle

Estrogen receptor-alpha (ER-alpha) is important for male reproduction in mammals; however, no information is available on ER-alpha protein distribution in the testes of fishes. The cellular localization of the rainbow trout (Oncorhynchus mykiss) ER-alpha (rtER-alpha) protein, throughout the annual reproductive cycle was determined in this study. An antibody was designed based on a 15-amino acid sequence from the D-domain of the rtER-alpha, and its specificity was confirmed using Western blot analysis. Immunohistochemical analysis revealed rtER-alpha protein to be present only in the testicular interstitium, at every stage of the annual reproductive cycle. The localization of rtER-alpha protein in the interstitial fibroblasts, the Leydig cell precursor in the rainbow trout, suggests a role for estrogens in the differentiation of these precursor cells into mature Leydig cells. This is the first study to report the cellular localization of an estrogen receptor protein in the testis of any fish species.

Male goldfish reproductive behaviour and physiology are severely affected by exogenous exposure to 17beta-estradiol

Mature male goldfish were exposed to different concentrations of the natural hormone 17beta-estradiol (E2). Two methods of exposure were employed, via ingestion at 0, 1, 10 and 100 microg/g food and via the water at 0, 1 and 10 microg/l. The fish were exposed for 24-28 days during the spawning period. The males were then paired with an artificially induced, spawning female and their sexual behaviour was observed during a 15 min period. The physiological status of the fish was also examined with respect to GSI, presence of milt and spawning tubercles and the blood plasma concentration of E2. Despite the relatively short exposure period, exposure to physiological levels of E2 was shown to severely affect the male goldfish reproductive behaviour and physiology. In conclusion, the results from this study and the ability to interpret the effects on this well-studied species, show that the effects of E2, and possibly other estrogenic EDCs, have severe effects at several vital levels of male goldfish reproduction. The results also suggests that the hormone E2 can act as an endocrine disrupting chemical (EDC) in the environment.

Effects of estrogens and xenoestrogens on androgen production by Atlantic croaker testes in vitro: evidence for a nongenomic action mediated by an estrogen membrane receptor

The short-term effects of estrogens and xenoestrogens on testicular androgen production were investigated in an in vitro incubation bioassay system using testicular tissue from the Atlantic croaker (Micropogonias undulatus). Incubation of testicular tissue fragments with estradiol over the concentration range of 37 nM to 37 microM caused concentration-dependent decreases in gonadotropin-stimulated 11-ketotestosterone (11-KT) production. The effect was specific for estrogens; progesterone, cortisol, and the synthetic androgen mibolerone did not significantly alter 11-KT production at similar concentrations. Diethylstilbestrol, the antiestrogen ICI 182,780, and several xenoestrogens including Kepone (chlordecone), 4-nonylphenol, and a hydroxylated polychlorinated biphenyl metabolite also significantly decreased gonadotropin-stimulated 11-KT production. The action of estradiol was rapid (<5 min) and was not blocked by actinomycin D and cycloheximide, inhibitors of transcription and translation, respectively. Moreover, estradiol conjugated to BSA, which cannot pass through the cell membrane, also caused a decrease in 11-KT production. In addition, an estrogen-binding moiety was identified in testicular membrane preparations that had a single class of high-affinity (K(d) 1.6 nM), saturable (1.2 nM), displaceable, finite (B(max) 0.03 nM, 26 fmol/g testis) binding sites specific for estrogens and exhibited rapid association (t(1/2) = 5 min), characteristics typical of steroid membrane receptors. Overall the relative binding affinities of estrogens, other steroids, antiestrogens, and xenoestrogens for the membrane preparation correlated with their activities in the androgen production bioassay, thereby satisfying the final criteria for the designation of this estrogen-binding moiety as a steroid membrane receptor. The results demonstrate that estrogens and also probably xenoestrogens can act on the cell surface via a nongenomic mechanism to alter testicular androgen production in this vertebrate species.

Binding characteristics of estrogen receptor (ER) in Atlantic croaker (Micropogonias undulatus) testis: different affinity for estrogens and xenobiotics from that of hepatic ER

An estrogen receptor (ER) was identified in cytosolic and nuclear fractions of the testis in a marine teleost, Atlantic croaker (Micropogonias undulatus). A single class of high affinity, low capacity, and displaceable binding sites was identified by saturation analysis, with a Kd of 0.40 nM in cytosolic extracts and a Kd of 0.33 nM in nuclear extracts. Competition studies demonstrated that the receptor was highly specific for estrogens (diethylstilbestrol > estradiol >> estriol = estrone) and also bound several antiestrogens. Testosterone and 5alpha-dihydrotestosterone had much lower affinities for the receptor, whereas no displacement of specific binding occurred with 11-ketotestosterone or any of the C21 maturation-inducing steroids. A variety of xenoestrogens, including o,p'-dichlorodiphenyltrichloroethane (DDT), chlordecone (Kepone), nonylphenol, hydroxylated polychlorinated biphenyls (PCBs), and the mycotoxin zearalenone, bound to the receptor with relatively low binding affinities, 10(-3) to 10(-5) that of estradiol. A comparison of the binding affinities of various ligands for the testicular ER and the hepatic ER in this species revealed that the testicular ER was saturated at a lower [3H]estradiol concentration (1 nM vs. 4 nM). The binding affinities of several compounds, including testosterone and nafoxidine, exhibited marked differences for the two ERs; and most of the estrogens and xenoestrogens tested had higher binding affinities for the testicular receptor. Minor amounts of estradiol (0.12 ng/g tissue/h) were produced by testicular tissue fragments incubated in vitro, and estradiol was detected in male Atlantic croaker plasma. The identification of a testicular ER and evidence that estradiol is produced by the testes in croaker suggest that estrogens participate in the hormonal control of testicular function in teleosts.

Negative feedback control of the spermatogenic progression by testicular oestrogen synthesis: insights from the shark testis model

The organisation of the testis of the dogfish shark is technically advantageous for stage-by-stage analysis of spermatogenesis in vivo and in vitro. Prior studies using this model show that total oestrogen receptors (ER) are concentrated in regions where spermatocysts ("follicle-like" germ cell-Sertoli cell units) are in stem cell and spermatogonial stages: respectively, germinal zone (GZ) and premeiotic (PrM) regions. By contrast, key enzymes regulating oestrogen (E) concentrations (aromatase, 17 alpha-hydroxylase) are maximal in meiotic (M) and postmeiotic (PoM) regions, respectively, which are upstream in the intratesticular vascular pathway. To investigate the hypothesis that E is part of a signalling mechanism between stages of development, studies were undertaken to test direct effects of oestradiol-17 beta (E2) on processes in ER-rich regions. As measured by [3H]thymidine (-Tdr) incorporation. DNA synthesis in GZ and PrM regions was inhibited by E2 (0-1000 nM) in a dose-response fashion. The maximal response (30-40%) was significant, reproducible and observed within 72 hr of treatment. Insulin differentially affected DNA synthesis and the response to E2 in GZ in GZ and PrM regions. As measured by [3H]Tdr release after prelabelling spermatocysts of GZ regions, apoptosis progressively decreased with increasing concentrations of E2. At the maximal dose of E2 used, there was no effect on total protein synthesis or secretion in combined GZ/PrM cysts, indicating that effects on DNA synthesis and cell death were authentically physiological, not pharmacological, and consistent with a state of developmental arrest. These results support the hypothesis that E synthesised within the testis is part of a negative feedback regulatory mechanism whereby more mature stages regulate the developmental advance of less mature stages. A growth control mechanism of this type could explain the strict temporal, spatial and quantitative order of succeeding stages characteristic of normal spermatogenesis in all vertebrates. Further study is required to determine whether E signalling in this model is restricted to Sertoli cells or has a germ cell component.

Identification and characterization of estrogen and progesterone receptors from the oviduct of the American alligator (Alligator mississippiensis)

A protein extract prepared from the egg shell fiber-secreting region of the oviduct of Alligator mississippiensis was assayed for the presence of receptors for estrogen and progesterone. In the presence of [3H]-estradiol-17 beta, the extract contained an estrogen-binding activity which reached equilibrium at 25 degrees C in 1 h. Scatchard analysis demonstrated that a single estrogen-binding activity was present in the extract with a Kd of 0.5 nM for [3H]estradiol-17 beta. A steroid specificity competition assay showed the estrogen binding activity strongly recognized estradiol-17 beta and diethylstilbestrol (DES) and weakly interacted with estrone, estriol, estradiol-17 alpha, and dihydrotestosterone (DHT). The estrogen binding activity did not recognize testosterone, dexamethasone or progesterone. The extract exhibited a DNA-binding activity that recognized an estrogen response element in a gel mobility shift assay. We have also identified a high affinity binding activity in the extract that specifically recognized the synthetic progestin R5020 with a Kd of 0.9 nM. This binding activity recognized 17 alpha-estradiol, dexamethasone, testosterone, and estriol. This activity did not recognize DHT, DES, or estradiol-17 beta. These data suggest the presence of estrogen and progesterone receptors in the oviduct of the alligator.

Culture of intact Sertoli/germ cell units and isolated Sertoli cells from Squalus testis. II. Stimulatory effects of insulin and IGF-I on DNA synthesis in premeiotic stages

To investigate growth control mechanisms during spermatogenesis in vitro, [3H]thymidine incorporation into acid-insoluble macromolecules was used to quantify DNA synthesis in cultured spermatocysts (intact Sertoli cell/germ cell clones) derived from premeiotic (PrM), meiotic (M), and postmeiotic (PoM) regions of dogfish (Squalus acanthias) testis. Forty-eight hours after seeding in basal medium, DNA synthesis was > 7-fold higher in PrM cysts than in other stages, thus verifying the staging procedure. In autoradiograms, germ cells of PrM cysts (e.g., spermatogonial and preleptotene stages) were labeled all-or-none, but not all cysts were labeled, and later developmental stages (e.g., cysts with round or elongating spermatids) were never labeled. Fetal bovine serum (FBS, 10%) and insulin-transferrin-selenite (ITS, 10 micrograms-10 ng/ml) doubled DNA synthesis in PrM cyst cultures but had no effect at other stages. Bovine insulin (10 micrograms/ml) and human recombinant insulin-like growth factor-I (IGF-I, 15 ng/ml) also doubled [3H]thymidine uptake in PrM cultures, but lower doses were less effective and estradiol-17 beta, transferrin, adult shark serum, purified shark relaxin, and a variety of other known growth factors were neither stimulatory nor inhibitory at the doses and conditions tested. Sertoli cell monolayers derived from PrM- or M-stage spermatocysts displayed a dose-response increase in DNA synthesis after addition of IGF-I (15-75 ng/ml), with a maximal increment significantly greater than with 10% FBS. Using [3H]thymidine incorporation by PrM cysts as an end-point, stimulatory bioactivity was detected in the < 30,000 kDa fraction of spent media from PrM Sertoli cells, whereas the low molecular weight fraction of M-stage Sertoli cells was inhibitory. Gel electrophoretic analysis of the two fractions revealed qualitative and quantitative differences in protein banding patterns, reinforcing the view that secretory activity of Sertoli cells is stage related. Results of these studies implicate insulin/IGF-I in mechanisms governing proliferation of male germ cells and support the view that Sertoli cells have an autocrine or paracrine role as both targets and sources of growth regulatory factors.

Sulfoconjugation of steroids and the vascular pathway of communication in dogfish testis

The zonal testis of the dogfish (Squalus acanthias) has proven advantageous to study biochemical changes in relation to stage of spermatogenesis, including information on steroidogenic enzymes and steroid receptors. To investigate whether sulfotransferase is part of a mechanism regulating the availability of biologically active hormone in close proximity to receptors, we measured in vitro conversion of [3H]estrone (E1) to sulfoconjugated metabolites in cytosolic subfractions of testes grossly dissected according to germ cell composition (premeiotic-PrM, meiotic-M, and postmeiotic-PoM stages). Assays were carried out in the presence of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) at 22 degrees C and optimized for time (60 min) and protein (500 micrograms/ml). Michaelis-Menten kinetics and saturation analysis gave the following reaction constants for [3H]E1: Km = 0.33 microM, Vmax = 2.5 pmol/min/mg; and for PAPS: Km = 33 microM, Vmax = 1.1 pmol/min/mg; competition studies carried out in the absence or presence of 1- or 5-fold excess radioinert steroids indicated that estrogen (E2 > E1) as well as androgens (T = DHEA > 5 alpha dihydrotestosterone, DHT) were effective inhibitors. Sulfotransferase activity was found to be stage-related, being highest in PoM regions (2.31 +/- 0.24 pmol/min/mg protein) when compared to M and PrM regions (1.22 +/- 0.22 and 1.28 +/- 0.21 pmol/min/mg protein, respectively). Sulfoconjugation and the intratesticular distribution of steroid sulfates were also measured in vivo by perfusion of the intact testis with [3H]androgen or -estrogen. The pathway of blood flow via the genital artery was epigonal organ-->PoM-->M-->PrM (mature-->immature). Perfused [3H]E2, T, and DHT were all extensively metabolized in a one-pass, 1 hr perfusion, less than 10% of perfused [3H] steroid being recovered from testicular tissues as unchanged steroid. In general, recovery of polar metabolites was greater than non-polar metabolites from all three substrates. Sequential hydrolysis with glucuronidase and glusulase indicated that sulfoconjugation is a minor component (< 20%) of several "inactivating" pathways, which include glucuronide conjugation, 17-ketosteroid synthesis, and pathways leading to unidentified polar metabolites. No consistent stage-related distribution patterns were observed for any of the metabolite subfractions; however, total recovered radioactive steroid (polar plus non-polar) formed a decreasing concentration gradient from point of entry of perfusate (PoM region) to point of exit (PrM region). These data support the conclusion that access to receptors by steroid ligands may be controlled by a balance between activating and inactivating pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Autocrine and paracrine role of steroids during spermatogenesis: studies in Squalus acanthias and Necturus maculosus

Due to a cystic mode of spermatogenesis and zonal testes, the spiny dogfish shark (Squalus acanthias) and salamander (Necturus maculosus) are advantageous for studying the relationship between steroidogenesis and germ cell development. Direct analysis of steroidogenic enzymes and steroid receptors in staged tissue samples, together with light and electron microscopic observation, suggests that androgens and estrogens produced by Sertoli cells or Leydig cells immediately before or after spermiation serve as intratesticular regulators of events specific to premeiotic stages of spermatogenesis. These correlative data are consistent with limited observations in mammalian testis and provide a conceptual framework for direct testing of functional interactions between spermatogenesis and steroidogenesis in future studies.

Culture of intact Sertoli/germ cell units and isolated Sertoli cells from Squalus testis: I. Evidence of stage-related functions in vitro

As part of an ongoing program of research using the testis of the dogfish shark (Squalus acanthias) to characterize morphologic and functional changes during spermatogenesis, we have developed procedures for culturing intact spermatocysts (germ cell/Sertoli cell clones) and isolated Sertoli cells from premeiotic, meiotic, and postmeiotic stages of development. Phase contrast and light microscopy confirmed the stage and cellular composition of spermatocysts and showed that they retained their closed, spherical configuration for at least 15 d in culture. Stage-related variations in [3H]thymidine incorporation (premeiotic much greater than meiotic = postmeiotic) were observed, a pattern that was the same quantitatively and qualitatively after one or seven days of culture. [3H]Leucine-labeled protein synthesis was twofold greater in cultures with premeiotic spermatocysts than in cultures with more mature stages, whether medium or cysts were analyzed. Sertoli cells isolated from spermatocysts of different stages differed in size, shape, cytological appearance, ability to form flattened monolayers, and rate of DNA synthesis. One day after seeding, [3H]thymidine labeling of Sertoli cells corresponded to the pattern obtained with intact spermatocysts (premeiotic much greater than meiotic = postmeiotic); however, 7 days in culture effected a 40- to 200-fold increase in this parameter and altered the stage-dependent pattern (premeiotic = meiotic greater than postmeiotic). Also, when [3H]leucine-labeled macromolecules secreted by Sertoli cells from premeiotic versus meiotic stages were analyzed by polyacrylamide gel electrophoresis (PAGE), banding patterns differed. Initial results demonstrate the feasibility and potential of this in vitro system for studying qualitative and quantitative changes during spermatogenesis.

Progesterone and oestradiol-17 beta receptors in the porcine myometrium during the oestrous cycle

The concentrations of the tissue receptors for oestradiol (E) and progesterone (P) in the porcine myometrium at different stages of the oestrous cycle have been investigated by in vitro binding and exchange methods. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptors proteins with high affinity. The amount of ERc did not vary significantly throughout the cycle. Significant variations in the amount of myometrial ERn were observed with high concentrations during late pro-oestrus. The amount of PRc reached a top value in early pro-oestrus. A significant increase in PRn levels was observed at early luteal phase, and it remained high during the rest of the luteal phase. The temporal relationships between the variations in levels of oestradiol and progesterone nuclear receptors in myometrial tissue and those of the circulating plasma levels were established. The data obtained in this study suggest a relationship between the changes in levels of oestradiol and progesterone myometrial binding and the uterine motility pattern during the oestrous cycle.

The effect of homogenization temperature upon the apparent cellular compartmentalization of unoccupied estrogen receptor

Homogenization of rat uterus at elevated temperatures results in an increased nuclear localization of unoccupied estrogen receptor. This is a nonlinear effect which is accounted for by an increased population of KCl-resistant nuclear binding sites at the elevated homogenization temperatures.

Regulation of spermatogenesis: the shark testis model

Spermatogenesis is a unique developmental sequence dependent on FSH and androgen. Due to the complex organization of the mammalian testis, however, mechanistic details of regulation are largely unknown. Using the dogfish shark (Squalus acanthias) in which there is a cystic mode of spermatogenesis and a topographic separation of different germ cell stages within the testis, we have obtained new information of general relevance on stage-related biochemical and morphological changes and have proposed a model in which steroids serve as parahormonal regulators of the spermatogenic progression. In addition, techniques developed for culturing staged spermatocysts (intact Sertoli/germ cell units) and isolated, staged Sertoli cells demonstrate the usefulness of this model for studying spermatogenic regulation under defined conditions in vitro.

Immunohistological localization of 17 beta-estradiol and testosterone in the ovary of the rainbow trout (Salmo gairdneri Richardson) during the preovulatory period

Antisera (AS) raised in rabbits against 17 beta-estradiol (E) and testosterone (T) were tested for their suitability to localize E and T on deparaffinized, rehydrated sections of preovulatory trout ovaries, using the unlabeled antibody technique. Conventional control experiments demonstrated the specificity of the staining reactions. Furthermore, no staining was observed after the removal of T-specific antibodies by affinity chromatography, or following gonadectomy when non-gonadal tissue sections of male trout were incubated with T-AS. Antiserum, raised against 11-oxotestosterone and devoid of antibodies cross-reacting with T, did not stain ovarian sections. The loci at which E and T are detected in the somatic compartment are consistent with the two-cell concept of estrogen synthesis, where aromatizable androgens are produced in the thecal/interstitial layer and serve as substrates for estrogen synthesis in granulosa cells. Both steroids were detected in yolk vesicles from the stage of endogenous vitellogenesis. T-AS showed affinity for nuclei of vitellogenic oocytes. Nucleoli were not stained.