Steroids and oocyte maturation--a new look at an old story

Gonadotropin elevation is ootoxic to ovulatory oocytes and inhibits oocyte maturation, and activin decoy receptor ActRIIB:Fc therapeutically restores maturation

BACKGROUND

Elevated FSH often occurs in women of advanced maternal age (AMA, age ≥ 35) and in infertility patients undergoing controlled ovarian stimulation (COS). There is controversy on whether high endogenous FSH contributes to infertility and whether high exogenous FSH adversely impacts patient pregnancy rates.

METHODS

The senescence-accelerated mouse-prone-8 (SAMP8) model of female reproductive aging was employed to assess the separate impacts of age and high FSH activity on the percentages (%) of viable and mature ovulated oocytes recovered after gonadotropin treatment. Young and midlife mice were treated with the FSH analog equine chorionic gonadotropin (eCG) to model both endogenous FSH elevation and exogenous FSH elevation. Previously we showed the activin inhibitor ActRIIB:Fc increases oocyte quality by preventing chromosome and spindle misalignments. Therefore, ActRIIB:Fc treatment was performed in an effort to increase % oocyte viability and % oocyte maturation.

RESULTS

The high FSH activity of eCG is ootoxic to ovulatory oocytes, with greater decreases in % viable oocytes in midlife than young mice. High FSH activity of eCG potently inhibits oocyte maturation, decreasing the % of mature oocytes to similar degrees in young and midlife mice. ActRIIB:Fc treatment does not prevent eCG ootoxicity, but it restores most oocyte maturation impeded by eCG.

CONCLUSIONS

FSH ootoxicity to ovulatory oocytes and FSH maturation inhibition pose a paradox given the well-known pro-growth and pro-maturation activities of FSH in the earlier stages of oocyte growth. We propose the FOOT Hypothesis ("FSH OoToxicity Hypothesis), that FSH ootoxicity to ovulatory oocytes comprises a new driver of infertility and low pregnancy success rates in DOR women attempting spontaneous pregnancy and in COS/IUI patients, especially AMA women. We speculate that endogenous FSH elevation also contributes to reduced fecundity in these DOR and COS/IUI patients. Restoration of oocyte maturation by ActRIB:Fc suggests that activin suppresses oocyte maturation in vivo. This contrasts with prior studies showing activin A promotes oocyte maturation in vitro. Improved oocyte maturation with agents that decrease endogenous activin activity with high specificity may have therapeutic benefit for COS/IVF patients, COS/IUI patients, and DOR patients attempting spontaneous pregnancies.

A fatty acid anabolic pathway in specialized-cells sustains a remote signal that controls egg activation in Drosophila

Egg activation, representing the critical oocyte-to-embryo transition, provokes meiosis completion, modification of the vitelline membrane to prevent polyspermy, and translation of maternally provided mRNAs. This transition is triggered by a calcium signal induced by spermatozoon fertilization in most animal species, but not in insects. In Drosophila melanogaster, mature oocytes remain arrested at metaphase-I of meiosis and the calcium-dependent activation occurs while the oocyte moves through the genital tract. Here, we discovered that the oenocytes of fruitfly females are required for egg activation. Oenocytes, cells specialized in lipid-metabolism, are located beneath the abdominal cuticle. In adult flies, they synthesize the fatty acids (FAs) that are the precursors of cuticular hydrocarbons (CHCs), including pheromones. The oenocyte-targeted knockdown of a set of FA-anabolic enzymes, involved in very-long-chain fatty acid (VLCFA) synthesis, leads to a defect in egg activation. Given that some but not all of the identified enzymes are required for CHC/pheromone biogenesis, this putative VLCFA-dependent remote control may rely on an as-yet unidentified CHC or may function in parallel to CHC biogenesis. Additionally, we discovered that the most posterior ventral oenocyte cluster is in close proximity to the uterus. Since oocytes dissected from females deficient in this FA-anabolic pathway can be activated in vitro, this regulatory loop likely operates upstream of the calcium trigger. To our knowledge, our findings provide the first evidence that a physiological extra-genital signal remotely controls egg activation. Moreover, our study highlights a potential metabolic link between pheromone-mediated partner recognition and egg activation.

Pubertal sexual development and endpoints for disrupted spermatogenesis in the model Xenopus tropicalis

Peripubertal models to determine effects of anti-androgenic endocrine disrupting chemicals are needed. Using the toxicological model species Xenopus tropicalis, the aims of the study were to 1) provide data on sexual maturation and 2) characterise effects of short-term exposure to an anti-androgenic model substance. Juvenile (2.5 weeks post metamorphosis old) X. tropicalis were exposed to 0, 250, 500 or 1000 µg flutamide/L (nominal) for 2.5 weeks. Upon exposure termination, histology of gonads and Müllerian ducts was characterised in detail. New sperm stages were identified: pale and dark spermatogonial stem cells (SSCs). The testes of control males contained spermatozoa, indicating pubertal onset. The ovaries were immature, and composed of non-follicular and pre-vitellogenic follicular oocytes. The Müllerian ducts were more mature in females than males indicating development/regression in the females and males, respectively. In the 500 µg/L group, the number of dark SSCs per testis area was decreased and the number of secondary spermatogonia was increased. No treatment effects on ovaries or Müllerian ducts were detected. To conclude, our present data provide new knowledge on spermatogenesis, and pubertal onset in X. tropicalis. New endpoints for evaluating spermatogenesis are suggested to be added to existing assays used in endocrine and reproductive toxicology.

Follicular cells protect Xenopus oocyte from abnormal maturation via integrin signaling downregulation and O-GlcNAcylation control

Xenopus oocytes are encompassed by a layer of follicular cells that contribute to oocyte growth and meiosis in relation to oocyte maturation. However, the effects of the interaction between follicular cells and the oocyte surface on meiotic processes are unclear. Here, we investigated Xenopus follicular cell function using oocyte signaling and heterologous-expressing capabilities. We found that oocytes deprotected from their surrounding layer of follicular cells and expressing the epidermal growth factor (EGF) receptor (EGFR) and the Grb7 adaptor undergo accelerated prophase I to metaphase II meiosis progression upon stimulation by EGF. This unusual maturation unravels atypical spindle formation but is rescued by inhibiting integrin β1 or Grb7 binding to the EGFR. In addition, we determined that oocytes surrounded by their follicular cells expressing EGFR-Grb7 exhibit normal meiotic resumption. These oocytes are protected from abnormal meiotic spindle formation through the recruitment of O-GlcNAcylated Grb7, and OGT (O-GlcNAc transferase), the enzyme responsible for O-GlcNAcylation processes, in the integrin β1-EGFR complex. Folliculated oocytes can be forced to adopt an abnormal phenotype and exclusive Grb7 Y338 and Y188 phosphorylation instead of O-GlcNAcylation under integrin activation. Furthermore, an O-GlcNAcylation increase (by inhibition of O-GlcNAcase), the glycosidase that removes O-GlcNAc moieties, or decrease (by inhibition of OGT) amplifies oocyte spindle defects when follicular cells are absent highlighting a control of the meiotic spindle by the OGT-O-GlcNAcase duo. In summary, our study provides further insight into the role of the follicular cell layer in oocyte meiosis progression.

A review of the reproductive system in anuran amphibians

Reproductive biology is an important topic that is well explored in many vertebrates, but information about frogs' reproductive mechanisms could be improved. Therefore, this review aims to provide organized and specific information on frog reproduction. First, we developed schemes that illustrate the general information regarding reproductive biological mechanisms in frogs in a specific way. Then, we described the physiological, histological, and morphological mechanisms of each organ of the reproductive system of male and female frogs. Finally, this manuscript may contribute to a broader understanding of anuran reproductive biology. Since, understanding frogs' reproductive system permits one to make a comparison with reproduction with other anurans.

Preconception exposure to perfluoroalkyl and polyfluoroalkyl substances and couple fecundity: A couple-based exploration

Numerous studies have examined the adverse health effects of perfluoroalkyl and polyfluoroalkyl substances (PFAS) but it remains unclear whether preconception exposure to PFAS affects couple fecundity. This prospective preconception cohort study with 936 Chinese couples aimed to comprehensively assess the effects of PFAS on couple fecundity [measured by the time to pregnancy (TTP)] and infertility (i.e., TTP > 12 menstrual cycles) with a focus on the effects of partner-specific exposure and joint-effects of couple-based exposure. Twenty-five PFAS were quantified in plasma from each partner, including seven branched isomers, two chlorinated polyfluoroalkyl ether sulfonic acids, four emerging PFAS replacements [i.e., 6:2 fluorotelomer phosphate diester (6:2 diPAP) and three short-chain alternatives: perfluoro-n-butanoicacid, perfluorobutane sulfonate and perfluoroheptanoic acid (PFHpA)]. Using a two-phase regression approach composed of elastic net regression and principal component analysis, we found that exposure to 6:2 diPAP and PFHpA rather than legacy PFAS in women and the couple-based exposure patterns characterized by high level of female 6:2 diPAP were significantly associated with reduced couple fecundity, which was independent of the adjustment of co-exposed PFAS homogenous from both partners. For example, a ln unit increase in female 6:2 diPAP was associated with 15 % [fecundity odds ratio (FOR) = 0.85, 95 %CI: 0.76, 0.96)] lower odds of couple fecundability (i.e., longer TTP) and 45 % increased risk of infertility [OR = 1.45 (95 %CI: 1.16, 1.81)], respectively. While most PFAS in men were not associated with couple fecundity, certain PFAS (e.g., perfluorohexane sulfonic acid) in men were negatively associated with infertility risk. However, the combined effects of PFAS mixture in couples were nonsignificant. Our findings suggest that PFAS in men and women may exert different impacts on couple fecundity. Preconception exposure to 6:2 diPAP and PFHpA in women may have the potential to impair couple fecundity.

Regulation of oocyte maturation: Role of conserved ERK signaling

During oogenesis, oocytes arrest at meiotic prophase I to acquire competencies for resuming meiosis, fertilization, and early embryonic development. Following this arrested period, oocytes resume meiosis in response to species-specific hormones, a process known as oocyte maturation, that precedes ovulation and fertilization. Involvement of endocrine and autocrine/paracrine factors and signaling events during maintenance of prophase I arrest, and resumption of meiosis is an area of active research. Studies in vertebrate and invertebrate model organisms have delineated the molecular determinants and signaling pathways that regulate oocyte maturation. Cell cycle regulators, such as cyclin-dependent kinase (CDK1), polo-like kinase (PLK1), Wee1/Myt1 kinase, and the phosphatase CDC25 play conserved roles during meiotic resumption. Extracellular signal-regulated kinase (ERK), on the other hand, while activated during oocyte maturation in all species, regulates both species-specific, as well as conserved events among different organisms. In this review, we synthesize the general signaling mechanisms and focus on conserved and distinct functions of ERK signaling pathway during oocyte maturation in mammals, non-mammalian vertebrates, and invertebrates such as Drosophila and Caenorhabditis elegans.

Reproduction and Maturation of Sea Bass, Lateolabrax japonicus, after Transportation from Net-Cages to Indoor Tanks

To determine whether the reproductive processes of sea bass, Lateolabrax japonicus, proceed normally after transportation from an outdoor net-cage into indoor tanks, we examined changes in the gonadosomatic index (GSI), histological gonadal tissue, and plasma levels of sex hormones (testosterone and estradiol-17ß) during their annual reproductive cycle. We also measured maturation and spawning across two sea water salinity levels (full and low salinity). Fecundity was estimated by the relationship between egg number and body size in female sea bass. Monthly changes in the GSI, histological gonadal tissues, and oocyte size showed both male and female sea bass reach final maturation in January and February, respectively, indicating that the spermiation of males occurs earlier than the spawning of females. The histological results indicated that the sea bass is a multiple spawner, similar to many marine teleosts, exhibiting group-synchronous oocyte development. Female maturation and spawning were enhanced in lower salinity seawater (29.6–31.0 psu) compared to that of normal salinity (34.5–35.1 psu). These results confirm that sea bass reproduction can occur successfully in captivity and imply that fertilized eggs can be collected from February to March. Additionally, our results show that lower salinity enhances oocyte maturation and spawning of female sea bass.

Functional characterization of two 20β-hydroxysteroid dehydrogenase type 2 homeologs from Xenopus laevis reveals multispecificity

The African clawed frog, Xenopus laevis, is a versatile model for biomedical research and is largely similar to mammals in terms of organ development, anatomy, physiology, and hormonal signaling mechanisms. Steroid hormones control a variety of processes and their levels are regulated by hydroxysteroid dehydrogenases (HSDs). The subfamily of 20β-HSD type 2 enzymes currently comprises eight members from teleost fish and mammals. Here, we report the identification of three 20β-HSD type 2 genes in X. tropicalis and X. laevis and the functional characterization of the two homeologs from X. laevis. X. laevis Hsd20b2.L and Hsd20b2.S showed high sequence identity with known 20β-HSD type 2 enzymes and mapped to the two subgenomes of the allotetraploid frog genome. Both homeologs are expressed during embryonic development and in adult tissues, with strongest signals in liver, kidney, intestine, and skin. After recombinant expression in human cell lines, both enzymes co-localized with the endoplasmic reticulum and catalyzed the conversion of cortisone to 20β-dihydrocortisone. Both Hsd20b2.L and Hsd20b2.S catalyzed the 20β-reduction of further C₂₁ steroids (17α-hydroxyprogesterone, progesterone, 11-deoxycortisol, 11-deoxycorticosterone), while only Hsd20b2.S was able to convert corticosterone and cortisol to their 20β-reduced metabolites. Estrone was only a poor and androstenedione no substrate for both enzymes. Our results demonstrate multispecificity of 20β-HSD type 2 enzymes from X. laevis similar to other teleost 20β-HSD type 2 enzymes. X. laevis 20β-HSD type 2 enzymes are probably involved in steroid catabolism and in the generation of pheromones for intraspecies communication. A role in oocyte maturation is unlikely.

Dissection of the Ovulatory Process Using ex vivo Approaches

Ovulation is a unique physiological phenomenon that is essential for sexual reproduction. It refers to the entire process of ovarian follicle responses to hormonal stimulation resulting in the release of mature fertilization-competent oocytes from the follicles and ovaries. Remarkably, ovulation in different species can be reproduced out-of-body with high fidelity. Moreover, most of the molecular mechanisms and signaling pathways engaged in this process have been delineated using in vitro ovulation models. Here, we provide an overview of the major molecular and cytological events of ovulation observed in frogs, primarily in the African clawed frog Xenopus laevis, using mainly ex vivo approaches, with the focus on meiotic oocyte maturation and follicle rupture. For the purpose of comparison and generalization, we also refer extensively to ovulation in other biological species, most notoriously, in mammals.

Embryos from polycystic ovary syndrome patients with hyperandrogenemia reach morula stage faster than controls

Objective

To investigate if patients with polycystic ovary syndrome (PCOS) have altered embryo morphokinetics when compared with controls.

Design

Retrospective cohort analysis.

Setting

Single academic fertility clinic in a tertiary hospital setting.

Patients

Age- and body mass index-matched patients who underwent in vitro fertilization diagnosed with PCOS using the Rotterdam criteria. A subanalysis was performed on patients with PCOS with hyperandrogenemia. Sixty-four patients with PCOS were identified with 990 embryos that were matched with 64 control patients with 628 embryos.

Interventions

None.

Main Outcome Measures

Time to blastulation.

Results

Embryos from women with PCOS displayed faster growth rate at t7, t8, and t9; all other morphokinetic points were similar. Patients with PCOS also had a higher number of oocytes retrieved. No differences were seen in the fertilization rate or blastulation rate. Patients with PCOS had a higher miscarriage rate (38.1% in PCOS vs. 18.8% in controls). Patients with hyperandrogenic PCOS showed a faster growth rate at t5, t6, t7, t8, t9, and morula.

Conclusions

Embryos from women with PCOS grew faster until 9-cell stage and women with hyperandrogenic PCOS until morula. Patients with PCOS also showed a higher miscarriage rate. The alterations in early embryo development are consistent with altered fertility and obstetric outcomes in the population with PCOS and may be due to the hyperandrogenic microenvironment in the ovarian follicle.

Effects of 11-Ketotestosterone on Development of the Previtellogenic Ovary in the Sterlet, Acipenser ruthenus

11-ketotestosterone (11-KT) is a non-aromatizable and the most potent androgen in a few teleost. It has been reported that 11-KT in serum had a high concentration and increased sharply before the period of yolk deposition in females of few fishes. The aim of this study was to analyze the role of 11-KT both in vivo and in vitro on ovarian development, related gene expression levels, Vitellogenin (Vtg) synthesis, and serum sex steroid concentrations in previtellogenic cultured sterlet (Acipenser ruthenus). Silastic strips embedded with 11-KT (5 or 25 mg/kg) were implanted in vivo for 30 days. Ovarian masculinization or sex reversal was not observed. Histological analysis showed that 11-KT promoted sterlet ovarian development in a dose-dependent manner. Vtg and testosterone (T) increased significantly, while 17β-estradiol (E2) decreased with no significant difference among groups. The expression of genes androgen receptor (ar), vtg and lipoprotein lipase (lpl) were significantly increased in liver. However, 11-KT had no effect on the expression of foxl2 and cyp19a1 in ovary. In vitro, after incubation with 11-KT (10 and 100 μM) for 5 days, both T and E2 concentrations increased in both hepatic explants and ovarian explants culture medium; the concentration of Vtg also increased in hepatic explants culture medium. The expression of ar, era, vtg, and lpl increased significantly in hepatic explants. However, only the expression of era significantly increased in cultured ovarian explants. Altogether, these results suggest that 11-KT induced ovarian development, as well as Vtg and lipid synthesis, and could be an important factor facilitating the initiation of Vtg synthesis in the liver of the previtellogenic sterlet.

In Vitro Reconstruction of Xenopus Oocyte Ovulation

Progesterone is widely used to induce maturation of isolated fully grown oocytes of the African clawed frog, Xenopus laevis. However, the hormone fails to release oocytes from the layer of surrounding follicle cells. Here, we report that maturation and follicle rupture can be recapitulated in vitro by treating isolated follicular oocytes with progesterone and low doses of the matrix metalloproteinase (MMP), collagenase, which are ineffective in the absence of the steroid. Using this in vitro ovulation model, we demonstrate that germinal vesicle breakdown (GVBD) and oocyte liberation from ovarian follicles occur synchronously during ovulation. Inhibition of the MAPK pathway in these experimental settings suppresses both GVBD and follicular rupture, whereas inhibition of MMP activity delays follicular rupture without affecting GVBD. These results highlight importance of MAPK and MMP activities in the ovulation process and provide the first evidence for their involvement in the release of oocytes from ovarian follicles in frogs. The in vitro ovulation model developed in our study can be employed for further dissection of ovulation.

The myo-inositol effect on the oocyte quality and fertilization rate among women with polycystic ovary syndrome undergoing assisted reproductive technology cycles: a randomized clinical trial

PURPOSE

The aim of the present study was to evaluate the effect of myo-Inositol administration on oocyte quality, fertilization rate and embryo quality in patients with PCOS during assisted reproductive technology (ART) cycles.

METHODS

Fifty infertile PCOS patients were randomly designated in two groups. In the study group, patients received daily doses of 4 g myo-Inositol combined with 400 mg folic acid and in the control group patients received only 400 mg folic acid from 1 month before starting the antagonist cycle until the day of ovum pick up. Oocyte and embryo qualities were assessed according to European Society of Human Reproduction and Embryology (ESHRE) guidelines. The gene expression of PGK1, RGS2 and CDC42 as a factor of oocyte quality in granulosa cells was analyzed using real-time RT-PCR. Levels of total antioxidant capacity (TAC) and reactive oxygen species (ROS) were evaluated by chemiluminescence assay in follicular fluid.

RESULTS

The percentage of metaphase II oocyte, fertilization rate and embryo quality significantly improved in the study group (p < 0.05), but the number of retrieved oocytes and follicle count were not statistically different between groups. Furthermore, the gene expression of PGK1, RGS2 and CDC42 was significantly higher in the study group (p < 0.05) but no differences were found between two groups in terms of TAC and ROS levels.

CONCLUSIONS

The present study findings suggest that myo-Inositol alters the gene expression in granulosa cells and improves oocyte and embryo quality among PCOS patients undergoing ART.

Oocyte maturation in the toad Rhinella arenarum (Amphibia, Anura): Evidence of cAMP involvement in steroid production and action

In this work, we describe the participation of the adenylate cyclase/3'-5'-cyclic adenonsine monophosphate (cAMP) pathway in the seasonal follicular secretion of progesterone (P₄ ) and testosterone (T), and its relationship with the maturation of Rhinella arenarum oocytes. Under gonadotropin stimulation, P₄ secretion was the dominant steroid produced during the reproductive period, resulting in 100% germinal vesicle breakdown (GVBD) in oocytes in vitro; in contrast, T and estradiol (E₂ ) secretion increased (∼16 nM/20 follicles and ∼80 pM/20 follicles, respectively) during the non-reproductive period, but only yielded 50% GVBD. Treatment of the follicles with dibutyryl-cAMP or forskolin induced a significant increase in T secretion during both periods, but P₄ secretion did not significantly change and GVBD did not occur. These results suggest that high cAMP levels in the oocyte maintain meiotic arrest and prevent the induction effect of follicular steroids. An increase in cAMP levels in denuded oocytes, however, negatively regulated T-induced maturation since treatment with increasing db-cAMP or forskolin inhibited their maturation. Therefore, we hypothesize that an elevation in T during the non-reproductive period favors its aromatization to E₂ , leading to follicle growth. During the reproductive period, P₄ production might promote oocyte maturation when environmental conditions are favorable for reproduction. Together, the results indicate that steroidogenesis is seasonal and depends on gonadotropic activity in R. arenarum.

Scientific Opinion on the state of the science on pesticide risk assessment for amphibians and reptiles

Following a request from EFSA, the Panel on Plant Protection Products and their Residues developed an opinion on the science to support the potential development of a risk assessment scheme of plant protection products for amphibians and reptiles. The coverage of the risk to amphibians and reptiles by current risk assessments for other vertebrate groups was investigated. Available test methods and exposure models were reviewed with regard to their applicability to amphibians and reptiles. Proposals were made for specific protection goals aiming to protect important ecosystem services and taking into consideration the regulatory framework and existing protection goals for other vertebrates. Uncertainties, knowledge gaps and research needs were highlighted.

Low glucose availability stimulates progesterone production by mouse ovaries in vitro

Steroid production by the ovary is primarily stimulated by gonadotropins but can also be affected by biological cues that provide information about energy status and environmental stress. To further understand which metabolic cues the ovary can respond to, we exposed gonadotropin-stimulated mouse ovaries in vitro to glucose metabolism inhibitors and measured steroid accumulation in media. Gonadotropin-stimulated ovaries exposed to 2-deoxy-d-glucose increased progesterone production and steroidogenic acute regulatory protein mRNA levels. However, oocytes and granulosa cells in antral follicles do not independently mediate this response because targeted treatment of these cell types with a different inhibitor of glucose metabolism (bromopyruvic acid) did not affect progesterone production. Elevated progesterone production is consistent with the homeostatic role of progesterone in glucose regulation in mammals. It also may regulate follicle growth and/or atresia within the ovary. These results suggest that ovaries can regulate glucose homeostasis in addition to their primary role in reproductive activity.

Relationship between time post-ovulation and progesterone on oocyte maturation and pregnancy in canine cloning

Canine oocytes ovulated at prophase complete meiosis and continue to develop in presence of a high progesterone concentration in the oviduct. Considering that meiotic competence of canine oocyte is accomplished in the oviductal environment, we postulate that hormonal milieu resulting from the circulating progesterone concentration may affect oocyte maturation and early development of embryos. From 237 oocyte donors, 2620 oocytes were collected and their meiotic status and morphology were determined. To determine optimal characteristics of the mature oocytes subjected to nuclear transfer, a proportion of the meiotic status of the oocytes were classified in reference to time post-ovulation as well as progesterone (P4) level. A high proportion of matured oocytes were collected from >126h (55.5%) post-ovulation or 40-50ngmL^-1 (46.4%) group compared to the other groups. Of the oocyte donors that provided mature oocytes in vivo, there was no correlation between serum progesterone of donors and time post ovulation, however, time post-ovulation were significantly shorter for <30ng/mL group (P<0.05). Using mature oocytes, 1161 cloned embryos were reconstructed and transferred into 77 surrogates. In order to determine the relationship between pregnancy performance and serum progesterone level, embryos were transferred into surrogates showing various P4 serum levels. The highest pregnancy (31.8%) and live birth cloning efficacy (2.2%) rates were observed when the embryos were transferred into surrogates with circulating P4 levels were from 40 to 50ngmL^-1. In conclusion, measurement of circulating progesterone of female dog could be a suitable an indicator of the optimal time to collect quality oocyte and to select surrogates for cloning.

Derivation and Evaluation of Putative Adverse Outcome Pathways for the Effects of Cyclooxygenase Inhibitors on Reproductive Processes in Female Fish

Cyclooxygenase (COX) inhibitors are ubiquitous in aquatic systems and have been detected in fish tissues. The exposure of fish to these pharmaceuticals is concerning because COX inhibitors disrupt the synthesis of prostaglandins (PGs), which modulate a variety of essential biological functions, including reproduction. In this study, we investigated the effects of well-characterized mammalian COX inhibitors on female fathead minnow reproductive health. Fish (n = 8) were exposed for 96 h to water containing indomethacin (IN; 100 µg/l), ibuprofen (IB; 200 µg/l) or celecoxib (CX; 20 µg/l), and evaluated for effects on liver metabolome and ovarian gene expression. Metabolomic profiles of IN, IB and CX were not significantly different from control or one another. Exposure to IB and CX resulted in differential expression of comparable numbers of genes (IB = 433, CX = 545). In contrast, 2558 genes were differentially expressed in IN-treated fish. Functional analyses (canonical pathway and gene set enrichment) indicated extensive effects of IN on PG synthesis pathway, oocyte meiosis, and several other processes consistent with physiological roles of PGs. Transcriptomic data were congruent with PG data; IN-reduced plasma PG F2α concentration, whereas IB and CX did not. Five putative AOPs were developed linking the assumed molecular initiating event of COX inhibition, with PG reduction and the adverse outcome of reproductive failure via reduction of: (1) ovulation, (2) reproductive behaviors mediated by exogenous or endogenous PGs, and (3) oocyte maturation in fish. These pathways were developed using, in part, empirical data from the present study and other publicly available data.

A study of temporal effects of the model anti-androgen flutamide on components of the hypothalamic-pituitary-gonadal axis in adult fathead minnows

The aim of this study was to investigate temporal changes in the hypothalamic-pituitary-gonadal (HPG) axis of fathead minnows (Pimephales promelas) treated with the model androgen receptor (AR) antagonist flutamide. Reproductively-mature fish were exposed in a flow-through test to analytically-confirmed concentrations of either 50 or 500μg flutamide/L for 8 d, followed by an 8-d recovery period in clean water. Fish were sampled at 1, 2, 4 and 8days during each phase of the experiment. Flutamide (500μg/L) caused significant reductions in relative gonad size of the females on day 8 of the exposure and day 1 of the recovery, and reduced expression of secondary sex characteristics in males during the exposure phase of the experiment. Ex vivo gonadal synthesis of testosterone in both sexes (and 17β-estradiol in females) was reduced in the 500μg/L treatment within 2 d of exposure; however, steroid synthesis returned to levels comparable to controls by the end of the exposure portion of the test. Ex vivo testosterone synthesis in males exposed to 50μg flutamide/L was greater than in controls on days 4 and 8 of the exposure. Both the enhanced steroid production in the low treatment males, and return to control levels in the high treatment males and females during chemical exposure are indicative of a compensatory HPG response. One contributor to this response could be increased expression of genes responsible for enzymes involved in steroid synthesis; for example, transcripts for both cytochrome P450 side- chain cleavage and 11β-hydroxysteroid dehydrogenase were significantly elevated in flutamide-exposed males. Overall, responses of the HPG axis in adult male and female fathead minnows exposed to flutamide were both dynamic and comparatively rapid during exposure and recovery. These observations have ramifications both for the development of short-term fish assays to detect endocrine-active chemicals, and the derivation of robust adverse outcome pathways for AR antagonists in fish.

Epigenetic alterations of CYP19A1 gene in Cumulus cells and its relevance to infertility in endometriosis

PURPOSE

The purpose of the present study was to investigate the epigenetic mechanisms responsible for the aberrant aromatase expression (CYP19A1) in Cumulus Cells (CCs) of infertile endometriosis patients.

METHOD

Cumulus cells were obtained from 24 infertile patients with and without endometriosis who underwent ovarian stimulation for intracytoplasmic sperm injection. Expression of CYP19A1 gene was quantified using Reverse Transcription Q-PCR. DNA methylation, histone modifications, and binding of Estrogen Receptor, ERβ to regulatory DNA sequences of CYP19A1 gene were evaluated by Chromatin ImmunoPrecipitation (ChIP) assay.

RESULTS

CYP19A1 gene expression in CCs of endometriosis patients was significantly lower than the control group (P = 0.04). Higher incorporation of MeCP2 (as a marker of DNA methylation) on PII and PI.4 promoters, and hypoacetylation at H3K9 in PII and hypermethylation at H3K9 in PI.4 were observed in CYP19A1 gene in endometriosis patients (P < 0.05). Moreover, a decreased level of ERβ binding to PII and an increased level of its binding to PI.3 and PI.4 promoters of CYP19A1 were observed in endometriosis patients when compared to control.

CONCLUSION

Significant reduction of CYP19A1 gene expression in CCs of endometriosis patients may be the result of epigenetic alterations in its regulatory regions, either by DNA methylation or histone modifications. These epigenetic changes along with differential binding of ERβ (as a transcription factor) in CYP19A1 promoters may impair follicular steroidogenesis, leading to poor Oocyte and embryo condition in endometriosis patients.

Overlapping nongenomic and genomic actions of thyroid hormone and steroids

The genomic actions of thyroid hormone and steroids depend upon primary interactions of the hormones with their specific nuclear receptor proteins. Formation of nuclear co-activator or co-repressor complexes involving the liganded receptors subsequently result in transcriptional events-either activation or suppression-at genes that are specific targets of thyroid hormone or steroids. Nongenomic actions of thyroid hormone and steroids are in contrast initiated at binding sites on the plasma membrane or in cytoplasm or organelles and do not primarily require formation of intranuclear receptor protein-hormone complexes. Importantly, hormonal actions that begin nongenomically outside the nucleus often culminate in changes in nuclear transcriptional events that are regulated by both traditional intranuclear receptors as well as other nuclear transcription factors. In the case of thyroid hormone, the extranuclear receptor can be the classical "nuclear" thyroid receptor (TR), a TR isoform, or integrin αvβ3. In the case of steroid hormones, the membrane receptor is usually, but not always, the classical "nuclear" steroid receptor. This concept defines the paradigm of overlapping nongenomic and genomic hormone mechanisms of action. Here we review some examples of how extranuclear signaling by thyroid hormone and by estrogens and androgens modulates intranuclear hormone signaling to regulate a number of vital biological processes both in normal physiology and in cancer progression. We also point out that nongenomic actions of thyroid hormone may mimic effects of estrogen in certain tumors.

A low-testosterone state associated with endometrioma leads to the apoptosis of granulosa cells

Although endometriosis is suspected to be a cause of premature ovarian insufficiency (POI), the mechanism(s) underlying this process have not been elucidated. Recently, androgens were shown to promote oocyte maturation and to play a role in folliculogenesis. In addition, several reports have documented low testosterone levels in the follicular fluid obtained from endometriosis patients. We therefore examined whether the low levels of serum testosterone are associated with the apoptosis of granulosa cells in follicles obtained from endometriosis patients. Serum samples were collected from 46 patients with endometriosis and from 62 patients without endometriosis who received assisted reproductive therapy. Specimens of the ovaries obtained from 10 patients with endometrioma were collected using laparoscopy. The mean serum testosterone concentration in the patients with endometriosis was significantly lower than that observed in the patients without endometriosis. Furthermore, high expression of a pro-apoptotic Bcl-2 member, BimEL, in the follicles was found to be associated with a low serum testosterone level. We clarified the underlying mechanisms using a basic approach employing human immortalized granulosa cells derived from a primary human granulosa cell tumor, the COV434 cell line. The in vitro examination demonstrated that testosterone inhibited apoptosis induced by sex steroids depletion via the PI3K/Akt-FoxO3a pathway in the COV434 cells. In conclusion, we elucidated the mechanism underlying the anti-apoptotic effects of testosterone on granulosa cells, and found that a low-testosterone status is a potentially important step in the development of premature ovarian insufficiency in patients with endometriosis.

Gonad RNA-specific qRT-PCR analyses identify genes with potential functions in schistosome reproduction such as SmFz1 and SmFGFRs

In the search for new strategies to fight schistosomiasis, the unique reproductive biology of Schistosoma mansoni has come into the focus of research. The development of the gonads and the ability of egg production are fundamental not only for continuing the life cycle but also for pathogenicity. Previous studies of schistosome biology demonstrated an influence of pairing on gonad development of the female and on gene expression profiles in both genders. Due to the limited access to specific tissues, however, most of these studies were done at the level of whole worms neglecting individual tissues that may be targets of pairing-dependent processes. Recently, we established a protocol allowing the isolation of testes and ovaries from adult S. mansoni. Here, we describe tissue-specific qRT-PCR analyses comparing transcript levels of selected genes on the basis of RNA from gonads and whole worms. Gene expression in ovary and testes was in some cases found to be significantly influenced by pairing, which was not traceable in whole worms. Among the candidate genes identified as regulated by pairing in gonads were the frizzled homolog SmFz1 and the two fibroblast growth factor receptor homologs SmFGFR-A and SmFGFR-B. First functional characterizations were done, including comparative qRT-PCR analyses, in situ-localization experiments, heterologous expression in Xenopus oocytes (SmFGFR-A/B), and inhibitor studies using the Fz/Dvl-pathway inhibitor 3289-8625, or BIBF1120 blocking FGFR-signaling. Besides confirming gonad localization and receptor functions, inhibitor-induced phenotypes were observed in vitro such as decreased egg production as well as drastic effects on gonad differentiation, morphology, embryogenesis, and survival of adult worms. In summary, these results emphasise the usefulness of tissue-specific qRT-PCRs for selection of candidate genes with important roles in reproduction, allowing subsequent studies to determine their suitability as drug targets.

Glycolytic metabolites are critical modulators of oocyte maturation and viability

The maturation of an oocyte into an egg is a key step in preparation for fertilization. In Xenopus, oocyte maturation is independent of transcription, being regulated at the level of translation and post-translational modifications of proteins. To identify factors involved in the maturation process we used two-dimensional differential gel electrophoresis to compare the proteome of oocytes and eggs. Protein abundance changes were observed in multiple cellular pathways during oocyte maturation. Most prominent was a general reduction in abundance of enzymes in the glycolytic pathway. Injection into oocytes of the glycolytic intermediates glyceraldehyde-3-phosphate, phosphoenolpyruvate and glucose-6-phosphate prevented oocyte maturation. Instead, these metabolites stimulated ROS production and subsequent apoptosis of the oocyte. In contrast, all other metabolites tested had no effect on oocyte maturation and did not induce apoptosis. These data suggest that a subset of glycolytic metabolites have the capacity to regulate oocyte viability.

Membrane receptor cross talk in steroidogenesis: recent insights and clinical implications

Steroid production by all three major steroidogenic tissues, the adrenals, testes, and ovaries, is critical for survival and reproduction of all animals. As such, the pathways that regulate steroidogenesis are conserved between these tissues, from the steroidogenic enzymes and cofactors that synthesize steroids, to the intracellular signaling molecules and Gαs-coupled receptors that mediate the activity of these enzymes. Recent work has revealed another important conserved pathway in steroidogenesis: crosstalk between membrane G protein-coupled receptors and membrane receptor tyrosine kinases. Luteinizing hormone (LH) or adrencorticotropic hormone (ACTH) binding to their cognate Gαs-coupled membrane receptors in the gonads and adrenals, respectively, leads to cAMP-induced trans-activation of the epidermal growth factor (EGF) receptor, followed by activation of Akt and Erk signaling. These kinase signals then activate Steroidogenic Acute Regulatory (StAR) protein, which promotes steroid production. Inhibition of this pathway abrogates both LH- and ACTH-induced steroidogenesis. Interestingly, LH-induced transactivation of the EGF receptor in the ovary uniquely requires matrix metalloproteinase-mediated release of EGF receptor ligands, and inhibition of these proteases blocks LH-induced steroidogenesis. Given this unique need for matrix metalloproteinases in ovarian steroidogenesis, MMP inhibition may prove to be useful when treating diseases of excess ovarian steroid production, such as polycystic ovary syndrome.

In-depth tanscriptomic analysis on giant freshwater prawns

Gene discovery in the Malaysian giant freshwater prawn (Macrobrachium rosenbergii) has been limited to small scale data collection, despite great interest in various research fields related to the commercial significance of this species. Next generation sequencing technologies that have been developed recently and enabled whole transcriptome sequencing (RNA-seq), have allowed generation of large scale functional genomics data sets in a shorter time than was previously possible. Using this technology, transcriptome sequencing of three tissue types: hepatopancreas, gill and muscle, has been undertaken to generate functional genomics data for M. rosenbergii at a massive scale. De novo assembly of 75-bp paired end Ilumina reads has generated 102,230 unigenes. Sequence homology search and in silico prediction have identified known and novel protein coding candidate genes (∼24%), non-coding RNA, and repetitive elements in the transcriptome. Potential markers consisting of simple sequence repeats associated with known protein coding genes have been successfully identified. Using KEGG pathway enrichment, differentially expressed genes in different tissues were systematically represented. The functions of gill and hepatopancreas in the context of neuroactive regulation, metabolism, reproduction, environmental stress and disease responses are described and support relevant experimental studies conducted previously in M. rosenbergii and other crustaceans. This large scale gene discovery represents the most extensive transcriptome data for freshwater prawn. Comparison with model organisms has paved the path to address the possible conserved biological entities shared between vertebrates and crustaceans. The functional genomics resources generated from this study provide the basis for constructing hypotheses for future molecular research in the freshwater shrimp.

Androgen/androgen receptor pathway regulates expression of the genes for cyclooxygenase-2 and amphiregulin in periovulatory granulosa cells

It is well known that the androgen/androgen receptor (AR) pathway is involved in both male and female fertility in mammals. AR knockout female mice are reported to exhibit various abnormalities in follicle development, and a subfertile phenotype. In exogenous gonadotropin-induced superovulation, serum androgen levels were robustly elevated in female mice at the periovulatory stage after human chorionic gonadotropin (hCG) treatment. At this stage, ovarian AR proteins were strongly expressed in cumulus cells. Because these results suggested that the androgen/AR pathway is involved in ovulation, we investigated the expression of ovulation-related genes in the mouse ovary treated with the nonaromatizable androgen, 5α-dihydrotestosterone (DHT). DHT treatment induced the expression of the genes for cyclooxyganase-2 (Cox-2 or prostaglandin endoperoxidase synthase 2) and the epidermal growth factor-like factor, amphiregulin (Areg), in the ovary, whereas their hCG-induced expression was suppressed by the AR antagonist flutamide. These genes were also induced by DHT in AR-expressing primary granulosa and granulosa tumor-derived cells. Reporter assays, electrophoretic shift mobility assays and chromatin immunoprecipitation assays demonstrated that androgen response sequence(s) existing upstream of each gene were responsible for androgen responsiveness and were occupied by the AR in periovulatory granulosa cells. Our results suggest that the androgen/AR pathway is involved in the ovulatory process via expression of the Cox-2 and Areg genes in periovulatory granulosa cells.

The influence of the antiandrogen 2-hydroxyflutamide on the androgen receptor expression in the porcine ovarian follicles - an in vitro study

Androgens are one of the most important agents influencing ovarian follicles growth and development. The biological action of androgens is primarily exerted through transcriptional regulation by the androgen receptor (AR), a member of the steroid hormone receptor superfamily. The purpose of this study was to test the role of androgen receptor agonist testosterone (T) or antagonist 2-hydroxyflutamide (2-Hf) and in combination on AR expression in cultured porcine granulosa cells (GC) or whole follicles. Granulosa cells isolated from mature pig follicles were cultured for 48 h. During the last 12 and 24 h of culture, they were incubated in the presence of T (10(-7)  m/ml), 2-Hf (1.7 × 10(-4)  m) or both T and 2-Hf (T + 2-Hf, at the same concentrations as when added separately). To better imitate in vivo conditions, whole follicles (6-8 mm in diameter) isolated from porcine ovaries have been incubated (for 12 and 24 h) in an organ culture system with the addition of the same factors. Thereafter, cells or sections obtained from cultured follicles were processed for AR detection by immunocytochemistry or immunohistochemistry. Moreover, expression of AR mRNA and protein was determined by real-time PCR and Western blot analysis. It was shown that the addition of 2-Hf in the presence of T had a positive effect on AR mRNA and protein expression in porcine GC and ovarian follicles. Moreover, the addition of 2-Hf influenced AR distribution in GC cultures which is seen as change of its localization from nuclear to perinuclear. Our results suggest that androgens acting through AR could be involved in the control of AR expression in porcine GC in vitro and in vivo.

Activity of long-chain acyl-CoA synthetase is required for maintaining meiotic arrest in Xenopus laevis

In most vertebrates, fully grown oocytes are arrested in meiotic prophase I and only resume the cell cycle upon external stimuli, such as hormones. The proper arrest and resumption of the meiotic cycle is critical for reproduction. A Galpha(S) signaling pathway essential for the arrest is conserved in organisms from Xenopus to mouse and human. A previous gene association study implicated that mutations of human ACSL6 may be related to premature ovarian failure. However, functional roles of ACSL6 in human infertility have yet to be reported. In the present study, we found that triacsin C, a potent and specific inhibitor for ACSL, triggers maturation in Xenopus and mouse oocytes in the absence of hormone, suggesting ACSL activity is required for the oocyte arrest. In Xenopus, acsl1b may fulfill a major role in the process, because inhibition of acsl1b by knocking down its RNA results in abnormal acceleration of oocyte maturation. Such abnormally matured eggs cannot support early embryonic development. Moreover, direct inhibition of protein palmitoylation, which lies downstream of ACSLs, also causes oocyte maturation. Furthermore, palmitoylation of Galpha(s), which is essential for its function, is inhibited when the ACSL activity is blocked by triacsin C in Xenopus. Thus, disruption of ACSL activity causes inhibition of the Galpha(s) signaling pathway in the oocytes, which may result in premature ovarian failure in human.

Minireview: Recent advances in extranuclear steroid receptor actions

The participation of extranuclear steroid receptor signaling in organ physiology and the impact for pathobiology has increasingly been demonstrated. Important functions of membrane estrogen receptors in the cardiovascular system demonstrate new mechanisms of rapid steroid signaling to gene regulation, preventing cardiovascular disease and maintaining healthy arterial function. In cancer cells, kinase signaling initiated by extranuclear estrogen, progesterone, and androgen receptors modulates transcriptional events in the nucleus, which in turn regulate proliferation, migration, and invasion. Important mediators of cross talk between cytoplasmic and nuclear steroid receptor signaling are the proline-, glutamic acid-, and leucine-rich protein-1 and paxillin proteins, both of which modulate membrane and nuclear receptor pool signaling to promote a variety of cell biological functions.

Understanding extranuclear (nongenomic) androgen signaling: what a frog oocyte can tell us about human biology

Steroids are key factors in a myriad of mammalian biological systems, including the brain, kidney, heart, bones, and gonads. While alternative potential steroid receptors have been described, the majority of biologically relevant steroid responses appear to be mediated by classical steroid receptors that are located in all parts of the cell, from the plasma membrane to the nucleus. Interestingly, these classical steroid receptors modulate different signals depending upon their location. For example, receptors in the plasma membrane interact with membrane signaling molecules, including G proteins and kinases. In contrast, receptors in the nucleus interact with nuclear signaling molecules, including transcriptional co-regulators. These extranuclear and intranuclear signals function together in an integrated fashion to regulate important biological functions. While most studies on extranuclear steroid signaling have focused on estrogens, recent work has demonstrated that nongenomic androgen signaling is equally important and that these two steroids modulate similar signaling pathways. In fact, by taking advantage of a simple model system whereby a physiologically relevant androgen-mediated process is regulated completely independent of transcription (Xenopus laevis oocyte maturation), many novel and conserved concepts in nongenomic steroid signaling have been uncovered and characterized.

Ca2+ signaling during maturation of cumulus-oocyte complex in mammals

Under the influence of gonadotropins or growth factors, a close cooperation develops between cumulus cells and the oocyte that is implicated in transmitting signals involved in maintaining or releasing the meiotic arrest in the oocyte. While cyclic adenosine 5'-monophosphate (cAMP) is a key molecule in maintaining the meiotic arrest, calcium (Ca(2+)) may play a role in controlling either spontaneous or gonadotropin-induced oocyte maturation, possibly by modulating intracytoplasmic cAMP concentrations via Ca(2+)-sensitive adenylate cyclases. This review focuses on the mechanisms related to the origin of the Ca(2+) wave that travels from the cumulus cells to the oocyte, and discusses the source of variations affecting the dynamics of this wave.

Hormonal induction of gamete release, and in-vitro fertilisation, in the critically endangered southern corroboree frog, Pseudophryne corroboree

BACKGROUND

Conservation Breeding Programs (CBP's) are playing an important role in the protection of critically endangered anuran amphibians, but for many species recruitment is not successful enough to maintain captive populations, or provide individuals for release. In response, there has been an increasing focus on the use of Assisted Reproductive Technologies (ART), including the administration of reproductive hormones to induce gamete release followed by in vitro fertilisation. The objective of this study was to test the efficacy of two exogenous hormones to induce gamete release, for the purpose of conducting in vitro fertilisation (IVF), in one of Australia's most critically endangered frog species, Pseudophryne corroboree.

METHODS

Male frogs were administered a single dose of either human chorionic gonadotropin (hCG) or luteinizing hormone-releasing hormone (LHRHa), while female frogs received both a priming and ovulatory dose of LHRHa. Spermiation responses were evaluated at 3, 7, 12, 24, 36, 48, 60 and 72 h post hormone administration (PA), and sperm number and viability were quantified using fluorescent microscopy. Ovulation responses were evaluated by stripping females every 12 h PA for 5 days. Once gametes were obtained, IVF was attempted by combining spermic urine with oocytes in a dilute solution of simplified amphibian ringer (SAR).

RESULTS

Administration of both hCG and LHRHa induced approximately 80% of males to release sperm over 72 h. Peak sperm release occurred at 12 h PA for hCG treated males and 36 h PA for LHRHa treated males. On average, LHRHa treated males released a significantly higher total number of live sperm, and a higher concentration of sperm, over a longer period. In female frogs, administration of LHRHa induced approximately 30% of individuals to release eggs. On average, eggs were released between 24 and 48 h PA, with a peak in egg release at 36 h PA. IVF resulted in a moderate percentage (54.72%) of eggs being fertilised, however all resultant embryos failed prior to gastrulation.

CONCLUSIONS

Hormone treatment successfully induced spermiation and ovulation in P. corroboree, but refinement of gamete induction and IVF techniques will be required before ART protocols can be used to routinely propagate this species.

Immunolocalization of androgen receptor and steroidogenic enzymes in cumuli oophori of pre- and post-ovulatory rats

Immunolocalization of 3β-hydroxysteroid dehydrogense (3β-HSD), cytochrome P450c17 (P450c17) and androgen receptor (AR) were investigated in rat cumuli oophori (COCs) of late pre-ovulatory follicles and in post-ovulatory COCs bearing fertilized oocytes. A gradient of intensity of 3β-HSD immunolabelling was observed in the granulosa layer of pre-ovulatory follicles, with almost negative immunolabelling in COCs and with the strongest immunoreaction in the mural granulosa cells. Post-ovulatory COCs showed strong 3β-HSD immunolabelling in the peripheral regions and weak labelling near the oocyte, suggestive of responsiveness of cumulus cells to an anti-luteinizing effect exerted by the fertilized oocyte. In pre-ovulatory follicles, a weak P450c17 immunopositivity was limited to expanded cumulus granulosa cells and the positive labelling persisted in post-ovulatory COCs. P450c17 immunopositivity was also found in ampullary epithelial cells. A strong AR immunopositivity was confined mainly to the COCs in pre-ovulatory follicles and a similar immunoreaction was present in the granulosa cells of ovulated COCs. Simultaneous AR and cytochrome P450c17 immunolabelling in the pre- and post-ovulatory COCs is suggestive of an intra- and paracrine androgen regulation of the cumulus granulosa cell function.

PAK thread from amoeba to mammals

The p21-activated kinases (PAKs) are signaling nodes that play a crucial role in cellular processes including cell motility, differentiation, survival, gene transcription, and hormone signaling. PAKs are highly conserved family of serine-threonine kinases that act as effector for small GTPases Rac and Cdc42. Most of our knowledge about PAK functions has been derived from genetic approaches in lower organisms and many of these functions are similar to that seen in mammalian cells. In this review, we have summarized the extensive information generated in lower eukaryotes and very briefly discussed the current status of PAKs in humans.

Nemo-like kinase induces apoptosis and inhibits androgen receptor signaling in prostate cancer cells

BACKGROUND

The mitogen-activated protein kinases (MAPKs) regulate cell growth, differentiation, and stress responses, and many critical signaling pathways are subject to cross-regulation by MAPK signaling. Previous studies have yielded evidence of cross-talk between the MAPK pathways and androgen receptor (AR) signaling, which plays a critical role in growth control of both normal prostate and prostate cancer (PCa). Objective of this study was to evaluate the expression of MAPK-like protein nemo-like kinase (NLK) in PCa and its effects on AR-mediated transcription.

METHODS

Real-time PCR and IHC were used to evaluate levels of NLK in prostatic samples. Effects of over-expression of NLK on apoptosis and proliferation were determined using Western blot and flow cytometry. Effects on AR signaling were evaluated using over-expression and knockdown of NLK in PCa cells in combination with PCR, Western blotting and reporter assays.

RESULTS

Our results show that the expression of NLK is decreased in PCa metastases in comparison to normal prostate epithelium and primary PCa. Our results also show that over-expression of NLK resulted in induction of apoptosis, which was more pronounced in AR-expressing LNCaP versus AR-negative PC-3 cells. Higher levels of NLK decreased levels of AR mRNA and protein as well as inhibited AR-mediated transcription.

CONCLUSIONS

NLK expression is altered during PCa progression and it is involved in regulation of AR signaling in these cells. A deeper understanding of the roles of NLK in regulation of AR-mediated transcription and control of PCa progression may point the way to new modes of therapeutic intervention in this disease.

Nongenomic steroid-triggered oocyte maturation: of mice and frogs

Luteinizing hormone (LH) mediates many important processes in ovarian follicles, including cumulus cell expansion, changes in gap junction expression and activity, sterol and steroid production, and the release of paracrine signaling molecules. All of these functions work together to trigger oocyte maturation (meiotic progression) and subsequent ovulation. Many laboratories are interested in better understanding both the extra-oocyte follicular processes that trigger oocyte maturation, as well as the intra-oocyte molecules and signals that regulate meiosis. Multiple model systems have been used to study LH-effects in the ovary, including fish, frogs, mice, rats, pigs, and primates. Here we provide a brief summary of oocyte maturation, focusing primarily on steroid-triggered meiotic progression in frogs and mice. Furthermore, we present new studies that implicate classical steroid receptors rather than alternative non-classical membrane steroid receptors as the primary regulators of steroid-mediated oocyte maturation in both of these model systems.

The signal pathway of gonadotrophins-induced mammalian oocyte meiotic resumption

Fully grown mammalian oocytes are arrested at the first meiotic prophase until a surge of gonadotrophin at the mid-cycle. The actions of gonadotrophins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), on oocyte meiotic resumption are believed to be mediated in large part through increasing the production of cyclic adenosine 3',5'-monophosphate and subsequent activation of mitogen-activated protein kinase (MAPK) in its surrounding cumulus granulosa cells. Recent findings indicate that gonadotrophins-induced epidermal growth factor-like growth factors, meiosis activating sterol and gonadal steroid hormones, possibly via protein kinase A II and protein kinase C pathways, are involved in the activation of MAPK. Another second messenger cyclic guanosine 3',5'-monophosphate induced by nitric oxide or natriuretic peptides system mediates the function of gonadotrophins during oocyte meiotic resumption. FSH and LH induced pathways may either directly overlap or each hormone may utilize redundant pathways in oocyte maturation. A detailed appreciation of different FSH and LH-activated signaling pathways in mammalian oocytes will be needed in understanding their actions in follicular development and oocyte maturation.

Connexin37 mRNA expression in in vivo and in vitro mouse oocyte

To evaluate gene expression of Connexin37 (Cx37) in oocytes from in vitro follicles at different stages, mouse preantral follicles were isolated and cultured for 12 days in vitro. Compared with in vitro follicles, follicles grown in vivo were collected at day 14 (d14), d16, d18, d20, d22 and d24 with the same stages for gene expression of Cx37 in oocytes. Our results showed that Cx37 mRNA increased along with follicular development, reached the highest level at the onset of antrum cavity formation and decreased after antrum formation in both in vivo and in vitro mouse oocytes. However, Cx37 mRNA was significant higher (p < 0.01) in in vitro cultured oocytes than in vivo oocytes. Moreover, significantly higher levels of Cx37 mRNA were found in oocytes from in vitro disrupted follicles (p < 0.01) and non-grown follicles (p < 0.05) than those from normal follicles with a similar size. These data determine temporal gene expression of Cx37 in oocytes from follicules at different stages and indicate that the gene expression level of Cx37 in oocytes could be evaluated as a criterion to the regulatory mechanism of Cx37 in an in vitro model.

Oocyte maturation: converting the zebrafish oocyte to the fertilizable egg

The process of oogenesis culminates in steroid-induced oocyte maturation to produce the fertilizable egg. A quintessential biological entity, the egg is central to the production of new individuals. The result of egg fertilization by a sperm cell is the production of the mother of all stem cells (i.e. the zygote). Furthermore, the egg cytoplasm is the only one known to support reprogramming a transplanted nucleus to give rise to an individual (i.e. animal cloning). Zebrafish oocyte maturation is a complex event encompassing a number of cellular changes including germinal vesicle migration (GVM) and dissolution or breakdown (GVD), ooplasmic clearing (OC) with correlated yolk protein changes (YP), development of osmoregulation (OR) in fresh water, the formation of the future embryonic pole, the blastodisc (BF) and activatibility (AC) or cortical maturation. In zebrafish, and many other teleosts, 17alpha, 20beta-dihydroxy-4-pregnen-3-one (17alpha, 20beta-DP) has been shown to be the normal inducer of oocyte maturation. A 17alpha, 20beta-DP membrane-resident receptor mediates oocyte maturation via non-genomic mechanisms that are beginning to be understood. This paper will highlight some of the cellular markers resulting from the signaling initiated by 17alpha, 20beta-DP. By describing these markers, it is hoped that workers in the field will have additional tools to help further elucidate the signaling events of oocyte maturation.

Androgen receptor's destiny in mammalian oocytes: a new hypothesis

Unlike the well-established roles of androgen and androgen receptor (AR) in males, the functions of this steroid and its receptor in the ovary are still unclear. For decades, androgen and AR have long been considered to play a negative (at least not a positive) role in mammalian oocyte maturation. However, recent studies by us and others showed their positive influence in promoting meiotic maturation. On the other hand, rapid non-genomic effects of androgens have been observed and are now generally accepted as contributing to the physiological effects of the steroids and their related receptors in somatic cells, and this has stimulated us to explore the complex roles of AR in the ovary. Based on the classic dogma and new findings, we collected evidence to propose that the expression of AR shifts from the oocytes to the theca cells and finally disappears in the oocytes during evolution. It is suggested that the non-genomic pathway involving androgen and AR in the mammalian oocytes, unlike somatic cells, cells will undergo elimination. The function of androgen and AR in promoting meiotic maturation may have been replaced gradually by gonadotrophins. Moreover, a possible relationship between AR and polycystic ovary syndrome is also discussed, which might provide a clue for the pathology of the disease.

Rapid signaling by steroid receptors

Steroid receptors transcribe genes that lead to important biological processes, including normal organ development and function, tissue differentiation, and promotion of oncogenic transformation. These actions mainly result from nuclear steroid receptor action. However, for 50 years, it has been known that rapid effects of steroid hormones occur and could result from rapid signal transduction. Examples of these effects include stress responses to secreted glucocorticoids, rapid actions of thyroid hormones in the heart, and acute uterine/vaginal responses to injected estrogen. These types of responses have increasingly been attributed to rapid signaling by steroid hormones, upon engaging binding proteins most often at the cell surface of target organs. It is clear that rapid signal transduction serves an integrated role to modify existing proteins, altering their structure and activity, and to modulate gene transcription, often through collaboration with the nuclear pool of steroid receptors. The biological outcomes of steroid hormone actions thus reflect input from various cellular pools, cocoordinating the necessary events that are restrained in temporal and kinetic fashion. Here I describe the current understanding of rapid steroid signaling that is now appreciated to extend to virtually all members of this family of hormones and their receptors.

Testosterone potentially triggers meiotic resumption by activation of intra-oocyte SRC and MAPK in porcine oocytes

The role of androgen and androgen receptors (ARs) in males has been well established. This steroid and its receptor also exist in follicles, but their functions are still unclear. In this study, using a culture system containing a low dose of hypoxanthine, we revealed the positive contribution of testosterone to oocyte meiotic resumption. By performing ultracentrifugation to allow clear visualization of porcine germinal vesicles, our results provide evidence that mitogen-activated protein kinase (MAPK) in the oocyte itself but not in cumulus cells was activated before germinal vesicle breakdown (GVBD) after testosterone treatment. We further explored the signal cascade of testosterone-triggered GVBD and showed significant contributions of AR to testosterone-induced MAPK activation and GVBD. By using a potent and selective inhibitor of SRC and detecting activation of the kinase, we found that testosterone activated SRC in oocytes but not in cumulus cells and that SRC (as an essential upstream molecule of MAPK) mediated this testosterone- and AR-promoted reinitiation of meiosis. The present findings propose an undefined signaling pathway and suggest the potential competence of testosterone for meiotic resumption in mammalian oocytes.