Induction of early growth response protein-1 gene expression in the rat ovary in response to an ovulatory dose of human chorionic gonadotropin

Cellular atlas of the human ovary using morphologically guided spatial transcriptomics and single-cell sequencing

The reproductive and endocrine functions of the ovary involve spatially defined interactions among specialized cell populations. Despite the ovary's importance in fertility and endocrine health, functional attributes of ovarian cells are largely uncharacterized. Here, we profiled >18,000 genes in 257 regions from the ovaries of two premenopausal donors to examine the functional units in the ovary. We also generated single-cell RNA sequencing data for 21,198 cells from three additional donors and identified four major cell types and four immune cell subtypes. Custom selection of sampling areas revealed distinct gene activities for oocytes, theca, and granulosa cells. These data contributed panels of oocyte-, theca-, and granulosa-specific genes, thus expanding the knowledge of molecular programs driving follicle development. Serial samples around oocytes and across the cortex and medulla uncovered previously unappreciated variation of hormone and extracellular matrix remodeling activities. This combined spatial and single-cell atlas serves as a resource for future studies of rare cells and pathological states in the ovary.

A delayed ovulation of progestin-primed ovarian stimulation (PPOS) by downregulating the LHCGR/PGR pathway

Progestin-primed ovarian stimulation (PPOS) is a new ovulation stimulation protocol, and its role in ovulation and regulatory mechanism is unclear. The clinical PPOS protocol was simulated in mice. The ovulated oocytes, estradiol, progesterone, and luteinizing hormone (LH) levels were analyzed at different hours after trigger. mRNA extraction and real-time PCR, hematoxylin and eosin staining, and immunofluorescence of ovaries were used to explore the involved signaling pathways. The PPOS group had a delayed ovulation at 12.5 h after trigger. Its suppressed LH level reduced the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) on the preovulatory follicles before trigger and significantly decreased the following progesterone synthesis, blood progesterone level, and progesterone receptor (PGR) expression within 4-6 h after trigger. Furthermore, the important ovulatory genes regulated by PGR including ADAMTS-1, VEGF-A, and EDN2 were downregulated, ultimately delaying the ovulation. PPOS suppresses the LH level before trigger and decreases the synthesis of progesterone after trigger, thus delaying the ovulation by downregulating the LHCGR-PGR pathway.

EGR1 Promotes Ovarian Hyperstimulation Syndrome Through Upregulation of SOX9 Expression

Angiogenesis is strongly associated with ovarian hyperstimulation syndrome (OHSS) progression. Early growth response protein 1 (EGR1) plays an important role in angiogenesis. This study aimed to investigate the function and mechanism of EGR1 involved in OHSS progression. RNA-sequencing was used to identify differentially expressed genes. In vitro OHSS cell model was induced by treating KGN cells with human chorionic gonadotropin (hCG). In vivo OHSS model was established in mice. The expression levels of EGR1, SOX1, and VEGF were determined by Quantitative Real-Time polymerase chain reaction (qRT-PCR), Western blot, immunofluorescence staining, and immunochemistry assay. The content of VEGF in the culture medium of human granulosa-like tumor cell line (KGN) cells was accessed by the ELISA assay. The regulatory effect of EGR1 on SRY-box transcription factor 9 (SOX9) was addressed by luciferase reporter assay and chromatin immunoprecipitation. The ERG1 and SOX9 levels were significantly upregulated in granulosa cells from OHSS patients and there was a positive association between EGR1 and SOX9 expression. In the ovarian tissues of OHSS mice, the levels of EGR1 and SOX9 were also remarkedly increased. Treatment with hCG elevated the levels of vascular endothelial growth factor (VEGF), EGR1, and SOX9 in KGN cells. Silencing of EGR1 reversed the promoting effect of hCG on VEGF and SOX9 expression in KGN cells. EGR1 transcriptionally regulated SOX9 expression through binding to its promoter. In addition, administration of dopamine decreased hCG-induced VEGF in KGN cells and ameliorated the progression of OHSS in mice, which were companied with decreased EGR1 and SOX9 expression. EGR1 has a promoting effect on OHSS progression and dopamine protects against OHSS through suppression of EGR1/SOX9 cascade. Our findings may provide new targets for the treatment of OHSS.

Single-Cell Sequencing Reveals an Intrinsic Heterogeneity of the Preovulatory Follicular Microenvironment

The follicular microenvironment, including intra-follicular granulosa cells (GCs), is responsible for oocyte maturation and subsequent ovulation. However, the functions of GCs and cellular components of the follicular microenvironment in preovulatory follicles have not been extensively explored. Here, we surveyed the single-cell transcriptome of the follicular microenvironment around MII oocytes in six human preovulatory follicles in in vitro fertilization. There were six different cell types in the preovulatory follicles, including GCs and various immune cells. In GCs, we identified nine different functional clusters with different functional transcriptomic profiles, including specific clusters involved in inflammatory responses and adhesive function. Follicular macrophages are involved in immune responses, extracellular matrix remoulding and assist GCs in promoting the oocyte meiotic resumption. Interestingly, we observed that the specific terminal state subcluster of GCs with high levels of adhesive-related molecules should result in macrophage recruitment and residence, further contributing to an obvious heterogeneity of the immune cell proportion in preovulatory follicles from different patients. Our results provide a comprehensive understanding of the transcriptomic landscape of the preovulatory follicular microenvironment at the single-cell level. It provides valuable insights into understanding the regulation of the oocyte maturation and ovulation process, offering potential clues for the diagnosis and treatment of oocyte-maturation-related and ovulation-related diseases.

Tie1 contributes to the development of ovarian hyperstimulation syndrome under the regulation of EGR1 in granulosa cells

The expression of tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 1 (Tie1), a transmembrane protein expressed almost exclusively by endothelial cells, has been reported in granulosa cells. However, its significance in ovarian hyperstimulation syndrome (OHSS), which can occur after the injection of gonadotropins in infertile women undergoing controlled ovarian stimulation, is unknown. Here, we report significantly increased Tie1 and vascular endothelial growth factor (VEGF) expression in cultured granulosa cells from OHSS patients, as well as ovaries from rats with experimentally established OHSS, compared to controls, with the levels of both proteins also increasing in granulosa and SVOG cells (a nontumorigenic human granulosa-lutein cell line) treated with an acute dose of human chorionic gonadotropin (hCG). Tie1 silencing abolished the hCG-induced VEGF level in SVOG cells and attenuated the progression of OHSS in rats, as determined by histological analysis. Further studies in SVOG cells revealed that the hCG-induced upregulation of Tie1 expression involved the phosphoinositide 3-kinase/protein kinase B signaling pathway. We also report that early growth response protein 1 (EGR1), whose expression was also upregulated by hCG, bound directly to the Tie1 promoter and activated its transcription. Taken together, our results indicate that Tie1 may be a therapeutic target in cases of moderate-to-severe OHSS. Further studies are needed to address its clinical relevance.

Luteinizing Hormone Regulation of Inter-Organelle Communication and Fate of the Corpus Luteum

The corpus luteum is an endocrine gland that synthesizes the steroid hormone progesterone. luteinizing hormone (LH) is a key luteotropic hormone that stimulates ovulation, luteal development, progesterone biosynthesis, and maintenance of the corpus luteum. Luteotropic and luteolytic factors precisely regulate luteal structure and function; yet, despite recent scientific progress within the past few years, the exact mechanisms remain largely unknown. In the present review, we summarize the recent progress towards understanding cellular changes induced by LH in steroidogenic luteal cells. Herein, we will focus on the effects of LH on inter-organelle communication and steroid biosynthesis, and how LH regulates key protein kinases (i.e., AMPK and MTOR) responsible for controlling steroidogenesis and autophagy in luteal cells.

Hypo-glycosylated hFSH drives ovarian follicular development more efficiently than fully-glycosylated hFSH: enhanced transcription and PI3K and MAPK signaling

STUDY QUESTION

Does hypo-glycosylated human recombinant FSH (hFSH18/21) have greater in vivo bioactivity that drives follicle development in vivo compared to fully-glycosylated human recombinant FSH (hFSH24)?

SUMMARY ANSWER

Compared with fully-glycosylated hFSH, hypo-glycosylated hFSH has greater bioactivity, enabling greater follicular health and growth in vivo, with enhanced transcriptional activity, greater activation of receptor tyrosine kinases (RTKs) and elevated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling.

WHAT IS KNOWN ALREADY

Glycosylation of FSH is necessary for FSH to effectively activate the FSH receptor (FSHR) and promote preantral follicular growth and formation of antral follicles. In vitro studies demonstrate that compared to fully-glycosylated recombinant human FSH, hypo-glycosylated FSH has greater activity in receptor binding studies, and more effectively stimulates the PKA pathway and steroidogenesis in human granulosa cells.

STUDY DESIGN, SIZE, DURATION

This is a cross-sectional study evaluating the actions of purified recombinant human FSH glycoforms on parameters of follicular development, gene expression and cell signaling in immature postnatal day (PND) 17 female CD-1 mice. To stimulate follicle development in vivo, PND 17 female CD-1 mice (n = 8-10/group) were treated with PBS (150 µl), hFSH18/21 (1 µg/150 µl PBS) or hFSH24 (1 µg/150 µl PBS) by intraperitoneal injection (i.p.) twice daily (8:00 a.m. and 6:00 p.m.) for 2 days. Follicle numbers, serum anti-Müllerian hormone (AMH) and estradiol levels, and follicle health were quantified. PND 17 female CD-1 mice were also treated acutely (2 h) in vivo with PBS, hFSH18/21 (1 µg) or hFSH24 (1 µg) (n = 3-4/group). One ovary from each mouse was processed for RNA sequencing analysis and the other ovary processed for signal transduction analysis. An in vitro ovary culture system was used to confirm the relative signaling pathways.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The purity of different recombinant hFSH glycoforms was analyzed using an automated western blot system. Follicle numbers were determined by counting serial sections of the mouse ovary. Real-time quantitative RT-PCR, western blot and immunofluorescence staining were used to determine growth and apoptosis markers related with follicle health. RNA sequencing and bioinformatics were used to identify pathways and processes associated with gene expression profiles induced by acute FSH glycoform treatment. Analysis of RTKs was used to determine potential FSH downstream signaling pathways in vivo. Western blot and in vitro ovarian culture system were used to validate the relative signaling pathways.

MAIN RESULTS AND THE ROLE OF CHANCE

Our present study shows that both hypo- and fully-glycosylated recombinant human FSH can drive follicular growth in vivo. However, hFSH18/21 promoted development of significantly more large antral follicles compared to hFSH24 (P < 0.01). In addition, compared with hFSH24, hFSH18/21 also promoted greater indices of follicular health, as defined by lower BAX/BCL2 ratios and reduced cleaved Caspase 3. Following acute in vivo treatment with FSH glycoforms RNA-sequencing data revealed that both FSH glycoforms rapidly induced ovarian transcription in vivo, but hypo-glycosylated FSH more robustly stimulated Gαs and cAMP-mediated signaling and members of the AP-1 transcription factor complex. Moreover, hFSH18/21 treatment induced significantly greater activation of RTKs, PI3K/AKT and MAPK/ERK signaling compared to hFSH24. FSH-induced indices of follicle growth in vitro were blocked by inhibition of PI3K and MAPK.

LARGE SCALE DATA

RNA sequencing of mouse ovaries. Data will be shared upon reasonable request to the corresponding author.

LIMITATIONS, REASONS FOR CAUTION

The observations that hFSH glycoforms have different bioactivities in the present study employing a mouse model of follicle development should be verified in nonhuman primates. The gene expression studies reflect transcriptomes of whole ovaries.

WIDER IMPLICATIONS OF THE FINDINGS

Commercially prepared recombinant human FSH used for ovarian stimulation in human ART is fully-glycosylated FSH. Our findings that hypo-glycosylated hFSH has greater bioactivity enabling greater follicular health and growth without exaggerated estradiol production in vivo, demonstrate the potential for its development for application in human ART.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by NIH 1P01 AG029531, NIH 1R01 HD 092263, VA I01 BX004272, and the Olson Center for Women's Health. JSD is the recipient of a VA Senior Research Career Scientist Award (1IK6 BX005797). This work was also partially supported by National Natural Science Foundation of China (No. 31872352). The authors declared there are no conflicts of interest.

Regulation of the early growth response-1 binding protein NAB2 in bovine granulosa cells and effect on connective tissue growth factor expression

Ovarian fibrosis is associated with increased expression of the transcription factor, Early growth response-1 (EGR1) and connective tissue growth factor (CCN2) in granulosa cells. The transcriptional activity of EGR1 is under negative feedback control by NAB1 and NAB2, but little is known about NAB expression in granulosa cells. Using a well-defined bovine in-vitro granulosa cell model, we show that NAB2 but not NAB1 mRNA is upregulated by fibroblast growth factor (FGF)1 and FGF2, but not by FGF4 or FGF8b. Overexpressing NAB2 abrogated the ability of FGF8b to increase EGR1 and CCN2 mRNA, as well as mRNAs encoding other FGF-target genes. Surprisingly, overexpression of NAB2 in the absence of growth factor stimulation increased abundance of mRNA encoding CCN2 and EGR1, and decreased estradiol secretion. We conclude that NAB2 is expressed in granulosa cells and plays a role in regulating EGR1-induced CCN2 expression, although cross-talk with other signaling pathways is likely occurring.

Effect of genistein on the gene and protein expressions of CXCL-12 and EGR-1 in the rat ovary

The effect of genistein (GEN) on the gene expression level of stromal cell-derived factor-1/CXCL-12 and early growth response gene-1 was studied in ovarian tissue of young and initially ageing (early stages in the ageing process) female rats. Forty, young female Sprague Dawley (SD) rats of 2-3 months old (200 ±20 g) and forty, initially ageing female SD rats of 10-12 months (490 ± 20 g) old were selected. According to the weight, rats were divided into control group, low-dose group (L), medium-dose group (M) and a high-dose group (H) and were given 15, 30 and 60 mg/kg GEN respectively. The positive control (Oestrogen) group was given 0.5 mg/kg diethylstilbestrol. The treatment lasted for 30 days. The mRNA expression of C-X-C motif chemokine ligand 12 (CXCL-12) and early growth response factor-1 (EGR-1) was measured by real-time PCR, and protein expression of EGR-1 was detected by Western blot. When compared to the negative control group (NC), the ovary/body weight ratio in the young rats decreased in the GEN group, but the difference was not significant. Similarly, compared with NC, the ovary/body weight ratio in the initially ageing rats also decreased with the increase in GEN concentration, but the decrease was significant in M and H groups (p < .01). The administration of GEN enhanced both the gene and protein expression levels of CXCL-12 and EGR-1 in the ovary. Pearson's correlation analysis showed a synergistic effect between CXCL-12 and EGR-1. Thus, we conclude that the effect of GEN on CXCL-12 and EGR-1 in the initially ageing group was obvious than that in the younger group.

Proteomic Analysis of Porcine Pre-ovulatory Follicle Differentiation Into Corpus Luteum

The luteinization of the follicular cells, following a LH surge, causes extensive molecular and structural changes in preovulatory follicles (POF) that lead to ovulation and ultimate formation of the corpus luteum (CL). The objective of this study was to identify proteins expressed in porcine POF before the LH surge and a new CL formed, 2-3 days after ovulation, and evaluate proteome changes associated with formation of the CL from a follicle. We used 2D-gel electrophoresis-based proteomics and tandem mass spectrometry followed by a functional analysis using Ingenuity Pathway analysis (IPA) to evaluate functional pathways associated with the luteinization process. Protein lysates were prepared from isolated POFs and from the newly formed CL. A total of 422 protein spots were identified in both structures. A total of 15 and 48 proteins or their proteoforms were detected only in the POFs and CL, respectively. An IPA analysis of a POF proteome showed that most of the follicular proteins were involved in cellular infiltration, endoplasmic stress responses, and the protein ubiquitination pathway. Most of the early luteal proteins were associated with steroid metabolism, cell death and survival, free radical scavenging, and the protein ubiquitination pathway. A comparison of a follicular proteome with that of an early luteal proteome revealed that 167 identified proteins or their proteoforms were differentially regulated between POFs and the newly formed CL (p < 0.05 and a fold change of >1.8). Proteins that were significantly more abundant in follicles included cAMP-dependent protein kinase, histone binding protein RBBP4, reticulocalbin, vimentin, and calumenin; more abundant luteal proteins included albumin, farnesyl diphosphate synthase, serine protease inhibitors, elongation factor-1, glutaredoxin, and selenium-binding protein. Proteins that were significantly altered with luteal formation were found to be associated with cholesterol biosynthesis, cell death and survival, and acute phase response. Moreover, upstream regulators of differentially abundant proteins in CL were identified that included insulin growth factor-1, sterol regulatory element-binding transcription factor-1, and nuclear factor erythroid-derived 2. We have identified novel proteins that advance our understanding of (1) processes associated with differentiation of POFs into the CL, (2) possible mechanisms of luteal cell survival, and (3) pathways regulating steroidogenesis in the newly formed CL.

Regulation and function of runt-related transcription factors (RUNX1 and RUNX2) in goat granulosa cells

Transcription factors, runt-related transcription factor 1 (RUNX1) and 2 (RUNX2), belong to the runt-related (RUNX) gene family and play critical roles in mammalian reproduction processes. However, the regulatory mechanisms of RUNX1 and RUNX2 expression or their functions in goat follicles remain largely unknown. Herein, RUNX1 and RUNX2 proteins were detected in the oocytes and granulosa cells of preantral and antral follicles, as well as corpus luteum by immunohistochemistry. Treatments with human chorionic gonadotropin (hCG) or with the agonists and inhibitors of hCG-induced intracellular signaling pathways in granulosa cells in vitro, we found that hCG increased RUNX1 expression by activating PKC and PI3K signaling molecules, and increased RUNX2 expression by activating adenylate cyclase, PKC, and PI3K signaling molecules. We also demonstrated that miR-181b expression is dependent on the hCG-induced activation of PKC and PKA, and miR-222 expression is dependent on the hCG-induced activation of PI3K and PKC in cultured granulosa cells. Meanwhile, miR-181b and miR-222 suppressed RUNX1 and RUNX2 expression by targeting RUNX1 and RUNX2 3' untranslated regions (3'UTRs) with or without hCG, respectively. These results suggested that hCG-mediated miR-181b and miR-222 expression are important for the regulation of RUNX1 and RUNX2 expression levels in granulosa cells. To explore the specific functions of RUNX1 and RUNX2, we transfected RUNX1 and RUNX2 small interfering RNAs into primary cultured granulosa cells. Knockdown of RUNX1 and RUNX2 significantly decreased progesterone productions and the mRNA abundance of key steroidogenic enzymes (StAR, CYP11A1 and HSD3B) after hCG treatment. But only miR-222 increased estradiol secretion in goat granulosa cells. In addition, knockdown of RUNX1 and RUNX2 also promoted granulosa cell proliferation. The hormonally regulated expression of RUNX1 and RUNX2 in granulosa cells, their involvement in progesterone production, and promoted granulosa cell proliferation suggest important roles of RUNX1 and RUNX2 in follicular development and luteinization.

From Follicular Development and Ovulation to Ovarian Cancers: An Unexpected Journey

Follicular development and ovulation are complex development processes that are regulated by multiple, interacting pathways and cell types. The oocyte, cumulus cells, granulosa cells, and theca cells communicate to impact follicular development and ovulation. Many hormones and cytokines control intracellular regulatory networks and transcription factors, some of which are cell type specific. Molecular biology approaches and mutant mouse models have contributed immensely to our knowledge of what genes and signaling cascades impact each stage of follicular development and ovulation, and how the alteration of gene expression profiles and the activation of specific signaling pathways can impact ovarian cancer development in ovarian surface epithelial cells as well as granulosa cells. This chapter explores how pathways controlling normal follicle development and ovulation can be diverted to abnormal development.

Luteolysis and the Auto-, Paracrine Role of Cytokines From Tumor Necrosis Factor α and Transforming Growth Factor β Superfamilies

Successful pregnancy establishment demands optimal luteal function in mammals. Nonetheless, regression of the corpus luteum (CL) is absolutely necessary for normal female cyclicity. This dichotomy relies on intricate molecular signals and rapidly activated biological responses, such as angiogenesis, extracellular matrix (ECM) remodeling, or programmed cell death. The CL establishment and growth after ovulation depend not only on the luteinizing hormone-mediated endocrine signal but also on a number of auto-, paracrine interactions promoted by cytokines and growth factors like fibroblast growth factor 2, vascular endothelial growth factor A, and tumor necrosis factor α (TNF), which coordinate vascularigenesis and ECM reorganization as well as steroidogenesis. With the organ fully developed, the release of the uterine prostaglandin F2α activates luteolysis, an intricate process supported by intraluteal interactions that ensure the loss of steroidogenic function (functional luteolysis) and the involution of the organ (structural luteolysis). This chapter provides an overview of the local action of cytokines during luteal function, with particular emphasis on the role of TNF and transforming growth factor β superfamilies during luteolysis.

CXADR-like membrane protein (CLMP) in the rat ovary: stimulation by human chorionic gonadotrophin during the periovulatory period

CXADR-like membrane protein (CLMP) is a novel cell-cell adhesion molecule. The present study investigated the spatiotemporal expression pattern of CLMP and its regulation in the rat ovary during the periovulatory period. Real-time polymerase chain reaction analysis revealed that Clmp mRNA was rapidly stimulated in intact ovaries by 4h after human chorionic gonadotrophin (hCG) treatment. In situ hybridisation analysis demonstrated that Clmp mRNA expression was stimulated in theca cells at 4h after hCG and remained elevated until 12h. Clmp mRNA was also upregulated in granulosa cells and was present in forming corpora lutea. Our data indicate that the protein kinase A but not the protein kinase C pathway regulates the expression of Clmp mRNA in granulosa cells. Phosphatidylinositol 3 kinase and p38 kinase are also involved in regulating Clmp mRNA expression. The stimulation of Clmp mRNA by hCG requires new protein synthesis. Furthermore, inhibition of epidermal growth factor receptor activation significantly inhibited Clmp mRNA expression, whereas inhibition of prostaglandin synthesis or progesterone action had no effect. The stimulation of CLMP in the rat ovary may be important in cell adhesion events during ovulation and luteal formation such as maintaining the structure and communication of ovarian follicular and luteal cells.

Induction of Ectonucleotide Pyrophosphatase/Phosphodiesterase 3 During the Periovulatory Period in the Rat Ovary

Ectonucleotide pyrophosphatase/phosphodiesterase 3 ( Enpp3) is involved in multiple physiological processes, such as morphological changes and inflammatory processes. The present study investigated the spatiotemporal expression pattern and regulatory mechanisms controlling expression of Enpp3 in the rat ovary during the periovulatory period. Immature female rats were injected with pregnant mare serum gonadotropin to stimulate follicular development. Ovaries, granulosa cells, or theca-interstitial cells were collected at various times after human chorionic gonadotropin (hCG) administration. Real-time polymerase chain reaction analysis revealed that messenger RNA (mRNA) for Enpp3 was highly induced in both granulosa cells and theca-interstitial cells by hCG. In situ hybridization analysis demonstrated that Enpp3 mRNA expression was induced in theca cells at 4 hours after hCG, and the expression remained elevated until 12 hours after hCG. The expression of Enpp3 mRNA was stimulated in granulosa cells at 8 hours and reached the highest expression at 12 hours. Localization of Enpp3 mRNA was observed in newly forming corpora lutea by in situ hybridization. The hCG-stimulated expression of Enpp3 mRNA was blocked by a protein kinase C inhibitor (GF109203) instead of the protein kinase A inhibitor (H89). Furthermore, Enpp3 induction is dependent on new protein synthesis. Inhibition of progesterone action did not alter Enpp3 mRNA expression, whereas inhibition of prostaglandin synthesis or the epidermal growth factor pathway diminished Enpp3 mRNA levels. In conclusion, our findings suggest that the induction of the Enpp3 mRNA may be important for the morphological changes and inflammatory response during ovulation and luteinization.

Melatonin and its receptor MT1 are involved in the downstream reaction to luteinizing hormone and participate in the regulation of luteinization in different species

The functions of melatonin in preovulatory fluid remain elusive. In the current study, we observed that the extremely high level of expression of MT1 in mice granulosa cells was rapidly induced by hCG (equivalent LH) within 2 hours and this was referred as MT1 surge. In cumulus cells, serotonin N-acetyltransferase (SNAT) was also upregulated by hCG and led to elevated melatonin levels in ovarian follicle fluid. Melatonin application before MT1 surge significantly promoted embryo implantation, and this was probably attributed to a rise in progesterone levels in the serum. The mechanistic studies indicated that melatonin/MT1 (MLT/MT1) signaling remarkably improved the expression of corpus luteum marker genes, that is, Akr1c18 and Cyp11a1. High-throughput sequencing results suggested that extracellular matrix (ECM) receptor interaction, focal adhesion, and activation of PI3K/Akt pathway which are involved in granulosa cell luteinization might mediate the actions of MLT/MT1 signal. In addition, this effect on luteinization was compared in different species. It was verified that high melatonin levels exist in serum at estrum of cows and help to improve the first estrus fecundation rate. These results suggested that both melatonin and MT1 are involved in the downstream reaction of hCG (LH) and they play important roles in luteinization. These findings provide the novel information on the physiology of melatonin in animal reproduction.

Maternal obesity is associated with ovarian inflammation and upregulation of early growth response factor 1

Obesity impairs reproductive functions through multiple mechanisms, possibly through disruption of ovarian function. We hypothesized that increased adiposity will lead to a proinflammatory gene signature and upregulation of Egr-1 protein in ovaries from obese (OB; n = 7) compared with lean (LN; n = 10) female Sprague-Dawley rats during the peri-implantation period at 4.5 days postcoitus (dpc). Obesity was induced by overfeeding (40% excess calories for 28 days) via total enteral nutrition prior to mating. OB dams had higher body weight (P < 0.001), greater fat mass (P < 0.001), and reduced lean mass (P < 0.05) and developed metabolic dysfunction with elevated serum lipids, insulin, leptin, and CCL2 (P < 0.05) compared with LN dams. Microarray analyses identified 284 differentially expressed genes between ovaries from LN vs. OB dams (±1.3 fold, P < 0.05). RT-qPCR confirmed a decrease in expression of glucose transporters GLUT4 and GLUT9 and elevation of proinflammatory genes, including CCL2, CXCL10, CXCL11, CCR2, CXCR1, and TNFα in ovaries from OB compared with LN (P < 0.05). Protein levels of PI3K and phosphorylated Akt were significantly decreased (P < 0.05), whereas nuclear levels of Egr-1 (P < 0.05) were increased in OB compared with LN ovaries. Moreover, Egr-1 was localized to granulosa cells, with the highest expression in cumulus cells of preovulatory follicles. mRNA expression of VCAN, AURKB, and PLAT (P < 0.05) correlated with %visceral fat weight (r = 0.51, -0.77, and -0.57, respectively, P ≤ 0.05), suggesting alterations in ovarian function with obesity. In summary, maternal obesity led to an upregulation of inflammatory genes and Egr-1 expression in peri-implantation ovarian tissue and a concurrent downregulation of GLUTs and Akt and PI3K protein levels.

Expression, regulation and function of Egr1 during implantation and decidualization in mice

Abstract Early growth response gene 1 (Egr1), a zinc finger transcriptional factor, plays an important role in regulating cell proliferation, differentiation and angiogenesis. Current data have shown that Egr1 is involved in follicular development, ovulation, luteinization and placental angiogenesis. However, the expression, regulation and function of Egr1 in mouse uterus during embryo implantation and decidualization are poorly understood. Here we showed that Egr1 was strongly expressed in the subluminal stroma surrounding the implanting blastocyst on day 5 of pregnancy. Injection of Egr1 siRNA into the mouse uterine horn could obviously reduce the number of implanted embryos and affect the uterine vascular permeability. Further study found that Egr1 played a role through influencing the expression of cyclooxygenase-2 (Cox-2), microsomal prostaglandin E synthase 1 (mPGES-1), vascular endothelial growth factor (Vegf), transformation related protein 53 (Trp53) and matrix metallopeptidase 9 (Mmp9) genes in the process of mouse embryo implantation. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) might direct the expression of Egr1 in the uterine stromal cells. Under in vivo and in vitro artificial decidualization, Egr1 expression was significantly decreased. Overexpression of Egr1 downregulated the expression of decidual marker decidual/trophoblast PRL-related protein (Dtprp) in the uterine stromal cells, while inhibition of Egr1 upregulated the expression of Dtprp under in vitro decidualization. Estrogen and progesterone could regulate the expression of Egr1 in the ovariectomized mouse uterus and uterine stromal cells. These results suggest that Egr1 may be essential for embryo implantation and decidualization.

Effect of the transient pharmacological inhibition of Mapk3/1 pathway on ovulation in mice

Mitogen-activated protein kinase 3/1 (Mapk3/1) pathway is critical for LH signal transduction during ovulation. However, the mechanisms remain incompletely understood. We hypothesized that Mapk pathway regulates ovulation through transcriptional regulation of ovulatory genes. To test this hypothesis we used immature mice superovulated with equine and human chorionic gonadotropins (eCG and hCG) and PD0325901, to inhibit hCG-induced Mapk3/1 activity. Mice received either the inhibitor PD0325901 (25 μg/g, i.p.) or vehicle at 2h before hCG stimulation. Administration of the inhibitor abolished Mapk3/1 phosphorylation in granulosa cells. While vehicle-treated mice ovulated normally, there were no ovulations in inhibitor-treated mice. First, we analyzed gene expression in granulosa cells at 0h, 1h and 4h post-hCG. There was expected hCG-driven increase in mRNA abundance of many ovulation-related genes including Ptgs2 in vehicle-treated granulosa cells, but not (P<0.05) in inhibitor-treated group. There was also reduced mRNA and protein abundance of the transcription factor, early growth response 1 (Egr1) in inhibitor-treated granulosa cells. We then used GRMO2 cell-line to test if Egr1 is recruited to promoter of Ptgs2 followed by chromatin immunoprecipitation with either Egr1 or control antibody. Enrichment of the promoter regions in immunoprecipitants of Egr1 antibody indicated that Egr1 binds to the Ptgs2 promoter. We then knocked down Egr1 expression in mouse primary granulosa cells using siRNA technology. Treatment with Egr1-siRNA inhibited Egr1 transcript accumulation, which was associated with reduced expression of Ptgs2 when compared to control-siRNA treated granulosa cells. These data demonstrate that transient inhibition of LH-stimulated MAPK3/1 activity abrogates ovulation in mice. We conclude that Mapk3/1 regulates ovulation, at least in part, through Egr1 and its target gene, Ptgs2 in granulosa cells of ovulating follicles in mice.

Expression of prostaglandin synthesizing enzymes (cyclooxygenase 1 and cyclooxygenase 2) in the ovary of the ostrich (Struthio camelus)

Cyclooxygenase is the rate limiting enzyme in the production of prostaglandins. In birds two isoforms are present: cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2). Despite evidence implicating that cyclooxygenases and PGs are critical factors in female reproduction in birds, little is known about COX expression in the avian ovary. In birds, cyclooxygenases have been studied in very few species only. In this study we report on the expression of COX-1 and COX-2 in the ovary of the ostrich (Struthio camelus) using immunohistochemistry and non-radioactive in situ hybridization techniques. Our results demonstrate that COX-1 is strongly expressed in the cytoplasm of oocytes of previtellogenic follicles, whereas COX-2 shows the strongest immunostaining in the granulosa cells of previtellogenic follicles. The signals of both isoenzymes fade significantly with increasing diameter and finally nearly vanish in the vitellogenic follicles with a size >1.8 cm. This expression pattern in the ostrich (S. camelus) is, therefore, completely different from the localization of COX-1 and COX-2 in the hen (Gallus gallus), a finding which also suggests different functions of the cyclooxygenases in the ostrich species. Non-radioactive in situ hybridization confirmed that COX-1 is synthesized in the ooplasm and COX-2 in the granulosa layers of early previtellogenic follicles. According to the results of this study it appears unlikely that COX-1 or COX-2 play a major role in ovulation and oviposition in the ostrich.

Nitric oxide synthase activity is critical for the preovulatory epidermal growth factor-like cascade induced by luteinizing hormone in bovine granulosa cells

In rabbits and rodents, nitric oxide (NO) is generally considered to be critical for ovulation. In monovulatory species, however, the importance of NO has not been determined, nor is it clear where in the preovulatory cascade NO may act. The objectives of this study were (1) to determine if nitric oxide synthase (NOS) enzymes are regulated by luteinizing hormone (LH) and (2) to determine if and where endogenous NO is critical for expression of genes essential for the ovulatory cascade in bovine granulosa cells in serum-free culture. Time- and dose-response experiments demonstrated that LH had a significant stimulatory effect on endothelial NOS (NOS3) mRNA abundance, but in a prostaglandin-dependent manner. NO production was stimulated by LH before a detectable increase in NOS3 mRNA levels was observed. Pretreatment of cells with the NOS inhibitor L-NAME blocked the effect of LH on the epidermal growth factor (EGF)-like ligands epiregulin and amphiregulin, as well as prostaglandin-endoperoxide synthase-2 mRNA abundance and protein levels. Similarly, EGF treatment increased mRNA encoding epiregulin, amphiregulin, and the early response gene EGR1, and this was inhibited by pretreatment with L-NAME. Interestingly, pretreatment with L-NAME had no effect on either ERK1/2 or AKT activation. Taken together, these results suggest that endogenous NOS activity is critical for the LH-induced ovulatory cascade in granulosa cells of a monotocous species and acts downstream of EGF receptor activation but upstream of the EGF-like ligands.

Cooperation of luteinizing hormone signaling pathways in preovulatory avian follicles regulates circadian clock expression in granulosa cell

Ovulation in birds is triggered by a surge of luteinizing hormone (LH), and the ovulatory cycle is affected by the circadian rhythms of clock genes transcription levels in follicles. The influence of LH signaling cascades action on circadian clock genes was investigated using granulosa cells of preovulatory follicles from Roman hens cultured in a serum-free system. The expression of core oscillators (Bmal1, Clock, Cry1, Per2, and Rev-erbβ), clock-controlled gene (Star), Egr-1 and LHr was measured by quantitative real-time PCR. Significant changes in clock genes transcription levels were observed in control groups over 24 h, indicating that cell-autonomous rhythms exist in granulosa cells. Intriguingly, the transcript levels of clock genes increased with LH treatment during 24 h of culture; they peaked 4 h in advance of controls and second but weaker oscillations were also observed. It appeared that LH changed the cell-autonomous rhythm and cycle time of clock genes. To further investigate the LH signaling cascades, inhibitors of cyclic adenosine monophosphate (cAMP), p38 mitogen-activated protein kinases (p38MAPK) and extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathways were used. The transcript levels of clock genes were suppressed by blocking cAMP, but increased with similar expression patterns by blocking the p38MPAK and ERK1/2 pathways over 24 h. Thus, the influence of LH signaling cascades in chicken ovulation is mediated by the cAMP pathway and also involves the p38MAPK and ERK1/2 pathways.

Elevated peritoneal fluid TNF-α incites ovarian early growth response factor 1 expression and downstream protease mediators: a correlation with ovulatory dysfunction in endometriosis

Endometriosis-associated infertility manifests itself via multiple, poorly understood mechanisms. Our goal was to characterize signaling pathways, between peritoneal endometriotic lesions and the ovary, leading to failed ovulation. Genome-wide microarray analysis comparing ovarian tissue from an in vivo endometriosis model in the rat (Endo) with controls (Sham) identified 22 differentially expressed genes, including transiently expressed early growth response factor 1 (Egr1). The Egr1 regulates gene requisites for ovulation. The Egr1 promoter is responsive to tumor necrosis factor-alpha (TNF-α) signaling. We hypothesized that altered expression of ovarian EGR1 is induced by elevated peritoneal fluid TNF-α which is upregulated by the presence of peritoneal endometriosis. Endo rats, compared to controls, had more peritoneal fluid TNF-α and quantitative, spatial differences in Egr1 mRNA and EGR1 protein localization in follicular compartments. Interactions between elevated peritoneal fluid TNF-α and overexpression of follicular Egr1/EGR1 expression may affect downstream protease pathways impeding ovulation in endometriosis. Preliminary studies identified similar patterns of EGR1 protein localization in human ovaries from women with endometriosis and compared to those without endometriosis.

Hormonal induction of polo-like kinases (Plks) and impact of Plk2 on cell cycle progression in the rat ovary

The highly conserved polo-like kinases (Plks) are potent regulators of multiple functions in the cell cycle before and during mitotic cell division. We investigated the expression pattern of Plk genes and their potential role(s) in the rat ovary during the periovulatory period. Plk2 and Plk3 were highly induced both in intact ovaries and granulosa cells in vivo after treatment with the luteinizing hormone (LH) agonist, human chorionic gonadotropin (hCG). In vitro, hCG stimulated the expression of Plk2 in granulosa cells, but not Plk3. This induction of Plk2 expression was mimicked by both forskolin and phorbol 12 myristate 13-acetate (PMA). Moreover, Plk2 expression was reduced by inhibitors of prostaglandin synthesis or the EGF pathway, but not by progesterone receptor antagonist (RU486) treatment. At the promoter level, mutation of the Sp1 binding sequence abolished the transcriptional activity of the Plk2 gene. ChIP assays also revealed the interaction of endogenous Sp1 protein in the Plk2 promoter region. Functionally, the over-expression of Plk2 and Plk3 arrested granulosa cells at the G0/G1 phase of the cell cycle. In contrast, the knockdown of Plk2 expression in granulosa cells decreased the number of cells in the G0/G1 stage of the cell cycle, but increased granulosa cell viability. In summary, hCG induced Plk2 and Plk3 expression in the rat ovary. Prostaglandins and the EGF signaling pathway are involved in regulating Plk2 expression. The transcription factor Sp1 is important for Plk2 transcriptional up-regulation. Our findings suggest that the increase in Plk2 and Plk3 expression contributes to the cell cycle arrest of granulosa cells which is important for the luteinization of granulosa cells during the periovulatory period.

Molecular characterization and expression of DERL1 in bovine ovarian follicles and corpora lutea

The endoplasmic reticulum (ER) is a major site of protein synthesis and facilitates the folding and assembly of newly synthesized proteins. Misfolded proteins are retrotranslocated across the ER membrane and destroyed at the proteasome. DERL1 is an important protein involved in the retrotranslocation and degradation of a subset of misfolded proteins from the ER. We characterized a 2617 bp cDNA from bovine granulosa cells that corresponded to bovine DERL1. Two transcripts of 3 and 2.6 kb were detected by Northern blot analysis, and showed variations in expression among tissues. During follicular development, DERL1 expression was greater in day 5 dominant follicles compared to small follicles, ovulatory follicles, or corpus luteum (CL). Within the CL, DERL1 mRNA expression was intermediate in midcycle, and lowest in late cycle as compared to early in the estrous cycle. Western blot analyses demonstrated the presence of DERL1 in the bovine CL at days 5, 11, and 18 of the estrous cycle. Co-immunoprecipitation using luteal tissues showed that DERL1 interacts with class I MHC but not with VIMP or p97 ATPase. The interaction between DERL1 and MHC I suggests that, in the CL, DERL1 may regulate the integrity of MHC I molecules that are transported to the ER membrane. Furthermore, the greater expression of DERL1 mRNA is associated with the active follicular development and early luteal stages, suggesting a role of DERL1 in tissue remodeling events and maintenance of function in reproductive tissues.

Sustained activity of the EGF receptor is an absolute requisite for LH-induced oocyte maturation and cumulus expansion

Mammalian reproduction depends on the release of a mature oocyte from the ovarian follicle. Maturation of the oocyte and rupture of the follicle wall constitute part of the responses to the preovulatory surge of LH, which also include cumulus expansion and granulosa cell luteinization. It was previously shown that the epidermal growth factor receptor (EGFR) mediates the ovulatory response to LH in the ovarian follicle. We hypothesized that it is a sustained activity of the EGFR that generates oocyte maturation and cumulus expansion. We demonstrated that, whereas a transient exposure of rat isolated, intact, preovulatory follicles to either LH or forskolin was sufficient to induce oocyte maturation and cumulus expansion, these LH-induced responses were only generated upon a prolonged activity of the EGFR. In addition, the continuous activity of the EGFR is essential for the chronic phosphorylation of the ERK1/2 downstream signaling molecules, which were shown to be essential for oocyte maturation and cumulus expansion. Interestingly, EGFR-sustained activity was also necessary to maintain the up-regulation of Ptgs2, a gene essential for cumulus expansion. The unusual prolonged duration of ERK1/2 activity may possibly be attributed to the late induction of the ERK-specific phosphatase 3, demonstrated herein. These new data shed light on the unique characteristics of EGFR-ERK1/2 activity in the ovarian follicle and emphasize the fact that the ovulatory process involves a nonclassical activation of this pathway.

Rapid effects of LH on gene expression in the mural granulosa cells of mouse periovulatory follicles

LH acts on periovulatory granulosa cells by activating the PKA pathway as well as other cell signaling cascades to increase the transcription of specific genes necessary for ovulation and luteinization. Collectively, these cell signaling responses occur rapidly (within minutes); however, presently no high throughput studies have reported changes before 4 h after the LH surge. To identify early response genes that are likely critical for initiation of ovulation and luteinization, mouse granulosa cells were collected before and 1 h after hCG. Fifty-seven gene transcripts were significantly (P<0.05) upregulated and three downregulated following hCG. Twenty-four of these transcripts were known to be expressed after the LH/hCG surge at later time points, while 36 were unknown to be expressed by periovulatory granulosa cells. Temporal expression of several transcripts, including the transcription factors Nr4a1, Nr4a2, Egr1, Egr2, Btg1, and Btg2, and the epidermal growth factor (EGF)-like ligands Areg and Ereg, were analyzed by quantitative RT-PCR, and their putative roles in granulosa cell function are discussed. Epigen (Epgn), another member of the family of EGF-like ligands was identified for the first time in granulosa cells as rapidly induced by LH/hCG. We demonstrate that Epgn initiates cumulus expansion, similar to the other EGF-receptor ligands Areg and Ereg. These studies illustrate that a number of changes in gene expression occur in vivo in response to LH, and that many of the differentially expressed genes are transcription factors that we would predict in turn modulate granulosa cell gene expression to ultimately impact the processes of ovulation and luteinization.

Changes in global gene expression in rat myometrium in transition from late pregnancy to parturition

The process of parturition involves the complex interplay of factors that change the excitability and contractile activity of the uterus. We have compared the relative gene expression profile of myometrium from rats before parturition (21 days pregnant) and during delivery, using high-density DNA microarray. Of 8,740 sequences available in the array, a total of 3,782 were detected as present. From the sequences that were significantly altered, 59 genes were upregulated and 82 genes were downregulated. We were able to detect changes in genes described to have altered expression level at term, including connexin 43 and 26, cyclooxygenase 2, and oxytocin receptor, as well as novel genes that have been not previously associated with parturition. Quantitative real-time PCR on selected genes further confirmed the microarray data. Here we report for the first time that aquaporin5 (AQP5), a member of the aquaporin water channel family, was dramatically downregulated during parturition (approximately 100-fold by microarray and approximately 50-fold by real-time PCR). The emerging profile highlights biochemical cascades occurring in a period of approximately 36 h that trigger parturition and the initiation of myometrium reverse remodeling postpartum. The microarray analysis uncovered genes that were previously suspected to play a role in parturition. This regulation involves genes from immune/inflammatory response, steroid/lipid metabolism, calcium homeostasis, cell volume regulation, cell signaling, cell division, and tissue remodeling, suggesting the presence of multiple and redundant mechanisms altered in the process of birth.

Exendin-4 induction of Egr-1 expression in INS-1 beta-cells: interaction of SRF, not YY1, with SRE site of rat Egr-1 promoter

Glucagon-like peptide-1 (GLP-1) induces several immediate early response genes such as c-fos, c-jun, and early growth response-1 (Egr-1), which are involved in cell proliferation and differentiation. We recently reported that exendin-4 (EX-4), a potent GLP-1 agonist, upregulated Egr-1 expression via phosphorylation of CREB, a transcription factor in INS-1 beta-cells. This study was designed to investigate the role of another transcription factors, serum response factor (SRF) and Yin Yang-1 (YY1), in EX-4-induced Egr-1 expression. EX-4 significantly increased Egr-1 mRNA and subsequently its protein level. EX-4-induced Egr-1 expression was inhibited by pretreatment with a PKA inhibitor, H-89, and an MEK inhibitor, PD 98059. The siRNA-mediated inhibition of PKA and ERK1 resulted in significant reduction of EX-4-induced Egr-1 expression. Promoter analyses showed that SRE clusters were essential for Egr-1 transcription, and YY1 overexpression did not affect Egr-1 promoter activity. EMSA results demonstrated that EX-4-induced transient increase in DNA-protein complex on SRE site, and that both SRF and phospho-SRF were bound to this site. Treatment of either YY1 consensus oligonucleotide or YY1 antibody did not effect the change of density or migration of the DNA-protein complex. Collectively, EX-4-induced Egr-1 expression is largely dependent on cAMP-mediated extracellular signal-regulated kinase activation, and EX-4 induces Egr-1 transcription via the interaction of SRF and phospho-SRF to SRE sites.

Identification of differentially expressed markers in human follicular cells associated with competent oocytes

BACKGROUND

The development of an accurate method for selection of high-quality embryos is essential to achieve high pregnancy rates with single embryo transfer in human IVF. The developmental competence of the oocyte is acquired during follicle maturation and strong communication also exists between the follicular cells (FCs) and the oocytes; thus oocyte developmental competence may be determined by markers expressed in the surrounding FCs.

METHODS

From consenting patients (n = 40), FCs were recovered on a per follicle basis by individual follicle puncture. Hybridization analyses using a custom-made complementary DNA microarray containing granulosa/cumulus expressed sequence tags (ESTs) from subtracted libraries and an Affymetrix GeneChip were performed to identify specific genes expressed in follicles leading to a pregnancy. The selected candidate genes were validated by quantitative-PCR (Q-PCR).

RESULTS

Subtractive libraries prepared from pooled samples representing pregnant versus non-pregnant patients produced 1694 ESTs. Hybridization data analysis discriminated 115 genes associated with competent follicles. Selected candidates were confirmed by Q-PCR: 3-beta-hydroxysteroid dehydrogenase 1 (P = 0.0078), Ferredoxin 1 (P = 0.0203), Serine (or cysteine) proteinase inhibitor clade E member 2 (P = 0.0499), Cytochrome P450 aromatase (P = 0.0359) and Cell division cycle 42 (P = 0.0396).

CONCLUSIONS

Microarray technologies are useful to mine the transcriptome of FCs expressed in follicles associated with competent oocytes and could be used to improve embryo selection with the objective of successful single embryo transfer.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Identification of candidate mRNAs associated with gonadotropin-induced maturation of murine cumulus oocyte complexes using serial analysis of gene expression

In cultured cumulus oocyte complexes (COC), FSH induces gene transcription required for germinal vesicle breakdown (GVBD). Experiments were performed to determine the critical period when gene transcription is required for GVBD and to identify candidate mRNAs involved. Experiment I: murine COC were cultured 4 h in the presence of FSH with 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB) added at different intervals after the start of culture. COC cultured with FSH underwent GVBD (82 ± 7%). When DRB was added at 0, 5, or 10 min after culture initiation, oocyte maturation was blocked (17 ± 7, 14 ± 6, and 21 ± 6% GVBD, respectively). When DRB was added after 15, 20, or 30 min, progressively more COC underwent GVBD (37 ± 6, 39 ± 6, and 66 ± 6%, respectively). The critical period of transcription required for GVBD occurred between 15 and 30 min after culture initiation. Experiment II: COC were cultured for 25 min in the presence (plusDRB) or absence (minusDRB) of DRB. SAGE libraries were generated from COC RNA of each treatment group. A total of 48,431 and 45,367 tags were sequenced for the plusDRB and minusDRB libraries, respectively. Criteria used to identify transcripts of interest included a total tag count of at least 10 across both libraries and a threefold or greater difference in expression between libraries. Using these criteria, 39 and 27 transcripts were identified as differentially expressed at the P ≤ 0.01 and P ≤ 0.001 levels, respectively. Differentially expressed transcripts were classed into major categories that included cell growth, development, and regulation of gene expression. Differentially expressed transcripts represent candidates potentially involved in regulating maturation of murine COC.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Expression of phospholipase A2 group IVA (PLA2G4A) is upregulated by human chorionic gonadotropin in bovine granulosa cells of ovulatory follicles

Prostaglandins are required for the ovulatory process, and their biosynthesis depends on the initial release of arachidonic acid from membrane phospholipids. We hypothesized that phospholipase A2 group IVA (PLA2G4A) expression is upregulated in granulosa cells (GC) at ovulation. We have characterized bovine PLA2G4A cDNA, and investigated its spatiotemporal regulation at the mRNA and protein levels in hCG-induced ovulatory follicles and in vitro, using forskolin-stimulated GC. Regulation of PLA2G4A mRNA expression was studied in GC obtained from bovine follicles collected at different developmental stages: small follicles (2-4 mm), dominant follicles at Day 5 (D5) of the estrous cycle, ovulatory follicles 24 h following injection of hCG, and corpus luteum at D5. PLA2G4A mRNA increased by 14-fold in GC of hCG-stimulated versus dominant follicles (P < 0.0001). Follicular walls obtained from ovulatory follicles recovered at 0, 6, 12, 18, and 24 h post-hCG injection showed an initial 16-fold increase in PLA2G4A transcript at 12 h that reached a 45-fold increase at 24 h, as compared to 0 h (P < 0.0001). Immunoblots of GC extracts showed an initial induction of the PLA2G4A protein at 18 h post-hCG, reaching a maximum at 24 h. Immunohistochemistry observations showed that PLA2G4A signal was mainly observed in mural GC compared to antral GC in hCG-stimulated follicles. Stimulation of cultured bovine GC with 10 microM of forskolin caused an increase in PLA2G4A mRNA and protein. Ovulation is associated with an LH/hCG-dependent induction of PLA2G4A in GC via the adenylyl cyclase/cAMP pathway.

Adipose Differentiation-Related Protein: A Gonadotropin- and Prostaglandin-Regulated Protein in Primate Periovulatory Follicles1

The midcycle LH surge stimulates a rise in follicular fluid prostaglandin E2 (PGE2), which is necessary for normal ovulation. To examine PGE2-regulated processes in primate follicles, monkey granulosa cells were cultured with hCG alone or with hCG and PGE2, and the resulting total RNA was subjected to microarray analysis. Twenty PGE2-regulated mRNAs were identified, and we selected a lipid droplet protein, adipose differentiation-related protein (ADRP), for further study. To determine whether hCG and PGE2 regulate ADRP expression in vivo, monkeys received gonadotropins to stimulate multiple follicular development. Human chorionic gonadotropin was then administered alone or with the PG synthesis inhibitor celecoxib, and follicular aspirates or whole ovaries were obtained at times that span the 40-h periovulatory interval. Administration of hCG increased granulosa cell ADRP mRNA and protein, with peak levels measured just before the expected time of ovulation. Treatment with hCG and celecoxib decreased granulosa cell ADRP mRNA levels compared with those of animals treated with hCG only. ADRP was detected by immunocytochemistry in many monkey tissues that synthesize prostaglandins but was not consistently expressed by steroidogenic tissues. Granulosa cells of periovulatory follicles immunostained for ADRP after, but not before, hCG administration; ADRP colocalized with large lipid droplets within the granulosa cell cytoplasm. These studies identify ADRP as a novel gonadotropin- and PGE2-regulated protein in the granulosa cells of primate periovulatory follicles. Because ADRP facilitates arachidonic acid uptake in non-ovarian cells, ADRP-associated lipid droplets may enhance arachidonic acid uptake by granulosa cells to provide a precursor for periovulatory prostaglandin production.

Development and application of a rat ovarian gene expression database

The pituitary gonadotropins play a key role in follicular development and ovulation through the induction of specific genes. To identify these genes, we have constructed a genome-wide rat ovarian gene expression database (rOGED). The database was constructed from total RNA isolated from intact ovaries, granulosa cells, or residual ovarian tissues collected from immature pregnant mare serum gonadotropin (PMSG)/human chorionic gonadotropin-treated rats at 0 h (no PMSG), 12 h, and 48 h post PMSG, as well as 6 and 12 h post human chorionic gonadotropin. The total RNA was used for DNA microarray analysis using Affymetrix Rat Expression Arrays 230A and 230B (Affymetrix, Santa Clara, CA). The microarray data were compiled and used for display of individual gene expression profiles through specially developed software. The final rOGED provides immediate analysis of temporal gene expression profiles for over 28,000 genes in intact ovaries, granulosa cells, and residual ovarian tissue during follicular growth and the preovulatory period. The accuracy of the rOGED was validated against the gene profiles for over 20 known genes. The utility of the rOGED was demonstrated by identifying six genes that have not been described in the rat periovulatory ovary. The mRNA expression patterns and cellular localization for each of these six genes (estrogen sulfotransferase, synaptosomal-associated protein 25 kDa, runt-related transcription factor, calgranulin B, alpha1-macroglobulin, and MAPK phosphotase-3) were confirmed by Northern blot analyses and in situ hybridization, respectively. The current findings demonstrate that the rOGED can be used as an instant reference for ovarian gene expression profiles, as well as a reliable resource for identifying important yet, to date, unknown ovarian genes.

Decreased expression of early growth response-1 and its role in uterine leiomyoma growth

Expression of early growth response (Egr)-1, a transcriptional factor implicated in growth regulation, is suppressed in several malignant tumors. The present study investigated the expression of Egr-1 and related genes in uterine leiomyoma and normal myometrium to determine possible contributions of Egr-1 to neoplastic growth in leiomyoma cells. Levels of Egr-1 transcripts were decreased in all leiomyomas (n = 20) to approximately 10% of levels in corresponding myometrium, where basal expression was high. Preoperative leuprorelin acetate therapy increased levels of Egr-1 mRNA in normal myometrium only. Northern blot analysis using additional sample sets (n = 5) revealed the full-length Egr-1 transcript. Western blot analysis (n = 5) confirmed decreased expression of Egr-1 protein. Southern blot analysis of the Egr-1 gene and microsatellite analysis of the chromosomal location at 5q31 (D5S414, D5S500, and D5S476) revealed neither DNA recombination nor loss of heterozygosity in leiomyomas. Moreover, Egr-1 retained identical responsiveness to phorbol 12-myristate 13-acetate in primary cultures derived from both leiomyoma and normal tissues. Electrophoretic mobility shift analysis revealed that phorbol 12-myristate 13-acetate-induced Egr-1 in leiomyoma cells retained DNA binding ability. Egr-1 thus appears functionally intact in leiomyoma cells. Finally, consistent with the role of Egr-1 in growth inhibition, transfection of Egr-1 expression vector into a myometrial cell line (KW) that expresses low levels of Egr-1 and displays rapid growth inhibited thymidine uptake in these cells. Egr-1 may display tumor-suppressing activity and offers a potential target for leiomyoma management.

Coordinate transcription of the ADAMTS-1 gene by luteinizing hormone and progesterone receptor

ADAMTS-1 (a disintegrin and metalloproteinase with thrombospondin-like motifs) is a multifunctional protease that is expressed in periovulatory follicles. Herein we show that induction of ADAMTS-1 message in vivo and transcription of the ADAMTS-1 promoter in cultured granulosa cells are dependent on separable but coordinate actions of LH and the progesterone receptor (PR). To analyze the molecular mechanisms by which LH and PR regulate this gene, truncations and site-specific mutants of ADAMTS-1 promoter-luciferase reporter constructs (ADAMTS-1-Luc) were generated and transfected into rat granulosa cell cultures. Three regions of the promoter were found to be important for basal activity, two of which were guanine cytosine-rich binding sites for specificity proteins Sp1/Sp3 and the third bound a nuclear factor 1-like factor. Despite the absence of a consensus PR DNA response element in the proximal ADAMTS-1 promoter, cotransfection of a PRA (or PRB) expression vector stimulated ADAMTS-1 promoter activity, a response that was reduced by the PR antagonist ZK98299. Forskolin plus phorbol myristate acetate also increased promoter activity and, when added to cells cotransfected with PRA, ADAMTS-1 promoter activity increased further. Activation of the ADAMTS-1 promoter by PRA involves functional CAAT enhancer binding protein beta, nuclear factor 1-like factor, and three Sp1/Sp3 binding sites as demonstrated by transfection of mutated promoter constructs. In summary, LH and PRA/B exert distinct but coordinate effects on transactivation of the ADAMTS-1 gene in granulosa cells in vivo and in vitro with PR acting as an inducible coregulator of the ADAMTS-1 gene.

Luteinizing hormone-induced connexin 43 down-regulation: inhibition of translation

The coordinated function of the different compartments of the follicle, the oocyte and the somatic cumulus/granulosa cells, is enabled by the presence of a network of cell-to-cell communication generated by gap junctions. Connexin 43 (Cx43) is the most abundant gap junction protein expressed by the ovarian follicle. The expression of Cx43 is subjected to the control of gonadotropins as follows: FSH up-regulates, whereas LH down-regulates its levels. The aim of this study was to explore the mechanism by which LH reduces the levels of Cx43 and to identify the signal transduction pathway involved in this process. The effect of LH was studied in vitro using isolated intact ovarian follicles. The possible mediators of LH-induced Cx43 down-regulation were examined by incubating the follicles with LH in the presence or absence of inhibitors of protein kinase A (PKA) and of MAPK signaling pathways. Our experiments revealed a 3-h half-life of Cx43 in both control and LH-treated follicles, suggesting that LH did not affect the rate of Cx43 degradation. We further demonstrated that the level of Cx43 mRNA was not significantly influenced by this gonadotropin. However, upon LH administration, [(35)S]methionine incorporation into Cx43 protein was remarkably reduced. The LH-induced arrest of Cx43 synthesis was counteracted by inhibitors of both the PKA and the MAPK cascades. We show herein that LH inhibits Cx43 expression by reducing its rate of translation and that this effect is mediated by both PKA and MAPK.

Cathepsin L gene expression and promoter activation in rodent granulosa cells

The cysteine protease cathepsin L exhibits hormone-regulated expression during ovulation. In situ hybridization analyses of immature and pregnant mare serum gonadotropin-treated mouse and rat ovaries showed that cathepsin L expression in granulosa cells of small, growing follicles increased in periovulatory follicles after human chorionic gonadotropin stimulation. In the rat ovary, cathepsin L was also expressed in follicles with signs of atresia. To determine the molecular mechanisms that mediate the diverse regulation of this gene in granulosa cells, rat cathepsin L promoter-reporter constructs were analyzed by transient transfection assays in rat granulosa cells and EMSAs. A construct containing the transcriptional start site and -244 bp of upstream promoter sequence (-244/+33 bp) exhibited inducibility by forskolin, the phorbol ester phorbol myristate acetate, and an additive effect of both. Within this region, three functional specificity protein 1 (Sp1) sites, an overlapping early growth response protein-1 site, and a cAMP regulatory element-binding protein site were identified. Single or double mutants of the above-mentioned sites did not alter forskolin/phorbol myristate acetate inducibility of the promoter. Mutation of all three Sp1/specificity protein 3 (Sp3) sites, which also mutated the early growth response protein-1 site, reduced the promoter activation. Mutation of the cAMP regulatory element-binding protein site in the triple Sp1 mutant construct completely blocked the inducibility of the promoter. When these same constructs were transfected into MCF-7 human breast cancer cells or were cotransfected with an Sp1 expression vector in Drosophila SL2 cells, similar results were obtained. Collectively, the data document that three Sp1/specificity protein 3 binding GC-rich regions and a functional cAMP regulatory element constitute an important transcriptional regulatory complex for expression of the cathepsin L gene in rat granulosa cells.

Metallothionein-1 messenger RNA transcription in steroid-secreting cells of the rat ovary during the periovulatory period

An increase in metallothionein 1 (MT-1) mRNA was detected in the ovaries of immature Wistar rats that were primed with s.c. injection of 10 IU eCG followed 48 h later by 10 IU hCG s.c. to initiate the ovulatory process. Ovarian RNA was extracted at 0, 2, 4, 8, 12, 24, 72, 144, and 288 h after the primed animals were injected with hCG. These extracts were used for reverse transcription polymerase chain reaction (RT-PCR) differential display and Northern analyses that yielded complementary gene fragments for MT-1. Expression of MT-1 mRNA increased significantly by 24 h after hCG treatment and reached a peak at 144 h after hCG. In contrast, a disintegrin and metalloproteinase with thrombospondin motifs and a tissue inhibitor of metalloproteinase 1, which were also detected by the RT-PCR differential display procedure, reached a peak at 12 h after hCG and returned to control levels in the ovaries by 72 h after hCG. In situ hybridization indicated that most of the MT-1 mRNA was expressed in the vicinity of the theca interna of preovulatory follicles and in the lutein granulosa of postovulatory follicles. Thus, MT-1 mRNA expression is primarily in the vicinity of steroid-secreting areas of the ovary. The substantial increase in MT-1 mRNA expression might be important in protecting the ovarian tissues from oxidative stress generated by ovarian inflammatory events during the ovulatory process and luteinization.

Egr-1 induction in rat granulosa cells by follicle-stimulating hormone and luteinizing hormone: combinatorial regulation by transcription factors cyclic adenosine 3',5'-monophosphate regulatory element binding protein, serum response factor, sp1, and early growth response factor-1

Early growth response factor (Egr-1) is an inducible zinc finger transcription factor that binds specific GC-rich enhancer elements and impacts female reproduction. These studies document for the first time that FSH rapidly induces Egr-1 expression in granulosa cells of small growing follicles. This response is transient but is reinitiated in preovulatory follicles exposed to the LH analog, human chorionic gonadotropin. Immunohistochemical analysis also showed gonadotropin induced Egr-1 in theca cells. The Egr-1 gene regulatory region responsive to gonadotropin signaling was localized within -164 bp of the transcription initiation site. Binding of Sp1/Sp3 to a proximal GC-box at -64/-46 bp was enhanced by FSH in immature granulosa cells but reduced after human chorionic gonadotropin stimulation of preovulatory follicles despite constant protein expression. This dynamic regulation of Sp1 binding was dependent on gonadotropin-regulated mechanisms that modulate Sp1/3-DNA binding activity. Serum response factor was active in granulosa cells and bound a consensus CArG-box/serum response element site, whereas two putative cAMP response elements within the -164-bp region bound cAMP regulatory element (CRE) binding protein (CREB) and a second cAMP-inducible protein immunologically related to CREB. Transient transfection analyses using Egr-1 promoter-luciferase constructs and site-specific mutations show that the serum response element, GC-box, and CRE-131 are involved in gonadotropin regulation of Egr-1 expression in granulosa cells. Specific kinase inhibitors of Erk or protein kinase A antagonized this induction while exogenously expressed Egr-1 enhanced reporter expression. These observations indicate that the Egr-1 gene is a target of both FSH and LH action that may mediate molecular programs of proliferation and/or differentiation during follicle growth, ovulation, and luteinization.

Transactivation of the progesterone receptor gene in granulosa cells: evidence that Sp1/Sp3 binding sites in the proximal promoter play a key role in luteinizing hormone inducibility

LH induction of the progesterone receptor (PR) in granulosa cells is a central event in ovulation. To identify critical regions of the mouse PR promoter that confer LH inducibility in granulosa cells, a mouse PR promoter (-384/+680) genomic fragment was ligated to a luciferase reporter construct and transfected into primary cultures of granulosa cells. Forskolin/phorbol myristate (PMA) induced PR promoter-luciferase reporter activity in granulosa cells greater than 15-fold. A deletion construct comprised only of the distal promoter alone (-348/+64) was inactive. Conversely, deletion constructs eliminating putative distal promoter-regulatory elements that bind Sp1, nuclear factor Y, and GATA-4 as well as the transcription start site (+1) failed to reduce forskolin/PMA activation of reporter activity. Additional 5'-deletions identified a minimal promoter region (+420/+680) sufficient to bestow cAMP responsiveness approximately 8- to 10-fold. Two GC-rich regions Sp1(A)[+440/+461] and Sp1(B) [+473/+490] bound Sp1/Sp3. Site-directed mutagenesis of Sp1(A) and Sp1(B) reduced activity of the proximal (+357/+680) promoter reporter construct approximately 50% and 99%, respectively. When the same Sp1(B) mutation was introduced into the intact promoter (-145/+680), forskolin/PMA induction of promoter activity was reduced by 70-80%. When the distal GC box as well as the proximal Sp1(B) site were both mutated in the context of the intact promoter, inducibility of the transgene was even more severely reduced. The importance of these Sp1/Sp3 binding regions was confirmed in human MCF-7 cells and Drosophila SL2 cells. Collectively, these results indicate that the Sp1/Sp3 binding sites within the mouse PR proximal promoter are essential for transactivation of the gene by agonists in granulosa cells. The molecular mechanisms by which LH activates Sp1/Sp3 at this region within the PR gene remain unknown but do not involve changes in the binding of Sp1/Sp3 to the critical GC boxes. Rather, Sp1/Sp3 appear to recruit other factors to the promoter.

Ovarian acetylcholine and muscarinic receptors: hints of a novel intrinsic ovarian regulatory system

More than two decades ago, the degrading enzyme of the neurotransmitter acetylcholine (ACH) was reported in nerve fibers of the rat ovary. Subsequently, it was assumed that ACH is a neurotransmitter of ovarian nerves, although the sole presence of the degrading enzyme, ACH-esterase, does not allow such a conclusion. That ACH may be involved in the complex regulation of ovarian functions, including hormone production, was indicated by studies using, for example, granulosa cells (GCs). The lack of detailed information about both source(s) and functions of ACH in the ovary prompted us to examine sites of ovarian ACH-synthesis and ACH-receptor-bearing target cells. We also started to identify functions of ACH in cultured human GCs. While ovarian innervation and recently described neuron-like cells of the ovary were not immunoreactive for the ACH-synthesizing enzyme, choline-acetyl transferase (CHAT), we found immunoreactivity in GCs of rodents and primates. Isolated human and rat GCs produced ACH and contained the vesicular ACH transporter (VACHT). These results indicate that endocrine GCs are an unexpected non-neuronal source of ACH in the ovary. Moreover, these cells and GCs in vivo contain ACH-receptors of the muscarinic subtype (MR), namely M1R and M5R. In contrast, oocytes express M3R. MR of human GCs are functional and cholinergic stimulation is linked to rapid increases in intracellular Ca(++) levels. M1/5R activation also led to increased cell proliferation of human GCs in vitro and this stimulatory effect was found to be associated with rapid disruption of gap junction communication. Ongoing studies begin to identify regulation of ion channels and altered gene expression as consequences of MR stimulation. Thus, our results outline first details of an unexpected intraovarian, non-neuronal cholinergic system, and suggest that it may be involved in the regulation of cell proliferation in the ovary.

Temporal and spatial patterns of ovarian gene transcription following an ovulatory dose of gonadotropin in the rat

In recent years, there have been a number of efforts to identify genes that are expressed in mature ovarian follicles in response to an ovulatory dose of LH or its homologue hCG. This review keys on 20 ovulation-specific genes that we have identified by the molecular procedure known as differential display. The objective is to use this sampling of genes to illustrate the diversity in the temporal and spatial patterns of expression of genes in the ovary following the stimulus of this gonadal target tissue by a single glycoprotein hormone. The specific genes that are surveyed include 5-aminolevulinate synthase; early growth response protein-1; gamma-glutamylcysteine synthetase; cyclooxygenase-2; epiregulin; pituitary adenylate cyclase-activating polypeptide; tumor necrosis factor-stimulated gene-6; regulator of G-protein signaling protein-2; adrenodoxin; steroidogenic acute regulatory protein; 3alpha-hydroxysteroid dehydrogenase; CD63, a disintegrin and metalloproteinase with thrombospondin motifs; tissue inhibitor of metalloproteinase-1; carbonyl reductase, a G-protein-coupled receptor; pancreatitis-associated protein-III; glutathione S-transferase; and metallothionein-1. The ovulatory expression of these different genes is predominantly within the granulosa layer of mature follicles. However, there were also instances of expression in the thecal and stromal tissue of the ovary, as well as in vascular endothelial cells and in luteal tissue. The overwhelming impression is that the molecular events of ovulation are far more complex, and therefore more highly ordered, than originally imagined.

Early growth response gene-1 regulates the expression of the rat luteinizing hormone receptor gene

LH receptor gene expression is primarily regulated via specific interactions of trans-acting proteins and cis-acting DNA sequences in the upstream region of the gene. In this study, we report, using luciferase assays, that the region between -171 and -137 base pairs (bp) is essential for basal expression of the rat LH receptor gene. To identify factors that interact with the region between -171 and -137 bp and regulate expression of the gene, a rat granulosa cell cDNA library was screened using a yeast one-hybrid system. A positive clone, isolated by the screening, encodes a transcription factor early growth response gene-1 (Egr-1). To determine the sequence to which Egr-1 protein binds, electrophoretic mobility shift assay (EMSA) was employed. The Egr-1 protein was produced by an in vitro transcription/translation system using a full-length rat Egr-1 cDNA. The upstream region between -171 and -137 bp contains 2 overlapping Egr-1 consensus sequences. The EMSA revealed that Egr-1 binds independently to both sites. The overexpression of Egr-1 in MA-10 cells caused an approximately 2-fold increase in reporter luciferase activity. However, no induction of the luciferase activity was observed when luciferase constructs that lacked or had mutations in either or both of the Egr-1 sites were used, indicating that Egr-1 positively regulates LH receptor gene expression. In differentiated granulosa cells that had been pretreated with FSH for 48 h, the levels of both mRNA and Egr-1 protein were induced by hCG or cAMP, reaching maximal levels approximately 1.5 h after treatment and then returning to basal levels 8 h thereafter. No Egr-1 mRNA or protein was detected in undifferentiated granulosa cells, even after stimulation with 8-bromoadenosine-cAMP. These results suggest that Egr-1 functions only in luteinized granulosa cells after stimulation with hCG or cAMP. In conclusion, the findings demonstrate that Egr-1 actually binds to the regulatory upstream region of the LH receptor gene and positively regulates receptor gene expression. In addition, Egr-1 expression was observed only in luteinized granulosa cells after stimulation with hCG or cAMP. The present study provides further support to the hypothesis that Egr-1 plays important roles in the pituitary-gonadal axis.

3alpha-hydroxysteroid dehydrogenase messenger RNA transcription in the immature rat ovary in response to an ovulatory dose of gonadotropin

The ovulatory process in mammals involves a substantial increase in the metabolism of steroids and eicosanoids in response to a surge in LH or to an injection of hCG into experimental animals. This study provides evidence that the ovulatory stimulus causes induction of the gene for 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), an enzyme that belongs to several oxidoreductase superfamilies that affect steroid and eicosanoid metabolism. Immature Wistar rats were primed with 10 IU eCG s.c., and 48 h later the 12-h ovulatory process was initiated by 10 IU hCG s.c. Ovarian RNA was extracted at 0, 2, 4, 8, 12, and 24 h after injecting the animals with hCG. The RNA extracts were used for reverse transcription-polymerase chain reaction (PCR) differential display to detect gene expression in the stimulated ovarian tissue. One of the PCR primer sets differentially amplified a cDNA fragment that is 52.3% homologous with a 3alpha-HSD gene in rat liver. Northern analyses revealed that maximum transcription was at 8 h after the animals had been treated with hCG. The Northerns also indicated that the 3alpha-HSD cDNA probe cross-hybridized with as many as six different bands of mRNA on the blots. In situ hybridization localized 3alpha-HSD mRNA in the granulosa and thecal layers of mature follicles and in newly formed corpora lutea at 24 h after the ovulatory stimulus. In conclusion, gene(s) for 3alpha-HSD are transcribed in ovarian follicles in response to an ovulatory dose of gonadotropin. A possible function of the oxidoreductase enzyme that is translated from the 3alpha-HSD mRNA may be to reduce the toxic aldehyde and ketone components of the steroids and eicosanoids that accumulate in the mammalian ovary at the time of ovulation.

Gonadotropin regulation of NGFI-B messenger ribonucleic acid expression during ovarian follicle development in the rat

NGFI-B is an immediate-early gene that encodes an orphan nuclear receptor. The present study was designed to examine the localization and gonadotropin regulation of NGFI-B expression in the rat ovary. Northern blot analysis of ovaries obtained from prepubertal rats revealed the increased expression of NGFI-B during prepubertal development. Treatment of immature rats with PMSG, however, decreased ovarian NGFI-B expression. The major cell types expressing NGFI-B messenger RNA were thecal cells of follicles in different sizes. In contrast, treatment of PMSG-primed rats with human (h) CG resulted in the rapid and transient stimulation of ovarian NGFI-B messenger RNA, reaching a peak within 1 h. In situ hybridization analysis revealed that hCG treatment induced the expression of NGFI-B in granulosa cells of preovulatory follicles. Treatment of cultured preovulatory follicles in vitro with LH further confirmed the time- and dose-dependent stimulation of NGFI-B messenger RNA and protein. LH-stimulated NGFI-B expression in preovulatory follicles was abolished by alpha-amanitin, but was superinduced by cycloheximide. Furthermore, treatment of adult cycling rats with pentobarbital abolished NGFI-B expression on proestrus, and exogenous administration of hCG restored it, indicating the role of the preovulatory surge of LH in the stimulation of NGFI-B expression. These results demonstrate the cell type-specific expression and gonadotropin induction of NGFI-B in granulosa cells of preovulatory follicles and suggest a role for NGFI-B in the ovulatory process.

DNA array analysis of changes in preovulatory gene expression in the rat ovary

During the periovulatory period, the mammalian ovary is the site of dramatic functional and structural changes, leading to oocyte maturation, follicle rupture, and corpus luteum formation. To a large extent, these processes result from changes in the transcriptome of various ovarian cell types. To develop a broader view of periovulatory changes in gene expression in the ovary and to identify further genes involved in periovulatory events, we used the recently developed DNA array technology. Immature female eCG-primed rats were killed either immediately before or 6 h after ovulation induction with hCG. Total ovarian RNA was isolated and used to prepare radiolabeled cDNA probes, which were hybridized to DNA arrays representing approximately 600 rat genes. Quantitative analysis identified a multitude of regulated gene messages, including several genes involved in extracellular matrix degradation and lipid/steroid metabolism previously reported to be induced by hCG. This screening also identified a group of candidate genes whose ovarian expression and gonadotropin regulation was hitherto unknown. The induction of three of these genes, encoding cutaneous fatty acid-binding protein, the interleukin-4 receptor alpha chain, and prepronociceptin, was confirmed and further characterized by Northern blot analysis. In addition, in situ hybridization analysis showed that hCG administration resulted in exclusive or predominant expression of all three genes in theca cells. These results demonstrate that DNA arrays can be used to identify genes regulated during the periovulatory period, thus contributing to a more detailed understanding of the molecular mechanisms of ovulation.