Gene expression profiling of bovine preovulatory follicles: gonadotropin surge and prostanoid-dependent up-regulation of genes potentially linked to the ovulatory process

Copy number variants in genomes of local sheep breeds from Russia

Copy number variants (CNVs) are genomic structural variations that contribute to many adaptive and economically important traits in livestock. In this study, we detected CNVs in 354 animals from 16 Russian indigenous sheep breeds and analysed their possible functional roles. Our analysis of the entire sample set resulted in 4527 CNVs forming 1450 CNV regions (CNVRs). When constructing CNVRs for individual breeds, a total of 2715 regions ranging from 88 in Groznensk to 337 in Osetin breeds were identified. To make interbreed CNVR frequency comparison possible, we also identified core CNVRs using CNVs with overlapping chromosomal locations found in different breeds. This resulted in 137 interbreed CNVRs with frequency >15% in at least one breed. Functional enrichment analysis of genes affected by CNVRs in individual breeds revealed 12 breeds with significant enrichments in olfactory perception, PRAME family proteins, and immune response. Function of genes affected by interbreed and breed-specific CNVRs revealed candidates related to domestication, adaptation to high altitudes and cold climates, reproduction, parasite resistance, milk and meat qualities, wool traits, fat storage, and fat metabolism. Our work is the first attempt to uncover and characterise the CNV makeup of Russian indigenous sheep breeds. Further experimental and functional validation of CNVRs would help in developing new and improving existing sheep breeds.

An increase of phosphatidylcholines in follicular fluid implies attenuation of embryo quality on day 3 post-fertilization

Background

Although oocyte quality is the dominant factor determining embryo quality, few studies have been conducted to evaluate embryo quality based on the metabolites related to the oocyte. With quantification of the follicular fluid (FF) metabolites, in assisted reproductive technology (ART), this study sought to evaluate the embryo or oocyte quality through an informative approach.

Results

An evaluation model consisting of 17 features was generated to distinguish the embryo quality on day 3 post-fertilization, and phosphatidylcholines (PCs) were the key contributors to the evaluation. The model was extended to the patients under different ages and hyperstimulations, and the features were further enriched to facilitate the evaluation of the embryo quality. The metabolites were clustered through pathway analysis, leading to a hypothesis that accumulation of arachidonic acid induced by PCs might weaken embryo quality on day 3 post-fertilization.

Conclusions

A discriminating model with metabolic features elicited from follicular fluid was established, which enabled the evaluation of the embryo or oocyte quality even under certain clinical conditions, and the increase of PCs in follicular fluid implies the attenuation of embryo quality on day 3 post-fertilization.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01118-w.

Ankyrin-repeat and SOCS box-containing protein 9 (ASB9) regulates ovarian granulosa cells function and MAPK signaling

Ankyrin-repeat and SOCS box-containing proteins (ASB) interact with the elongin B-C adapter via their SOCS box domain and with the cullin and ring box proteins to form E3 ubiquitin ligase complexes within the protein ubiquitination pathway. ASB9 in particular is a differentially expressed gene in ovulatory follicles (OFs) induced by the luteinizing hormone (LH) surge or hCG injection in ovarian granulosa cells (GC) while downregulated in growing dominant follicles. Although ASB9 has been involved in biological processes such as protein modification, the signaling network associated with ASB9 in GC is yet to be fully defined. We previously identified and reported ASB9 interactions and binding partners in GC including PAR1, TAOK1, and TNFAIP6/TSG6. Here, we further investigate ASB9 effects on target binding partners regulation and signaling in GC. CRISPR/Cas9-induced inhibition of ASB9 revealed that ASB9 regulates PAR1, TAOK1, TNFAIP6 as well as genes associated with proliferation and cell cycle progression such as PCNA, CCND2, and CCNE2 while CCNA2 was not affected. Inhibition of ASB9 was also associated with increased GC number and decreased caspase3/7 activity, CASP3 expression, and BAX/BCL2 ratio. Furthermore, ASB9 induction in OF in vivo 24 h post-hCG is concomitant with a significant decrease in phosphorylation levels of MAPK3/1 while pMAPK3/1 levels increased following ASB9 inhibition in GC in vitro. Together, these results provide strong evidence for ASB9 as a regulator of GC activity and function by modulating MAPK signaling likely through specific binding partners such as PAR1, therefore controlling GC proliferation and contributing to GC differentiation into luteal cells.

Exogenous insulin-like growth factor 1 accelerates growth and maturation of follicles in human cortical xenografts and increases ovarian output in mice

OBJECTIVE

To measure the influence of exogenous insulin-like growth factor 1 (IGF1) on follicle growth and maturation in human ovarian cortical xenografts.

DESIGN

Xenotransplantation model.

SETTING

University-based research laboratory.

PATIENTS/ANIMALS

Ovarian tissue was donated with consent and institutional review board approval by brain-dead organ donors or patients undergoing ovarian tissue cryopreservation for fertility preservation. Cortical fragments were transplanted into immunocompromised mice.

INTERVENTIONS

Cryopreserved ovarian cortical fragments from four women (aged 19, 25, 33, and 46 years) were transplanted into the gluteus muscle of immunocompromised mice in a fibrin matrix containing endothelial cells that were transduced with lentiviral particles encoding secreted IGF1. Xenografts were recovered after 3, 8, and 14 weeks. In addition, C57/Bl6 mice underwent intraovarian injection of saline or recombinant IGF1 (60 μg), followed by superovulation, analysis of ethynyl-deoxyuridine incorporation, and ribonucleic acid sequencing of the whole ovaries.

MAIN OUTCOME MEASURES

For xenografts: follicle count and distribution; antral follicle count; and corpora lutea/albicans count. For mice: follicle count and distribution; oocyte yield, ethynyl-deoxyuridine incorporation (granulosa cell proliferation); and ovarian transcriptomic signature.

RESULTS

At 3 weeks, xenografts in the IGF1 condition revealed a decreased percentage of primary follicles and increased percentage of secondary follicles that were concentrated in the preantral subtype; at 8 weeks, an increase in secondary follicles was concentrated in the simple subtype; after 14 weeks, primordial follicles were reduced, and while the number of advanced follicles did not power the experiment to demonstrate significance, antral follicles reduced and corpora lutea increased. Supporting experiments in mice revealed an increase in normal oocytes following intraovarian injection of recombinant IGF1 (60 μg) as well as increased proliferative index among follicles of secondary and preantral stages. Ribonucleic acid sequencing analysis of the whole ovaries following injection of recombinant IGF1 (25 μg) revealed an acute (24 hours) upregulation of transcripts related to steroidogenesis and luteinization.

CONCLUSIONS

Exogenous IGF1 advances the pace of growth among primordial, primary, and secondary stage follicles but results in near absence of antral stage follicles in long-term (14 weeks) xenografts. In mice, acute administration of IGF1 promotes follicle advance and increased oocyte yield. The results suggest that while superphysiological IGF1 alone advances the pace of growth among early/preantral follicles, a sustained and/or later-stage influence undermines antral follicle growth/survival or promotes premature luteinization. These findings provide a temporal framework for interpreting follicle growth/mobilization and may be useful in understanding the clinical application of human growth hormone in the context of assisted reproduction.

Hypothalamic Astrocyte Development and Physiology for Neuroprogesterone Induction of the Luteinizing Hormone Surge

Neural circuits in female rats sequentially exposed to estradiol and progesterone underlie so-called estrogen positive feedback that induce the surge release of pituitary luteinizing hormone (LH) leading to ovulation and luteinization of the corpus hemorrhagicum. It is now well-established that gonadotropin releasing hormone (GnRH) neurons express neither the reproductively critical estrogen receptor-α (ERα) nor classical progesterone receptor (PGR). Estradiol from developing ovarian follicles acts on ERα-expressing kisspeptin neurons in the rostral periventricular region of the third ventricle (RP3V) to induce PGR expression, and kisspeptin release. Circulating estradiol levels that induce positive feedback also induce neuroprogesterone (neuroP) synthesis in hypothalamic astrocytes. This local neuroP acts on kisspeptin neurons that express PGR to augment kisspeptin expression and release needed to stimulate GnRH release, triggering the LH surge. In vitro and in vivo studies demonstrate that neuroP signaling in kisspeptin neurons occurs through membrane PGR activation of Src family kinase (Src). This signaling cascade has been also implicated in PGR signaling in the arcuate nucleus of the hypothalamus, suggesting that Src may be a common mode of membrane PGR signaling. Sexual maturation requires that signaling between neuroP synthesizing astrocytes, kisspeptin and GnRH neurons be established. Prior to puberty, estradiol does not facilitate the synthesis of neuroP in hypothalamic astrocytes. During pubertal development, levels of membrane ERα increase in astrocytes coincident with an increase of PKA phosphorylation needed for neuroP synthesis. Currently, it is not clear whether these developmental changes occur in existing astrocytes or are due to a new population of astrocytes born during puberty. However, strong evidence suggests that it is the former. Blocking new cell addition during puberty attenuates the LH surge. Together these results demonstrate the importance of pubertal maturation involving hypothalamic astrocytes, estradiol-induced neuroP synthesis and membrane-initiated progesterone signaling for the CNS control of ovulation and reproduction.

Induction of cystic ovarian follicles (COFs) in cattle by using an intrafollicular injection of indomethacin

The aim of this study was to establish a model to induce cystic ovarian follicles (COFs) in cattle using the cyclooxygenase inhibitor, indomethacin. Eighteen Holstein-Frisian cattle were synchronized with prostaglandin F2alpha (PGF2α) and gonadotropin-releasing hormone (GnRH). Ultrasound-guided transvaginal intrafollicular injections were performed in 23 preovulatory follicles with different concentrations of indomethacin 16 h after GnRH administration. An injection of 0.2 ml 35 µM indomethacin solution (resulting in a final concentration of 8 µg/ml in the follicular fluid) was the minimal dosage leading to COF formation. The induced COFs reached a maximum mean diameter of 36.9 ± 4.5 mm eleven days after injection. The estrous cycle was extended to 25-39 days. Luteinization was first observed 4 days after injection, accompanied by a slight increase in plasma progesterone concentration. The bioactivity of indomethacin was demonstrated by the decrease of prostaglandin E2 in the follicular fluid of three animals. The method presented here is minimally invasive and allows for the generation of defined COFs for further investigations.

Contribution of the immune system to follicle differentiation, ovulation and early corpus luteum formation

Much of what we know about the involvement of the immune system in periovulatory follicle differentiation, ovulation and subsequent formation of the corpus luteum in cattle is drawn from the findings of studies in several mammalian livestock species. By integrating published histological data from cattle, sheep and pigs and referring back to the more comprehensive knowledge bank that exists for mouse and humans we can sketch out the key cells of the immune system and the cytokines and growth factors that they produce that are involved in follicle differentiation and luteinization, ovulation and early follicle development. These contributions are reviewed and the key findings, discussed.

Selection signatures in candidate genes and QTL for reproductive traits in Nellore heifers

The identification of selection signature genes may help to detect genomic regions that underwent artificial selection and contributed to phenotypic diversity. The aim of this study, therefore, was to detect selection signatures in candidate genes and quantitative trait locus (QTL) for reproductive traits in a Nellore population being selected for sexual precocity. A total of 2035 Nellore heifers, sourced from breeding programs focused on sexual precocity, were used. Candidate genes and some specific QTL related to reproductive traits were chosen based on published literature and Animal QTL databases, respectively, for investigation whether these regions were affected by selection. Selection signature DNA sequences were detected in the selected regions using the extended haplotype homozygosity (EHH) and relative extended haplotype homozygosity (REHH) methods. From 22,241 single nucleotide polymorphisms (SNPs) located in the candidate genes and QTL, 17,312 SNPs generated 2756 haplotype blocks. A total of 7518 EHH tests were analyzed using haplotypes with a frequency of more than 25%, for which there were 39 tests that were significant for REHH (P<0.01). Selection signature DNA sequences were detected that contained several QTLs for important reproductive traits in cattle, suggesting that reproductive traits may have been affected by selection for sexual precocity in this population. Forty-six genes were located in the selection signature regions, whereas 24 genes participated in important biological processes or pathways that may underlie sexual precocity. These results indicate there are possible molecular mechanisms related to sexual precocity in the Nellore breed.

Genotype-by-environment interaction of fertility traits in Danish Holstein cattle using a single-step genomic reaction norm model

Genotype-by-environment (G × E) interactions could play an important role in cattle populations, and it should be considered in breeding programmes to select the best sires for different environments. The objectives of this study were to study G × E interactions for female fertility traits in the Danish Holstein dairy cattle population using a reaction norm model (RNM), and to detect the particular genomic regions contributing to the performance of these traits and the G × E interactions. In total 4534 bulls were genotyped by an Illumina BovineSNP50 BeadChip. An RNM with a pedigree-based relationship matrix and a pedigree-genomic combined relationship matrix was used to explore the existence of G × E interactions. In the RNM, the environmental gradient (EG) was defined as herd effect. Further, the genomic regions affecting interval from calving to first insemination (ICF) and interval from first to last insemination (IFL) were detected using single-step genome-wide association study (ssGWAS). The genetic correlations between extreme EGs indicated that G × E interactions were sizable for ICF and IFL. The genomic RNM (pedigree-genomic combined relationship matrix) had higher prediction accuracy than the conventional RNM (pedigree-based relationship matrix). The top genomic regions affecting the slope of the reaction norm included immunity-related genes (IL17, IL17F and LIF), and growth-related genes (MC4R and LEP), while the top regions influencing the intercept of the reaction norm included fertility-related genes such as EREG, AREG and SMAD4. In conclusion, our findings validated the G × E interactions for fertility traits across different herds and were helpful in understanding the genetic background of G × E interactions for these traits.

The cAMP-EPAC Pathway Mediates PGE2-Induced FGF2 in Bovine Granulosa Cells

During the periovulatory period, the profile of fibroblast growth factor 2 (FGF2) coincides with elevated prostaglandin E2 (PGE2) levels. We investigated whether PGE2 can directly stimulate FGF2 production in bovine granulosa cells and, if so, which prostaglandin E2 receptor (PTGER) type and signaling cascades are involved. PGE2 temporally stimulated FGF2. Accordingly, endoperoxide-synthase2-silenced cells, exhibiting low endogenous PGE2 levels, had reduced FGF2. Furthermore, elevation of viable granulosa cell numbers by PGE2 was abolished with FGF2 receptor 1 inhibitor, suggesting that FGF2 mediates this action of PGE2. Epiregulin (EREG), a known PGE2-inducible gene, was studied alongside FGF2. PTGER2 agonist elevated cAMP as well as FGF2 and EREG levels. However, a marked difference between cAMP-induced downstream signaling was observed for FGF2 and EREG. Whereas FGF2 upregulated by PGE2, PTGER2 agonist, or forskolin was unaffected by the protein kinase A (PKA) inhibitor H89, EREG was significantly inhibited. FGF2 was dose-dependently stimulated by the exchange protein directly activated by cAMP (EPAC) activator; a similar induction was observed for EREG. However, forskolin-stimulated FGF2, but not EREG, was inhibited in EPAC1-silenced cells. These findings ascribe a novel autocrine role for PGE2, namely, elevating FGF2 production in granulosa cells. This study also reveals that cAMP-activated EPAC1, rather than PKA, mediates the effect of PGE2/PTGER2 on the expression of FGF2. Stimulation of EREG by PGE2 is also mediated by PTGER2 but, in contrast to FGF2, EREG was found to be PKA sensitive. PGE2-stimulated FGF2 can act to maintain granulosa cell survival; it can also act on ovarian endothelial cells to promote angiogenesis.

Luteinizing hormone upregulates NPPC and downregulates NPR3 mRNA abundance in bovine granulosa cells through activation of the EGF receptor

During folliculogenesis, the luteinizing hormone (LH) surge triggers dynamic events in granulosa cells that culminate with ovulation. The aim of this study was to evaluate if the epidermal growth factor receptor (EGFR) is required for ovulation in cattle, and if it regulates the expression of the natriuretic peptide (NP) system in granulosa cells after gonadotropin-releasing hormone (GnRH)/LH stimulation. It was observed that GnRH induces amphiregulin (AREG) and epiregulin (EREG) mRNA at 3 and 6 h after in vivo treatment, but the expression of these genes was not regulated by atrial (ANP) and C-type (CNP) NPs in granulosa cells cultured in vitro. The abundance of mRNA encoding the NP receptors (NPR1, 2 and 3) was not altered by LH supplementation and/or EGFR inhibition (AG1478; AG) in granulosa cells after 6 h of in vitro culture. However, in the same conditions, mRNA encoding the natriuretic peptide precursor C (NPPC) was upregulated by LH, whereas AG (0.5 and 5 μM) inhibited the LH effect. In order to confirm those results, 5 μM AG or saline were intrafollicularly injected in preovulatory follicles and cows were simultaneously treated with GnRH intramuscularly. Granulosa cells harvested at 6 h after GnRH injection revealed higher NPR3 and lower NPPC mRNA levels in AG-treated, compared to control cows. However, intrafollicular injection of AG did not inhibit GnRH-induced ovulation. In granulosa cells cultured in vitro, ANP associated with LH increased prostaglandin-endoperoxide synthase 2 (PTGS2) mRNA abundance. In conclusion, we inferred that LH modulated NPPC and NPR3 mRNA abundance through EGFR in bovine granulosa cells, but ovulation in cattle did not seem to depend on EGFR activation.

Gene expression profiling of upregulated mRNAs in granulosa cells of bovine ovulatory follicles following stimulation with hCG

BACKGROUND

Ovulation and luteinization of follicles are complex biological processes initiated by the preovulatory luteinizing hormone surge. The objective of this study was to identify genes that are differentially expressed in bovine granulosa cells (GC) of ovulatory follicles.

METHODS

Granulosa cells were collected during the first follicular wave of the bovine estrous cycle from dominant follicles (DF) and from ovulatory follicles (OF) obtained 24 h following injection of human chorionic gonadotropin (hCG). A granulosa cell subtracted cDNA library (OF-DF) was generated using suppression subtractive hybridization and screened.

RESULTS

Detection of genes known to be upregulated in bovine GC during ovulation, such as ADAMTS1, CAV1, EGR1, MMP1, PLAT, PLA2G4A, PTGES, PTGS2, RGS2, TIMP1, TNFAIP6 and VNN2 validated the physiological model and analytical techniques used. For a subset of genes that were identified for the first time, gene expression profiles were further compared by semiquantitative RT-PCR in follicles obtained at different developmental stages. Results confirmed an induction or upregulation of the respective mRNAs in GC of OF 24 h after hCG-injection compared with those of DF for the following genes: ADAMTS9, ARAF, CAPN2, CRISPLD2, FKBP5, GFPT2, KIT, KITLG, L3MBLT3, MRO, NUDT10, NUDT11, P4HA3, POSTN, PSAP, RBP1, SAT1, SDC4, TIMP2, TNC and USP53. In bovine GC, CRISPLD2 and POSTN mRNA were found as full-length transcript whereas L3MBLT3 mRNA was alternatively spliced resulting in a truncated protein missing the carboxy-terminal end amino acids, ⁷⁷⁴KNSHNEL⁷⁸⁰. Conversely, L3MBLT3 is expressed as a full-length mRNA in a bovine endometrial cell line. The ⁷⁷⁴KNSHNEL⁷⁸⁰ sequence is well conserved in all mammalian species and follows a SAM domain known to confer protein/protein interactions, which suggest a key function for these amino acids in the epigenetic control of gene expression.

CONCLUSIONS

We conclude that we have identified novel genes that are upregulated by hCG in bovine GC of OF, thereby providing novel insight into peri-ovulatory regulation of genes that contribute to ovulation and/or luteinization processes.

Bovine ovarian follicular growth and development correlate with lysophosphatidic acid expression

The basis of successful reproduction is proper ovarian follicular growth and development. In addition to prostaglandins and vascular endothelial growth factor, a number of novel factors are suggested as important regulators of follicular growth and development: PGES, TFG, CD36, RABGAP1, DBI and BTC. This study focuses on examining the expression of these factors in granulosa and thecal cells that originate from different ovarian follicle types and their link with the expression of lysophosphatidic acid (LPA), known local regulator of reproductive functions in the cow. Ovarian follicles were divided into healthy, transitional, and atretic categories. The mRNA expression levels for PGES, TFG, CD36, RABGAP1, DBI and BTC in granulosa and thecal cells in different follicle types were measured by real-time PCR. The correlations among expression of enzymes synthesizing LPA (autotaxin, phospholipase A2), receptors for LPA and examined factors were measured. Immunolocalization of PGES, TFG, CD36, RABGAP1, DBI and BTC was examined by immunohistochemistry. We investigated follicle-type dependent mRNA expression of factors potentially involved in ovarian follicular growth and development, both in granulosa and thecal cells of bovine ovarian follicles. Strong correlations among receptors for LPA, enzymes synthesizing LPA, and the examined factors in healthy and transitional follicles were observed, with its strongest interconnection with TFG, DBI and RABGAP1 in granulosa cells, and TFG in thecal cells; whereas no correlations in atretic follicles were detected. A greater number of correlations were found in thecal cells than in granulosa cells as well as in healthy follicles than in transitional follicles. These data indicate the role of LPA in the growth, development and physiology of the bovine ovarian follicle.

Potential role of polyunsaturated fatty acids, with particular regard to the signaling pathways of arachidonic acid and its derivatives in the process of maturation of the oocytes: Contemporary review

Oocyte meiotic maturation is one of the significant physiological requirements for ovulation and fertility. It is believed that Cyclic Adenosine Monophosphate, protein kinase A and protein kinase C pathways along with eicosanoids, particularly prostaglandin E_2, and steroids are the key factors regulating mammalian oocyte maturation. The aim of the current study was to highlight the molecular events triggered by arachidonic acid during oocyte meiotic arrest and resumption at the time of gonadotrophin surge. It should be noted that arachidonic acid release is tightly regulated by Follicle-stimulating and Luteinizing hormones during oocyte development.

Progesterone receptor and prostaglandins mediate luteinizing hormone-induced changes in messenger RNAs for ADAMTS proteases in theca cells of bovine periovulatory follicles

Little is known about the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family of extracellular proteases in ovarian follicles of non-rodent species, particularly in theca cells. In the present study, temporal changes in the abundance of mRNA encoding four ADAMTS subtypes and hormonal regulation of mRNA encoding two subtypes were investigated in theca interna cells during the periovulatory period in cattle. Gonadotropin-releasing hormone (GnRH) was injected into animals to induce a luteinizing hormone (LH)/follicle-stimulating hormone (FSH) surge, and follicles were obtained at 0 hr post-GnRH (preovulatory) or at 6, 12, 18, or 24 hr (periovulatory). ADAMTS1, -2, -7, and -9 transcript abundance was then determined in the isolated theca interna. ADAMTS1 and -9 mRNA levels were up-regulated at 24 hr post-GnRH, whereas ADAMTS2 mRNA was higher at 12-24 hr post-GnRH and ADAMTS7 mRNA increased transiently at 12 hr post-GnRH compared to other time points. Subsequent in vitro experiments using preovulatory theca interna (0 hr post-GnRH) showed that application of LH in vitro can mimic the effects of the gonadotropin surge on mRNAs encoding ADAMTS1 and -9 and that progesterone/progesterone receptor and/or prostaglandins may regulate the levels of mRNA encoding ADAMTS1 and -9 in theca interna, downstream of the LH surge. Time- and subtype-specific changes in ADAMTS mRNA abundance in vivo, and their regulation in vitro by hormones, indicate that ADAMTS family members produced by theca cells may play important roles in follicle rupture and the accompanying tissue remodeling in cattle. Mol. Reprod. Dev. 84: 55-66, 2017. © 2016 Wiley Periodicals, Inc.

Gene expression profiling of bovine ovarian follicular and luteal cells provides insight into cellular identities and functions

After ovulation, somatic cells of the ovarian follicle (theca and granulosa cells) become the small and large luteal cells of the corpus luteum. Aside from known cell type-specific receptors and steroidogenic enzymes, little is known about the differences in the gene expression profiles of these four cell types. Analysis of the RNA present in each bovine cell type using Affymetrix microarrays yielded new cell-specific genetic markers, functional insight into the behavior of each cell type via Gene Ontology Annotations and Ingenuity Pathway Analysis, and evidence of small and large luteal cell lineages using Principle Component Analysis. Enriched expression of select genes for each cell type was validated by qPCR. This expression analysis offers insight into cell-specific behaviors and the differentiation process that transforms somatic follicular cells into luteal cells.

Studies on lysophosphatidic acid action during in vitro preimplantation embryo development

Assisted reproductive technologies, including in vitro embryo production (IVP), have been successfully used in animal reproduction to optimize breeding strategies for improved production and health in animal husbandry. Despite the progress in IVP techniques over the years, further improvements in in vitro embryo culture systems are required for the enhancement of oocyte and embryo developmental competence. One of the most important issues associated with IVP procedures is the optimization of the in vitro culture of oocytes and embryos. Studies in different species of animals and in humans have identified important roles for receptor-mediated lysophosphatidic acid (LPA) signaling in multiple aspects of human and animal reproductive tract function. The data on LPA signaling in the ovary and uterus suggest that LPA can directly contribute to embryo-maternal interactions via its influence on early embryo development beginning from the influence of the ovarian environment on the oocyte to the influence of the uterine environment on the preimplantation embryo. This review discusses the current status of LPA as a potential supplement in oocyte maturation, fertilization, and embryo culture media and current views on the potential involvement of the LPA signaling pathway in early embryo development.

Molecular characterization of a disintegrin and metalloprotease-17 (ADAM17) in granulosa cells of bovine preovulatory follicles

A disintegrin and metalloprotease-17 (ADAM17) is thought to play a key role in the release of soluble and active epiregulin (EREG) and amphiregulin (AREG) in ovarian follicles but its transcriptional regulation in follicular cells remains largely unknown. The objectives of this study were to characterize the regulation of ADAM17 transcripts in bovine follicles prior to ovulation and to investigate its transcriptional control in bovine granulosa cells. To study the regulation of ADAM17 transcripts, RT-PCR analyses were performed using total RNA extracted from bovine follicles collected between 0 h and 24 h post-hCG. Results showed that levels of ADAM17 mRNA were low prior to hCG (0 h), markedly and transiently increased 6-12 h post-hCG (P <0.05), and returned to low baseline levels at 24 h post-hCG in granulosa and theca interna cells of preovulatory follicles. To determine the transcriptional control of ADAM17 expression, primary cultures of bovine granulosa cells were used. Forskolin (FSK) stimulation induced a pattern of ADAM17 mRNA up-regulation in vitro similar to that observed by hCG in vivo. 5'-Deletion mutagenesis studies identified a minimal region of the bovine ADAM17 promoter containing basal and FSK-inducible activities, which were dependent on the presence of a consensus AP1 cis-element. Electrophoretic mobility shift assays revealed an interaction between AP1 and the trans-acting factor Fra2. Chromatin immunoprecipitation assays confirmed an endogenous interaction between Fra2 and the ADAM17 promoter in granulosa cell cultures. FSK-inducible ADAM17 promoter activity and mRNA expression were suppressed by PKA and ERK1/2 inhibitors but not by a p38MAPK inhibitor, pointing to the importance of PKA and ERK1/2 signaling pathways in the up-regulation of bovine ADAM17 mRNA. Collectively, these findings describe the gonadotropin/FSK-dependent up-regulation of ADAM17 transcripts in bovine preovulatory follicles and unravel for the first time some of the molecular mechanisms involved in ADAM17 gene expression in granulosa cells of a monoovulatory species.

The effect of lysophosphatidic acid during in vitro maturation of bovine cumulus-oocyte complexes: cumulus expansion, glucose metabolism and expression of genes involved in the ovulatory cascade, oocyte and blastocyst competence

BACKGROUND

In the cow, lysophosphatidic acid (LPA) acts as an auto-/paracrine factor, through its receptors LPAR1-4, on oocytes and cumulus cells during in vitro maturation (IVM). The aim of the present work was to determine the effect of LPA during IVM of bovine oocytes on: 1) oocyte maturation; 2) apoptosis of COCs; 3) expression of genes involved in developmental competence and apoptosis in bovine oocytes and subsequent blastocysts; 4) cumulus expansion and expression of genes involved in the ovulatory cascade in cumulus cells; 5) glucose metabolism and expression of genes involved in glucose utilization in cumulus cells; 6) cleavage and blastocyst rates on Day 2 and Day 7 of in vitro culture, respectively.

METHODS

Cumulus-oocyte complexes (COCs) were matured in vitro in the presence or absence of LPA (10(-5) M) for 24 h. Following maturation, we determined: oocyte maturation stage, cumulus expansion, COCs apoptosis and glucose and lactate levels in the maturation medium. Moreover, COCs were either used for gene expression analysis or fertilized in vitro. The embryos were cultured until Day 7 to assess cleavage and blastocyst rates. Oocytes, cumulus cells and blastocysts were used for gene expression analysis.

RESULTS

Supplementation of the maturation medium with LPA enhanced oocyte maturation rates and stimulated the expression of developmental competence-related factors (OCT4, SOX2, IGF2R) in oocytes and subsequent blastocysts. Moreover, LPA reduced the occurrence of apoptosis in COCs and promoted an antiapoptotic balance in the transcription of genes involved in apoptosis (BAX and BCL2) either in oocytes or blastocysts. LPA increased glucose uptake by COCs via augmentation of GLUT1 expression in cumulus cells as well as stimulating lactate production via the enhancement of PFKP expression in cumulus cells. LPA did not affect cumulus expansion as visually assessed, however, it stimulated upstream genes of cumulus expansion cascade, AREG and EREG.

CONCLUSIONS

Supplementation of the maturation medium with LPA improves oocyte maturation rates, decreases extent of apoptosis in COCs and sustains the expression of developmental competence related factors during oocyte maturation and subsequently affects gene expression profile at the blastocyst stage. We also demonstrate that LPA directs glucose metabolism toward the glycolytic pathway during IVM.

Differential expression of lysosome-associated protein transmembrane-4 beta (LAPTM4B) in granulosa cells of ovarian follicles and in other bovine tissues

Background

LAPTM4B is a member of the lysosome-associated transmembrane protein superfamily that is differentially expressed in normal human tissues and upregulated in various types of carcinomas. These proteins are thought to be involved in the regulation of cell proliferation and survival. The objective of this study was to investigate the expression of bovine LAPTM4B during ovarian follicular development and in various bovine tissues.

Methods and results

Northern blot analysis revealed a 1.8 kb transcript, with highly variable steady state levels among tissues. RT-PCR analysis showed that LAPTM4B mRNA transcripts were low in granulosa cells of small antral follicles, increased in large dominant follicles, and decreased in ovulatory follicles following injection of human chorionic gonadotropin (hCG; P < 0.003). Ovulatory follicles collected at various times after hCG injection revealed a significant reduction of LAPTM4B mRNA starting at 18 h post-hCG (P < 0.029). Immunobloting analysis using antibodies generated against bovine LAPTM4B recognized proteins of 26.3 and 31.5 kDa in granulosa cells of developing follicles and corpus luteum. Further analyses of affinity-purified His-tag LAPTM4B overexpressed in HEK cells showed that the 31.5 kDa protein represented the ubiquinated isoform of the 26.3 kDa native protein. The 26.3 kDa protein was differentially expressed showing highest amounts in dominant follicles and lowest amounts in ovulatory follicles 24 h post-hCG. Immunohistochemical analyses of LAPTM4B showed marked heterogeneity of labeling signal among tissues, with LAPTM4B mainly localized to perinuclear vesicles, in keeping with its putative lysosomal membrane localization.

Conclusion

This study reports for the first time that bovine LAPTM4B in granulosa cells is present in both unubiquinated and ubiquinated forms, and is differentially expressed in developing ovarian follicles, suggesting a possible role in terminal follicular growth.

The contribution of the maternal immune system to the establishment of pregnancy in cattle

Immune cells play an integral role in affecting successful reproductive function. Indeed, disturbed or aberrant immune function has been identified as primary mechanisms behind infertility. In contrast to the extensive body of literature that exists for human and mouse, studies detailing the immunological interaction between the embryo and the maternal endometrium are quite few in cattle. Nevertheless, by reviewing the existing studies and extrapolating from sheep, pig, mouse, and human data, we can draw a reasonably comprehensive picture. Key contributions of immune cell populations include granulocyte involvement in follicle differentiation and gamete transfer, monocyte invasion of the peri-ovulatory follicle and their subsequent role in corpus luteum formation and the pivotal roles of maternal macrophage and dendritic cells in key steps of the establishment of pregnancy, particularly, the maternal immune response to the embryo. These contributions are reviewed in detail below and key findings are discussed.

Regulation of ovulatory genes in bovine granulosa cells: lessons from siRNA silencing of PTGS2

Prostaglandin endoperoxide synthase-2 (PTGS2), tumour necrosis factor-alpha-induced protein-6 (TNFAIP6), pentraxin-3 (PTX3), epidermal growth factor-like factors: amphiregulin (AREG) and epiregulin (EREG) are essential for successful ovulation. In this study, we compared the induction of these ovulatory genes in bovine granulosa cells (GCs) in vivo (after LH surge) and in vitro (forskolin (FRS) treatment). These genes were markedly stimulated in GCs isolated from cows 21 h after LH-surge. In isolated GCs, FRS induced a distinct temporal profile for each gene. Generally, there was a good agreement between the in vivo and in vitro inductions of these genes except for PTX3. Lack of PTX3 induction in isolated GCs culture suggests that other follicular compartments may mediate its induction by LH. Next, to study the role of PTGS2 and prostaglandins (PGs) in the cascade of ovulatory genes, PTGS2 was silenced with siRNA. PTGS2 siRNA caused a marked and specific knockdown of PTGS2 mRNA and PGE2 production (70% compared with scrambled siRNA) in bovine GCs. Importantly, PTGS2 silencing also reduced AREG, EREG and TNFAIP6 mRNA levels but not PTX3. Exogenous PGE2 increased AREG, EREG and TNFAIP6 mRNA levels, further confirming that these genes are prostanoid dependent. A successful and specific knockdown of PTGS2 was also achieved in endometrial cells (EndoCs) expressing PTGS2. Then, cholesterol-conjugated PTGS2 (chol-PTGS2) siRNA that facilitates cells' entry was investigated. In EndoCs, but not in GCs, chol-PTGS2 siRNA succeeded to reduce PTGS2 and PGE2 levels even without transfection reagent. PTGS2 knockdown is a promising tool to critically examine the functions of PTGS2 in the reproductive tract.

Expression and regulation of regulator of G-protein signaling protein-2 (RGS2) in equine and bovine follicles prior to ovulation: molecular characterization of RGS2 transactivation in bovine granulosa cells

The luteinizing hormone preovulatory surge stimulates several signal pathways essential for ovulation, and the regulator of G-protein signaling protein-2 (RGS2) is thought to be involved in this process. The objectives of this study were to characterize the regulation of RGS2 transcripts in equine and bovine follicles prior to ovulation and to determine its transcriptional control in bovine granulosa cells. To assess the regulation of equine RGS2 prior to ovulation, RT-PCR was performed using total RNA extracted from equine follicles collected at various times after human chorionic gonadotropin (hCG) injection. Results showed that RGS2 mRNA levels were very low at 0 h but markedly increased 12-39 h post-hCG (P < 0.05). In the bovine species, results revealed that RGS2 mRNA levels were low in small and dominant follicles and in ovulatory follicles obtained at 0 h, but markedly increased in ovulatory follicles 6-24 h post-hCG (P < 0.05). To study the molecular control of RGS2 expression, primary cultures of bovine granulosa cells were used. Stimulation with forskolin induced an up-regulation of RGS2 mRNA in vitro. Studies using 5'-deletion mutants identified a minimal region containing full-length basal and forskolin-inducible RGS2 promoter activities. Site-directed mutagenesis indicated that these activities were dependent on CRE and ETS1 cis-elements. Electrophoretic mobility shift assays confirmed the involvement of these elements and revealed their interactions with CREB1 and ETS1 proteins. Chromatin immunoprecipitation assays confirmed endogenous interactions of these proteins with the RGS2 promoter in granulosa cells. Forskolin-inducible RGS2 promoter activity and mRNA expression were markedly decreased by PKA and ERK1/2 inhibitors, and treatment with an antagonist of PGR (RU486) and inhibitors of PTGS2 (NS398) and EGFR (PD153035) blocked the forskolin-dependent RGS2 transcript expression, suggesting the importance of RGS2 in ovulation. Collectively, this study reports for the first time the gonadotropin-dependent up-regulation of RGS2 in equine and bovine preovulatory follicles and presents some of the regulatory controls involved in RGS2 gene expression in granulosa cells.

Transcriptome profiling of granulosa and theca cells during dominant follicle development in the horse

Several aspects of equine ovarian physiology are unique among domestic species. Moreover, follicular growth patterns are very similar between horses and humans. This study aimed to characterize, for the first time, global gene expression profiles associated with growth and preovulatory (PO) maturation of equine dominant follicles. Granulosa cells (GCs) and theca interna cells (TCs) were harvested from follicles (n = 5) at different stages of an ovulatory wave in mares corresponding to early dominance (ED; diameter ≥22 mm), late dominance (LD; ≥33 mm) and PO stage (34 h after administration of crude equine gonadotropins at LD stage), and separately analyzed on a horse gene expression microarray, followed by validation using quantitative PCR and immunoblotting/immunohistochemistry. Numbers of differentially expressed transcripts (DETs; ≥2-fold; P < 0.05) during the ED-LD and LD-PO transitions were 546 and 2419 in GCs and 5 and 582 in TCs. The most prominent change in GCs was the down-regulation of transcripts associated with cell division during both ED-LD and LD-PO. In addition, DET sets during LD-PO in GCs were enriched for genes involved in cell communication/adhesion, antioxidation/detoxification, immunity/inflammation, and cholesterol biosynthesis. In contrast, the largest change in TCs during the LD-PO transition was an up-regulation of genes involved in immune activation, with other DET sets mapping to GPCR/cAMP signaling, lipid/amino acid metabolism, and cell proliferation/survival and differentiation. In conclusion, distinct expression profiles were identified between growing and PO follicles and, particularly, between GCs and TCs within each stage. Several DETs were identified that have not been associated with follicle development in other species.

Protein kinase C (PKC) increases TACE/ADAM17 enzyme activity in porcine ovarian somatic cells, which is essential for granulosa cell luteinization and oocyte maturation

During in vitro maturation of porcine cumulus cell-oocyte complexes and in vitro luteinization of porcine granulosa cells, FSH induces the expression of the protease TNFα-converting enzyme/A disintegrin and metalloproteinase domain 17 (TACE/ADAM17) and the epidermal growth factor (EGF)-like factors, which activate the EGF receptor (EGFR)-MAPK3/1 pathway in both cumulus and granulosa cells. FSH is known to activate not only protein kinase A and p38MAPK pathways in both cell types but also activates protein kinase C (PKC). Because PKC-induced association of cellular-Sarcoma (c-Src) and TACE/ADAM17 is required for TACE/ADAM17 enzyme activation in some cancer cells, we hypothesized that PKC and c-Src impact TACE/ADAM17-mediated activation of EGFR signaling pathway in porcine granulosa and cumulus cells. When granulosa cells or cumulus cell-oocyte complexes were cultured with FSH, PKC activity and c-Src phosphorylation increased and were associated with increased TACE/ADAM17 enzyme activity. The PKC inhibitor calphostin C (CalC) and the c-Src inhibitor (4 amino 5 (4 chlorophenyl) 7 (t butyl)pyrazolo[3,4 d]pyrimidine [PP2]) suppressed TACE/ADAM17 enzyme activity, whereas these inhibitors did not affect Tace/Adam17 mRNA expression. Immunoprecipitation analysis showed that FSH mediated the association of c-Src with TACE/ADAM17 via a PKC-dependent mechanism. Either CalC or PP2 suppressed EGFR downstream signaling pathway (MAPK3/1) in these ovarian cell types and reduced cumulus expansion, meiotic maturation of oocytes, and progesterone production. The negative effects were overcome by the addition of amphiregulin. Collectively, these results indicate that activation of TACE/ADAM17 via a PKC-induced c-Src-dependent manner mediates proteolytic activation of the EGF-like factors that are involved in the induction of granulosa cell differentiation, cumulus expansion, and meiotic maturation of porcine oocytes in vitro.

Bone morphogenetic protein 15 and fibroblast growth factor 10 enhance cumulus expansion, glucose uptake, and expression of genes in the ovulatory cascade during in vitro maturation of bovine cumulus-oocyte complexes

Oocyte-secreted factors (OSFs) regulate differentiation of cumulus cells and are of pivotal relevance for fertility. Bone morphogenetic protein 15 (BMP15) and fibroblast growth factor 10 (FGF10) are OSFs and enhance oocyte competence by unknown mechanisms. We tested the hypothesis that BMP15 and FGF10, alone or combined in the maturation medium, enhance cumulus expansion and expression of genes in the preovulatory cascade and regulate glucose metabolism favouring hyaluronic acid production in bovine cumulus-oocyte complexes (COCs). BMP15 or FGF10 increased the percentage of fully expanded COCs, but the combination did not further stimulate it. BMP15 increased cumulus cell levels of mRNA encoding a disintegrin and metalloprotease 10 (ADAM10), ADAM17, amphiregulin (AREG), and epiregulin (EREG) at 12 h of culture and of prostaglandin (PG)-endoperoxide synthase 2 (PTGS2), pentraxin 3 (PTX3) and tumor necrosis factor alpha-induced protein 6 (TNFAIP6 (TSG6)) at 22 h of culture. FGF10 did not alter the expression of epidermal growth factor-like factors but enhanced the mRNA expression of PTGS2 at 4 h, PTX3 at 12 h, and TNFAIP6 at 22 h. FGF10 and BMP15 stimulated glucose consumption by cumulus cells but did not affect lactate production or levels of mRNA encoding glycolytic enzymes phosphofructokinase and lactate dehydrogenase A. Each growth factor increased mRNA encoding glucosamine:fructose-6-PO4 transaminases, key enzymes in the hexosamine pathway leading to hyaluronic acid production, and BMP15 also stimulated hyaluronan synthase 2 (HAS2) mRNA expression. This study provides evidence that BMP15 and FGF10 stimulate expansion of in vitro-matured bovine COCs by driving glucose metabolism toward hyaluronic acid production and controlling the expression of genes in the ovulatory cascade, the first acting upon ADAM10, ADAM17, AREG, and EREG and the second on downstream genes, particularly PTGS2.

Research resource: preovulatory LH surge effects on follicular theca and granulosa transcriptomes

The molecular mechanisms that regulate the pivotal transformation processes observed in the follicular wall following the preovulatory LH surge, are still not established, particularly for cells of the thecal layer. To elucidate thecal cell (TC) and granulosa cell (GC) type-specific biologic functions and signaling pathways, large dominant bovine follicles were collected before and 21 hours after an exogenous GnRH-induced LH surge. Antral GCs (aGCs; aspirated by follicular puncture) and membrane-associated GCs (mGCs; scraped from the follicular wall) were compared with TC expression profiles determined by mRNA microarrays. Of the approximately 11 000 total genes expressed in the periovulatory follicle, only 2% of thecal vs 25% of the granulosa genes changed in response to the LH surge. The majority of the 203 LH-regulated thecal genes were also LH regulated in GCs, leaving a total of 57 genes as LH-regulated TC-specific genes. Of the 57 thecal-specific LH-regulated genes, 74% were down-regulated including CYP17A1 and NR5A1, whereas most other genes are being identified for the first time within theca. Many of the newly identified up-regulated thecal genes (eg, PTX3, RND3, PPP4R4) were also up-regulated in granulosa. Minimal expression differences were observed between aGCs and mGCs; however, transcripts encoding extracellular proteins (NID2) and matrix modulators (ADAMTS1, SASH1) dominated these differences. We also identified large numbers of unknown LH-regulated GC genes and discuss their putative roles in ovarian function. This Research Resource provides an easy-to-access global evaluation of LH regulation in TCs and GCs that implicates numerous molecular pathways heretofore unknown within the follicle.

Global gene expression in the bovine corpus luteum is altered after stimulatory and superovulatory treatments

Equine chorionic gonadotrophin (eCG) has been widely used in superovulation and artificial insemination programmes and usually promotes an increase in corpus luteum (CL) volume and stimulates progesterone production. Therefore, to identify eCG-regulated genes in the bovine CL, the transcriptome was evaluated by microarray analysis and the expression of selected genes was validated by qPCR and western blot. Eighteen Nelore crossbred cows were divided into control (n = 5), stimulated (n = 6) and superovulated groups (n = 7). Ovulation was synchronised using a progesterone device-based protocol. Stimulated animals received 400 IU of eCG at device removal and superovulated animals received 2000 IU of eCG 4 days prior. Corpora lutea were collected 7 days after gonadotrophin-releasing hormone administration. Overall, 242 transcripts were upregulated and 111 transcripts were downregulated in stimulated cows (P ≤ 0.05) and 111 were upregulated and 113 downregulated in superovulated cows compared to the control animals (1.5-fold, P ≤ 0.05). Among the differentially expressed genes, many were involved in lipid biosynthesis and progesterone production, such as PPARG, STAR, prolactin receptors and follistatin. In conclusion, eCG modulates gene expression differently depending on the treatment, i.e. stimulatory or superovulatory. Our data contribute to the understanding of the pathways involved in increased progesterone levels observed after eCG treatment.

Human chorionic gonadotropin-dependent up-regulation of epiregulin and amphiregulin in equine and bovine follicles during the ovulatory process

Little is known about the expression and regulation of epiregulin (EREG) and amphiregulin (AREG) in ovarian follicles of large monoovulatory animal species. To characterize the gonadotropin-dependent regulation of EREG and AREG mRNAs in equine follicles prior to ovulation, extracts were prepared from equine follicles collected during estrus between 0 and 39h post-hCG and corpora lutea obtained on day 8 of the estrous cycle (day 0=day of ovulation). Results from RT-PCR/Southern blot analyses showed that levels of EREG and AREG mRNAs were very low in follicles obtained at 0h but increased thereafter (P<0.05), with maximal levels observed 33-39h post-hCG. This significant increase was observed in both granulosa and theca cells. Immunohistochemistry and immunoblot analyses confirmed the hCG-dependent induction of EREG protein in both cell types. RT-PCR/Southern blot analyses of ADAM17, which encodes an enzyme that cleaves and releases soluble bioactive EREG and AREG, showed that levels of its transcript were high and remained constant throughout the period studied. Studies on the hCG-dependent regulation of EREG and AREG in bovine preovulatory follicles in vivo showed that the induction of both transcripts was transient, observed predominantly at 6h post-hCG and localized only in granulosa cells. To characterize the effect of epidermal growth factor receptor (EGFR) activation on the expression of ovulation-related genes in granulosa cells of a large monoovulatory animal species, primary cultures of bovine granulosa cells were established. Results from RT-PCR analyses revealed that EREG and AREG mRNAs were induced by forskolin treatment in vitro; but the EGFR inhibitor PD153035 suppressed the forskolin-dependent induction of several ovulation-related transcripts, including PTGS2, PTGER2, TNFAIP6, PGR, MMP1, VEGFA, and CTSL2 mRNAs. Moreover, these transcripts were induced in granulosa cell cultures by EGF, an analog of EREG and AREG. Collectively, this study identifies differences in the temporal and cellular localization of EREG and AREG expression in equine and bovine preovulatory follicles, and underscores the potential role of follicular EGFR activation in the regulation of ovulation-regulated genes in large monoovulatory species.

Role of angiotensin in ovarian follicular development and ovulation in mammals: a review of recent advances

Angiotensin (Ang) II is widely known for its role in the control of systemic blood vessels. Moreover, Ang II acts on the vascular control of ovarian function, corpus luteum formation, and luteolysis. Over the past 10 years, our research group has been studying the new concept of the renin–angiotensin system (RAS) as an autocrine/paracrine factor regulating steroidogenesis and promoting different cellular responses in the ovary, beyond vascular function. We have developed and used differentin vivoandin vitroexperimental models to study the role of RAS in the ovary and a brief overview of our findings is presented here. It is widely accepted that there are marked species differences in RAS function in follicle development. Examples of species-specific functions of the RAS in the ovary include the involvement of Ang II in the regulation of follicle atresia in rats vs the requirement of this peptide for the dominant follicle development and ovulation in rabbits and cattle. More recently, Ang-(1–7), its receptor, and enzymes for its synthesis (ACE2, NEP, and PEP) were identified in bovine follicles, implying that Ang-(1–7) has an ovarian function. Other novel RAS components (e.g. (pro)renin receptor and renin-binding protein) recently identified in the bovine ovary show that ovarian RAS is poorly understood and more complex than previously thought. In the present review, we have highlighted the progress toward understanding the paracrine and autocrine control of ovarian antral follicle development and ovulation by ovarian tissue RAS, focusing onin vivostudies using cattle as a model.

Gene expression profiling of preovulatory follicle in the buffalo cow: effects of increased IGF-I concentration on periovulatory events

The preovulatory follicle in response to gonadotropin surge undergoes dramatic biochemical, and morphological changes orchestrated by expression changes in hundreds of genes. Employing well characterized bovine preovulatory follicle model, granulosa cells (GCs) and follicle wall were collected from the preovulatory follicle before, 1, 10 and 22 h post peak LH surge. Microarray analysis performed on GCs revealed that 450 and 111 genes were differentially expressed at 1 and 22 h post peak LH surge, respectively. For validation, qPCR and immunocytochemistry analyses were carried out for some of the differentially expressed genes. Expression analysis of many of these genes showed distinct expression patterns in GCs and the follicle wall. To study molecular functions and genetic networks, microarray data was analyzed using Ingenuity Pathway Analysis which revealed majority of the differentially expressed genes to cluster within processes like steroidogenesis, cell survival and cell differentiation. In the ovarian follicle, IGF-I is established to be an important regulator of the above mentioned molecular functions. Thus, further experiments were conducted to verify the effects of increased intrafollicular IGF-I levels on the expression of genes associated with the above mentioned processes. For this purpose, buffalo cows were administered with exogenous bGH to transiently increase circulating and intrafollicular concentrations of IGF-I. The results indicated that increased intrafollicular concentrations of IGF-I caused changes in expression of genes associated with steroidogenesis (StAR, SRF) and apoptosis (BCL-2, FKHR, PAWR). These results taken together suggest that onset of gonadotropin surge triggers activation of various biological pathways and that the effects of growth factors and peptides on gonadotropin actions could be examined during preovulatory follicle development.

Human oocyte maturation is dependent on LH-stimulated accumulation of the epidermal growth factor-like growth factor, amphiregulin

BACKGROUND

The LH surge promotes ovulation via activation of multiple signaling networks in the ovarian follicle. Studies in animal models have shown the importance of LH-induced activation of the epidermal growth factor (EGF)signaling network in critical peri-ovulatory events. We investigated the biological significance of regulatory mechanisms mediated by EGF-like growth factors during LH stimulation in humans.

METHODS

We characterized the EGF signaling network in mature human ovarian follicles using in vivo and in vitro approaches. Amphiregulin (AREG) levels were measured in 119 follicular fluid (FF) samples from IVF/ICSI patients. Biological activity of human FF was assessed using in vitro oocyte maturation, cumulus expansion and cell mitogenic assays.

RESULTS

AREG is the most abundant EGF-like growth factor accumulating in the FF of mature follicles of hCG-stimulated patients. No AREG was detected before the LH surge or before hCG stimulation of granulosa cells in vitro, demonstrating that the accumulation of AREG requires gonadotrophin stimulation. Epiregulin and betacellulin mRNA were detected in both human mural and cumulus granulosa cells, although at significantly lower levels than AREG. FF from stimulated follicles causes cumulus expansion and oocyte maturation in a reconstitution assay. Immunodepletion of AREG abolishes the ability of FF to stimulate expansion (P < 0.0001) and oocyte maturation (P < 0.05), confirming the biological activity of AREG. Conversely, mitogenic activity of FF remained after depletion of AREG, indicating that other mitogens accumulate in FF. FF from follicles yielding an immature germinal vesicle oocyte or from an oocyte that develops into an aberrant embryo contains lower AREG levels than that from follicles yielding a healthy oocyte (P = 0.008).

CONCLUSIONS

EGF-like growth factors play a role in critical peri-ovulatory events in humans, and AREG accumulation is a useful marker of gonadotrophin stimulation and oocyte competence.