Mechanisms of amino acid uptake in cumulus-enclosed mouse oocytes

Electro-Metabolic Coupling of Cumulus-Oocyte Complex

Oocyte-cumulus cell interaction is essential for oocyte maturation and competence. The bidirectional crosstalk network mediated by gap junctions is fundamental for the metabolic cooperation between these cells. As cumulus cells exhibit a more glycolytic phenotype, they can provide metabolic substrates that the oocyte can use to produce ATP via oxidative phosphorylation. The impairment of mitochondrial activity plays a crucial role in ovarian aging and, thus, in fertility, determining the success or failure of assisted reproductive techniques. This review aims to deepen the knowledge about the electro-metabolic coupling of the cumulus-oocyte complex and to hypothesize a putative role of potassium channel modulators in order to improve fertility, promote intracellular Ca2+ influx, and increase the mitochondrial biogenesis and resulting ATP levels in cumulus cells.

Impact of preovulatory follicle maturity on oocyte metabolism and embryo development

Improved oocyte competence for embryo development and pregnancy was observed following ovulation of preovulatory follicles with greater physiological maturity, as indicated by estradiol production, prior to the gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) surge. It was hypothesized that follicular fluid from preovulatory follicles of greater maturity better supports the maturing oocyte's metabolic requirements and improves embryo development. The objective was to determine if differences in preovulatory follicular fluid due to follicle maturity influence oocyte metabolism during in vitro maturation (IVM) and affect embryo development. Bovine preovulatory follicular fluid was collected 18 h after a GnRH-induced LH surge. Serum estradiol concentration at GnRH administration categorized follicles as greater or lesser maturity. Immature bovine oocytes were submitted to 24 h IVM in medium supplemented with 20% follicular fluid from preovulatory follicles of greater or lesser maturity. Embryo development was recorded. Oocyte maturation media and media conditioned by developing embryos were submitted for metabolomics. A randomized block design was utilized to determine differences in embryo development and media metabolites (P ≤ 0.05). Blastocysts from oocytes matured in greater vs. lesser maturity follicular fluid had a more moderate rate of development (P = 0.01). At the conclusion of 24 h IVM, abundance of 66 metabolites differed between greater and lesser follicle maturity treatments. Nine metabolites differed in media conditioned by developing embryos. Metabolome results suggest improved amino acid, purine, and glucose metabolism, followed by a more efficient rate of embryo development, in oocytes matured in greater vs lesser maturity follicular fluid.

Oocyte and cumulus cell cooperativity and metabolic plasticity under the direction of oocyte paracrine factors

Mammalian oocytes develop and mature in a mutually dependent relationship with surrounding cumulus cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble paracrine oocyte-secreted factors (OSFs). We characterized the molecular mechanisms by which two model OSFs, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Exposure to these OSFs during mouse oocyte maturation in vitro altered the proteomic and multispectral autofluorescence profiles of both the oocyte and cumulus cells. In oocytes, cumulin significantly upregulated proteins involved in nuclear function. In cumulus cells, both OSFs elicited marked upregulation of a variety of metabolic processes (mostly anabolic), including lipid, nucleotide, and carbohydrate metabolism, whereas mitochondrial metabolic processes were downregulated. The mitochondrial changes were validated by functional assays confirming altered mitochondrial morphology, respiration, and content while maintaining ATP homeostasis. Collectively, these data demonstrate that cumulin and BMP15 remodel cumulus cell metabolism, instructing them to upregulate their anabolic metabolic processes, while routine cellular functions are minimized in the oocyte during maturation, in preparation for ensuing embryonic development.NEW & NOTEWORTHY Oocyte-secreted factors (OSFs) promote oocyte and cumulus cell cooperativity by altering the molecular composition of both cell types. OSFs downregulate protein catabolic processes and upregulate processes associated with DNA binding, translation, and ribosome assembly in oocytes. In cumulus cells, OSFs alter mitochondrial number, morphology, and function, and enhance metabolic plasticity by upregulating anabolic pathways. Hence, the oocyte via OSFs, instructs cumulus cells to increase metabolic processes on its behalf, thereby subduing oocyte metabolism.

Multi-omics reveal the metabolic patterns in mouse cumulus cells during oocyte maturation

Bi-directional communication between cumulus cells and the surrounded oocytes is important for the development and functions of both compartments. However, the metabolic framework in cumulus cells has not been systematically described. In the present study, cumulus cells from cumulus-oocyte complexes (COCs) at three key time points were isolated (arrested GV stage, post-hCG 0h; meiotic resumption GVBD stage, post-hCG 3h; and metaphase II stage, post-hCG 12h), and the temporal metabolomic and proteomic profiling were performed. Integrated multi-omics analysis reveals the global metabolic patterns in cumulus cells during mouse oocyte maturation. In particular, we found the active hyaluronic acid metabolism, steroid hormone synthesis, and prostaglandin E2 (PGE2) production in cumulus cells. Meanwhile, accompanying the oocyte maturation, a progressive increase in nucleotide and amino acid metabolism was detected in the surrounding cumulus cells. In sum, the data serve as a valuable resource for probing metabolism during terminal differentiation of ovarian granulosa cells, and provide the potential biomarkers for improving and predicting oocyte quality.

Identification and validation of immune cells and hub genes alterations in recurrent implantation failure: A GEO data mining study

Introduction: Recurrent implantation failure (RIF) is a distressing problem in assisted reproductive technology (ART). Immunity plays a vital role in recurrent implantation failure (RIF) occurrence and development, but its underlying mechanism still needs to be fully elucidated. Through bioinformatics analysis, this study aims to identify the RIF-associated immune cell types and immune-related genes. Methods: The differentially expressed genes (DEGs) were screened based on RIF-associated Gene Expression Omnibus (GEO) datasets. Then, the enrichment analysis and protein-protein interaction (PPI) analysis were conducted with the DEGs. The RIF-associated immune cell types were clarified by combining single sample gene set enrichment analysis (ssGSEA) and CIBERSORT. Differentially expressed immune cell types-related modules were identified by weighted gene co-expression network analysis (WGCNA) and local maximal quasi-clique merger (lmQCM) analysis. The overlapping genes between DEGs and genes contained by modules mentioned above were delineated as candidate hub genes and validated in another two external datasets. Finally, the microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) that interacted with hub genes were predicted, and the competing endogenous RNA (ceRNA) regulatory network was structured. Results: In the present study, we collected 324 DEGs between RIF and the control group, which functions were mainly enriched in immune-related signaling pathways. Regarding differential cell types, the RIF group had a higher proportion of activated memory CD4 T cells and a lower proportion of γδ T cells in the endometrial tissue. Finally, three immune-related hub genes (ALOX5AP, SLC7A7, and PTGS2) were identified and verified to effectively discriminate RIF from control individuals with a specificity rate of 90.8% and a sensitivity rate of 90.8%. In addition, we constructed a key ceRNA network that is expected to mediate molecular mechanisms in RIF. Conclusion: Our study identified the intricate correlation between immune cell types and RIF and provided new immune-related hub genes that offer promising diagnostic and therapeutic targets for RIF.

Stage-Specific L-Proline Uptake by Amino Acid Transporter Slc6a19/B0AT1 Is Required for Optimal Preimplantation Embryo Development in Mice

L-proline (Pro) has previously been shown to support normal development of mouse embryos. Recently we have shown that Pro improves subsequent embryo development when added to fertilisation medium during in vitro fertilisation of mouse oocytes. The mechanisms by which Pro improves embryo development are still being elucidated but likely involve signalling pathways that have been observed in Pro-mediated differentiation of mouse embryonic stem cells. In this study, we show that B⁰AT1, a neutral amino acid transporter that accepts Pro, is expressed in mouse preimplantation embryos, along with the accessory protein ACE2. B⁰AT1 knockout (Slc6a19^-/-) mice have decreased fertility, in terms of litter size and preimplantation embryo development in vitro. In embryos from wild-type (WT) mice, excess unlabelled Pro inhibited radiolabelled Pro uptake in oocytes and 4-8-cell stage embryos. Radiolabelled Pro uptake was reduced in 4-8-cell stage embryos, but not in oocytes, from Slc6a19^-/- mice compared to those from WT mice. Other B⁰AT1 substrates, such as alanine and leucine, reduced uptake of Pro in WT but not in B⁰AT1 knockout embryos. Addition of Pro to culture medium improved embryo development. In WT embryos, Pro increased development to the cavitation stage (on day 4); whereas in B⁰AT1 knockout embryos Pro improved development to the 5-8-cell (day 3) and blastocyst stages (day 6) but not at cavitation (day 4), suggesting B⁰AT1 is the main contributor to Pro uptake on day 4 of development. Our results highlight transporter redundancy in the preimplantation embryo.

Transzonal projections: Essential structures mediating intercellular communication in the mammalian ovarian follicle

The development of germ cells relies on contact and communication with neighboring somatic cells that provide metabolic support and regulatory signals. In females, contact is achieved through thin cytoplasmic processes that project from follicle cells surrounding the oocyte, extend through an extracellular matrix (ECM) that lies between them, and reach its surface. In mammals, the ECM is termed the zona pellucida and the follicular cell processes are termed transzonal projections (TZPs). TZPs become detectable when the zona pellucida is laid down during early folliculogenesis and subsequently increase in number as oocyte growth progresses. They then rapidly disappear at the time of ovulation, permanently breaking germ-soma contact. Here we review the life cycle and functions of the TZPs. We begin with an overview of the morphology and cytoskeletal structure of TZPs, in the context of actin- and tubulin-based cytoplasmic processes in other cell types. Next, we review the roles played by TZPs in mediating progression through successive stages of oocyte development. We then discuss two mechanisms that may generate TZPs-stretching at pre-existing points of granulosa cell-oocyte contact and elaboration of new processes that push through the zona pellucida-as well as gene products implicated in their formation or function. Finally, we describe the signaling pathways that cause TZPs to be retracted in response to signals that also trigger meiotic maturation and ovulation of the oocyte. The principles and mechanisms that govern TZP behavior may be relevant to understanding communication between physically separated cells in other physiological contexts.

Mammalian cumulus-oocyte complex communication: a dialog through long and short distance messaging

Communications are crucial to ovarian follicle development and to ovulation, and while both folliculogenesis and oogenesis are distinct processes, they share highly interdependent signaling pathways. Signals from distant organs such as the brain must be processed and compartments within the follicle have to be synchronized. The hypothalamic–pituitary–gonadal (HPG) axis relies on long-distance signalling analogous to wireless communication by which data is disseminated in the environment and cells equipped with the appropriate receptors receive and interpret the messages. In contrast, direct cell-to-cell transfer of molecules is a very targeted, short distance messaging system. Numerous signalling pathways have been identified and proven to be essential for the production of a developmentally competent egg. The development of the cumulus-oocyte complex relies largely on short distance communications or direct transfer type via extensions of corona radiata cells through the zona pellucida. The type of information transmitted through these transzonal projections is still largely uncharacterized. This review provides an overview of current understanding of the mechanisms by which the gamete receives and transmits information within the follicle. Moreover, it highlights the fact that in addition to the well-known systemic long-distance based communications from the HPG axis, these mechanisms acting more locally should also be considered as important targets for controlling/optimizing oocyte quality.

Metabolic control of oocyte development

Well balanced and timed metabolism is essential for oocyte development. The effects of extrinsic nutrients on oocyte maturation have been widely reported. In contrast, intrinsic control of oogenesis by intracellular metabolites and metabolic enzymes has received little attention. The comprehensive characterization of metabolic patterns could lead to more complete understanding of regulatory mechanisms underlying oocyte development. A cell's metabolic state is integrated with epigenetic regulation. Epigenetic modifications in germ cells are therefore sensitive to parental environmental exposures. Nevertheless, direct genetic evidence for metabolites involvement in epigenetic establishment during oocyte development is still lacking. Moreover, metabolic disorder-induced epigenetic perturbations during oogenesis might mediate the inter/transgenerational effects of environmental insults. The molecular mechanisms responsible for this deserve further investigation. Here, we summarize the findings on metabolic regulation in oocyte maturation, and how it contributes to oocyte epigenetic modification. Finally, we propose a mouse model that metabolic disorder in oocyte serves as a potential factor mediating the maternal environment effects on offspring health.

Correlation between Pre-Ovulatory Follicle Diameter and Follicular Fluid Metabolome Profiles in Lactating Beef Cows

Induced ovulation of small pre-ovulatory follicles reduced pregnancy rates, embryo survival, day seven embryo quality, and successful embryo cleavage in beef cows undergoing fixed-time artificial insemination. RNA-sequencing of oocytes and associated cumulus cells collected from pre-ovulatory follicles 23 h after gonadotropin-releasing hormone (GnRH) administration to induce the pre-ovulatory gonadotropin surge suggested reduced capacity for glucose metabolism in cumulus cells of follicles ≤11.7 mm. We hypothesized that the follicular fluid metabolome influences metabolic capacity of the cumulus-oocyte complex and contributes to reduced embryo cleavage and quality grade observed following induced ovulation of small follicles. Therefore, we performed a study to determine the correlation between pre-ovulatory follicle diameter and follicular fluid metabolome profiles in lactating beef cows (Angus, n = 130). We synchronized the development of a pre-ovulatory follicle and collected the follicular contents approximately 20 h after GnRH administration. We then performed ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) metabolomic studies on 43 follicular fluid samples and identified 38 metabolites within pre-ovulatory follicles of increasing size. We detected 18 metabolites with a significant, positive correlation to follicle diameter. Individual and pathway enrichment analysis of significantly correlated metabolites suggest that altered glucose and amino acid metabolism likely contribute to reduced developmental competence of oocytes when small pre-ovulatory follicles undergo induced ovulation.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

Resveratrol depolarizes the membrane potential in human granulosa cells and promotes mitochondrial biogenesis

OBJECTIVE

To study the biological effects of resveratrol on the growth, electrophysiology, and mitochondrial function of human granulosa cells (h-GCs).

DESIGN

Preclinical study.

SETTING

Electrophysiology laboratory and in vitro fertilization unit.

PATIENT(S)

This study included h-GCs from seven infertile women undergoing assisted reproductive techniques.

INTERVENTION(S)

Human ovarian Granulosa Cell Tumor (GCT) cell line COV434 and h-GCs obtained after oocyte retrieval were cultured in the absence or presence of resveratrol.

MAIN OUTCOME MEASURE(S)

Granulosa cells were evaluated for cell viability and mitochondrial activity. Electrophysiological recordings and evaluation of potassium current (IKur) and Ca₂₊ concentration were also performed.

RESULT(S)

Resveratrol induced mitochondrial activity in a bell-shaped, dose-effect-dependent manner. Specifically, resveratrol treatment (3 μM, 48 hours) increased ATP production and cell viability and promoted the induction of cellular differentiation. These biological changes were associated with mitochondrial biogenesis. Electrophysiological recordings showed that resveratrol reduced the functional expression of an ultra rapid activating, slow inactivating, delayed rectifier potassium current (IKur) that is associated with a plasma membrane depolarization and that promotes an increase in intracellular Ca₂⁺_. CONCLUSION(S): The effects of resveratrol on potassium current and mitochondrial biogenesis in h-GCs could explain the beneficial effects of this polyphenol on the physiology of the female reproductive system. These findings suggest there are therapeutic implications of resveratrol in a clinical setting.

Embryo and Its Mitochondria

The mitochondria, present in almost all eukaryotic cells, produce energy but also contribute to many other essential cellular functions. One of the unique characteristics of the mitochondria is that they have their own genome, which is only maternally transmitted via highly specific mechanisms that occur during gametogenesis and embryogenesis. The mature oocyte has the highest mitochondrial DNA copy number of any cell. This high mitochondrial mass is directly correlated to the capacity of the oocyte to support the early stages of embryo development in many species. Indeed, the subtle energetic and metabolic modifications that are necessary for each of the key steps of early embryonic development rely heavily on the oocyte’s mitochondrial load and activity. For example, epigenetic reprogramming depends on the metabolic cofactors produced by the mitochondrial metabolism, and the reactive oxygen species derived from the mitochondrial respiratory chain are essential for the regulation of cell signaling in the embryo. All these elements have also led scientists to consider the mitochondria as a potential biomarker of oocyte competence and embryo viability, as well as a key target for future potential therapies. However, more studies are needed to confirm these findings. This review article summarizes the past two decades of research that have led to the current understanding of mitochondrial functions in reproduction

Mitochondrial Stress Response Gene Clpp Is Not Required for Granulosa Cell Function

Mitochondrial unfolded protein response (UPR^mt) is a highly conserved mechanism, which is activated upon cellular or metabolic stress and aims to help cells maintain homeostasis. CLPP (caseinolytic peptidase P) plays a crucial factor for UPR^mt; it promotes the degradation of unfolded mitochondrial proteins. Global germline deletion of Clpp in mice results in female infertility and accelerated follicular depletion. Here, we asked whether CLPP is necessary for granulosa/cumulus cell function. Clpp^flox/flox mice were generated and crossbred with Cyp19a1-Cre mice to generate mice with granulosa/cumulus cell-specific Clpp deletion (Clpp^-/-). Mature (8-week-old) Clpp^-/- female mice (8-week-old) were compared to same age wild type (WT) mice. We found that mature Clpp^-/- female mice were fertile and produced a similar number of pups per litter compared to WT. Folliculogenesis was not affected by the loss of CLPP in granulosa/cumulus cells as Clpp^-/- and WT mice had a similar number of primordial, primary, secondary, early antral, and antral follicles. The number of germinal vesicles (GV) and MII oocytes collected from Clpp^-/- and WT female mice were also similar. Our findings demonstrate that fertility in female mice is not affected by granulosa/cumulus cell-specific UPR^mt disruption through CLPP deletion.

A prematuration approach to equine IVM: considering cumulus morphology, seasonality, follicle of origin, gap junction coupling and large-scale chromatin configuration in the germinal vesicle

Several studies report that a two-step culture where mammalian oocytes are first kept under meiosis-arresting conditions (prematuration) followed by IVM is beneficial to embryo development. The most promising results were obtained by stratifying the oocyte population using morphological criteria and allocating them to different culture conditions to best meet their metabolic needs. In this study, horse oocytes were characterised to identify subpopulations that may benefit from prematuration. We investigated gap-junction (GJ) coupling, large-scale chromatin configuration and meiotic competence in compact and expanded cumulus-oocyte complexes (COCs) according to follicle size (<1, 1-2, >2cm) and season. Then we tested the effect of cilostamide-based prematuration in compact COCs collected from follicles <1 and 1-2cm in diameter on embryo development. Meiotic competence was not affected by prematuration, whereas COCs from follicles 1-2cm in diameter yielded embryos with a higher number of cells per blastocyst than oocytes that underwent direct IVM (P<0.01, unpaired Mann-Whitney test), suggesting improved developmental competence. Oocytes collected from follicles <1cm in diameter were not affected by prematuration. This study represents an extensive characterisation of the functional properties of immature horse oocytes and is the first report of the effects of cilostamide-based prematuration in horse oocyte IVM on embryo development.

Effects of increasing lipopolysaccharide concentrations on in vitro developmental competence of ovine oocytes

Although a considerable number of studies have investigated the effects of lipopolysaccharide (LPS) on the reproductive performance of dairy cows, the response of ovine oocytes to LPS during their in vitro maturation and development is not well defined yet. Ewe’s ovaries were obtained from a slaughterhouse, the oocytes were collected and matured in the presence of increasing concentrations (0, 0.01, 0.1, 1 and 10 µg/mL) of LPS in order to evaluate the meiotic maturation by measuring the proportion of oocytes reaching the MII stage. The concentration of intracellular glutathione (GSH) was measured in oocytes following maturation in vitro. In addition, concentrations of selected metabolites including glucose, pyruvate, lactate and glutamine were quantified in the medium following maturation. A number of treated matured oocytes along with the control group were subsequently fertilized using frozen semen and assessed for the rate of cleavage and for the proportion reaching the blastocyst stage. The number of oocytes in MII stage was significantly reduced in response to the increasing concentrations of LPS (77.83%, 70.64%, 68.86%, 66.32%, respectively, in case of 0.01, 0.1, 1 and 10 µg/mL LPS when compared to the control group, 76.34%; P<0.05). There were no differences neither in the intracellular concentration of GSH in the oocytes nor in case of the metabolites in the maturation medium. Although the rate of cleaved oocytes was not affected by increasing levels of LPS, the blastocyst rate was reduced in a dose dependent manner (36.69%, 34.21%, 30.35%, 17.27% and 14.03% for the control, 0.01, 0.1, 1 and 10 µg/mL LPS, respectively (P<0.05). These results demonstrate that the developmental competence of ovine oocytes may be affected detrimentally by LPS and such deleterious effects could be related to the maturation process.

l-Serine transport in growing and maturing mouse oocytes

Serine has roles in cell metabolism besides protein synthesis including providing one-carbon units to the folate cycle. Since growing mouse oocytes undergo a burst of folate accumulation as they near full size, we have investigated whether oocytes transport serine. Substantial serine transport appeared in oocytes near the end of their growth. Serine transport continued when oocytes resumed meiosis but ceased partway through first meiotic metaphase, remaining quiescent in mature eggs in second meiotic metaphase. The serine transporter was sodium dependent and inhibited by alanine, cysteine, leucine, or histidine, and had a Michaelis-Menten constant (K_m ) for serine of 200 µM. Unexpectedly, exposing cumulus cell-enclosed oocytes to the physiological mediator of meiotic arrest, natriuretic peptide precursor Type C, substantially stimulated serine transport by the enclosed oocyte. Finally, in addition to transport by the oocyte itself, cumulus cells also supply serine to the enclosed oocyte via gap junctions within intact cumulus-oocyte complexes.

Dynamin 2-dependent endocytosis is essential for mouse oocyte development and fertility

During folliculogenesis, oocytes are dependent on metabolic and molecular support from surrounding somatic cells. Here, we examined the role of the dynamin (DNM) family of mechanoenzymes in mediating endocytotic uptake into growing follicular oocytes. We found DNM1 and DNM2 to be highly expressed in growing follicular oocytes as well as in mature germinal vesicle (GV) and metaphase II (MII) stage oocytes. Moreover, oocyte-specific conditional knockout (cKO) of DNM2 (DNM2Δ) led to complete sterility, with follicles arresting at the preantral stage of development. In addition, DNM2Δ ovaries were characterized by disrupted follicular growth as well as oocyte and follicle apoptosis. Further, the loss of DNM activity, either through DNM2 cKO or through pharmacological inhibition (Dyngo 6a) led to the impairment of endocytotic pathways in preantral oocytes as well as in mature GV and MII oocytes, respectively. Loss of DNM activity resulted in the redistribution of endosomes and the misslocalization of clathrin and actin, suggesting dysfunctional endocytosis. Notably, there was no observable effect on the fertility of DNM1Δ females. Our study has provided new insight into the complex and dynamic nature of oocyte growth during folliculogenesis, suggesting a role for DNM2 in mediating the endocytotic events that are essential for oocyte development.

Interaction between growing oocytes and granulosa cells in vitro

BACKGROUND

Oocyte growth is accompanied by follicular development in mammalian ovaries. Since the discovery of two oocyte-derived factors, growth differentiation factor 9 (GDF9), and bone morphogenetic protein 15 (BMP15), knowledge of the bidirectional communication between oocytes and granulosa cells for ovarian function and fertility has been accumulated. In addition, the growth culture system of oocytes has been improved, further promoting the studies on the communication between oocytes and granulosa cells in vitro.

METHODS

We provide an overview of the role of granulosa cells in oocyte growth and the role of oocytes in follicular development along with our recent findings in culture experiments of bovine growing oocytes.

MAIN FINDINGS

Granulosa cells supply nutrients and metabolites through gap junctions to oocytes and secrete paracrine signals to regulate oocytes. Oocytes regulate granulosa cell proliferation and differentiation and induce antrum formation via GDF9 and BMP15.

CONCLUSION

Oocytes actively participate in various aspects of follicular development, including antrum formation via the oocyte-derived factors GDF9 and BMP15, whose synthesis is probably regulated by granulosa cells. In vitro studies will reveal the precise communication loop between oocytes and granulosa cells that facilitates the coordinated development of oocytes and granulosa cells in the follicles.

Transcriptional status of mouse oocytes corresponds with their ability to generate Ca2+ release

In fully grown ovarian follicles both transcriptionally active (NSN) and inactive (SN) oocytes are present. NSN oocytes have been shown to display lower developmental potential. It is possible that oocytes that have not completed transcription before meiosis resumption accumulate less RNA and proteins required for their further development, including those responsible for regulation of Ca2+ homeostasis. Oscillations of the cytoplasmic concentration of free Ca2+ ions ([Ca2+]i) are triggered in oocytes by a fertilizing spermatozoon and are crucial for inducing and regulating further embryonic development. We showed that NSN-derived oocytes express less inositol 1,4,5-triphosphate receptor type 1 (IP3R1), store less Ca2+ ions and generate weaker spontaneous [Ca2+]i oscillations during maturation than SN oocytes. Consequently, NSN oocytes display aberrant [Ca2+]i oscillations at fertilization. We speculate that this defective regulation of Ca2+ homeostasis might be one of the factors responsible for the lower developmental potential of NSN oocytes.

Urea influences amino acid turnover in bovine cumulus-oocyte complexes, cumulus cells and denuded oocytes, and affects in vitro fertilization outcome

High-protein diets often lead to an increase in urea concentration in follicular fluid of dairy cows, which may reduce oocyte competence. In the present study, maturation media were supplemented with urea (0, 20, 40 mg/dl), and amino acids (AAs) turnover was evaluated in the 24-h spent media of specimens (cell types), bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), or denuded oocytes (DOs). The main effects of urea and cell type, and their interaction were significant on the individual turnover (expect threonine, glycine, and tyrosine) and total turnover, depletion, and appearance of AAs. The results showed a high level of urea and DOs increased the depletion of all AAs and that of essential and non-AAs, respectively. Sensitivity analysis revealed the highest sensitivity of isoleucine, lysine, and tryptophan to urea, especially in DOs. Principal component analysis (PCA) evaluated the strong correlations between the turnover of: (1) glutamine, aspartic acid or glycine, and developmental competence and fertilization of COCs; (2) serine, isoleucine, valine or glutamic acid, and cleavage rate of DOs; and (3) serine, glutamine, aspartic acid or alanine, and CCs viability. In conclusion, urea significantly changed the turnover of AAs by COCs, CCs and DOs, and reduced the subsequent developmental competence of bovine oocytes.

Positive Regulation of Decidualization by l-Type Amino Acid Transporter 1 (lat1) in Pregnant Mice

Amino acids have an important role in the pre and post implantation of placenta and embryo development. l-type amino-acid transporter 1 (lat1) is responsible for the transportation of large neutral amino acids and is mainly expressed in human fetal liver, placenta, brain, etc. This study is the first to investigate the expression of lat1 in the early pregnancy of mouse uteri and its role in the process of decidualization. Endometrial stromal cells of a mouse model were used to evaluate decidualization from Day 4–8 of pregnancy in vitro followed by lat1 knock down by small interfering RNA and by a competitive inhibitor of Leucine transport 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH). The effects of lat1 on decidualization in vivo were assessed by injecting BCH into the uterine horns. The mRNA and protein expressions of lat1 in the implantation sites were higher than that in the inter-implantation sites and were localized in the luminal and gland epithelium, stromal and decidual cells. Its increased expression (p < 0.05) was associated with artificial decidualization as well as activation of prl expression. Down-regulation of lat1 expression in these cells by siRNA and BCH inhibited the decidual progression in vitro. Inhibition of lat1 transportation by BCH controlled decidual progression in vivo also accompanied the down-regulation of prl, lat1 expression in the decidual area and embryo size on Day 8 of pregnancy. In conclusion, these results revealed that lat1 might play an important role in the decidual progression both in vitro and in vivo.

Ovarian ageing: the role of mitochondria in oocytes and follicles

BACKGROUND

There is a great inter-individual variability of ovarian ageing, and almost 20% of patients consulting for infertility show signs of premature ovarian ageing. This feature, taken together with delayed childbearing in modern society, leads to the emergence of age-related ovarian dysfunction concomitantly with the desire for pregnancy. Assisted reproductive technology is frequently inefficacious in cases of ovarian ageing, thus raising the economic, medical and societal costs of the procedures.

OBJECTIVE AND RATIONAL

Ovarian ageing is characterized by quantitative and qualitative alteration of the ovarian oocyte reserve. Mitochondria play a central role in follicular atresia and could be the main target of the ooplasmic factors determining oocyte quality adversely affected by ageing. Indeed, the oocyte is the richest cell of the body in mitochondria and depends largely on these organelles to acquire competence for fertilization and early embryonic development. Moreover, the oocyte ensures the uniparental transmission and stability of the mitochondrial genome across the generations. This review focuses on the role played by mitochondria in ovarian ageing and on the possible consequences over the generations.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed original articles and reviews concerning mitochondria and ovarian ageing, in animal and human species. Searches were performed using keywords belonging to three groups: 'mitochondria' or 'mitochondrial DNA'; 'ovarian reserve', 'oocyte', 'ovary' or 'cumulus cells'; and 'ageing' or 'ovarian ageing'. These keywords were combined with other search phrases relevant to the topic. References from these articles were used to obtain additional articles.

OUTCOMES

There is a close relationship, in mammalian models and humans, between mitochondria and the decline of oocyte quality with ageing. Qualitatively, ageing-related mitochondrial (mt) DNA instability, which leads to the accumulation of mtDNA mutations in the oocyte, plays a key role in the deterioration of oocyte quality in terms of competence and of the risk of transmitting mitochondrial abnormalities to the offspring. In contrast, some mtDNA haplogroups are protective against the decline of ovarian reserve. Quantitatively, mitochondrial biogenesis is crucial during oogenesis for constituting a mitochondrial pool sufficiently large to allow normal early embryonic development and to avoid the untimely activation of mitochondrial biogenesis. Ovarian ageing also seriously affects the dynamic nature of mitochondrial biogenesis in the surrounding granulosa cells that may provide interesting alternative biomarkers of oocyte quality.

WIDER IMPLICATIONS

A fuller understanding of the involvement of mitochondria in cases of infertility linked to ovarian ageing would contribute to a better management of the disorder in the future.

Cumulus Cell Mitochondrial Resistance to Stress In Vitro Predicts Oocyte Development During Assisted Reproduction

CONTEXT

Complex cumulus cell-oocyte interactions govern energy utilization during oocyte development.

OBJECTIVE

This study investigates the relationship of cumulus cell mitochondria with oocyte development during ovarian stimulation for in vitro fertilization (IVF).

DESIGN

This is a prospective cohort study.

SETTING

The setting was an academic center.

PATIENTS

Thirty women underwent ovarian stimulation for IVF.

INTERVENTION(S)

Pooled cumulus cells were collected; numbers of total and mature oocytes and two-pronuclear (day 1), six- to eight-cell cleavage (day 3), and blastocyst (day 5) embryos were recorded.

MAIN OUTCOME MEASURE(S)

A mitochondrial bioassay was developed with Jurkat cells and used with cumulus cells from IVF patients to correlate mitochondrial membrane potential resistance to carbonyl cyanide 3-chlorophenylhydrazone (CCCP) stress with oocyte development and embryogenesis.

RESULTS

Adjusting for FSH administered and maternal age, cumulus cell mitochondrial membrane potential resistance to CCCP positively correlated with numbers of total (P < .025) and mature (P < .025) oocytes retrieved. The highest oocyte numbers that correlated with cumulus cell mitochondrial membrane potential occurred in women with the greatest ovarian response to FSH (mitochondrial membrane potential resistance to CCCP-log FSH interactions: total oocytes P < .025; mature oocytes P < .05). Multiple regression modeling of mature oocyte numbers, age, and cumulus cell mitochondrial membrane potential resistance to CCCP showed that numbers of mature oocytes best correlated with numbers of embryos at all stages (P < .0001).

CONCLUSION

During ovarian stimulation for IVF, cumulus cell mitochondrial membrane potential resistance to stress correlates with numbers of total and mature oocytes retrieved, suggesting that cumulus cell-oocyte interactions involving energy facilitate oocyte development.

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

In the mammalian ovary, each oocyte grows and develops within its own structural and developmental niche-the follicle. Together with the female germ cell in the follicle are somatic granulosa cells, specialized companion cells that surround the oocyte and provide support to it, and an outer layer of thecal cells that serve crucial roles including steroid synthesis. These follicular compartments function as a single physiological unit whose purpose is to produce a healthy egg, which upon ovulation can be fertilized and give rise to a healthy embryo, thus enabling the female germ cell to fulfill its reproductive potential. Beginning from the initial stage of follicle formation and until terminal differentiation at ovulation, oocyte and follicle growth depend absolutely on cooperation between the different cellular compartments. This cooperation synchronizes the initiation of oocyte growth with follicle activation. During growth, it enables metabolic support for the follicle-enclosed oocyte and allows the follicle to fulfill its steroidogenic potential. Near the end of the growth period, intra-follicular interactions prevent the precocious meiotic resumption of the oocyte and ensure its nuclear differentiation. Finally, cooperation enables the events of ovulation, including meiotic maturation of the oocyte and expansion of the cumulus granulosa cells. In this chapter, we discuss the cellular interactions that enable the growing follicle to produce a healthy oocyte, focusing on the communication between the germ cell and the surrounding granulosa cells.

HUMAN FOLLICLE STIMULATING HORMONE (hFSH) AND THYROXINE (T4) IN SURVIVAL MAINTENANCE AND IN VITRO GROWTH PROMOTION OF CAPRINE PREANTRAL FOLLICLES

The aim of this study was to investigate the interaction of human FSH (10ng/ml) with T4 (20ng/mL) on survival, activation and growth of preantral follicles cultured in vitro for 28 days. Fragments of non-cultured and cultured ovarian tissue were processed for classic histology and transmission electron microscopy. The results showed a reduction in the survival rate in all the media tested (one to 28 days) when compared to the fresh control. However the treatment with T4/hFSH for seven days of culture maintained the rate similar to the control. The media tested by one and 28 days reduced the percentage of primordial follicles in all periods of culture. However, T4/hFSH on day one of culture remained similar to the fresh control. None of the media were able to keep the percentage of the developing follicles. It was observed that the follicular diameter in the medium with T4/hFSH remained similar to the fresh control. The ultrastructural analysis confirmed the integrity of follicles cultured for seven days in a medium supplemented with T4/hFSH. In conclusion, the medium with T4/hFSH is able to maintain the survival, promote the activation, and the ultrastructural integrity of caprine preantral follicles for until seven days.

Mcl-1 is a key regulator of the ovarian reserve

A majority of ovarian follicles are lost to natural death, but the disruption of factors involved in maintenance of the oocyte pool results in a further untimely follicular depletion known as premature ovarian failure. The anti-apoptotic B-cell lymphoma 2 (Bcl-2) family member myeloid cell leukemia-1 (MCL-1) has a pro-survival role in various cell types; however, its contribution to oocyte survival is unconfirmed. We present a phenotypic characterization of oocytes deficient in Mcl-1, and establish its role in maintenance of the primordial follicle (PMF) pool, growing oocyte survival and oocyte quality. Mcl-1 depletion resulted in the premature exhaustion of the ovarian reserve, characterized by early PMF loss because of activation of apoptosis. The increasingly diminished surviving cohort of growing oocytes displayed elevated markers of autophagy and mitochondrial dysfunction. Mcl-1-deficient ovulated oocytes demonstrated an increased susceptibility to cellular fragmentation with activation of the apoptotic cascade. Concomitant deletion of the pro-apoptotic Bcl-2 member Bcl-2-associated X protein (Bax) rescued the PMF phenotype and ovulated oocyte death, but did not prevent the mitochondrial dysfunction associated with Mcl-1 deficiency and could not rescue long-term breeding performance. We thus recognize MCL-1 as the essential survival factor required for conservation of the postnatal PMF pool, growing follicle survival and effective oocyte mitochondrial function.

Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes

Obesity, diabetes, and related metabolic disorders are major health issues worldwide. As the epidemic of metabolic disorders continues, the associated medical co-morbidities, including the detrimental impact on reproduction, increase as well. Emerging evidence suggests that the effects of maternal nutrition on reproductive outcomes are likely to be mediated, at least in part, by oocyte metabolism. Well-balanced and timed energy metabolism is critical for optimal development of oocytes. To date, much of our understanding of oocyte metabolism comes from the effects of extrinsic nutrients on oocyte maturation. In contrast, intrinsic regulation of oocyte development by metabolic enzymes, intracellular mediators, and transport systems is less characterized. Specifically, decreased acid transport proteins levels, increased glucose/lipid content and elevated reactive oxygen species in oocytes have been implicated in meiotic defects, organelle dysfunction and epigenetic alteration. Therefore, metabolic disturbances in oocytes may contribute to the diminished reproductive potential experienced by women with metabolic disorders. In-depth research is needed to further explore the underlying mechanisms. This review also discusses several approaches for metabolic analysis. Metabolomic profiling of oocytes, the surrounding granulosa cells, and follicular fluid will uncover the metabolic networks regulating oocyte development, potentially leading to the identification of oocyte quality markers and prevention of reproductive disease and poor outcomes in offspring.

Dynamic medium containing growth differentiation factor-9 and FSH maintains survival and promotes in vitro growth of caprine preantral follicles after long-term in vitro culture

The aim of the present study was to evaluate the effects of growth differentiation factor 9 (GDF-9) and FSH on the in vitro development of caprine preantral follicles cultured for 16 days. Ovarian fragments were cultured in αMEM+ (α-minimum essential medium, pH 7.2–7.4, 10 μg mL–1 insulin, 5.5 μg mL–1 transferrin, 5.0 ng mL–1 selenium, 2 mM glutamine, 2 mM hypoxanthine and 1.25 mg mL–1 bovine serum albumin) in the absence or presence of 200 ng mL–1 GDF-9 and/or 50 ng mL–1 FSH added during the first (Days 0–8) and/or second (Days 8–16) half of the culture period. Non-cultured and cultured fragments were processed for histological and ultrastructural analyses. After 16 days, all treatments using GDF-9 or FSH showed higher rates of follicular survival compared with αMEM+ alone. Compared with non-cultured control, sequential culture media containing GDF-9 and/or FSH significantly increased the percentage of developing follicles and follicle diameter. Moreover, a progressive increase in oocyte diameter was observed only with sequential culture medium containing GDF-9 until Day 8 followed by FSH (GDF-9/FSH) in the second half of the culture period. After 16 days of culture, ultrastructural analysis confirmed the integrity of follicles cultured in the presence of GDF-9/FSH. In conclusion, a dynamic medium containing GDF-9 and FSH (GDF-9/FSH) maintained follicular integrity and promoted activation of primordial follicles and growth during long-term in vitro culture of goat preantral follicles.

Measuring transport and accumulation of radiolabeled substrates in oocytes and embryos

Radiolabeled compounds that are substrates for transmembrane transporters can be used to study transport and metabolism in mammalian oocytes and preimplantation embryos. Because even very small amounts of radioisotopes can be detected, these techniques are feasible to use with only a few oocytes or embryos, even down to the level of single oocytes or embryos. Here, we describe the methods for determining the transport and accumulation of radiolabeled compounds into oocytes and preimplantation embryos and the determination of the rate of saturable transport via specific transporters in the plasma membrane.

Molecular control of oogenesis

Oogenesis is a complex process regulated by a vast number of intra- and extra-ovarian factors. Oogonia, which originate from primordial germ cells, proliferate by mitosis and form primary oocytes that arrest at the prophase stage of the first meiotic division until they are fully-grown. Within primary oocytes, synthesis and accumulation of RNAs and proteins throughout oogenesis are essential for oocyte growth and maturation; and moreover, crucial for developing into a viable embryo after fertilization. Oocyte meiotic and developmental competence is gained in a gradual and sequential manner during folliculogenesis and is related to the fact that the oocyte grows in interaction with its companion somatic cells. Communication between oocyte and its surrounding granulosa cells is vital, both for oocyte development and for granulosa cells differentiation. Oocytes depend on differentiated cumulus cells, which provide them with nutrients and regulatory signals needed to promote oocyte nuclear and cytoplasmic maturation and consequently the acquisition of developmental competence.The purpose of this article is to summarize recent knowledge on the molecular aspects of oogenesis and oocyte maturation, and the crucial role of cumulus-cell interactions, highlighting the valuable contribution of experimental evidences obtained in animal models. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Spinal cord injury induced arrest in estrous cycle of rats is ameliorated by S-nitrosoglutathione: novel therapeutic agent to treat amenorrhea

INTRODUCTION

Amenorrhea following spinal cord injury (SCI) has been well documented. There has been little research on the underlying molecular mechanisms and therapeutics.

AIM

The purpose of the present study was to investigate the effect of GSNO in ameliorating SCI-induced amenorrhea through affecting the expression of CX43, NFkB, and ERβ protein.

METHODS

SCI was induced in female SD rats at the T9-T10 level. Estrous stage was determined by vaginal smear. GSNO (50 µg/kg body weight) was gavage fed daily. Animals were sacrificed on day 7 and 14 post SCI. Ovaries were fixed for histological and biochemical studies. Expression levels of ERβ, CX-43, and NFkB were analyzed by Western blot and immunofluorescence.

MAIN OUTCOME MEASURES

GSNO hastens resumption of the estrous cycle following SCI-induced transient arrest.

RESULTS

Resumption of estrous cycle was hastened by GSNO. Atretic and degenerating follicles seen in the ovary of SCI rats on day 14 post-SCI were decreased in GSNO treated animals. The increased CX43 expression observed with SCI ovary was decreased by GSNO. ERβ expression decreased significantly on day 7 and 14 post-SCI and was restored with GSNO treatment. Following SCI, NFkB expression was increased in the ovarian follicles and the expression was reduced with GSNO administration. The number of terminal deoxynucleotidyl transferase-mediated biotinylated uridine triphosphate (UTP) nick end labeling positive follicular and luteal cells was increased after SCI. GSNO-treated animals had significantly fewer apoptotic cells in the ovary.

CONCLUSION

SCI-induced amenorrhea is accompanied by an increase in CX43 expression and a decrease in ERβ expression. SCI animals treated with GSNO resumed the estrous cycle significantly earlier. These results indicate a potential therapeutic value for GSNO in treating amenorrhea among SCI patients.

Amino acid transport system L activity in developing mouse ovarian follicles

BACKGROUND

Little is known about metabolic processes in the developing ovarian follicle. Using mouse ovarian follicles, we investigated uptake of L-leucine by follicles at varying stages of maturity in the presence of insulin-like growth factor (IGF)-1. METHODS Mouse ovarian follicles were cultured in vitro for 5 days in increasing concentrations of IGF-1, and follicle diameter and atresia measured as endpoints for growth. Uptake of (3)H-leucine was measured in follicles at different stages of development. In optimal IGF-1-mediated growth conditions, competitive inhibition of (3)H-leucine uptake by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), a non-metabolizable substrate analogue of L-leucine, was performed to demonstrate specificity of influx, via system L transporters. To test whether uptake rates were dependent on intracellular amino acid availability, follicles from in vitro cultures were pre-treated with L-phenylalanine prior to (3)H-leucine uptake.

RESULTS

Follicle development (P< 0.001) and survival (P< 0.001) increased with IGF-1 treatment. As pre-antral follicles progressed to late antral stage, we observed an increase in L-leucine uptake, which was reduced in pre-ovulatory follicles. BCH decreased L-leucine uptake rates in early antral (P< 0.05), antral (P< 0.001) and pre-ovulatory follicles (P< 0.01). L-leucine influx increased in follicles preloaded with phenylalanine (trans-stimulation). In follicles lacking free intracellular amino acids (zero-trans suppression), uptake rate was reduced (P< 0.05).

CONCLUSIONS

These results demonstrate, for the first time, evidence of specific system L amino acid transport in intact, mouse ovarian follicles and profile L-leucine uptake during folliculogenesis. A better understanding of ovarian follicle metabolic pathways is necessary for improved in vitro maturation as well as determining the impact of altered metabolism on fertility.

Hydrogen peroxide fuels aging, inflammation, cancer metabolism and metastasis: the seed and soil also needs "fertilizer"

In 1889, Dr. Stephen Paget proposed the "seed and soil" hypothesis, which states that cancer cells (the seeds) need the proper microenvironment (the soil) for them to grow, spread and metastasize systemically. In this hypothesis, Dr. Paget rightfully recognized that the tumor microenvironment has an important role to play in cancer progression and metastasis. In this regard, a series of recent studies have elegantly shown that the production of hydrogen peroxide, by both cancer cells and cancer-associated fibroblasts, may provide the necessary "fertilizer," by driving accelerated aging, DNA damage, inflammation and cancer metabolism, in the tumor microenvironment. By secreting hydrogen peroxide, cancer cells and fibroblasts are mimicking the behavior of immune cells (macrophages/neutrophils), driving local and systemic inflammation, via the innate immune response (NFκB). Thus, we should consider using various therapeutic strategies (such as catalase and/or other anti-oxidants) to neutralize the production of cancer-associated hydrogen peroxide, thereby preventing tumor-stroma co-evolution and metastasis. The implications of these findings for overcoming chemo-resistance in cancer cells are also discussed in the context of hydrogen peroxide production and cancer metabolism.

Understanding the Warburg effect and the prognostic value of stromal caveolin-1 as a marker of a lethal tumor microenvironment

Cancer cells show a broad spectrum of bioenergetic states, with some cells using aerobic glycolysis while others rely on oxidative phosphorylation as their main source of energy. In addition, there is mounting evidence that metabolic coupling occurs in aggressive tumors, between epithelial cancer cells and the stromal compartment, and between well-oxygenated and hypoxic compartments. We recently showed that oxidative stress in the tumor stroma, due to aerobic glycolysis and mitochondrial dysfunction, is important for cancer cell mutagenesis and tumor progression. More specifically , increased autophagy/mitophagy in the tumor stroma drives a form of parasitic epithelial-stromal metabolic coupling. These findings explain why it is effective to treat tumors with either inducers or inhibitors of autophagy, as both would disrupt this energetic coupling. We also discuss evidence that glutamine addiction in cancer cells produces ammonia via oxidative mitochondrial metabolism. Ammonia production in cancer cells, in turn, could then help maintain autophagy in the tumor stromal compartment. In this vicious cycle, the initial glutamine provided to cancer cells would be produced by autophagy in the tumor stroma. Thus, we believe that parasitic epithelial-stromal metabolic coupling has important implications for cancer diagnosis and therapy, for example, in designing novel metabolic imaging techniques and establishing new targeted therapies. In direct support of this notion, we identified a loss of stromal caveolin-1 as a marker of oxidative stress, hypoxia, and autophagy in the tumor microenvironment, explaining its powerful predictive value. Loss of stromal caveolin-1 in breast cancers is associated with early tumor recurrence, metastasis, and drug resistance, leading to poor clinical outcome.

Transcriptional effect of the LH surge in bovine granulosa cells during the peri-ovulation period

The LH surge induces a multitude of events that are essential for ovulation and corpus luteum formation. The transcriptional responses to the LH surge of preovulatory granulosa cells (GCs) are complex and still poorly understood. In this study, a genome-wide bovine oligo array was used to determine how the gene expression profile of GCs is modulated by the LH surge. GCs from three different stages were used to assess the short- and long-term effects of this hormone on follicle differentiation: 1) 2 h before induction of the LH surge, 2) 6 h and 3) 22 h after the LH surge. The results obtained were a list of differentially expressed transcripts for each GC group. To provide a comprehensive understanding of the processes at play, biological annotations were used to reveal the different functions of transcripts, confirming that the LH surge acts in a temporal manner. The pre-LH group is involved in typical tasks such as cell division, development, and proliferation, while the early response to the LH surge included features such as response to stimulus, vascularization, and lipid synthesis, which are indicative of cells preparing for ovulation. The late response of GCs revealed terms associated with protein localization and intracellular transport, corresponding to the future secretion task that will be required for the transformation of GCs into corpus luteum. Overall, results described in this study provide new insights into the different transcriptional steps that GCs go through during ovulation and before luteinization.

Bidirectional communication between oocytes and follicle cells: ensuring oocyte developmental competence

Female fertility is determined to a large extent by the quality (developmental competence) of the oocyte as reflected in its ability to undergo meiosis, be fertilized, and give rise to a healthy embryo. Growth of the mammalian oocyte is coordinated with that of the follicle that encloses it by the actions of signals that pass in both directions between the germline and somatic components. This review summarizes what is known about the roles played by 2 different modes of intrafollicular signalling in oogenesis: paracrine factors activating receptors on the opposite cell type, and direct sharing of small molecules throughout the follicle via gap junction channels. Recent evidence indicates that these 2 modes of signalling interact to regulate oocyte growth and granulosa cell proliferation and that defects in either can contribute to female infertility.

Noninvasive index of cryorecovery and growth potential for human follicles in vitro

Cryopreservation of oocytes and embryos is commonly used to preserve fertility. However, women undergoing cancer treatment may not have the time or may not be good candidates for these options. Ovarian cortical tissue cryopreservation and subsequent tissue transplant has been proven successful yet inefficient in preserving larger secondary follicles, and is not recommended as a fertility preservation option for women with certain cancers. We evaluated cryopreservation of individual follicles as an alternative option in rodents, nonhuman primates, and human primates. Under optimal conditions, cryopreserved mouse secondary follicles were able to reestablish granulosa cell-oocyte interactions, which are essential for subsequent follicle growth. Individual secondary follicles survived cryopreservation, were able to be cultured in a three-dimensional alginate hydrogel matrix to the antral stage, and the enclosed oocytes were competent for fertilization. Using a vital imaging technique (pol-scope) employed in many fertility centers, we were able to bioassay the thawed, cultured follicles for the presence of transzonal connections between the somatic and germ cells. Perturbations in these linkages were shown to be reversed when follicles were cryopreserved under optimal freezing conditions. We applied the optimized cryopreservation protocol to isolated rhesus monkey and human secondary follicles, and using the birefringent bioassay, we were able to show good correlation between early follicle growth and healthy somatic cell-oocyte connections. Our results suggest that ovarian follicles can be cryopreserved, thawed, and analyzed noninvasively, making follicle preservation an additional option for young cancer patients.

Amino Acid transport mechanisms in mouse oocytes during growth and meiotic maturation

Amino acids are transported into cells by a number of different transport systems, each with their own specific range of substrates. The amino acid transport systems active in preimplantation embryos and the amino acids required by embryos for optimal development have been extensively investigated. Much less is known about amino acid transport systems active in growing and meiotically maturing oocytes or about developmental changes in their activity. As a first step in determining the array of amino acid transporters active in oocytes, the transport characteristics of nine amino acids were measured in small, medium, and large growing oocytes; in fully grown germinal vesicle (GV)-stage oocytes; in metaphase I oocytes; and in metaphase II eggs. Whether each of 11 classically defined amino acid transport systems was likely active in oocytes at each stage was determined using assays based on measuring the transport of radiolabeled amino acids into oocytes and the effect of a limited set of potential competitive inhibitors. Six amino acid transport systems were found to be active during oocyte growth or maturation. L, b(0,+), and ASC/asc were active throughout oocyte growth and maturation, increasing during growth. In contrast, GLY, beta, and x(c)(-) had little or no activity during growth but became activated during meiotic maturation. Surprisingly, the presence of follicular cells surrounding medium growing oocytes or cumulus cells surrounding GV oocytes did not confer amino acid transport by additional transport systems not present in the oocyte. In some cases, however, follicular cells coupled to the oocyte enhanced uptake of amino acids by the same systems present in the oocyte.

Regulation of intracellular pH during oocyte growth and maturation in mammals

Regulation of intracellular pH (pH(i)) is a fundamental homeostatic process essential for the survival and proliferation of virtually all cell types. The mammalian preimplantation embryo, for example, possesses Na(+)/H(+) and HCO(3)(-)/Cl(-) exchangers that robustly regulate against acidosis and alkalosis respectively. Inhibition of these transporters prevents pH corrections and, perhaps unsurprisingly, leads to impaired embryogenesis. However, recent studies have revealed that the role and regulation of pH(i) is somewhat more complex in the case of the developing and maturing oocyte. Small meiotically incompetent growing oocytes are apparently incapable of regulating their own pH(i), and instead rely upon the surrounding granulosa cells to correct ooplasmic pH, until such a time that the oocyte has developed the capacity to regulate its own pH(i). Later, during meiotic maturation, pH(i)-regulating activities that were developed during growth are inactivated, apparently under the control of MAPK signalling, until the oocyte is successfully fertilized. Here, we will discuss pH homeostasis in early mammalian development, focussing on recent developments highlighting the unusual and unexpected scenario of pH regulation during oocyte growth and maturation.

Disruption of bidirectional oocyte-cumulus paracrine signaling during in vitro maturation reduces subsequent mouse oocyte developmental competence

Oocyte-cumulus cell bidirectional communication is essential for normal development of the oocyte and cumulus cells (CCs) within the follicle. We showed recently that addition of recombinant growth differentiation factor 9 (GDF9), which signals through the SMAD2/3 pathway, during mouse oocyte in vitro maturation (IVM) increased fetal viability. This study thus aimed to observe the effects of disrupting oocyte-CC bidirectional communication during IVM on oocyte developmental competence and fetal outcomes. Cumulus-oocyte complexes (COCs) from equine chorionic gonadotropin-primed prepubertal (CBA/C57BL6) mice were cultured with or without 50 mIU/ml follicle-stimulating hormone (FSH) and 10 ng/ml epidermal growth factor (EGF) or 4 muM SMAD2/3 inhibitor SB-431542. Cumulus expansion and first polar body extrusion were then assessed, or COCs were fertilized and stained to evaluate sperm entry or cultured to the blastocyst stage. Embryo development and blastocyst quality were assessed, and Day 4.5 blastocysts were transferred to pseudopregnant recipients to analyze fetal outcomes. SMAD2/3 inhibition or FSH/EGF absence during IVM resulted in decreased cumulus expansion. First polar body extrusion and sperm entry were decreased in the absence of FSH/EGF, whereas only sperm entry was affected in SB-431542-matured COCs. Embryo development and blastocyst rates were unaffected; however, blastocyst quality was significantly altered, with reduced inner cell mass cell numbers in embryos derived from COCs matured in both treatments. When COCs were matured with SB-431542 in the absence of FSH/EGF, cumulus expansion was reduced, but fertilization, embryo development, and embryo quality were not. Inhibition of SMAD2/3 signaling in the presence of FSH/EGF significantly reduced fetal survival but had no effect on implantation or fetal and placental dimensions and morphology.

Mouse oocyte control of granulosa cell development and function: paracrine regulation of cumulus cell metabolism

Bidirectional communication between oocytes and the companion granulosa cells is essential for the development and functions of both compartments. Oocytes are deficient in their ability to transport certain amino acids and in carrying out glycolysis and cholesterol biosynthesis. Cumulus cells must provide them with the specific amino acids and the products in these metabolic pathways. Oocytes control metabolic activities in cumulus cells by promoting the expression of genes in cumulus cells encoding specific amino acid transporters and enzymes essential for the oocyte-deficient metabolic processes. Hence oocytes outsource metabolic functions to cumulus cells to compensate for oocyte metabolic deficiencies. Oocyte control of granulosa cell metabolism may also participate in regulating the rate of follicular development in coordination with endocrine, paracrine, and autocrine signals. Oocytes influence granulosa cell development mainly by secretion of paracrine factors, although juxtacrine signals probably also participate. Key oocyte-derived paracrine factors include growth differentiation factor 9, bone morphogenetic protein 15, and fibroblast growth factor 8B.