Rat oocytes induced to mature by epidermal growth factor are successfully fertilized

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

Ganglioside GD1a promotes oocyte maturation, furthers preimplantation development, and increases blastocyst quality in pigs

Gangliosides are key lipid molecules required for the regulation of cellular processes such as proliferation, differentiation, and cell signaling, including signaling of epidermal growth factor receptor (EGFR). Epidermal growth factor (EGF) has long been considered a potential regulator of meiotic and cytoplasmic maturation in mammalian oocytes. However, there is no report on the direct effect of ganglioside GD1a in porcine oocyte maturation. In this study, we first investigated a functional link between GD1a and meiotic maturation during in vitro maturation (IVM) of porcine embryos. Moreover, we confirmed the effect of exogenous GD1a treatment on blastocyst development, quality, and fertilization rate in early embryonic development. First, we observed that the protein level of ST3GAL2, a GD1a synthesizing enzyme, significantly increased (P < 0.01) in cumulus-oocyte-complexes (COCs) during IVM progress. The proportion of arrested germinal vesicles (GV) increased in oocytes treated with EGF+GD1a (41.6 ± 1.5%) at the IVM I stage. Upon completion of meiotic maturation, the proportion of metaphase II (M II) was significantly higher (P < 0.05) in the EGF+GD1a (89.9 ± 3.6%) treated group. After IVF, the percentage of penetrated oocytes was significantly higher (P < 0.05) in the EGF+GD1a (89.1 ± 2.3%) treated group than in the control group. Furthermore, exogenous GD1a treatment improved the developmental competence and quality of blastocysts during preimplantation embryo development stage. These results suggest that ganglioside GD1a may play an important role in IVM mechanisms of porcine maturation capacity. Furthermore, our findings will be helpful for better promoting the embryo development and blastocyst quality in pigs.

Optimized Protocols for In Vitro Maturation of Rat Oocytes Dramatically Improve Their Developmental Competence to a Level Similar to That of Ovulated Oocytes

The developmental capacity of in vitro-matured (IVM) oocytes is markedly lower than that of their in vivo-matured (IVO) counterparts, suggesting the need for optimization of IVM protocols in different species. There are few studies on IVM of rat oocytes, and there are even fewer attempts to improve ooplasmic maturation compared to those reported in other species. Furthermore, rat oocytes are well known to undergo spontaneous activation (SA) after leaving the oviduct; however, whether IVM rat oocytes have lower SA rates than IVO oocytes and can potentially be used for nuclear transfer is unknown. In this study, we investigated the effects of maturation protocols on cytoplasmic maturation of IVM rat oocytes and observed the possibility to reduce SA by using IVM rat oocytes. Ooplasmic maturation was assessed using multiple markers, including pre- and postimplantation development, meiotic progression, CG redistribution, redox state, and the expression of developmental potential- and apoptosis-related genes. The results showed that the best protocol consisting of modified Tissue Culture Medium-199 (TCM-199) supplemented with cysteamine/cystine and the cumulus cell monolayer dramatically improved the developmental competence of rat oocytes and supported both pre- and postimplantation development and other ooplasmic maturation makers to levels similar to that observed in ovulated oocytes. Rates of SA were significantly lower in IVM oocytes than in IVO oocytes when observed at the same intervals after nuclear maturation. In conclusion, we have optimized protocols for IVM of rat oocytes that sustain ooplasmic maturation to a level similar to ovulated oocytes. The results suggest that IVM rat oocytes might be used to reduce SA for rat cloning.

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

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

Epidermal growth factor-like growth factors in the follicular fluid: role in oocyte development and maturation

The growth and maturation of the ovarian follicle requires the coordinate function of somatic cells and the oocyte. Over the past three decades, numerous growth factors involved in the bidirectional signals between the somatic and germ cells have been identified. A possible function of epidermal growth factor (EGF) signaling at selected stages of follicle maturation had been proposed early on and is supported by many observations of in vitro effects of this growth factor on steroidogenesis, oocyte maturation, and cumulus expansion. However, attempts to link EGF levels in the follicular fluid with the state of follicle and oocyte maturation have been inconclusive. More recently, data generated using mouse genetic models perturbing ovulation and fertility indicate that EGF-like growth factors, rather than EGF itself, accumulate in the follicle at the time of ovulation. EGF-like growth factor mRNA is regulated by the luteinizing hormone surge, and corresponding proteins are detected in the follicle. The EGF-like growth factors amphiregulin, epiregulin, and betacellulin are potent stimulators of oocyte maturation and cumulus expansion, and perturbation of this EGF network in vivo impairs ovulation. Similar findings in species other than the mouse confirm an important physiological role for this network at the time of ovulation. Whether this network also plays a critical role in humans and whether it can be used as a biological marker of follicle development or for the improvement of fertility remains to be determined. This review summarizes the most recent findings on the EGF network during ovulation and the potential clinical applications of manipulating this intercellular communication pathway in the control of fertility.

EGF-like peptides mediate FSH-induced maturation of cumulus cell-enclosed mouse oocytes

This study was carried out to examine the participation of epidermal growth factor (EGF)-like peptides in the induction of germinal vesicle breakdown (GVB) in mouse cumulus cell-enclosed oocytes (CEO). The EGF-like peptide, amphiregulin (AR), dose-dependently stimulated meiotic resumption in CEO, but not denuded oocytes (DO) maintained in meiotic arrest with 300 microM dbcAMP. The EGF receptor (EGFR) kinase inhibitor, AG1478, blocked meiotic resumption induced by FSH and AR in CEO, but had no effect in DO. FSH-induced maturation was also suppressed by antisera to both EGFR and EGF. Maturation occurred with slightly faster kinetics in AR-stimulated CEO when compared to FSH-stimulated CEO. When CEO were maintained in meiotic arrest with a low level of dbcAMP, FSH was initially inhibitory to maturation and later stimulatory; the stimulatory phase was prevented by AG1478, indicating mediation by EGF-like peptides. Pulsing CEO with high levels of dbcAMP also stimulated GVB and could be blocked by AG1478. Treatment of arrested CEO with PKC agonists stimulated maturation and this was prevented with AG1478 as well as antibodies to EGFR. FSH-induced maturation of dbcAMP-arrested CEO was blocked by bisindolylmaleimide I (BIM-I), an inhibitor of PKC, implicating PKC in FSH action. EGF-stimulated CEO failed to resume maturation in the presence of glycerrhetinic acid, a gap junction inhibitor, suggesting transfer of positive signal through the cell-cell coupling pathway. These data support the idea that EGF-like peptides provide a common pathway mediating the meiosis-inducing influence of FSH, cAMP pulsing, and PKC activation in mouse CEO by a gap junction-dependent process.

Effect of Prolactin in the Absence of hCG on Maturation, Fertilization, and Embryonic Development of in Vitro Matured Mouse Oocytes

Oocyte maturation is a complex process involving both the progression of meiotic cycle and the reprogramming of cytoplasmic events. The aim of this study was to investigate the effects of prolactin (PRL) in the in vitro maturation (IVM) of preantral mouse oocytes, in the absence of human chorionic gonadotrophin (hCG). Mouse preantral follicles were collected from female mice without prior hormonal ovarian stimulation and were cultured in the presence of varying concentrations of PRL (20, 100, 200, and 300 ng/mL) for 12 days. A group of in vitro matured oocytes were assessed for polar body (PB) formation, while the rest were fertilized and embryonic development was recorded. The maturation of preantral mouse follicles, as well as their fertilization and cleavage rates, observed when the culture medium was supplemented with middle- and high-range doses of PRL was beneficially affected. This effect was considerably high, although the culture media lacked hCG, a hormone extensively used in modern ovulation induction regiments, as well as in IVM media.

GnRH actions on rat preovulatory follicles are mediated by paracrine EGF-like factors

Gonadotropin releasing hormone (GnRH) has been shown to mimic the actions of LH/hCG on oocyte maturation and ovulation. Recent studies demonstrated that induction of ovulation by LH/hCG is mediated, at least in part, by transactivation of epidermal growth factor receptors (EGFR) by autocrine/paracrine EGF-like factors activated by metalloproteases. Here we have examined whether the action of GnRH on the preovulatory follicles is exerted through similar mechanisms involving activation of EGFR. The EGFR kinase inhibitor, AG1478, inhibited GnRH-induced oocyte maturation in explanted follicles in vitro. Its inactive analog, AG43, did not affect GnRH-stimulated resumption of meiosis. GnRH, like LH, stimulated transient follicular expression of EGF-like agents, as well as rat cycloxygenase-2 (rCOX-2), rat hyaluronan synthase-2 (rHAS-2), and rat tumor necrosis factor-alpha-stimulated gene 6 (rTSG-6) mRNAs, known ovulatory enzymes. Likewise, GnRH stimulated follicular progesterone synthesis. Conversely AG1478 inhibited all these actions of GnRH. Furthermore, Galardin, a broad-spectrum metalloprotease inhibitor, blocked GnRH-induced oocyte maturation and follicular progesterone synthesis. In conclusion, we have demonstrated that follicular EGF-like factors mediate also the GnRH-stimulation of ovulatory changes, like these of LH/hCG.

G-protein-coupled receptor signaling and the EGF network in endocrine systems

The epidermal growth factor (EGF) network is composed of a complex array of growth factors synthesized as precursors and expressed on the cell surface. These latent growth factors are activated by cleavage and shedding from the cell surface and act by binding to various homo- and hetero-dimers of the EGF receptors (ErbBs). Although the exact molecular steps are poorly understood, ligand binding to G-protein-coupled receptors as diverse as the beta-adrenoceptors or the lysophosphatidic acid receptors leads to shedding of EGF growth factors and activation of EGF receptors. Recent observations from the pituitary and in the ovary are providing new insight into the role of this network in endocrine systems.

EGF-like factor epiregulin and amphiregulin expression is regulated by gonadotropins/cAMP in human ovarian follicular cells

Epiregulin and amphiregulin are growth factors involved in cancer development, but their potential role in signaling in the gonads is still obscure. We report here that basal expression of these growth factors is evident in human granulosa cells obtained from women treated for in vitro fertilization, when examined by RT-PCR using RNA isolated from primary cultures of ovarian granulosa cells. Expression of these factors was elevated concomitantly with elevation of progesterone production in these cells upon stimulation with luteinizing hormone (LH), and to a lesser extent with follicle stimulating hormone (FSH), both essential stimulants for ovulation and luteinization. Epiregulin and amphiregulin gene expression was dose- and time-dependent when measured subsequent to LH stimulation. Moreover, forskolin, which activates adenylate cyclase, was as efficient as LH in stimulating expression of these growth factors. It is suggested that upregulation of the epiregulin and amphiregulin expression is part of the signal transduction pathway which leads to ovulation and luteinization in the human ovary.

Effects of epidermal growth factor on early embryonic development after in vitro fertilization of oocytes collected from ewes treated with follicle stimulating hormone

Epidermal growth factor (EGF) has been shown to enhance the in vitro rate of blastocyst formation in several species. Follicular development was induced in ewes (n=15) by twice daily administration of FSH-P on Days 13 and 14 of the estrous cycle. Cumulus oocyte complexes (COCs) were collected from all visible follicles (n=25+/-2.4/ewe) on Day 15. COCs from each ewe were cultured separately for 24h in maturation medium (containing 10% serum, LH, FSH and estradiol) with (8.2+/-0.9 per ewe) or without (7.8+/-0.8 per ewe) EGF (10 ng/ml). Oocytes were then denuded by hyaluronidase treatment, and healthy oocytes were cultured in the presence of frozen-thawed semen in synthetic oviductal fluid (SOF) medium containing 2% sheep serum. After 18-20 h, zygotes were transferred to SOF medium without glucose and cultured for about 36 h until they reached the 4-8 cell stage. Embryos were transferred to SOF medium with glucose for further development. Medium was changed every other day until blastocyst formation on Day 8 of culture (Day 1=day of fertilization). The rate of embryonic development was evaluated throughout the culture period. After maturation, cumulus cells were more expanded in the presence than in the absence of EGF. The rates of fertilization (overall 75.7+/-3.9%) and morula formation (overall 40.6+/-7.1%) were similar (P>0.05) for COCs cultured with or without EGF. However, EGF increased (P<0.01) the number of blastocysts (1.4+/-0.1 versus 0.6+/-0.2 per ewe) and tended to increase (P<0.1) the rate of blastocyst formation (21.0+/-6.6% versus 13.4+/-4.3% per ewe). These data demonstrate that EGF increases blastocyst formation in FSH-treated ewes. Therefore, EGF is recommended as a supplement to maturation medium to enhance embryonic development in vitro in FSH-treated sheep.

Presence of epidermal growth factor during in vitro maturation of pig oocytes and embryo culture can modulate blastocyst development after in vitro fertilization

The present study examined the effect of epidermal growth factor (EGF) during in vitro maturation (IVM) and embryo culture on blastocyst development in the pig. In experiment 1, cumulus oocyte complexes were cultured in North Carolina State University (NCSU) 23 medium containing porcine follicular fluid, cysteine, hormonal supplements, and with or without EGF (0-40 ng/ml) for 20-22 hr. They then were cultured for an additional 20-22 hr without hormones. After maturation, cumulus-free oocytes were co-incubated with frozen-thawed spermatozoa for 5-6 hr. Putative embryos were transferred to NCSU 23 containing 0.4% BSA and cultured for 144 hr. In experiment 2, oocytes were matured in medium containing 10 ng/ml EGF, inseminated, and putative embryos were cultured in the presence of 0-40 ng/ml EGF. In experiment 3, oocytes were cultured in the presence of 0, 10 and 40 ng/ml EGF to examine the kinetics of meiotic maturation. In experiment 4, 2- to 4-cell and 8-cell to morula stage embryos derived from oocytes matured with 10 ng/ml EGF were transferred to the oviduct and uterus, respectively, of each of three recipient gilts (3 and 4 days post-estrus, respectively). The presence or absence of EGF during IVM did not affect cumulus expansion, nuclear maturation, fertilization parameters, or cleavage rate. However, compared to no addition (21%), presence of 1 (33%) and 10 ng/ml EGF (42%) during IVM increased (P < 0.01) the rate of blastocyst development in a concentration-dependent manner. Compared to 10 ng/ml EGF, higher concentrations (20 and 40 ng/ml) reduced (P < 0.01) blastocyst development in a concentration-dependent manner (35% and 24%, respectively). No difference was observed between no addition and 40 ng/ml EGF (22%). Compared to no addition and 10 ng/ml EGF, a significantly (P < 0.001) higher proportion (25% vs. 55%) of oocytes reached metaphase II stage 33 hr after IVM with 40 ng/ml EGF. However, no difference was observed at 44 hr. Transfer of embryos to six recipient gilts resulted in three pregnancies and birth of 18 piglets. The results show that EGF at certain concentrations in IVM medium can influence the developmental competence of oocytes. However, addition of EGF during the culture of pig embryos derived from oocytes matured in the presence of EGF is without effect. Birth of piglets provides evidence that embryos derived from oocytes matured in a medium containing EGF are viable.

Mechanisms leading to cortical reaction in the mammalian egg

Activation of the mammalian egg results in cortical reaction (CR), which is correlated with an increase in intracellular Ca2+ concentration and PKC activation. The CR is a gradual rather then an "all or none" response, and can be regulated by different concentrations of parthenogenetic activators. To evaluate the biological significance of parthenogenetic induced CR, rat eggs were fertilized or activated by different concentrations of ionomycin and TPA. Cortical granules (CG) were monitored by electron microscopy, while the CG exudate was visualized by Lens culinaris lectin and Texas Red, using light and confocal microscopy. The ability of the CR to trigger a full block to polyspermy was examined in an IVF system. Our study demonstrates the existence of light and dark CG, which differ by number, distribution in the egg cortex, and sensitivity to parthenogenetic activators. Sperm penetration or high concentration of activators, trigger depletion of both light and dark CG, leading to a full CR. Low concentration of activators altered the CG density, the ratio of dark/light CG, and induced partial CR that was sufficient to cause a block to polyspermy. The results imply that Ca2+ rise or PKC activation have different effects on light and dark CG. In recently fertilized or parthenogenetically activated eggs, CG exudate appeared as evenly distributed spots, whereas in more advanced stages of fertilization the exudate was scattered as patchy aggregates. This observation suggests a difference in the dispersion of CG exudate after fertilization as compared to parthenogenetic activation.

Mechanism of action of epidermal growth factor-induced porcine oocyte maturation

EGF has been reported to promote oocyte maturation in several species, although the mechanism of action is not yet known. The present study is designed to determine the pathway used by EGF to enhance porcine oocyte maturation. Oocytes were aspirated from 2-5 mm follicles and cultured with various treatments in Medium-199 at 37 degrees C, 100% relative humidity, and 5% CO2 for 48 hr for the maturation study and 3 hr for intracellular cAMP measurement. Although treatment with 100 IU/ml hCG stimulated both intracellular cAMP formation and oocyte maturation, 10 ng/ml EGF stimulated oocyte maturation only. Dibutyryl cAMP (dbcAMP) inhibited oocyte maturation at 10(-5), 10(-4), and 10(-3) M concentration s in the control medium. However, in the presence of 10 ng/ml EGF, dbcAMP inhibited oocyte maturation only at a concentration of 10(-3) M. Increasing concentrations of EGF (i.e., 25 and 50 ng/ml) were ineffective in overcoming the inhibitory effect of dbcAMP at 10(-3) M. In contrast, EGF reversed the decreased maturation rate caused by transforming growth factor-beta. Phorbol myristate acetate (PMA), a tumor-promoting phorbol ester, enhanced the spontaneous maturation rate; 4 alpha-phorbol dideconoate, an inactive phorbol ester, did not show this effect. PMA- and EGF-stimulated porcine oocyte maturation is reversed by calphostin-C, a PKC inhibitor. In conclusion, EGF's promotional activity on porcine oocyte maturation is independent of the cAMP pathway and probably mediated by the PKC pathway.

Bovine activin A does not affect the in vitro maturation of bovine oocytes

The effect of recombinant bovine activin A on the in vitro maturation of bovine oocytes was investigated. Culture of cumulus enclosed bovine oocytes in the presence of activin at the concentration of 100 or 500 ng/ml did not change the proportion of oocytes in which germinal vesicle breakdown had occurred at 4 and 7 h after the onset of culture. Activin had also no effect on the progression of maturation to the M II stage. The transient inhibition of germinal vesicle breakdown by 10 mM dibutyryl cyclic AMP was not affected by the addition of activin A at the onset of culture. Radiolabeling with 35S-methionine at 4 h and at 18 h after culture in the presence or absence of activin A did not show any effect of activin either on the total incorporation of radiolabel into acid precipitable material or on the protein synthesis patterns obtained after SDS-PAGE.

Fertilization and early development of rat oocytes induced to mature by forskolin

Forskolin has been shown to successfully induce maturation of rat oocytes as assessed by morphological markers. The present study was designed in an attempt to elucidate whether oocytes, induced to mature by forskolin (10(-4) M, group A) in a follicle-enclosed oocyte culture, are fertilizable and can further develop into two-cell embryos. Oocytes exposed in vitro to either luteinizing hormone (LH, 5 micrograms/ml, group B) or a GnRH agonist analogue (10(-7) M, group C) as well as oocytes that underwent maturation in vivo (group D), served as positive controls. We found that similar rates of fertilization were obtained in the experimental and all of the above mentioned control groups (A = 78.9 +/- 4.2%, B = 77.9 +/- 3.1%, C = 77.5 +/- 5.5% and D = 84.7 +/- 2.7%). Cleavage rate of fertilized eggs from group A was significantly higher than that of eggs from groups B & C, and similar to that of eggs from group D (A = 63.1 +/- 6.7%, B = 37.8 +/- 4.9%, C = 50.0 +/- 4.1%, D = 67.8 +/- 4.1%). Using functional parameters we hereby demonstrate that forskolin and LH are at least equally potent in producing fertilizable eggs that have a high potential of development into two cell embryos. These results further support the idea that cAMP is a mediator of LH action in inducing oocyte maturation.