Developmental regulation of effect of epidermal growth factor on porcine oocyte-cumulus cell complexes: nuclear maturation, expansion, and F-actin remodeling

The signaling pathways linking to lysophosphatidic acid-promoted meiotic maturation in mice

The signaling pathways linking to lysophosphatidic acid-promoted meiotic maturation in mice were studied. When mouse oocyte-cumulus cells complexes were cultured with 10(-5) M lysophosphatidic acid (the LPA group), the rate of oocyte nuclear maturation was significantly increased. Additions of pertussis toxin, genistein, U73122, Ro320432, PD98059 or SB203580 significantly suppressed the increase in lysophosphatidic acid-stimulated nuclear maturation rate. These results suggested that Gi/o-coupled lysophosphatidic acid receptors activate phosphatidylinositol-specific phospholipase C, and result in ERK and MAP kinase activation, which is triggered by diacylglycerol-dependent protein kinase C. When intracellular cAMP concentrations of oocytes in the LPA and control groups were measured using the acetylation assay, the intracellular cAMP concentration of an oocyte in the LPA group was significantly lower than the control oocyte (0.117+/-0.04 fmol/oocyte vs. 0.176+/-0.036 fmol/oocyte, p<0.05). In conclusion, our results suggested that lysophosphatidic acid stimulates phospholipase C through a Gi-protein linked receptor on the surface of mouse cumulus cells and stimulates both extracellular signal-regulated kinase and p38 mitogen-activated kinase, resulting in the closure or loose of gap junctions between cumulus cells and the oocyte. The resultant early decrease of oocyte cAMP levels may promote nuclear maturation of mouse oocytes in vitro.

Successful piglet production by IVF of oocytes matured in vitro using NCSU-37 supplemented with fetal bovine serum

Recently, piglets have been obtained from in vitro-produced blastocysts by using in vitro maturation systems in which oocytes have been matured in North Carolina State University (NCSU) solution supplemented with porcine follicular fluid (PFF). However, PFF is not available commercially. To prepare PFF from the ovaries required time and effort and there is substantial variation in quality among batches. Furthermore, PFF is considered a potential source of infectious agents. We evaluated another commercially available potential protein source, fetal bovine serum (FBS), for in vitro maturation, to produce embryos and piglets. Cumulus-oocyte complexes were matured in NCSU-37 with PFF or with one of four batches of FBS. The proportions of oocytes with expanded cumulus cells were lower in all FBS batch groups (P < 0.05, 15-41%) than that in the PFF group (74%). The proportions of oocytes that matured were also lower in all FBS batch groups (P < 0.05, 26-41%) than in the PFF group (73%), irrespective of cumulus expansion. However, the proportions of oocytes that underwent germinal vesicle breakdown were almost the same in all groups (76-96%). After in vitro fertilization, the rate of sperm penetration into matured oocytes was higher in the PFF group (P < 0.05, 63%) than in one batch of FBS (22%) and removal of the compacted cumulus cells after maturation did not affect fertilization status (21%). Subsequent in vitro embryo culture of the PFF and FBS groups for 6 day resulted in similar rates of blastocyst formation (17 and 19%, respectively) and similar numbers of cells per blastocyst (43 and 46 cells, respectively). When blastocysts obtained from oocytes matured with FBS were transferred into two recipients, one became pregnant and farrowed seven piglets. Transfer of blastocysts obtained from oocytes matured with PFF into two other recipients resulted in one pregnancy and production of four piglets. These data suggested that porcine in vitro maturation in NCSU-37 supplemented with FBS reduced the maturational ability of oocytes, but once oocytes have matured, they have the same ability to develop to term after in vitro fertilization and embryo transfer as those matured with PFF.

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.

Low oxygen tension during in vitro maturation of porcine follicular oocytes improves parthenogenetic activation and subsequent development to the blastocyst stage

To establish a reliable in vitro maturation system for activation and subsequent development as nuclear recipients for the effective production of pig clones, we assessed maturation, activation and parthenogenetic development in response to the following: (1) type of immature oocytes (cumulus-oocyte complexes (COCs) or parietal granulosa plus cumulus-oocyte complexes (GCOCs)); (2) oxygen (O(2)) tension (5 or 20%); and (3) maturation period (36-60 h). The rate of nuclear maturation to metaphase-II (M-II) in the GCOC group (73.0 +/- 3.1%) was higher than that in the COC group (P < 0.05, 60.6 +/- 3.5%), but the rates did not differ between the 5 and 20% O(2) tension groups. M-II rate increased (P < 0.05) to about 70% after 42 h and then remained constant until 60 h of culture. When oocytes were matured under 5% O(2) tension and stimulated, the rate of normal oocyte activation (a female pronucleus formation and emission of the second polar body) was higher (P < 0.05, 38.5 +/- 3.9%) than when oocytes were matured under 20% O(2) tension (24.5 +/- 3.9%). On the other hand, the rate of normal activation was not significantly different between the COC and GCOC groups, and the highest (P < 0.05) normal activation rate was obtained in oocytes cultured for 48 and 54 h (48.4 +/- 5.5% and 47.9 +/- 8.2%, respectively). When COC and GCOC matured for 48 h under 5 and 20% O(2) tension were stimulated and subsequently cultured in vitro for 6 days, the rate of blastocyst formation did not differ between the oocyte types nor between the O(2) tension groups. However, blastocyst quality, as measured by mean total cell number, was significantly higher in the 5% O(2) group (P < 0.05, 34.6 +/- 2.0 for COC; 33.8 +/- 1.8 for GCOC) compared with the 20% O(2) group (25.9 +/- 1.8 for COC; 27.0 +/- 2.0 for GCOC). In conclusion, low O(2) tension (5%) during in vitro maturation of porcine oocytes promoted their ability to be activated normally and improved the quality of parthenogenetic blastocysts developed in vitro in modified NCSU-37 solutions. This knowledge may be applicable for preparation of in vitro matured oocytes with good quality as recipient oocytes for generating pig clones.

Epidermal growth factor family members: endogenous mediators of the ovulatory response

Previous studies showed that epidermal growth factor (EGF) and TGFalpha mimic the action of LH on the resumption of oocyte maturation. We tested whether EGF-like agents, such as amphiregulin (AR), epiregulin (ER), and betacellulin (BTC), also mediate the LH stimulation of the ovulatory response in the rat. LH induced transient follicular expression of AR, ER, and BTC mRNA, reaching a maximum after 3-h incubation. Furthermore, the addition of ER, AR, and BTC to the culture medium could mimic some of LH actions. AR and ER fully simulated LH-induced resumption of meiosis in vitro, whereas BTC was less effective. To study the putative involvement of EGF-like factors in mediation of LH signal, the effect of the EGF receptor kinase inhibitor AG1478 was tested. When added with LH, AG1478, but not its inactive analog AG43, reduced EGF receptor phosphorylation and oocyte maturation compared with follicles treated with LH only. In addition to the inhibition of resumption of meiosis, AG1478 administration into the bursa (3 microg/bursa) resulted in 51% (P < 0.0005) inhibition of ovulation in the treated ovaries, compared with the untreated contralateral ones, as well as to the vehicle-treated ovaries (P < 0.02). LH, as well as ER, induced the expression of genes associated with the ovulatory response like rat hyaluronan synthase-2, cyclooxygenase-2, and TNFalpha-stimulated gene 6 mRNA, whereas AG1478 inhibited this effect of LH. Release of EGF-like factors from the membrane is dependent on activated metalloproteases. Indeed, Galardin, a broad-spectrum metalloprotease inhibitor, but not a specific matrix metalloprotease 2 and 9 inhibitor, suppressed meiotic maturation induced by LH. Conversely, meiotic maturation induced by ER was not affected by Galardin, thus, supporting the notion that LH releases follicular membrane-bound EGF-like agents. In summary, EGF-like factors such as ER, AR, and BTC seem to mediate, at least partially, the LH stimulation of oocyte maturation, ovulatory enzyme expression, and ovulation.

Expression of epidermal growth factor receptor in the goat cumulus-oocyte complex

It has been previously reported that epidermal growth factor (EGF) influences meiotic maturation and development competence of oocytes in various mammalian species. The present study was undertaken to analyze the expression of the gene encoding the EGF-receptor (EGF-R) in the goat cumulus-oocyte complex during meiotic competence acquisition. Expression of EGF-R mRNA was evaluated by PCR on reverse transcribed mRNA from follicular cells and oocytes, using EGF-R specific primers designed from human cDNA. The presence of the EGF-R transcript was evidenced in follicular cells as well as in meiotically competent and incompetent oocytes. Western blot analysis performed with specific anti EGF-R antibody revealed in meiotically competent and incompetent oocytes and in follicular cells a 170 kD polypeptide corresponding to the goat EGF-R protein. In oocytes the amount of EGF-R increased with meiotic competence acquisition. EGF-R distribution was examined by indirect immunofluorescence on frozen sections of cumulus-oocyte complexes (COCs). EGF-R immunoreactivity was observed in cumulus cells and in oocytes. Staining appeared to be confined to the periphery of the cells for both oocytes and cumulus cells. In this study, we identified the main component required for signaling via EGF-R in the goat oocyte and in follicular cells. These results suggest a possible involvement of EGF in the regulation of follicular growth and oocyte maturation in goat.

EGF-Like Growth Factors As Mediators of LH Action in the Ovulatory Follicle

Before ovulation in mammals, a cascade of events resembling an inflammatory and/or tissue remodeling process is triggered by luteinizing hormone (LH) in the ovarian follicle. Many LH effects, however, are thought to be indirect because of the restricted expression of its receptor. Here, we demonstrate that LH stimulation induces the transient and sequential expression of the epidermal growth factor (EGF) family members amphiregulin, epiregulin, and beta-cellulin. Incubation of follicles with these growth factors recapitulates the morphological and biochemical events triggered by LH, including cumulus expansion and oocyte maturation. Thus, these EGF-related growth factors are paracrine mediators that propagate the LH signal throughout the follicle.

Effects of 17.BETA.-Estradiol on In Vitro Maturation of Pig Oocytes in Protein-Free Medium

The present study examined the effects of 17 beta-estradiol (E(2)) on in vitro maturation and subsequent in vitro fertilization of pig oocytes matured with or without cumulus cells. When E(2) (10 ng/ml) was added to the protein-free maturation medium, the proportions of cumulus-enclosed oocytes that underwent germinal vesicle breakdown and reached metaphase II were significantly reduced (P<0.05), and cumulus expansion was also significantly inhibited (P<0.05) compared with the control (no E(2) added). Although oocytes matured in the presence of E(2) were penetrated by sperm in vitro at the same level as the control, the incidences of male pronuclear (MPN) formation and activated oocytes were significantly lower (P<0.05) than the control. These inhibitory effects of E(2) were prevented when the medium was supplemented with E(2) together with its antagonist, ICI 182,780 (1 microg/ml), although the presence of the antagonist alone in the medium had no effect on the maturation and fertilization in vitro of oocytes. In cumulus-free oocytes, E(2) had no effect on nuclear maturation and penetration in vitro, but low MPN formation was observed in oocytes matured in the presence and absence of E(2). When cumulus-enclosed oocytes were cultured in the presence of progesterone (P(4); 600 ng/ml) alone or together with E(2), no significant differences in nuclear maturation, cumulus expansion or penetration in vitro were observed compared with control oocytes. The concentration of P(4) in maturation medium was significantly (P<0.01) lower when cumulus-enclosed oocytes were cultured for 44 h in the medium with E(2) than in medium without E(2). These results indicate that E(2) inhibits both nuclear and cytoplasmic maturation of cumulus-enclosed pig oocytes, and that this inhibition can be prevented by an E(2) antagonist or P(4). This E(2) inhibition may occur indirectly via the cumulus cells and inhibition of P(4) synthesis.

Effect of follicle-stimulating hormone on nuclear and cytoplasmic maturation of sow oocytes in vitro

A series of experiments were conducted to evaluate the effects of FSH supplementation during IVM on porcine oocyte nuclear maturation, and subsequent fertilization, cleavage and embryo development. Cumulus-oocyte complexes (COCs) were cultured 40 h without FSH (control), 40 h with FSH (FSH 0-40 h), or 20 h with FSH followed by a 20-h culture period without FSH (FSH 0-20 h). Nuclear stage of oocytes was assessed at intervals from 12 to 40 h of IVM. Furthermore, oocytes were in vitro fertilized, fixed and stained to determine normally fertilized and polyspermic oocytes. Additionally, COCs were matured with FSH, fertilized and zygotes cultured in NCSU-23. The percentage of cleaved embryos and blastocysts were determined and the number of nuclei was counted. The presence of FSH during the first 20 h of IVM retarded germinal vesicle breakdown. After 40 h of culture 84, 67 and 58% MII oocytes were observed in the FSH 0-20 h, FSH 0-40 h and control groups, respectively. After IVF, penetration rates were similar at 27, 26 and 29%, while the proportion of polyspermic oocytes was 7, 19 and 11% of penetrated oocytes for control, FSH 0-40 and FSH 0-20 h groups, respectively. Cleavage and blastocyst rates differed among treatments (21, 29 and 38%, and 7, 15 and 20% for control, FSH 0-40 and FSH 0-20 h groups, respectively). No differences in blastocyst cell number were found among groups. Blastocyst rates, based on number of cleaved embryos, were 51 and 52% for the FSH 0-40 and FSH 0-20 h groups, which differed significantly from the control group (31%). The results indicate that FSH has a stimulatory effect on nuclear and cytoplasmic maturation of sow oocytes. Addition of FSH for the first 20 h of culture was most beneficial, based on cleavage and blastocyst development rates.

Epidermal growth factor-receptor tyrosine kinase activity regulates expansion of porcine oocyte-cumulus cell complexes in vitro

We have recently shown that epidermal growth factor (EGF) strongly stimulates expansion of porcine oocyte-cumulus complexes (OCCs) isolated from large follicles (>6 mm) and does not promote expansion of OCCs from small (3-4-mm) follicles. In order to elucidate the role of EGF in OCCs expansion, in the present study, we first examined the presence of EGF receptors (EGFRs) in cumulus cells isolated from follicles of different sizes. Surprisingly, immunoblotting showed that cumulus cells obtained from all follicular size categories contained similar amounts of EGFR protein. On the other hand, we found a dramatic difference in the pattern of protein tyrosine phosphorylation in a comparison of cumulus cells isolated from small and large follicles treated by EGF. Furthermore, tyrosine-phosphorylated EGFR was specifically immunoprecipitated with antiphosphotyrosine antibodies from EGF-treated cumulus cells isolated from the large follicles. This result strongly indicates that only OCCs from the large follicles contain mature EGFRs that are capable of becoming activated by EGF. Remarkably, preincubation of cumulus cells from small follicles (3-4 mm) with FSH strongly increased EGF-stimulated tyrosine phosphorylation to levels comparable with OCCs from large follicles. The FSH-dependent activation of EGFRs was beneficial for expansion of OCCs isolated from the small follicles since OCCs treated sequentially by FSH (3 h) and EGF (1 h) underwent expansion significantly better then OCCs cultured in FSH or EGF alone. We conclude that a FSH-dependent pathway has an important role in the maturation of the EGFR in cumulus cells and that activation of EGFR-dependent signaling is sufficient to induce expansion.

In vitro maturation of bitch oocytes from advanced preantral follicles in synthetic oviduct fluid medium: serum is not essential

The ability of oocytes from preantral follicles to mature in vitro was assessed using a synthetic oviduct fluid (SOF) medium. Advanced preantral follicles (approximately 210 microm diameter) were isolated from the ovaries of domestic bitches and assigned to one of four treatment groups: (1) SOF (n = 230); (2) SOF + 3 mg/ml bovine serum albumin (+BSA, n = 220); (3) SOF + 20% fetal bovine serum (+FBS, n = 227); or (4) SOF + 3 mg/ml BSA + 20% FBS (+BSA+FBS, n = 232), then cultured for up to 72 h. A group of control follicles was not cultured (n = 103). The percentages of oocytes reaching metaphase I to metaphase II stages (MI to MII) did not differ between treatments at each culture period. Within treatments, the percentages of oocytes at MI to MII stages did not differ with duration of culture. However, when compared to the control group (0.97%) the percentages of oocytes at MI to MII increased (P < 0.05) in the SOF group after 48 h (10.0%) and 72 h (12.2%) of culture. In the +BSA (10.1%) and +FBS (9.7%) groups, the percentages of oocytes at MI to MII increased (P < 0.05) above control values only after 72 h of culture. The percentage of oocytes at MI to MII did not significantly increase in the +BSA+FBS group (3.9,6.6 and 7.6% at 24,48 and 72 h of culture, respectively) compared to the control group. These results indicate that under the described conditions supplementation of culture medium with BSA or FBS is not essential, and the simple medium SOF can support nuclear maturation of a small proportion of bitch oocytes in vitro.

Equine oocyte maturation with epidermal growth factor

Epidermal growth factor (EGF) has been shown to have a positive effect during oocyte in vitro maturation in several species. This study was performed to establish the capacity of equine oocytes to undergo nuclear maturation in the presence of EGF and to localise its receptor in the equine ovary by immunohistochemical methods. Oocytes were obtained by aspiration and subsequent scraping from equine follicles (15-25 mm diameter) and cultured in 3 different treatment groups for 36 h: control Group (modified TCM 199 with 0.003% BSA), EGF Group (TCM-199 supplemented with 50 ng/ml EGF) and EMS Group (TCM 199 supplemented with 10% v/v oestrous mare serum). Each group was divided further into 3 treatments with tyrphostin A-47, a specific tyrosine kinase inhibitor, at 0, 10(-4) and 10(-6) mmol/l. Maturation was determined as the percentage of oocytes reaching metaphase II stage at the end of the culture period. Immunohistochemical detection of EGF-receptor (EGFR) was performed using a streptoavidin-biotin method. The recovery rate and oocyte retrieval were 84.6% (recovered oocytes/follicles aspirated) and 6.55 (oocytes/mare), respectively. Treatment with EGF significantly (P<0.05) increased the incidence of metaphase II stage compared with the control group (69.4 vs. 26.9% in controls, respectively). The specific-tyrosine kinase inhibitor A-47 was effective in suppressing EGF-effect on EGF-cultured oocytes; no significant differences were observed in EMS-supplemented oocytes when cultured with A-47. EGF-receptor was localised in follicles, with localisation being more prominent in the cumulus than in mural granulosa cells. This finding, together with the increase of oocyte nuclear maturation rate when using EGF in culture media and the inhibition of maturation by tyrphostin A-47, suggests a physiological role for EGF in the regulation of equine oocyte maturation. The results should help successful development of assisted reproductive technology in the horse.

Effect of follicular size on meiotic and developmental competence of porcine oocytes

In several species, the developmental competence of the oocyte is acquired progressively during late follicular growth, after the acquisition of the competence to resume and complete meiosis. In the pig, full meiotic competence of the oocyte is reached in ovarian follicles with a diameter of 3 mm or more. However, there is no information about developmental competence acquisition. We analyzed the ability of oocytes from three foll icular size classes to resume and complete meiosis, to be fertilized, and to develop in vitro to the blastocyst stage. A total of 941 follicles were dissected from slaughterhouse gilt ovaries and classified as small (<3 mm, n = 330), medium (3-5 mm, n = 373), or large (>5 mm, n = 238). The cumulus-oocyte complexes recovered from these follicles were submitted to in vitro maturation for 44 h in TCM199 supplemented with 10 ng/ml EGF, 400 ng/ml pFSH and 570 microM cysteamine; in vitro fertilized for 18 h in mTBM with 10(5) frozen-thawed percoll-selected sperms/ml; and developed for 7 days in mSOF. Samples of oocytes or presumptive zygotes were fixed and stained at the end of maturation and fertilization. Groups of oocytes were cultured for 3 h in the presence of 35S-methionine before or after maturation for SDS-PAGE analysis of protein neosynthesis. More oocytes originating from medium and large follicles were competent for maturation than oocytes from small follicles (77 and 86% of metaphase II, respectively, versus 44%, P < 0.05). More oocytes from medium and large follicles werepenetratedby spermatozoa during in vitro fertilization, resulting in significantly more oocytes presenting two or more pronuclei at the end of fertilization (73 and 77% for medium and large follicles, respectively, versus 53% for small follicles, P < 0.05). More oocytes from medium and large follicles developed to the blastocyst stage (14 and 23%, respectively) than those from small follicles (3%, P < 0.05), even if the development rates were corrected by the maturation or fertilization rates. It is concluded that a high proportion of oocytes harvested from follicles of less than 3 mm in the pig are not fully competent for meiosis and are cytoplasmically deficient for development.

In vitro production of embryos in swine

In recent years, progress has been achieved in the production of pig embryos through IVM and IVF techniques. Cytoplasmic maturation of oocytes has been improved by modifications to IVM procedures. However, the historical problem of polyspermic penetration still remains a major issue to be solved. Recent studies indicate that the type of IVF medium and certain modifications to that medium can reduce polyspermy. Efforts should be directed to increase the developmental competence and quality of embryos. At present, many embryo culture (EC) media are available that can overcome the historical 4-cell block and support development of early in vivo derived embryos to the blastocyst stage. In contrast, blastocyst development of in vitro produced embryos in these culture media varies significantly. Furthermore, morphology and cell numbers in in vitro produced blastocysts are inferior to their in vivo counterparts. However, several modifications to EC techniques have improved embryo quality and developmental competence. Testing embryo viability through surgical transfer to recipient animals has resulted in acceptable pregnancy rates with moderate litter sizes. Although reliable in vitro systems are available for the generation of pig embryos, the problem of polyspermy and poor embryo development hamper their large-scale implementation. Further research efforts should be directed to improve oocyte/embryo quality and the methods to minimize polyspermy through development of novel IVM, IVF, and EC techniques.