Developmental stage of the oocyte during antral follicle growth and cumulus investment determines in vitro embryo development of sow oocytes

Melatonin Supplementation during In Vitro Maturation of Porcine Oocytes Alleviates Oxidative Stress and Endoplasmic Reticulum Stress Induced by Imidacloprid Exposure

Imidacloprid (IMI) is an endogenous neonicotinoid insecticide widely used in agriculture and has attracted researchers' attention because of its risks to the environment and human health. Melatonin (MT) is an antioxidant hormone produced by the pineal gland of the brain. Studies have shown that it has a variety of physiological functions and plays a crucial role in the development of animal germ cells and embryos. The potential protective effects of MT against oocyte damage caused by neonicotinoid pesticide toxicity remain unclear. In this study, we report the toxicity of IMI against, and its effects on the quality of, porcine oocytes and the protective effect of MT on IMI-exposed oocytes. The results show that IMI exposure adversely affected oocyte maturation, while MT supplementation ameliorated its toxic effects. Specifically, IMI exposure increased oxidative stress (OS), endoplasmic reticulum stress (ERS), and apoptosis, which may affect polar body expulsion rates and blastocyst formation. Also, IMI exposure reduced oocyte cleavage rates and the number of cells in blastocysts. However, all of these toxic effects can be restored after a melatonin supplementation treatment. In conclusion, these results suggest that melatonin has a protective effect on IMI-induced defects during porcine oocyte maturation.

Neither gonadotropin nor cumulus cell expansion is needed for the maturation of competent porcine oocytes in vitro†

In-vitro maturation (IVM) of oocytes from immature females is widely used in assisted reproductive technologies. Here we illustrate that cumulus cell (CC) expansion, once considered a key indicator of oocyte quality, is not needed for oocytes to mature to the metaphase II (MII) stage and to gain nuclear and cytoplasmic competence to produce offspring. Juvenile pig oocytes were matured in four different media: (1) Basal (-gonadotropins (GN) - FLI); (2) -GN + FLI (supplement of FGF2, LIF, and IGF1); (3) +GN - FLI; and (4) +GN + FLI. There was no difference in maturation to MII or progression to the blastocyst stage after fertilization of oocytes that had been matured in -GN + FLI medium and oocytes matured in +GN + FLI medium. Only slight CC expansion occurred in the two media lacking GN compared with the two where GN was present. The cumulus-oocytes-complexes (COC) matured in +GN + FLI exhibited the greatest expansion. We conclude that FLI has a dual role. It is directly responsible for oocyte competence, a process where GN are not required, and, when GN are present, it has a downstream role in enhancing CC expansion. Our study also shows that elevated phosphorylated MAPK may not be a necessary correlate of oocyte maturation and that the greater utilization of glucose by COC observed in +GN + FLI medium probably plays a more significant role to meet the biosynthetic needs of the CC to expand than to attain oocyte developmental competence. Gene expression analyses have not been informative in providing a mechanism to explain how FLI medium enhances oocyte competence without promoting CC expansion.

Susceptibility of Oocytes from Gilts and Sows to Beauvericin and Deoxynivalenol and Its Relationship with Oxidative Stress

Beauvericin (BEA) and deoxynivalenol are toxins produced by Fusarium species that can contaminate food and feed. The aim of this study was to assess the effects of these mycotoxins on the maturation of oocytes from gilts and sows. Furthermore, the antioxidant profiles in the oocytes' environment were assessed. Cumulus-oocyte-complexes (COCs) from gilts and sows were exposed to beauvericin (BEA) or deoxynivalenol (DON) and matured in vitro. As an extra control, these COCs were also exposed to reactive oxygen species (ROS). The maturation was mostly impaired when oocytes from gilts were exposed to 0.02 μmol/L DON. Oocytes from sows were able to mature even in the presence of 5 μmol/L BEA. However, the maturation rate of gilt oocytes was already impaired by 0.5 μmol/L BEA. It was observed that superoxide dismutase (SOD) and glutathione (GSH) levels in the follicular fluid (FF) of gilt oocytes was higher than that from sows. However, the expression of SOD1 and glutathione synthetase (GSS) was higher in the oocytes from sows than in those from gilts. Although DON and BEA impair cell development by diverse mechanisms, this redox imbalance may partially explain the vulnerability of gilt oocytes to these mycotoxins.

Cortical Granule Distribution and Expression Pattern of Genes Regulating Cellular Component Size, Morphogenesis, and Potential to Differentiation are Related to Oocyte Developmental Competence and Maturational Capacity In Vivo and In Vitro

Polyspermia is an adverse phenomenon during mammalian fertilization when more than one sperm fuses with a single oocyte. The egg cell is prepared to prevent polyspermia by, among other ways, producing cortical granules (CGs), which are specialized intracellular structures containing enzymes that aim to harden the zona pellucida and block the fusion of subsequent sperm. This work focused on exploring the expression profile of genes that may be associated with cortical reactions, and evaluated the distribution of CGs in immature oocytes and the peripheral density of CGs in mature oocytes. Oocytes were isolated and then processed for in vitro maturation (IVM). Transcriptomic analysis of genes belonging to five ontological groups has been conducted. Six genes showed increased expression after IVM (ARHGEF2, MAP1B, CXCL12, FN1, DAB2, and SOX9), while the majority of genes decreased expression after IVM. Using CG distribution analysis in immature oocytes, movement towards the cortical zone of the oocyte during meiotic competence acquisition was observed. CGs peripheral density decreased with the rise in meiotic competence during the IVM process. The current results reveal important new insights into the in vitro maturation of oocytes. Our results may serve as a basis for further studies to investigate the cortical reaction of oocytes.

Expression Changes in Fatty acid Metabolic Processrelated Genes in Porcine Oocytes During in Vitro Maturation

Mammalian oocytes undergo compound processes of nuclear and cytoplasmic maturation that allow them to reach MII stage. Only fully mature, oocyte can be successfully fertilized by a single spermatozoon. Fatty acids, apart from their role in cellular metabolism, inflammation and tissue development, have positive and detrimental effects on oocyte maturation, fertilization, blastocyst cleavage rate and embryo development in mammals. Using microarrays, we have analyzed the expression changes in fatty acids- -related genes during in vitro maturation of porcine oocytes. The oocytes were recovered from ovaries of 45 pubertal crossbred Landrace gilts and subsequently subjected to BCB test. For further analyses, only granulosa cell-free BCB+ oocytes were used and divided into two groups. The first one, described as “before IVM”, was directly exposed to molecular assays, the second one, described as “after IVM”, was first in vitro matured and then subjected to a second BCB test. Oocytes, if classified as BCB+, were then passed to corresponding molecular analyses. We found significant down-regulation of genes involved in fatty acid metabolic process, such as: ACSL6, EPHX2, FADS2, PTGES, TPI1, TBXAS1, NDUFAB1, MIF, ACADSB and DECR1 in porcine oocytes analyzed after IVM, in comparison to those analyzed before IVM. In conclusion, apart from poor data available concerning analyzed genes in relation to reproductive events, significant changes in their expression point to their potential role as an oocyte developmental competence markers in pigs. Introducing molecular diagnostics of oocytes could be the prospective tool for selection of best gametes, leading to improved outcomes of in vitro fertilization.

Fluoride-induced oxidative stress and apoptosis are involved in the reducing of oocytes development potential in mice

The present study was conducted to investigate the mechanisms of excessive-fluoride-induced reduction of oocyte development potential in mice. The development morphology of oocyte and the changes of pathomorphology in ovary were observed. The protein expression levels of apoptosis factors, including Bax, Bcl-2, casepase-3, casepase-9 and cytochrome c, and the mRNA expression levels of antioxidant enzymes, including SOD1, GSH-Px1, CAT and inducible nitric oxide synthase were measured by Western blot and real-time PCR, respectively. DNA damage in the ovary was analysed by single cell gel electrophoresis and TUNEL staining. Results indicated that the structure and function of ovarian cells were seriously damaged, followed, the development potential of oocyte was reduced by excessive fluoride. The expression levels of apoptosis factors were up-regulated and antioxidant enzymes were significantly down-regulated. Meanwhile, the contents of ROS, MDA, NO and iNOS were significantly increased. Whereas, the activities of SOD1, GSH-Px1 and CAT was significantly decreased compared with the control group. Simultaneously, the results of DNA analysis indicated that the tail length and tailing ratio of ovarian cells were significantly increased in the fluoride group. In summary, the results provided compelling evidence that excessive fluoride intake can reduce the development potential of oocyte by inducing oxidative stress and apoptosis in the ovary of female mice.

The Role of Antioxidant Enzymes in the Ovaries

Proper physiological function of the ovaries is very important for the entire female reproductive system and overall health. Reactive oxygen species (ROS) are generated as by-products during ovarian physiological metabolism, and antioxidants are indicated as factors that can maintain the balance between ROS production and clearance. A disturbance in this balance can induce pathological consequences in oocyte maturation, ovulation, fertilization, implantation, and embryo development, which can ultimately influence pregnancy outcomes. However, our understanding of the molecular and cellular mechanisms underlying these physiological and pathological processes is lacking. This article presents up-to-date findings regarding the effects of antioxidants on the ovaries. An abundance of evidence has confirmed the various significant roles of these antioxidants in the ovaries. Some animal models are discussed in this review to demonstrate the harmful consequences that result from mutation or depletion of antioxidant genes or genes related to antioxidant synthesis. Disruption of antioxidant systems may lead to pathological consequences in women. Antioxidant supplementation is indicated as a possible strategy for treating reproductive disease and infertility by controlling oxidative stress (OS). To confirm this, further investigations are required and more antioxidant therapy in humans has to been performed.

Levels of cyclic-AMP and cyclic-GMP in porcine oocyte-cumulus complexes and cumulus-free oocytes derived from small and middle follicles during the first 24-hour period of in vitro maturation

The objective of this study was to compare the cAMP and cGMP levels in cumulus-oocyte complexes (COCs) derived from the middle follicles (MFs, 3-6 mm in diameter) and small follicles (SFs, 1-3 mm in diameter) of pre-pubertal gilts during the first 24-h period of maturation in vitro (IVM). Both cAMP and cGMP levels in MF- and SF-derived oocytes did not change during this period. Although the cAMP levels increased in the COCs at 10 and 20 h after the start of IVM, the levels of cAMP were significantly higher in MF-derived COCs than in SF-derived COCs at 20 h after the start of IVM. On the other hand, the cGMP levels in COCs decreased to basal levels between 10 and 20 h after the start of the IVM, whereas cGMP levels were lower in SF-derived COCs than in MF-derived COCs during the first 10 h. The number of cumulus cells was larger in the MF-derived COCs than in the SF-derived COCs during the first 20-h period of IVM. The estimated cAMP level per cumulus cell at 10 h after the start of the IVM was higher in SF-derived COCs than in MF-derived COCs, whereas the estimated cGMP level per cumulus cell was no different between MF- and SF-derived COCs. From these results, we conclude that cAMP and cGMP levels in COCs, but not in oocytes, drastically change during the first 20-h period of IVM, and that both cAMP and cGMP levels significantly differ between MF- and SF-derived COCs.

Selection of porcine oocytes in vitro through brilliant cresyl blue staining in distinct incubation media

Staining with brilliant cresyl blue (BCB) may be used for oocyte selection, but BCB staining itself and the most commonly used selection medium (DMPBS) may compromise the development of porcine oocytes in vitro. This study evaluated DNA fragmentation, nuclear maturation, the area of migration of cortical granules (CG) and embryo development for stained (BCB+) and unstained (BCB-) oocytes incubated in DMPBS and in a modified medium (ReproPel) tested for the first time. Unexposed (UN), BCB+ and BCB- oocytes were incubated composing six groups: DMPBS/UN; DMPBS/BCB+; DMPBS/BCB-; ReproPel/UN; ReproPel/BCB+; and ReproPel/BCB-. There were more BCB+ oocytes in ReproPel than in DMPBS (P < 0.05). The DNA fragmentation was evaluated for oocytes in DMPBS/BCB+, DMPBS/BCB-, ReproPel/BCB+, ReproPel/BCB- and in porcine follicular fluid (control). The frequency of oocytes with no DNA fragmentation was greatest (64.6%) in DMPBS/BCB+ and lowest in ReproPel/BCB+ and ReproPel/BCB- (26.8 and 34.1%, respectively) (P < 0.05). Nuclear maturation rates were greater (P < 0.05) for DMPBS/BCB+ (63.1%), ReproPel/UN (55.1%) and ReproPel/BCB+ (50.2%) than for DMPBS/UN (40.8%) and ReproPel/BCB- (35.5%). The area of CG was greater (P < 0.05) for ReproPel/BCB- (80.7%) and DMPBS/UN (77.6%) than for ReproPel/UN (34.7%). Cleavage rates for DMPBS/BCB+ and ReproPel/BCB+ were greater than for DMPBS/UN (P < 0.05). Blastocyst development rates were greatest (P < 0.05) for ReproPel/UN and ReproPel/BCB+. In both media, BCB staining was apparently unable to select competent oocytes, which likely occurred due to toxicity. Despite the similar nuclear maturation and area of CG compared with DMPBS, oocytes selected in ReproPel presented impaired DNA integrity.

Effect of Follicle Size on In Vitro Maturation of Pre-Pubertal Porcine Cumulus Oocyte Complexes

Very small follicles (<3.0 mm diameter) are over-represented on the surface of ovaries of non-cycling pigs, and the oocytes collected from these follicles generally have reduced developmental competence in vitro. This study examined the effect of follicle size on the nuclear maturation (n = 608), the potential of parthenogenetic activation (n = 243) and the cyclic AMP (cAMP) content of pre-pubertal porcine oocytes (n = 480). In addition, the influence of follicle size on steroid hormone synthesis was analysed. Cumulus oocyte complexes (COCs) flushed from small (2.5-4.0 mm) or large (4.5-6.0 mm) ovarian follicles were cultured for 0, 28 and 46 h. After 46 h of IVM, a greater proportion of oocytes from 4.5- to 6.0-mm follicles reach metaphase II (MII) compared with those from follicles with 2.5-4.0 mm of diameter (96.1 vs 77.0%, respectively; p < 0.001). Parthenogenetic activation of oocytes from large follicles produced higher developmental rates than oocytes from large follicles (p < 0.05). At 28 h, the IVM medium with oocytes from large follicles contained significantly more 17ß-oestradiol (E2 ) than the medium with oocytes from small follicles (5.55 vs 3.45 ng/ml, respectively; p < 0.05) and at 46 h, the medium with oocytes from small follicles contained significantly more progesterone (P4 ) than the medium with oocytes from large follicles (276.7 vs 108.2 ng/ml, respectively, p < 0.05). Porcine oocytes from large follicles have higher nuclear and cytoplasmic maturation capacities, but the differences did not appear to be cAMP-mediated. Our findings also suggest that COCs from small follicles undergo more intensive luteinization than COCs from large follicles. The results show that oocytes from follicles with a diameter greater than 4.0 mm are more suitable for in vitro studies.

The new system of shorter porcine oocyte in vitro maturation (18 hours) using ≥8 mm follicles derived from cumulus-oocyte complexes

Despite recent efforts to improve in vitro maturation (IVM) systems for porcine oocytes, developmental competence of in vitro-matured oocytes is still suboptimal compared with those matured in vivo. In this study, we compared oocytes obtained from large (≥8 mm; LF) and medium (3-7 mm; MF) sized follicles in terms of nuclear maturation, intracellular glutathione and reactive oxygen species levels, gene expression, and embryo developmental competence after IVM. In the control group, cumulus-oocyte complexes (COCs) were aspirated from MF and matured for 22 hours with hormones and subsequently matured for 18 to 20 hours without hormones at 39 °C, 5% CO2 in vitro. In the LF group, COCs were obtained from follicles larger than 8 mm and were subjected to IVM for only 18 hours. The ovaries have LF were averagely obtained with 1.7% per day during 2012 and it was significantly higher in the winter season. The results of the nuclear stage assessment of the COCs from the LFs are as follows: before IVM (0 hours); germinal vesicle stage (15.2%), metaphase I (MI) stage (55.4%), anaphase and telophase I stages (15.8%), and metaphase II (MII) stage (13.6%). After 6 hours IVM; germinal vesicle (4.2%), MI (43.6%), anaphase and telophase I (9.4%), and MII (42.8%). After 18-hour IVM; MI (9.7%) and MII (90.3%). Oocytes from LF showed a significant (P < 0.001) increase in intracellular glutathione (1.41 vs. 1.00) and decrease in reactive oxygen species (0.8 vs. 1.0) levels compared with the control. The cumulus cells derived from LFs showed lower (P < 0.1) mRNA expression of COX-2 and TNFAIP6, and higher (P < 0.1) mRNA expression of PCNA and Nrf2 compared with the control group-derived cumulus cells. After parthenogenetic activation, in vitro fertilization and somatic cell nuclear transfer (SCNT) using matured oocytes from LFs, the embryo development was significantly improved (greater blastocyst formation rates and total cell numbers in blastocysts) compared with the control group. In conclusion, oocytes from LFs require only 18 hours to complete oocyte maturation in vitro and their developmental competence is significantly greater than those obtained from MFs. Although their numbers are limited, oocytes from LFs might offer an alternative source for the efficient production of transgenic pigs using SCNT.

Effects of cumulus cells on in vitro maturation of oocytes and development of cloned embryos in the pig

The purpose of this study was to investigate the role of porcine cumulus cells (CC) in oocyte maturation and somatic cell nuclear transfer (SCNT) embryo development in vitro. Denuded pig oocytes were co-cultured with CC or routinely cultured in maturation medium without a feeder layer. Porcine CC inactivated with mitomycin C or non-inactivated were used for the feeder layer in co-culture with porcine SCNT embryos to investigate comparatively the developmental competence of cloned embryos. The DNA damage aspects of apoptosis and expression pattern of genes implicated in apoptosis (Fas/FasL) as well as the mRNA expression of DNA methyltransferase (Dnmt1, Dnmt3a) of porcine SCNT embryos were also evaluated by comet assay or real-time RT-PCR, respectively. The results showed that co-culture with CC improved the extrusion rate of pbI (49.3% vs 31.5%, p<0.05) and survival rate (75.7% vs 53.3%, p<0.05) of denuded oocytes, but had no effects on blastocyst developmental rate or 2-cell-stage survival rate of in vitro fertilization embryos. Co-culture with CC inactivated by mitomycin C improved the blastocyst developmental rate (26.6% vs 13.0%, p<0.05) and decreased the apoptotic incidence (27.6% vs 46.2%, p<0.05) of porcine cloned embryos. Co-culture with inactivated CC reduced Fas and FasL mRNA expression of cloned embryos at the blastocyst stage compared with NT controls (p<0.05), but there were no differences in Dnmt1 and Dnmt3a mRNA expression among groups. Co-culture with inactivated cumulus cell monolayer significantly increased blastocyst formation and decreased the apoptotic incidence in porcine cloned embryos during in vitro development.

Effect of lycopene on cytoplasmic maturation of porcine oocytes in vitro

The aim of the present study was to improve cytoplasmic maturation of porcine oocytes by the addition of lycopene into in vitro maturation (IVM) media. We designed six experimental groups; IVM medium was supplemented with 10 IU/ml FSH, FSH and 10 IU/ml human chorionic gonadotrophin (hCG), or FSH and 7 μm lycopene in the first half of the IVM culture (0-22 h) followed by further culture (22-44 h) with or without hCG. The addition of lycopene into IVM media delayed the interruption of communication between an oocyte and the cumulus cells. Although meiotic competence was similar among the six groups, the glutathione level of matured oocytes was significantly higher in the lycopene-supplemented group (9.89 pmol per oocyte) than that in other groups (7.25 and 7.81 pmol per oocyte). Fertilization rate was significantly improved in lycopene-supplemented groups (58.3%) more than that in the group supplemented with FSH only (43.1%), whereas there were no differences in developmental competence among the groups (blastocyst rate: 20.1-29.5%). These results indicate that insufficient cytoplasmic maturation during conventional IVM resulted by disconnection of the gap junction between an oocyte and the cumulus cells in the early phase during IVM culture. We concluded that lycopene induced a prolonged sustainment of gap junctional communication between an oocyte and the cumulus cells during porcine IVM culture, which was an effective cytoplasmic maturation of porcine IVM oocytes.

Efficiency of in vitro fertilization is influenced by the meiotic competence of porcine oocytes and time of their maturation

The effect of meiotic competence of oocytes and time of their maturation on the efficiency of fertilization was studied in pigs. Cycling gilts with synchronized estrous cycles were used as oocyte donors. To obtain oocytes with different meiotic competence, oocytes were recovered separately from small and medium follicles in the early, middle and late luteal or early follicular phase. They were matured for 40 h, 43 h or 47 h and fertilized by spermatozoa of a proven boar. The penetration and monospermy rates, and total efficiency of fertilization were assessed. The same data were related to the follicle size, with or without regard to the phase, and to the maturation time. Regardless of the phase and the time of maturation, the monospermy rate and total efficiency of fertilization were significantly lower for the small follicle-derived oocytes than for the medium follicle-derived oocytes (38.5±10.4% vs 63.1±7.0% and 24.7±6.3% vs 42.5±3.8%). With regard to the phase, in the small follicle-derived oocytes, the monospermy rate increased significantly (P<0.05) from the early luteal to the late luteal phase (from 25.4±2.4% to 46.4±3.9%) and remained unchanged in the early follicular phase. A similar tendency was observed in the total efficiency of fertilization. No differences were found in either of these parameters in medium follicle-derived oocytes in the late luteal and early follicular phase. With regard to the time of maturation, the total efficiency of fertilization was significantly higher (P<0.05) in the small follicle-derived oocytes matured for 47 h than in those matured for 40 h (27.7±7.4% vs. 20.5±6.1%) and in the medium follicle-derived oocytes matured for 40 h as compared with those matured for 47 h (47.1±1.9% vs. 32.7±1.1%). With regard to the phase and the time of maturation, the differences were significant only in the late luteal and early follicular phases. It can be concluded that greater meiotic competence of porcine oocytes positively influences monospermy rate and total efficiency of fertilization process. However adequate time of maturation is an important factor for oocytes with different meiotic competence to improve the IVF procedure.

A method for immediate comparative assessment of microinjected mammalian oocytes

Manipulation of mammalian oocytes at the molecular level is hampered by low transcriptional activity and the presence of large stores of mRNA and protein. Microinjection of interfering macromolecules has become an important tool in studying oocyte maturation, although injection success, final concentrations of injected substances and viability after injection remain difficult to assess with current techniques. To address these problems, we developed an epifluorescence microscopy based technique to evaluate oocytes directly after (co-)injection of green fluorescent protein (GFP).

Oocyte developmental competence is reduced in sows during the seasonal infertility period

The modern domestic sow exhibits a period of impaired reproductive performance during the late summer and early autumn months, known as 'seasonal infertility'. A reduction in farrowing rate due to pregnancy loss is the most economically important manifestation of seasonal infertility. The aim of the present study was to determine whether there are changes in oocyte developmental competence associated with season. Ovaries were collected in pairs from sows sourced from commercial piggeries and slaughtered 4 days after weaning during winter and summer-autumn. Following oocyte IVM and parthenogenetic activation, the ability of oocytes from large follicles to form blastocysts was greater in winter (54.94 ± 6.11%) than in summer (21.09 ± 5.59%). During winter, the proportion of oocytes developing to the blastocyst stage from large follicles was significantly higher (54.94 ± 6.11%) than those oocytes from small follicles (23.17 ± 6.02%). There was no effect of season on the proportion of oocytes developing to the blastocyst stage from small follicles. There was no effect of follicle size on blastocyst formation from those oocytes recovered during summer. Blastocysts derived from small follicles during summer had the lowest number of cells (24.25 ± 1.48) compared with blastocysts derived from large follicles during winter (37.5 ± 1.3; P < 0.05). The mean progesterone concentration in follicular fluid collected from small follicles was greater in winter than summer (1235.55 ± 164.47 v. 701.3 ± 115.5 nmol L(-1), respectively; P < 0.001). The mean progesterone concentration in the follicular fluid of large follicles was also greater in winter than in summer (2470.9 ± 169.1 v. 1469.2 ± 156.5 nmol L(-1), respectively; P < 0.001). Regression analysis revealed a positive correlation between progesterone concentration and oocyte developmental competence. The results indicate that porcine oocytes fail to reach their full developmental potential during the period of seasonal infertility, suggesting that the pregnancy losses observed at this time of year may be due to reduced oocyte developmental competence.

Effects of follicular size and FSH on granulosa cell apoptosis and atresia in porcine antral follicles

The purpose of this study was to establish a culture model for isolated intact porcine antral follicles and investigate the relationship between granulosa cell apoptosis and follicular atresia. Small (<3 mm), medium (3-5 mm) and large (>5 mm) healthy porcine follicles were isolated and cultured in serum-free TCM199 with or without follicular stimulating hormone (FSH). Microscopic identification of healthy follicles was confirmed by histology. A spontaneous onset of apoptotic cell death in granulosa cells was observed from cultured antral follicles. The apoptotic rate of granulosa cells from small follicles cultured for 24 hr was higher than those of large and medium follicles, accompanied with high FasL mRNA abundance in granulosa cells. Supplementation with 3 or 5 IU/ml FSH significantly inhibited the percentage of granulosa cells that became apoptotic. FSH did not significantly alter estradiol secretion from cultured follicles. Progesterone secretion significantly decreased after culture for 48 hr, coinciding with the morphological changes observed. FasL and Fas mRNA were expressed in the healthy, early atretic, and progressed atretic porcine follicles regardless of follicular size. However, FasL but not Fas mRNA levels increased during follicular atresia. Addition of FSH significantly decreased FasL rather than Fas mRNA levels in granulosa cells and could attenuate apoptosis. Small follicles seemed to be more susceptible to atresia as compared to medium and large follicles.

Identification of genes targeted by FSH and oocytes in porcine granulosa cells

In the mammalian ovarian follicle maturing oocytes are nurtured and supported by surrounding somatic cells, the mural granulosa cells and the cumulus cells. These cells are regulated by follicle-stimulating hormone (FSH), originating from the pituitary, and paracrine factors derived from the oocyte. To gain insight into the mechanisms involved in the regulation of granulosa cell function, this study aimed to identify genes in mural granulosa cells that are regulated by FSH and oocyte secreted factors using the pig as a model organism. Mural granulosa cells were collected from 3-6 mm follicles from sow ovaries and cultured in serum free medium in the presence or absence of FSH and/or isolated cumulus oocyte complexes (COCs). FSH significantly increased both the metabolic activity and progesterone production of granulosa cells, while the presence of COCs reversed these FSH effects. Expression levels of mRNA in the absence/presence of FSH and COCs were analyzed on porcine specific microarrays representing 11,300 genes. Both previously identified and novel FSH target genes as well as some oocyte affected genes were found. Expression of inhibitor of DNA binding protein 2 and 3, ID2 and ID3, was decreased by FSH but increased by COCs, as validated by quantitative PCR. These proteins function as dominant negative basic helix loop helix (bHLH) transcription factors and since all regulated genes contain the consensus E-box sequence that can bind bHLH factors, our data suggest that FSH and COCs may regulate granulosa cell function by tuning the activity of bHLH factors, through ID2 and ID3.

Meiotic progression, mitochondrial features and fertilisation characteristics of porcine oocytes with different G6PDH activities

The aim of the present study was to investigate the developmental competence, mitochondrial characteristics and chromatin status of immature follicular porcine oocytes selected for their glucose-6-phosphate dehydrogenase (G6PDH) activity by brilliant cresyl blue (BCB) staining. In Experiment 1, the oocyte parameters were determined in parallel right after BCB staining (T(0)), after 22 h of in vitro maturation (IVM) (T(22)) and after 44 h of IVM (T(44)) (n = 496). BCB-stained oocytes (BCB+) at T(0) were characterised by fibrillated chromatin filaments in their germinal vesicles (GV) and diakinesis stages whereas unstained (BCB-) oocytes at T(0) contained in their GV mainly condensed stages of chromatin (P < 0.05). After 22 h of IVM BCB+ oocytes showed a prominent chromatin configuration of metaphase I and after 44 h the majority developed a M II nuclear configuration in contrast to the BCB- group (P < 0.0001). Differences were also observed between the two oocyte populations in their mitochondrial activity (P < 0.05). At the beginning of IVM BCB+ oocytes were characterised by high mitochondrial activity in their cytoplasm. The BCB+ oocytes showed clear visible homogenous distributions of mitochondria (P < 0.005) and contained more aggregated clusters of mitochondria in contrast to BCB- oocytes (P < 0.005). In Experiment 2, 318 oocytes were tested for their G6PDH activity and introduced to IVM and IVF. Only oocytes from the BCB+ group, which were matured after 44 h up to the stage of M II (81.6%) were fertilised (17.4%), penetrated (46%) or activated (15.6%) after IVF. These results indicate a relationship between the G6PDH activity of porcine oocytes before IVM and their subsequent nuclear development, mitochondrial activity and aggregation.

Porcine oocytes are most vulnerable to the mycotoxin deoxynivalenol during formation of the meiotic spindle

Deoxynivalenol (DON, vomitoxin) is a secondary metabolite and mycotoxin produced by Fusarium species that occurs with a high prevalence in cereals and grains intended for human and animal consumption. Pigs are considered to be the most sensitive animal species and exposure to DON results in reduced feed intake, reduced performance and cause alterations in the expression of markers of inflammation and cell cycle regulation. The objective of this study was to determine how DON possibly affects the oocyte developmental potential in vitro at concentrations which correspond to those observed in practice. To evaluate DON toxicity during specific stages of oocyte meiosis, cumulus-oocyte complexes were exposed to 0.02, 0.2, or 2 microM DON. Exposure to the highest DON concentration inhibited cumulus expansion and induced cumulus cell death. After exposure for 42 h, DON at all concentrations reduced Metaphase II formation and led to malformations of the meiotic spindle. Despite spindle malformations, exposure to different concentrations of DON did not lead to increased percentages of blastomeres with abnormal ploidy in embryos. Spindle malformation occurred by DON exposure during formation of meiotic spindles at Metaphase I and II, but embryo development was also reduced when oocytes were exposed to DON during Prophase I. Together, these results indicate that exposure to DON via contaminated food or feed can affect oocyte developmental competence by interfering directly with microtubule dynamics during meiosis, and by disturbing oocyte cytoplasmic maturation through other as yet undetermined mechanisms.

Comparative proteome analysis of porcine follicular fluid and serum reveals that excessive alpha(2)-macroglobulin in serum hampers successful expansion of cumulus-oocyte complexes

Porcine follicular fluid (pFF) constitutes the micro-environment of the maturing oocyte. Although pFF is a transudate of serum, in pigs, it is superior to serum in promoting in vitro expansion of the cumulus cells, a specialized cell population surrounding the oocyte. A comparative proteome analysis of autologous serum and pFF was performed to investigate proteins involved in successful cumulus expansion of porcine oocytes. iTRAQ labeling followed by 2-D LC ESI-Q-TOF MS/MS revealed 63 proteins common to both fluids of which the abundance of 13 proteins was significantly different (p<0.05). Seven proteins were more concentrated in serum whereas six proteins were more abundant in pFF. To investigate the importance of these proteins, the cumulus matrices of COCs were collected after in vitro maturation in media supplemented with either of both biologically fluids and then subjected to 2-D PAGE analysis. alpha(2)-Macroglobulin and CH4 and secrete domains of swine IgM, which were both less abundant in pFF, were absent from cumulus matrix extracts after in vitro maturation in pFF. Although both proteins were incorporated in the matrices of cumulus-oocyte complexes matured in serum, depletion of alpha(2)-macroglobulin from serum could significantly compensate for the impaired cumulus expansion of oocytes matured in serum.

Successful piglet production in a chemically defined system for in-vitro production of porcine embryos: dibutyryl cyclic amp and epidermal growth factor-family peptides support in-vitro maturation of oocytes in the absence of gonadotropins

To induce meiotic resumption of porcine oocytes, it is thought to be necessary to expose the cumulus-oocyte complexes (COCs) to gonadotropins during in-vitro maturation (IVM). However, the detailed mechanism of meiotic resumption by gonadotropins is still unknown, and successful piglet production has not been reported by using oocytes matured in gonadotropin-free media and fertilized in vitro. The present study was undertaken to examine the combinational effects of epidermal growth factor (EGF)-family members and dibutyryl cyclic AMP (cAMP) in a chemically defined medium on IVM of porcine oocytes and the developmental competence following in vitro fertilization (IVF). The basic IVM medium was a chemically defined medium, modified porcine oocyte medium (mPOM). Supplementation of the IVM medium with 10 or 1000 ng/ml EGF, amphiregulin and betacellulin during the whole IVM period, except for 10 ng/ml amphiregulin, increased the percentage of oocytes maturing to the metaphase-II stage. When COCs were exposed to both dibutyryl cAMP and EGF-family members during the first 20-h of IVM and then culture was continued in the absence of EGF-family members and dibutyryl cAMP, the incidence of metaphase-II oocytes was significantly increased and was not different from that of oocytes cultured in a standard IVM system with gonadotropins. The developmental competence of the oocytes to the blastocyst stage following IVF was no different from that of control oocytes matured with gonadotropins. When these blastocysts were transferred into the uterine horn of three recipients, all of gilts became pregnant and delivered a total of 11 piglets. These observations indicate that supplementation of a chemically defined maturation medium with EGF-family members and dibutyryl cAMP during the first 20 h of IVM can support well the meiotic progress and developmental competence of porcine oocytes.

CDC2/SPDY transiently associates with endoplasmic reticulum exit sites during oocyte maturation

BACKGROUND

Mammalian oocytes acquire competence to be fertilized during meiotic maturation. The protein kinase CDC2 plays a pivotal role in several key maturation events, in part through controlled changes in CDC2 localization. Although CDC2 is involved in initiation of maturation, a detailed analysis of CDC2 localization at the onset of maturation is lacking. In this study, the subcellular distribution of CDC2 and its regulatory proteins cyclin B and SPDY in combination with several organelle markers at the onset of pig oocyte maturation has been investigated.

RESULTS

Our results demonstrate that CDC2 transiently associates with a single domain, identified as a cluster of endoplasmic reticulum (ER) exit sites (ERES) by the presence of SEC23, in the cortex of maturing porcine oocytes prior to germinal vesicle break down. Inhibition of meiosis resumption by forskolin treatment prevented translocation of CDC2 to this ERES cluster. Phosphorylated GM130 (P-GM130), which is a marker for fragmented Golgi, localized to ERES in almost all immature oocytes and was not affected by forskolin treatment. After removal of forskolin from the culture media, the transient translocation of CDC2 to ERES was accompanied by a transient dispersion of P-GM130 into the ER suggesting a role for CDC2 in redistributing Golgi components that have collapsed into ERES further into the ER during meiosis. Finally, we show that SPDY, rather than cyclin B, colocalizes with CDC2 at ERES, suggesting a role for the CDC2/SPDY complex in regulating the secretory pathway during oocyte maturation.

CONCLUSION

Our data demonstrate the presence of a novel structure in the cortex of porcine oocytes that comprises ERES and transiently accumulates CDC2 prior to germinal vesicle breakdown. In addition, we show that SPDY, but not cyclin B, localizes to this ERES cluster together with CDC2.

Osmotic stress induced by sodium chloride, sucrose or trehalose improves cryotolerance and developmental competence of porcine oocytes

Exposure of porcine oocytes to increased concentrations of NaCl prior to manipulation has been reported not only to increase cryotolerance after vitrification, but also to improve developmental competence after somatic cell nuclear transfer (SCNT). In the present study we compared the effects of NaCl with those of concentrated solutions of two non-permeable osmotic agents, namely sucrose and trehalose, on the cryotolerance and developmental competence of porcine oocytes. In Experiment 1, porcine in vitro-matured cumulus–oocyte complexes (COCs; n = 1200) were exposed to 588 mOsmol NaCl, sucrose or trehalose solutions for 1 h, allowed to recover for a further 1 h, vitrified, warmed and subjected to parthenogenetic activation. Both Day 2 (where Day 0 is the day of activation) cleavage and Day 7 blastocyst rates were significantly increased after NaCl, sucrose and trehalose osmotic treatments compared with untreated controls (cleavage: 46 ± 5%, 44 ± 7%, 45 ± 4% and 26 ± 6%, respectively; expanded blastocyst rate: 6 ± 1%, 6 ± 2%, 7 ± 2% and 1 ± 1%, respectively). In Experiment 2, COCs (n = 2000) were treated with 588 mOsmol NaCl, sucrose or trehalose, then used as recipients for SCNT (Day 0). Cleavage rates on Day 1 did not differ between the NaCl-, sucrose-, trehalose-treated and the untreated control groups (92 ± 3%, 95 ± 3%, 92 ± 2% and 94 ± 2%, respectively), but blastocyst rates on Day 6 were higher in all treated groups compared with control (64 ± 2%, 69 ± 5%, 65 ± 3% and 47 ± 4%, respectively). Cell numbers of Day 6 blastocysts were higher in the control and NaCl-treated groups compared with the sucrose- and trehalose-treated groups. In conclusion, treatment of porcine oocytes with osmotic stress improved developmental competence after vitrification combined with parthenogenetic activation, as well as after SCNT.

High hydrostatic pressure treatment of porcine oocytes before handmade cloning improves developmental competence and cryosurvival

An innovative technique, called the high hydrostatic pressure (HHP) treatment, has been recently reported to improve the cryosurvival of gametes or embryos in certain mammalian species. The aim of the present study was to investigate the in vitro and in vivo developmental competence and cryotolerance of embryos produced by handmade cloning (HMC) after pressure treatment of recipient oocytes. In vitro-matured porcine oocytes were treated with a sublethal hydrostatic pressure of 20 MPa (200 times greater than atmospheric pressure) and recovered for either 1 or 2 h (HHP1 and HHP2 groups, respectively) before they were used for HMC. After 7 days of in vitro culture, blastocyst rates and mean cell numbers were determined. Randomly selected blastocysts were vitrified with the Cryotop method based on minimum volume cooling procedure. The blastocyst rate was higher in the HHP2 group than in the control group (68.2 +/- 4.1% vs. 46.4 +/- 4.2%; p < 0.01), while there was no difference between HHP1 and control group (52.1 +/- 1.2% vs. 49.0 +/- 2.7%; p > 0.05). Similar mean cell numbers of produced blastocysts were obtained in HHP2 and control groups (56 +/- 4 vs. 49 +/- 5; p > 0.05). Subsequent blastocyst vitrification with the Cryotop method resulted in significantly higher survival rate after thawing in the HHP2 group than in the control group (61.6 +/- 4.0% vs. 30.2 +/- 30.9%; p < 0.01). Fifty-six and 57 day 5 to day 7 fresh blastocysts in HHP1 group were transferred into two recipient sows on day 5 of the estrous cycle. One recipient was diagnosed pregnant and gave birth to two healthy piglets by naturally delivery on day 122 of gestation. This pilot study proved that the sublethal HHP treatment of porcine oocytes before HMC results in improved in vitro developmental competence and cryotolerance, and supports embryonic and fetal development as well as pregnancy establishment and maintenance up to the birth of healthy piglets.