Relationship between DNA fragmentation and nuclear status of in vitro-matured porcine oocytes: role of cumulus cells

Chlorogenic acid supplementation during in vitro maturation improves maturation, fertilization and developmental competence of porcine oocytes

Chlorogenic acid (CGA) is a quinic acid conjugate of caffeic acid, and a phytochemical found in many fruits and beverages that acts as an antioxidant. The present study investigated the effects of CGA supplementation during in vitro maturation (IVM), on in vitro development of porcine oocytes, to improve the porcine in vitro production (IVP) system. Oocytes were matured either without (control) or with CGA (10, 50, 100 and 200 μM). Subsequently, the matured oocytes were fertilized and cultured in vitro for 7 day. The rates of maturation, fertilization and blastocyst formation of oocytes matured with 50 μM CGA were significantly (p < .05) higher than those of the control oocytes. Hydrogen peroxide (H₂ O₂ ) is one of the reactive oxygen species and induces DNA damage in porcine oocytes. When oocytes were matured with 1 mM H₂ O₂ to assess the protective effect of CGA, 50 μM CGA supplementation improved the maturation rate and the proportion of DNA-fragmented nuclei in oocytes compared with control oocytes matured without CGA. Moreover, when oocytes were matured with either 50 μM CGA (control) or caffeic acid (10, 50 and 100 μM), the rates of maturation, fertilization and the blastocyst formation of oocytes matured with 50 μM CGA were similar to those of oocytes matured with 10 and 50 μM caffeic acid. Our results suggest that CGA has comparable effects to caffeic acid, and IVM with 50 μM CGA is particularly beneficial to IVP of porcine embryos and protects oocytes from DNA damage induced by oxidative stress. Supplementation of CGA to the maturation medium has a potential to improve porcine IVP system.

The Defensive Role of Cumulus Cells Against Reactive Oxygen Species Insult in Metaphase II Mouse Oocytes

We investigated the ability of reactive oxygen species (ROS), such as hydrogen peroxide (H(2)O(2)), hydroxyl radical ((·)OH), and hypochlorous acid (HOCl), to overcome the defensive capacity of cumulus cells and elucidate the mechanism through which ROS differentially deteriorate oocyte quality. Metaphase II mouse oocytes with (n = 1634) and without cumulus cells (n = 1633) were treated with increasing concentration of ROS, and the deterioration in oocyte quality was assessed by the changes in the microtubule morphology and chromosomal alignment. Oocyte and cumulus cell viability and cumulus cell number were assessed by indirect immunofluorescence, staining of gap junction protein, and trypan blue staining. The treated oocytes showed decreased quality as a function of increasing concentrations of ROS when compared to controls. Cumulus cells show protection against H(2)O(2) and (·)OH insult at lower concentrations, but this protection was lost at higher concentrations (>50 μmol/L). At higher H(2)O(2) concentrations, treatment dramatically influenced the cumulus cell number and viability with resulting reduction in the antioxidant capacity making the oocyte more susceptible to oxidative damage. However, cumulus cells offered no significant protection against HOCl at any concentration used. In all circumstances in which cumulus cells did not offer protection to the oocyte, both cumulus cell number and viability were decreased. Therefore, the deterioration in oocyte quality may be caused by one or more of the following: a decrease in the antioxidant machinery by the loss of cumulus cells, the lack of scavengers for specific ROS, and/or the ability of the ROS to overcome these defenses.

Procedure used for denuding pig oocytes influences oocyte damage, and development of in vitro and nuclear transfer embryos

The effects of different denuding procedures used during the in vitro culture of porcine embryos on oocyte damage and aspects of porcine embryo development were investigated in a series of studies. Oocytes were denuded by vortexing or pipetting after 44h in vitro maturation (IVM) or pre-denuded after 22h IVM. The total oocyte death rate was significantly (P<0.05) higher for pre-denuded (27.3±1.4%) than for vortexed (20.3±1.2%) or pipetted (16.2±2.2%) oocytes. There was no significant difference between the treatments in the percentage of oocytes that extruded the first polar body. The type I cortical granule distribution (reflecting complete maturity) and normal spindle formation rates were significantly lower in the pre-denuding than in the vortexing and pipetting treatments. Blastocyst formation rates were significantly lower for the pre-denuding treatment in PA (25.7±4.5%) and IVF (6.1±1.5%) culture than in the vortexing (PA 42.0±4.5%; IVF 11.2±0.5%) and pipetting (PA 43.4±3.1%; IVF 9.4±1.6%) treatments. The proportion of oocytes developing to blastocysts in SCNT culture was not significantly different between treatments ranging from 9.9±1.8% for pre-denuding to 12.3±2.7% for vortexing. No significant differences in apoptosis or embryonic fragmentation were observed. This study shows that the denuding procedure used for porcine oocytes during the in vitro production of embryos can significantly affect oocyte damage, spindle patterns, oocyte maturation, embryo development but not embryonic apoptosis or the frequency of fragmentation.

Co-culture embedded in cumulus clumps promotes maturation of denuded oocytes and reconstructs gap junctions between oocytes and cumulus cells

The present study was undertaken to establish an effective method for in vitro maturation (IVM) of denuded oocytes (DOs) by simulating the ovarian three-dimensional status in vivo using buffalo ovarian tissues or cumulus cells, so as to provide a model for investigating the mechanisms of oocyte maturation. Buffalo cumulus-oocyte complexes from ovaries taken at slaughter were denuded by pipetting, and then allocated randomly into four groups for IVM by direct culture in maturation medium (M1, control group), co-culture with a monolayer of cumulus cells (M2), embedded in cumulus cell clumps (M3) and ovarian tissue (M4) for 24 h. The nuclear maturation of DOs was assessed by the extrusion of the first polar body and the cytoplasmic maturation was evaluated by subsequently developmental capacity after parthenogenetic activation. More DOs matured to MII (56.89%) and developed to blastocysts (25.75%) when they were matured in vitro with M3 in comparison with DOs matured in vitro with M1 (45.14 and 15.97%) and M4 (40.48 and 13.49%). Further detection of gap junctions by injecting Lucifer yellow directly into cytoplasm of matured DOs with adherent cumulus cells and scanning with confocal microscope showed that Lucifer yellow were found in nine out of 11 the adherent cumulus cells in M3, indicating that the gap junctions between oocytes and cumulus cells was reconstructed in vitro. These results indicate that co-culture of DOs embedded in cumulus cell clumps can improve their nuclear and cytoplasmic maturation of DOs, possibly through the reconstruction of gap junctions in vitro.

In vitro production of porcine embryos: current status, future perspectives and alternative applications

The pig is considered to be a suitable source of cells and organs for xenotransplants, as well as a transgenic animal to produce specific proteins, given the biological similarities it shares with human beings. However, the in vitro embryo production system in pigs is inefficient compared with those in other mammals, such as cattle or mice. Although numerous modifications have been applied to improve the efficiency of in vitro embryo production systems in pigs, not much progress has been made to overcome the problem of polyspermy, and low developmental ability due to insufficient cytoplasmic abilities of in vitro matured oocytes and improper culture conditions for the in vitro produced embryos. Recent achievements, such as the establishment of chemically defined medium and utilization of 'zona hardening' technique, have gained some success. However, further research for the reduction of polyspermy and detrimental effects of the culture systems in pigs is still needed.

In vitro thermal stress induces apoptosis and reduces development of porcine parthenotes

The precise physiological causes that result in reduced development of oocytes after heat shock (HS) are not clear. In this study, apoptosis, heat shock protein70 (hsp70), and in vitro development of porcine oocytes were evaluated after HS. Porcine cumulus-oocyte complexes (COCs) were subjected to in vitro maturation for 42 h. The matured oocytes were then heated at 41.5 degrees C for 0 h (control, C0h), 1 h (HS1h), 2 h (HS2h), or 4 h (HS4h). An additional group of oocytes was cultured for 4 h without HS (control, C4h). In Experiment 1, expression of hsp70 was detected by Western-blotting and no difference between controls and HS groups was observed. In Experiment 2, apoptosis of matured oocytes after HS was examined by Annexin V-FITC and TUNEL. No significant TUNEL-positive signals were detected in the heated oocytes compared to the controls, but the intensity of Annexin V-FITC labeling among different groups increased with length of HS and in vitro culture (P<0.05). Oocytes were parthenogenetically activated by an electric pulse plus 6-DMAP (Experiment 3). Mean (+/-S.E.M.) embryonic development in HS2h (cleavage: 42+/-29%; blastocyst: 11+/-10%) and HS4h (cleavage: 36+/-28%; blastocyst: 11+/-8%) were decreased when compared to those in C0h (cleavage: 63+/-12%; blastocyst: 24+/-14%) and C4h (cleavage: 66+/-8%; blastocyst: 21+/-11%). Numbers of blastocysts with TUNEL-positive signals were similar among groups, but the signals increased before the eight-cell stage in HS groups (P<0.05). In conclusion, developmental competence of matured pig oocytes was compromised after heat shock, but it was not closely associated with the expression of oocyte hsp70. However, there may be a link between apoptosis and developmental competence of porcine oocytes.

Denuding and centrifugation of maturing bovine oocytes alters oocyte spindle integrity and the ability of cytoplasm to support parthenogenetic and nuclear transfer embryo development

The effects of cumulus cell removal and centrifugation of maturing bovine oocytes on nuclear maturation and subsequent embryo development after parthenogenetic activation and nuclear transfer were examined. Removal of cumulus cells at 4, 8, and 15 hr after in vitro maturation (IVM) or the centrifugation of denuded oocytes had no effect on maturation rates. Oocytes treated at 0 hr of IVM had a lower expulsion rate (50%) of the first polar body (PB1). The removal of cumulus cells and centrifugation affected the pattern of spindle microtubule distribution and division of chromosomes. There were almost no spindle microtubules allocated to PB1 and the spindles were swollen in anaphase I and telophase I oocytes. Approximately 20% of PB1 oocytes contained tripolar or multipolar spindles. After activation, oocytes denuded with or without centrifugation at 8 hr of IVM resulted in the lowest rate of development (3.0%). Denuded oocytes at 4, 15, and 24 hr of IVM with centrifugation or not resulted in similar blastocyst development rates (9.6%-13.2%). However, centrifugation of oocytes denuded at the beginning of IVM resulted in lower blastocyst development rate (8.1%, P < 0.05) than the noncentrifuged oocytes (17.3%). After nuclear transfer, the blastocyst development rates of oocytes denuded and centrifuged at 0, 4, and 8 hr of IVM were not different when compared to the same patch of noncentrifuged oocytes. However, oocytes denuded and centrifuged at 15 hr of IVM resulted in lower (P < 0.05) blastocyst development rates than the noncentrifuged oocytes. The results of this study suggest that removal of cumulus cells and centrifugation of denuded oocytes affect the spindle pattern. Embryo development of denuded and centrifuged oocytes may differ depending on the time of removal of cumulus cells.