Dual labeling of the cytoskeleton and DNA strand breaks in porcine embryos produced in vivo and in vitro

The effect of L-carnitine supplementation during in vitro maturation on oocyte maturation and somatic cloned embryo development

The quality of the recipient cytoplasm was reported as a crucial factor in maintaining the vitality of SCNT embryos and SCNT efficiency for dairy cows. Compared with oocytes matured in vivo, oocytes matured in vitro showed abnormal accumulation and metabolism of cytoplasmic lipids. L-carnitine treatment was found to control fatty acid transport into the mitochondrial β-oxidation pathway, which improved the process of lipid metabolism. The results of this study show that 0.5 mg/ml L-carnitine significantly reduced the cytoplasmic lipid content relative to control. No significant difference was observed in the rate of oocyte nuclear maturation, but the in vitro developmental competence of SCNT embryos was improved in terms of increased blastocyst production and lower apoptotic index in the L-carnitine treatment group. In addition, the pregnancy rate with SCNT embryos in the treatment group was significantly higher than in the control group. In conclusion, the present study demonstrated that adding L-carnitine to the maturation culture medium could improve the developmental competence of SCNT embryos both in vitro and in vivo by reducing the lipid content of the recipient cytoplasm.

Embryo structure reorganisation reduces the probability of apoptosis in preimplantation mouse embryos

Programmed cell death plays a key role in mammalian development because the morphological events of an organism's formation are dependent on apoptosis. In the mouse development, the first apoptotic waves occur physiologically at the blastocyst stage. Cell number and the mean nucleus to cytoplasm (N/C) ratio increase exponentially throughout subsequent embryo cleavages, while cell volume concurrently decreases from the zygote to blastocyst stage. In this study we tested the hypothesis that reorganisation of the embryo structure by manipulating cell number, the N/C ratio and the cell volume of 2-cell embryos may result in the earlier and more frequent occurrence of apoptosis. The results indicate that doubling ('Aggregates' group) or halving ('Embryos 1/2' group) the initial cell number and modifying embryo volume, ploidy ('Embryos 4n' group) and the N/C ratio ('Embryos 2/1' group) reduce the probability of apoptosis in the resulting embryos. There was a higher probability of apoptosis in the inner cell mass of the blastocyst, but apoptotic cells were never observed at the morula stage in any of the experimental groups. Thus, manipulation of cell number, embryo volume, the N/C ratio and ploidy cause subtle changes in the occurrence of apoptosis, although these are mostly dependent on embryo stage and cell lineage (trophectoderm or inner cell mass), which have the greatest effect on the probability of apoptosis.

Lycopene Improves In Vitro Development of Porcine Embryos by Reducing Oxidative Stress and Apoptosis

In vitro culture (IVC) for porcine embryo development is inferior compared to in vivo development because oxidative stress can be induced by the production of excessive reactive oxygen species (ROS) under high oxygen tension in the in vitro environment. To overcome this problem, we investigated the effect of lycopene, an antioxidant carotenoid, on developmental competence and the mechanisms involved in mitochondria-dependent apoptosis pathways in porcine embryos. In vitro fertilized (IVF) embryos were cultured in IVC medium supplemented with 0, 0.02, 0.05, 0.1, or 0.2 μM lycopene. The results indicate that 0.1 μM lycopene significantly increased the rate of blastocyst formation and the total cell numbers, including trophectoderm cell numbers, on Day In terms of mitochondria-dependent apoptosis, IVF embryos treated with 0.1 μM lycopene exhibited significantly decreased levels of ROS, increased mitochondrial membrane potential, and decreased expression of cytochrome c on Days 2 and Furthermore, 0.1 μM lycopene significantly decreased the number and percentage of caspase 3-positive and apoptotic cells in Day-6 blastocysts. In addition, Day-2 embryos and Day-6 blastocysts treated with 0.1 μM lycopene showed significantly reduced mRNA expression related to antioxidant enzymes (SOD1, SOD2, CATALASE) and apoptosis (BAX/BCL2L1 ratio). These results indicate that lycopene supplementation during the entire period of IVC enhanced embryonic development in pigs by regulating oxidative stress and mitochondria-dependent apoptosis.

Embryotropic effects of vascular endothelial growth factor on porcine embryos produced by in vitro fertilization

Current research suggests that supplementing in vitro culture (IVC) media with vascular endothelial growth factor (VEGF) may have beneficial effects on the development of porcine embryos in vitro. However, the molecular signaling mechanisms underlying this effect are unclear. Therefore, we aimed to investigate the effects of VEGF on molecular signaling events during in vitro embryonic development of porcine embryos. Porcine oocytes matured in vitro were fertilized, and the resultant zygotes were cultured with 5 ng/mL of VEGF supplemented with or without fetal bovine serum from day 4 till day 7. Without VEGF and/or FBS served as the control group. Real-time quantitative PCR was used to detect expression patterns of apoptosis- and oxidative stress-related genes in day 7 blastocysts (BLs). Early-stage apoptosis was detected by annexin-V assays in day 2 and day 7 embryos. We found that the addition of VEGF throughout the culture period with or without FBS supplementation significantly improved embryo survival and development. Supplementation with VEGF in the IVC medium significantly increased early BL formation (p < 0.05), although addition of FBS on day 4 significantly increased hatched BL formation (p < 0.05) regardless of VEGF supplementation. However, supplementation of media with both VEGF and FBS increased the formation of expanded BLs synergistically. The average total cell numbers per BL were significantly (p < 0.05) higher in embryos supplemented with VEGF and FBS than in those supplemented with either VEGF or FBS alone. We also found that accumulation of reactive oxygen species in VEGF-treated embryos was significantly lower (p < 0.05) than that in untreated embryos. The mRNA levels of caspase-3 were significantly lower (p < 0.05), and those of Bcl-2 and Nrf-2 were significantly higher (p < 0.05) in embryos grown in VEGF-supplemented media than in embryos grown in non-supplemented media. Furthermore, on day 2, the numbers of viable embryos (44.06 ± 3.94%) and blastomeres (67.18 ± 3.60%) were significantly higher (p < 0.05), and the numbers of early apoptotic embryos (55.94 ± 3.94) and blastomeres (23.23 ± 4.22) were significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Furthermore, the numbers of early apoptotic cells in BLs on day 7 were also significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Overall, our results indicate that supplementing IVC media with VEGF during in vitro culture of porcine embryos increases their developmental potential.

Viability and DNA fragmentation of rainbow trout embryos (Oncorhynchus mykiss) obtained from eggs stored at 4 °C

In vitro storage of salmonid eggs leads to aging of the cells causing a decline in quality and reducing their capacity to develop and produce embryos. The quality of salmonid embryos is assessed by morphologic analyses; however, data on the application of biomarkers to determine the cell viability and DNA integrity of embryos in these species are limited. The aim of this study was to evaluate the effect on embryo development, viability and DNA fragmentation in the embryonic cells of in vitro storage time at 4 °C of rainbow trout (Oncorhynchus mykiss) eggs. The embryos were obtained by IVF from eggs stored for 0 (control), 48, and 96 hours at 4 °C. At 72 hours after fertilization, dechorionated embryos were examined to determine percentages of developed embryos (embryos with normal cell division morphology), viability (LIVE/DEAD sperm viability kit), and DNA integrity (terminal deoxynucleotidyl transferase [TdT] dUTP nick-end labeling assay). The percentage of developing embryos decreased (P < 0.05) with storage time of the eggs (95.10 ± 2.55; 88.14 ± 4.50; 79.99 ± 6.60 for 0, 48, and 96 hours, respectively). Similarly, cell viability decreased (P < 0.05; 96.07 ± 7.15; 80.42 ± 8.55; 77.47 ± 7.88 for 0, 48, and 96 hours, respectively), and an increase (P < 0.05) in DNA fragmentation in the embryos was observed at 96-hour storage. A positive correlation was found between cell DNA fragmentation and storage time (r = 0.8173; P < 0.0001). The results revealed that terminal deoxynucleotidyl transferase [TdT] dUTP nick-end labeling assay technique is reliable mean to assess the state of the DNA in salmonid embryos and that in vitro eggs storage for 96h reduces embryo development and cell DNA integrity. DNA integrity evaluation constitutes a biomarker of the quality of the ova and resulting embryos so as to predict their capacity to produce good-quality embryos in salmonids, particularly under culture conditions.

Actin Disorganization Plays a Vital Role in Impaired Embryonic Development of In Vitro-Produced Mouse Preimplantation Embryos

Assisted reproductive technology (ART) is being increasingly applied to overcome infertility. However, the in vitro production process, the main procedure of ART, can lead to aberrant embryonic development and health-related problems in offspring. Understanding the mechanisms underlying the ART-induced side effects is important to improve the ART process. In this study, we carried out comparative transcriptome profiling between in vivo- (IVO) and in vitro- produced (IVP) mouse blastocysts. Our results suggested that aberrant actin organization might be a major factor contributing to the impaired development of IVP embryos. To test this, we examined the effect of actin disorganization on the development of IVP preimplantation embryos. Specific disruption of actin organization by cytochalasin B (CB) indicated that well-organized actin is essential for in vitro embryonic development. Supplementing the culture medium with 10^–9 M melatonin, a cytoskeletal modulator in adult somatic cells, significantly reversed the disrupted expression patterns of genes related to actin organization, including Arhgef2, Bcl2, Coro2b, Flnc, and Palld. Immunofluorescence analysis showed that melatonin treatment of IVP embryos significantly improved the distribution and organization of actin filaments (F-actin) from the 8-cell stage onwards. More importantly, we found that melatonin alleviated the CB-mediated aberrant F-actin distribution and organization and rescued CB-induced impaired embryonic development. This is the first study to indicate that actin disorganization is implicated in impaired development of IVP embryos during the preimplantation stage. We also demonstrated that improving actin organization is a promising strategy to optimize existing IVP systems.

Cryotolerance of in vitro-produced porcine blastocysts is improved when using glucose instead of pyruvate and lactate during the first 2 days of embryo culture

The objective of the present study was to determine the effects of replacing glucose with pyruvate and lactate during the first 48 h of in vitro culture (IVC) in NCSU-23 medium on embryo development, embryo quality and survival of porcine blastocysts after vitrification. To this end, in vitro-produced (IVP) porcine oocytes were cultured with either glucose for 6 days (IVC-Glu) or pyruvate–lactate from Day 0 to Day 2 and then with glucose until Day 6 (IVC-PyrLac). Blastocysts were vitrified on Day 6 using the Cryotop device and, after warming, survival rate and the apoptosis index were evaluated after 24 h incubation in NCSU-23 medium. No significant differences were observed between IVC-Glu and IVC-PyrLac in terms of cleavage rate, blastocyst yield, total number of cells per blastocyst or the apoptosis index (1.82 ± 0.75% vs 3.18 ± 0.88%, respectively) of non-vitrified embryos. However, a significant increase was seen in hatching/hatched blastocysts in the IVC-PyrLac compared with IVC-Glu treatment group (12.71 ± 1.20% vs 3.54 ± 0.47%, respectively). Regardless of treatment, vitrification impaired the survival rate and the apoptosis index. When comparing both treatments after warming, the percentage of apoptotic cells was significantly higher for blastocysts in the IVC-PyrLac compared with IVC-Glu group (18.55 ± 3.49% vs 9.12 ± 2.17%, respectively). In conclusion, under the conditions of the present study, replacement of glucose with pyruvate–lactate during the first 48 h of culture resulted in a lower cryotolerance of IVP porcine embryos.

Glucose and glycine synergistically enhance the in vitro development of porcine blastocysts in a chemically defined medium

In the present study, the effects of glucose and/or glycine on the in vitro development of Day 5 (Day 0=IVF) porcine blastocysts were determined. The addition of 2.5-10 mM glucose to the chemically defined culture medium porcine zygote medium (PZM)-5 significantly increased blastocyst survival rates compared with those of blastocysts cultured in the absence of glucose. The addition of 5 and 10 mM glycine to PZM-5 containing 5 mM glucose significantly enhanced the development to hatching and the number of hatched blastocysts compared with no addition of glycine. However, the addition of glycine to PZM-5 with no glucose did not improve blastocyst development. The ATP content of Day 6 blastocysts cultured with glucose was significantly higher than that of blastocysts cultured in the absence of glucose, regardless of glycine supplementation. The diameter and total cell numbers were significantly greater, and the apoptotic index was significantly lower, in Day 6 blastocysts cultured with both glucose and glycine. These results indicate that glucose is an important energy source for the porcine blastocyst and that glucose and glycine act synergistically to enhance development to the hatching and hatched blastocyst stage in vitro.

Relationship Between Apoptotic-Like Changes in Stored Boar Semen and DNA Fragmentation in Preimplantation Embryos

The aim of this experiment was to study the relationship between apoptotic-like changes in spermatozoa and DNA fragmentation in embryos obtained after insemination with fresh and stored semen. The ejaculates collected from three boars (five ejaculates from the same boar) were extended in Biosolwens Plus extender and stored for five days at 15-17°C. Semen, both fresh (Day 0) and stored (Day 5) used for insemination was analysed to detect apoptotic-like changes using fluorescence method: an assay to assess early changes in the membrane integrity of the sperm using the YO-PRO-1 fluorophore. After 5.5 days of insemination embryos were flushed out of the uterus and DNA fragmentation using TUNEL was analysed. In the fresh semen an average of 2.7, 3.7 and 6.2% of apoptotic sperm was observed in boar nos. 1, 2 and 3, respectively. After five days of storage the percentage of apoptotic sperm significantly increased up to 8.0, 15.7 and 23.2% in each analysed boar. The TUNEL index was 7.1% in the morphologically normal expanded blastocysts obtained after insemination with stored semen, and approximately 1.7% after insemination with fresh semen. A greater number of degenerated embryos and higher incidence of DNA fragmentation in the morphologically normal blastocysts were observed after insemination with stored semen which consists of higher percentage of apoptotic sperm compared to results from insemination with fresh semen.

Presence of cleaved caspase 3 in swine embryos of different developmental capacities produced by parthenogenetic activation

This study assessed the presence of cleaved caspase 3 (CC3) during the in vitro development of swine embryos produced by parthenogenetic activation (PA). Embryos with high and low capacity to develop into blastocysts and the exposure to a caspase inhibitor (z-DEVD-fmk) were used to investigate the effect of CC3 on embryo development. The blastocyst rate (64.3% vs. 16.4%) and the average number of nuclei per blastocyst (39.7 vs. 19.8) were significantly higher (P < 0.05) in early- (before 24 hr) compared to late- (between 24 and 48 hr) cleaving embryos after PA. CC3 was mainly detected in the cytoplasm of Day-2 and -4 embryos, but was primarily localized in the nucleus of Day-5 and -6 embryos. The fluorescence signal for CC3 relative to negative controls was significantly higher (P < 0.05) in early- (2.42-fold) compared to late-cleaving (1.39-fold) embryos at Day 2 of culture. Treatment with z-DEVD-fmk during the first 24 or 48 hr of the culture period resulted in more embryos developing into blastocysts compared to the control group (55.8% and 55.1% vs. 37%, respectively; P < 0.05). This study confirmed the presence of CC3 in PA embryos from the two-cell to the blastocyst stage, and revealed that CC3 cellular-localization changed during embryo development. CC3 was shown to be more abundant in early-cleaving and more developmentally competent embryos compared to late-cleaving and less developmentally competent embryos. The inhibition of caspase activity at the beginning, but not at the end, of the culture period affected development of PA embryos.

L-carnitine enhances oocyte maturation and development of parthenogenetic embryos in pigs

The objective was to determine whether adding L-carnitine in IVM/IVC medium enhanced maturation and developmental competence of porcine oocytes in vitro. Oocyte maturation rates did not differ significantly among groups supplemented with 0, 0.25, 0.5, or 1 mg/mL of L-carnitine added during IVM (although 2 mg/mL of L-carnitine reduced maturation rate). Compared with control oocytes, those treated with 0.5 mg/mL of L-carnitine during IVM had greater (P < 0.05) rates of blastocyst formation after parthenogenetic activation, and these blastocysts had less (P < 0.05) apoptosis. Adding 0.5 mg/mL of L-carnitine during IVM also significantly reduced intracellular reactive oxygen species (ROS), and increased glutathione (GSH) concentrations. With or without glucose supplementation, 0.5 mg/mL of L-carnitine in the IVM medium significantly hastened nuclear maturation of oocytes. Moreover, supplementing the IVM medium with either glucose or L-carnitine increased (P < 0.05) percentages of oocytes that reached the metaphase II (MII) stage, relative to a control group. Final maturation rates in IVM medium containing either glucose or L-carnitine were not significantly different. Adding L-carnitine (0 to 2 mg/mL) to IVC medium for activated porcine oocytes did not significantly affect development. However, 0.5 mg/mL of L-carnitine in IVC medium significantly reduced reactive oxygen species levels and apoptosis in activated blastocysts, although glutathione concentrations were not significantly altered. In conclusion, adding L-carnitine during IVM/IVC improved developmental potential of porcine oocytes, and also the quality of parthenogenetic embryos, probably by accelerating nuclear maturation, and preventing oxidative damage and apoptosis.

Effect of semen quality in transgenic boars on the developmental competence of preimplantation embryos

The aim of this study was to compare the fertilising capacity of sperm from 6 transgenic (TG) and 6 non-transgenic (NTG) boars based on analyses of embryos resulting from insemination with sperm from these particular boars. Expanded blastocysts were collected from five groups of synchronised gilts (six gilts per group) inseminated by TG boars bearing a gene construct containing the human alpha1,2-fucosyltransferase gene and by NTG boars. The ejaculates used for insemination were analysed to detect apoptotic changes using two fluorescence methods: an assay to assess early changes in the membrane integrity of the sperm using the YO-PRO-1 fluorophore and an assay for phosphatidylserine (PS) translocation across the plasma membranes using fluorescein-labelled Annexin-V. Our results, using a combination of YO-PRO-1 and PI fluorophores, revealed no significant differences in the percentage of sperm subpopulations between non-transgenic and transgenic boars (P<0.01). Moreover, the second fluorescent probe also revealed no significant differences between the average values of live (Ann-V(-)/PI(-)), early apoptotic (Ann-V(+)/PI(-)), and late apoptotic/early necrotic sperm (Ann-V(+)/PI(+)) as calculated for TG and NTG boars. Only the percentage of necrotic sperm (Ann-V(-)/PI(+)) was significantly different (P<0.05) between transgenic and non-transgenic boars (3.4%+/-2.7; 7.2%+/-2.1, respectively). The quality of the preimplantation embryos at the blastocyst stage was determined by counting the number of cells, observing a TUNEL-positive reaction and by caspase-3 labelling. We found that expanded blastocysts that were derived from gilts inseminated with TG and NTG boar semen showed almost no DNA fragmentation (80%) and 70% caspase-3 activity. The expanded blastocysts that were derived from gilts inseminated with TG and NTG boar semen did not differ significantly in their DNA fragmentation, and there were no differences in caspase-3 activity. These results revealed a positive correlation between the percentage of blastocysts with TUNEL-positive nuclei and the percentage of blastocysts with caspase-3 activity (r=0.9787; P<0.0001).

Superfine open pulled straws vitrification of porcine blastocysts does not require pretreatment with cytochalasin B and/or centrifugation

The present study investigated the in vitro development of and cytoskeletal disruption suffered by in vivo-derived porcine blastocysts subjected to superfine open pulled straws (SOPS) vitrification. Blastocysts were either untreated prior to SOPS vitrification or were subjected to one of the following three pretreatment protocols: (1) centrifugation (12 min, 13 000g); (2) 25 min equilibration with 7.5 μg mL–1 cytochalasin B; or (3) equilibration with cytochalasin B followed by centrifugation. After 24 h culture, fresh (n = 32) and vitrified–warmed (n = 188) blastocysts were evaluated by stereomicroscopy, with survival and hatching rates recorded. Some blastocysts were stained with 4′,6′-diamidino-2-phenylindole and processed for cytoskeletal evaluation. Three cytoskeletal patterns were identified: Grade I, intact cytoskeleton; Grade II, gross maintenance of integrity, but with some clumps of actin within the cytoplasm; and Grade III, a highly disrupted cytoskeleton. There were no differences in the survival, hatching and cell death rats, total cell number or cytoskeletal integrity between the different vitrification groups. Cell death was greater for vitrified blastocysts than for fresh blastocysts (3.6 ± 0.4% v. 0.4 ± 0.7%, respectively; P < 0.05) and the percentage of blastocysts with a Grade I cytoskeletal pattern was lower for vitrified compared with fresh blastocysts (60.8% v. 92%, respectively; P < 0.05). The vitrified–warmed blastocysts that hatched during culture exhibited a Grade I cytoskeletal pattern. In conclusion, successful SOPS vitrification of porcine blastocysts does not require pretreatment with cytochalasin B and/or centrifugation.

The importance of growth factors for preimplantation embryo development and in-vitro culture

PURPOSE OF REVIEW

The present paper reviews evidence that preimplantation embryos are naturally exposed and designed to respond to growth factors during preimplantation development.

RECENT FINDINGS

Recent studies have demonstrated that in-vivo human preimplantation embryos are exposed to a mixture of many different growth factors, expressed by the follicles, oviducts and endometrium. Receptors for many of these growth factors have also been shown to be expressed by preimplantation embryos, suggesting a functional role during preimplantation development. Studies of in-vitro fertilization in both animals and humans indicate that in-vitro culture of embryos in conventional media lacking growth factors can result in suboptimal growth and a variety of short-term and long-term developmental abnormalities. Studies of embryo coculture indirectly suggest that growth factors can improve in-vitro development. Many studies of defined growth factor supplements demonstrate that their inclusion in culture media can substantially improve preimplantation development and efficacy of in-vitro fertilization, and may reduce long-term developmental abnormalities as well.

SUMMARY

Embryos are naturally exposed to a complex mixture of growth factors that play an important role in preimplantation embryo development and that are likely to be of substantial benefit if added to in-vitro culture media.

Role of nonessential amino acids on porcine embryos produced by parthenogenesis or somatic cell nuclear transfer

Amino acids play a multitude of roles during early embryonic development and have been demonstrated to facilitate improved development of in vivo or in vitro fertilized and parthenogenetic embryos in several species. However, review of emerging literatures, shows that culture milieu of cloned embryos might be different from those of in vitro fertilized embryos. This study therefore, evaluated the effect of nonessential amino acids (NEAA) on yield and quality of porcine embryos produced by somatic cell nuclear transfer (SCNT) and compared them with parthenogenetic embryos as control. Analysis showed that, supplementation of NEAA to culture medium significantly improved the blastocyst rate of parthenogenetic (38.9 +/- 8.8 vs. 27.5 +/- 9.0%) as well as SCNT (22.5 +/- 2.2 vs. 13.8 +/- 3.4%) embryos although cleavage rates were not different (P < 0.05). These blastocysts also had higher hatching ability and contained higher cell number than control blastocysts (P < 0.05). TUNEL labeling revealed that blastocysts cultured in the presence of NEAA were less predisposed to biochemical apoptosis and showed lower indices of TUNEL, fragmentation, and total apoptosis than those cultured in the absence of NEAA (P < 0.05). Real-time qRT-PCR analysis further revealed that NEAA decreased the expression ratio of BAX:BCL-xL and enhanced the relative abundance of IGF2 transcripts. Therefore, our study suggests that NEAA improves the yield and quality of cloned porcine embryos by enhancing blastocyst expansion, hatching, and total cell number and decreasing the apoptosis by positively modulating the expression of embryo survival related genes, similar to those reported for in vivo or in vitro fertilized embryos. Nonessential amino acids improve the yield and quality of cloned and parthenogenetic porcine embryos and modulate the expression of embryo survival related genes.

Sexual maturity and reproductive phase of oocyte donor influence the developmental ability and apoptosis of cloned and parthenogenetic porcine embryos

This study investigated the influence of the sexual maturity and reproductive phase of oocyte donor on the developmental ability and quality of porcine embryos produced by somatic cell nuclear transfer (SCNT) or parthenogenesis (PA). Blastocyst quality was evaluated in terms of hatching ability, total nuclei number and types of apoptosis. Results revealed that maturation rate was not influenced by the reproductive status of the oocyte donor. However, when subjected to PA or SCNT, embryos derived from sexually mature sow oocytes developed to blastocysts at higher rates and had higher cell number than those derived from immature gilt oocytes (p<0.05). Significant effect of reproductive phase, luteal versus follicular, was also noted with luteal stage oocytes yielding higher (p<0.05) rate of blastocyst formation (PA: 54.3+/-1.3% versus 44.8+/-0.3%; SCNT: 29.4+/-0.2% versus 22.7+/-0.1%). Blastocysts derived from luteal phase oocytes also had higher (p<0.05) hatching ability (PA: 44.2+/-1.1%; SCNT: 39.6+/-4.7%) and cell number (PA: 77.4+/-4.9; SCNT: 54.9+/-2.4) than those derived from follicular phase oocytes (PA: 34.9+/-0.9%, 67.2+/-3.9; SCNT: 34.6+/-2.7%, 47.5+/-2.9). TUNEL assay and Hoechst 33342 staining revealed that percentage of blastocysts showing total apoptosis did not differ among the groups. However, luteal phase oocyte-derived blastocysts had the highest incidence of nuclear fragmentation. Among cloned blastocysts that showed the signs of apoptosis, the highest index of total apoptosis was observed in prepubertal oocyte-derived blastocysts (5.2+/-0.7). Blastocysts derived from luteal phase oocytes showed the lowest TUNEL index (2.0+/-0.5). The present study therefore, indicates that the sexual maturity and reproductive phase of cytoplast donor significantly influences the developmental ability, apoptosis and quality of blastocysts produced by SCNT or PA. Oocytes from sexually mature sows in luteal phase of their reproductive cycle may be better cytoplast recipients for SCNT.

Active caspase-3 and ultrastructural evidence of apoptosis in spontaneous and induced cell death in bovine in vitro produced pre-implantation embryos

In this study we investigated chronological onset and involvement of active caspase-3, apoptotic nuclear morphology, and TUNEL-labeling, as well as ultrastructural evidence of apoptosis, in both spontaneous and induced cell death during pre-implantation development of bovine in vitro produced embryos. Pre-implantation embryos (2-cell to Day 8 blastocysts) were cultured with either no supplementation (untreated) or with 10 microM staurosporine for 24 hr (treated). Embryos were subjected to immunohistochemical staining of active caspase-3, TUNEL-reaction for detection of DNA degradation and DAPI staining for detection of apoptotic nuclear morphology, and subjected to fluorescence microscopy. Additionally, treated and untreated blastocysts were fixed and processed for ultrastructural identification of apoptosis. Untreated embryos revealed no apoptotic features at 2- and 4-cell stages. However, active caspase-3 and apoptotic nuclear morphology were observed in an untreated 8-cell stage, and TUNEL-labeling was observed from the 16-cell stage. Blastomeres concurrently displaying all apoptotic features were present in a few embryos at 16-cell and morula stages and in all blastocysts. All three features were observed from the 8-cell stage in treated embryos, and blastomeres with apoptotic features appeared more numerous in treated than in untreated embryos. Ultrastructural evidence of apoptosis occurred with a comparable distribution pattern as apoptotic features detected by fluorescence microscopy in both treated and untreated blastocysts. Activation of caspase-3 is likely involved in both spontaneous and induced apoptosis in bovine pre-implantation embryos, and immunohistochemical staining of active caspase-3 may be used in combination with other markers to identify apoptosis in pre-implantation embryos.

The effectiveness of the stereomicroscopic evaluation of embryo quality in vitrified-warmed porcine blastocysts: an ultrastructural and cell death study

The objective of this study was to analyze the validity of the stereomicroscopic evaluation of vitrified-warmed (V-W) porcine blastocysts. Unhatched blastocysts were obtained from Large-white gilts (n=10). Blastocysts (n=156) were vitrified using the Open Pulled Straw technology. After warming, V-W blastocysts were cultured for 24h (V24). Then, their developmental progression was morphologically assessed by stereomicroscopy and classified as: V24 viable re-expanded blastocysts; V24 viable hatched blastocysts or V24 degenerated. Blastocysts which re-expanded or hatched after warming were considered viable. Some fresh blastocysts were not vitrified and were evaluated after 24h in culture (F24). By stereomicroscopic analysis all the fresh blastocysts were considered viable. Some F24, V24 re-expanded viable, V24 hatched viable and V24 degenerated blastocysts were processed for transmission electron microscopy (n=13, 19, 9 and 9, respectively) or assessed by TUNEL for cell-death evaluation (n=16, 21, 11 and 21, respectively). All V24 hatched blastocysts showed similar ultrastructure to fresh blastocysts. However, some V24 re-expanded blastocysts considered viable (6/19) revealed ultrastructural alterations. Degenerated V24 blastocysts showed ultrastructural disintegration. Hatched V24 blastocysts did not differ (p>0.05) from F24 hatched blastocysts with regard to the ratio of dead cells (2.8+/-0.5% versus 1.9+/-0.3%, respectively). However, V24 expanded blastocysts had higher (p<0.01) cell death levels (4.3+/-3.4%) than those observed in the F24 expanded blastocysts (1.1+/-0.3%). The degenerated blastocysts showed the highest cell-death index (19.4+/-6.3%). In summary, V-W blastocyst hatching during in vitro culture appears to coincide with good ultrastructure and low cell-death index, suggesting that the hatching rate assessed by stereomicroscopy is more appropriate than embryo re-expansion for an evaluation of V-W blastocyst quality.

Differential but beneficial effect of phytohemagglutinin on efficiency of in vitro porcine embryo production by somatic cell nuclear transfer or in vitro fertilization

In vitro production of porcine embryos has become routine in most laboratories but the yield and quality of the resultant blastocysts remains sub-optimal. Phytohemagglutinin (PHA) is an N-acetylgalactosamine/galactose sugar-specific lectin with a wide variety of biological activities including mitogenesis, mediation of cell recognition and agglutination of cells. This study was therefore, designed to investigate the effect of PHA on the preimplantation development and quality of parthenogenetic, somatic cell nuclear transferred (SCNT) and in vitro fertilized (IVF) porcine embryos cultured in the absence or presence of PHA. Analysis showed that, supplementation of PHA significantly improved the blastocyst rate of parthenogenetic (70.6 +/- 0.2 vs. 51.4 +/- 0.6%) and SCNT (27.7 +/- 1.7 vs. 12.5 +/- 0.3%) embryos but not IVF embryos (25.0 +/- 14.3 vs. 20.1 +/- 12.7%). Nonetheless, PHA-treated blastocysts had higher hatching ability and contained higher cell number than control blastocysts in all the groups (P < 0.05). TUNEL labeling revealed that blastocysts cultured in the presence of PHA were less predisposed to biochemical apoptosis and showed lower indices of TUNEL, fragmentation and total apoptosis than those cultured in the absence of PHA (P < 0.05). Real time qRT-PCR analysis of parthenogenetic blastocysts revealed that PHA decreased the expression ratio of BAX:BCL-xL transcripts. Therefore, our study suggests that PHA improves the blastocyst yield and quality by enhancing blastocyst expansion, hatching and total cell number and decreasing the apoptosis. However, PHA has a differential effect on development rate of IVF derived embryos. These results may represent an approach towards achieving better preimplantation development of porcine embryos in vitro.

Embryo quality and production efficiency of porcine parthenotes is improved by phytohemagglutinin

In vitro production of porcine embryos has become routine in most laboratories but the yield and quality of the resultant blastocysts remain suboptimal. Phytohemagglutinin (PHA) is an N-acetylgalactosamine/galactose sugar-specific lectin with a wide variety of biological activities including mitogenesis, mediation of cell recognition, and agglutination of cells. This study was therefore, designed to investigate the effect of PHA on the preimplantation embryo development and quality of in vitro produced porcine parthenotes. Parthenogenetic presumptive diploid zygotes were produced in vitro by electrical activation and cultured in the absence or presence of PHA at different concentrations (0, 5, 10, 15, 20 microg/ml). There were no significant differences in the cleavage rate of porcine parthenotes in control and treatment groups at all tested concentrations of PHA (P < 0.05). However, supplementation of PHA at the concentration of 15 microg/ml significantly improved the blastocyst rate (68.9 +/- 1.5% vs. 43.1 +/- 4.1%), hatching rate (25.8 +/- 3.1% vs. 8.9 +/- 2.0%), and total nuclei number (95.5 +/- 9.3 vs. 63.4 +/- 4.3) when compared to control group (P > 0.05). TUNEL labeling revealed that blastocysts in PHA group were less predisposed to biochemical apoptosis than in control group while total apoptosis and nuclear fragmentation remained unaltered. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis further revealed that PHA decreased the expression ratio of BAX/BCL-XL and enhanced the relative abundance of IGF2 transcripts. Therefore, our study suggests that PHA improves the blastocyst yield and quality by enhancing blastocyst expansion, hatching, and total cell number and decreasing the apoptosis by positively modulating the expression of embryo survival related genes.

Glucose utilization and the PI3-K pathway: mechanisms for cell survival in preimplantation embryos

The maintenance of optimal glucose utilization during the preimplantation period is critical for embryo survival. A decrease in glucose transport during preimplantation development has been linked to the early steps of programmed cell death in these embryos. Decreased glucose transport is not thought to be simply a consequence of cell death, rather it is thought to be a trigger that can initiate the apoptotic cascade. Extensive apoptosis during the preimplantation period may manifest later in pregnancy as a malformation – or miscarriage, if cell loss is excessive. Phosphatidylinositol 3-kinase (PI3-K) is a known regulator of a number of physiologic responses including cellular proliferation, growth, and survival as well as glucose metabolism. Studies performed in other cell systems have demonstrated that the PI3-K pathway plays a critical role in maintaining glucose transport and metabolism. This review will present the current evidence that suggests that PI3-K is vital for preimplantation embryo survival and development. In addition, data demonstrating that PI3-K activity is important for glucose metabolism during this early developmental period will be discussed.

Ultrastructure and cell death of in vivo derived and vitrified porcine blastocysts

Morphological and molecular signs of injury and cell death and subsequent regeneration following vitrification of porcine blastocysts were evaluated by light (LM) and transmission electron microscopy (TEM) as well as TUNEL/propidium iodide (PI) nuclear staining followed by confocal microscopy (CSM). In vivo derived blastocysts were assigned to one of the following four groups: Controls-(1) fixed immediately after collection (C0h) and (2) after 24 hr culture in vitro (C24h) and vitrified embryos-(3) fixed immediately after vitrification and warming (V0h), and (4) after 24 hr of culture upon warming after vitrification (V24h). Observation by LM and TEM showed that the V0h embryos displayed collapse of the blastocoele cavity (BC) and cell swelling, a general distension or shrinkage of mitochondria and massive increase in the amount of vesicles, vacuoles, and secondary lysosomes (SLs). Approximately 2/3 of the V24h embryos had recovered, whereas the remaining 1/3 were degenerated. Recovered embryos displayed almost normal blastocyst morphology, except for a widening of the perivitelline space, accumulation of debris and partial distension of mitochondria, whereas degenerated embryos were disintegrated into a poorly defined mass of cells and debris including cells with abundant degeneration of mitochondria and other organelles. Both recovered and degenerated embryos displayed a persistent abundance of presence of small membrane bounded vesicles, vacuoles, and SLs. Evaluation of TUNEL/PI stained embryos showed only occasional appearance of TUNEL positive nuclei with typical apoptotic morphology in controls (C0h 0.67%, C24h 1.22%) and in the V0h embryos (0.93%). The percentage of apoptotic nuclei in embryos at V24h was significantly higher than in all other groups (2.64%). Vitrified embryos showed significantly increased appearance of DNA fragmented nuclei without typical morphological features of apoptosis (V0h 1.43%, V24h 4.30%) compared with controls (C0h 0.26%, C24h 0.45%). The observed morphological changes and increased DNA fragmentation observed immediately after vitrification and warming probably reflects a direct damaging effect of vitrification. During 24 hr of culture a portion of the embryos was able to regenerate and along with the regenerative process, apoptosis--a possible pathway for elimination of damaged cells--became evident.

Porcine embryo development and fragmentation and their relation to apoptotic markers: a cinematographic and confocal laser scanning microscopic study

Porcine embryo selection prior to transfer is mainly influenced by morphological criteria. However, the relationship between embryonic morphology, developmental potential and cell death by apoptosis in porcine embryos is still unclear. The aim of this study was to establish embryo quality parameters for in vivo fertilised porcine embryos based on timing of development in vitro, embryo morphology and the presence of apoptosis. The kinetics of development and morphological parameters were investigated in a time-lapse cinematographic experiment. Possible links between embryo morphology and apoptosis were examined via a confocal laser scanning experiment, analysing nuclear changes, annexin V and terminal dUTP nick-end labelling. The timing of early cleavages was firmly linked to embryo developmental competence in vitro. Attainment of at least the 5-cell stage before 77 h post insemination and attainment of the morula stage before 102 h post insemination significantly increased the odds for reaching the early blastocyst stage. Overall, a negative effect of fragmentation percentage and fragmentation pattern on subsequent embryonic development was observed, but the developmental potential of embryos experiencing slight fragmentation (0–5%) was not different from embryos without fragmentation. Correlations detected between developmental arrest and fragmentation, and fragmentation and apoptosis were 0.60 and 0.87 (P < 0.05) respectively. Only a minority of the embryos arrested between the 1- and 4-cell stage displayed biochemical characteristics of apoptosis. Consequently, a significant correlation (0.57) between developmental arrest and apoptosis could only be established for embryos arrested after embryonic genome activation.

Apoptotic processes during mammalian preimplantation development

The paper provides a review of the current state of knowledge on apoptosis during normal preimplantation development based on the literature and on the authors' own findings. Information is focused on the occurrence and the characteristics of spontaneous apoptotic processes. Reports concerning the chronology and the incidence of programmed cell death in mouse, cow, pig and human embryos in early preimplantation stages up to the blastocyst stage are summarized. In addition, specific attributes of the apoptotic process in mammalian preimplantation development are provided, including the description of both morphological and biochemical features of cell death.

Effects of oxygen tension on the development and quality of porcine in vitro fertilized embryos

The present study was conducted to examine the effect of oxygen tension during in vitro culture (IVC) of porcine oocytes/embryos on their development and quality using two different culture systems. Porcine cumulus oocyte complexes (COCs) were matured (IVM) and fertilized (IVF) in vitro, and subsequently cultured for 6 days in a simple and economical portable incubator or a standard CO(2) incubator. While the same temperature (38.5 degrees C) and CO(2) concentration (5%) were used in the both systems, the portable incubator was operated in a negative air pressure (- 300 mmHg) to create an O(2) level at 8-10% (low O(2) concentration), or in a positive air pressure (high O(2) concentration). To compare the two culture systems, IVM and IVF of COCs and subsequent IVC of in vitro produced (IVP) embryos were carried out in the portable incubator with a low O(2) concentration (Group I) or in the standard incubator with a high O(2) concentration (Group II). To assess the effect of O(2) concentration on IVC of IVP embryos, some oocytes that had been cultured in the standard incubator for IVM and IVF were subsequently cultured in the portable incubator with a low O(2) concentration (Group III) or a high O(2) concentration (Group IV). The occurrence of DNA fragmentation in the blastocysts produced under different culture conditions was examined by TUNEL staining to assess embryo quality. The rates of oocytes that reached MII and were penetrated by spermatozoa following IVF did not differ between the two incubation systems. In contrast, the proportions of development to blastocysts and the mean cell number of blastocysts in Group I were higher than those in Group II and Group IV. The index of DNA-fragmented nucleus in the blastocysts of Group I was significantly lower than that in the blastocysts of Group II. Therefore, low oxygen tension during IVM, IVF and IVC enhanced the subsequent development of IVP embryos to the blastocyst stage and improved their quality.

Quality of porcine blastocysts produced in vitro in the presence or absence of GH

GH receptor (GHR) mRNA is expressed in bovinein vitroproduced embryos up to the blastocyst stage and GH improves the quality of bovine embryos by increasing blastocyst cell numbers and reducing the incidence of apoptosis as evaluated by DNA strand-break labelling. Porcinein vitroproduced blastocysts have lower cell numbers thanin vivoblastocysts and exhibit higher incidences of apoptosis. Therefore we investigated the effects of 100 ng GH/ml NCSU23 medium duringin vitroculture of presumptivein vitrofertilized sow zygotes on embryo development and blastocyst quality (defined by diameter, cell number, apoptosis and survival after non-surgical transfer).In vivoproduced blastocysts were analysed concurrently as a reference value. GHR was expressed in embryos from the 2-cell to blastocyst stages. GH had no effect on blastocyst development or cell numbers, but increased the mean blastocyst diameter. The incidence of apoptosis, detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL), was decreased by GH, but when non-TUNEL-labelled apoptotic fragmented nuclei were included, no difference was seen. GH appeared to slow down the progression of apoptosis though.In vivoproduced blastocysts presented no apoptotic nuclei, and contained higher cell numbers and larger diameters. Pregnancy rates on day 11 were similar for all groups, but survival was poorer forin vitrothanin vivoproduced blastocysts. In this study GH appeared to be beneficial only from the blastocyst stage, but the presence of GHR from early cleavage stages nevertheless indicates a role for GH throughout porcine embryo development and deserves further investigation.

Development, DNA fragmentation and cell death in porcine embryos after 24 h storage under different conditions

For practical applications of porcine embryo transfer (ET) it is important to develop feasible embryo storage conditions. The aim of the present study was to evaluate the effect of short-term storage (24 h) on the quality of in vivo produced porcine embryos. Three temperatures 18, 25 and 38 degrees C and three different media: Dulbecco's phosphate buffered saline (DPBS), TCM199 and Emcare, were tested for two different embryo ages: D4 embryos (collected 144 h after hCG treatment) and D5 embryos (collected 168 h after hCG). After slaughter of the donor gilts, embryos were collected and transported at 25 degrees C to the lab where morulas and blastocyst were selected (D4 n = 222; D5 n = 167) and randomly used as controls or distributed over the treatment groups. Developmental stage and embryo diameter were assessed by normal light microscopy, while total number of cells and incidence of apoptosis were assessed using a fluorescent embryo quality staining technique that combines three different dyes: Ethidium Homodimer (EthD-1), TUNEL and Hoechst 33342. Following 24 h storage, D5 embryos had higher rates of hatching (24%) and degeneration (9%) compared to D4 embryos (10 and 4%, respectively; P < 0.05). Embryos stored at 38 degrees C had higher rates of hatching (37%) compared to those ones stored at 25 degrees C (13%) or 18 degrees C (0%; P < 0.01). More embryos hatched when stored in medium Dulbecco's phosphate buffered saline (DPBS) or in TCM199 compared to those stored in Emcare (P < 0.05). A higher percentage of embryos stored at 18 degrees C degenerated compared to those stored at 25 or 38 degrees C (P < 0.01). No significant increase in apoptosis was observed after storage compared to the rates of apoptosis at 0 h (controls) or between the different storage groups. Based on the results we conclude that D4 porcine embryos produced in vivo, selected under normal light microscopy and stored at 25 degrees C in a serum free medium for 24 h will have a suitable developmental stage for ET and a high embryo quality.

Integrating new technologies with embryology and animal production

The present review describes a range of selected farm animal embryo technologies used in embryological research and applied in animal breeding and production. Some of the techniques are driven by the breeder’s wish to obtain animals with higher breeding values, whereas others are primarily driven by the curiosity of researchers. The interaction between basic research and practical application in these areas is still a characteristic feature for people who contribute to the International Embryo Transfer Society (IETS) and has been an advantage for both researchers and breeders. One example of such an interaction is that detailed structural analyses have described quality differences between embryos of various origins and, following embryo transfer, the pregnancy results have confirmed the correlation between morphology and viability. Another example is that polymerase chain reaction technology has allowed detection of Y-specific sequences in male embryos and has become a tool in animal production today. Data from domestic animal genome sequencing will provide a great deal of new information. A major challenge for the years to come will be using this information in a physiologically meaningful context and to continue the efforts to convert the laboratory experience into use in practise. Finally, it is important to obtain societal acceptance for a wider application of many of the technologies, such as in vitro embryo production and cloning.

Chronology of apoptosis in bovine embryos produced in vivo and in vitro

The postimplantation developmental potential of embryos can be affected by various forms of cell death, such as apoptosis, at preimplantation stages. However, correct assessment of apoptosis is needed for adequate inference of the developmental significance of this process. This study is the first to investigate the independent chronological occurrence of apoptotic changes in nuclear morphology and DNA degradation (detected by the TUNEL reaction) and incidences of nuclei displaying these features at various preimplantation stages of bovine embryos produced both in vivo and in vitro. Different elements of apoptosis were observed at various developmental stages and appeared to be differentially affected by in vitro production. Nuclear condensation was observed from the 6-cell stage in vitro and the 8-cell stage in vivo, whereas the TUNEL reaction was first observed at the 6-cell stage in vitro and the 21-cell stage in vivo. Morphological signs of other forms of cell death were also observed in normally developing embryos produced both in vivo and in vitro. The onset of apoptosis seems to be developmentally regulated in a stage-specific manner, but discrete features of the apoptotic process may be differentially regulated and independently modulated by the mode of embryo production. Significant differences in indices of various apoptotic features were not evident between in vivo- and in vitro-produced embryos at the morula stage, but such differences could be observed at the blastocyst stage, where in vitro production was associated with a higher degree of apoptosis in the inner cell mass.

TUNEL analyses of bovine blastocysts after culture with EGF and IGF-I

Experiments were carried out to investigate the beneficial effects of IGF-I or EGF on bovine embryo development in chemically defined embryo culture media and resultant incidences of nuclear DNA fragmentation as an indication of embryo quality. Presumptive IVF zygotes were randomly cultured in either control (with no added growth factor) or treatment groups, i.e., with 50 ng/ml IGF-I (experiment 1) or 5 ng/ml EGF (experiment 2). IGF-I supplemented to culture media significantly improved proportions of blastocysts from oocytes inseminated compared to untreated controls (38.0% vs. 28.5%). Only embryos reaching the blastocyst stage on day 8 showed significant effects of IGF-I treatment by resulting in higher blastocyst cell numbers (162 vs. 141) and lower percentages of TUNEL positive nuclei (2.1% vs. 3.3%) when compared to controls. Blastocyst development from oocytes was also improved by EGF supplementation compared to untreated controls (38.5% vs. 30.7%). Cell numbers of either day 7 or day 8 blastocysts were not affected by EGF treatment, nor were percentages of TUNEL positive nuclei when compared with controls. Similar proportions of parthenogenetically activated oocytes developed to blastocysts as for inseminated oocytes (28.8%). Parthenogenetic blastocysts contained fewer cells (93) and an increased percentage of TUNEL positive nuclei (5.7%) than were found for IVF embryos.

Assessment of mammalian embryo quality: what can we learn from embryo morphology?

Embryo morphology assessment, however imperfect it may be, is at present the most popular method for embryo selection prior to transfer, both in human and bovine assisted reproduction. A major difference between human and bovine embryos is the fact that in the latter, assessment of morphology is jeopardized by the opacity of the blastomeres, which is caused by lipid droplet accumulation. This opacity makes it difficult to assess nuclear and nucleolar morphology, aspects which can easily be evaluated in human zygotes or early cleaving embryos. However, recent research which focused on correlation between bovine embryo morphology and embryonic ultrastructure, gene expression and cryoresistance, has provided evidence that much more can be deduced from mere embryo morphology than previously thought. Morphological features such as colour of the blastomeres, the extent of compaction, timing of blastocyst formation and expansion and diameter of the embryo at hatching can be linked with embryo quality. On the other hand, cattle embryos of deviant chromosomal constitution or with aberrant genetic make-up cannot be selected against by means of the current morphological techniques. Possible solutions include the visualization of bovine pronuclei at the zygote stage by means of ultracentrifugation or multiphoton laser scanning microscopy, and adjustment of genetic analysis in order to reconstruct embryo genetic make-up starting from the biopsy material.

Expression of Bcl-2 and Bax proteins in relation to quality of bovine oocytes and embryos produced in vitro

The mechanisms underlying the visual assessment and selection of immature oocytes resulting in optimum embryonic development following in vitro maturation, fertilization and culture (in vitro maturation (IVM)/in vitro fertilization (IVF)/in vitro embryo culture (IVC)) are unknown. Also, the reasons for the more frequent occurrence of cytoplasmic fragmentation in in vitro produced bovine embryos, resulting in poor survival following cryopreservation and decreased pregnancy rates following embryo transfer are not clear. The objectives of this study are: (1) to investigate whether differences in the quality of immature oocytes and embryo fragmentation are associated with apoptosis; and (2) to study the pattern of Bcl-2 and Bax expression in oocytes and embryos to help elucidate their potential roles in the regulation of apoptosis during development. Bovine oocytes were obtained from slaughterhouse ovaries and divided into four grades (grades I-IV) based on their morphology. Oocytes of different grades were cultured in serum-free medium for 48h. Embryos were produced only from grade I oocytes (highest quality) via IVM, IVF and IVC procedures. The morphological analysis of apoptosis in oocytes and embryos was carried out using propidium iodide staining and terminal deoxynucleotidyl transferase mediated dUTP nick end labeling. The expression of Bcl-2 and Bax in oocytes and embryos of different qualities and stages was determined using western blotting. The results showed that the number of morphologically abnormal oocytes with shrinkage and/or fragmentation of the ooplasm, which are typical features of apoptosis, was significantly higher in grade IV oocytes (denuded oocytes, the lowest quality) than in grade I oocytes after 48h in vitro culture (P<0.05). DNA fragmentation, a hallmark of the biochemical changes seen in apoptotic cell death, was observed in morphologically fragmented oocytes and embryos. The expression of Bcl-2 was high in good quality oocytes and embryos, low in fragmented embryos, and hardly detectable in denuded oocytes. In contrast, the expression of Bax was found in all types of oocytes and embryos with the highest expression in the denuded oocytes. This implies that the ratio of Bcl-2 to Bax may be used to gauge the tendency of oocytes and embryos towards either survival or apoptosis. Overall, our results show that apoptosis appears to be an underlying mechanism of bovine oocyte degeneration and embryo fragmentation. Interactions between the Bcl-2 family of proteins may play a critical role in pre-implantation embryo development. These findings could have important implications for improving IVF and related techniques.

Blastocyst evaluation by means of differential staining: a practical approach

Techniques for in vitro production of embryos have been developed world-wide in different species, with promising results in human and ruminants. Thousands of human IVF-babies have been born during the last 20 years and thousands of in vitro-produced calves have been born since the late 1980s. With current methods for bovine in vitro fertilization, about 30-40% of in vitro-fertilized bovine oocytes develop further to the blastocyst stage and can be used for transfer. A proper evaluation of blastocyst quality remains however, an important challenge for every researcher involved in embryology and for every clinician who wants to select the best embryos for transfer. This review attempts to summarize the different methods available for estimation of blastocyst quality with a special emphasis upon differential staining.

Genetic regulation of embryo death and senescence

The survival of the preimplantation mammalian embryo depends not only on providing the proper conditions for normal development but also on acquiring the mechanisms by which embryos cope with adversity. The ability of the early conceptus to resist stress as development proceeds may be regulated by diverse factors such as the attainment of a cell death program and protective mechanisms involving stress-induced genes and/or cell cycle modulators. This paper reviews the recent research on the genetic regulation of early embryo cell death and senescence focussing on the bovine species where possible. The different modes of cell death will be explained, clarifying the confusing cell death terminology, by advocating the recommendations set forth by the Cell Death Nomenclature Committee to extend to the embryology research field. Specific pro-death and anti-death genes will be discussed with reference to their expression patterns during early mammalian embryogenesis.

Expression pattern of Oct-4 in preimplantation embryos of different species

POU transcription factors are involved in transcriptional regulation during early embryonic development and cell differentiation. Oct-4, a member of this family, has been shown to be under strict regulation during murine development. The expression of Oct-4 correlates with the undifferentiated cell phenotype of the mouse preimplantation embryo. In this study, expression of a gene construct consisting of selected parts of the region upstream from the murine Oct-4 gene as promoter/enhancer, enhanced green fluorescent protein (EGFP) as reporter and the five exons of the murine Oct-4 gene (GOF18-delta PE EGFP) was evaluated in murine, porcine, and bovine preimplantation embryos. For comparison, expression of the endogenous Oct-4 gene was also analyzed in all three species by immunocytochemistry. The transgene construct was microinjected into zygotes cultured in vitro to various developmental stages. The EGFP fluorescence was visualized in developing embryos by excitation with blue light at different days following microinjection and showed similar expression patterns in all three species. Most embryos displayed a mosaic pattern of transgene expression. The EGFP fluorescence was not restricted to the inner cell mass (ICM) but was also seen in trophoblastic cells. An affinity-purified polyclonal antibody specific to Oct-4 was used for immunocytochemical analysis of in vivo- and in vitro-derived bovine and porcine blastocysts and also of in vivo-derived murine blastocysts. In the in vivo-derived murine embryos, Oct-4 protein was detectable in the ICM but not the trophectoderm, whereas in porcine and bovine blastocysts, derived in vivo or in vitro, Oct-4 protein was detected in both the ICM and the trophectoderm. Thus, in the two large animal species, Oct-4 expression from the endogenous gene was clearly not restricted to the pluripotent cells of the early embryo. These results show that Oct-4 regulation differs between these species and that the presence of Oct-4 protein may not be sufficient for selection of undifferentiated cell lines in domestic animals.

Changes in porcine oocyte germinal vesicle development as follicles approach preovulatory maturity

This study was conducted to determine the distribution of oocytes in meiotic arrest as a function of follicle maturation, atresia status, and follicular fluid steroid concentrations. Oocytes (n = 138) from > or = 3 mm follicles were recovered from gilts (n = 3/d) on Days 1, 3, 5, and 7 of the follicular phase initiated by withdrawal of altrenogest treatment. They were fixed in 4% paraformaldehyde, stained with Hoechst 33342, and examined by laser scanning confocal microscopy using combined bright field Nomarski optics and ultraviolet laser illumination. The number of oocytes in complete meiotic arrest increased (P < 0.05) as a function of the stage of maturation from 29% on Day 1 to 79 and 67% on Days 3 and 5, respectively. Oocytes showing complete germinal vesicle breakdown (GVBD) were found only on Day 7 (24 to 36 h after the preovulatory LH surge). The distribution of GV stages on Days 1 to 5 did not differ between atretic (n = 27) and nonatretic follicles (n = 81). In nonatretic follicles, GV stage was inversely related to the concentration of estradiol on Day 7 and to the concentrations of progesterone and androstenedione (P < 0.05) on Days 5 and 7 indicating that meiotically arrested oocytes were likely to be found in follicles with highest levels of steroidogenesis. In conclusion, a large proportion of oocytes present in 3 to 5 mm follicles had begun GVBD. The follicles in the ovulatory cohort may be recruited or selected from preexisting 3 to 5 mm follicles, or younger population with oocytes that are in complete meiotic arrest.