EDTA stimulates cleavage stage bovine embryo development in culture but inhibits blastocyst development and differentiation

Oxidative Stress in Oocytes and Embryo Development: Implications for In Vitro Systems

Significance: To improve the outcomes of in vitro culture of human oocytes and embryos, the dynamic balance and roles of reactive oxygen species (ROS) in folliculogenesis and embryo development merit further consideration. Recent Advances: ROS have been demonstrated to participate in various signaling processes and act as mediators in various physiological events in germ cells. An imbalance between pro-oxidants and antioxidants seems to explain the high failure rate of assisted reproduction. Critical Issues: Oxidative stress induced by excessive ROS or insufficient antioxidant protection can cause detrimental effects on both male and female reproduction. In this study, oxidative stress in folliculogenesis and embryo development are summarized and the multiple modifiable factors of in vitro culture systems in relation to ROS are discussed. Future Directions: More studies are needed to establish an optimal redox state in in vitro culture systems for human oocytes and embryos.

Recent progress in bovine in vitro-derived embryo cryotolerance: Impact of in vitro culture systems, advances in cryopreservation and future considerations

Cryopreservation of in vitro-derived bovine embryos is a crucial step for the widespread reproduction and conservation of valuable high-merit animals. Given the current popularity of bovine in vitro embryo production (IVP), there is a demand for a highly efficient ultra-low temperature storage method in order to maximize donor ovum pickup (OPU) turn-over, recipient availability/utilization and domestic/overseas commercial trading opportunities. However, IVP bovine embryos are still very sensitive to chilling and cryopreservation, and despite recent progress, a convenient (simple and robust) protocol has not yet been developed. At the moment, there are two methods for bovine IVP embryo cryopreservation: slow programmable freezing and vitrification. Both of the aforementioned techniques have pros and cons. While controlled-rate slow cooling can easily be adapted for direct transfer (DT), ice crystal formation remains an issue. On the other hand, vitrification solved this problem but the possibility of successful DT commercial incorporation remains to be determined. Moreover, simplification of the vitrification protocol (including warming) through the use of an in-straw dilution without the use of a microscope is a prerequisite for its use under farm conditions. This review summarizes the bovine IVP embryo cryopreservation achievements, strengths and limitations of both freezing systems and prospective improvements to enhance cryosurvival, as well as perspectives on future directions of this assisted reproductive technology.

Role of Embryo Glue as a transfer medium in the outcome of fresh non-donor in-vitro fertilization cycles

BACKGROUND

EmbryoGlue is a hyaluronan-enriched embryo transfer (ET) medium which aids in implantation of embryos, hence, improves pregnancy rates in in-vitro fertilization-ET cycles (IVF-ET).

AIM

To evaluate the role of EmbryoGlue in improving implantation and pregnancy rates.

DESIGN AND SETTING

A prospective case-control study conducted at assisted reproductive center of a tertiary care hospital.

METHOD

In 42 women undergoing IVF, embryos were transferred into 50 μL of EmbryoGlue for 10 min prior to transfer inside uterine cavity. In the control group (n = 42), embryos were transferred to conventional blastocyst culture medium. Statistical analysis was performed using SPSS IBM version 19.0.

RESULTS

Clinical pregnancy rate in the study group was 7% higher than the control group. The difference, however, was not statistically significant. In addition, no improvement in implantation rates was observed in the study group. However, significant difference (P = 0.04) in clinical pregnancy rate was observed with the EmbryoGlue in patients with previous IVF failure. In the study group, 50% patients (6/12) with previous IVF failure had successful implantation, but in the control group none of the patients (0/11) with previous implantation failure could achieve pregnancy.

CONCLUSION

It is difficult to conclude a favourable role of EmbryoGlue in IVF-ET cycles with a good prognosis. However, in patients with recurrent implantation failure, it may be considered as a useful transfer medium.

When two obese parents are worse than one! Impacts on embryo and fetal development

The prevalence of overweight and obesity in reproductive-age adults is increasing worldwide. While the effects of either paternal or maternal obesity on gamete health and subsequent fertility and pregnancy have been reported independently, the combination of having both parents overweight/obese on fecundity and offspring health has received minimal attention. Using a 2 × 2 study design in rodents we established the relative contributions of paternal and maternal obesity on fetal and embryo development and whether combined paternal and maternal obesity had an additive effect. Here, we show that parental obesity reduces fetal and placental weights without altering pregnancy establishment and is not dependent on an in utero exposure to a high-fat diet. Interestingly combined parental obesity seemed to accumulate both the negative influences of paternal and maternal obesity had alone on embryo and fetal health rather than an amplification, manifested as reduced embryo developmental competency, reduced blastocyst cell numbers, impaired mitochondrial function, and alterations to active and repressive embryonic chromatin marks, resulting in aberrant placental gene expression and reduced fetal liver mtDNA copy numbers. Further understanding both the maternal cytoplasmic and paternal genetic interactions during this early developmental time frame will be vital for understanding how developmental programming is regulated and for the proposition of interventions to mitigate their effects.

Female offspring sired by diet induced obese male mice display impaired blastocyst development with molecular alterations to their ovaries, oocytes and cumulus cells

PURPOSE

To investigate the impacts that a paternal high fat diet (HFD) has on embryology, ovarian/cumulus cell gene expression and COC metabolism from female offspring, using a mouse model.

METHODS

Founder male mice were either fed a control diet (CD) or a HFD for 12 weeks. The HFD induced obesity but not diabetes, and founder males were then mated to normal weight CD fed female mice. Female offspring were maintained on a CD, super-ovulated, mated and the resultant zygotes were cultured to the blastocyst stage for embryo morphology, blastocyst cell number and apoptosis assessment. Ovaries and cumulus cells from offspring were collected for gene expression analysis of selected genes that maintain chromatin remodeling and endoplasmic reticulum (ER), metabolic and inflammatory homeostasis. Cumulus/oocyte complexes were also investigated for glucose uptake and lipid accumulation.

RESULTS

Female offspring sired by obese fathers produced embryos with delayed development and impaired quality, displayed increases in ovarian expression of Glut1, Glut3 and Glut4, and an increase in cumulus cell expression of Glut4. Interestingly their COCs did take up more glucose, but did accumulate more lipid.

CONCLUSIONS

A paternal HFD is associated with subfertility in female offspring despite the offspring being fed a CD and this subfertility is concomitant with ovarian/cumulus cell molecular alterations and increased lipid accumulation.

Oxidative stress in mouse sperm impairs embryo development, fetal growth and alters adiposity and glucose regulation in female offspring

Paternal health cues are able to program the health of the next generation however the mechanism for this transmission is unknown. Reactive oxygen species (ROS) are increased in many paternal pathologies, some of which program offspring health, and are known to induce DNA damage and alter the methylation pattern of chromatin. We therefore investigated whether a chemically induced increase of ROS in sperm impairs embryo, pregnancy and offspring health. Mouse sperm was exposed to 1500 µM of hydrogen peroxide (H₂O₂), which induced oxidative damage, however did not affect sperm motility or the ability to bind and fertilize an oocyte. Sperm treated with H₂O₂ delayed on-time development of subsequent embryos, decreased the ratio of inner cell mass cells (ICM) in the resulting blastocyst and reduced implantation rates. Crown-rump length at day 18 of gestation was also reduced in offspring produced by H₂O₂ treated sperm. Female offspring from H₂O₂ treated sperm were smaller, became glucose intolerant and accumulated increased levels of adipose tissue compared to control female offspring. Interestingly male offspring phenotype was less severe with increases in fat depots only seen at 4 weeks of age, which was restored to that of control offspring later in life, demonstrating sex-specific impacts on offspring. This study implicates elevated sperm ROS concentrations, which are common to many paternal health pathologies, as a mediator of programming offspring for metabolic syndrome and obesity.

The presence of 1 mM glycine in vitrification solutions protects oocyte mitochondrial homeostasis and improves blastocyst development

PURPOSE

Embryos generated from oocytes which have been vitrified have lower blastocyst development rates than embryos generated from fresh oocytes. This is indicative of a level of irreversible damage to the oocyte possibly due to exposure to high cryoprotectant levels and osmotic stress. This study aimed to assess the effects of vitrification on the mitochondria of mature mouse oocytes while also examining the ability of the osmolyte glycine, to maintain cell function after vitrification.

METHODS

Oocytes were cryopreserved via vitrification with or without 1 mM Glycine and compared to fresh oocyte controls. Oocytes were assessed for mitochondrial distribution and membrane potential as well as their ability to fertilise. Blastocyst development and gene expression was also examined.

RESULTS

Vitrification altered mitochondrial distribution and membrane potential, which did not recover after 2 h of culture. Addition of 1 mM glycine to the vitrification media prevented these perturbations. Furthermore, blastocyst development from oocytes that were vitrified with glycine was significantly higher compared to those vitrified without glycine (83.9 % vs. 76.5 % respectively; p<0.05) and blastocysts derived from oocytes that were vitrified without glycine had significantly decreased levels of IGF2 and Glut3 compared to control blastocysts however those derived from oocytes vitrified with glycine had comparable levels of these genes compared to fresh controls.

CONCLUSION

Addition of 1 mM glycine to the vitrification solutions improved the ability of the oocyte to maintain its mitochondrial physiology and subsequent development and therefore could be considered for routine inclusion in cryopreservation solutions.

Differential gene expression profile in bovine blastocysts resulting from hyperglycemia exposure during early cleavage stages

To understand the compromised survival of embryos derived from assisted reproductive techniques, transcriptome survey of early embryonic development has shown the impact of in vitro culture environment on gene expression in bovine or other living species. However, how the differentially expressed genes translate into developmentally compromised embryos is unresolved. We therefore aimed to characterize transcriptomic markers expressed by bovine blastocysts cultured in conditions that are known to impair embryo development. As increasing glucose concentrations has been shown to be stressful for early cleavage stages of mammalian embryos and to decrease subsequent blastocyst survival, in vitro-matured/fertilized bovine zygotes were cultured in control (0.2 mM) or high-glucose (5 mM) conditions until the 8- to 16-cell stage, and then transferred to control media until they reached the blastocyst stage. The concentration of 5 mM glucose was chosen as a stress treatment because there was a significant effect on blastocyst rate without the treatment's being lethal as with 10 mM. Microarray analysis revealed gene expression differences unrelated to embryo sex or hatching. Overrepresented processes among differentially expressed genes in treated blastocysts were extracellular matrix signalling, calcium signaling, and energy metabolism. On a pathophysiological level, higher glucose treatment impacts pathways associated with diabetes and tumorigenesis through genes controlling the Warburg effect, i.e., emphasis on use of anaerobic glycolysis rather than oxidative phosphorylation. These results allowed us to conclude that disruption of in vitro preattachment development is concomitant with gene expression modifications involved in metabolic control.

Media composition: antioxidants/chelators and cellular function

Protection of embryos against oxidative insults during culture is necessary to maintain viability. Generation of excessive levels of reactive oxygen species (ROS) is triggered by various components of the in vitro environment, most of which embryos do not normally encounter in vivo. To compensate for these deficiencies in the culture environment, antioxidants and chelators are often used to control or suppress ROS levels as embryos develop. However, there is no consensus regarding dosage, time of exposure, or appropriate combinations of antioxidants and chelators in embryo culture. In order to elucidate this aspect of an embryo's chemical surroundings in vitro, we present the current knowledge on the function and effect of each antioxidant or chelator that is often included in an embryo culture medium.

Paternal diet-induced obesity impairs embryo development and implantation in the mouse

OBJECTIVE

To use a rodent model of male diet-induced obesity (DIO) to examine resultant preimplantation embryo development and implantation rate, as well as fetal and placental growth.

DESIGN

Experimental animal study.

SETTING

University research facilities.

ANIMAL(S)

C57BL/6 male and CBAxC57BL/6 female mice.

INTERVENTION(S)

Male mice were fed a standard rodent chow (lean) or a high-fat diet (obese) for up to 13 weeks. After mating, zygotes were collected and cultured to the blastocyst stage, then assessed or transferred into recipient females.

MAIN OUTCOME MEASURE(S)

Embryo morphology and cell number were assessed and pregnancy outcomes determined at postmortem day 18.

RESULT(S)

Embryos from obese males had reduced cleavage and decreased development to blastocyst stage during culture relative to control males. Blastocysts from obese males implanted at a reduced rate, and the proportion of fetuses that developed was significantly decreased, although fetal and placental weight did not differ between groups.

CONCLUSION(S)

This study demonstrates that paternal obesity impairs preimplantation embryo development and implantation but does not influence gross fetal or placental morphology. It highlights the important contribution that paternal health and lifestyle choices have for achieving a viable pregnancy.

Simulated physiological oocyte maturation (SPOM): a novel in vitro maturation system that substantially improves embryo yield and pregnancy outcomes

BACKGROUND

Oocyte in vitro maturation (IVM) reduces the need for gonadotrophin-induced ovarian hyperstimulation and its associated health risks but the unacceptably low conception/pregnancy rates have limited its clinical uptake. We report the development of a novel in vitro simulated physiological oocyte maturation (SPOM) system.

METHODS AND RESULTS

Bovine or mouse cumulus-oocyte complexes (COCs) were treated with cAMP modulators for the first 1-2 h in vitro (pre-IVM), increasing COC cAMP levels ∼100-fold. To maintain oocyte cAMP levels and prevent precocious oocyte maturation, COCs were treated during IVM with an oocyte-specific phosphodiesterase inhibitor and simultaneously induced to mature with FSH. Using SPOM, the pre-IVM and IVM treatments synergized to increase bovine COC gap-junctional communication and slow meiotic progression (both P < 0.05 versus control), extending the normal IVM interval by 6 h in bovine and 4 h in mouse. FSH was required to complete maturation and this required epidermal growth factor signalling. These effects on COC had profound consequences for oocyte developmental potential. In serum-free conditions, SPOM increased bovine blastocyst yield (69 versus 27%) and improved blastocyst quality (184 versus 132 blastomeres; both P < 0.05 versus standard IVM). In mice, SPOM increased (all P < 0.05) blastocyst rate (86 versus 55%; SPOM versus control), implantation rate (53 versus 28%), fetal yield (26 versus 8%) and fetal weight (0.9 versus 0.5 g) to levels matching those of in vivo matured oocytes (conventional IVF).

CONCLUSIONS

SPOM is a new approach to IVM, mimicing some characteristics of oocyte maturation in vivo and substantially improving oocyte developmental outcomes. Adaption of SPOM for clinical application should have significant implications for infertility management and bring important benefits to patients.

Disruption of bidirectional oocyte-cumulus paracrine signaling during in vitro maturation reduces subsequent mouse oocyte developmental competence

Oocyte-cumulus cell bidirectional communication is essential for normal development of the oocyte and cumulus cells (CCs) within the follicle. We showed recently that addition of recombinant growth differentiation factor 9 (GDF9), which signals through the SMAD2/3 pathway, during mouse oocyte in vitro maturation (IVM) increased fetal viability. This study thus aimed to observe the effects of disrupting oocyte-CC bidirectional communication during IVM on oocyte developmental competence and fetal outcomes. Cumulus-oocyte complexes (COCs) from equine chorionic gonadotropin-primed prepubertal (CBA/C57BL6) mice were cultured with or without 50 mIU/ml follicle-stimulating hormone (FSH) and 10 ng/ml epidermal growth factor (EGF) or 4 muM SMAD2/3 inhibitor SB-431542. Cumulus expansion and first polar body extrusion were then assessed, or COCs were fertilized and stained to evaluate sperm entry or cultured to the blastocyst stage. Embryo development and blastocyst quality were assessed, and Day 4.5 blastocysts were transferred to pseudopregnant recipients to analyze fetal outcomes. SMAD2/3 inhibition or FSH/EGF absence during IVM resulted in decreased cumulus expansion. First polar body extrusion and sperm entry were decreased in the absence of FSH/EGF, whereas only sperm entry was affected in SB-431542-matured COCs. Embryo development and blastocyst rates were unaffected; however, blastocyst quality was significantly altered, with reduced inner cell mass cell numbers in embryos derived from COCs matured in both treatments. When COCs were matured with SB-431542 in the absence of FSH/EGF, cumulus expansion was reduced, but fertilization, embryo development, and embryo quality were not. Inhibition of SMAD2/3 signaling in the presence of FSH/EGF significantly reduced fetal survival but had no effect on implantation or fetal and placental dimensions and morphology.

Metabolic and mitochondrial dysfunction in early mouse embryos following maternal dietary protein intervention

Dietary supply of nutrients, both periconception and during pregnancy, influence the growth and development of the fetus and offspring and their health into adult life. Despite the importance of research efforts surrounding the developmental origins of health and disease hypothesis, the biological mechanisms involved remain elusive. Mitochondria are of major importance in the oocyte and early embryo, particularly as a source of ATP generation, and perturbations in their function have been related to reduced embryo quality. The present study examined embryo development following periconception exposure of females to a high-protein diet (HPD) or a low-protein diet (LPD) relative to a medium-protein diet (MPD; control), and we hypothesized that perturbed mitochondrial metabolism in the mouse embryo may be responsible for the impaired embryo and fetal development reported by others. Although the rate of development to the blastocyst stage did not differ between diets, both the HPD and LPD reduced the number of inner cell mass cells in the blastocyst-stage embryo. Furthermore, mitochondrial membrane potential was reduced and mitochondrial calcium levels increased in the 2-cell embryo. Embryos from HPD females had elevated levels of reactive oxygen species and ADP concentrations, indicative of metabolic stress and, potentially, the uncoupling of oxidative phosphorylation, whereas embryos from LPD females had reduced mitochondrial clustering around the nucleus, suggestive of an overall quietening of metabolism. Thus, although periconception dietary supply of different levels of protein is permissive of development, mitochondrial metabolism is altered in the early embryo, and the nature of the perturbation differs between HPD and LPD exposure.

Choosing a culture medium: making informed choices

OBJECTIVE

To analyze critically the reasons justifying the choice of two-step protocols requiring two media for the culture of human preimplantation embryos from the zygote to the blastocyst.

DESIGN

Literature review.

RESULT(S)

Two types of protocol are used for the culture of human preimplantation embryos from the zygote to the blastocyst, using either one medium (one-step protocol) or two media of different composition (two-step protocol). Two-step protocols are the most widely used, largely because all but one of the commercially available protocols are of this type. The reasons for the adoption of two-step protocols are described and critically analyzed. They are based on considerations of the functions of glucose, ethylenediaminetetraacetic acid (EDTA), glutamine, and amino acids that are included in the media. A reappraisal of the reasons for selecting two-step protocols is important because recent animal experiments and clinical observations have raised doubts as to whether the more complex, two-step protocols have any advantage over one-step protocols. The analyses show that all of conclusions reached should be considered equivocal.

CONCLUSION(S)

Clinical embryologists should evaluate the justification for selecting two-step protocols for the culture of human preimplantation embryos from the zygote to the blastocyst.

Disruption of mitochondrial malate-aspartate shuttle activity in mouse blastocysts impairs viability and fetal growth

The nutrient requirements and metabolic pathways used by the developing embryo transition from predominantly pyruvate during early cleavage stages to glucose at the blastocyst; however, the complexities involved in the regulation of metabolism at different developmental stages are not clear. The aims of this study were to examine the role of the malate-aspartate shuttle (MAS) in nutrient metabolism pathways in the developing mouse blastocyst and the consequences of impaired metabolism on embryo viability and fetal and placental growth. Eight-cell-stage mouse embryos were cultured in the presence of the MAS inhibitor amino-oxyacetate, with or without pyruvate as an energy substrate in the media. When the MAS was inhibited, the rate of glycolysis and lactate production was significantly elevated and glucose uptake reduced, relative to control cultured embryos in the presence of pyruvate. Despite these changes in embryo metabolism, this did not influence development to the blastocyst stage, but it did reduce the number of inner cell mass and trophectoderm cells. When these embryos were transferred to psuedopregnant females, inhibition of the MAS significantly reduced the proportion of embryos that implanted and developed into fetuses on Day 18 of pregnancy. Finally, fetal growth was reduced while placental weight was maintained, leading to a decreased fetal:placental weight ratio relative to control embryos. These results suggest that impaired metabolism of glucose in the blastocyst via the MAS alters the ability of the embryos to implant and form a pregnancy and leads to reduced fetal weight, likely via altered placental development and function.

Embryo culture medium: which is the best?

With the growing move in in-vitro fertilization (IVF) clinics to transfer fewer embryos to women, there is an increasing reliance on the IVF laboratory to maximize embryo viability. Subsequently, there is justified scrutiny on the culture system and the media used to sustain the human embryo in vitro. The transfer of fewer embryos to patients also creates an increased dependence on the ability to cryopreserve embryos successfully. Therefore, in addition to the ability of a culture system to produce a single top-quality embryo for transfer, it is also necessary to enhance the cryotolerance of sibling embryos so that they can survive freezing or vitrification. Therefore, when examining which culture media is the best, it is prudent to not only examine the ability of a culture system to produce a pregnancy with the one or two highest-grade embryos, but also to determine how many embryos from the entire cohort (both fresh and frozen embryos) are capable of producing a live birth. Additionally, research on animal models has demonstrated that stress, and the resultant adaptation to conditions during pre-implantation stages, can affect pregnancy loss and fetal growth. It is therefore important to understand the role of each medium component and to identify possible sources of cellular stress to the embryo that will ultimately affect the function and viability of the conceptus.

Embryotrophic effects of ethylenediaminetetraacetic acid and hemoglobin on in vitro porcine embryos development

This study investigated the embryotrophic effects of ethylenediaminetetraacetic acid (EDTA) and hemoglobin (Hb) on porcine preimplantation embryo development. Porcine embryos produced by in vitro maturation/fertilization were cultured for 6 days in modified North Carolina State University-23 medium (mNCSU-23) supplemented with EDTA and/or Hb. In Exp. 1, culturing porcine zygotes with 100 microM EDTA significantly increased cleavage frequencies (85.3%) at 48 h post insemination and the number of inner cell mass (ICM) (9.6+/-5.5) compared to the control (7.0+/-2.8). However, 100 microM EDTA did not improve blastocyst formation compared to 0, 1 or 10 microM EDTA. In Exp. 2, in vitro fertilized oocytes were cultured with 0, 1 or 10 microg/ml Hb. Culturing with Hb did not promote porcine embryo development, but significantly increased the cell numbers of blastocysts in 1 microg/ml Hb compared to 0 or 10 microg/ml Hb. In Exp. 3, culturing embryos with 100 microM EDTA+1 microg/ml Hb significantly improved frequencies of cleavage, blastocyst formation, and total cell numbers in blastocysts compared to the control. Moreover, 100 microM EDTA, 1 microg/ml Hb and their combination reduced reactive oxygen species (ROS) accumulation and decreased the incidence of apoptosis. In conclusion, the present study clearly demonstrated that the combining treatment of EDTA and Hb improved IVF porcine embryo development.

Efficacy of a human embryo transfer medium: a prospective, randomized clinical trial study

PURPOSE

The aim of this prospective, randomized trial was to evaluate the efficacy of Embryo-Glue as a human embryo transfer medium in IVF/ICSI cycles.

METHOD

A total of 815 nonselected patients undergoing IVF/ICSI treatment between September 2003 and February 2004 were randomly allocated into the test (417 patients) and the control (398 patients) groups. In both groups, embryos were cultured in G-1ver 3, supplemented with 10% recombinant human albumin. On the day of embryo transfer (day 3), the best or good quality embryos were selected for intrauterine transfer. In the test group, the selected embryos were treated with EmbryoGlue prior to the transfer, whereas in the control group they were transferred without any treatment.

RESULTS

The patients' characteristics such as age and the number of ART cycles and also the number of patients in each indication of infertility and the number of embryos selected for transfer were all similar between the two groups. In the test group, the clinical pregnancy rate in the tubal factors and the implantation rate in the tubal factors and recurrent implantation failures increased significantly compared with those in the control group. In the test group, life birth and the triplet delivery rates increased significantly compared with those in the control group.

CONCLUSION

EmbryoGlue is a useful embryo transfer medium, and at least in some infertile patients it can improve clinical implantation and ongoing pregnancy rates.

Higher survival rate of vitrified and thawed in vitro produced bovine blastocysts following culture in defined medium supplemented with β-mercaptoethanol

The present study was conducted to compare bovine embryo developmental quality, after culture in different defined culture media, up to blastocyst stage, and subsequently cultured in media supplemented with beta-mercaptoethanol (beta-ME) following blastocyst vitrification and thawing. In part one of this study, presumptive zygotes were randomly allocated into the following media: (1) CR1, (2) KSOM, (3) SOF, and (4) sequential KSOM-SOF. In the second part of the study, blastocysts derived from four different culture media were subjected to a solid surface vitrification (35% (v/v) ethylene glycol+0.5M Sucrose+5% (w/v) Polyvinylpyrrolidone (PVP), and tested for the effect of beta-ME on their post-vitrification survival. Following thawing, blastocysts were cultured with or without beta-ME. Culture medium had no effect on cleavage rates; however, a significantly greater number of zygotes cultured in KSOM, KSOM-SOF, or SOF developed to the 8-cell stage, compared with those cultured in CR1. A greater proportion of the zygotes cultured in SOF or KSOM-SOF reached blastocysts, than did those cultured in CR1 or KSOM. The use of sequential KSOM-SOF significantly increased total cell numbers of Day 7 expanded-blastocysts when compared to those cultured in CR1, KSOM, or SOF. Addition of beta-ME into culture media after vitrification and thawing improved blastocyst survival, hatching rates, and total cell numbers of blastocysts. In conclusion, supplementation of beta-ME into culture medium after vitrification and thawing significantly increased blastocyst survival, hatching rates, and their total cell numbers. These results suggest that vitrified IVF embryos should be thawed and briefly cultured in beta-ME medium prior to embryo transfer.

Perturbations in Mouse Embryo Development and Viability Caused by Ammonium Are More Severe after Exposure at the Cleavage Stages1

The presence of ammonium in culture medium has a detrimental effect on embryo physiology and biochemistry; however, the stage at which the embryo is most sensitive to this effect is unknown. The aim of this study was to determine the exact stage at which the embryo is most vulnerable to ammonium by exposing the preimplantation embryo to 300 muM ammonium either at the precompaction stage (between the zygote and two-cell or the two-cell to eight-cell) or at the postcompaction stage (between the eight-cell and blastocyst). This study determined that exposure of embryos to ammonium at the precompaction stage from either the zygote to two-cell stage or from the two-cell to the eight-cell stage did not affect the rate of development to the blastocyst stage; however, the resultant blastocysts had decreased cell numbers and inner cell mass cells. Furthermore, these blastocysts had increased levels of cellular apoptosis and perturbed levels of Slc2a3 expression and glucose uptake. Transfer of these blastocysts revealed that, while implantation was not affected, the number of fetuses was reduced by culture with ammonium at the precompaction stage and fetal development was delayed, as observed by reduced crown-rump length and maturity. In contrast, the later stage embryo was more resistant to the negative effects of ammonium, with only Slc2a3 expression and fetal maturity affected. This raises the possibility that the later stage embryo is more able to protect itself from in vitro-derived stress and that the majority of in vitro-induced damage to mouse embryos is inflicted at the early stages of development.

Human Embryo Culture

Human embryonic stem cells (hESCs) are derived from preimplantation embryos. Approximately 60% of human embryos are blocked during in vitro development. Although statistics are inconclusive, experience demonstrates that hESCs are more effectively derived from high-quality embryos. In this way, optimal human embryo culture conditions are a crucial aspect in any derivation laboratory. Embryos can be cultured solely with sequential media or cocultured on a monolayer of a given cell type. This chapter explores general aspects of human embryonic development, the concept of sequential culture and coculture, and specific protocols and procedures in which the authors are experienced, including the results obtained.

Effect of Potassium Simplex Optimization Medium and NCSU23 Supplemented with Beta-mercaptoethanol and Amino Acids of In Vitro Fertilized Porcine Embryos

The present study was conducted to examine the comparative efficacy of potassium simplex optimization medium (KSOM) and North Carolina State University (NCSU)-23 medium supplemented with beta-mercaptoethanol (beta-ME) and amino acids (AA) on the developmental competence of porcine in vitro fertilized (IVF) embryos. Four experiments were conducted. KSOM and NCSU-23 medium were used to culture porcine parthenogenetic (Exp. 1) and IVF (Exp. 2) embryos. KSOM and NCSU-23 were equally effective in supporting porcine parthenogenetic and IVF embryo development from the 1-cell stage to blastocysts. The NCSU-23 medium (Exp. 3) and KSOM (Exp. 4) were supplemented with amino acid (AA; 5 microl/ml non-essential amino acids + 10 microl/ml essential amino acids) and/or 10 microM beta-mercaptoethanol (beta-ME). The quality of blastocysts from Exp. 3 and 4 was evaluated by counting the number of total cells and determining the ratio of the inner cell mass (ICM) to trophoectoderm (TE) cells. Supplementing with AA and beta-ME or beta-ME alone in NCSU-23 produced significant (p<0.05) differences in terms of rate of cleavage to the 2- to 4- cell (80.8 to 85.4% vs. 73.6%) and blastocyst (30.4 to 30.5 vs. 23.5%) stages and the number of TE (51.4 to 53.8 vs. 35.8) and total cells (67.2 to 71.2 to 48.8) over the control group. On the other hand, supplementing KSOM with AA and/or beta-ME produced significant (p<0.05) differences in terms of rate of cleavage to the 2- to 4-cell (78.8% vs. 67.7%) and morula (57.8% vs. 46.3%) stages and the number of ICM (18.6 to 19.2 vs. 11.6) and total cells (62.8 to 70.6 vs. 42.8) over control group. In conclusion, our study demonstrates that both KSOM and NCSU-23 medium supplemented with AA and beta-ME and/or only beta-ME alone are superior to normal KSOM and NCSU-23 for porcine IVF embryo culture in terms of embryo developmental competence and quality.

Metabolic regulation of in-vitro-produced bovine embryos. I. Effects of metabolic regulators at different glucose concentrations with embryos produced by semen from different bulls

The toxic and/or beneficial effects of four metabolic regulators on embryo development were evaluated. In-vitro-produced compact morulae were cultured for 3 days in a chemically defined medium + bovine serum albumin (BSA; CDM-2) plus regulators (4991 total embryos). Phenazine ethosulfate (PES), phloretin (PL), pyrroline-5-carboxylate (P5C), and sodium azide (NaN3) were evaluated at four doses each in factorial combinations with four concentrations of glucose: 0, 0.5, 2, and 8 mm. Phenazine ethosulfate at 0.9 μm resulted in poorer development than lower or no PES. Phloretin was, in general, detrimental for embryo development, but most markedly at the highest dose (270 µm). Pyrroline-5-carboxylate had little effect on post-compaction embryos at the doses studied, 9 to 81 μm. Sodium azide at the concentrations used (3, 9, and 27 μm) had little effect on embryo development compared with controls. Concentrations of glucose had little effect on development of embryos. A fifth metabolic regulator, 2,4-dinitrophenol (DNP), was studied at various doses at pre-morula or morula-blastocyst stages cultured in 2 mm glucose. Embryos (2189 total) cultured in 90 µm DNP developed more slowly and were darker than embryos cultured at lower doses. Embryos cultured in 30 µm DNP had a higher blastocyst rate (48.3%) than controls (34.9%). In the last experiment using G1.2/G2.2 media, DNP (30 μm) resulted in a marked decrease in embryonic development when embryos were exposed at the zygote to 8- to 16-cell stages but had little effect when morulae were exposed for 2 days. The dose–response information for these metabolic regulators is crucial for designing future experiments.

One-step versus two-step culture of mouse preimplantation embryos: is there a difference?

BACKGROUND

A comparison has been made of the development of mouse zygotes in either one-step or two-step culture systems.

METHODS

Embryo culture, blastocyst cell counts and embryo transfer were done.

RESULTS

No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the inner cell mass (ICM) and trophectoderm (TE) that developed in protocols: one-step culture in potassium-enriched simplex optimized medium supplemented with glucose and amino acids (KSOMg(AA)), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in G1.2/G2.2. No gross abnormalities were observed in the fetuses that developed from zygotes in the one-step protocol using KSOMg(AA) and a two-step protocol using G1.2/G2.2. The body weights of these two groups of fetuses were not significantly different and no developmental abnormalities were observed. No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the ICM and TE that developed in protocols: one-step culture in KSOMg(AA), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in DM2/DM1. EDTA is not toxic to the initial cleavage stages of development at a concentration of 0.01 mmol/l in KSOMg(AA).

CONCLUSIONS

Two-step culture protocols are sufficient for the support of preimplantation mouse development in vitro but they are not necessary.

Granulocyte-macrophage colony-stimulating factor stimulates mouse blastocyst inner cell mass development only when media lack human serum albumin

The aim of the current study was to examine the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the development and differentiation of preimplantation mouse embryos from different strains and under different culture conditions. Embryos from F1 hybrid mice were cultured in a modified G1 medium lacking amino acids and EDTA (simple G1), human tubal fluid medium (HTF) or in G1/G2 sequential media, supplemented with GM-CSF (0, 2, 4, 8, and 16 ng/ml). Embryos from CF1 mice were subsequently cultured in G1/G2 with (5 mg/ml) or without HSA, in the absence or presence of GM-CSF (2 ng/ml). GM-CSF had no effect at any concentration on F1 embryo development and blastocyst cell numbers, irrespective of the culture media used. Similarly, GM-CSF had no effect on CF1 blastocyst development. However, a stimulatory effect of GM-CSF was evident on total blastocyst cell number and ICM development when CF1 embryos were cultured in the absence of HSA. When HSA was present in the media the beneficial effect of GM-CSF was negated. There was no difference in the number of apoptotic cells in CF1 blastocysts when G1/G2 were supplemented with GM-CSF with or without HSA. These data indicate that there is no beneficial effect of supplementing either simple (simple G1 or HTF) or more complete (G1/G2) media with GM-CSF when protein is present in the medium. However, when culture conditions are suboptimal and non-physiological, i.e. the absence of protein, GM-CSF stimulates development of both total cell numbers and ICM development of CF1 blastocysts.

Comparison of two sequential media for culturing cleavage-stage embryos and blastocysts: embryo characteristics and clinical outcome

This study was undertaken to compare the outcome of day 3, day 5, and frozen-thawed embryo transfer cycles where embryo culture was undertaken using the G1.2-G2.2 versus GIII series sequential media. A total of 400 day 3, 73 day 5 and 126 frozen-thawed embryo transfer cycles were analysed. Treatment cycles were quasi-randomized on the day of oocyte retrieval to embryo culture in G1.2-G2.2 versus GIII series sequential media. Randomization was undertaken according to alternating weekdays. Significantly more embryos were of grade 1 or 2 quality on day 3 in the GIII group (P < 0.05). Likewise, more embryos in the GIII group had eight blastomeres on day 3 (P < 0.05) and were able to hatch spontaneously (P < 0.05). For day 3 embryo transfer cycles, implantation and clinical pregnancy rates were 14.4 and 25.7% versus 37.8 and 50.3% in G1.2-G2.2 and GIII groups respectively (P < 0.05). For day 5 embryo transfer cycles, implantation rates were significantly higher (29 versus 45%; P < 0.05) in the GIII group. There was a trend towards higher pregnancy rates; however, this did not reach statistical significance due to fewer cycles analysed in this group. In-vitro culture in GIII series sequential media yields better quality embryos that implant more efficiently, compared with culture in G1.2-G2.2 media.

Effect of protein supplementation in potassium simplex optimization medium on preimplantation development of bovine non-transgenic and transgenic cloned embryos

The present study evaluated the effect of protein supplementation in potassium simplex optimization medium (KSOM) on bovine preimplantation embryo development. The in vitro fertilized (IVF) (Experiment 1), non-transgenic (Experiment 2) and transgenic cloned embryos (Experiment 3) were cultured for 192 h in KSOM supplemented with 0.8% BSA (KSOM-BSA), 10% FBS (KSOM-FBS) or 0.01% PVA (KSOM-PVA). Transfected cumulus cells with an expression plasmid for human alpha1-antitrypsin gene and a green fluorescent protein (GFP) marker were used to produce transgenic cloned embryos. Modified synthetic oviductal fluid (mSOF) supplemented with 0.8% BSA (mSOF-BSA) was used as a control medium. In Experiment 1, cleavage rate was significantly (P < 0.05) lower (69.1%) in IVF embryos cultured in KSOM-FBS than in KSOM-BSA (80.3%). The rate of hatching/hatched blastocyst formation was significantly (P < 0.05) lower in embryos cultured in KSOM-PVA than in KSOM-FBS (2.2% versus 10.8%). Blastocysts cultured in KSOM-FBS contained significantly (P < 0.06) higher numbers of inner cell mass cells (50.4 +/- 20.2) than those cultured in mSOF-BSA (36.9 +/- 19.2). In Experiment 2, the rate of blastocyst formation was significantly (P < 0.05) lower (20.5%) in embryos cultured in KSOM-PVA than in other culture media (33.3-38.5%). The rate of hatching/hatched blastocysts was significantly (P < 0.05) lower in KSOM-PVA (13.9%) and KSOM-FBS (17.1%) than in KSOM-BSA (30.8%) and mSOF-BSA (33.9%). The numbers of total and trophectoderm cells (104.6 +/- 32.2 and 71.7 +/- 25.5, respectively) were significantly (P < 0.05) lower in blastocysts cultured in KSOM-PVA than in KSOM-BSA (125.7 +/- 39.7 and 91.7 +/- 36.2, respectively). In Experiment 3, no significant differences in embryo development, GFP expression and blastocyst cell numbers were observed among the culture groups. In conclusion, the present study demonstrated that KSOM and mSOF supplemented with BSA were equally effective in supporting development of bovine non-transgenic and transgenic cloned embryos. Moreover, different developmental competence in response to protein supplementation of KSOM was observed between bovine non-transgenic and transgenic cloned embryos.

Oestradiol, cyclodextrin-encapsulated 17beta-oestradiol and the oestradiol solubilizer 2-hydroxypropyl-beta-cyclodextrin all impair preimplantation mouse embryo development

The aim of this study was to examine the effects of 2-hydroxypropyl-beta-cyclodextrin (HbetaC) used as a solubilizer for oestradiol, 17beta-oestradiol (ethanol soluble) and HbetaC-encapsulated-17beta-oestradiol on mouse embryo development in vitro. HbetaC had no effect on day 3 development. In contrast, blastocyst development and blastocyst cell number were significantly reduced in the presence of 10(-4) mol/l solubilizer equivalent, but not at lower concentrations. The proportion of compacted embryos was significantly reduced with 10(-4) mol/l 17beta-oestradiol. No blastocysts were formed at 10(-4) mol/l concentration of 17beta-oestradiol, although the rate of blastocyst formation did not differ at lower concentrations. Blastocyst cell number was significantly decreased compared with controls at 10(-5) mol/l 17beta-oestradiol. The dose-response using HbetaC-encapsulated-17beta-oestradiol revealed that at 17beta-oestradiol concentrations of 10(-4) and 10(-5) mol/l, blastocyst development was significantly reduced. Blastocyst cell number was significantly reduced compared with controls for all concentrations of HbetaC-encapsulated-17beta-oestradiol. Exposure of embryos to 17beta-oestradiol (10(-4) mol/l) reduced blastocyst development on days 4 and 5 significantly in cultures initiated at the zygote, 2-cell and 8-cell, but not the morulae, stages of development. Trophectoderm, ICM and blastocyst cell numbers as well as percentage ICM development were reduced significantly, regardless of the stage of development. Therefore, 17beta-oestradiol does compromise embryo development.

Addition of β-mercaptoethanol or Trolox® at the morula/blastocyst stage improves the quality of bovine blastocysts and prevents induction of apoptosis and degeneration by prooxidant agents

This study was conducted to evaluate the effect of beta-mercaptoethanol (a stimulator of glutathione synthesis) and Trolox (an hydrosoluble analogue of Vitamin E) on bovine embryos cultured from the morula stage (Day 5 post-insemination; pi) under oxidative stress conditions. Culture of embryos with increased doses of Trolox showed a dose-dependent embryotoxicity on Day 8 pi. The use of 400 microM Trolox as well as beta-mercaptoethanol at 100 microM prevented at least partly (P < 0.05) the prooxidant-induced blastocyst degeneration on Day 8. Hatching rates of surviving blastocysts were significantly increased by both antioxidants and beta-mercaptoethanol alone improved their mean cell numbers, which was significant in the ICM (P < 0.05). Analysis of their effect on Day 7 pi showed that both the antioxidants significantly reduced the prooxidant-induced apoptosis and beta-mercaptoethanol diminished the physiological level of apoptosis as well as it stimulated the glutathione synthesis (P < 0.05). In addition, a comparison between in vitro- and in vivo-produced embryos showed that the levels of apoptosis were similar at the same age post-insemination (morulae and blastocysts) but increased steadily with the embryonic age in in vitro ones. In conclusion, beta-mercaptoethanol and Trolox added separately from the morula stage protected embryos against oxidative stress and improved the quality of the resulting blastocysts.

Cell cycle duration at the time of maternal zygotic transition for in vitro produced bovine embryos: effect of oxygen tension and transcription inhibition

Early embryonic cleavages are mostly regulated by maternal components then control of development progressively depends on newly synthesized zygotic products. The timing of the first cleavages is a way to assess embryo quality. The goal of this study was to evaluate the duration of the fourth cell cycle, at the time of maternal-to-zygotic transition (MZT) in in vitro-produced bovine embryos by means of cinematographic analysis. We found that 75% of the embryos displayed a long fourth cycle (43.5 +/- 5.4 h) whereas the remaining embryos had a very short fourth cell cycle (8.9 +/- 2.9 h). Both groups did not differ in cleavage rhythm up to the eight-cell stage and timing of cavitation and blastocyst expansion was identical. However, embryos with a short fourth cell cycle had a better blastocyst rate than embryos with a long cycle (59% versus 38%, P < 0.01). Total cell number, inner cell mass (ICM):total cell ratio, and hatching rate were identical for blastocysts produced from embryos with either a long or a short fourth cell cycle. In a second experiment, we showed that increasing the oxygen tension, from 5% to 20%, decreased the percentage of embryos with a short fourth cell cycle, from 25% to 11% (P < 0.01), indicating that suboptimal culture conditions can influence the length of this cycle. Finally, we investigated whether fourth cell cycle duration could be influenced by transcription inhibition. With alpha-amanitin added at 18 h postinsemination (HPI), cleavage was reduced (66% versus 79%) and, at 70 HPI, the 9- to 16-cell rate increased (50% versus 25%) concomitantly with a 5- to 8-cell rate decrease (16% versus 47%). A similar pattern was observed when the drug was added at 6 HPI or 42 HPI but not at 0 HPI. Cinematographic analysis revealed that alpha-amanitin increased the first cell cycle duration whereas the second and third cell cycles were not affected. With the drug, one third of the embryos could develop up to the 9- to 16-cell stage and they all had a short fourth cell cycle (11.2 +/- 3.7 h) with a good synchrony of cleavage between blastomeres. These results suggest that duration of the fourth cell cycle of bovine embryo, during the MZT, is under a zygotic transcriptional control that can be affected by oxidative conditions.

Ammonium induces aberrant blastocyst differentiation, metabolism, pH regulation, gene expression and subsequently alters fetal development in the mouse

The presence of ammonium in the culture medium has significant detrimental effects on the regulation of embryo physiology and genetics. Ammonium levels build up linearly over time in the culture medium when media containing amino acids are incubated at 37 degrees C. Ammonium in the culture media significantly reduces blastocyst cell number, decreases inner cell mass development, increases apoptosis, perturbs metabolism, impairs the ability of embryos to regulate intracellular pH, and alters the expression of the imprinted gene H19. In contrast, the rate of blastocyst development and blastocyst morphology appear to be normal. The transfer of blastocysts exposed to ammonium results in a significant reduction in the ability to establish a pregnancy. Furthermore, of those embryos that manage to implant, fetal growth is significantly impaired. Embryos exposed to 300 microM ammonium are retarded by 1.5 days developmentally at Day 15 of pregnancy. It is therefore essential that culture conditions for mammalian embryos are designed to minimize the buildup of ammonium to prevent abnormalities in embryo physiology, genetic regulation, pregnancy, and fetal development.

Effects of gas conditions, time of medium change, and ratio of medium to embryo on in vitro development of horse oocytes fertilized by intracytoplasmic sperm injection

This study was conducted to evaluate the effects of two different gas conditions (5% CO(2) in air or 5% CO(2), 5% O(2), 90% N(2), mixed gas), time of medium change (Day 3 or 4) and ratio of medium to embryo (2, 5 or 10 microl per presumptive zygote) on the development of horse oocytes fertilized by intracytoplasmic sperm injection and cultured in G1.2/2.2 medium. Oocytes from slaughterhouse-derived ovaries were matured in vitro for 24 h and fertilized by injection of frozen-thawed sperm using micromanipulation with a Piezo drill. Presumptive zygotes were randomly assigned to 5% CO(2) in air or mixed gas and fixed after 96 h of culture. Cleavage rates between two gas conditions were similar (67 and 63%), but the mean nucleus number of embryos in the mixed gas treatment was significantly (P<0.05) higher than that of embryos cultured in 5% CO(2) in air (15.2 versus 7.0, respectively). Further experiments were done with mixed gas incubation. Development of embryos was compared after change from G1.2 to G2.2 medium at Day 3 or 4. There was no significant difference in cleavage rate (56 and 65%, respectively) or development to the blastocyst stage after 7 days of culture (5% and 46%, respectively) between embryos changed on different days. To evaluate the effect of the ratio of medium to embryo, zygotes were cultured at a ratio of 2, 5 or 10 microl medium per zygote. There were no significant differences among ratio treatments in rates of cleavage or development to blastocyst.

Cryo-survival and development of bovine blastocysts are enhanced by culture with recombinant albumin and hyaluronan

Recombinant albumin can be used to supplement culture medium for the maturation and fertilization of bovine oocytes and subsequent embryo development to the blastocyst stage. Recombinant albumin was able to support blastocyst development at rates equivalent to that of bovine serum albumin (BSA) supplemented media. Supplementation of media containing recombinant albumin and citrate stimulated blastocyst expansion. Culture with recombinant albumin and citrate significantly increased the ability of the resultant blastocysts to re-expand and hatch following cryopreservation. The further addition of the glycosaminoglycan hyaluronan to the culture medium containing either BSA or recombinant albumin also increased the ability of blastocysts to survive cryopreservation. Inclusion of recombinant albumin and hyaluronan in culture media facilitates the development of physiological defined culture conditions. For bovine embryos this has implications for both research and commercial applications where defined reproducible conditions are desirable.

Inhibiting 3-phosphoglycerate kinase by EDTA stimulates the development of the cleavage stage mouse embryo

Addition of EDTA to the medium significantly enhances mouse embryo development in culture. Embryos cultured in the absence of EDTA exhibit abnormal increases in glycolytic activity that result in reduced development. Culture with EDTA was able to prevent this increase in glycolysis and, therefore, maintain developmental competence. EDTA was shown to inhibit the activity of the glycolytic enzyme, 3-phosphoglycerate kinase. Additionally, the effect of EDTA on maintaining high rates of embryo development in culture could be mimicked by the addition of Cibacron blue, an inhibitor of 3-phosphoglycerate kinase. The inhibition of 3-phosphoglycerate kinase by EDTA could be overcome by the addition of exogenous magnesium, indicating that the effect of EDTA was to reduce the availability of this co-factor to the glycolytic kinases. Embryos cultured with EDTA had significantly lower levels of intracellular magnesium compared to embryos cultured without EDTA. Therefore, the effect of EDTA appears to be as a chelator of divalent cations such as magnesium, that are required for normal activity of kinases such as 3-phosphoglycerate kinase.

Effect of essential amino acids on mouse embryo viability and ammonium production

PURPOSE

To examine the effect of essential amino acids concentrations on mouse embryo development.

METHODS

Mouse embryos were cultured in medium with different concentrations of essential amino acids and development to the blastocyst stage and viability assessed. Ammonium production resulting from medium breakdown and amino acid metabolism by embryos were also assessed.

RESULTS

Reducing the essential amino acid concentration significantly increased blastocyst development and cell numbers. Lowering the essential amino acid concentration decreased ammonium production in the medium.

CONCLUSIONS

Culture media for the development of preimplantation embryos should have a reduced essential amino acid concentration to facilitate embryo development.

Protection against reactive oxygen species during mouse preimplantation embryo development: role of EDTA, oxygen tension, catalase, superoxide dismutase and pyruvate

Oxidative damage due to the production of reactive oxygen species (ROS) is one of a number of culture-induced stresses which may compromise preimplantation embryo development in vitro. Ethylenediaminetetraacetic acid (EDTA), reduced oxygen tension, superoxide dismutase (SOD) and catalase (CAT) offer protection against oxidative stress, but few attempts have been made to determine which of these agents, or which combination, is the most effective. In particular, no systematic investigation of their actions and interactions has been made using a multifactorial experimental design. Murine zygotes were cultured in the presence or absence of 10 miccroM EDTA, SOD (100-7,000 U/ml) and CAT (50-100 U/ml) at atmospheric (20%) and reduced (5%) oxygen tensions. Blastocyst formation and hatching rates (at various time points), and cell numbers were recorded, whilst parallel groups of embryos had their consumption of pyruvate, a hydrogen peroxide scavenger, measured. All parameters interacted significantly and affected blastocyst formation, hatching rate and cell numbers but the effect of EDTA was the most pronounced. There were beneficial effects of 5% O2, CAT and SOD, while 20% O2 had a deleterious effect on development. EDTA improved blastocyst formation and hatching rates but paradoxically led to a reduction in cell number. 5% O2 was the next most significant parameter to enhance embryo development and also increased cell numbers. No differences in pyruvate uptake were apparent between the various treatment groups. The results suggest that embryo culture in EDTA-free medium under 5% O2 provides the most practical and physiological conditions for in vitro murine embryo culture.