Calcium homeostasis in early hamster preimplantation embryos

An expert commentary on essential equipment, supplies and culture media in the ART laboratory

The ART laboratory is a complex system designed to sustain the fertilization, survival, and culture of the preimplantation embryo to the blastocyst stage. ART outcomes depend on numerous factors, among which are the equipment, supplies and culture media used. The number and type of incubators also may affect ART results. While large incubators may be more suitable for media equilibration, bench-top incubators may provide better embryo culture conditions in separate or smaller chambers and may be coupled with time-lapse systems that allow continuous embryo monitoring. Microscopes are essential for observation, assessment, and micromanipulation. Workstations provide a controlled environment for gamete and embryo handling and their quantity should be adjusted according to the number of ART cycles treated in order to provide a steady and efficient workflow. Continuous maintenance, quality control and monitoring of equipment is essential and quality control devices such as the thermometer, and pH-meter are necessary to maintain optimal culture conditions. Tracking, appropriate delivery and storage conditions, and quality control of all consumables is recommended so that the adequate quantity and quality is available for use. Embryo culture media have evolved: preimplantation embryos are cultured either by sequential media or single-step media that can be used for interrupted or uninterrupted culture. There is currently no sufficient evidence that any individual commercially-available culture system is better than others in terms of embryo viability. In this review, we aim to analyse the various parameters that should be taken into account when choosing the essential equipment, consumables and culture media systems that will create optimal culture conditions and provide the most effective patient treatment.

Composition of single-step media used for human embryo culture

OBJECTIVE

To determine compositions of commercial single-step culture media and test with a murine model whether differences in composition are biologically relevant.

DESIGN

Experimental laboratory study.

SETTING

University-based laboratory.

ANIMAL(S)

Inbred female mice were superovulated and mated with outbred male mice.

INTERVENTION(S)

Amino acid, organic acid, and ions content were determined for single-step culture media: CSC, Global, G-TL, and 1-Step. To determine whether differences in composition of these media are biologically relevant, mouse one-cell embryos were cultured for 96 hours in each culture media at 5% and 20% oxygen in a time-lapse incubator.

MAIN OUTCOME MEASURE(S)

Compositions of four culture media were analyzed for concentrations of 30 amino acids, organic acids, and ions. Blastocysts at 96 hours of culture and cell cycle timings were calculated, and experiments were repeated in triplicate.

RESULT(S)

Of the more than 30 analytes, concentrations of glucose, lactate, pyruvate, amino acids, phosphate, calcium, and magnesium varied in concentrations. Mouse embryos were differentially affected by oxygen in G-TL and 1-Step.

CONCLUSION(S)

Four single-step culture media have compositions that vary notably in pyruvate, lactate, and amino acids. Blastocyst development was affected by culture media and its interaction with oxygen concentration.

The beneficial effects of reduced magnesium during the oocyte-to-embryo transition are conserved in mice, domestic cats and humans

In many cell types Mg2+ can antagonise Ca2+ -stimulated signalling pathways, but information regarding the effects of these ions on IVF and subsequent embryonic development is limited. Our objectives were to evaluate the effects of Mg2+ in the IVF medium on embryonic development in mice and then determine if similar effects occurred in domestic cats and humans. Oocytes from hybrid and outbred mice, domestic cats and humans were fertilised (IVF, mice and cats; intracytoplasmic sperm injection (ICSI), humans) in the presence of 0.2 or 1.2 (mouse and human) or 1.0 (cat) mM Mg2+ and the resulting embryos were cultured to the blastocyst stage. Decreased concentrations of Mg2+ during IVF increased (P<0.05) cleavage of oocytes from outbred mice (77.9 vs. 51.0%), development of embryos from hybrid mice (74.5 vs. 51.0% hatching blastocyst per cleaved embryo) and both cleavage (68.4 vs. 46.8%) and blastocyst development (53.0 vs. 26.2% per cleaved embryo) in cats. Development to the blastocyst stage (52.1 vs. 40.2%) was also improved (P<0.05) when ICSI was performed on human oocytes in the presence of 0.2 mM Mg2+, compared with a commercial culture medium. Sensitivity to increased (1.0 to 1.2 mM) concentrations of Mg2+ in the medium during the oocyte-to-embryo transition appears to be conserved in three different species.

Reduction of Mitochondrial Function by FCCP During Mouse Cleavage Stage Embryo Culture Reduces Birth Weight and Impairs the Metabolic Health of Offspring

The periconceptual environment represents a critical window for programming fetal growth trajectories and susceptibility to disease; however, the underlying mechanism responsible for programming remains elusive. This study demonstrates a causal link between reduction of precompaction embryonic mitochondrial function and perturbed offspring growth trajectories and subsequent metabolic dysfunction. Incubation of embryos with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP), which uncouples mitochondrial oxidative phosphorylation, significantly reduced mitochondrial membrane potential and ATP production in 8-cell embryos and the number of inner cell mass cells within blastocysts; however, blastocyst development was unchanged. This perturbed embryonic mitochondrial function was concomitant with reduced birth weight in female offspring following embryo transfer, which persisted until weaning. FCCP-treated females also exhibited increased adiposity at 4 wk, increased adiposity gain between 4 and 14 wk, glucose intolerance at 8 wk, and insulin resistance at 14 wk. Although FCCP-treated males also exhibited reduced glucose tolerance, but their insulin sensitivity and adiposity gain between 4 and 14 wk was unchanged. To our knowledge, this is one of the first studies to demonstrate that reducing mitochondrial function and, thus, decreasing ATP output in the precompacting embryo can influence offspring phenotype. This is of great significance as a large proportion of patients requiring assisted reproductive technologies are of advanced maternal age or have a high body mass index, both of which have been independently linked with perturbed early embryonic mitochondrial function.

Composition of commercial media used for human embryo culture

OBJECTIVE

To determine the composition of commercially available culture media and test whether differences in composition are biologically relevant in a murine model.

DESIGN

Experimental laboratory study.

SETTING

University-based laboratory.

ANIMAL(S)

Cryopreserved hybrid mouse one-cell embryos were used in experiments.

INTERVENTION(S)

Amino acid, organic acid, ions, and metal content were determined for two different lots of media from Cook, In Vitro Care, Origio, Sage, Vitrolife, Irvine CSC, and Global. To determine whether differences in the composition of these media are biologically relevant, mouse one-cell embryos were thawed and cultured for 120 hours in each culture media at 5% and 20% oxygen in the presence or absence of protein in an EmbryoScope time-lapse incubator.

MAIN OUTCOME MEASURE(S)

The compositions of seven culture media were analyzed for concentrations of 39 individual amino acids, organic acids, ions, and elements. Blastocyst rates and cell cycle timings were calculated at 96 hours of culture, and the experiments were repeated in triplicate.

RESULT(S)

Of the 39 analytes, concentrations of glucose, lactate, pyruvate, amino acids, phosphate, calcium, and magnesium were present in variable concentrations, likely reflecting differences in the interpretation of animal studies. Essential trace elements, such as copper and zinc, were not detected. Mouse embryos failed to develop in one culture medium and were differentially affected by oxygen in two other media.

CONCLUSION(S)

Culture media composition varies widely, with differences in pyruvate, lactate, and amino acids especially notable. Blastocyst development was culture media dependent and showed an interaction with oxygen concentration and presence of protein.

Dynamic regulation of mitochondrial function in preimplantation embryos and embryonic stem cells

Mitochondrial function is dependent upon regulation of biogenesis and dynamics. A number of studies have documented the importance of these organelles in both preimplantation embryos and embryonic stem cells (ESCs), however it remains unclear how mitochondria respond to their immediate microenvironment through modulation of morphology and movement, or whether perturbations in these processes will have a significant impact following differentiation/implantation. Here we review existing literature on two key aspects of nuclear-mitochondrial cross-talk and the dynamic processes involved in mediating mitochondrial function through regulation of mitochondrial biogenesis, morphology and movement, with particular emphasis on embryos and ESCs.

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.

Molecular control of mitochondrial function in developing rhesus monkey oocytes and preimplantation-stage embryos

The mitochondrion undergoes significant functional and structural changes, as well as an increase in number, during preimplantation embryonic development. The mitochondrion generates ATP and regulates a range of cellular processes, such as signal transduction and apoptosis. Therefore, mitochondria contribute to overall oocyte quality and embryo developmental competence. The present study identified, for the first time, the detailed temporal expression of mRNAs related to mitochondrial biogenesis in rhesus monkey oocytes and embryos. Persistent expression of maternally encoded mRNAs was observed, in combination with transcriptional activation and mRNA accumulation at the eight-cell stage, around the time of embryonic genome activation. The expression of these transcripts was significantly altered in oocytes and embryos with reduced developmental potential. In these embryos, most maternally encoded transcripts were precociously depleted. Embryo culture and specific culture media affected the expression of some of these transcripts, including a deficiency in the expression of key transcriptional regulators. Several genes involved in regulating mitochondrial transcription and replication are similarly affected by in vitro conditions and their downregulation may be instrumental in maintaining the mRNA profiles of mitochondrially encoded genes observed in the present study. These data support the hypothesis that the molecular control of mitochondrial biogenesis, and therefore mitochondrial function, is impaired in in vitro-cultured embryos. These results highlight the need for additional studies in human and non-human primate model species to determine how mitochondrial biogenesis can be altered by oocyte and embryo manipulation protocols and whether this affects physiological function in progeny.

Maternal supply of omega-3 polyunsaturated fatty acids alter mechanisms involved in oocyte and early embryo development in the mouse

Despite the well-known benefits of omega-3 (n-3) polyunsaturated fatty acid (PUFA) supplementation on human health, relatively little is known about the effect of n-3 PUFA intake on fertility. More specifically, the aim of this study was to determine how oocyte and preimplantation embryo development might be influenced by n-3 PUFA supply and to understand the possible mechanisms underlying these effects. Adult female mice were fed a control diet or a diet relatively high in the long-chain n-3 PUFAs for 4 wk, and ovulated oocytes or zygotes were collected after gonadotropin stimulation. Oocytes were examined for mitochondrial parameters (active mitochondrial distribution, mitochondrial calcium and membrane potential) and oxidative stress, and embryo developmental ability was assessed at the blastocyst stage following 1) in vitro fertilization (IVF) or 2) culture of in vivo-derived zygotes. This study demonstrated that exposure of the oocyte during maturation in the ovary to an environment high in n-3 PUFA resulted in altered mitochondrial distribution and calcium levels and increased production of reactive oxygen species. Despite normal fertilization and development in vitro following IVF, the exposure of oocytes to an environment high in n-3 PUFA during in vivo fertilization adversely affected the morphological appearance of the embryo and decreased developmental ability to the blastocyst stage. This study suggests that high maternal dietary n-3 PUFA exposure periconception reduces normal embryo development in the mouse and is associated with perturbed mitochondrial metabolism, raising questions regarding supplementation with n-3 PUFAs during this period of time.

Reduced polyspermic fertilization of porcine oocytes utilizing elevated bicarbonate and reduced calcium concentrations in a single-medium system

The development of efficient systems for in vitro production of porcine embryos has been hampered by a high incidence of polyspermic fertilization. A recently developed single-medium system for porcine in vitro maturation (IVM), IVF and in vitro embryo culture (IVC) (Purdue Porcine Medium; PPM) was modified with elevated bicarbonate (44 mM) and reduced calcium concentrations (1.7 mM) for IVF (PPMfert.2). Oocyte penetration was evaluated after maturation in PPMmat (0.5 mg mL(-1) hyaluronan, 0.6 mM cysteine, 10 ng mL(-1) epidermal growth factor (EGF), 0.1 U mL(-1) porcine LH and FSH, and 1 x Minimal Essential Medium (MEM) vitamins) and fertilization (5 h with 5 x 10(5) sperm mL(-1)) in either PPMfert.2 or mTBM (20 mM Tris, 0.0 mM bicarbonate, 7.5 mM calcium). Embryonic development (cleavage and blastocyst stages) was assessed after culture in PPM1 and PPM2. Although penetration was lower in PPMfert.2 (69.9%) compared with mTBM (83.9%), 48.8% of penetrated oocytes were fertilized normally in PPMfert.2 compared with only 27.8% normal fertilization in mTBM. More oocytes cleaved in PPMfert.2 (77.9% v. 53.7%), but development to the blastocyst stage was not different between treatments (14.1% v. 14.3%). Further work is needed to improve embryonic development, but reduced polyspermic penetration is an important step in the optimization of the PPM system for in vitro porcine embryo production.

Impact of Assisted Reproductive Technologies: A Mitochondrial Perspective of Cytoplasmic Transplantation

Many of the assisted reproductive techniques associated with maternal aging, disease states, or implantation failure aim to correct poor developmental capacity. These techniques are highly invasive and require the exchange of nuclear or cytoplasmic material from a donor oocyte to compensate for deficiencies inherent in the affected individual. These techniques are based on the assumption that the cytoplasm of the donor oocyte can effectively substitute the necessary component(s) to enable development to proceed. Several studies have attempted to inject cytoplasm from "normal" (young) donors, into aged eggs, again assuming that beneficial components of the cytoplasm are transferred to restore developmental capacity. These invasive assisted reproduction technology (ART) procedures aim to eliminate chromosomal abnormalities, improve the quality of oocytes deficient in some important cytoplasmic factors necessary for maturation and/or subsequent development, and eliminate maternally inherited diseases (particularly mitochondrial myopathies). However, in order to develop such ART, understanding the processes involving mitochondrial DNA replication and transcription is imperative, as asynchrony between mitochondrial and nuclear genomes may cause problems in mitochondrial function, localization, and biogenesis.

Understanding cellular disruptions during early embryo development that perturb viability and fetal development

An inability to regulate ionic and metabolic homeostasis is related to a reduction in the developmental capacity of the embryo. The early embryo soon after fertilisation and up until compaction appears to have a reduced capacity to regulate its homeostasis. The reduced ability to regulate homeostasis, such as intracellular pH and calcium levels, by the precompaction-stage embryo appears to impact on the ability to regulate mitochondrial function and maintain adequate levels of energy production. This reduction in ATP production causes a cascade of events leading to disrupted cellular function and, perhaps ultimately, disrupted epigenetic regulation and aberrant placental and fetal development. In contrast, after compaction the embryo takes on a more somatic cell-like physiology and is better able to regulate its physiology and therefore appears less vulnerable to stress. Therefore, for human IVF it would seem important for the establishment of healthy pregnancies that the embryos are maintained in systems that are designed to minimise homeostatic stress, particularly for the cleavage-stage embryos, as exposure to stress is likely to culminate in impaired embryo function.

Influence of ovarian hyperstimulation and ovulation induction on the cytoskeletal dynamics and developmental competence of oocytes

This study was undertaken to determine the effects of gonadotrophin on cytoskeletal dynamics and embryo development and its role in improving the retrieval of developmentally competent oocytes. Female golden hamsters were injected with human chorionic gonadotrophin (hCG; 5-, 7.5- or 15-IU) on the day 4 of estrus, pregnant mare serum gonadotrophin (PMSG; 5-, 7.5- or 15-IU) on the day 1 of estrus, or 15-IU hCG at 56 hr post-15-IU PMSG injection in any cycle except estrus. Increasing the hCG dose decreased not only retrieval rate of 2-cell embryo but development to blastocyst after subsequent in vitro culture. Whereas, although increasing the PMSG dose induced increasing the number of 2-cell embryo and blastocyst, 15-IU PMSG injection caused retardation of development to blastocyst. No 2-cell embryos were retrieved by injecting both PMSG and hCG. The injections of 15-IU hCG and 7.5- or 15-IU PMSG inhibited the proliferation of trophectodermal and inner cell mass cells, respectively. Gonadotrophin injection didn't influence microtubular spindle formation, but 5- or 15-IU hCG, 15-IU PMSG, or PMSG and hCG injections induced aberrant cortical granule (CG) and microfilament distribution. After 15-IU hCG or PMSG and hCG injections, fewer oocytes had enriched cortical actin domains, and the expression of alpha-, beta- and gamma-actin genes was greatly increased. In conclusion, a high dose of gonadotrophins alters the microfilament and CG distribution, which in turn reduces the developmental competence of oocytes. Injecting a reduced dose of PMSG to initiate ovarian hyperstimulation without triggering ovulation contributes to the efficient retrieval of developmentally competent oocytes.

The significance of mitochondria for embryo development in cloned farm animals

The role of mitochondria in remodeling of the donor cell nucleus in cloned animals has gained increased attention, as mitochondria interact in direct or indirect ways with the donor cell nuclear DNA. Mitochondria comprise 1% of the genetic material that is contributed to the developing embryo by the recipient oocyte and provide the energy that is required for embryo development. In this review we compare mitochondria distribution in various species and the importance of mitochondria distribution for embryo development. We also compare the inheritance pattern of mitochondria in cloned embryos that remains unresolved, as the donor cell nucleus is typically transferred with surrounding cytoplasm including mitochondria which become destroyed in some but not all species. We review the role of mitochondria in cloned farm animals with emphasis on nucleo-cytoplasmic interactions and consequences for embryo development.

Mitochondrial Malate-Aspartate Shuttle Regulates Mouse Embryo Nutrient Consumption

Pyruvate has been considered the sole substrate that can support development of the mouse zygote to the two-cell stage, with lactate able to support development from the two-cell stage. This study has determined for the first time that mitochondrial reducing equivalent shuttles regulate metabolism in the early embryo. Activity of the malate-aspartate shuttle was found to be essential for the metabolism of lactate in the two-cell embryo. Furthermore, the inability of the mouse zygote to use lactate as an energy source was a result of a lack of malate-aspartate shuttle activity. The mRNA for the four enzymes for shuttle activity were detected at all stages of development. It was determined that aspartate was a rate-limiting factor in the activity of the malate-aspartate shuttle in mouse zygotes probably due to the high K(m) of the cytoplasmic aspartate aminotransferase. Addition of high concentrations of exogenous aspartate to the culture medium enabled mouse zygotes to utilize lactate in the absence of pyruvate and develop normally to the blastocyst stage as well as produce normal viable offspring. This study determined that the malate-aspartate shuttle is a key regulator of embryo metabolism and therefore viability and is the first report that mouse zygotes can develop normally to term in the absence of pyruvate.

Bioactive aldehydes from diatoms block the fertilization current in ascidian oocytes

The effects of bioactive aldehydes from diatoms, unicellular algae at the base of the marine food web, were studied on fertilization and early development processes of the ascidian Ciona intestinalis. Using whole-cell voltage clamp techniques, we show that 2-trans-4-trans-decadienal (DD) and 2-trans-4-cis-7-cis-decatrienal (DT) inhibited the fertilization current which is generated in oocytes upon interaction with the spermatozoon. This inhibition was dose-dependent and was accompanied by inhibition of the voltage-gated calcium current activity of the plasma membrane. DD and DT did not inhibit the subsequent contraction of the cortex. Moreover, DD specifically acted as a fertilization channel inhibitor since it did not affect the steady state conductance of the plasma membrane or gap junctional (GJ) communication within blastomeres of the embryo. On the other hand, DD did affect actin reorganization even though the mechanism of action on actin filaments differed from that of other actin blockers. Possibly this effect on actin reorganization was responsible for the subsequent teratogenic action on larval development. The effect of DD was reversible if oocytes were washed soon after fertilization indicating that DD may specifically target certain fertilization mechanisms. Thus, diatom reactive aldehydes such as DD may have a dual effect on reproductive processes, influencing primary fertilization events such as gating of fertilization channels and secondary processes such as actin reorganization which is responsible for the segregation of cell lineages. These findings add to a growing body of evidence on the antiproliferative effects of diatom-derived aldehydes. Our results also report, for the first time, on the action of a fertilization channel blocker in marine invertebrates.

Improvement in early human embryo development using new formulation sequential stage-specific culture media

OBJECTIVE

To determine whether altering selected components of sequential culture media can improve early development variables of human embryos.

DESIGN

Prospective, randomized, sibling oocyte split trial.

SETTING

Private ART center.

PATIENT(S)

Two hundred eight undergoing treatment with in vitro fertilization or microinjection.

INTERVENTION(S)

Oocytes from each patient were randomly allocated to fertilization and cleavage media of a control and a trial culture medium formulation.

MAIN OUTCOME MEASURE(S)

Rates of fertilization, cleavage, and uncontrolled division; average embryo morphology score; blastomeres per embryo; embryo score parameter (number of blastomeres x embryo morphology grade); and embryo utilization. The trial media resulted in a higher fertilization rate, higher cleavage rate, lower rate of uncontrolled division, higher number of blastomeres per embryo, higher average embryo morphology score, a higher embryo score parameter, and higher embryo utilization rate compared to the control media. All differences were statistically significant.

CONCLUSION(S)

Improved sequential stage-specific culture media can reduce the occurrence of severe human embryo fragmentation and improve developmental variables in early IVF- and ICSI-generated embryos.

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.

Mechanisms for managing cellular and homeostatic stress in vitro

The ability to maintain embryo development in culture depends upon the ability of the embryo to maintain cellular homeostasis. Disruptions in the ability to regulate cellular homeostasis such as pH, calcium levels and osmotic pressure result in perturbed development and a reduced ability to establish and maintain a pregnancy following transfer. Therefore, it is important that in vitro conditions are designed to minimize stress on the embryo and maximize the ability of the embryo to maintain cellular homeostasis. While embryos do exhibit a degree of plasticity and can adapt to their environment, this requires expenditures of extra energy which negatively impacts viability. Therefore, reducing stress by taking into account the physiology of the embryo is essential for the maintenance of developmental competence in vitro.

Reproductive biotechnologies: current status in porcine reproduction

During the past decade, considerable attention has been directed toward the development of reproductive technologies for both research purposes and for more controlled swine reproduction. Artificial insemination is an example of a technology that has continued to be expanded from early use in European countries to the USA and Canada where it is now estimated that a majority of the sows bred are artificially inseminated. In addition, several significant technological advancements have been made in the genetic modification of swine and interest has been generated in the possible use of swine as donors of specific tissues and of organs for the improvement of human health. At the same time, the systems for production of swine for human food continue to undergo major changes including, in some countries, the consolidation of swine into large, integrated units. These swine operations are very receptive to the use of technologies to reduce labor costs as well as a basis for increased production efficiency. Therefore, the combined interest in swine reproductive technologies by both the medical field and the swine industry creates an increased effort for the development of new technologies as well as for the implementation of existing ones. One of the more rapid technological advancements this decade has been the progress in in vitro production (IVP) of swine embryos. Major advancements have been made on the development of procedures for production of large numbers of embryos from oocytes collected at slaughter houses which are then matured (IVM) and fertilized (IVF) in the laboratory. Success in IVP has stimulated increased research in other areas that can be enhanced by the availability of embryos without a requirement for surgical collection from gilts or sows. One example is the combined use of IVF, gender-sorted sperm cells, and embryo transfer to produce offspring of a predicted sex. In a related area, instrumentation for non-surgical embryo transfer has recently been developed that results in significant improvement in this technology. Similar achievements have been gained in cryopreservation of embryos by vitrification. These developments will be reviewed with emphasis on the in vitro production of embryos from immature oocytes.

Phosphate induced developmental arrest of hamster two-cell embryos is associated with disrupted ionic homeostasis

Culture of hamster embryos with 0.35 mM inorganic phosphate results in developmental arrest at the 2-cell stage. These arrested 2-cell embryos were found to have significantly elevated levels of both intracellular pH and intracellular free calcium. Culture of 2-cell embryos with both glucose and phosphate did not further alter intracellular ionic homeostasis. Developmental arrest of 2-cell embryos was dependent on the concentration of phosphate used. Culture with 1.25 microM phosphate did not alter development, while concentrations of 2.5 microM and 5.0 microM resulted in a percentage of embryos arresting development at the 2-cell stage. Analysis of intracellular levels of pH and calcium after culture with different phosphate concentrations revealed a significant negative correlation between intracellular calcium levels and development beyond the 2-cell stage. There was no correlation between the increase in intracellular pH and embryo development in the presence of phosphate. The increase in intracellular calcium levels after culture with phosphate appears to be derived from intracellular pools, as preventing the influx of extracellular calcium did not alter development beyond the 2-cell stage. Therefore, it is apparent that a disruption in ionic homeostasis is associated with developmental arrest of hamster embryos cultured with phosphate.