Applying metabolomic analyses to the practice of embryology: physiology, development and assisted reproductive technology

Metabolic regulation of preimplantation embryo development in vivo and in vitro: Molecular mechanisms and insights

Understanding of embryonic development has led to the clinical application of Assisted Reproductive technologies (ART), with the resulting birth of millions of children. Recent developments in metabolomics, proteomics, and transcriptomics have brought to light new insights into embryonic growth dynamics, with implications spanning reproductive medicine, stem cell research, and regenerative medicine. The review explores the key metabolic processes and molecular pathways active during preimplantation embryo development, including PI3K-Akt, mTOR, AMPK, Wnt/β-catenin, TGF-β, Notch and Jak-Stat signaling pathways. We focused on analyzing the differences occurring in vitro as opposed to in vivo development and we discussed significant physiological and clinical implications.

FGF2, LIF, and IGF-1 supplementation improves mouse oocyte in vitro maturation via increased glucose metabolism†

Chemically defined oocyte maturation media supplemented with FGF2, LIF, and IGF-1 (FLI medium) enabled significantly improved oocyte quality in multiple farm animals, yet the molecular mechanisms behind such benefits were poorly defined. Here, we first demonstrated that FLI medium enhanced mouse oocyte quality assessed by blastocyst formation after in vitro fertilization and implantation and fetal development after embryo transfer. We then analyzed the glucose concentrations in the spent media; reactive oxygen species concentrations; mitochondrial membrane potential; spindle morphology in oocytes; and the abundance of transcripts of endothelial growth factor-like factors, cumulus expansion factors, and glucose metabolism-related genes in cumulus cells. We found that FLI medium enabled increased glucose metabolism through glycolysis, pentose phosphate pathway, and hexosamine biosynthetic pathway, as well as more active endothelial growth factor-like factor expressions in cumulus cells, resulting in improved cumulus cell expansion, decreased spindle abnormality, and overall improvement in oocyte quality. In addition, the activities of MAPK1/3, PI3K/AKT, JAK/STAT3, and mTOR signaling pathways in cumulus cells were assessed by the phosphorylation of MAPK1/3, AKT, STAT3, and mTOR downstream target RPS6KB1. We demonstrated that FLI medium promoted activations of all these signaling pathways at multiple different time points during in vitro maturation.

In Vitro Culture Alters Cell Lineage Composition and Cellular Metabolism of Bovine Blastocyst

Profiling bovine blastocyst transcriptome at the single-cell level has enabled us to reveal the first cell lineage segregation, during which the inner cell mass (ICM), trophectoderm (TE), and an undefined population of transitional cells were identified. By comparing the transcriptome of blastocysts derived in vivo (IVV), in vitro from a conventional culture medium (IVC), and in vitro from an optimized reduced nutrient culture medium (IVR), we found a delay of the cell fate commitment to ICM in the IVC and IVR embryos. Developmental potential differences between IVV, IVC, and IVR embryos were mainly contributed by ICM and transitional cells. Pathway analysis of these non-TE cells between groups revealed highly active metabolic and biosynthetic processes, reduced cellular signaling, and reduced transmembrane transport activities in IVC embryos that may lead to reduced developmental potential. IVR embryos had lower activities in metabolic and biosynthetic processes but increased cellular signaling and transmembrane transport, suggesting these cellular mechanisms may contribute to improved blastocyst development compared to IVC embryos. However, the IVR embryos had compromised development compared to IVV embryos with notably over-active transmembrane transport activities that impaired ion homeostasis.

Preimplantation genetic testing: A remarkable history of pioneering, technical challenges, innovations, and ethical considerations

Preimplantation genetic testing (PGT) has emerged as a powerful companion to assisted reproduction technologies. The origins and history of PGT are reviewed here, along with descriptions of advances in molecular assays and sampling methods, their capabilities, and their applications in preventing genetic diseases and enhancing pregnancy outcomes. Additionally, the potential for increasing accuracy and genome coverage is considered, as well as some of the emerging ethical and legislative considerations related to the expanding capabilities of PGT.

Metabolomic profiling implicates mitochondrial and immune dysfunction in disease syndromes of the critically endangered black rhinoceros (Diceros bicornis)

The critically endangered black rhinoceros (Diceros bicornis; black rhino) experiences extinction threats from poaching in-situ. The ex-situ population, which serves as a genetic reservoir against impending extinction threats, experiences its own threats to survival related to several disease syndromes not typically observed among their wild counterparts. We performed an untargeted metabolomic analysis of serum from 30 ex-situ housed black rhinos (Eastern black rhino, EBR, n = 14 animals; Southern black rhino, SBR, n = 16 animals) and analyzed differences in metabolite profiles between subspecies, sex, and health status (healthy n = 13 vs. diseased n = 14). Of the 636 metabolites detected, several were differentially (fold change > 1.5; p < 0.05) expressed between EBR vs. SBR (40 metabolites), female vs. male (36 metabolites), and healthy vs. diseased (22 metabolites). Results suggest dysregulation of propanoate, amino acid metabolism, and bile acid biosynthesis in the subspecies and sex comparisons. Assessment of healthy versus diseased rhinos indicates involvement of arachidonic acid metabolism, bile acid biosynthesis, and the pentose phosphate pathway in animals exhibiting inflammatory disease syndromes. This study represents the first systematic characterization of the circulating serum metabolome in the black rhinoceros. Findings further implicate mitochondrial and immune dysfunction as key contributors for the diverse disease syndromes reported in ex-situ managed black rhinos.

In Vitro Culture Alters Cell Lineage Composition and Cellular Metabolism of Bovine Blastocyst

Profiling transcriptome at single cell level of bovine blastocysts derived in vivo (IVV), in vitro from conventional culture medium (IVC), and reduced nutrient culture medium (IVR) has enabled us to reveal cell lineage segregation, during which forming inner cell mass (ICM), trophectoderm (TE), and an undefined population of transitional cells. Only IVV embryos had well-defined ICM, indicating in vitro culture may delay the first cell fate commitment to ICM. Differences between IVV, IVC and IVR embryos were mainly contributed by ICM and transitional cells. Pathway analysis by using the differentially expressed genes of these non-TE cells between groups pointed to highly active metabolic and biosynthetic processes, with reduced cellular signaling and membrane transport in IVC embryos, which may lead to reduced developmental potential. IVR embryos had lower activities in metabolic and biosynthetic processes, but increased cellular signaling and membrane transport, suggesting these cellular mechanisms may contribute to the improved blastocyst development compared to IVC embryos. However, the IVR embryos had compromised development when compared to IVV embryos with notably over-active membrane transport activities that led to impaired ion homeostasis.

LC-MS Analysis Revealed the Significantly Different Metabolic Profiles in Spent Culture Media of Human Embryos with Distinct Morphology, Karyotype and Implantation Outcomes

In this study we evaluated possible differences in metabolomic profiles of spent embryo culture media (SECM) of human embryos with distinct morphology, karyotype, and implantation outcomes. A total of 153 samples from embryos of patients undergoing in vitro fertilization (IVF) programs were collected and analyzed by HPLC-MS. Metabolomic profiling and statistical analysis revealed clear clustering of day five SECM from embryos with different morphological classes and karyotype. Profiling of day five SECM from embryos with different implantation outcomes showed 241 significantly changed molecular ions in SECM of successfully implanted embryos. Separate analysis of paired SECM samples on days three and five revealed 46 and 29 molecular signatures respectively, significantly differing in culture media of embryos with a successful outcome. Pathway enrichment analysis suggests certain amino acids, vitamins, and lipid metabolic pathways to be crucial for embryo implantation. Differences between embryos with distinct implantation potential are detectable on the third and fifth day of cultivation that may allow the application of culture medium analysis in different transfer protocols for both fresh and cryopreserved embryos. A combination of traditional morphological criteria with metabolic profiling of SECM may increase implantation rates in assisted reproductive technology programs as well as improve our knowledge of the human embryo metabolism in the early stages of development.

The effects of temperature variation treatments on embryonic development: a mouse study

Since the development of ART, embryos have been cultured at 37 °C in an attempt to mimic the in vivo conditions and the average body temperature of an adult. However, a gradient of temperatures within the reproductive tract has been demonstrated in humans and several other mammalian species. Therefore, the aim of this study was to evaluate the effects of temperature variation treatments on mouse embryo quality through morphokinetic events, blastocyst morphology, the relative gene expression of Igf2, Bax, Bcl2 and Apaf1 and the metabolomics of individual culture media. Study groups consisted of 2 circadian treatments, T1 with embryos being cultured at 37 °C during the day and 35.5 °C during the night, T2 with 38.5 °C during the day and 37 °C during the night and a control group with constant 37 °C. Our main findings are that the lower-temperature group (T1) showed a consistent negative effect on mouse embryo development with “slow” cleaving embryos, poor-quality blastocysts, a higher expression of the apoptotic gene Apaf1, and a significantly different set of amino acids representing a more stressed metabolism. On the other hand, our higher-temperature group (T2) showed similar results to the control group, with no adverse effects on blastocyst viability.

Raman Spectrum of Follicular Fluid: A Potential Biomarker for Oocyte Developmental Competence in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder in reproductive women where abnormal folliculogenesis is considered as a common characteristic. Our aim is to evaluate the potential of follicular fluid (FF) Raman spectra to predict embryo development and pregnancy outcome, so as to prioritize the best promising embryo for implantation, reducing both physiological and economical burdens of PCOS patients. In addition, the altered metabolic profiles will be identified to explore the aetiology and pathobiology of PCOS. In this study, follicular fluid samples obtained from 150 PCOS and 150 non-PCOS women were measured with Raman spectroscopy. Individual Raman spectrum was analyzed to find biologic components contributing to the occurrence of PCOS. More importantly, the Raman spectra of follicular fluid from the 150 PCOS patients were analyzed via machine-learning algorithms to evaluate their predictive value for oocyte development potential and clinical pregnancy. Mean-centered Raman spectra and principal component analysis (PCA) showed global differences in the footprints of follicular fluid between PCOS and non-PCOS women. Two Raman zones (993-1,165 cm^-1 and 1,439-1,678 cm^-1) were identified for describing the largest variances between the two groups, with the former higher and the latter lower in PCOS FF. The tentative assignments of corresponding Raman bands included phenylalanine and β -carotene. Moreover, it was found that FF, in which oocytes would develop into high-quality blastocysts and obtain high clinical pregnancy rate, were detected with lower quantification of the integration at 993-1,165 cm^-1 and higher quantification of the integration at 1,439-1,678 cm^-1 in PCOS. In addition, based on Raman spectra of PCOS FF, the machine-learning algorithms via the fully connected artificial neural network (ANN) achieved the overall accuracies of 90 and 74% in correctly assigning oocyte developmental potential and clinical pregnancy, respectively. The study suggests that the PCOS displays unique metabolic profiles in follicular fluid which could be detected by Raman spectroscopy. Specific bands in Raman spectra have the biomarker potential to predict the embryo development and pregnancy outcome for PCOS patients. Importantly, these data may provide some valuable biochemical information and metabolic signatures that will help us to understand the abnormal follicular development in PCOS.

Parameters to identify good quality oocytes and embryos in cattle

Oocyte/embryo selection methodologies are either invasive or noninvasive and can be applied at various stages of development from the oocyte to cleaved embryos and up to the blastocyst stage. Morphology and the proportion of embryos developing to the blastocyst stage are important criteria to assess developmental competence. Evaluation of morphology remains the method of choice for selecting viable oocytes for IVP or embryos prior to transfer. Although non-invasive approaches are improving, invasive ones have been extremely helpful in finding candidate genes to determine oocyte/embryo quality. There is still a strong need for further refinement of existing oocyte and embryo selection methods and quality parameters. The development of novel, robust and non-invasive procedures will ensure that only embryos with the highest developmental potential are chosen for transfer. In the present review, various methods for assessing the quality of oocytes and preimplantation embryos, particularly in cattle, are considered. These methods include assessment of morphology including different staining procedures, transcriptomic and proteomic analyses, metabolic profiling, as well as the use of artificial intelligence technologies.

Challenges and Considerations during In Vitro Production of Porcine Embryos

Genetically modified pigs have become valuable tools for generating advances in animal agriculture and human medicine. Importantly, in vitro production and manipulation of embryos is an essential step in the process of creating porcine models. As the in vitro environment is still suboptimal, it is imperative to examine the porcine embryo culture system from several angles to identify methods for improvement. Understanding metabolic characteristics of porcine embryos and considering comparisons with other mammalian species is useful for optimizing culture media formulations. Furthermore, stressors arising from the environment and maternal or paternal factors must be taken into consideration to produce healthy embryos in vitro. In this review, we progress stepwise through in vitro oocyte maturation, fertilization, and embryo culture in pigs to assess the status of current culture systems and address points where improvements can be made.

Environmental Exposures around Conception: Developmental Pathways Leading to Lifetime Disease Risk

Environment around conception can influence the developmental programme with lasting effects on gestational and postnatal phenotype and with consequences for adult health and disease risk. Peri-conception exposure comprises a crucial part of the 'Developmental Origins of Health and Disease' (DOHaD) concept. In this review, we consider the effects of maternal undernutrition experienced during the peri-conception period in select human models and in a mouse experimental model of protein restriction. Human datasets indicate that macronutrient deprivation around conception affect the epigenome, with enduring effects on cardiometabolic and neurological health. The mouse model, comprising maternal low protein diet exclusively during the peri-conception period, has revealed a stepwise progression in altered developmental programming following induction through maternal metabolite deficiency. This progression includes differential effects in extra-embryonic and embryonic cell lineages and tissues, leading to maladaptation in the growth trajectory and increased chronic disease comorbidities. The timeline embraces an array of mechanisms across nutrient sensing and signalling, cellular, metabolic, epigenetic and physiological processes with a coordinating role for mTORC1 signalling proposed. Early embryos appear active participants in environmental sensing to optimise the developmental programme for survival but with the trade-off of later disease. Similar adverse health outcomes may derive from other peri-conception environmental experiences, including maternal overnutrition, micronutrient availability, pollutant exposure and assisted reproductive treatments (ART) and support the need for preconception health before pregnancy.

Less is more: Reduced nutrient concentration during in vitro culture improves embryo production rates and morphophysiology of bovine embryos

Reproducing the environment to which the embryo is naturally exposed may be an alternative to improve viability of embryos produced in vitro. In the first part of this work, we describe a novel culture media, namely Embryonic Culture Supplementation (ECS100). The composition of this media was based on the contents of carbohydrates and amino acids found in oviductal and uterine fluids. Because it was a new formulation, we investigated the performance of ECS100 in comparison with conventionally used SOFaa, and possible benefits to embryo development. Embryo production rates (cleavage, morula and blastocyst conversion, blastocyst and hatching rates) and morphophysiological parameters (total cell number, cell allocation, Mitochondrial membrane potential (MMP), Reactive Oxygen Species (ROS), NADH, FAD⁺ and ATP content) were similar between ECS100 and SOFaa. Next, we tested if a reduction of ECS100 concentration could positively contribute to embryo viability by resembling the more dynamic availability of nutrients that reach the embryos in vivo. Therefore, embryos were cultured in ECS100 or in its serial dilution (ECS75, 50 and 25). Despite the fact that the lowest concentration (ECS25) still supported blastocyst formation, halving the concentration of metabolites (ECS50) actually improved embryo production rates. Thus, embryos produced in ECS100 or ECS50 were submitted to further analyses on Days 4 and 7. Embryos cultured in ECS50 presented better developmental rates and morphophysiological profile than embryos cultured in ECS100. Additionally, physiological traits (MMP, ROS and NADH levels) of embryos cultured in ECS50 presented the expected pattern for embryos produced in vivo. In conclusion, we presented a novel, more personalized and effective culture media for bovine IVP embryos. And although the ECS media formulation was based on the contents of female reproductive fluids, it is worth mentioning that adaptations must be specifically directed for in vitro conditions rather than reproduced exactly from in vivo state.

Biochemical markers for pregnancy in the spent culture medium of in vitro produced bovine embryos†

The present study aimed to identify biomarkers to assess the quality of in vitro produced (IVP) bovine embryos in the culture media. IVP embryos on Day (D) 5 of development were transferred to individual drops, where they were maintained for the last 48 h of culture. Thereafter, the medium was collected and the embryos were transferred to the recipients. After pregnancy diagnosis, the media were grouped into the pregnant and nonpregnant groups. The metabolic profiles of the media were analyzed via electrospray ionization mass spectrometry, and the concentrations of pyruvate, lactate, and glutamate were assessed using fluorimetry. The spectrometric profile revealed that the media from embryos from the pregnant group presented a higher signal intensity compared to that of the nonpregnant group; the ions 156.13 Da [M + H]+, 444.33 Da [M + H]+, and 305.97 Da [M + H]+ were identified as biomarkers. Spent culture medium from expanded blastocysts (Bx) that established pregnancy had a greater concentration of pyruvate (p = 0.0174) and lesser concentration of lactate (p = 0.042) than spent culture medium from Bx that did not establish pregnancy. Moreover, pyruvate in the culture media of Bx can predict pregnancy with 90.9% sensitivity and 75% specificity. In conclusion, we identified markers in the culture media that helped in assessing the most viable IVP embryos with a greater potential to establish pregnancy.

Metabolomic Analysis Reveals Changes in Preimplantation Embryos Following Fresh or Vitrified Transfer

Although assisted reproduction technologies (ARTs) are recognised as safe, and most of the offspring seem apparently healthy, there is clear evidence that ARTs are associated with changes in the embryo’s developmental trajectory, which incur physiological consequences during the prenatal and postnatal stages of life. The present study aimed to address the influence of early (day-3 embryos) embryo transfer and cryopreservation on embryo survival, size, and metabolome at the preimplantation stage (day-6 embryos). To this end, fresh-transferred (FT) and vitrified-transferred (VT) embryos were compared using naturally-conceived (NC) embryos as a control reference. The results show that as in vitro manipulation was increased (NC < FT < VT), both embryo survival rate (0.91 ± 0.02, 0.78 ± 0.05 and 0.63 ± 0.05, for NC, FT, and VT groups, respectively) and embryo size (3.21 ± 0.49 mm, 2.15 ± 0.51 mm, 1.76 ± 0.46 mm of diameter for NC, FT, and VT groups, respectively) were significantly decreased. Moreover, an unbiased metabolomics analysis showed overall down-accumulation in 40 metabolites among the three experimental groups, with embryo transfer and embryo cryopreservation procedures both exerting a cumulative effect. In this regard, targeted metabolomics findings revealed a significant reduction in some metabolites involved in metabolic pathways, such as the Krebs cycle, amino acids, unsaturated fatty acids, and arachidonic acid metabolisms. Altogether, these findings highlight a synergistic effect between the embryo transfer and vitrification procedures in preimplantation embryos. However, the ex vivo manipulation during embryo transfer seemed to be the major trigger of the embryonic changes, as the deviations added by the vitrification process were relatively smaller.

A novel culture medium with reduced nutrient concentrations supports the development and viability of mouse embryos

Further refinement of culture media is needed to improve the quality of embryos generated in vitro. Previous results from our laboratory demonstrated that uptake of nutrients by the embryo is significantly less than what is supplied in traditional culture media. Our objective was to determine the impact of reduced nutrient concentrations in culture medium on mouse embryo development, metabolism, and quality as a possible platform for next generation medium formulation. Concentrations of carbohydrates, amino acids, and vitamins could be reduced by 50% with no detrimental effects, but blastocyst development was impaired at 25% of standard nutrient provision (reduced nutrient medium; RN). Addition of pyruvate and L-lactate (+PL) to RN at 50% of standard concentrations restored blastocyst development, hatching, and cell number. In addition, blastocysts produced in RN + PL contained more ICM cells and ATP than blastocysts cultured in our control (100% nutrient) medium; however, metabolic activity was altered. Similarly, embryos produced in the RN medium with elevated (50% control) concentrations of pyruvate and lactate in the first step medium and EAA and Glu in the second step medium were competent to implant and develop into fetuses at a similar rate as embryos produced in the control medium. This novel approach to culture medium formulation could help define the optimal nutrient requirements of embryos in culture and provide a means of shifting metabolic activity towards the utilization of specific metabolic pathways that may be beneficial for embryo viability.

Oocyte and embryo evaluation by AI and multi-spectral auto-fluorescence imaging: Livestock embryology needs to catch-up to clinical practice

A highly accurate 'non-invasive quantitative embryo assessment for pregnancy' (NQEAP) technique that determines embryo quality has been an elusive goal. If developed, NQEAP would transform the selection of embryos from both Multiple Ovulation and Embryo Transfer (MOET), and even more so, in vitro produced (IVP) embryos for livestock breeding. The area where this concept is already having impact is in the field of clinical embryology, where great strides have been taken in the application of morphokinetics and artificial intelligence (AI); while both are already in practice, rigorous and robust evidence of efficacy is still required. Even the translation of advances in the qualitative scoring of human IVF embryos have yet to be translated to the livestock IVP industry, which remains dependent on the MOET-standardised 3-point scoring system. Furthermore, there are new ways to interrogate the biochemistry of individual embryonic cells by using new, light-based methodologies, such as FLIM and hyperspectral microscopy. Combinations of these technologies, in particular combining new imaging systems with AI, will lead to very accurate NQEAP predictive tools, improving embryo selection and recipient pregnancy success.

ATP mediates the interaction between human blastocyst and endometrium

OBJECTIVE

Embryo implantation needs a reciprocal interaction between competent embryo and receptive endometrium. Adenosine triphosphate (ATP) produced by stressed or injured cells acts as an important signalling molecule. This study aims to investigate whether adenosine triphosphate (ATP) plays an important role in the dialogue of human blastocyst-endometrium.

MATERIALS AND METHODS

The concentration of lactate was analysed in culture medium from human embryos collected from in vitro fertilization patients. Extracellular ATP was measured by ATP Bioluminescent Assay Kit. Ishikawa cells and T-HESCs were treated with ATP, ATP receptor antagonist, ATP hydrolysis enzyme or inhibitors of ATP metabolic enzymes. The levels of gene expression were evaluated by real-time PCR and immunoassay.

RESULTS

We showed that injured human endometrial epithelial cells could rapidly release ATP into the extracellular environment as an important signalling molecule. In addition, blastocyst-derived lactate induces the release of non-lytic ATP from human endometrial receptive epithelial cells via connexins. Extracellular ATP stimulates the secretion of IL8 from epithelial cells to promote the process of in vitro decidualization. Extracellular ATP could also directly promote the decidualization of human endometrial stromal cells via P2Y-purinoceptors. More importantly, the supernatants of injured epithelial cells clearly induce the decidualization of stromal cells in time-dependent manner.

CONCLUSION

Our results suggest that ATP should play an important role in human blastocyst-endometrium dialogue for the initiation of decidualization.

Metabolic compounds within the porcine uterine environment are unique to the type of conceptus present during the early stages of blastocyst elongation

The objective of this study was to identify metabolites within the porcine uterine milieu during the early stages of blastocyst elongation. At Days 9, 10, or 11 of gestation, reproductive tracts of White cross-bred gilts (n = 38) were collected immediately following harvest and flushed with Roswell Park Memorial Institute-1640 medium. Conceptus morphologies were assessed from each pregnancy and corresponding uterine flushings were assigned to one of five treatment groups based on these morphologies: (a) uniform spherical (n = 8); (b) heterogeneous spherical and ovoid (n = 8); (c) uniform ovoid (n = 8); (d) heterogeneous ovoid and tubular (n = 8); and (e) uniform tubular (n = 6). Uterine flushings from these pregnancies were submitted for nontargeted profiling by gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography (UPLC)-MS techniques. Unsupervised multivariate principal component analysis (PCA) was performed using pcaMethods and univariate analysis of variance was performed in R with false discovery rate (FDR) adjustment. PCA analysis of the GC-MS and UPLC-MS data identified 153 and 104 metabolites, respectively. After FDR adjustment of the GC-MS and UPLC-MS data, 38 and 59 metabolites, respectively, differed (p < .05) in uterine flushings from pregnancies across the five conceptus stages. Some metabolites were greater (p  < .05) in abundance for uterine flushings containing earlier stage conceptuses (i.e., spherical), such as uric acid, tryptophan, and tyrosine. In contrast, some metabolites were greater (p < .05) in abundance for uterine flushings containing later stage conceptuses (i.e., tubular), such as creatinine, serine, and urea. These data illustrate several putative metabolites that change within the uterine milieu during early porcine blastocyst elongation.

Reproductive technologies in swine

This chapter highlights the importance of reproductive technologies that are applied to porcine breeds. Nowadays the porcine industry, part of a high technological and specialized sector, offers high-quality protein food. The development of the swine industry is founded in the development of breeding/genetics, nutrition, animal husbandry, and animal health. The implementation of reproductive technologies in swine has conducted to levels of productivity never reached before. In addition, the pig is becoming an important species for biomedicine. The generation of pig models for human disease, xenotransplantation, or production of therapeutic proteins for human medicine has in fact generated a growing field of interest.

In vitro culture and non-invasive metabolic profiling of single bovine embryos

Selecting high-quality embryos for transfer has been a difficult task when producing bovine embryos invitro. The most used non-invasive method is based on visual observation. Molecular characterisation of embryo growth media has been proposed as a complementary method. In this study we demonstrate a culture medium sampling method for identifying potential embryonic viability markers to predict normal or abnormal embryonic development. During single embryo culture, 20µL culture media was removed at Days 2, 5 and 8 after fertilisation from the same droplet (60µL). In all, 58 samples were analysed using liquid chromatography-mass spectrometry. We demonstrate that it is possible to remove samples from the same culture medium droplets and not significantly affect blastocyst rate (25.2%). Changes in any single low molecular weight compound were not predictive enough. Combining multiple low molecular weight signals made it possible to predict Day 2 and 5 embryo development to the blastocyst stage with an accuracy of 64%. Elevated concentrations of lysophosphatidylethanolamines (m/z=453, 566, 588) in the culture media of Day 8 well-developing embryos were observed. Choline (104m/z) and citrate (215m/z) concentrations were increased in embryos in which development was retarded. Metabolic profiling provides possibilities to identify well-developing embryos before transfer, thus improving pregnancy rates and the number of calves born.

Glutamine supplementation enhances development of in vitro-produced porcine embryos and increases leucine consumption from the medium

Improper composition of culture medium contributes to reduced viability of in vitro-produced embryos. Glutamine (Gln) is a crucial amino acid for preimplantation embryos as it supports proliferation and is involved in many different biosynthetic pathways. Previous transcriptional profiling revealed several upregulated genes related to Gln transport and metabolism in in vitro-produced porcine blastocysts compared to in vivo-produced counterparts, indicating a potential deficiency in the culture medium. Therefore, the objective of this study was to determine the effects of Gln supplementation on in vitro-produced porcine embryo development, gene expression, and metabolism. Cleaved embryos were selected and cultured in MU2 medium supplemented with 1 mM Gln (control), 3.75 mM Gln (+Gln), 3.75 mM GlutaMAX (+Max), or 3.75 mM alanine (+Ala) until day 6. Embryos cultured with +Gln or +Max had increased development to the blastocyst stage and total number of nuclei compared to the control (P < 0.05). Moreover, expression of misregulated transcripts involved in glutamine and glutamate transport and metabolism was corrected when embryos were cultured with +Gln or +Max. Metabolomics analysis revealed increased production of glutamine and glutamate into the medium by embryos cultured with +Max and increased consumption of leucine by embryos cultured with +Gln or +Max. As an indicator of cellular health, mitochondrial membrane potential was increased when embryos were cultured with +Max which was coincident with decreased apoptosis in these blastocysts. Lastly, two embryo transfers by using embryos cultured with +Max resulted in viable piglets, confirming that this treatment is consistent with in vivo developmental competence.

Applications of omics and nanotechnology to improve pig embryo production in vitro

An appropriate environment to optimize porcine preimplantation embryo production in vitro is required as genetically modified pigs have become indispensable for biomedical research and agriculture. To provide suitable culture conditions, omics technologies have been applied to elucidate which metabolic substrates and pathways are involved during early developmental processes. Metabolomic profiling and transcriptional analysis comparing in vivo- and in vitro-derived embryos have demonstrated the important role of amino acids during preimplantation development. Transcriptional profiling studies have been helpful in assessing epigenetic reprogramming agents to allow for the correction of gene expression during the cloning process. Along with this, nanotechnology, which is a highly promising field, has allowed for the use of engineered nanoplatforms in reproductive biology. A growing number of studies have explored the use of nanoengineered materials for sorting, labeling, and targeting purposes; which demonstrates their potential to become one of the solutions for precise delivery of molecules into gametes and embryos. Considering the contributions of omics and the recent progress in nanoscience, in this review, we focused on their emerging applications for current in vitro pig embryo production systems to optimize the generation of genetically modified animals.

The never-ending search of an ideal culture system for domestic cat oocytes and embryos

In the domestic cat, in vitro fertilization started 40 years ago, but an ideal culture system has yet to be achieved. The physiological microenvironments, which interact with oocytes and embryos promoting their competence, have been investigated. However, recreating in vitro follicle- and oviduct-like conditions is challenging and a matter of both chemistry and physics. This review presents an excursus of the experimental investigations focused on the improvement of feline oocytes and embryos culture through the modulation of chemical and physical factors. Medium supplementation with components of follicular and oviductal fluids, or the use of different co-cultures, supports or substrata have been considered. Innovative and sophisticated systems as "organ-on-a-chip" might lead to the creation of artificial follicles and oviducts and they may represent the ideal combination of chemical and physical factors. Will the search ever end?

Comparison of the Oocyte Quality Derived from Two-Dimensional Follicle Culture Methods and Developmental Competence of In Vitro Grown and Matured Oocytes

In vitro follicle growth (IVFG) is an emerging fertility preservation technique, which can obtain fertilizable oocytes from an in vitro culture system in female. This study aimed to compare efficiency of the most widely used two-dimensional follicle culture methods [with or without oil layer (O+ or O- group)]. Preantral follicles were isolated from mice and randomly assigned. Follicles were cultured for 10 days and cumulus-oocyte complexes harvested 16-18 hours after hCG treatment. Follicle and oocyte growth, hormones in spent medium, meiotic spindle localization, expression of reactive oxygen species (ROS), mitochondrial activity, and gene expression were evaluated. In follicle growth, survival, pseudoantral cavity formation, ovulation, and oocyte maturation were also significantly higher in O+ group than O- group. Hormone production was significantly higher in follicles cultured in O+ than O-. There were no significant differences in mRNA expression related to development. On the other hand, the level of ROS was increased while the mitochondrial activity of in vitro grown matured oocyte was less than in vivo matured oocytes. In conclusion, follicle culture with O+ group appears to be superior to the culture in O- group in terms of follicle growth, development, oocyte growth, maturation, and microorganelles in oocyte.

The role of cGMP as a mediator of lipolysis in bovine oocytes and its effects on embryo development and cryopreservation

This study aimed to determine the influence of cyclic guanosine 3’5’-monophosphate (cGMP) and cGMP-dependent kinase (PKG) during in vitro maturation (IVM) on lipolysis-related parameters in bovine cumulus-oocyte complexes (COCs), and on embryo development and cryosurvival. COCs were matured with cGMP/PKG modulators and assessed for metaphase II rates (MII), cGMP levels, lipid content in oocytes (OO), transcript abundance for genes involved in lipolysis (ATGL) and lipid droplets (PLIN2) in cumulus cells (CC) and OO, and presence of phosphorylated (active) hormone sensitive lipase (HSL^ser563) in OO. Embryo development, lipid contents and survival to vitrification were also assessed. Phosphodiesterase 5 inhibition (PDE5; cGMP-hydrolyzing enzyme) with 10^-5M sildenafil (SDF) during 24 h IVM increased cGMP in COCs (56.9 vs 9.5 fMol/COC in untreated controls, p<0.05) and did not affect on maturation rate (84.3±6.4% MII). Fetal calf serum (FCS) in IVM medium decreased cGMP in COCs compared to bovine serum albumin (BSA) + SDF (19.6 vs 66.5 fMol/COC, respectively, p<0.05). FCS increased lipid content in OO (40.1 FI, p<0.05) compared to BSA (34.6 FI), while SDF decreased (29.8 and 29.6 FI, with BSA or FCS, respectively p<0.05). PKG inhibitor (KT5823) reversed this effect (38.9 FI, p<0.05). ATGL and PLIN2 transcripts were detected in CC and OO, but were affected by cGMP and PKG only in CC. HSL^ser563 was detected in OO matured with or without modulators. Reduced lipid content in embryos were observed only when SDF was added during IVM and IVC (27.6 FI) compared to its use in either or none of the culture periods (34.2 FI, p<0.05). Survival to vitrification was unaffected by SDF. In conclusion, cGMP and PKG are involved in lipolysis in OO and possibly in CC and embryos; serum negatively affects this pathway, contributing to lipid accumulation, and cGMP modulation may reduce lipid contents in oocytes and embryos, but without improving embryo cryotolerance.

Exogenous growth factors do not affect the development of individually cultured murine embryos

PURPOSE

The objective of this study was to evaluate the effects of multiple growth factors on the development of individually cultured murine embryos.

METHODS

Embryos produced by in vitro fertilization using in vitro (IVM) or in vivo (IVO) matured oocytes from three strains of mice (CF1, Swiss Webster, B6D2F1) were cultured individually (10 μl) in the absence (control) or presence of growth factors (paf, epidermal growth factor [EGF], insulin-like growth factor 1 [IGF-1], and granulocyte-macrophage colony-stimulating factor [GM-CSF]). Blastocyst formation, hatching, and blastocyst cell numbers (trophectoderm, inner cell mass, and total) were evaluated on days 4 and 5 of culture. Post-hatching development of CF1 IVO embryos was also evaluated in vitro and in vivo.

RESULTS

The presence of growth factors did not improve the proportion of embryos forming blastocysts or initiating hatching for any of the types of embryos tested. The only significant (P < 0.05) effect of growth factors was a decrease in the proportion of embryos that formed blastocysts by day 5 in CF1 IVM embryos. The presence of growth factors also did not affect blastocyst cell numbers. For CF1 IVO embryos, the presence of growth factors during culture did not affect the proportion of embryos that attached to fibronectin-coated dishes, the size of the resulting outgrowths, or in vivo development following transfer.

CONCLUSION

Combinations of paf, EGF, GM-CSF, and IGF-1 did not improve development of murine embryos cultured individually in a sequential medium containing a defined protein source.

Direct and Osmolarity-Dependent Effects of Glycine on Preimplantation Bovine Embryos

Concentrations of glycine (Gly) in embryo culture media are often lower (~0.1 mM) than those in oviductal or uterine fluids (≥1.2 mM). The objective of this study was to determine direct and osmolarity-dependent effects of physiological concentrations of Gly on blastocyst formation and hatching, cell allocation to the trophectoderm (TE) and inner cell mass (ICM), and metabolic activity of bovine embryos. In experiment 1, zygotes were cultured with 100 or 120 mM NaCl and 0 or 1 mM Gly for the first 72 h of culture. Blastocyst formation and hatching were improved (P<0.05) when embryos were cultured with 100 compared to 120 mM NaCl. Inclusion of 1 mM Gly improved (P<0.05) blastocyst formation compared to 0 mM Gly, but this effect was only significant (P<0.05) for embryos cultured with 120 mM NaCl, suggesting bovine embryos can utilize Gly as an osmolyte. In experiment 2, embryos were cultured with 0.1, 1.1, 2.1, or 4.1 mM Gly (100 mM NaCl) for the final 96 h of culture. Blastocyst development was not affected (P>0.05) by Gly, but hatching (0.1 mM Gly, 18.2%) was improved (P<0.05) when embryos were cultured with 1.1 (31.4%) or 2.1 (29.4%) mM Gly. Blastocyst, TE, and ICM cell numbers were not affected (P>0.05) by Gly in either experiment. Blastocysts produced alanine, glutamine, pyruvate, and urea and consumed aspartate, but this metabolic profile was not affected (P>0.05) by Gly. In conclusion, Gly (1.0 mM) improves the development of both early and late stage embryos, but beneficial effects are more pronounced for early embryos exposed to elevated osmolarity.

Omics in Reproductive Medicine: Application of Novel Technologies to Improve the IVF Success Rate

Treatment for many infertile couples often consists of in vitro fertilization (IVF) but an estimated 70% of IVF cycles fail to produce a live birth. In an attempt to improve the live birth rate, the vast majority of IVF cycles performed in the United States involve the transfer of multiple embryos, a practice that increases the risk of multiple gestation pregnancy. This is a concern because multiple gestation pregnancies are associated with an increased incidence of maternal and fetal complications and significant cost associated with the care of preterm infants. As the ideal outcome of each IVF cycle is the birth of a single healthy baby, significant effort has focused on identifying embryos with the greatest developmental potential. To date, selection of euploid embryos using comprehensive chromosome screening (CCS) is the most promising approach while metabolomic and proteomic assessment of spent culture medium have the potential to noninvasively assess embryo viability. Endometrial gene expression profiling may help determine the optimal time to perform embryo transfer. While CCS has been implemented in some clinics, further development and optimization will be required before analysis of spent culture medium and endometrial gene expression profiling make the transition to clinical use. This review will describe efforts to identify embryos with the greatest potential to result in a healthy, live birth, with a particular emphasis on detection of embryo aneuploidy and metabolic profiling of spent embryo culture medium. Assessment of endometrial receptivity to identify the optimal time to perform embryo transfer will also be discussed.

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.