The role of paf in embryo physiology

Events Leading to the Establishment of Pregnancy and Placental Formation: The Need to Fine-Tune the Nomenclature on Pregnancy and Gestation

Today, there is strong and diversified evidence that in humans at least 50% of early embryos do not proceed beyond the pre-implantation period. This evidence comes from clinical investigations, demography, epidemiology, embryology, immunology, and molecular biology. The purpose of this article is to highlight the steps leading to the establishment of pregnancy and placenta formation. These early events document the existence of a clear distinction between embryonic losses during the first two weeks after conception and those occurring during the subsequent months. This review attempts to highlight the nature of the maternal-embryonic dialogue and the major mechanisms active during the pre-implantation period aimed at "selecting" embryos with the ability to proceed to the formation of the placenta and therefore to the completion of pregnancy. This intense molecular cross-talk between the early embryo and the endometrium starts even before the blastocyst reaches the uterine cavity, substantially initiating and conditioning the process of implantation and the formation of the placenta. Today, several factors involved in this dialogue have been identified, although the best-known and overall, the most important, still remains Chorionic Gonadotrophin, indispensable during the first 8 to 10 weeks after fertilization. In addition, there are other substances acting during the first days following fertilization, the Early Pregnancy Factor, believed to be involved in the suppression of the maternal response, thereby allowing the continued viability of the early embryo. The Pre-Implantation Factor, secreted between 2 and 4 days after fertilization. This linear peptide molecule exhibits a self-protective and antitoxic action, is present in maternal blood as early as 7 days after conception, and is absent in the presence of non-viable embryos. The Embryo-Derived Platelet-activating Factor, produced and released by embryos of all mammalian species studied seems to have a role in the ligand-mediated trophic support of the early embryo. The implantation process is also guided by signals from cells in the decidualized endometrium. Various types of cells are involved, among them epithelial, stromal, and trophoblastic, producing a number of cellular molecules, such as cytokines, chemokines, growth factors, and adhesion molecules. Immune cells are also involved, mainly uterine natural killer cells, macrophages, and T cells. In conclusion, events taking place during the first two weeks after fertilization determine whether pregnancy can proceed and therefore whether placenta's formation can proceed. These events represent the scientific basis for a clear distinction between the first two weeks following fertilization and the rest of gestation. For this reason, we propose that a new nomenclature be adopted specifically separating the two periods. In other words, the period from fertilization and birth should be named "gestation", whereas that from the completion of the process of implantation leading to the formation of the placenta, and birth should be named "pregnancy".

Reducing time to pregnancy and facilitating the birth of healthy children through functional analysis of embryo physiology†

An ever-increasing number of couples rely on assisted reproductive technologies (ART) in order to conceive a child. Although advances in embryo culture have led to increases in the success rates of clinical ART, it often takes more than one treatment cycle to conceive a child. Ensuring patients conceive as soon as possible with a healthy embryo is a priority for reproductive medicine. Currently, selection of embryos for transfer relies predominantly on the morphological assessment of the preimplantation embryo; however, morphology is not an absolute link to embryo physiology, nor the health of the resulting child. Non-invasive quantitation of individual embryo physiology, a key regulator of both embryo viability and health, could provide valuable information to assist in the selection of the most viable embryo for transfer, hence reducing the time to pregnancy. Further, according to the Barker Hypothesis, the environment to which a fetus is exposed to during gestation affects subsequent offspring health. If the environment of the preimplantation period is capable of affecting metabolism, which in turn will affect gene expression through the metaboloepigenetic link, then assessment of embryo metabolism should represent an indirect measure of future offspring health. Previously, the term viable embryo has been used in association with the potential of an embryo to establish a pregnancy. Here, we propose the term healthy embryo to reflect the capacity of that embryo to lead to a healthy child and adult.

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.

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a ‘soluble factor’ released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Individual culture and atmospheric oxygen during culture affect mouse preimplantation embryo metabolism and post-implantation development

RESEARCH QUESTION

Does single embryo culture under atmospheric or reduced oxygen alter preimplantation metabolism and post-implantation development compared with culture in groups?

DESIGN

Mouse embryos were cultured under 5% or 20% oxygen, individually or in groups of 10. Spent media were analysed after 48, 72 and 96 h of culture. Blastocysts were assessed by outgrowth assay or transferred to pseudo-pregnant recipients, and fetal and placental weight, length and morphology were assessed.

RESULTS

Compared with group culture, individually cultured blastocysts had lower net consumption of glucose and aspartate and higher glutamate production. Atmospheric oxygen reduced uptake of glucose and aspartate and increased production of glutamate and ornithine compared with 5% oxygen. Combining 20% oxygen and single culture resulted in further metabolic changes: decreased leucine, methionine and threonine consumption. Under 5% oxygen, individual culture decreased placental labyrinth area but had no other effects on fetal and placental development or outgrowth size compared with group culture. Under 20% oxygen, however, individual culture reduced outgrowth size and fetal and placental weight compared with group-cultured embryos.

CONCLUSIONS

Preimplantation metabolism of glucose and amino acids is altered by both oxygen and individual culture, and fetal weight is reduced by individual culture under atmospheric oxygen but not 5% oxygen. This study raises concerns regarding the increasing prevalence of single embryo culture in human IVF and adds to the existing evidence regarding the detrimental effects of atmospheric oxygen during embryo culture. Furthermore, these data demonstrate the cumulative nature of stress during embryo culture and highlight the importance of optimizing each element of the culture system.

Intracellular localisation of platelet-activating factor during mammalian embryo development in vitro: a comparison of cattle, mouse and human

Platelet-activating factor (PAF) is a well-known marker for embryo quality and viability. For the first time, we describe an intracellular localisation of PAF in oocytes and embryos of cattle, mice and humans. We showed that PAF is represented in the nucleus, a signal that was lost upon nuclear envelope breakdown. This process was confirmed by treating the embryos with nocodazole, a spindle-disrupting agent that, as such, arrests the embryo in mitosis, and by microinjecting a PAF-specific antibody in bovine MII oocytes. The latter resulted in the absence of nuclear PAF in the pronuclei of the zygote and reduced further developmental potential. Previous research indicates that PAF is released and taken up from the culture medium by preimplantation embryos invitro, in which bovine serum albumin (BSA) serves as a crucial carrier molecule. In the present study we demonstrated that nuclear PAF does not originate from an extracellular source because embryos cultured in polyvinylpyrrolidone or BSA showed similar levels of PAF in their nuclei. Instead, our experiments indicate that cytosolic phospholipase A2 (cPLA2) is likely to be involved in the intracellular production of PAF, because treatment with arachidonyl trifluoromethyl ketone (AACOCF3), a specific cPLA2 inhibitor, clearly lowered PAF levels in the nuclei of bovine embryos.

The enigma of embryonic diapause

Embryonic diapause – a period of embryonic suspension at the blastocyst stage – is a fascinating phenomenon that occurs in over 130 species of mammals, ranging from bears and badgers to mice and marsupials. It might even occur in humans. During diapause, there is minimal cell division and greatly reduced metabolism, and development is put on hold. Yet there are no ill effects for the pregnancy when it eventually continues. Multiple factors can induce diapause, including seasonal supplies of food, temperature, photoperiod and lactation. The successful reactivation and continuation of pregnancy then requires a viable embryo, a receptive uterus and effective molecular communication between the two. But how do the blastocysts survive and remain viable during this period of time, which can be up to a year in some cases? And what are the signals that bring it out of suspended animation? Here, we provide an overview of the process of diapause and address these questions, focussing on recent molecular data.

The induction of tumour suppressor protein P53 limits the entry of cells into the pluripotent inner cell mass lineage in the mouse embryo

The early preimplantation embryo is susceptible to a range of exogenous stresses which result in their reduced long-term developmental potential. The P53 tumour suppressor protein is normally held at low levels in the preimplantation embryo and we show that culture stress induces the expression of a range of canonical P53-response genes (Mdm2, Bax and Cdkn1a). Culture stress caused a P53-dependent loss of cells from resulting blastocysts, and this was most evident within the inner cell mass population. Culture stress increased the proportion of cells expressing active caspase-3 and undergoing apoptosis, while inhibition of caspase-3 increased the number of cells within the inner cell mass. The P53-dependent loss of cells from the inner cell mass was accompanied by a loss of NANOG-positive epiblast progenitors. Pharmacological activation of P53 by the MDM2 inhibitor, Nutlin-3, also caused increased P53-dependent transcription and the loss of cells from the inner cell mass. This loss of cells could be ameliorated by simultaneous treatment with the P53 inhibitor, Pifithrin-α. Culture stress causes reduced signalling via the phosphatidylinositol-3-kinase signalling pathway, and blocking this pathway caused P53-dependent loss of cells from the inner cell mass. These results point to P53 acting to limit the accumulation and survival of cells within the pluripotent lineage of the blastocyst and provide a molecular framework for the further investigation of the factors determining the effects of stressors on the embryo's developmental potential.

In vitro production of bovine embryos derived from individual donors in the Corral® dish

Background

Since the identity of the embryo is of outmost importance during commercial in vitro embryo production, bovine oocytes and embryos have to be cultured strictly per donor. Due to the rather low yield of oocytes collected after ovum pick-up (OPU) per individual cow, oocyte maturation and embryo culture take place in small groups, which is often associated with inferior embryo development. The objective of this study was to improve embryonic development in small donor groups by using the Corral^® dish. This commercial dish is designed for human embryo production. It contains two central wells that are divided into quadrants by a semi-permeable wall. In human embryo culture, one embryo is placed per quadrant, allowing individual follow-up while embryos are exposed to a common medium. In our study, small groups of oocytes and subsequently embryos of different bovine donors were placed in the Corral^® dish, each donor group in a separate quadrant.

Results

In two experiments, the Corral^® dish was evaluated during in vitro maturation (IVM) and/or in vitro culture (IVC) by grouping oocytes and embryos of individual bovine donors per quadrant. At day 7, a significantly higher blastocyst rate was noted in the Corral^® dish used during IVM and IVC than when only used during IVM (12.9% ± 2.10 versus 22.8% ± 2.67) (P < 0.05). However, no significant differences in blastocyst yield were observed anymore between treatment groups at day 8 post insemination.

Conclusions

In the present study, the Corral^® dish was used for in vitro embryo production (IVP) in cattle; allowing to allocate oocytes and/or embryos per donor. As fresh embryo transfers on day 7 have higher pregnancy outcomes, the Corral^® dish offers an added value for commercial OPU/IVP, since a higher blastocyst development at day 7 is obtained when the Corral^® dish is used during IVM and IVC.

Impact of the IVF laboratory environment on human preimplantation embryo phenotype

The phenotype of the human embryo conceived through in vitro fertilization (IVF), that is its morphology, developmental kinetics, physiology and metabolism, can be affected by numerous components of the laboratory and embryo culture system (which comprise the laboratory environment). The culture media formulation is important in determining embryo phenotype, but this exists within a culture system that includes oxygen, temperature, pH and whether an embryo is cultured individually or in a group, all of which can influence embryo development. Significantly, exposure of an embryo to one suboptimal component of the culture system of laboratory typically predisposes the embryo to become more vulnerable to a second stressor, as has been well documented for atmospheric oxygen and individual culture, as well as for oxygen and ammonium. Furthermore, the inherent viability of the human embryo is derived from the quality of the gametes from which it is created. Patient age, aetiology, genetics, lifestyle (as well as ovarian stimulation in women) are all known to affect the developmental potential of gametes and hence the embryo. Thus, as well as considering the impact of the IVF laboratory environment, one needs to be aware of the status of the infertile couple, as this impacts how their gametes and embryos will respond to an in vitro environment. Although far from straight forward, analysing the interactions that exist between the human embryo and its environment will facilitate the creation of more effective and safer treatments for the infertile couple.

Impacts of and interactions between environmental stress and epigenetic programming during early embryo development

The processes of assisted reproductive technologies (ART) involve a variety of interventions that impact on the oocyte and embryo. Critically, these interventions cause considerable stress and coincide with important imprinting events throughout gametogenesis, fertilisation and early embryonic development. It is now accepted that the IVM and in vitro development of gametes and embryos can perturb the natural course of development to varying degrees of severity. Altered gene expression and, more recently, imprinting disorders relating to ART have become a focused area of research. Although various hypotheses have been put forward, most research has been observational, with little attempt to discover the mechanisms and periods of sensitivity during embryo development that are influenced by the culture conditions following fertilisation. The embryo possesses innate survival factor signalling pathways, yet when an embryo is placed in culture, this signalling in response to in vitro stress becomes critically important in mitigating the effects of stresses caused by the in vitro environment. It is apparent that not all embryos possess this ability to adequately adapt to the stresses experienced in vitro, most probably due to an inadequate oocyte. It is speculated that it is important that embryos use their survival signalling mechanisms to maintain normal epigenetic programming. The seeming redundancy in the function of various survival signalling pathways would support this notion. Any invasion into the natural, highly orchestrated and dynamic process of sexual reproduction could perturb the normal progression of epigenetic programming. Therefore the source of gametes and the subsequent culture conditions of gametes and embryos are critically important and require careful attention. It is the aim of this review to highlight avenues of research to elucidate the effects of stress and the relationship with epigenetic programming. The short- and long-term health and viability of human and animal embryos derived in vitro will also be discussed.

Actions of activin A, connective tissue growth factor, hepatocyte growth factor and teratocarcinoma-derived growth factor 1 on the development of the bovine preimplantation embryo

The reproductive tract secretes bioactive molecules collectively known as embryokines that can regulate embryonic growth and development. In the present study we tested four growth factors expressed in the endometrium for their ability to modify the development of the bovine embryo to the blastocyst stage and alter the expression of genes found to be upregulated (bone morphogenetic protein 15 (BMP15) and keratin 8, type II (KRT8)) or downregulated (NADH dehydrogenase 1 (ND1) and S100 calcium binding protein A10 (S100A10)) in embryos competent to develop to term. Zygotes were treated at Day 5 with 0.01, 0.1 or 1.0 nM growth factor. The highest concentration of activin A increased the percentage of putative zygotes that developed to the blastocyst stage. Connective tissue growth factor (CTGF) increased the number of cells in the inner cell mass (ICM), decreased the trophectoderm : ICM ratio and increased blastocyst expression of KRT8 and ND1. The lowest concentration of hepatocyte growth factor (HGF) reduced the percentage of putative zygotes becoming blastocysts. Teratocarcinoma-derived growth factor 1 increased total cell number at 0.01 nM and expression of S100A10 at 1.0 nM, but otherwise had no effects. Results confirm the prodevelopmental actions of activin A and indicate that CTGF may also function as an embryokine by regulating the number of ICM cells in the blastocyst and altering gene expression. Low concentrations of HGF were inhibitory to development.

Hypoxia and hyperoxia potentiate PAF receptor-mediated effects in newborn ovine pulmonary arterial smooth muscle cells: significance in oxygen therapy of PPHN

Platelet-activating factor (PAF) acting via its receptor (PAFR) is implicated in the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN). Effects of long-term oxygen therapy on newborn lung are not well understood; therefore, we studied the effect of oxygen tension on ovine newborn pulmonary artery smooth muscle cells (NBPASMC). Our global hypothesis is that PPHN results from failure of newborn lamb pulmonary system to downregulate PAFR activity or to upregulate vasodilatory cyclic nucleotides (Cnucs) activity. NBPASMC from newborns 6-12 days old were studied in vitro at three different oxygen tensions (pO2, [Torr]: hypoxia, <40; normoxia, 80-100; and hyperoxia, >100 Torr often clinically imposed upon newborns with PPHN) PAFR- and Cnucs mediated effects were determined. PAFR and PKA Cα mRNA expression as well as prostacyclin, thromboxane, cAMP production, and DNA synthesis was studied to assess PAFR-mediated hypertrophy and/or hyperplasia. Hypoxia and hyperoxia increased specific PAFR binding. PAF treatment during hyperoxia increased PAFR gene, but decreased PKA-Cα gene expression. Hypoxia and hyperoxia increased NBPASMC proliferation via PAFR signaling. Baseline prostacyclin level was ninefold greater than in fetal PASMC, whereas baseline thromboxane was sevenfold less suggesting greater postnatal cyclooxygenase activity in NBPASMC PAF decreased, while forskolin and 8-Br-cAMP increased cAMP production. Decrease of PAFR effects by Cnucs indicates that normal newborn PA physiology favors vasodilator pathways to minimize PAF-induced hypertrophy or hyperplasia. We speculate that failure of newborn lung to anchor downregulation of vasoconstrictors with upregulation of vasodilators leads to PPHN.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

Autocrine embryotropins revisited: how do embryos communicate with each other in vitro when cultured in groups?

In the absence of the maternal genital tract, preimplantation embryos can develop in vitro in culture medium where all communication with the oviduct or uterus is absent. In several mammalian species, it has been observed that embryos cultured in groups thrive better than those cultured singly. Here we argue that group-cultured embryos are able to promote their own development in vitro by the production of autocrine embryotropins that putatively serve as a communication tool. The concept of effective communication implies an origin, a signalling agent, and finally a recipient that is able to decode the message. We illustrate this concept by demonstrating that preimplantation embryos are able to secrete autocrine factors in several ways, including active secretion, passive outflow, or as messengers bound to a molecular vehicle or transported within extracellular vesicles. Likewise, we broaden the traditional view that inter-embryo communication is dictated mainly by growth factors, by discussing a wide range of other biochemical messengers including proteins, lipids, neurotransmitters, saccharides, and microRNAs, all of which can be exchanged among embryos cultured in a group. Finally, we describe how different classes of messenger molecules are decoded by the embryo and influence embryo development by triggering different pathways. When autocrine embryotropins such as insulin-like growth factor-I (IGF-I) or platelet activating factor (PAF) bind to their appropriate receptor, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) pathway will be activated which is important for embryo survival. On the other hand, the mitogen-activated protein kinase (MAPK) pathway is activated when compounds such as hyaluronic acid and serotonin bind to their respective receptors, thereby acting as growth factors. By activating the peroxisome-proliferator-activated receptor family (PPAR) pathway, lipophilic autocrine factors such as prostaglandins or fatty acids have both survival and anti-apoptotic functions. In conclusion, considering different types of messenger molecules simultaneously will be crucial to understanding more comprehensively how embryos communicate with each other in group-culture systems. This approach will assist in the development of novel media for single-embryo culture.

The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction

BACKGROUND

Although laboratory procedures, along with culture media formulations, have improved over the past two decades, the issue remains that human IVF is performed in vitro (literally 'in glass').

METHODS

Using PubMed, electronic searches were performed using keywords from a list of chemical and physical factors with no limits placed on time. Examples of keywords include oxygen, ammonium, volatile organics, temperature, pH, oil overlays and incubation volume/embryo density. Available clinical and scientific evidence surrounding physical and chemical factors have been assessed and presented here.

RESULTS AND CONCLUSIONS

Development of the embryo outside the body means that it is constantly exposed to stresses that it would not experience in vivo. Sources of stress on the human embryo include identified factors such as pH and temperature shifts, exposure to atmospheric (20%) oxygen and the build-up of toxins in the media due to the static nature of culture. However, there are other sources of stress not typically considered, such as the act of pipetting itself, or the release of organic compounds from the very tissue culture ware upon which the embryo develops. Further, when more than one stress is present in the laboratory, there is evidence that negative synergies can result, culminating in significant trauma to the developing embryo. It is evident that embryos are sensitive to both chemical and physical signals within their microenvironment, and that these factors play a significant role in influencing development and events post transfer. From the viewpoint of assisted human reproduction, a major concern with chemical and physical factors lies in their adverse effects on the viability of embryos, and their long-term effects on the fetus, even as a result of a relatively brief exposure. This review presents data on the adverse effects of chemical and physical factors on mammalian embryos and the importance of identifying, and thereby minimizing, them in the practice of human IVF. Hence, optimizing the in vitro environment involves far more than improving culture media formulations.

Mechanism by which nuclear factor-kappa beta (NF-kB) regulates ovine fetal pulmonary vascular smooth muscle cell proliferation

Platelet activating factor (PAF) modulates ovine fetal pulmonary hemodynamic. PAF acts through its receptors (PAFR) in pulmonary vascular smooth muscle cells (PVSMC) to phosphorylate and induce nuclear translocation of NF-kB p65 leading to PVSMC proliferation. However, the interaction of NF-kB p65 and PAF in the nuclear domain to effect PVSMC cell growth is not clearly defined. We used siRNA-dependent translation initiation arrest to study a mechanism by which NF-kB p65 regulates PAF stimulation of PVSMC proliferation. Our hypotheses are: (a) PAF induces NF-kB p65 DNA binding and (b) NF-kB p65 siRNA attenuates PAF stimulation of PVSMC proliferation. For DNA binding, cells were fed 10 nM PAF with and without PAFR antagonists WEB 2170, CV 3988 or BN 52021 and incubated for 12 h. DNA binding was measured by specific ELISA. For NF-kB p65 siRNA effect, starved cells transfected with the siRNA were incubated for 24 h with and without 10 nM PAF. Cell proliferation was measured by DNA synthesis while expression of NF-kB p65 and PAFR protein was measured by Western blotting. In both studies, the effect of 10% FBS alone was used as the positive control. In general, PAF stimulated DNA binding which was inhibited by PAFR antagonists. siRNAs to NF-kB p65 and PAFR significantly attenuated cell proliferation compared to 10% FBS and PAF effect. Inclusion of PAF in siRNA-treated cells did not reverse inhibitory effect of NF-kB p65 siRNA on DNA synthesis. PAFR expression was inhibited in siRNA-treated cells. These data show that PAF-stimulation of PVSMC proliferation occurs via a PAFR-NF-kB p65 linked pathway.

Omics as a window to view embryo viability

The advent of advanced omics technologies and the application of these techniques to the analysis of extremely limited material have opened the door to the investigation of embryo physiology in a focused, in-depth approach never before possible. The application of noninvasive metabolomic and proteomic platforms to understanding embryo viability permits the characterization of individual embryos in culture. Initial clinical data have highlighted the promise of these technologies for the development of noninvasive embryo selection criteria. In this way, a complex view of embryo function can be compiled and related to embryo development, quality, and outcome. Application of knowledge gained from omics will transform both our understanding of embryo physiology as well as our ability to select viable embryos for transfer in assisted reproductive technology.

Characterization of secreted proteins of 2-cell mouse embryos cultured in vitro to the blastocyst stage with and without protein supplementation

PURPOSE

To identify the secreted proteins of murine embryos grown in vitro.

METHODS

Two-cell mouse embryos (n=432) were randomly allocated to culture to the blastocyst stage in protein-free and in protein-supplemented (3 % BSA) media. Proteins were separated by SDS-PAGE; bands were visualized by coomassie staining, followed by in-gel trypsin digestion and liquid chromatography-tandem mass spectrometry. RT-PCR and confocal microscopy were used to confirm gene/protein expression in blastocysts.

RESULTS

Of all individually identified proteins, 34 and 23 were found in embryos cultured without and with BSA, respectively, and 20 were common. Identified proteins having an N-terminal secretory sequence or transmembrane domains located on the extracellular backbone were postulated as secreted proteins. Gene and protein expression for two selected molecules were confirmed. Functional analysis revealed over-represented processes related to lipid metabolism, cyclase activity, and cell adhesion/membrane functions.

CONCLUSIONS

This study provided evidence to further characterize secreted proteins by mouse embryos grown from the 2-cell to the blastocyst stage in vitro. Because of homology between murine and human, these results may provide information to be translated to the clinical setting.

Soluble ligands and their receptors in human embryo development and implantation

Extensive evidence suggests that soluble ligands and their receptors mediate human preimplantation embryo development and implantation. Progress in this complex area has been ongoing since the 1980s, with an ever-increasing list of candidates. This article specifically reviews evidence of soluble ligands and their receptors in the human preimplantation stage embryo and female reproductive tract. The focus will be on candidates produced by the human preimplantation embryo and those eliciting developmental responses in vitro, as well as endometrial factors related to implantation and receptivity. Pathways to clinical translation, including innovative diagnostics and other technologies, are also highlighted, drawing from this collective evidence toward facilitating joint improvements in embryo quality and endometrial receptivity. This strategy could not only benefit clinical outcomes in reproductive medicine but also provide broader insights into the peri-implantation period of human development to improve fetal and neonatal health.

Individual commitment to a group effect: strengths and weaknesses of bovine embryo group culture

Recently, new culture devices such as Corral and Primo Vision dishes have been designed for the culture of human embryos to allow the combination of group culture plus follow-up of individual embryos. Bovine inseminated oocytes were allocated to Primo Vision dishes, Corral dishes, individual culture or classical group culture. Blastocyst development in Primo Vision dishes was similar to classical group culture (34.3 and 39.0% respectively), and better than Corral dishes or individual culture (28.9 and 28.5% respectively). In Primo Vision dishes, a higher number of ‘slow’ embryos developed to the blastocyst stage compared with their individually cultured counterparts, while no differences were observed for ‘fast’ embryos. ‘Slow’ embryos in a ‘standard drop’ had a higher chance of becoming a blastocyst compared with individual culture (OR: 2.3), whereas blastulation of ‘fast’ embryos was less efficient in a ‘delayed drop’ than in individual culture (OR: 0.3). The number of non-cleaved embryos in Primo Vision dishes did not negatively influence blastocyst development. Likewise, removing non-cleaved embryos (NC removed) and regrouping the cleaved embryos afterwards (ReGR) did not affect blastocyst development and quality compared with group culture in Primo Vision dishes (CTRL, 31.6%, NC removed, 29.3% and ReGR, 29.6%). The experiments revealed that group culture of bovine embryos in Primo Vision dishes is superior to individual culture, primarily because of the higher blastocyst rate achieved by slow embryos. Non-cleaved or arrested embryos do not hamper the ability of co-cultured bovine embryos to reach the blastocyst stage in group culture.

OMICS: Current and future perspectives in reproductive medicine and technology

Many couples present fertility problems at their reproductive age, and although in the last years, the efficiency of assisted reproduction techniques has increased, these are still far from being 100% effective. A key issue in this field is the proper assessment of germ cells, embryos and endometrium quality, in order to determine the actual likelihood to succeed. Currently available analysis is mainly based on morphological features of oocytes, sperm and embryos and although these strategies have improved the results, there is an urgent need of new diagnostic and therapeutic tools. The emergence of the - OMICS technologies (epigenomics, genomics, transcriptomics, proteomics and metabolomics) permitted the improvement on the knowledge in this field, by providing with a huge amount of information regarding the biological processes involved in reproductive success, thereby getting a broader view of complex biological systems with a relatively low cost and effort.

The regulation of the expression and activation of the essential ATF1 transcription factor in the mouse preimplantation embryo

The co-expression of the CREB and ATF1 transcription factors is required for the development of preimplantation embryos. Embryotropin-mediated, calcium/calmodulin-dependent signalling activates CREB-induced transcription in the two-cell embryo, but the regulation of ATF1 in the embryo is not known. This study demonstrates that ATF1 begins to accumulate within both pronuclei of the mouse zygote by 20 h post-human chorionic gonadotrophin. This did not require new transcription (not blocked by α-amanitin), but was dependent upon protein synthesis (blocked by puromycin) and the activity of P38 MAP kinase. ATF1 becomes an active transcription factor upon being phosphorylated. A marked accumulation of phosphorylated ATF1 was evident in two-cell embryos and this persisted in subsequent stages of development. This phosphorylation was enhanced by the actions of autocrine embryotropic mediators (including Paf) and required the mutual actions of P38 MAP kinase and calmodulin-dependent pathways for maximum levels of phosphorylation. The combined inhibition of these two pathways blocked embryonic genome activation (EGA) and caused embryos to enter a developmental block at the two-cell stage. The members of the CREB family of transcription factors can generate one of the most diverse transcriptomes of any transcription factor. The demonstration of the presence of activated CREB and ATF1 within the embryonic nucleus at the time of EGA places these transcription factors as priority targets as key regulators of EGA.

Platelet-activating factor synthesis and receptor-mediated signaling are downregulated in ovine newborn lungs: relevance in postnatal pulmonary adaptation and persistent pulmonary hypertension of the newborn

Platelet-activating factor (PAF) is a phospholipid with a wide range of biological activities. We studied PAF metabolism and PAF receptor (PAFR) signaling in perinatal ovine lungs to understand PAF's role in transition of the perinatal pulmonary hemodynamics and pathophysiology of persistent pulmonary hypertension of the newborn. We hypothesized that downregulation of PAF synthesis with upregulation of PAF catabolism by acetylhydrolase (PAF-Ah) in the newborn lung is needed for fetus-to-newborn pulmonary adaptation. Studies were conducted on fetal and newborn lamb pulmonary arteries (PA), veins (PV) and smooth muscle cells (SMC). PAF metabolism, PAFR binding and cell proliferation were studied by cell culture; gene expression was studied by qPCR. Fetal lungs synthesized 60% more PAF than newborn lungs. Compared with the fetal PVs and SMCs, PAF-Ah activity in newborn was 40-60% greater. PAF-Ah mRNA expression in newborn vessels was different from the expression by fetal PA. PAF-Ah gene clone activity confirmed deletion of hypoxia-sensitive site. PAFR mRNA expression by the PVs and SMC-PV of the fetus and newborn was greater than by corresponding PAs and SMC-PA. Q-PCR study of PAFR expression by the SMC-PV of both groups was greater than SMC-PA. Fetal SMCs bound more PAF than the newborn SMCs. PAFR antagonist, CV-3988, inhibited PAFR binding and DNA synthesis by the fetal SMCs, but augmented binding and DNA synthesis by newborn cells. We show different PAF-PAFR mediated effects in perinatal lungs, suggesting both transcriptional and translational regulation of PAF-Ah and PAFR expression in the perinatal lamb lungs. These indicate that the downregulation of PAF-mediated effects postnatally protects against persistent pulmonary hypertension of the newborn.

Systematic analysis of the factors that adversely affect the rate of cell accumulation in mouse embryos during their culture in vitro

BACKGROUND

Retarded embryo growth is a pervasive effect of culture in vitro.

METHODS

A systematic analysis of the interactions between media design, embryo culture density, oxygen tension, amino acids, trophic ligands and the genetic background of the mouse on embryo growth rates in vitro was performed.

RESULTS

Growth retardation of mouse zygotes was greater in 20% O2 than 5%, a sequential media design was superior to static simple media designs, but the supplementation of simple media with mixed amino acids mitigated this difference. There was a beneficial effect of communal culture in small volumes, and supplementation with a trophic ligand (Paf) further enhanced growth rates. For hybrid strain zygotes (B6CBF1) communal culture in KSOM media supplemented with amino acids, albumin and Paf under 5% O₂ resulted in complete rescue of their rate of accumulation of cells and blastocyst formation. Inbred strain (C57BL6/J) zygotes, however, still showed some retardation of development under these conditions. The additional supplementation of media with another trophic ligand (IGF1) showed a further additive beneficial effect on development of inbred strain embryos but they still showed a growth deficit of ~ 23% cell number. The results show that optimising the interactions between a range of culture conditions and media design can rescue hybrid strain embryos from a retarded rate of cell proliferation caused by culture in vitro, but this was incomplete for the B6 strain.

CONCLUSIONS

The results indicate that the growth requirement of embryos in vitro varies depending upon their genetic background and provide models for the further genetic analysis of embryo growth.

Paf receptor expression in the marsupial embryo and endometrium during embryonic diapause

The control of reactivation from embryonic diapause in the tammar wallaby (Macropus eugenii) involves sequential activation of the corpus luteum, secretion of progesterone that stimulates endometrial secretion and subsequent changes in the uterine environment that activate the embryo. However, the precise signals between the endometrium and the blastocyst are currently unknown. In eutherians, both the phospholipid Paf and its receptor, platelet-activating factor receptor (PTAFR), are present in the embryo and the endometrium. In the tammar, endometrial Paf releasein vitroincreases around the time of the early progesterone pulse that occurs around the time of reactivation, but whether Paf can reactivate the blastocyst is unknown. We cloned and characterised the expression of PTAFR in the tammar embryo and endometrium at entry into embryonic diapause, during its maintenance and after reactivation. Tammar PTAFR sequence and protein were highly conserved with mammalian orthologues. In the endometrium, PTAFR was expressed at a constant level in the glandular epithelium across all stages and in the luminal epithelium during both diapause and reactivation. Thus, the presence of the receptor appears not to be a limiting factor for Paf actions in the endometrium. However, the low levels of PTAFR in the embryo during diapause, together with its up-regulation and subsequent internalisation at reactivation, supports earlier results suggesting that endometrial Paf could be involved in reactivation of the tammar blastocyst from embryonic diapause.

Media composition: macromolecules and embryo growth

Most embryo culture media are still supplemented with proteins rather than with nonprotein macromolecules or recombinant protein products. HSA is probably the most common supplement followed by globulin-enriched preparations. Serum supplementation and Co-Culture of embryos belong to the past. Defined nonprotein or recombinant protein supplements are becoming a viable alternative during gamete and embryo manipulation procedures. Biological protein supplements are still preferred for any extended period of embryo culture. Understanding the goals and purpose of supplemented macromolecules in embryo culture media during each step of the laboratory IVF process should assist us in choosing the safest and most consistent macromolecule for each step, but also selecting a product that has the capability of delivering the best clinical outcome. Each batch of biological protein supplement is unique, even if supplied by the same manufacturer. Each lot of protein supplement typically contains many lot-specific, potentially harmful, and unintended hormone and protein contaminants. Macromolecular embryo culture medium supplements should be identified as one of the highest risk factors in an IVF laboratory that may contribute towards clinical compromise. All efforts should be made to use a proven batch of supplement for as long as the expiration date will allow. The beneficial effect of more complex protein supplements is evident after the activation of the embryonic genome and probably due to the presence of growth factors. Lower live-birth rates due to suboptimum protein supplementation may be a direct result of the preferential loss of female embryos. When deciding on a culture system, thought should be given specifically to the interaction between the culture medium and the macromolecular supplement. Ready-to-use pre-supplemented culture media may be advisable over a more complex product if a comprehensive macromolecular quality management program is not feasible. However, the question remains as to whether the increasing simplification of embryo culture media supplements is ready for large-scale clinical use.

Proteomics in reproductive biology: beacon for unraveling the molecular complexities

Proteomics, an interface of rapidly evolving advances in physics and biology, is rapidly developing and expanding its potential applications to molecular and cellular biology. Application of proteomics tools has contributed towards identification of relevant protein biomarkers that can potentially change the strategies for early diagnosis and treatment of several diseases. The emergence of powerful mass spectrometry-based proteomics technique has added a new dimension to the field of medical research in liver, heart diseases and certain forms of cancer. Most proteomics tools are also being used to study physiological and pathological events related to reproductive biology. There have been attempts to generate the proteomes of testes, sperm, seminal fluid, epididymis, oocyte, and endometrium from reproductive disease patients. Here, we have reviewed proteomics based investigations in humans over the last decade, which focus on delineating the mechanism underlying various reproductive events such as spermatogenesis, oogenesis, endometriosis, polycystic ovary syndrome, embryo development. The challenge is to harness new technologies like 2-DE, DIGE, MALDI-MS, SELDI-MS, MUDPIT, LC-MS etc., to a greater extent to develop widely applicable clinical tools in understanding molecular aspects of reproduction both in health and disease.

Survival signaling in the preimplantation embryo

The autopoietic development of the preimplantation embryo may in part be explained by the actions of autocrine tropic ligands. The net effect of these mediators is to support the survival of cells within the early embryo. In the mouse, the actions of autocrine ligands are required by the 2-cell stage of development, and they can act in concert with paracrine mediators present within the reproductive tract. These mediators act via 1-o-phosphatidylinositol-3-kinase signaling which has the dual effects of activating calcium/calmodulin-dependent kinase/CREB transcription factor and AKT (protein kinase B)/MDM2 mediated survival pathways. The activated CREB drives transcription of prosurvival effectors, including the proto-oncogenes c-Fos and Bcl2. The AKT induces the phosphorylation and activation of MDM2 which causes the ubiquitination and resultant degradation of P53 resulting in the latency of P53 action. Tropic signals provide coordinated mechanisms for maintaining the survival of the cells of the early embryo. Disturbance of survival signaling has the net effect of reducing the number of cells populating the early embryo, due in part to the P53-mediated reduction in the pluripotent inner cell mass stem cell population within the embryo. The resultant embryos have a markedly reduced capacity for development beyond the implantation stage and those that do implant tend to be anembryonic.

Identification of apolipoprotein A1 in the human embryonic secretome

OBJECTIVE

To identify factors secreted by the human embryo and correlate levels with embryo morphology and pregnancy outcome.

DESIGN

A laboratory-based study of human embryo protein synthesis and secretion and a retrospective analysis of spent embryo culture media as it relates to pregnancy outcome.

SETTING

University-based academic IVF program.

PATIENT(S)

IVF patients who had donated cryopreserved human pronuclear-stage embryos. Patients undergoing fresh IVF cycles resulting in a blastocyst transfer who donated spent media drops.

INTERVENTION(S)

In vitro embryo culture and collection of spent media.

MAIN OUTCOME MEASURE(S)

Protein analysis and identification by two-dimensional gel electrophoresis and mass spectrometry, ApoA1 quantification by ELISA, and mRNA analysis by quantitative reverse transcriptase-polymerase chain reaction.

RESULT(S)

By protein gel electrophoresis, apolipoprotein A1 (ApoA1) was increased in the culture media from good-quality blastocysts (n = 6 embryos) compared to either cleavage-arrested embryos (n = 6 embryos) or poor-quality blastocysts (n = 6 embryos) using spent media from culture days 4 and 5, respectively. Apolipoprotein A1 concentrations were 23.1% greater in day 5 spent culture media from good-grade blastocysts (n = 30) when compared to poor-grade embryos (n = 30). However, in a group of patients (n = 20) with transfer of two good-quality blastocysts, ApoA1 levels from day 5 spent media did not correlate with embryo implantation and pregnancy. Quantitative reverse transcriptase-polymerase chain reaction confirmed the presence of ApoA1 mRNA transcripts in human blastocysts.

CONCLUSION(S)

Apolipoprotein A1 is produced by human preimplantation embryos, and increased levels are present in spent culture media containing blastocysts of higher morphologic grade. These results suggest a role for lipoproteins in early embryologic development.

Differential gene expression between the porcine morula and blastocyst

The survival and development of pre-implantation embryos are determinant factors affecting the outcome of animal reproduction. It is essential to transfer the expression of the genetic material from maternal sources, that is the ovum to the zygote before implantation to ensure successful development. Differentiation and transformation of blastomeres initiated during the morula and blastocyst stages is an important step of the embryonic development prior to implantation. We collected morula and early blastocyst samples from pure-bred Landrace pigs in vivo to study the differential gene expression patterns at these two stages. Total RNA was extracted from individual embryos and two rounds of amplification were employed. Two micrograms of antisense RNA, targets, were prepared and hybridized with each of four custom made oligo microarrays representing 24,000 porcine genes. The analyses of replicate hybridizations showed that among the 24,000 genes, 162 genes were expressed fivefold or greater in the morula compared to early blastocysts and 2126 genes were expressed fivefold or greater in early blastocysts compared to the morula. Of these differentially expressed genes, 1429 genes were functionally annotated with related human Gene Ontology terms. In addition to basic metabolic processes, genes related to signal transduction, transportation and cell differentiation were found in both stages and were up-regulated as embryo development proceeded. Real time polymerase chain reaction was utilized to quantify 12 genes differentially expressed in the 2 embryonic stages and validated the reliability of major evidences shown in microarrays. In conclusion, we have obtained a preliminary landscape of genes differentially expressed during the transition from morula to early blastocysts in pigs and showed a generally increased transcriptional activity, perhaps in preparation for implantation. Our results provide an opportunity to study the functions of these genes in relation to the development and survival of pre-implantation porcine embryos.

Regulation of the expression of proto-oncogenes by autocrine embryotropins in the early mouse embryo

Autocrine embryotropins act as survival signals for the preimplantation embryo. In this study we examined the role of Paf in the transcription of the key proto-oncogenes Bcl2 and Fos. Transcripts were detected in oocytes and some cohorts of zygotes but not in cohorts of 2-cell, 8-cell, and blastocyst stage embryos. Immunolocalization of BCL2 and FOS showed little staining in oocytes and zygotes but increased staining in the embryo from the 2-cell to blastocyst stage. Paf (37 nM) treatment of 2-cell embryos caused an alpha-amanitin (26 μM)-sensitive increase in Bcl2 and Fos transcripts 20 min after treatment that subsided by 40 min. This increase was blocked by inhibition of calcium (by BAPTA-AM) or phosphatidylinositol-3-kinase signaling (by LY294002). Paf challenge also caused increased staining of BCL2 and FOS. Increased staining of FOS required new protein synthesis that had a half-life of 2-4 h after Paf challenge. Only a small proportion (∼12%) of individual 2-cell embryos collected from the reproductive tract had detectable Bcl2 and Fos. This dichotomous pattern of transcript expression is consistent with the known periodic actions of Paf (which has a periodicity of ∼90 min) and the relatively short half-life of the resulting transcripts. A BCL2 antagonist (HA14-1) caused a dose-dependent decrease in the capacity of cultured zygotes to develop to morphological blastocysts, which was partially reversed by the simultaneous addition of Paf to medium. The results show that Paf induces periodic transient transcriptions of key proto-oncogenes that result in the persistent presence of the resulting proteins in the preimplantation phase of development.

Characterization of a diverse secretome generated by the mouse preimplantation embryo in vitro

This study investigates the suitability of surface-enhanced laser desorption and ionization time-of-flight (SELDI-TOF) and electrospray ionization (ESI) mass spectrometry for analysis of the proteins released by the mouse preimplantation embryo in vitro. SELDI-TOF analysis with CM10 or IMAC30 (but not Q10) protein chips detected a protein peak at m/z approximately 8570 released by both C57BL6 and hybrid embryos. No other peaks unique to the presence of the embryo were identified with this method. ESI mass spectrometry of tryptic digests of embryo-conditioned media identified a total of 20 proteins released during development from the zygote to blastocyst stage. Four proteins were expressed in at least 7 out of 8 cultures tested, one of these (lactate dehydrogenase B) was in all cultures. A further five proteins were in at least half of the cultures and 11 more proteins were in at least one culture. The expression of two of these proteins is essential for preimplantation embryo development (NLR family, pyrin domain containing 5 and peptidyl arginine deiminase, type VI). A further four proteins detected have roles in redox regulation of cells, and three others are capable of inducing post-translational modifications of proteins. This study shows the feasibility of ESI mass spectrometry for identifying the proteins secreted by the preimplantation embryo in vitro. This analysis identifies a range of targets that now require detailed functional analysis to assess whether their release by the embryo is an important property of early embryo development.

Embryo Culture Media, Culture Techniques and Embryo Selection: A Tribute to Wesley Kingston Whitten

This review article gives a brief history of the classical experiments that led to the development of the embryo culture medium and in vitro embryo culture. It proposes that, in view of the outstanding and significant pioneering contributions of Wesley Kingston Whitten to the development of embryo culture medium, he be considered the “Father of Embryo Culture Medium”. Furthermore, it describes the nutritional requirements of early embryos and how these requirements with specific references to carbohydrates, amino acids, phosphates, growth factors, etc, have been utilized to formulate increasingly more complex embryo culture media. This has led to the development of progressively more efficacious embryo culture media including the formulation of completely defined and synthetic protein-free embryo culture medium. The review also describes physical factors, growth factors, insemination methods for the fertilization of oocytes and culture methods affecting embryo growth, development, metabolism, oxygen embryotoxicity and survival. In procedural terms, the review also summarizes the evolution of embryo culture techniques from tube culture to, microdrop culture under oil to co-culture to ultra microdrop culture techniques. It includes techniques of in vitro maturation and for the selection of potentially viable embryos of various developmental stages.

The presence and activation of two essential transcription factors (cAMP response element-binding protein and cAMP-dependent transcription factor ATF1) in the two-cell mouse embryo

The expression of two members of an important family of transcription factors, cAMP response element-binding protein (CREB) and cAMP-dependent transcription factor ATF1 (ATF1), is essential for normal preimplantation development. There is a high degree of functional similarity between these two transcription factors, and they can both homodimerize and heterodimerize with each other to form active transcription factors. CREB is present in all stages of mouse preimplantation embryo, and we show here that ATF1 is localized to the nucleus in all preimplantation stages. Activation of these transcription factors requires their phosphorylation, and this was only observed to occur for both transcription factors (serine 133 phosphorylation of CREB and serine 63 phosphorylation of ATF1) at the two-cell stage. Nuclear localization and phosphorylation of ATF1 were constitutive. The nuclear localization and phosphorylation of CREB showed a constitutive component that was further induced by the autocrine embryotropin Paf (1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine). Activation of CREB by Paf was independent of cAMP but was dependent on calcium, calmodulin, and calmodulin-dependent kinase activity. ATF1 nuclear localization was unaffected by inhibition of the calcium/calmodulin pathway. A complex pattern of expression of calmodulin-dependent kinases was observed throughout preimplantation development. At the two-cell stage, only mRNAs coding for calmodulin-dependent protein kinase kinase beta, calmodulin-dependent protein kinase II gamma, and calmodulin-dependent protein kinase IV were detected. A selective antagonist for calmodulin-dependent protein kinase kinase (STO-609) and calmodulin-dependent protein kinases I, II, and IV (KN-62) blocked the Paf-induced phosphorylation of CREB. The study demonstrates a role for trophic signaling and constitutive activation of two essential transcription factors at the time of zygotic genome activation.

The role of proteomics in defining the human embryonic secretome

Non-invasive gamete and embryo assessment is considered an important focus in assisted reproductive technologies (ART). Currently, the selection of embryos for transfer is based on morphological indices. Though successful, the field of ART would benefit from a non-invasive quantitative method of viability determination. Omics technologies, including transcriptomics, proteomics and metabolomics, have already begun providing evidence that viable gametes and embryos possess unique molecular profiles with potential biomarkers that can be utilized for developmental and/or viability selection. Unlike the human genome that is relatively fixed and steady throughout the human body, the human proteome, estimated at over a million proteins, is more complex, diverse and dynamic. It is the proteins themselves that contribute to the physiological homeostasis in any cell or tissue. Of particular interest in ART is the secretome, those proteins that are produced within the embryo and secreted into the surrounding environment. Defining the human embryonic secretome has the potential to expand our knowledge of embryonic cellular processes, including the complex dialogue between the developing embryo and its maternal environment, and may also assist in identifying those embryos with the highest implantation potential. Advances in proteomic technologies have allowed the non-invasive profiling of the human embryonic secretome with ongoing research focused on correlation with outcome. From a clinical perspective, embryo selection based on morphological assessment and non-invasive analysis of the human embryonic secretome may improve IVF success and lead to routine single embryo transfers.