Oocyte and zygote zona pellucida permeability to macromolecules

Unlocking a Decade of Research on Embryo-Derived Extracellular Vesicles: Discoveries Made and Paths Ahead

Over the past decade, research on embryo-derived extracellular vesicles (EVs) has unveiled their critical roles in embryonic development and intercellular communication. EVs secreted by embryos are nanoscale lipid bilayer vesicles that carry bioactive cargo, including proteins, lipids, RNAs, and DNAs, reflecting the physiological state of the source cells. These vesicles facilitate paracrine and autocrine signaling, influencing key processes such as cell differentiation, embryo viability, and endometrial receptivity. Studies reveal that EVs can traverse the zona pellucida, transferring molecular signals that enhance blastocyst formation and support embryo-maternal crosstalk. EVs have emerged as non-invasive biomarkers for embryo quality, with their cargo providing insights into genetic integrity and developmental competence. Advances in isolation and characterization techniques have identified specific microRNA (miRNAs) and transcription factors within EVs, offering potential for use in preimplantation genetic screening (PGS) and sex determination. Moreover, EV-mediated interactions with the maternal environment are critical for successful implantation, as they modulate gene expression and immune responses in endometrial and oviductal cells. Despite these advancements, challenges persist, including the standardization of EV isolation methods and the low yield of EVs DNA from spent culture media. Future research should aim to refine analytical techniques, explore EV-miRNA profiling, and investigate the mechanisms underlying EV-mediated signaling. By addressing these gaps, EVs could revolutionize embryo selection and reproductive technologies, offering new strategies to improve outcomes in assisted reproduction and animal breeding.

Application of amphiregulin in IVM culture of immature human oocytes and pre-insemination culture for COCs in IVF cycles

Background

Amphiregulin (AR) is a growth factor that resembles the epidermal growth factor (EGF) and serves various functions in different cells. However, no systematic studies or reports on the role of AR in human oocytes have currently been performed or reported. This study aimed to explore the role of AR in human immature oocytes during in vitro maturation (IVM) and in vitro fertilization (IVF) in achieving better embryonic development and to provide a basis for the development of a pre-insemination culture medium specific for cumulus oocyte complexes (COCs).

Methods

First, we examined the concentration of AR in the follicular fluid (FF) of patients who underwent routine IVF and explored the correlation between AR levels and oocyte maturation and subsequent embryonic development. Second, AR was added to the IVM medium to culture immature oocytes and investigate whether AR could improve the effects of IVM. Finally, we pioneered the use of a fertilization medium supplemented with AR for the pre-insemination culture of COCs to explore whether the involvement of AR can promote the maturation and fertilization of IVF oocytes, as well as subsequent embryonic development.

Results

A total of 609 FF samples were examined, and a positive correlation between AR levels and blastocyst formation was observed. In our IVM study, the development potential and IVM rate of immature oocytes, as well as the fertilization rate of IVM oocytes in the AR-added groups, were ameliorated significantly compared to the control group (All P < 0.05). Only the IVM-50 group had a significantly higher blastocyst formation rate than the control group (P < 0.05). In the final IVF study, the maturation, fertilization, high-quality embryo, blastocyst formation, and high-quality blastocyst rates of the AR-added group were significantly higher than those of the control group (All P < 0.05).

Conclusion

AR levels in the FF positively correlated with blastocyst formation, and AR involvement in pre-insemination cultures of COCs can effectively improve laboratory outcomes in IVF. Furthermore, AR can directly promote the in vitro maturation and developmental potential of human immature oocytes at an optimal concentration of 50 ng/ml.

Translocation of Oocytic HES1 into Surrounding Cumulus Cells in Bovine: Mechanism of Cellular Interaction during IVM?

HES1 (hairy and enhancer of split-1, effector of the NOTCH pathway) plays a role in oocyte maturation and has been detected so far mainly in somatic follicular cells. In this study, we aimed to investigate whether HES1 is present in both compartments of bovine cumulus oocyte complexes (COCs) and whether in vitro maturation itself has an effect on its distribution. We investigated the abundance of HES1 mRNA and protein in bovine COCs characterized by Brilliant-Cresyl-Blue (BCB) stainability by RT-PCR and immunofluorescence before and after in vitro maturation (IVM). To study the interaction of the compartments and the possible translocation of HES1, we injected GFP-HES1 mRNA into oocytes before maturation and analyzed fluorescence recovery after photobleaching (FRAP). The results showed that HES1 mRNA was detectable in oocytes but not in cumulus cells. The number of transcripts increased with maturation, especially in BCB-positive oocytes. In contrast, the protein was mainly visible in cumulus cells both before and after maturation. After GFP-HES1-mRNA injection into oocytes, a signal could be detected not only in the oocytes but also in cumulus cells. Our result shows a nearly exclusive distribution of HES1 mRNA and protein in oocytes and cumulus cells, respectively, that might be explained by the transfer of the protein from the oocyte into cumulus cells.

Effects of the timing of electroporation during in vitro maturation on triple gene editing in porcine embryos using CRISPR/Cas9 system

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Mosaicism is a serious problem for genome editing during embryogenesis.

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We hypothesized that genome-editing before in vitro fertilization can increase its efficiency.

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We introduced CRISPR/Cas9 system into oocytes during in vitro maturation using electroporation.

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Gene editing efficiency in matured oocytes was comparable with that in fertilized zygotes.

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Matured oocytes are suggested as functional material accepting gene editing application.

Mosaicism, including alleles comprising both wild-type and mutant, is a serious problem for gene modification by gene editing using electroporation. One-step generation of F0 pigs with completely desired gene modifications saves cost and time, but the major obstacles have been mosaic mutations. We hypothesized that the timing of electroporation prior to in vitro fertilization (IVF) can increase the rates of biallelic mutation for multiple gene knockout as the permeability of mature oocytes is greater than that of zygotes. Hence, we determined whether the timing of electroporation during in vitro maturation (IVM) culture enhances triple gene editing in the resulting blastocysts. Three gRNAs targeting KDR, PDX1, and SALL1 were simultaneously introduced into the oocytes that had been incubated for 40, 42, and 44 h from the start of the IVM culture. Electroporation with three gRNAs at 40 h and 42 h during IVM culture decreased the blastocyst formation rates and did not improve the mutation rates and target number of biallelic mutations in the resulting blastocysts. The blastocyst formation rate, mutation rates, and target numbers in the resulting blastocysts from oocytes treated by electroporation at 44 h of IVM culture were similar to those of control zygotes electroporated at 13 h after the initiation of IVF. In conclusion, multiple gene editing efficiency in the resulting blastocysts was comparable between oocytes electroporated before and after the fertilization, indicating that oocytes with completed maturation time may allow better functioning of materials accepting gene editing application.

Organelle targeting using a fluorescent probe that selectively penetrates the zona pellucida

The characteristics of oocytes, which are female germ cells, have not been studied using optical materials. The structural layers (zona pellucida, ZP) around oocytes make it difficult to deliver drugs aimed at treating infertility. Here, we investigated whether the fluorescent probes sulforhodamine, fluorescein 5(6)-isothiocyanate, tetramethylrhodamine isothiocyanate, cyanine 3 carboxylic acid, and cyanine 5 carboxylic acid penetrate oocytes. By targeting the ZP layer of the oocyte, the characteristics of the model drug, a fluorescent probe, were analyzed, and the position of the probe in the oocyte was confirmed for differences in the characteristics. Penetration of the ZP and delivery into the cytoplasm differed between the fluorescent probes. This was due to their different physiochemical properties, including hydrophobicity (contact angle and surface tension), surfactant activity, and electrical charge. Among the fluorescent probes delivered to cytoplasm, unlike TRITC, Cy3 and Cy5 perturbed oocyte development. These results suggest that in oocytes with high physical barriers (cell membrane, zona pellucida), the delivery efficiency can be estimated by considering the properties (molecular weight and structure, solubility and functional structure, etc.) of the drug. In addition, it suggests that an encapsulated or bound carrier of a drug with properties similar to that of a fluorescent probe can be efficiently delivered into oocytes.

Preimplantation Genetic Testing for Monogenic Conditions: Is Cell-Free DNA Testing the Next Step?

Genetic assessment of an embryo via preimplantation genetic testing (PGT) represents an important reproductive option for couples wanting to try and improve success rates from in vitro fertilisation (IVF) cycles, as well as reduce their risk of having a child born with a genetic condition. Currently, biopsy of the developing embryo prior to transfer allows genetic assessment of an embryo for either chromosome copy number (aneuploidy [PGT-A] or segmental rearrangement [PGT-SR]) or to avoid the transmission of a single gene condition (monogenic conditions [PGT-M]). However, this technology is invasive and commands considerable resources. Non-invasive PGT (niPGT) offers a potential alternate mode of embryonic analysis. Whilst the utility of niPGT-A has been recently explored, there has been limited consideration of niPGT-M as an option for couples at risk of passing on a single gene or chromosomal condition. This review examines the historical and current clinical context of preimplantation embryonic analysis for monogenic conditions, in addition to important considerations surrounding the origin and analysis of cell-free deoxyribose nucleic acid (cfDNA), whether it is sourced via blastocentesis or spent embryonic culture medium (SCM). Future capabilities of this testing modality will almost certainly be enhanced by integration of whole genome sequencing into everyday practice. In addition, the increased utilisation of reproductive carrier screening as part of standard reproductive healthcare will likely result in the identification of a larger high-risk population. As a result, stratification of limited and highly specialised reproductive genetic resources will be required. Prospective parents should continue to be made aware of the limitations of this technology, with prenatal confirmatory testing remaining an essential part of antenatal care in these patients. However, niPGT-M poses an important alternate testing modality for high-risk couples, particularly in the setting of embryos that cannot be biopsied for traditional PGT-M and as demand for this treatment continues to grow.

Clinical efficacy of hyaluronate-containing embryo transfer medium in IVF/ICSI treatment cycles: a cohort study

STUDY QUESTION

Does the duration of embryo exposure to hyaluronic acid (HA) enriched medium improve the rate of live birth events (LBEs)?

SUMMARY ANSWER

The use of embryo transfer (ET) medium rich in HA improves LBE (a singleton or twin live birth) regardless of the duration of exposure evaluated in this study, but does not alter gestation or birthweight (BW).

WHAT IS KNOWN ALREADY

HA-enriched medium is routinely used for ET in ART to facilitate implantation, despite inconclusive evidence on safety and efficacy.

STUDY DESIGN SIZE DURATION

A cohort study was performed evaluating clinical treatment outcomes before and after HA-enriched ET medium was introduced into routine clinical practice. In total, 3391 fresh ET procedures were performed using low HA and HA-rich medium in women undergoing publicly funded IVF/ICSI treatment cycles between May 2011 and April 2015 were included in this cohort study.

PARTICIPANTS/MATERIALS SETTING METHODS

A total of 1018 ET performed using low HA medium were compared with 1198, and 1175 ET following exposure to HA-rich medium for 2-4 h (long HA exposure) or for 10-30 min (short HA exposure), respectively. A multiple logistic regression analysis was used to compare clinical outcomes including BW, gestational age and sex ratios between groups, whilst adjusting for patient age, previous attempt, incubator type and the number of embryos transferred.

MAIN RESULTS AND THE ROLE OF CHANCE

The use of HA-rich medium for ET was positively and significantly associated with improved clinical pregnancy rate and LBE, for both exposure durations: long HA (odds ratio (OR) = 1.21, 95% CI: 0.99-1.48), short HA (OR = 1.32, 95% CI: 1.02-1.72) and pooled OR = 1.26, 95% CI: 1.03-1.54, relative to the use of low HA medium. A comparative analysis of the risks of early pregnancy loss following long HA exposure (OR = 0.76, 95% CI: 0.54-1.06), short HA exposure (OR = 0.84, 95% CI: 0.54-1.30) and late miscarriage (OR = 0.88, 95% CI: 0.51-1.53) (OR = 1.41, 95% CI 0.72-2.77), were lower and not statistically significant. Similarly, ordinary regression analysis of the differences in BW at both HA exposures; pooled OR = -0.9 (-117.1 to 115.3), and adjusted BW between both HA cohorts; pooled OR = -13.8 (-106.1 to 78.6) did not show any differences. However, a difference in gestational age (pooled OR -0.3 (-3.4 to 2.9)) and sex ratio (pooled OR 1.43 (0.95-2.15)) were observed but these were not statistically significant relative to low HA medium.

LIMITATIONS REASONS FOR CAUTION

The strength of a randomized treatment allocation was not available in this evaluation study, therefore effects of unmeasured or unknown confounding variables cannot be ruled out.

WIDER IMPLICATIONS OF THE FINDINGS

The result of this large cohort study strengthens the case for using HA-rich medium routinely at transfer, while adding the important clinical information that duration of exposure may not be critical. The composition and effects of commercial IVF culture media on success rate and safety remains a major controversy despite increasing calls for transparency and evidence-based practice in ART. Nonetheless, the lack of differences in BW and gestational age observed in this study were reassuring. However, an appraisal of clinical outcomes and appropriate research investigations are required for the continuous evaluation of efficacy and safety of HA.

STUDY FUNDING/COMPETING INTERESTS

T.A. is funded by a Clinical Doctoral Research Fellowship (CDRF) grant (reference: ICA-CDRF-2015-01-068) from the National Institute for Health Research (NIHR). The views expressed in this publication are those of the authors and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health. The authors declare no conflict of interest.

Non-invasive preimplantation genetic testing (niPGT): the next revolution in reproductive genetics?

BACKGROUND

Preimplantation genetic testing (PGT) encompasses methods that allow embryos to be tested for severe inherited conditions or for chromosome abnormalities, relevant to embryo health and viability. In order to obtain embryonic genetic material for analysis, a biopsy is required, involving the removal of one or more cells. This invasive procedure greatly increases the costs of PGT and there have been concerns that embryo viability could be compromised in some cases. The recent discovery of DNA within the blastocoele fluid (BF) of blastocysts and in spent embryo culture media (SCM) has led to interest in the development of non-invasive methods of PGT (niPGT).

OBJECTIVE AND RATIONALE

This review evaluates the current scientific evidence regarding non-invasive genetic assessment of preimplantation embryos. The success of different PGT methodologies in collecting and analysing extra-embryonic DNA is evaluated, and consideration is given to the potential biological and technical hindrances to obtaining a reliable clinical diagnosis.

SEARCH METHODS

Original research and review papers concerning niPGT were sourced by searching PubMed and Google Scholar databases until July 2019. Searches comprised the keywords: 'non-invasive'; 'cell-free DNA'; 'blastocentesis'; 'blastocoel fluid'; 'spent culture media'; 'embryo culture medium'; 'preimplantation genetic testing'; 'preimplantation genetic diagnosis'; 'preimplantation genetic screening'; and 'aneuploidy'.

OUTCOMES

Embryonic DNA is frequently detectable in BF and SCM of embryos produced during IVF treatment. Initial studies have achieved some success when performing cytogenetic and molecular genetic analysis. However, in many cases, the efficiency has been restricted by technical complications associated with the low quantity and quality of the DNA. Reported levels of ploidy agreement between SCM/BF samples and biopsied embryonic cells vary widely. In some cases, a discrepancy with respect to cytogenetic data obtained after trophectoderm biopsy may be attributable to embryonic mosaicism or DNA contamination (usually of maternal origin). Some research indicates that aneuploid cells are preferentially eliminated from the embryo, suggesting that their DNA might be over-represented in SCM and BF samples; this hypothesis requires further investigation.

WIDER IMPLICATIONS

Available data suggest that BF and SCM samples frequently provide DNA templates suitable for genetic analyses, offering a potential means of PGT that is less expensive than traditional methods, requires less micromanipulation skill and poses a lower risk to embryos. Critically, DNA isolation and amplification protocols must be optimised to reproducibly obtain an accurate clinical diagnosis, whilst minimising the impact of confounding factors such as contamination. Further investigations are required to understand the mechanisms underlying the release of embryonic DNA and to determine the extent to which this material reflects the true genetic status of the corresponding embryo. Currently, the clinic al potential of niPGT remains unknown.

Identification of 56 Proteins Involved in Embryo-Maternal Interactions in the Bovine Oviduct

The bovine embryo develops in contact with the oviductal fluid (OF) during the first 4–5 days of pregnancy. The aim of this study was to decipher the protein interactions occurring between the developing embryo and surrounding OF. In-vitro produced 4–6 cell and morula embryos were incubated or not (controls) in post-ovulatory OF (OF-treated embryos) and proteins were then analyzed and quantified by high resolution mass spectrometry (MS) in both embryo groups and in OF. A comparative analysis of MS data allowed the identification and quantification of 56 embryo-interacting proteins originated from the OF, including oviductin (OVGP1) and several annexins (ANXA1, ANXA2, ANXA4) as the most abundant ones. Some embryo-interacting proteins were developmental stage-specific, showing a modulating role of the embryo in protein interactions. Three interacting proteins (OVGP1, ANXA1 and PYGL) were immunolocalized in the perivitelline space and in blastomeres, showing that OF proteins were able to cross the zona pellucida and be taken up by the embryo. Interacting proteins were involved in a wide range of functions, among which metabolism and cellular processes were predominant. This study identified for the first time a high number of oviductal embryo-interacting proteins, paving the way for further targeted studies of proteins potentially involved in the establishment of pregnancy in cattle.

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.

Genome mutation after introduction of the gene editing by electroporation of Cas9 protein (GEEP) system in matured oocytes and putative zygotes

The application of CRISPR/Cas9 strategy promises to rapidly increase the production of genetically engineered animals since it yields stably integrated transgenes. In the present study, we investigated the efficiency of target mutations after electroporation with the CRISPR/Cas9 system using sgRNAs to target the MSTN or FGF10 genes in porcine-matured oocytes and putative zygotes. Effects of pulse number (3-7 pulse repetitions) during electroporation on the embryonic development and mutation efficiency were also investigated. Our results showed that the cleavage rate of matured oocytes with electroporation treatment significantly decreased as compared with electroporated putative zygotes (p < 0.05). Moreover, the rates of blastocyst formation from oocytes/zygotes electroporated with more than 5 pulses decreased. Mutation efficiency was then assessed after sequencing the target sites in individual blastocysts derived from oocytes/zygotes electroporated by 3 and 5 pulses. No bi-allelic mutations in all examined blastocysts were observed in this study. There were no differences in the mutation rates (50-60%) between blastocysts derived from matured oocytes electroporated by 3 and 5 pulses, irrespective of targeting gene. In the targeting MSTN gene, however, the mutation rate (12.5%) of blastocysts derived from putative zygotes electroporated by 3 pulses tended to be lower than that (60%) from 5-pulsed electroporated putative zygotes. These data indicate that the type of eggs may influence not only their development after electroporation treatment but also the mutation rate in the resulting blastocysts.

Delivery of CRISPR-Cas9 into Mouse Zygotes by Electroporation

The CRISPR-Cas9 system in bacteria and archaea has recently been exploited for genome editing in various model organisms, including the mice. In this scheme, components of the CRISPR-Cas9 system are delivered into the mouse zygote and mutant mice carrying genetic modifications derived. Although microinjection has been the technology of choice, electroporation has also emerged and been proven to be effective delivering CRISPR-Cas9 reagents into the mouse zygote. Here, we describe the experimental protocol employing electroporation to deliver CRISPR-Cas9 reagents into mouse embryos and derive gene-edited mutant mice.

THE EFFECT OF HSP60 ON FERTILIZATION AND PRE-IMPLANTATION EMBRYO DEVELOPMENT IN MICE: AN IN VITRO STUDY

Context

Heat Shock Protein 60 (HSP60) is a chaperone protein which is involved in proteins transfer and re-folding of proteins.

Objective

Importance of HSP60 in sperm capacitation and facility of sperm-oocyte membrane binding was confirmed, therefore in this study the effect of HSP60 on the rate of in vitro fertilization and the cleavage rate in mouse embryo was investigated.

Design

Ten male mice and twenty five female mice were involved to collect sperms and oocytes required for this study.

Subjects and Methods

Sperms were collected from the epididymis of male mouse and oocytes were collected from the oviduct of female mouse following ovarian hyperstimulation. Then, capacitated sperms and oocytes were placed together in fertilization medium in four groups in the presence of different concentrations of HSP60 (10, 50 and 100 ng/mL) and in the absence of HSP60. After calculation of the fertilization rate, zygotes were transformed into the other medium for development and the cleavage rate was monitored to blastocyst stage.

Results

There was not a significant difference in the rate of fertilization between 10 ng/mL HSP60 group and the control group. The rate of fertilization and two-cell embryo development decreased significantly (P≤0.05) in 100 ng/mL HSP60 compared to other experimental and control groups. Further, the rate of two-cell embryo development increased significantly (P≤0.05) in 10 ng/mL HSP60 compared to other experimental and control groups.

Conclusions

The present study demonstrated that HSP60 in low dose had a positive effect on two-cell embryo development, however it did not have any significant effect on the fertilization rate. Conversely, HSP60 had adverse effects on the fertilization and cleavage rates at higher doses.

Emerging role of extracellular vesicles in communication of preimplantation embryos in vitro

In vitro, efficient communication between mammalian embryos in groups or between embryos and cocultured somatic cells implies that there is a sender, a message and a receiver that is able to decode the message. Embryos secrete a variety of autocrine and paracrine factors and, of these, extracellular vesicles have recently been implicated as putative messengers in embryo-embryo communication, as well as in communication of the embryo with the maternal tract. Extracellular vesicles (EVs) are membrane-bound vesicles that are found in biofluids and in culture media conditioned by the presence of embryos or cells. EVs carry and transfer regulatory molecules, such as microRNAs, mRNAs, lipids and proteins. We conducted a systematic search of the literature to review and present the currently available evidence regarding the possible roles of EVs in in vitro embryo communication and embryo development. It is important to note that there is limited information available on the molecular mechanisms and many of the biologically plausible functions of EVs in embryo communication have not yet been substantiated by conclusive experimental evidence. However, indirect evidence, such as the use of media conditioned by embryos or by somatic cells with improved embryo development as a result, may indicate that EVs can be an important asset for the development of tailor-made media, allowing better embryo development in vitro, even for single embryo culture.

Association of high fetuin-B concentrations in serum with fertilization rate in IVF: a cross-sectional pilot study

STUDY QUESTION

Is serum fetuin-B associated with the fertilization rate in in vitro fertilization (IVF)?

SUMMARY ANSWER

Serum fetuin-B increased during IVF cycles when oocytes could be fertilized while remained unchanged in fertilization failure.

WHAT IS KNOWN ALREADY

Fetuin-B deficiency in mice causes premature zona pellucida hardening mediated by the zona protease ovastacin. Thus fetuin-B deficiency renders females infertile.

STUDY DESIGN, SIZE, DURATION

We determined the human serum fetuin-B reference range, studying longitudinally, over the course of one month, five male and seven female volunteers without hormone treatment and four female volunteers on varying hormonal contraception. We sampled blood and determined serum fetuin-B, luteinizing hormone (LH), estradiol (E2) and progesterone (P4). In addition, we determined serum fetuin-B and estradiol in eight women undergoing intracytoplasmatic sperm injection (ICSI, nine ICSI cycles) and 19 women undergoing IVF (21 IVF cycles) after ovarian stimulation with recombinant human follicular stimulating hormone (rFSH) and/or a combined medication of FSH and LH. At least three blood samples were analyzed in each cycle. We compared serum fetuin-B and follicular fluid fetuin-B in nine patients by measuring follicular fetuin-B in pooled follicular fluid, and in fluid obtained from individual follicles. Samples were drawn from January 2012 to March 2014.

PARTICIPANTS/MATERIALS, SETTING, METHOD

All volunteers and patients gave informed consent. Fetuin-B was measured employing a commercial sandwich enzyme-linked immunosorbent assay. Serum fetuin-B was determined as duplicates in 5 male (34 ± 14.6 years) and 11 female volunteers (29.4 ± 4.1 years) as well as in female volunteers on hormonal contraception (30.0 ± 6.5 years). The duplicate standard deviation was 4.0 ± 2.3%. The contraceptive drugs were mono or combined preparations containing 0-0.03 mg ethinyl estradiol, and 0.15-3.0 mg of various progestins. In addition, serum fetuin-B was determined as triplicates in 27 female patients undergoing conventional IVF (19) or ICSI (8). The triplicate standard deviation was 3.3 ± 1.8%. IVF was declared as 'successful', if at least one oocyte was fertilized, and 'unsuccessful', if no oocyte could be fertilized. Patient age was 34.4 ± 4.4 years in successful IVF, and 35.4 ± 3.3 years in unsuccessful IVF. Serum and follicular fluid of patients undergoing controlled ovarian hyperstimulation were analyzed. Serum was drawn at the day of follicle aspiration.

MAIN RESULTS AND THE ROLE OF CHANCE

Serum fetuin-B and follicular fluid fetuin-B were not significantly different in six out of nine patients suggesting, in principle, free exchange of fetuin-B between serum and follicular fluid. Thus serum fetuin-B may be used as a proxy of follicular fluid fetuin-B. Serum fetuin-B increased during successful IVF cycles (n = 15, P < 0.0001), but did not change in unsuccessful IVF cycles (n = 6, P = 0.118) despite increased estradiol levels (P = 0.0019 and P = 0.0254, respectively).

LIMITATIONS, REASONS FOR CAUTION

The female volunteers self-reported their respective hormone medication. Medication was verified by serum estradiol, LH and progesterone measurements. For oocyte harvesting, the vaginal wall was punctured once only to minimize co-morbidity. Low grade cross-contamination of individual follicular fluid aspirates and contamination of the follicular fluid with small amounts of blood were inevitable. Samples were routinely checked for the presence of hemoglobin that would suggest blood contamination. Only samples containing <250 erythrocyte equivalents/µl were used for analysis.

WIDER IMPLICATIONS OF THE FINDING

Serum fetuin-B may be used as a marker to predict the fertilization success in IVF. Fetuin-B levels attained during IVF stimulation may help to make an informed decision whether oocytes should be fertilized by IVF or by ICSI to overcome the zona pellucida as a barrier.

STUDY FUNDING/COMPETING INTERESTS

The research was supported by a grant from Deutsche Forschungsgemeinschaft and by the START program of the Medical Faculty of RWTH Aachen University. J.F., E.D., J.N., B.R. and W.J.-D. declare that they are named inventors on the RWTH Aachen University patent application EP 13157317.2, 'Use of fetuin-B for culture of oocytes', applied for by RWTH Aachen University.

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.

Immune Sensitization to the 60 kD Heat Shock Protein and Pregnancy Outcome

Heat shock proteins are highly conserved proteins present in organisms ranging from bacteria to man. They are both dominant microbial immunogens and among the first proteins produced during mammalian embryo development. Since bacterial and human heat shock proteins share a high degree of amino acid sequence homology, it has been suggested that sensitization to bacterial heat shock proteins during an infection may result in autoimmunity to human heat shock proteins. Infertile couples seeking in vitro fertilization (IVF) may have been previously sensitized to bacterial heat shock proteins as a consequence of an asymptomatic upper genital tract infection. Due to daily clinical monitoring and precisely timed fertilization these patients are an ideal study group to investigate the effect of prior sensitization to heat shock proteins on preimplantation embryo development and implantation failure. Immune sensitization at the level of the cervix to the 60 kD heat shock protein (hsp60) has been associated with implantation failure in some IVF patients. Similarly, the highest prevalence of circulating hsp60 antibodies among IVF patients was found in the sera of women whose embryos failed to develop in vitro. To more directly assess whether humoral immunity to hsp60 influenced in vitro embryo development, a mouse embryo culture model was established. Monoclonal antibody to mammalian hsp60 markedly impaired mouse embryo development in vitro. These data suggest that immune sensitization to human hsp60, possibly developed as a consequence of infection, may adversely affect pregnancy outcome in some patients.

Is the zona pellucida an efficient barrier to viral infection?

Although the transfer of embryos is much less likely to result in disease transmission than the transport of live animals, the sanitary risks associated with embryo transfer continue to be the subject of both scientific investigations and adaptations of national and international legislation. Therefore, the implications are important for veterinary practitioners and livestock breeders. In vivo-derived and in vitro-produced embryos are widely used in cattle and embryos from other species, such as sheep, goats, pigs and horses, are also currently being transferred in fairly significant numbers. Bearing in mind the wide variety of embryos of different species and the correspondingly large number of viruses that are of concern, it is expedient at this time to look again at the importance of the zona pellucida (ZP) as a barrier against viruses and at the susceptibility or otherwise of embryonic cells to viral infection if ever they are exposed. For embryos with an intact ZP, viral infection of the embryo is unlikely to occur. However, the virus may stick to the ZP and, in this case, International Embryo Transfer Society (IETS) washing procedures in combination with trypsin treatment are mandatory. A caveat is the fact that currently more and more types of embryos are becoming available for transfer and scientific data cannot be extrapolated from one species to another. These topics are discussed in the present review.

Amino acid carryover in the subzonal space of mouse fertilized ova affects subsequent transport kinetics

SummaryWe have investigated whether culture in glycine-containing medium affects subsequent glycine transport by the specific transport system, GLYT1, which is the sole glycine transporter in fertilized mouse ova. When fertilized ova were maintained for 6 h in culture with a physiological level of glycine (1 mM), subsequent transport of radiolabelled glycine was decreased by 40% compared with fertilized ova that had been maintained in glycine-free medium. Kinetic measurements showed that the apparent glycine affinity was decreased after culture with glycine (Km increased from 0.20 to 0.41 mM), but maximal transport rate was unchanged (similar Vmax of 20 and 23 fmol/fertilized ovum/min). These findings could have reflected activation of GLYT1 by prolonged substrate starvation, similar to some other amino acid transport systems. However, our findings were instead consistent with the alteration in glycine transport being due to trapping of glycine within the zona pellucida resulting in competitive transport inhibition even after ova were removed from glycine-containing media. First, even very brief exposures to glycine resulted in decreased subsequent glycine transport rates, with a maximal effect apparent within ~6 min. Second, extensive washing (at least six) reversed the effect. Third, the effect was absent when zona-free fertilized ova were used. Thus, it appears that components of the external environment of preimplantation embryos may continue to affect transport kinetics for a period even after embryos are removed from environments that contain them.

Heat-shock proteins modulate the incidence of apoptosis and oxidative stress in preimplantation mouse embryos

We investigated the effect of antibodies to heat-shock proteins 60 and 70 on development, reactive oxygen species production, and incidence of apoptosis in preimplantation mouse embryos. Supplementation of culture media with antibodies to heat-shock proteins 60 and 70 resulted in significantly lower blastocyst development, hatching rate, reduced total cell number, and trophectoderm cell number, and increased the incidence of apoptosis in blastocysts compared to the control group.

The effect of Vero cell coculture on the development of mouse embryos exposed to monoclonal antibodies specific for mammalian heat shock protein 60

Heat shock proteins (HSP) have been identified as an important factor of a very complex and highly conserved cellular defense mechanism to preserve cell survival under adverse environmental conditions. HSP 60 are immunodominant antigens of microbe such as Chlamydia trachomatis and have a potentiality to become a target antigen due to antigenic similarity between chlamydial and human HSP. This study was conducted to investigate the effects of Vero cell coculture to anti-HSP 60 on the early mouse embryo development in vitro. The 2-cell mouse embryos (ICR) were cultured and mouse embryo development was observed every 24 hr for 3 days. 45% and 22.1% of the embryos cultured in Ham's F-10 plus anti HSP 60 with Vero cells developed to the 4- to 8- cell stage (day 1) and morular stage (day 2) as compared with 29.2% and 2.7% of those cultured without Vero cells respectively. But at day 3, the beneficial effect of Vero cells was not noted. These findings suggest that Vero cells have some roles to overcome the detrimental effect of anti-HSP 60 to some degree. These results suggest that Vero cells coculture will promote reproductive outcome in patient previously sensitized to microbial (e.g. Chlamydia trachomatis) HSP 60.

Extra- and intracellular ice formation in mouse oocytes

The occurrence of intracellular ice formation (IIF) during freezing, or the lack there of, is the single most important factor determining whether or not cells survive cryopreservation. One important determinant of IIF is the temperature at which a supercooled cell nucleates. To avoid intracellular ice formation, the cell must be cooled slowly enough so that osmotic dehydration eliminates nearly all cell supercooling before reaching that temperature. This report is concerned with factors that determine the nucleation temperature in mouse oocytes. Chief among these is the concentration of cryoprotective additive (here, glycerol or ethylene glycol). The temperature for IIF decreases from -14 degrees C in buffered isotonic saline (PBS) to -41 degrees C in 1M glycerol/PBS and 1.5M ethylene glycol/PBS. The latter rapidly permeates the oocyte; the former does not. The initial extracellular freezing at -3.9 to -7.8 degrees C, depending on the CPA concentration, deforms the cell. In PBS that deformation often leads to IIF; in CPA it does not. The oocytes are surrounded by a zona pellucida. That structure appears to impede the growth of external ice through it, but not to block it. In most cases, IIF is characterized by an abrupt blackening or flashing during cooling. But in some cases, especially with dezonated oocytes, a pale brown veil abruptly forms during cooling followed by slower blackening during warming. Above -30 degrees C, flashing occurs in a fraction of a second. Below -30 degrees C, it commonly occurs much more slowly. We have observed instances where flashing is accompanied by the abrupt ejection of cytoplasm. During freezing, cells lie in unfrozen channels between the growing external ice. From phase diagram data, we have computed the fraction of water and solution that remains unfrozen at the observed flash temperatures and the concentrations of salt and CPA in those channels. The results are somewhat ambiguous as to which of these characteristics best correlates with IIF.

Archiving mouse strains by cryopreservation

A great deal of time and energy goes into the creation of each new line of transgenic mice; established lines are expensive and labor-intensive to maintain. Archiving of mice by cryopreservation of germ cells or embryos represents a means to free up facility space, while protecting the line from loss due to environmental disasters, genetic drift, or infectious disease. The author reviews the available cryopreservation techniques and presents considerations for setting up a cryopreservation facility.

Role of sperm sulfogalactosylglycerolipid in mouse sperm-zona pellucida binding

Sulfogalactosylglycerolipid (SGG) is the major sulfoglycolipid of mammalian male germ cells. Like other sulfoglycolipids, SGG is believed to be involved in cell-cell/extracellular matrix adhesion. Specifically, we investigated whether sperm SGG played a role in sperm-egg interaction. Initially, we produced an affinity-purified, rabbit polyclonal immunoglobulin (Ig) G antibody that specifically recognized SGG (anti-SGG). Indirect immunofluorescence using anti-SGG IgG localized SGG to the convex and concave ridges and the postacrosome of the mouse sperm head. Pretreatment of sperm with anti-SGG IgG/Fab inhibited sperm-zona pellucida (ZP) binding in vitro in a concentration-dependent manner (to a maximum of 62%). This inhibition was observed at the level of primary binding. Sperm treated with anti-SGG IgG underwent the spontaneous and ZP-induced acrosome reaction at the same rate as control sperm treated with preimmune rabbit serum IgG. Fluorescently labeled SGG liposomes were shown to associate specifically with the egg ZP, whereas fluorescently labeled liposomes of galactosylglycerolipid (SGG's parental lipid) and phosphatidylserine (negatively charged like SGG) did not. Furthermore, coincubation of SGG liposomes with sperm and isolated ZP inhibited sperm-ZP binding in a concentration-dependent manner. These results strongly suggest an involvement of sperm SGG in direct binding to the ZP.

Structural aspects of the zona pellucida of in vitro-produced bovine embryos: a scanning electron and confocal laser scanning microscopic study

Structural aspects of the bovine zona pellucida (ZP) of in vitro-matured (IVM) oocytes and in vitro-produced (IVP) embryos were studied in two experiments to find a tentative explanation for the zona's barrier function against viral infection. In Experiment 1, the ultrastructure of the outer ZP surface was studied. The diameter (nm) and the number of the outer pores within an area of 5000 microm(2) of 10 IVM oocytes, 10 zygotes, 10 8-cell-stage embryos, and 10 morulae were evaluated by scanning electron microscopy. In oocytes and morulae, the ZP surface showed a rough and spongy appearance with numerous pores. In zygotes, the ZP surface was found to have a smooth, melted appearance with only a few pores. In 8-cell-stage embryos, both surface patterns were found. The mean number (per 5000 microm(2)) and the mean diameter of the outer pores were different between the four stages of development (P < 0.001): 1511 pores in oocytes, 1187 in zygotes, 1658 in 8-cell-stage embryos, and 3259 in morulae, with mean diameters of 182, 223, 203, and 155 nm, respectively. In Experiment 2, the continuity of the meshes (network of pores) towards the embryonic cells was examined by confocal laser scanning microscopy. Therefore, the passage through and the location in the ZP of fluorescent microspheres, with similar dimensions as bovine viral diarrhea virus (BVDV, 40-50 nm) and bovine herpesvirus-1 (BHV-1; 180-200 nm), were evaluated. For all stages, the smallest beads were detected halfway through the thickness of the ZP, whereas the beads with a size of 200 nm were found only within the outer-fourth part of the ZP. It can be concluded that the intact ZP of bovine IVM oocytes and IVP embryos are constructed in such a way that BVDV and BHV-1 should not be able to traverse the ZP and reach the embryonic cells. However, the risk exists that viral particles can be trapped in the outer layers of the ZP.

Receptor-mediated transport of foreign DNA into preimplantation mammalian embryos

Mouse and rabbit preimplantation embryos with intact zona pellucida were incubated for 3 hr with DNA-carrying constructs containing insulin as an internalizable ligand: (insulin-polylysine)-DNA and (insulin-polylysine)-DNA-(streptavidin-polylysine)-(biotinylated adenovirus). Video-intensified microscopy demonstrated that the constructs penetrated the zona pellucida and accumulated in the blastomere perinuclear space. The percentage of blastocysts formed was about 70% after incubation of zygotes and two-cell embryos with the constructs. Foreign DNA was detected after 51 hr in 80% of rabbit embryos and after 96 hr in 73% of mouse embryos. Inclusion of various adenoviruses into the construct improved foreign DNA preservation in early embryos. Blot hybridization revealed genome-integrated foreign DNA in 12- and 15-day mouse embryos and in a newborn. Thus, the ligand-mediated mechanism can be employed for introducing foreign genetic material into early mammalian embryos; insulin provides for delivery inside the cell and to the nucleus, while adenoviruses ensure release from endosomes.

Characterization of antibodies generated against a conserved portion of oviductal glycoprotein (OGP) and endogenous hamster OGP and their ability to decrease sperm binding to the zona pellucida in vitro

PROBLEM

The effect of antibodies generated against hamster oviductal glycoprotein (OGP) on sperm binding to the zona pellucida (ZP) was evaluated.

METHOD OF STUDY

Antibodies against a 17-amino-acid sequence of the OGP core protein (amino acids 52-68) and the denatured hamster OGP protein were generated, characterized, and tested in an in vitro sperm binding assay.

RESULTS

Sperm binding was significantly decreased (P < 0.05) when oviductal oocytes were incubated for 2 hr with 4 or 8 mg/ml of immune IgG of both antibodies when compared with normal rabbit IgG. A fluorescence assay showed binding of both antibodies to the endogenous OGP associated with the ZP of ovulated hamster oocytes.

CONCLUSIONS

These results suggest that OGP may be a potential immunocontraceptive target because both antibodies significantly decreased sperm binding to the ZP of oviductal oocytes. Immunocontraception may be accomplished by attempting to generate active immunity to a recombinant OGP, to the region selected in this study (amino acids 52-68) or to some other region of the core protein.

Mammalian oocyte growth and development in vitro

This paper is a review of the current status of technology for mammalian oocyte growth and development in vitro. It compares and contrasts the characteristics of the various culture systems that have been devised for the culture of either isolated preantral follicles or the oocyte-granulosa cell complexes form preantral follicles. The advantages and disadvantages of these various systems are discussed. Endpoints for the evaluation of oocyte development in vitro, including oocyte maturation and embryogenesis, are described. Considerations for the improvement of the culture systems are also presented. These include discussions of the possible effects of apoptosis and inappropriate differentiation of oocyte-associated granulosa cells on oocyte development. Finally, the potential applications of the technology for oocyte growth and development in vitro are discussed. For example, studies of oocyte development in vitro could help to identify specific molecules produced during oocyte development that are essential for normal early embryogenesis and perhaps recognize defects leading to infertility or abnormalities in embryonic development. Moreover, the culture systems may provide the methods necessary to enlarge the populations of valuable agricultural, pharmaceutical product-producing, and endangered animals, and to rescue the oocytes of women about to undergo clinical procedures that place oocytes at risk.

Changes in glycoconjugate-lectin binding characteristics of in vitro and in vivo mouse blastocysts

OBJECTIVE

To investigate the influence of embryo culture, on blastocysts cultured from the zygote stage, on blastocyst cell surface glycoconjugates as an indicator of cellular metabolism.

METHOD

Eleven fluorescein isothiocyanate (FITC)-labelled lectins, which recognize different oligosaccharide structures, were applied to zona pellucida intact and zona pellucida free blastocysts which had developed either in vivo or in vitro. The differential binding patterns for the zona pellucida, trophectoderm and inner cell mass were determined using fluorescence microscopy.

RESULTS

With the exception of wheat germ agglutinin (WGA) and Limax flavus agglutinin (LFA) the remaining nine lectins bound less intensely to the zona pellucida of the in vitro blastocysts compared with the in vivo blastocysts. The trophectoderm from both groups bound seven lectins with equal intensity, of the remaining four Lotus tetragonolbus agglutinin (LTA), Bandeiraea simplicifolia 4 (BSB4), Phaseolus vulgaris agglutinin P (PHA-P) and Limulus polyphemus agglutinin (LPA) demonstrated differential binding. The inner cell mass from the two blastocyst groups bound only three lectins identically, peanut agglutinin (PNA), Bandeiraea simplicifolia 4 (BSB4) and Dolichos biflorus agglutinin (DBA).

CONCLUSION

Oviductal glycoproteins contribute to the zona pellucida glycoprotein content during early development, however embryo culture from the zygote stage may not provide adequate substrates for normal inner cell mass glycoconjugate biosynthesis.