What Criteria for the Definition of Oocyte Quality?

Biochemical profiling of the follicular environment to predict oocyte competence in cattle

To identify markers of oocyte competence, we compared the biochemical characteristics of fluid and cells from follicles containing oocytes with different capacities to form an embryo. Follicles (5-6 mm) were dissected, and follicular fluid (FF), granulosa cells (GC), cumulus cells (CC) from immature and mature cumulus-oocyte-complexes (COC) were individually collected. The oocytes were matured, fertilized, and cultured individually until day 8 (D8) of development. On D8, the samples were grouped according to embryo production into those that gave rise to blastocysts (EMB) and those that did not reach the blastocyst stage (NEMB). In CCs from immature and mature COCs and GCs, expression of CASP3, SERPINE2, VCAN, LUM, FSHR, EGFR, PGR, and GHR genes was quantified. Cell-free DNA (cfDNA), progesterone, and estradiol concentrations in the FF were determined. Data were analyzed by Mann-Whitney U test (GraphPad Prism 9). GHR was highly expressed in immature CCs from the EMB group, whereas CASP3 was highly expressed in mature CCs from the NEMB group (P<0.05). During maturation, the expression of CASP3 and GHR genes increased only in the NEMB group. ART2 cfDNA was highly detected in FF of the NEMB compared to the EMB group. Progesterone concentration was similar between the groups, whereas estradiol concentration was higher (P<0.05) in the EMB than in the NEMB group. It was concluded that a higher level of GHR transcripts in immature CCs, lower CASP3 expression in CCs from matured COCs, lower levels of ART2, and higher estradiol concentrations in FF may indicate oocytes with greater potential for development.

Efficient automated error detection in medical data using deep-learning and label-clustering

Medical datasets inherently contain errors from subjective or inaccurate test results, or from confounding biological complexities. It is difficult for medical experts to detect these elusive errors manually, due to lack of contextual information, limiting data privacy regulations, and the sheer scale of data to be reviewed. Current methods for training robust artificial intelligence (AI) models on data containing mislabeled examples generally fall into one of several categories-attempting to improve the robustness of the model architecture, the regularization techniques used, the loss function used during training, or selecting a subset of data that contains cleaner labels. This last category requires the ability to efficiently detect errors either prior to or during training, either relabeling them or removing them completely. More recent progress in error detection has focused on using multi-network learning to minimize deleterious effects of errors on training, however, using many neural networks to reach a consensus on which data should be removed can be computationally intensive and inefficient. In this work, a deep-learning based algorithm was used in conjunction with a label-clustering approach to automate error detection. For dataset with synthetic label flips added, these errors were identified with an accuracy of up to 85%, while requiring up to 93% less computing resources to complete compared to a previous model consensus approach developed previously. The resulting trained AI models exhibited greater training stability and up to a 45% improvement in accuracy, from 69 to over 99% compared to the consensus approach, at least 10% improvement on using noise-robust loss functions in a binary classification problem, and a 51% improvement for multi-class classification. These results indicate that practical, automated a priori detection of errors in medical data is possible, without human oversight.

The anti-infective crotalicidin peptide analog RhoB-Ctn[1-9] is harmless to bovine oocytes and able to induce parthenogenesis in vitro

Crotalicidin is a cathelicidin-related anti-infective (antimicrobial) peptide expressed in the venom glands of the South American rattlesnake Crotalus durissus terrificus. Congener peptides of crotalicidin, named vipericidins, are found in other pit vipers inhabiting South America. Crotalicidin is active against bacteria and pathogenic yeasts and has anti-proliferative activity for some cancer cells. The structural dissection of crotalicidin produced fragments (e.g., Ctn [15-34]) with multiple biological functionalities that mimic the native peptide. Another structural characteristic of crotalidicin and congeners is a unique repetitive stretch of amino acid sequences in tandem embedded in their primary structures. One of the encrypted vipericidn peptides (Ctn [1-9]) was synthesized, and the analog covalently conjugated with rhodamine B (RhoB-Ctn [1-9]) displayed considerable antimicrobial activity and selective cytotoxicity. Methods to evaluate antimicrobial peptides' toxicity include lysis of red blood cells (hemolysis) in vitro and cytotoxicity of healthy cultured cells (e.g., fibroblasts). Here, as a non-conventional model of toxicity, the bovine oocytes were exposed to two standardized concentrations of RhoB-Ctn [1-9], and embryo viability and development at its first stage of cleavage (division of cells) and blastocyst formation were evaluated. Oocytes treated with peptide at 10 and 40 μM induced cleavage rates of 44.94% and 51.53%, resulting in the formation of blastocysts of 7.07% and 11.73%, respectively. Light sheet microscopy and in silico prediction analysis indicated that RhoB-Ctn [1-9] peptide interacts with zona pellucida and internalizes into bovine oocytes and developing embryos. The ADMET prediction estimated good bioavailability of RhoB-Ctn [1-9]. In conclusion, the peptide appeared harmless to bovine oocytes and, remarkably, activated the parthenogenesis in vitro.

Preservation of Fertility in Cancer Patients: A Narrative Review

The survival rates for cancer patients have been steadily improving in recent years due to the improved efficacy of contemporary oncological care, including radiotherapy and chemotherapy. Modern technology makes it feasible to maintain fertility in cancer patients, and this practice needs to be included in oncological care. In many instances, it is impossible to avoid the harm that cancer treatments can cause to a patient's fertility; hence, research in fertility preservation techniques is being conducted to allow cancer patients to have future children biologically related to them. The development of fertility preservation approaches has grown in importance in the field of research over the past few years to increase patient's quality of life and survival. Oncologists must be aware of circumstances in which cancer patients' fertility will be impacted by their therapy and the avenues open for procedures like cryopreservation of the gametes or embryos. When cancer therapy is scheduled, all patients should receive prompt and thorough information on the fertility-related side effects of treatment and the prospects for fertility preservation. The article analyzes the literature, enlisting the factors that contribute to cancer and their effects on fertility, followed by a list of available and newly developed strategies for maintaining fertility in patients. The efficiency of the various fertility preservation techniques following cancer therapy is also discussed.

A Role of PI3K/Akt Signaling in Oocyte Maturation and Early Embryo Development

A serine/threonine-specific protein kinase B (PKB), also known as Akt, is a key factor in the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway that regulates cell survival, metabolism and proliferation. Akt phosphorylates many downstream specific substrates, which subsequently control the nuclear envelope breakdown (NEBD), centrosome maturation, spindle assembly, chromosome segregation, and cytokinesis. In vertebrates, Akt is also an important player during oogenesis and preimplantation development. In the signaling pathways regulating mRNA translation, Akt is involved in the control of mammalian target of rapamycin complex 1 (mTORC1) and thereby regulates the activity of a translational repressor, the eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1). In this review, we summarize the functions of Akt in mitosis, meiosis and early embryonic development. Additionally, the role of Akt in the regulation of mRNA translation is addressed with respect to the significance of this process during early development.

Oocyte quality evaluation: a review of engineering approaches toward clinical challenges

Although assisted reproductive technology has been very successful for the treatment of infertility, its steps are still dependent on direct human opinion. An important step of assisted reproductive treatments in lab for women is choosing an oocyte that has a better quality. This step would predict which oocyte has developmental competence leading to healthy baby. Observation of the oocyte morphological quality indicators under microscope by an embryologist is the most common evaluation method of oocyte quality. Such subjective method which relies on embryologist's experience may vary and leads to misdiagnosis. An alternative solution to eliminate human misjudging in traditional methods and overcome the limitations of them is always using engineering-based procedure. In this review article, we deeply study and categorize engineering-based methods applied for the evaluation of oocyte quality. Then, the challenges in laboratories and clinics settings move forward with translational medicine perspective in mind for all those methods which had been studied were discussed. Finally, a standardized process was presented, which may help improving and focusing the research in this field. Moreover, effective suggestion techniques were introduced that are expected they would be complementary methods to accelerate future researches. The aim of this review was to create a new prospect with the engineering approaches to evaluate oocyte quality and we hope this would help infertile couples to get a baby.

Multidrug resistance transporter-1 dysfunction perturbs meiosis and Ca2+ homeostasis in oocytes

In brief

Oocyte quality remains the most important and unsolved issue in reproduction. Our data show that multidrug resistance transporters and oocyte mitochondria are involved in determining oocyte quality in a mouse model.

Abstract

Multidrug resistance transporter-1 (MDR-1) is a transmembrane ATP-dependent effluxer present in organs that transport a variety of xenobiotics and by-products. Previous findings by our group demonstrated that this transporter is also present in the oocyte mitochondrial membrane and that its mutation led to abnormal mitochondrial homeostasis. Considering the importance of these organelles in the female gamete, we assessed the impact of MDR-1 dysfunction on mouse oocyte quality, with a particular focus on the meiotic spindle organization, aneuploidies, Ca2+ homeostasis, ATP production and mtDNA mutations. Our results demonstrate that young Mdr1a mutant mice produce oocytes characterized by lower quality, with a significant delay in the germinal vesicle to germinal vesicle breakdown transition, an increased percentage of symmetric divisions, chromosome misalignments and a severely altered meiotic spindle shape compared to the wild types. Mutant oocytes exhibit 7000 more SNPs in the exomic DNA and twice the amount of mitochondrial DNA (mtDNA) SNPs compared to the wild-type ones. Ca2+ analysis revealed the inability of MDR-1 mutant oocytes to manage Ca2+ storage content and oscillations in response to several stimuli, and ATP quantification shows that mutant oocytes trend toward lower ATP levels compared to wild types. Finally, 1-year-old mutant ovaries express a lower amount of SIRT1, SIRT3, SIRT5, SIRT6 and SIRT7 compared to wild-type levels. These results together emphasize the importance of MDR-1 in mitochondrial physiology and highlight the influence of MDR-1 on oocyte quality and ovarian aging.

Profiling of mitochondrial heteroplasmy in single human oocytes by next-generation sequencing

Mitochondrial DNA (mtDNA) plays a crucial role in the development of a competent oocyte. Indeed, mtDNA alterations may predispose to chromosome nondisjunction, resulting in infertility due to a reduced vitality and quality of oocytes and embryos. In this methods paper, the multiple displacement amplification approach was applied in combination with next-generation sequencing (NGS) to amplify and sequence, in single-end, the entire mtDNA of single human oocytes to directly construct genomic NGS libraries, and subsequently, to highlight and quantify the mutations they presented. The bioinformatic workflow was carried out with a specific ad hoc developed in-house software. This approach proved to be sensitive and specific, also highlighting the mutations present in heteroplasmy, showing deletion, insertion or substitution mutations in the genes involved in the respiratory chain, even if the found variants were benign or of uncertain meaning. The analysis of mtDNA mutations in the oocyte could provide a better understanding of specific genetic abnormalities and of their possible effect on oocyte developmental competence. This study shows how this approach, based on a massive parallel sequencing of clonally amplified DNA molecules, allows to sequence the entire mitochondrial genome of single oocytes in a short time and with a single analytical run and to verify mtDNA mutations.

Gestational Benzo[a]pyrene Exposure Destroys F1 Ovarian Germ Cells Through Mitochondrial Apoptosis Pathway and Diminishes Surviving Oocyte Quality

Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are products of incomplete combustion. In female mouse embryos primordial germ cells proliferate before and after arriving at the gonadal ridge around embryonic (E) 10 and begin entering meiosis at E13.5. Now oocytes, they arrest in the first meiotic prophase beginning at E17.5. We previously reported dose-dependent depletion of ovarian follicles in female mice exposed to 2 or 10 mg/kg-day BaP E6.5-15.5. We hypothesized that embryonic ovaries are more sensitive to gestational BaP exposure during the mitotic developmental window, and that this exposure results in persistent oxidative stress in ovaries and oocytes of exposed F1 female offspring. We orally dosed timed-pregnant female mice with 0 or 2 mg/kg-day BaP in oil from E6.5-11.5 (mitotic window) or E12.5-17.5 (meiotic window). Cultured E13.5 ovaries were utilized to investigate the mechanism of BaP-induced germ cell death. We observed statistically significant follicle depletion and increased ovarian lipid peroxidation in F1 pubertal ovaries following BaP exposure during either prenatal window. Culture of E13.5 ovaries with BaP induced germ cell DNA damage and release of cytochrome c from the mitochondria in oocytes, confirming that BaP exposure induced apoptosis via the mitochondrial pathway. Mitochondrial membrane potential, oocyte lipid droplet (LD) volume, and mitochondrial-LD colocalization were decreased and mitochondrial superoxide levels were increased in the MII oocytes of F1 females exposed gestationally to BaP. Results demonstrate similar sensitivity to germ cell depletion and persistent oxidative stress in F1 ovaries and oocytes following gestational BaP exposure during mitotic or meiotic windows.

Optical imaging detects metabolic signatures associated with oocyte quality

Oocyte developmental potential is intimately linked to metabolism. Existing approaches to measure metabolism in the cumulus oocyte complex (COC) do not provide information on the separate cumulus and oocyte compartments. Development of an assay that achieves this may lead to an accurate diagnostic for oocyte quality. Optical imaging of the autofluorescent cofactors NAD(P)H and FAD provides a spatially resolved indicator of metabolism via the optical redox ratio ($\mathrm{FAD}/\left[\mathrm{NAD}\left(\mathrm{P}\right)\mathrm{H}+\mathrm{FAD}\right]$). This may provide an assessment of oocyte quality. Here, we determined whether the optical redox ratio is a robust methodology for measuring metabolism in the cumulus and oocyte compartments compared with oxygen consumption in the whole COC. We also determined whether optical imaging could detect metabolic differences associated with poor oocyte quality (etomoxir-treated). We used confocal microscopy to measure NAD(P)H and FAD, and extracellular flux to measure oxygen consumption. We found that the optical redox ratio was an accurate reflection of metabolism in the oocyte compartment when compared with oxygen consumption (whole COC). Etomoxir-treated COCs showed significantly lower levels of NAD(P)H and FAD compared to control. While confocal imaging demonstrated the premise, we validated this approach using hyperspectral imaging, which is clinically compatible due to its low energy dose. This confirmed lower NAD(P)H and FAD in etomoxir-treated COCs. When comparing imaged vs non-imaged COCs, subsequent preimplantation development and post-transfer viability were comparable. Collectively, these results demonstrate that label-free optical imaging of metabolic cofactors is a safe and sensitive assay for measuring metabolism and has potential to assess oocyte developmental competence.

Comparing the IVM laboratory outcomes between stimulated IVF with unstimulated natural cycles

Recently, more attention has been raised towards fertility preservation in women with cancer. One option is in vitro maturation (IVM) of the immature oocytes as there is not enough time for induction of an ovarian stimulation protocol. The aim was to compare the IVM laboratory outcomes between stimulated and unstimulated (natural) in vitro fertilization (IVF) cycles. In total, 234 immature oocytes collected from 15 cancer patients who underwent an IVM programme (natural IVM) and 23 IVF cycles with a controlled ovarian hyperstimulation protocol (stimulated IVM) were analyzed. The oocyte morphology, zona pellucida (ZP), and meiotic spindle presence were measured using PolScope technology. Also, the rates of oocyte maturation and fertilization were assessed in both groups. The IVM rate was higher in the stimulated cycle (P < 0.05), but the fertilization rate was insignificant in comparison with unstimulated cycles. There were no significant differences in the spindle visualization and ZP birefringence scoring between the groups (P > 0.05). The oocyte normal morphology was better in the stimulated cycle compared with the natural cycle (P < 0.05). In conclusion, IVM can be recommended for cancer patients as an alternative treatment when there is insufficient time for conventional IVF before chemotherapy initiation.

Tea polyphenols alleviate the adverse effects of diabetes on oocyte quality

Maternal diabetes mellitus reduces oocyte quality, such as abnormalities of spindle assembly and chromosome segregation, mitochondrial dysfunction, decrease of fertilization rate, increase of ROS, and so on. So, it is important to research how to restore the decreased oocyte quality induced by maternal diabetes mellitus. Polyphenols are the most abundant bioactive components of green tea. It is reported that tea polyphenols have many health functions, for instance anti-oxidation, anti-inflammation, anti-obesity, and anti-diabetes. Thus, we hypothesize that tea polyphenols may play a crucial role in alleviating adverse effects of diabetes on oocyte quality. In the present study, we researched the effects of tea polyphenols on diabetic oocyte maturation in vitro. Compared with the control, oocytes from diabetic mice displayed a lower maturation rate and a higher frequency of spindle defects and chromosome misalignment. However, tea polyphenols significantly increased the oocyte maturation rate, and reduced the incidence of abnormal spindle assembly and chromosome segregation. Tea polyphenols also obviously decreased the reactive oxygen species (ROS) levels in diabetic oocytes, and increased the expression of antioxidant genes (Sod1 and Sod2). Abnormal mitochondrial membrane potential was also alleviated in diabetic oocytes, and the expression of genes regulating mitochondrial fusion (Opa1, Mfn1 and Mfn2) and fission (Drp1) was significantly increased while tea polyphenols were added. Meanwhile, tea polyphenols reduced DNA damage in diabetic oocytes which may be mediated by the increased expression of Rad51, related to DNA damage repair. Our results suggest that tea polyphenols would, at least partially, restore the adverse effects of diabetes mellitus on oocyte quality.

Revisiting ZAR proteins: the understudied regulator of female fertility and beyond

Putative RNA-binding proteins (RBPs), zygote arrested-1 (ZAR1), and ZAR2 (also known as ZAR1L), have been identified as maternal factors that mainly function in oogenesis and embryogenesis. Despite divergence in their spatio-temporal expression among species, the CxxC structure of the C-terminus of ZAR proteins is highly conserved and is reported to be the functional domain for the activity of the RBPs of ZAR proteins. In oocytes from Xenopus laevis and zebrafish, ZAR proteins have been reported to bind to maternal transcripts and inhibit translation in immature growing oocytes, whereas in fully grown mouse oocytes, they promote the translation during meiotic maturation. Thus, ZAR1 and ZAR2 may be required for the maternal-to-zygotic transition by stabilizing the maternal transcriptome in oocytes with partial functional redundancy. In addition, recent studies have suggested non-ovarian expression and function of ZAR proteins, particularly their involvement in tumorigenesis. ZAR proteins are potentially associated with tumor suppressors and can serve as epigenetically inactivated cancer biomarkers. In this review, studies on Zar1/2 are systematically summarized, and some issues that require discussion and further investigation are introduced as perspectives.

Preserving Oocytes in Oncofertility†

The prodigious rise of cancer survival rates enables many cancer survivors to live long lives. Therefore, the side effects of cancer treatments as well as the long-term quality of life after cancer have become more relevant. Ovarian toxicity is a major off-target effect of anticancer agents for childhood and young adult female cancer patients. Both chemotherapy and irradiation have been demonstrated to damage the ovary and increase the risks of premature ovarian failure (POF), early menopause, ovarian endocrine disorders, and sub- or infertility. Oncofertility is an emerging and multidisciplinary research and medical field that focuses on providing cancer patients with fertility preservation options. Oocyte quality and quantity are one of the most important factors to determine women's fertility success; therefore, preserving oocytes is paramount for maintaining the ability of young female cancer patients' reproduction after their recovery. This review summarizes peer-reviewed literature on current oocyte preservation options in oncofertility. We describe in-depth oocyte and embryo cryopreservation, ovarian suppression, ovarian tissue cryopreservation, in vitro maturation, ovarian transposition, and adjuvant therapy. Further, we discuss current guidelines and practices of female fertility preservation that cover preserving oocytes.

Oocyte Morphometric Assessment and Gene Expression Profiling of Oocytes and Cumulus Cells as Biomarkers of Oocyte Competence in Sheep

Oocyte quality is crucial for subsequent embryo development and so it is a major challenge in assisted reproductive technologies. The aim of the present work was to evaluate the morphometric parameters of oocytes (experiment 1) and the relative gene expression of oocytes and cumulus cells (CCs) (experiment 2) as biomarkers of oocyte quality after individually culturing them (one oocyte or embryo/drop). In experiment 1, individually matured oocytes were measured and classified into small, intermediate, and large oocytes after a cluster analysis, based on total diameter (with zona pellucida, ZP), oocyte diameter (without ZP), and ZP thickness. These oocytes were individually fertilized in vitro and cultured. The embryo development was evaluated up to the blastocyst stage. According to the total diameter, oocyte diameter, and ZP thickness, the blastocyst rate decreased in the small oocytes group (3.1 ± 3.1, 14.1 ± 9.4, and 26.7 ± 3.9, respectively) compared to the intermediate (29.4 ± 5.2, 30.5 ± 10.1, and 28.6 ± 9.6, respectively) and large oocytes groups (54.2 ± 13.5, 44.4 ± 3.9, and 67.6 ± 12.4, respectively). In addition, the probability of reaching the blastocyst stage was positively related to the total diameter (p < 0.001), oocyte diameter (p < 0.05), and ZP thickness (p < 0.001). Furthermore, the relative gene expression of BAX, BCL2, GDF9, and GJA1 was lower in oocytes classified as large. In experiment 2, the mRNA transcript relative abundance pattern of genes in CCs was evaluated according to oocyte total diameter and developmental stage reached. CCs from oocytes classified as large and oocytes capable of developing to the blastocyst stage had a lower relative expression of BAX, STAR, and PTGS2, while a higher expression of HAS2 and SDC2 transcript was observed for those oocytes. In conclusion, oocyte morphometric parameters and gene expression analysis in oocytes and CCs provide methods for the identification of the most competent oocytes for assisted reproductive technologies in sheep.

Probing morphological, genetic and metabolomic changes of in vitro embryo development in a microfluidic device

Assisted reproduction technologies for clinical and research purposes rely on a brief in vitro embryo culture which, despite decades of progress, remain suboptimal in comparison to the physiological environment. One promising tool to improve this technique is the development of bespoke microfluidic chambers. Here we present and validate a new microfluidic device in polydimethylsiloxane (PDMS) for the culture of early mouse embryos. Device material and design resulted embryo compatible and elicit minimal stress. Blastocyst formation, hatching, attachment and outgrowth formation on fibronectin-coated devices were similar to traditional microdrop methods. Total blastocyst cell number and allocation to the trophectoderm and inner cell mass lineages were unaffected. The devices were designed for culture of 10-12 embryos. Development rates, mitochondrial polarization and metabolic turnover of key energy substrates glucose, pyruvate and lactate were consistent with groups of 10 embryos in microdrop controls. Increasing group size to 40 embryos per device was associated with increased variation in development rates and altered metabolism. Device culture did not perturb blastocyst gene expression but did elicit changes in embryo metabolome, which can be ascribed to substrate leaching from PDMS and warrant further investigation.

The methylome of a human polar body reflects that of its sibling oocyte and its aberrance may indicate poor embryo development

STUDY QUESTION

Is it possible to evaluate the methylome of individual oocytes to investigate the DNA methylome alterations in metaphase II (MII) oocytes with reduced embryo developmental potential?

SUMMARY ANSWER

The DNA methylome of each human first polar body (PB1) closely mirrored that of its sibling MII oocyte; hypermethylated long interspersed nuclear element (LINE) and long terminal repeats (LTRs) and methylation aberrations in PB1 promoter regions may indicate poor embryo development.

WHAT IS KNOWN ALREADY

The developmental potential of an embryo is determined by the oocyte's developmental competence, and the PB1 is a good substitute to examine the chromosomal status of the corresponding oocyte. However, DNA methylation, a key epigenetic modification, also regulates gene expression and embryo development.

STUDY DESIGN, SIZE, DURATION

Twelve pairs of PB1s and sibling MII oocytes were biopsied and sequenced to compare their methylomes. To further investigate the methylome of PB1s and the potential epigenetic factors that may affect oocyte quality, MII oocytes (n = 74) were fertilized through ICSI, while PB1s were biopsied and profiled to measure DNA methylation. The corresponding embryos were further cultured to track their development potential. The oocytes and sperm samples used in this study were donated by healthy volunteers with signed informed consent.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single-cell methylome sequencing was applied to obtain the DNA methylation profiles of PB1s and oocytes. The DNA methylome of PB1s was compared between the respective group of oocytes that progressed to blastocysts and the group of oocytes that failed to develop. DNA methylation levels of corresponding regions and differentially methylated regions were calculated using customized Perl and R scripts. RNA-seq data were downloaded from a previously published paper and reanalysed.

MAIN RESULTS AND THE ROLE OF CHANCE

The results from PB1-MII oocyte pair validated that PB1 contains nearly the same methylome (average Pearson correlation is 0.92) with sibling MII oocyte. LINE and LTR expression increased markedly after fertilization. Moreover, the DNA methylation levels in LINE (including LINE1 and LINE2) and LTR were significantly higher in the PB1s of embryos that could not reach the blastocyst stage (Wilcoxon-Matt-Whitney test, P < 0.05). DNA methylation in PB1 promoters correlated negatively with gene expression of MII oocyte. Regarding the methylation status of the promoter regions, 66 genes were hypermethylated in the developmental arrested group, with their related functions (significantly enriched in several Gene Ontology terms) including transcription, positive regulation of adenylate cyclase activity, mitogen-activated protein kinase (MAPK) cascade and intracellular oestrogen receptor signalling pathway.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Data analysis performed in this study focused on the competence of human oocytes and compared them with maternal genetic and epigenetic profiles. Therefore, data regarding the potential regulatory roles of paternal genomes in embryo development are lacking.

WIDER IMPLICATIONS OF THE FINDINGS

The results from PB1-oocyte pairs demonstrated that PB1s shared similar methylomes with their sibling oocytes. The selection of the good embryos for transfer should not only rely on morphology but also consider the DNA methylation of the corresponding PB1 and therefore MII oocyte. The application of early-stage analysis of PB1 offers an option for high-quality oocyte and embryo selection, which provides an additional tool for elective single embryo transfer in assisted reproduction.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key Research and Development Program of China (2018YFC1004003, 2017YFA0103801), the National Natural Science Foundation of China (81730038, 3187144, 81521002) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16020703). The authors have no conflicts of interest to declare.

Characterization of porcine oocytes stained with Lissamine Green B and their developmental potential in vitro

Traditional methods for the evaluation of oocyte quality are based on morphological classification of the follicle, cumulus-oocyte complex, polar body and meiotic spindle. This study is focused on the differences between the morphological assessment of oocyte quality, the assessment based on Lissamine Green B (LB) staining and the analysis of oocytes using a proteomic approach. We evaluated the effectiveness of electrochemical and chemical parthenogenetic activation under our laboratory conditions and evaluated the applicability of Lissamine Green B staining of cumulus-oocyte complexes (COCs) as a non-invasive method for predicting the maturational and developmental competence of porcine oocytes cultured in vitro. We determined that chemical parthenogenetic activation using ionomycin and 6-dimethylaminopurine was slightly more effective than electrochemical activation. After oocyte selection according to LB staining, we found significant differences (P<0.05) between the LB- group and LB+ group and the control group in their maturation, cleavage rate and rate of blastocysts. Proteomic analyses identified a selection of proteins that were differentially expressed in each group of analysed oocytes. Oocytes of the LB- group exhibited an increased variability of proteins involved in transcription regulation, proteosynthesis and the protein folding crucial for oocyte maturation and further embryonic development. These results found a better competence of LB- oocytes in maturation, cleavage and ability to reach the blastocyst stage.

Oocyte Selection for In Vitro Embryo Production in Bovine Species: Noninvasive Approaches for New Challenges of Oocyte Competence

Simple Summary

The efficiency of producing embryos using in vitro technologies in cattle species remains lower when compared to mice, indicating that the proportion of female gametes that fail to develop after in vitro manipulation is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting embryo production, the precise identification of noninvasive markers that predict oocyte competence is of major interest. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, a large slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better embryonic development. In addition, the combination of oocyte and zygote selection, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in vitro technologies in livestock species.

Abstract

The efficiency of producing embryos using in vitro technologies in livestock species rarely exceeds the 30–40% threshold, indicating that the proportion of oocytes that fail to develop after in vitro fertilization and culture is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting blastocyst yield, the precise identification of noninvasive cellular or molecular markers that predict oocyte competence is of major interest to research and practical applications. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, large number of surrounding cumulus cells, slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better competence. In addition, the combination of oocyte and zygote selection via brilliant cresyl blue (BCB) test, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in-vitro-derived technologies in livestock species.

Assessing the impact of semen quality on embryo development in an egg donation model

Objective

To investigate if any of the World Health Organization semen parameters and/or male age are associated with embryo development.

Design

Retrospective chart review between January 2008 and May 2015.

Setting

Academic fertility practice.

Patients

Anonymous egg donors aged ≤30 years.

Interventions

Chart review.

Main Outcome Measures

Sperm parameters were evaluated on a continuum and were dichotomized to determine if low values (strict morphology < 4%, concentration < 15 × 10⁶, low motility < 40%) or older age (>50 years) are associated with embryo morphology. Repeated linear regression measures to determine the associations and multivariate testing to determine independent effects for each predictor were performed.

Results

Three hundred eighty-four donors with 574 egg donation cycles were identified, and 205 subjects with 275 cycles were included in the final analysis. The mean donor age was 25.31 ± 2.81 years, with a mean antral follicle count of 28.09 ± 10.5. The mean male age was 43.25 ± 6.65 years. The mean World Health Organization semen parameters at fertilization were 55.8 × 10⁶ ± 44.3 × 10⁶/mL concentration, 44.8% ± 20.2% motility, and 6.9% ± 5.3% strict morphology. Neither male age nor sperm morphology was associated with embryo morphology. A low total motile count was significantly associated with a higher cell number in day-3 embryos and a 1.56-times higher chance of poor day-3 cell symmetry. There was no statistically significant difference in blastocyst formation, clinical pregnancy, or live-birth rates.

Conclusions

Although statistically significant, the effect of the low total motile count on day-3 cell number and cell symmetry are likely clinically insignificant. Male age, race, or poor sperm morphology were not associated with a poor cycle outcome or impaired embryo development. The use of intracytoplasmic sperm injection likely alleviates the negative effect of diminished semen quality on treatment outcome.

Maternal C-reactive protein and in vitro fertilization (IVF) cycles

Embryo implantation is accompanied by a potent inflammatory response, and a gradient of cytokines and chemokines produced by endometrial cells supports the embryo-endometrial interaction. C-reactive protein (CRP) serves as an early marker of inflammation and recent studies have illustrated that controlled ovarian hyperstimulation (COH) could increase its levels. Interestingly, a high chance of pregnancy has been reported in women who had an elevated CRP level on the day of embryo transfer. It seems an elevated systemic inflammation in the in vitro fertilization (IVF) cycle can increase the implantation and pregnancy rates. However, the results regarding the association of CRP with ART outcomes are controversial. Therefore, in this review, we aimed to describe how CRP levels change during a cycle of IVF treatment and which factors can potentially affect this pattern of change. Furthermore, the association of CRP with ART outcomes has been discussed.

In Vitro Maturation of Fully Grown Mouse Antral Follicles in the Presence of 1 nM 2-Hydroxyestradiol Improves Oocytes' Developmental Competence

Cathecolestrogens are estradiol metabolites produced during folliculogenesis in the mammalian ovary. 2-Hydroxyestradiol (2-OHE₂) is one of the most abundant although its role remains unknown. The aim of this study is to investigate whether the presence of 2-OHE₂ during the germinal vesicle-to-metaphase II transition affects oocyte meiotic and preimplantation developmental competence. Mouse cumulus-oocyte complexes (COCs), isolated from fully grown antral follicles, were in vitro–matured (IVM) in the presence of 2-OHE₂ (0.1, 1, 10 or 100 nM) for 6 or 15 h; then, their meiotic and developmental competence was evaluated using a number of cytological quality markers. With the exception of the highest dose (100 nM), the addition of 2-OHE₂ to the IVM medium, did not alter, compared with untreated control, the frequency of oocytes that reached the MII stage. Instead, IVM in the presence of 1 nM 2-OHE₂ highly increased the rate of preimplantation development and blastocyst quality. To understand whether this positive effect could be attributed to the events occurring during meiosis resumption, we analysed a number of specific cytological quality markers of the asymmetric division, such as PB-I volume and position, presence and extension of the cortical F-actin cap, meiotic spindle shape and area, and microtubule organisation centre localisation. The results highlighted how the presence of 1 nM 2-OHE₂ significantly improved the overall cytological organisation required for a correct asymmetric division. Our results contribute a first step to acknowledge a potential role of this estradiol metabolite during the GV-to-MII transition, contributing to the acquisition of oocytes developmental competence.

Absence of correlation between follicular fluid volume and follicular granulocyte colony-stimulating factor, a predictor of embryo implantation and successful delivery

Follicular granulocyte colony-stimulating factor (G-CSF) is a documented marker of embryo implantation potential. The primary objective was to determine whether follicular G-CSF levels correlate with follicular fluid volume. The secondary objectives were to assess whether follicular G-CSF is associated with oocyte maturity at the time of harvest and with delivery rate after fresh or frozen embryo transfer. Thirty-two patients undergoing intracytoplasmic sperm injection (ICSI) cycles were recruited (Centre de Procréation Médicalement Assistée (CPMA), University of Liège, Belgium). A total of 211 follicular fluid (FF) samples were individually collected at the time of oocyte harvest. FF volume was recorded, and G-CSF concentration was assessed by ELISA. The embryos were individually cultured in vitro. Their implantation and live birth rates were recorded after fresh and frozen embryo transfers. The follicular fluid volume did not correlate with the follicular G-CSF concentration. There were no differences in follicular G-CSF levels between mature and immature oocytes. The probability of successful implantation and delivery was increased for embryos with FF containing a high G-CSF concentration. There was a trend toward lower follicular G-CSF levels in cases of miscarriage. Therefore, follicular fluid volume cannot be a substitute for follicular G-CSF as a marker of embryo implantation ability.

Raman spectroscopy-based approach to study the female gamete

In the last years, an increasing interest has emerged on the development of new non-invasive methods for the assessment of oocyte quality in order to improve outcomes of assisted reproductive technologies (ARTs) either in medical or veterinary fields. Raman microspectroscopy (RMS) has been proposed as a promising tool for the examination of the mammalian female gamete and identification of markers of its developmental competence. This technique provides a unique spectral fingerprint indicative of molecular composition of the cell and allows probing subcellular compartments. Studies have been carried out analysing by RMS fixed or living oocytes derived from different animal models. RMS imaging has been successfully applied to discriminate the biochemical changes of the global molecular architecture of mouse oocytes at different stages of maturation and those occurring in different conditions of maturation and oocyte aging. RMS can also detect modifications of specific structural components, including the oocyte zona pellucida and F-actin subcortical cytoskeleton in fresh sheep oocytes and those underwent to vitrification procedures. Finally, the recent application of Coherent anti-Stokes Raman scattering (CARS) microscopy for examination of oocyte lipid component will be briefly discussed. CARS overcomes some limits of RMS providing vibrational and spectral information with higher sensitivity, spatial resolution which is ideal to study living oocytes. This review summarizes the research on RMS approaches for oocyte evaluation showing the high potential use, current limitations and new improvements.

A paracrine interaction between granulosa cells and leukocytes in the preovulatory follicle causes the increase in follicular G-CSF levels

Objective

Follicular granulocyte colony-stimulating factor (G-CSF) is a new biomarker of oocyte quality and embryo implantation in in vitro fertilization (IVF) cycles. Its role in reproduction is poorly understood. Our study aimed to investigate the mechanisms and cells responsible for G-CSF production in the preovulatory follicle.

Design

Laboratory research study.

Setting

Single-center study.

Interventions

Granulosa cells and leukocytes were isolated from the follicular fluids (FF) or the blood of women undergoing IVF and from the blood of a control group of women with spontaneous ovulatory cycles to perform cocultures.

Main outcome measure

G-CSF-secreted protein was quantified in the conditioned media of cocultures.

Results

G-CSF secretion was considerably increased in cocultures of granulosa cells and leukocytes. This effect was maximal when leukocytes were isolated from the blood of women in the late follicular phase of the menstrual cycle or from the FF of women undergoing IVF. The leukocyte population isolated from the FF samples of women undergoing IVF had a higher proportion of granulocytes than that isolated from the corresponding blood samples. Leukocytes induced the synthesis and secretion of G-CSF by granulosa cells. Among a range of other FF cytokines/chemokines, only growth-regulated oncogene alpha (GROα) was also increased.

Conclusion

The notable rise in G-CSF at the time of ovulation coincides with the accumulation of follicular granulocytes, which stimulate G-CSF production by granulosa cells via paracrine interactions. High follicular G-CSF concentrations may occur in follicles with optimal granulosa–leukocyte interactions, which could explain the increased implantation rate of embryos arising from these follicles.

Electronic supplementary material

The online version of this article (10.1007/s10815-020-01692-y) contains supplementary material, which is available to authorized users.

Oocyte meiotic spindle morphology is a predictive marker of blastocyst ploidy-a prospective cohort study

OBJECTIVE

To evaluate oocyte meiotic spindle (OMS) morphology at intracytoplasmic sperm injection (ICSI) as a predictor of blastocyst ploidy and whether OMS morphology could aid standard morphology-based blastocyst selection.

DESIGN

Prospective cohort study.

SETTING

In vitro fertilization clinic.

PATIENT(S)

Patients undergoing ICSI cycles with an intention to perform preimplantation genetic testing for aneuploidy (PGT-A) from October 2014 to December 2017.

INTERVENTION(S)

The OMS was visualized with the use of polarized light microscopy at the time of ICSI and the morphology classified as normal, dysmorphic, translucent, not visible, or in telophase. Blastocyst biopsy for PGT-A was performed on embryos with suitable development.

MAIN OUTCOME MEASURE(S)

The association of OMS morphology with the resulting blastocyst ploidy was evaluated on an "intention-to-treat" (ITT) and an "as-treated analysis" (ATA) basis.

RESULT(S)

The morphology of 2,056 OMSs were classified. A strong association of OMS morphology with fertilization, cleavage to at least 6 cells on day 3, and good/top-quality blastocyst formation was present. Normal OMS was positively associated with blastocyst euploidy compared with all other OMS types combined, per either ITT or ATA. Even after controlling for female age, blastocyst quality, and developmental stage, the presence of a normal OMS was strongly associated with the probability of blastocyst euploidy.

CONCLUSION(S)

OMS morphology is a predictive marker of blastocyst ploidy and can potentially aid standard morphology-based blastocyst selection.

Sensing Cell Membrane Biophysical Properties for Detection of High Quality Human Oocytes

Oocyte quality plays a crucial role in the early development and implantation of the embryos, and consequently has a profound impact on the accomplishment of assisted reproductive technology (ART). A simple and efficient method for detecting high-quality human oocytes is urgently needed. However, the clinically used morphological method is time-consuming, subjective, and inaccurate. To this end, we propose a practical and effective approach for detecting high-quality oocytes via on-chip measurement of the oocyte membrane permeability. We found that oocytes can be divided into two subpopulations (high-quality versus poor-quality oocytes) according to their membrane permeability differences, and as was further confirmed by subsequent in vitro fertilization (IVF) and development experiments (the blastocyst rates of high-quality and poor-quality oocytes were 60% and 0%, respectively). This approach shows great potentials in improving the success of ART, including both the fertilization and development rates, and thus it may have wide applications in the clinic.

Phosphoric acid and phosphorylation levels are potential biomarkers indicating developmental competence of matured oocytes

We identified biomarkers for mice oocyte maturation in metaphase II in vivo and in situ using Raman spectroscopy.

Detrimental effects of lipopolysaccharides on maturation of bovine oocytes

Objective

Gram-negative bacteria lipopolysaccharide (LPS) has been reported to be associated with uterine impairment, embryonic resorption, ovarian dysfunction, and follicle retardation. Here, we aimed to investigate the toxic effects of LPS on the maturation ability and parthenogenetic developmental competence of bovine oocytes.

Methods

First, we developed an in vitro model to study the response of bovine cumulus-oocyte complexes (COCs) to LPS stress. After incubating germinal vesicle COCs in 10 μg/mL of LPS, we analyzed the following three aspects: the expression levels of the LPS receptor toll-like receptor 4 (TLR4) in COCs, activities of intracellular signaling protein p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappa B (NF-κB); and the concentrations of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-6. Furthermore, we determined the effects of LPS on the maturation ability and parthenogenetic developmental competence of bovine oocytes.

Results

The results revealed that LPS treatment significantly elevated TLR4 mRNA and protein expression levels in COCs. Exposure of COCs to LPS also resulted in a marked increase in activity of the intracellular signaling protein p-p38 MAPK and NF-κB. Furthermore, oocytes cultured in maturation medium containing LPS had significantly higher concentrations of the proinflammatory cytokines IL-1β, TNF-α, and IL-6. LPS exposure significantly decreased the first polar body extrusion rate. The cytoplasmic maturation, characterized by polar body extrusion and distribution of peripheral cortical granules, was significantly impaired in LPS-treated oocytes. Moreover, LPS exposure significantly increased intracellular reactive oxygen species levels and the relative mRNA abundance of the antioxidants thioredoxin (Trx), Trx2, and peroxiredoxin 1 in oocytes. Moreover, the early apoptotic rate and the release of cytochrome C were significantly increased in response to LPS. The cleavage, morula, and blastocyst formation rates were significantly lower in parthenogenetically activated oocytes exposed to LPS, while the incidence of apoptotic nuclei in blastocysts was significantly increased.

Conclusion

Together, these results provide an underlying mechanism by which LPS impairs maturation potential in bovine oocytes.

Cumulus cells surrounding oocytes with high developmental competence exhibit down-regulation of phosphoinositol 1,3 kinase/protein kinase B (PI3K/AKT) signalling genes involved in proliferation and survival

STUDY QUESTION

Is the phosphoinositol 1,3-kinase/protein kinase B (PI3K/AKT) pathway expression profile in cumulus cells (CCs) a potential marker of oocyte competence and predictive of pregnancy outcome?

SUMMARY ANSWER

Eleven genes (AKT1, ARHGEF7, BCL2L1, CCND1, E2F1, HRAS, KCNH2, PIK3C2A, SHC1, SOS1 and SPP1) in the PI3K/AKT pathway were significantly down-regulated in CCs from oocytes that went on to produce a pregnancy compared to CCs associated with a negative outcome.

WHAT IS KNOWN ALREADY

The PI3K/AKT pathway plays a pivotal role in the interdependence and continuous feedback between the oocyte and CCs.

STUDY DESIGN SIZE, DURATION

The expression analysis of 92 transcripts in the PI3K/AKT pathway in CCs from patients with negative or positive pregnancy outcome, after single embryo transfer, was performed. Mouse CCs target gene expression was conducted to associate the expression profile of PI3K/AKT pathway to oocyte developmental profile.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Fifty-five good prognosis IVF patients who had been referred to IVF or intracytoplasmic sperm injection treatment for male-factor infertility or tubal disease were enroled. CCs from single cumulus-oocyte complexes (COCs) from 16 patients who underwent a single embryo transfer were analyzed. Twenty-five CD-1 mice were used to assess gene expression in CCs associated with oocytes with different competence in relation to hCG priming. A total 220 human COCs were collected. The RNA extracted from CCs of 16 selected patients was used to analyze PI3K/AKT pathway gene expression employing a 96-well custom TaqMan Array. Expression data of CCs associated to positive IVF outcome were compared to data from negative outcome samples. Mice were sacrificed after 9, 12, 15, 21 and 24 h post-hCG administration to obtain CCs from MII oocytes with different developmental competence. Akt1, Bcl2l2 and Shc1 expression were tested in the collected mouse CCs. In addition, the expression of upstream regulator ESR1, the gene encoding for the oestrogen receptor ERβ, and the downstream effectors of the pathway FOXO1, FOXO3 and FOXO4 was evaluated in human and mouse samples.

MAIN RESULTS AND THE ROLE OF CHANCE

Transcripts involved in the PI3K Signaling Pathway were selectively modulated according to the IVF/ICSI outcome of the oocyte. Eleven transcripts in this pathway were significantly down-regulated in all samples of CCs from oocytes with positive when compared those with a negative outcome. These outcomes were confirmed in mouse CCs associated with oocytes at different maturation stages. Expression data revealed that the down-regulation of ESR1 could be related to oocyte competence and is likely to be the driver of expression changes highlighted in the PI3K/AKT pathway.

LIMITATIONS REASONS FOR CAUTION

Small sample size and retrospective design.

WIDER IMPLICATIONS OF THE FINDINGS

The CCs expression profile of PI3K/AKT signaling genes, disclosed a specific CCs gene signature related to oocyte competence. It could be speculated that CCs associated with competent oocytes have completed their role in sustaining oocyte development and are influencing their fate in response to metabolic and hormonal changes by de-activating anti-apoptotic signals.

STUDY FUNDING/COMPETING INTEREST(S)

Supported by Merck Serono an affiliate of Merck KGaA, Darmstadt, Germany (research grant for the laboratory session; Merck KGaA reviewed the manuscript for medical accuracy only before journal submission. The authors are fully responsible for the content of this manuscript, and the views and opinions described in the publication reflect solely those of the authors). The authors declare no conflict of interest.

The influence of ovarian hyperstimulation drugs on morphometry and morphology of human oocytes in ICSI program

OBJECTIVE

To compare the influences of controlled ovarian hyperstimulation (COH) drugs using recombinant follicular stimulating hormone (rFSH) versus human menopausal gonadotropins (hMG) on morphometry and morphology of MII oocytes in ICSI cycles.

MATERIALS AND METHODS

In this prospective study, 363 MII oocytes from 50 ICSI cycles with male factor infertility were evaluated. The patients were divided into two groups according to the protocols of COH: I- rFSH and II- hMG. The immature oocytes were excluded from the study. All oocytes were categorized into four morphological groups of normal, and those with single, double, or multiple defects. The inclusive morphometrical criteria were: areas and diameters of oocyte, ooplasm, and zona pellucida (ZP). Also, circumferences of oocyte and ooplasm were assessed.

RESULTS

The ZP area and ooplasm diameter for both normal and abnormal oocytes were significantly higher in group I (P: .05; P: .028, respectively) compared to group II (P: .023; P: .003, respectively). In abnormal oocytes, ooplasm diameter was higher in group I compared to group II. Furthermore, ooplasm area for abnormal oocytes was significantly higher in group I compared to group II. There was an increasing trend for number of mature oocytes, in abnormal oocytes, for group I (5.53 ± 3.1) in comparison with group II (4.4 ± 2.97; P = .25). The rate of oocytes with normal morphology was significantly higher in hMG, when compared to rFSH groups.

CONCLUSION

Morphometrical parameters were increased in rFSH group, but the normal morphology of oocytes were significantly enhanced in hMG group. Treatment with proper dosage of ovulation induction drugs may enhance the number of normal sized oocytes.

Novel Concepts for Inducing Final Oocyte Maturation in In Vitro Fertilization Treatment

Infertility affects one in six of the population and increasingly couples require treatment with assisted reproductive techniques. In vitro fertilization (IVF) treatment is most commonly conducted using exogenous FSH to induce follicular growth and human chorionic gonadotropin (hCG) to induce final oocyte maturation. However, hCG may cause the potentially life-threatening iatrogenic complication "ovarian hyperstimulation syndrome" (OHSS), which can cause considerable morbidity and, rarely, even mortality in otherwise healthy women. The use of GnRH agonists (GnRHas) has been pioneered during the last two decades to provide a safer option to induce final oocyte maturation. More recently, the neuropeptide kisspeptin, a hypothalamic regulator of GnRH release, has been investigated as a novel inductor of oocyte maturation. The hormonal stimulus used to induce oocyte maturation has a major impact on the success (retrieval of oocytes and chance of implantation) and safety (risk of OHSS) of IVF treatment. This review aims to appraise experimental and clinical data of hormonal approaches used to induce final oocyte maturation by hCG, GnRHa, both GnRHa and hCG administered in combination, recombinant LH, or kisspeptin. We also examine evidence for the timing of administration of the inductor of final oocyte maturation in relationship to parameters of follicular growth and the subsequent interval to oocyte retrieval. In summary, we review data on the efficacy and safety of the major hormonal approaches used to induce final oocyte maturation in clinical practice, as well as some novel approaches that may offer fresh alternatives in future.

Updating the markers for oocyte quality evaluation: intracellular temperature as a new index

BACKGROUND

The developmental competence of an embryo is principally dictated by the oocyte. Usually, oocyte selection is based on morphological properties; however, all morphological criteria that are currently used for the grading and screening of oocytes are not able to eliminate the subjectivity. Despite recent studies of the molecular factors related to oocyte quality, it is technically difficult to develop an index based on these factors, and new indices that reflect intracellular conditions are necessary.

METHODS

Morphological and molecular factors influencing developmental competence were comprehensively reviewed, and intracellular temperature was evaluated as a new marker of oocyte quality.

MAIN FINDINGS

The intracellular temperature of mature oocytes was high in fresh oocytes and decreased with time after polar body release. Under the same conditions, the intracellular temperature and its distribution differed among oocytes, suggesting that temperature represents the state of each oocyte.

CONCLUSION

Intracellular temperature is advantageous as an objective and quantitative indicator of oocyte quality. Further studies should evaluate the link between temperature and cellular phenomena to establish its use as an indicator of quality.

Subclinical mastitis interferes with ovulation, oocyte and granulosa cell quality in dairy cows

The objective was to evaluate the effect of mastitis by somatic cell count (SCC) on follicular growth, ovulation, oocytes and cumulus cells quality and on the concentration and size of exosomes in follicular fluid of dairy cows. In the study, crossbred cows (Bos taurus - Holstein x Bos indicus - Gir) were classified for analysis as Control (SCC<200.000 cells/mL) and Mastitis (SCC>400.000 cells/mL) groups. In experiment 1 (follicular dynamics), cows (n = 57) were submitted to ultrasound evaluations every 24 h, from progesterone-releasing-intravaginal-device (PRID) removal (D8) until 48 h later (D10). Thereafter, evaluations were performed every 12 h, until ovulation or up to 96 h after PRID removal. In experiment 2 (oocyte, cumulus complexes, and follicular fluid evaluation), cows (n = 26) were submitted to follicular aspiration (OPU) for oocyte quality and cumulus cells transcript evaluation. The amount of cumulus complexes transcripts (BCL2, BAX, PI3K, PTEN, FOXO3) was determined by Real-Time Polymerase Chain Reaction. Moreover, seven days after the OPU session, the dominant follicle was aspirated. Exosomes were isolated from the follicular fluid for evaluation of particle size and concentration. Ovulation rate [Control 77.4% (24/31) and Mastitis 57.7% (15/26); P = 0.09] and viable oocytes rate [Control 59.1% (130/220) and Mastitis 41.9% (125/298); P = 0.01] were higher in Control animals. Additionally, there was a greater number of degenerate oocytes [Control 6.7 ± 1.2 and Mastitis 13.3 ± 5.5; (P = 0.001)] in subclinical mastitis cows. There was greater abundance (P = 0.003) of BAX cumulus cell transcripts and exosome mean (P = 0.03) and mode (P = 0.02) was smaller in subclinical mastitis cows. In conclusion, ovulation rate, oocyte quality, and exosome diameter were smaller in cows with SCC>400.000 cells/mL.

Cytoplasmic and nuclear maturation of oocytes in mammals – living in the shadow of cells developmental capability

The pig is a polyestrous animal in which the ovarian cycle lasts about 21 days and results in ovulation of 10-25 oocytes. Ovum reaches 120-150 μm in diameter, with the surrounding corona radiata providing communication with the environment. The zona pellucida is composed of glycoproteins: ZP1, ZP2, ZP3. In the course of oogenesis, RNA and protein accumulation for embryonic development occurs. Maternal mRNA is the template for protein production. Nuclear, cytoplasmic and genomic maturity condition the ability of the ovum to undergo fertilization. There are several differences in protein expression profiles observed between in vitro and in vivo conditions. Oogenesis is the process of differentiating female primary sex cells into gametes. During development gonocytes migrate from the yolk sac into the primary gonads with TGF-1, fibronectin, and laminin regulating this process. Cell cycle is blocked in dictyotene. Primary oocyte maturation is resumed before each ovulation and lasts until the next block in metaphase II. At the moment of penetration of the sperm into the ovum, the metaphase block is broken. The oocytes, surrounded by a single layer of granular cells, form the ovarian follicle. The exchange of signals between the oocyte and the cumulus cells done by gap-junctions, as well as various endo and paracrine signals. The contact between the corona radiata cells provides substances necessary for growth, through the same gap junctions. Studies on follicular cells can be used to amplify the knowledge of gene expression in these cells, in order to open way for potential clinical applications.

Inherent inferior quality of follicular fluid in repeat breeder heifers as evidenced by low rates of in vitro production of bovine embryos

The aims of the present study were to determine the effect of follicular fluid obtained from the ovulatory follicle of repeat breeder heifers on in vitro oocyte maturation (Experiment 1), fertilization (Experiment 2) and production of bovine embryos (Experiment 3). Holstein virgin heifers (VH, n = 5) with normal fertility or repeat breeder syndrome (RBH, n = 5) were used in the present study. Follicular fluid of VH and RBH was aspirated from ovulatory follicles and used as maturation medium. Bovine oocytes were aspirated from follicles of slaughterhouse ovaries and randomly allocated in three groups; in Group 1, oocytes cultured in TCM-199 supplemented with 10% heat-treated fetal calf serum and hormones (5 IU/mL hCG plus 0.1 IU/mL rFSH); in Group 2, oocytes cultured in TCM-199 supplemented with 10% filtered follicular fluid of VH without hormones; in Group 3, oocytes cultured in TCM-199 supplemented with 10% filtered follicular fluid of RBH without hormones. The mean (±SEM) percentage of matured oocytes was different between VH and RBH groups (72.2 ± 4.0 vs 56.4 ± 4.6%; P < 0.05, respectively). Further, the mean (±SEM) percentage of normal oocyte fertilization was higher in the VH than the RBH group (49.3 ± 2.1 vs 32.0 ± 4.2; P < 0.05, respectively). The mean percentage of embryos developed to the blastocyst stage was higher in the VH than the RBH group (12.0 ± 1.3 vs 7.0 ± 1.6; respectively; P < 0.05). In conclusion, our findings support our hypothesis that the ovulatory follicle microenvironment of Holstein repeat breeder heifers places their oocytes at a developmental disadvantage compared with Holstein fertile virgin heifers and that this suggest the existence of an inherent inferior quality of the ovulatory follicle microenvironment in repeat breeding Holstein heifers.

Non-invasive assessment of porcine oocyte quality by supravital staining of cumulus-oocyte complexes with lissamine green B

We evaluated the usefulness of lissamine green B (LB) staining of cumulus-oocyte complexes (COC) as a non-invasive method of predicting maturational and developmental competence of slaughterhouse-derived porcine oocytes cultured in vitro. Cumulus cells of freshly aspirated COCs were evaluated either morphologically on the basis of thickness of cumulus cell layers, or stained with LB, which penetrates only non-viable cells. The extent of cumulus cell staining was taken as an inverse indicator of membrane integrity. The two methods of COC grading were then examined as predictors of nuclear maturation and development after parthenogenetic activation. In both cases LB staining proved a more reliable indicator than morphological assessment (P < 0.05). The relationship between LB staining and cumulus cell apoptosis was also examined. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for DNA fragmentation revealed that oocytes within COCs graded as low quality by either LB staining or visual morphology showed significantly greater DNA fragmentation (P < 0.05) than higher grades, and that LB and visual grading were of similar predictive value. Expression of the stress response gene TP53 showed significantly higher expression in COCs graded as low quality by LB staining. However expression of the apoptosis-associated genes BAK and CASP3 was not significantly different between high or low grade COCs, suggesting that mRNA expression of BAK and CASP3 is not a reliable method of detecting apoptosis in porcine COCs. Evaluation of cumulus cell membrane integrity by lissamine green B staining thus provides a useful new tool to gain information about the maturational and developmental competence of porcine oocytes.

Relationship between meiotic spindles visualization and intracytoplasmic sperm injection outcomes in human oocytes

In assisted reproductive techniques, the operator attempts to select morphologically best embryos to predict embryo viability. Development of polarized light microscope, which evaluates the oocytes' spindles according to birefringence of living cells, had been helpful in oocyte selection. The aim of this study is evaluating the relationship between meiotic spindles visualization and intracytoplasmic sperm injection (ICSI) outcomes in human oocytes. In this study, 264 oocytes from 24 patients with an average age of 30.5±7.5 years with infertility duration of 1 to 10 years were collected. The oocytes were randomly allocated to the control injection group (n=126) and the oocyte imaging group (spindle-aligned group) (n=138). In the spindle-aligned group, the meiotic spindle was identified by means of polarized light microscope to align the spindle at 6 or 12 o'clock. Then the spindle-aligned group was divided into three sub-groups based on spindle morphology: fine, average, and (poor). After ICSI, embryos were checked every 24 hours and scored; 72 hours later, high-grade embryos were transferred intravaginally to uterus. This study showed that the fertilization rate in the spindle-aligned group was higher than the control group (P<0.05). After cleavage, a positive correlation was observed between spindle morphology and embryo morphology. Among the sub-groups of spindle-aligned group, the embryos' morphology of the fine group was better than the other subgroups and embryos of the poor group had lower quality and more fragmentation. The results revealed that the selection of oocytes based on meiotic spindle imaging can significantly improve the rate of fertilization and embryo cleavage and certainly increase the rate of implantation.

MicroRNA Expression in Bovine Cumulus Cells in Relation to Oocyte Quality

Cumulus cells play an essential role during oocyte maturation and the acquisition of fertilizability and developmental competence. Micro(mi)RNAs can post-transcriptionally regulate mRNA expression, and we hypothesized that miRNA profiles in cumulus cells could serve as an indicator of oocyte quality. Cumulus cell biopsies from cumulus-oocyte-complexes that either yielded a blastocyst or failed to cleave after exposure to sperm cells were analyzed for miRNA expression. On average, 332 miRNA species with more than 10 reads and 240 miRNA species with more than 50 reads were identified in cumulus cells; this included nine previously undescribed microRNAs. The most highly expressed miRNAs in cumulus cells were miR-21, members of the let-7 family and miR-155. However, no repeatable differences in miRNA expression between the cumulus cells from oocytes that became blastocysts versus those from non-cleaved oocytes were identified. Further examination of individual cumulus cell samples showed a wide variability in miRNA expression level. We therefore conclude that miRNA expression in cumulus cells cannot be used as an oocyte quality marker.

Identification of molecular markers for oocyte competence in bovine cumulus cells

Cumulus cells (CCs) have an important role during oocyte growth, competence acquisition, maturation, ovulation and fertilization. In an attempt to isolate potential biomarkers for bovine in vitro fertilization, we identified genes differentially expressed in bovine CCs from oocytes with different competence statuses, through microarray analysis. The model of follicle size, in which competent cumulus-oocyte complexes (COCs) were recovered from bigger follicles (≥8.0 mm in diameter) and less competent ones from smaller follicles (1-3 mm), was used. We identified 4178 genes that were differentially expressed (P < 0.05) in the two categories of CCs. The list was further enriched, through the use of a 2.5-fold change in gene expression as a cutoff value, to include 143 up-regulated and 80 down-regulated genes in CCs of competent COCs compared to incompetent COCs. These genes were screened according to their cellular roles, most of which were related to cell cycle, DNA repair, energy metabolism, metabolism of amino acids, cell signaling, meiosis, ovulation and inflammation. Three candidate genes up-regulated (FGF11, IGFBP4, SPRY1) and three down-regulated (ARHGAP22, COL18A1 and GPC4) in CCs from COCs of big follicles (≥8.1 mm) were selected for qPCR analysis. The selected genes showed the same expression patterns by qPCR and microarray analysis. These genes may be potential genetic markers that predict oocyte competence in in vitro fertilization routines.

Expressão gênica em ovócitos suínos de diferentes classificações morfológicas

A produção in vitro de embriões suínos tem alcançado resultados insatisfatórios: ovócitos maturados in vivo produzem uma porcentagem maior de embriões em relação aos maturados in vitro. O sucesso da maturação in vitro está diretamente relacionado com a competência ovocitária. Somente ovócitos competentes são capazes de serem fecundados e terem desenvolvimento embrionário normal. A competência ovocitária pode ser avaliada por vários parâmetros. Recentemente têm sido utilizados como parâmetro os estudos da expressão de genes associados com a competência. O presente trabalho teve por objetivo avaliar diferenças na expressão dos genes BMP15, RYBP, MATER e ZAR1 em ovócitos imaturos de diferentes classes morfológicas, sendo elas: 1, 2, 3 e 4, com a finalidade de proporcionar importantes marcadores moleculares relacionados com a capacidade ovocitária. O RNA total dos ovócitos foi extraído e utilizado como molde para a síntese da primeira fita de cDNA. Os resultados da expressão gênica foram analisados utilizando-se modelo misto, considerando os dados de expressão gênica variável dependente e as classes ovocitárias variáveis independentes. Os genes BMP15, ZAR1 e RYBP apresentaram expressão semelhante nas classes ovocitárias 1, 2 e 3; somente a categoria 4 diferiu na expressão desses genes (P<0,05). O gene MATER foi expresso de forma semelhante em todas as classes ovocitárias estudadas (P>0,05). A técnica de RT-qPCR foi eficiente para detecção desses transcritos em ovócitos de diferentes classes. No entanto, para melhor entendimento do envolvimento desses transcritos na aquisição da competência ovocitária, são necessários mais estudos avaliando ovócitos de diferentes classes morfológicas, em diferentes fases de desenvolvimento, e implicação de outros genes envolvidos com a competência ovocitária.

Molecular markers for oocyte competence in bovine cumulus cells

This study aimed to quantify the expression of candidate genes in cumulus cells (CCs) from cumulus-oocyte complexes (COCs) with high and low potential for in vitro development up to the blastocyst stage. First, the effects of individual culture and biopsy on embryo development were evaluated. Individuals cultured using the well of the well system were compared with individuals cultured in 20 μL droplets (microdroplets) and those cultured in groups (control). Blastocyst rates were lower for the individual culture systems (P < 0.05; well of the well = 17.9%, n = 95; microdrop = 26.3%, n = 95) than for the control group (45.0%, n = 209). Second, the effects of biopsy on embryo production were compared between the control and microdroplet cultures, and no effects (P > 0.05) were observed for either group. Finally, the expression profiles of glypican 4 (GPC4), IGF4-binding protein, follicle-stimulating hormonereceptor, growth hormone receptor, epidermal growth factor receptor, fibroblast growth factor 11, solute carrier family 2 member 1, solute carrier family 2 member 3,sprouty homolog 1, versican, and keratin protein 8 in CCs obtained by biopsy were quantified by real-time polymerase chain reaction. Cumulus cells were categorized on the basis of the fates of the COCs: expanded blastocyst, cleaved and arrested, and uncleaved. The GPC4 gene was overexpressed (P = 0.007) in CCs from oocytes that formed embryos compared with those that produced cleaved and arrested embryos. We concluded that individual culture reduced blastocyst production; however, biopsy did not affect embryo development. The profile of GPC4 expression can be used as a marker to distinguish COCs with potential for embryo development from those with limited developmental potential.

Subclinical mastitis disrupts oocyte cytoplasmic maturation in association with reduced developmental competence and impaired gene expression in preimplantation bovine embryos

Subclinical chronic mastitis was induced to examine the effects on oocyte developmental competence. Uninfected Holstein cows were intramammary administrated with serial (every 48h for 20 days) low doses of toxin of Staphylococcus aureus origin (Gram-positive; G+), endotoxin of Escherichia coli origin (Gram-negative; G-) or sterile saline (control). Follicular fluid of toxin- and saline-treated cows was aspirated from preovulatory follicles and used as maturation medium. Oocytes harvested from ovaries collected at the abattoir were matured and then fertilised and cultured for 8 days. The percentage of oocytes undergoing nuclear maturation, determined by meiotic nuclear stages, did not differ between groups. Cytoplasmic maturation, determined by cortical granule distribution, was affected by both toxins (PPPPTGS2) mRNA increased, whereas that of growth differentiation factor 9 (GDF9) decreased in matured oocytes. In addition, PTGS2 expression increased and POU class 5 homeobox 1 (POU5F1) expression decreased in 4-cell embryos developed from both G+ and G- oocytes. Thus, regardless of toxin type, subclinical mastitis disrupts oocyte cytoplasmic maturation and alters gene expression in association with reduced developmental competence.

Developmental competence of equine oocytes: impacts of zona pellucida birefringence and maternally derived transcript expression

In the present study, equine oocytes were classified into groups of presumably high and low developmental competence according to cumulus morphology, as well as oocyte ability to metabolise brilliant cresyl blue (BCB) stain. All oocytes were evaluated individually in terms of morphometry, zona pellucida birefringence (ZPB) and relative abundance of selected candidate genes. Oocytes with an expanded cumulus (Ex), representing those with presumably high developmental competence, had a significantly thicker zona (18.2 vs 17.3µm) and a significantly higher ZPB (64.6 vs 62.1) than oocytes with a compacted cumulus (Cp). Concurrently, oocytes classified as highly developmentally competent (BCB+) had a significantly thicker zona (18.8 vs 16.1µm) and significantly higher ZPB (63.1 vs 61.3) compared with oocytes classified as having low developmental competence. Expression of TFAM, STAT3 and CKS2 was significantly higher in Ex compared with Cp oocytes, whereas expression of COX1, ATPV6E and DNMT1 was lower. Together, the data reveal that developmentally competent equine oocytes are larger in size, have higher ZPB values and exhibit a typical genetic signature of maternally derived transcripts compared with oocytes with lower in vitro developmental competence.

Use of both cumulus cells' transcriptomic markers and zona pellucida birefringence to select developmentally competent oocytes in human assisted reproductive technologies

BACKGROUND

Selection of the best oocyte for subsequent steps of fertilization and embryo transfer was shown to be the crucial step in human infertility treatment procedure. Oocyte selection using morphological criteria mainly Zona pellucida (ZP) has been the gold standard method in assisted reproductive technologies (ART) clinics, but this selection approach has limitations in terms of accuracy, objectivity and constancy. Recent studies using OMICs-based approaches have allowed the identification of key molecular markers that quantitatively and non-invasively predict the oocyte quality for higher pregnancy rates and efficient infertility treatment. These biomarkers are a valuable reinforcement of the morphological selection criteria widely used in in vitro fertilization (IVF) clinics. In this context, this study was designed to investigate the relationship between transcriptomic predictors of oocyte quality found by our group and the conventional morphological parameters of oocyte quality mainly the ZP birefringence.

RESULTS

Microarray data revealed that 48 and 27 differentially expressed candidate genes in cumulus cells (CCs) were respectively overexpressed and underexpressed in the ZGP (Zona Good Pregnant) versus ZBNP (Zona Bad Non Pregnant) groups. More than 70% of previously reported transcriptomic biomarkers of oocyte developmental competence were confirmed in this study. The analysis of possible association between ZP birefringence versus molecular markers approach showed an absence of correlation between them using the current set of markers.

CONCLUSIONS

This study suggested a new integrative approach that matches morphological and molecular approaches used to select developmentally competent oocytes able to lead to successful pregnancy and the delivery of healthy baby. For each ZP birefringence score, oocytes displayed a particular CCs' gene expression pattern. However, no correlations were found between the 7 gene biomarkers of oocyte developmental potential and the ZP birefringence score. Further studies using larger lists of candidate markers are required to identify suitable genes that are highly correlated with the morphological criteria, and therefore able to reinforce the accuracy of oocyte selection and the effectiveness of infertility treatment.

Microfluidic method of pig oocyte quality assessment in relation to different follicular size based on lab-on-chip technology

Since microfollicular environment and the size of the follicle are important markers influencing oocyte quality, the aim of this study is to present the spectral characterization of oocytes isolated from follicles of various sizes using lab-on-chip (LOC) technology and to demonstrate how follicle size may affect oocyte quality. Porcine oocytes (each, n = 100) recovered from follicles of different sizes, for example, from large (>5 mm), medium (3–5 mm), and small (<3 mm), were analyzed after preceding in vitro maturation (IVM). The LOC analysis was performed using a silicon-glass sandwich with two glass optical fibers positioned “face-to-face.” Oocytes collected from follicles of different size classes revealed specific and distinguishable spectral characteristics. The absorbance spectra (microspectrometric specificity) for oocytes isolated from large, medium, and small follicles differ significantly (P < 0.05) and the absorbance wavelengths were between 626 and 628 nm, between 618 and 620 nm, and less than 618 nm, respectively. The present study offers a parametric and objective method of porcine oocyte assessment. However, up to now this study has been used to evidence spectral markers associated with follicular size in pigs, only. Further investigations with functional-biological assays and comparing LOC analyses with fertilization and pregnancy success and the outcome of healthy offspring must be performed.