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

Influence of Long Non-Coding RNAs on Human Oocyte Development

Recent research findings have highlighted the pivotal roles played by lncRNAs in both normal human development and disease pathogenesis. LncRNAs are expressed in oocytes and early embryos, and their expression levels change dynamically once the embryonic genome is activated during early human embryonic development. Abnormal expression of lncRNAs was found in follicular fluid, granulosa cells and oocytes of patients, and these lncRNAs were related to cell proliferation and apoptosis, nuclear maturation and follicle development. The expression levels of some lncRNAs in cumulus cells demonstrate correlations with the quality of oocytes and early embryos. This paper aims to present a comprehensive overview of the influence of LncRNAs on the developmental process of human oocytes as well as their involvement in certain infertility-related diseases.

Nonerythroid hemoglobin promotes human cumulus cell viability and the developmental capacity of the human oocyte

OBJECTIVE

To determine the relationship between the levels of cumulus cell (CC) hemoglobin messenger ribonucleic acid (mRNA) and the developmental potential of the associated oocyte and whether hemoglobin protects the CCs from oxidative stress-induced apoptosis.

DESIGN

Laboratory-based study.

SETTING

University laboratory and university-affiliated in vitro fertilization center.

PATIENT(S)

Cumulus cells from the oocytes of patients who underwent in vitro fertilization with intracytoplasmic sperm injection with and without preimplantation genetic testing between 2018 and 2020.

INTERVENTION(S)

Studies on individual and pooled CCs collected at the time of oocyte retrieval or cultured under 20% or 5% O2.

MAIN OUTCOME MEASURE(S)

Quantitative polymerase chain reaction analysis of individual and pooled patient CC samples were used to monitor the hemoglobin mRNA levels. Reverse transcription-polymerase chain reaction arrays were used to assess genes that regulate oxidative stress in CCs associated with aneuploid and euploid blastocysts. Studies were conducted to assess the effect of oxidative stress on the rate of apoptosis, level of reactive oxygen species, and gene expression in CCs in vitro.

RESULT(S)

Compared with CCs associated with arrested and aneuploid blastocysts, the mRNA levels encoding the alpha and beta chains of hemoglobin increased by 2.9- and 2.3-fold in CCs associated with euploid blastocysts, respectively. The mRNA levels encoding the alpha and beta chains of hemoglobin also increased by 3.8- and 4.5-fold in CCs cultured under 5% O2 vs. 20% O2, respectively, and multiple regulators of oxidative stress were overexpressed in cells cultured under 20% O2 compared with those under 5% O2. However, the rate of apoptosis and amount of mitochondrial reactive oxidative species increased by 1.25-fold in CCs cultured under 20% O2 compared with those under 5% O2. Variable amounts of the alpha and beta chains of hemoglobin were also detected within the zona pellucida and oocytes.

CONCLUSION(S)

Higher levels of nonerythroid hemoglobin in CCs are associated with oocytes that result in euploid blastocysts. Hemoglobin may protect CCs from oxidative stress-induced apoptosis, which may enhance cumulus-oocyte interactions. Moreover, CC-derived hemoglobin may be transferred to the oocytes and protect it from the adverse effects of oxidative stress that occurs in vivo and in vitro.

The human cumulus cell transcriptome provides poor predictive value for embryo transfer outcome

RESEARCH QUESTION

Is the transcriptome of cumulus cells a good predictor of the embryo's developmental competence?

DESIGN

Cumulus cells were collected from donor oocytes and their transcriptome was analysed by RNA sequencing analysis at >30 × 10⁶ reads in samples grouped according to the developmental potential of their enclosed oocyte: not able to develop to the blastocyst stage (Bl-), able to develop to the blastocyst stage but failing to establish a pregnancy (P-), or able to develop to the blastocyst stage and to establish a clinical pregnancy (P+).

RESULTS

The cumulus cell trancriptome was largely independent of the developmental potential as, using a false dscovery rate-adjusted P-value of <0.05, only 10, 11 and 5 genes were differentially expressed for the comparisons P+ versus P-, P+ versus Bl-, and P- versus Bl-, respectively, out of a total of 17,469 genes expressed. Between the differentially expressed genes, those showing little overlap between samples from different groups were CHAC1, up-regulated in the P- and P+ groups compared with the Bl- group, and CENPE, CD93, PECAM1 and HSPA1B, which showed the opposite expression pattern. Focusing on the pregnancy potential, only EPN3 was consistently downregulated in the P+ compared with the P- and Bl- groups.

CONCLUSIONS

The cumulus cell transcriptome is largely unrelated to the establishment of clinical pregnancy following embryo transfer, although the expression level of a subset of genes in cumulus cells may indicate the ability to develop to the blastocyst stage.

Using Cumulus Cell Biopsy as a Non-Invasive Tool to Access the Quality of Bovine Oocytes: How Informative Are They?

The present study aimed to determine whether cumulus cells (CC) biopsy, acquired before or after in vitro maturation (IVM), presents similar gene expression pattern and if would compromises oocyte quality. First, immature cumulus oocyte complexes (COCs) were distributed: (1) maturated in groups (control); (2) individually maturated, but not biopsied; (3) subjected to CC biopsy before maturation and individually matured; (4) individually matured and submitted to CC biopsy after maturation; (5) individually matured and CC biopsied before and after maturation. Secondly, candidate genes, described as potential markers of COCs quality, were quantified by RT-qPCR in CCs before and after IVM. After in vitro fertilization (IVF), zygotes were tracked and sorted regarding their developmental potential: fully developed to embryo, cleaved and arrested, and not-cleaved. The COC’s biopsy negatively affects embryo development (p < 0.05), blastocyst cell number (p < 0.05), and apoptotic cell ratio (p < 0.05), both before and after IVM. The PTGS2, LUM, ALCAM, FSHR, PGR, SERPINE2, HAS2, and PDRX3 genes were differentially expressed (p < 0.05) on matured CCs. Only PGR gene (p = 0.04) was under-expressed on matured CCs on Not-Cleaved group. The SERPINE2 gene was overexpressed (p = 0.01) in the Cleaved group on immature CCs. In summary, none of the selected gene studies can accurately predict COC’s fate after fertilization.

Tight gene co-expression in BCB positive cattle oocytes and their surrounding cumulus cells

BACKGROUND

Cytoplasmic and nuclear maturation of oocytes, as well as interaction with the surrounding cumulus cells, are important features relevant to the acquisition of developmental competence.

METHODS

Here, we utilized Brilliant cresyl blue (BCB) to distinguish cattle oocytes with low activity of the enzyme Glucose-6-Phosphate Dehydrogenase, and thus separated fully grown (BCB positive) oocytes from those in the growing phase (BCB negative). We then analyzed the developmental potential of these oocytes, mitochondrial DNA (mtDNA) copy number in single oocytes, and investigated the transcriptome of single oocytes and their surrounding cumulus cells of BCB positive versus BCB negative oocytes.

RESULTS

The BCB positive oocytes were twice as likely to produce a blastocyst in vitro compared to BCB- oocytes (P < 0.01). We determined that BCB negative oocytes have 1.3-fold more mtDNA copies than BCB positive oocytes (P = 0.004). There was no differential transcript abundance of genes expressed in oocytes, however, 172 genes were identified in cumulus cells with differential transcript abundance (FDR < 0.05) based on the BCB staining of their oocyte. Co-expression analysis between oocytes and their surrounding cumulus cells revealed a subset of genes whose co-expression in BCB positive oocytes (n = 75) and their surrounding cumulus cells (n = 108) compose a unique profile of the cumulus-oocyte complex.

CONCLUSIONS

If oocytes transition from BCB negative to BCB positive, there is a greater likelihood of producing a blastocyst, and a reduction of mtDNA copies, but there is no systematic variation of transcript abundance. Cumulus cells present changes in transcript abundance, which reflects in a dynamic co-expression between the oocyte and cumulus cells.

Molecular Signatures Correlated With Poor IVF Outcomes: Insights From the mRNA and lncRNA Expression of Endometriotic Granulosa Cells

The outcomes of in vitro fertilization (IVF) for endometriotic women are significantly worse than for patients without ovarian endometriosis (OEM), as shown by fewer retrieved oocytes. However, the exact pathophysiological mechanism is still unknown. Thus, we conducted a prospective study that analyzed mRNA and lncRNA transcriptome between granulosa cells (GCs) from patients with fewer retrieved oocytes due to OEM and GCs from controls with male factor (MF) infertility using an RNA sequencing approach. We found a group of significantly differentially expressed genes (DEGs), including NR5A2, MAP3K5, PGRMC2, PRKAR2A, DEPTOR, ITGAV, KPNB1, GPC6, EIF3A, and SMC5, which were validated to be upregulated and negatively correlated with retrieved oocyte numbers in GCs of patients with OEM, while DUSP1 demonstrated the opposite. The molecular functions of these DEGs were mainly enriched in pathways involving mitogen-activated protein kinase (MAPK) signaling, Wnt signaling, steroid hormone response, apoptosis, and cell junction. Furthermore, we performed lncRNA analysis and identified a group of differentially expressed known/novel lncRNAs that were co-expressed with the validated DEGs and correlated with retrieved oocyte numbers. Co-expression networks were constructed between the DEGs and known/novel lncRNAs. These distinctive molecular signatures uncovered in this study are involved in the pathological regulation of ovarian reserve dysfunction in OEM patients.

Tannin Supplementation Improves Oocyte Cytoplasmic Maturation and Subsequent Embryo Development in Pigs

To investigate the effects of tannins (TA) on porcine oocyte in vitro maturation (IVM), different concentrations of TA (0, 1, 10 and 100 μg/mL) were supplemented with a maturation medium and the COCs and subsequent embryonic development were examined. The results showed that 10 µg/mL TA significantly improved the cumulus expansion index (CEI), cumulus-expansion-related genes (PTGS1, PTGS2, PTX-3, TNFAIP6 and HAS2) expression and blastocyst formation rates after parthenogenetic activation (PA), in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) compared to the control groups, but not oocyte nuclear maturation. Nevertheless, 10 µg/mL TA dramatically enhanced the mRNA expression of oocyte-development-related genes (BMP15, GDF9, CDC2 and CYCLIN B1), GSH, ATP, SOD1, PGC1α, BMP15, GDF9 and CDC2 levels and reduced intracellular ROS level in porcine oocytes. These results indicated that porcine oocyte cytoplasmic maturation was improved by 10 µg/mL TA treatment during IVM. In contrast, a high concentration of TA (100 μg/mL) significantly decreased the CEI and PTGS1, PTGS2, PTX-3 and HAS2 mRNA expressions in cumulus cells, and reduced oocyte nuclear maturation and the total cell numbers/blastocyst. In general, these data showed that 10 μg/mL TA supplementation has beneficial effects on oocyte cytoplasmic maturation and subsequent embryonic development in pigs.

Transcriptome profile of goat folliculogenesis reveals the interaction of oocyte and granulosa cell in correlation with different fertility population

To understand the molecular and genetic mechanisms related to the litter size in one species of two different populations (high litter size and low litter size), we performed RNA-seq for the oocytes and granulosa cells (GCs) at different developmental stages of follicle, and identified the interaction of genes from both sides of follicle (oocyte and GCs) and the ligand-receptor pairs from these two sides. Our data were very comprehensive to uncover the difference between these two populations regarding the folliculogenesis. First, we identified a set of potential genes in oocyte and GCs as the marker genes which can be used to determine the goat fertility capability and ovarian reserve ability. The data showed that GRHPR, GPR84, CYB5A and ERAL1 were highly expressed in oocyte while JUNB, SCN2A, MEGE8, ZEB2, EGR1and PRRC2A were highly expressed in GCs. We found more functional genes were expressed in oocytes and GCs in high fertility group (HL) than that in low fertility group (LL). We uncovered that ligand-receptor pairs in Notch signaling pathway and transforming growth factor-β (TGF-β) superfamily pathways played important roles in goat folliculogenesis for the different fertility population. Moreover, we discovered that the correlations of the gene expression in oocytes and GCs at different stages in the two populations HL and LL were different, too. All the data reflected the gene expression landscape in oocytes and GCs which was correlated well with the fertility capability.

Stratifying Cumulus Cell Samples Based on Molecular Profiling to Help Resolve Biomarker Discrepancies and to Predict Oocyte Developmental Competence

To increase the efficiency of assisted reproductive techniques (ART), molecular studies have been performed to identify the best predictive biomarkers for selecting the most suitable germ cells for fertilization and the best embryo for intra-uterine transfer. However, across different studies, no universal markers have been found. In this study, we addressed this issue by generating gene expression and CpG methylation profiles of outer cumulus cells obtained during intra-cytoplasmic sperm injection (ICSI). We also studied the association of the generated genomic data with the clinical parameters (spindle presence, zona pellucida birefringence, pronuclear pattern, estrogen level, endometrium size and lead follicle size) and the pregnancy result. Our data highlighted the presence of several parameters that affect analysis, such as inter-individual differences, inter-treatment differences, and, above all, specific treatment protocol differences. When comparing the pregnancy outcome following the long protocol (GnRH agonist) of ovarian stimulation, we identified the single gene markers (NME6 and ASAP1, FDR < 5%) which were also correlated with endometrium size, upstream regulators (e.g., EIF2AK3, FSH, ATF4, MKNK1, and TP53) and several bio-functions related to cell death (apoptosis) and cellular growth and proliferation. In conclusion, our study highlighted the need to stratify samples that are very heterogeneous and to use pathway analysis as a more reliable and universal method for identifying markers that can predict oocyte development potential.

Improved clinical outcomes after non-invasive oocyte selection and Day 3 eSET in ICSI patients

BACKGROUND

Non-invasive oocyte quality scoring, based on cumulus gene expression analysis, in combination with morphology scoring, can increase the clinical pregnancy (CPR) and live birth rates (LBR) in Day 3 eSET (elective single embryo transfer) ICSI patients. This was first investigated in a pilot study and is now confirmed in a large patient cohort of 633 patients. It was investigated whether CPR, LBR and time-to-pregnancy could be improved by analyzing the gene expression profile of three predictive genes in the cumulus cells, compared to patients with morphology-based embryo selection only.

METHODS

A large interventional, non-randomized, assessor-blinded cohort study with 633 ICSI patients was conducted in a tertiary fertility center. Non-PCOS patients, 22-39 years old, with good ovarian reserve, were stimulated with HP-hMG using a GnRH antagonist protocol and planned for fresh Day 3 eSET. The cumulus cells from individually denuded oocytes were ranked by a lab-developed cumulus cell test: qRT-PCR for three predictive genes (CAMK1D, EFNB2 and SASH1) and two control genes (UBC, B2M). The embryo selected for transfer was highest ranked from the pool of morphologically transferable Day 3 embryos. Patients in the control (n = 520) and experimental arm (n = 113) were compared for clinical pregnancy and live birth, using a weighted generalized linear model, and time-to-pregnancy using Kaplan-Meier curves.

RESULTS

The CPR was 61% in the experimental arm (n = 113) vs 29% in the control arm (n = 520, p < 0.0001). The LBR in the experimental arm (50%) was significantly higher than in the control arm (27%,p < 0.0001). Time-to-pregnancy was significantly shortened by 3 transfer cycles independent of the number of embryos available on Day 3 (Kaplan-Meier, p < 0.0001). Cumulus cell tested patients < 35 years (n = 65) or ≥ 35 years (n = 48) had a CPR of 62 and 60% respectively (ns). For cumulus cell tested patients with 2, 3-4, or > 4 transferable embryos, the CPR was 66, 52, and 67% (ns) respectively, and thus independent of the number of transferable embryos on Day 3.

CONCLUSIONS

This study provides further evidence of the clinical usefulness of the non-invasive cumulus cell test over time in a larger patient cohort.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03659786 / NCT02962466 (Registered 6Sep2018/11Nov2016, retrospectively registered.

Selection of competent oocytes by morphological criteria for assisted reproductive technologies

Invasive and noninvasive methods are commonly used to select developmentally competent oocytes that can improve the take-home baby rates in assisted reproductive technology (ART) centers. One of the noninvasive methods conventionally utilized to determine competent oocytes is the morphological analysis of cumulus complex, first polar body, zona pellucida, perivitelline space, meiotic spindle, and ooplasm. Successful fertilization, early embryo development, uterine implantation, and healthy pregnancy depend on the quality of oocytes, and morphological evaluation is one of the options used to predict quality levels. In this review, the morphological criteria being utilized in certain ART centers are comprehensively evaluated with special references to their predictive values and potential contributions to selecting high-quality oocytes.

Chromosome Missegregation in Single Human Oocytes Is Related to the Age and Gene Expression Profile

The growing trend for women to postpone childbearing has resulted in a dramatic increase in the incidence of aneuploid pregnancies. Despite the importance to human reproductive health, the events precipitating female age-related meiotic errors are poorly understood. To gain new insight into the molecular basis of age-related chromosome missegregation in human oocytes, we combined the transcriptome profiles of twenty single oocytes (derived from females divided into two groups according to age <35 and ≥35 years) with their chromosome status obtained by array comparative genomic hybridization (aCGH). Furthermore, we compared the transcription profile of the single oocyte with the surrounding cumulus cells (CCs). RNA-seq data showed differences in gene expression between young and old oocytes. Dysregulated genes play a role in important biological processes such as gene transcription regulation, cytoskeleton organization, pathways related to RNA maturation and translation. The comparison of the transcription profile of the oocyte and the corresponding CCs highlighted the differential expression of genes belonging to the G protein-coupled receptor superfamily. Finally, we detected the loss of a X chromosome in two oocytes derived from women belonging to the ≥35 years age group. These aneuploidies may be caused by the detriment of REEP4, an endoplasmic reticulum protein, in women aged ≥35 years. Here we gained new insight into the complex regulatory circuit between the oocyte and the surrounding CCs and uncovered a new putative molecular basis of age-related chromosome missegregation in human 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.

Is there a correlation between follicle size and gene expression in cumulus cells and is gene expression an indicator of embryo development?

BACKGROUND

In an article published in 2017, we discussed the results of the first part of our study into the morphokinetic development of embryos in relation to follicle diameter and homogeneity of follicular development. Our findings showed that embryos coming from small follicles in heterogeneous cycles had significantly higher rates of arrest or failure to reach blastocyst than embryos coming from large follicles in homogenous cycles. The aim of this further study was to investigate the relationship between follicular size and gene expression of cumulus cells (CCs) and evaluate whether gene expression could be an indicator of embryo development.

METHODS

This study was based on 2495 COCs from 184 patients. CC expressions of five genes (TNFAIP6, PTGS2, HAS2, PTX3 and GDF9) were studied by generalized linear mixed models (GLMMs) regarding follicular size. CC expressions were then separately analysed regarding patient-specific variables (age, BMI, AMH and follicular size) in relation to embryos reaching blastocyst (eRB) or top or good quality blastocysts (TQ + GQ) using GLMMs with logit link.

RESULTS

Follicular size significantly correlated with the potential of an oocyte to develop into a blastocyst: oocytes developing from large follicles were more than twice as likely to develop into an eRB than oocytes from small follicles (p < 0.001). Gene expression of HAS2 and GDF9 correlated with blastocyst quality when separately evaluated with follicular size and the patient specific variables of age, BMI and AMH. However, no such correlation was found in other gene expressions studied.

CONCLUSIONS

Our findings suggest that differences in the expression of genes studied could be related to follicular size rather than to embryo quality. Although gene expression of HAS2 and GDF9 correlated with blastocyst quality, the only variable correlating with eRB and TQ and GQ blastocysts for each of these five models was follicular size.

TRIAL REGISTRATION

This prospective cohort study was registered at clinicaltrials.gov (NCT02230449).

Functional signaling and gene regulatory networks between the oocyte and the surrounding cumulus cells

Background

The maturation and successful acquisition of developmental competence by an oocyte, the female gamete, during folliculogenesis is highly dependent on molecular interactions with somatic cells. Most of the cellular interactions identified, thus far, are modulated by growth factors, ions or metabolites. We hypothesized that this interaction is also modulated at the transcriptional level, which leads to the formation of gene regulatory networks between the oocyte and cumulus cells. We tested this hypothesis by analyzing transcriptome data from single oocytes and the surrounding cumulus cells collected from antral follicles employing an analytical framework to determine interdependencies at the transcript level.

Results

We overlapped our transcriptome data with putative protein-protein interactions and identified hundreds of ligand-receptor pairs that can transduce paracrine signaling between an oocyte and cumulus cells. We determined that 499 ligand-encoding genes expressed in oocytes and cumulus cells are functionally associated with transcription regulation (FDR < 0.05). Ligand-encoding genes with specific expression in oocytes or cumulus cells were enriched for biological functions that are likely associated with the coordinated formation of transzonal projections from cumulus cells that reach the oocyte’s membrane. Thousands of gene pairs exhibit significant linear co-expression (absolute correlation > 0.85, FDR < 1.8 × 10^− 5) patterns between oocytes and cumulus cells. Hundreds of co-expressing genes showed clustering patterns associated with biological functions (FDR < 0.5) necessary for a coordinated function between the oocyte and cumulus cells during folliculogenesis (i.e. regulation of transcription, translation, apoptosis, cell differentiation and transport).

Conclusion

Our analyses revealed a complex and functional gene regulatory circuit between the oocyte and surrounding cumulus cells. The regulatory profile of each cumulus-oocyte complex is likely associated with the oocytes’ developmental potential to derive an embryo.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4738-2) contains supplementary material, which is available to authorized users.

CUMULUS CELL GENES AS POTENTIAL BIOMARKERS OF OOCYTE AND EMBRYO DEVELOPMENTAL COMPETENCE

Bogomoletz Institute of Physiology NASU, Ukraine, Kiev. The selection of embryos with high implantation potential is the most important task in assisted reproductive technology. Today, this selection is based on subjective morphological criteria such as growth rate, early cleavage, the degree of fragmentation, blastocyst formation. However, the morphological assessment alone does not accurately predict oocyte/early stage embryo competence. Thus, the development of an objective, accurate, fast and affordable tests to determine oocyte quality and embryo viability could increase the chance of a successful pregnancy and reduce the number of embryos to transfer. The advent of new technologies, the so-called OMIKS, has allowed to identify novel biomarkers that can be used in cycle of in vitro fertilization (IVF) for oocyte and / or embryo selection. During folliculogenesis oocyte plays a dominant role in regulation of cumulus (CC) and granulosa cell (GC) functions, and it is consequently believed that functions of GC and CC indirectly reflect oocyte’s competence. Cell functions and active cell processes are regulated through gene expression therefore, gene expression analysis in GC and/or CC could provide a non-invasive method for identification of the most competent oocytes and embryos. In cumulus cells, genes have been identified that characterize the oocyte ability to undergo meiotic maturation, successful fertilization and early embryonic development. Among them cyclooxygenase 2, gremlin 1 and hyaluronan synthase-2, which play an important roles during oocyte development, ovulation and fertilization. This article reviews the recent data regarding these genes as potential biomarkers for selection of oocytes and embryos in the IVF program.

Zona pellucida gene mRNA expression in human oocytes is related to oocyte maturity, zona inner layer retardance and fertilization competence

STUDY QUESTION

Do the mRNA expression levels of zona pellucida (ZP) genes, ZP1, 2, 3 and 4 in oocyte and cumulus cells (CC) reveal relevant information on the oocyte?

SUMMARY ANSWER

The ZP mRNA expression in human oocytes is related to oocyte maturity, zona inner layer (IL) retardance and fertilization capacity.

WHAT IS KNOWN ALREADY

ZP structure and birefringence provide useful information on oocyte cytoplasmic maturation, developmental competence for embryonic growth, blastocyst formation and pregnancy. In order to understand the molecular basis of morphological changes in the ZP, in the current study, the polarized light microscopy (PLM) approach was combined with analysis of the expression of the genes encoding ZP1, 2, 3 and 4, both in the oocytes and in the surrounding CC.

STUDY DESIGN, SIZE, DURATION

This is a retrospective study comprising 98 supernumerary human cumulus oocyte complexes (COC) [80 Metaphase II (MII), 10 Metaphase I (MI) and 8 germinal vesicle (GV)] obtained from 39 patients (median age 33.4 years, range 22-42) after controlled ovarian stimulation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single oocytes and their corresponding CC were analysed. Oocytes were examined using PLM, and quantitative RT-PCR was performed for ZP1, 2, 3 and 4 in these individual oocytes and their CC. Ephrin-B2 (EFNB2) mRNA was measured in CC as a control. Presence of ZP3 protein in CC and oocytes was investigated using immunocytochemistry. Data were analysed using one-parametric and multivariate analysis and were corrected for the potential impact of patient and cycle characteristics.

MAIN RESULTS AND THE ROLE OF CHANCE

Oocytes contained ZP1/2/3 and 4 mRNA while in CC only ZP3 was quantifiable. Also ZP3 protein was detected in human CC. When comparing mature (MII) and immature oocytes (MI/GV) or their corresponding CC, ZP1/2 and 4 expression was lower in mature oocytes compared to the expression in immature oocytes (all P < 0.05) and ZP3 expression was lower in the CC of mature oocytes compared to the expression in CC of immature oocytes (P < 0.05). This coincided with a significantly smaller IL-ZP area and thickness in mature oocytes than in immature oocytes (all P < 0.05). In mature oocytes, IL-ZP retardance was significantly correlated with the expression of all four ZP mRNAs (all P < 0.05). The oocyte ZP3 expression was the main predictor of the fertilization capacity, next to IL-retardance and IL-thickness. Using stepwise regression analysis, IL-thickness combined with EFNB2 expression in CC and the patient's ovarian response resulted in a noninvasive oocyte fertilization prediction model.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

This is a retrospective study and the relation of oocyte mRNA levels to fertilization capacity is indirect as oocyte gene expression analysis required lysis of the oocyte.

WIDER IMPLICATIONS OF THE FINDINGS

Overall relations between PLM observations, mRNA expression changes and intrinsic oocyte competence were successfully documented. As such PLM and CC gene expression are confirmed as valuable noninvasive techniques to evaluate oocyte competence.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by University of Torino, Italy, WFWG UZ-Brussel and Agentschap voor Innovatie door Wetenschap en Technologie IWT 110680, Belgium. All authors declare that their participation in the study did not involve actual or potential conflicts of interests.

Distinct effect of fetal bovine serum versus follicular fluid on multipotentiality of human granulosa cells in in vitro condition

This study aimed to develop an appropriate medium for preservation of multipotentiality in human granulosa cells. To compare the possible effect of different media supplemented with follicular fluid or fetal bovine serum, granulosa cells were cultured in vitro over a period of 14 days. Stemness feature and any alteration in the cell phenotype were monitored using colony count assay and flow cytometry analysis by monitoring the expression of Oct3/4 and GATA-4 factors. Transcript expression level of Sox-2, Klf-4, and Nanog were investigated using quantitative real-time PCR analysis. Cells were cultured in the medium supplement with follicular fluid showed normal cell morphology and epithelial-like appearance, however, cells treated with fetal bovine serum, exhibited the clonogenic potential of granulosa cells which was increased after exposure to follicular fluid after 14 days (p < 0.05). Flow cytometry analysis revealed a significant reduction in the protein level of GATA-4 in cells cultured in presence of follicular fluid compared with cells received fetal bovine serum (p < 0.001). Quantitative real-time PCR analysis disclosed reduction of Sox-2, Klf-4 and Nanog levels in cells exposed to fetal bovine serum. Our experiment showed the exposure of human granulosa cells to follicular fluid efficiently preserves the stemness characteristics of the cells.

Prosurvival effect of cumulus prostaglandin G/H synthase 2/prostaglandin2 signaling on bovine blastocyst: impact on in vivo posthatching development

Apoptotic activity is a common physiological process which culminates at the blastocyst stage in the preimplantation embryo of many mammals. The degree of embryonic cell death can be influenced by the oocyte microenvironment. However, the prognostic significance of the incidence of apoptosis remains undefined. Prostaglandin E2 (PGE2) derived from prostaglandin G/H synthase-2 (PTGS2) activity is a well-known prosurvival factor that is mainly studied in oncology. PGE2 is the predominant PTGS2-derived prostaglandin present in the oocyte microenvironment during the periconceptional period. Using an in vitro model of bovine embryo production followed by transfer and collection procedures, we investigated the impact of periconceptional PGE2 on the occurrence of spontaneous apoptosis in embryos and on subsequent in vivo posthatching development. Different periconceptional PGE2 environments were obtained using NS-398, a specific inhibitor of PTGS2 activity, and exogenous PGE2. We assessed the level of embryonic cell death in blastocysts at day 8 postfertilization by counting total cell numbers, by the immunohistochemical staining of active caspase-3, and by quantifying terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling signals and apoptosis regulator (BCL-2/BAX) mRNA expression. Morphometric parameters were used to estimate the developmental stage of the embryonic disk and the extent of trophoblast elongation on day 15 conceptuses. Our findings indicate that periconceptional PGE2 signaling durably impacts oocytes, conferring increased resistance to spontaneous apoptosis in blastocysts and promoting embryonic disk development and the elongation process during preimplantation development.

[Biomarkers of the cumulus cells in medically assisted procreation: State-of-the-art]

The oocyte grows within a follicle composed of layers of somatic cells. It undergoes with the cumulus cells that form the innermost layer a dialogue that is critical for its maturation. Based on the assumption that the transcriptome of the cumulus cells reflects the physiology of the oocyte, it may prove a useful non-invasive tool in embryo selection to improve assisted reproduction outcomes. During the past decade, various studies have been conducted with the objective of identifying cumulus biomarker genes as prognosis tools for oocyte quality and competence. Remarkably no common biomarkers stand out among all these studies. In this review we perform a critical analysis of the literature in order to reveal some of the parameters that may account for these discrepancies, such as patients' inclusion criteria (maternal age, stimulation protocols), day of embryo transfer (day 3 or 5), outcome criteria (oocyte potential, embryo competence, pregnancy). Moreover there is a lack of standardization in the experimental designs used for RNA extraction and gene expression assessment (microarrays, RT-qPCR) and for the statistical analyses. In conclusion, critical analyses such as the present one are indispensable to pave the way for future searches of predictive biomarkers of pregnancy.