Current perspectives on in vitro maturation and its effects on oocyte genetic and epigenetic profiles

RNA Transcripts in Human Ovarian Cells: Two-Time Cryopreservation Does Not Affect Developmental Potential

Sometimes, for medical reasons, when a frozen tissue has already thawed, an operation by re-transplantation may be cancelled, and ovarian tissues should be re-frozen for transplantation next time. Research about the repeated cryopreservation of ovarian cells is rarely reported. It has been published that there is no difference in the follicle densities, proportions of proliferation of early preantral follicles, appearance of atretic follicles, or ultrastructural quality of frozen-thawed and re-frozen-rethawed tissue. However, the molecular mechanisms of a repeated cryopreservation effect on the developmental potential of ovarian cells are unknown. The aim of our experiments was to investigate the effect of re-freezing and re-thawing ovarian tissue on gene expression, gene function annotation, and protein-protein interactions. The morphological and biological activity of primordial, primary, and secondary follicles, aimed at using these follicles for the formation of artificial ovaries, was also detected. Second-generation mRNA sequencing technology with a high throughput and accuracy was adopted to determine the different transcriptome profiles in the cells of four groups: one-time cryopreserved (frozen and thawed) cells (Group 1), two-time cryopreserved (re-frozen and re-thawed after first cryopreservation) cells (Group 2), one-time cryopreserved (frozen and thawed) and in vitro cultured cells (Group 3), and two times cryopreserved (re-frozen and re-thawed after first cryopreservation) and in vitro cultured cells (Group 4). Some minor changes in the primordial, primary, and secondary follicles in terms of the morphology and biological activity were detected, and finally, the availability of these follicles for the formation of artificial ovaries was explored. It was established that during cryopreservation, the CEBPB/CYP19A1 pathway may be involved in regulating estrogen activity and CD44 is crucial for the development of ovarian cells. An analysis of gene expression in cryopreserved ovarian cells indicates that two-time (repeated) cryopreservation does not significantly affect the developmental potential of these cells. For medical reasons, when ovarian tissue is thawed but cannot be transplanted, it can be immediately re-frozen again.

Factors Influencing the In Vitro Maturation (IVM) of Human Oocyte

In vitro maturation (IVM) of oocytes is a promising assisted reproductive technology (ART) deemed as a simple and safe procedure. It is mainly used in patients with impaired oocyte maturation and in fertility preservation for women facing the risk of losing fertility. However, to date, it is still not widely used in clinical practice because of its underperformance. The influencing factors, such as biphasic IVM system, culture medium, and the supplementation, have a marked effect on the outcomes of oocyte IVM. However, the role of different culture media, supplements, and follicular priming regimens in oocyte IVM have yet to be fully clarified and deserve further investigation.

Epigallocatechin-3-Gallate Promotes the in vitro Maturation and Embryo Development Following IVF of Porcine Oocytes

Purpose

Epigallocatechin-3-gallate (EGCG) is a major ingredient of catechin polyphenols and exerts protective effects because of its strong antioxidant properties. As far as we know, there is still a lack of systematic research on the effects of EGCG on the in vitro maturation (IVM) and in vitro fertilization (IVF) of porcine oocytes. The present study aimed to determine the effects of EGCG on the IVM and IVF of porcine oocytes.

Methods

Porcine oocytes were treated with different concentrations of EGCG (5, 10 and 20 µM), and the cumulus cell expansion, oocyte maturation rate, reactive oxygen species (ROS), glutathione (GSH) and malondialdehyde (MDA) levels, total antioxidant capacity were determined. The mRNA expression levels of oxidative stress- and apoptosis-associated genes were determined by quantitative real-time PCR. The cleavage rate and blastocyst rate of oocytes after 10 μM EGCG treatment during IVM and IVF were also evaluated.

Results

EGCG at 5, 10 and 20 μM significantly promoted cumulus cell expansion, and EGCG at 10 μM increased the oocyte maturation rate. EGCG (10 μM) treatment reduced the ROS and MDA levels, while increased the antioxidant capacity and GSH concentrations in the mature oocytes. The qRT-PCR results showed that EGCG treatment up-regulated the mRNA expression of catalase, glutathione peroxidase and superoxide dismutase in the mature oocytes. In addition, EGCG treatment also decreased the mRNA expression levels of Bax and caspase-3 and increased the Bcl-2 mRNA expression level in the mature oocytes. In addition, the cleavage rate and blastocyst rate of oocytes treated with 10 μM EGCG during IVM and IVF were significantly higher than those of the control group.

Conclusion

Our results suggest that EGCG promotes the in vitro maturation and embryo development following IVF of porcine oocytes. The protective effects of EGCG on the oocytes may be associated with its antioxidant and anti-apoptosis properties.

Increased Environment-Related Metabolism and Genetic Expression in the In Vitro Matured Mouse Oocytes by Transcriptome Analysis

Infertility in humans at their reproductive age is a world-wide problem. Oocyte in vitro maturation (IVM) is generally used in such cases to acquire the embryo in assisted reproductive technology (ART). However, the differences between an in vivo (IVO) and IVM culture environment in the RNA expression profile in oocytes, remains unclear. In this study, we compared the global RNA transcription pattern of oocytes from in vitro and in vivo maturation. Our results showed that 1,864 genes differentially expressed between the IVO and IVM oocytes. Among these, 1,638 genes were up-regulated, and 226 genes were down-regulated, and these changes were mainly divided into environmental adaption, metabolism, and genetic expression. Our detailed analysis showed that the expression of genes that belonged to metabolism-related processes such as energy metabolism, nucleotide metabolism, and carbohydrate metabolism was changed; and these genes also belonged to organismal systems including environmental adaptation and the circulatory system; moreover, we also found that the relative gene expression of genetic expression processes, such as protein synthesis, modification, and DNA replication and repair were also altered. In conclusion, our data suggests that in vitro maturation of mouse oocyte resulted in metabolism and genetic expression changes due to environmental changes compared with in vivo matured oocytes.

Oocyte IVM or vitrification significantly impairs DNA methylation patterns in blastocysts as analysed by single-cell whole-genome methylation sequencing

To explore the mechanisms leading to the poor quality of IVF blastocysts, the single-cell whole-genome methylation sequencing technique was used in this study to analyse the methylation patterns of bovine blastocysts derived from invivo, fresh (IVF) or vitrified (V_IVF) oocytes. Genome methylation levels of blastocysts in the IVF and V_IVF groups were significantly lower than those of the invivo group (P<0.05). In all, 1149 differentially methylated regions (DMRs) were identified between the IVF and invivo groups, 1578 DMRs were identified between the V_IVF and invivo groups and 151 DMRs were identified between the V_IVF and IVF groups. For imprinted genes, methylation levels of insulin-like growth factor 2 receptor (IGF2R) and protein phosphatase 1 regulatory subunit 9A (PPP1R9A) were lower in the IVF and V_IVF groups than in the invivo group, and the methylation level of paternally expressed 3 (PEG3) was lower in the V_IVF group than in the IVF and invivo groups. Genes with DMRs between the IVF and invivo and the V_IVF and IVF groups were primarily enriched in oocyte maturation pathways, whereas DMRs between the V_IVF and invivo groups were enriched in fertilisation and vitrification-vulnerable pathways. The results of this study indicate that differences in the methylation of critical DMRs may contribute to the differences in quality between invitro- and invivo-derived embryos.

Ex vivo Retrieval of Mature Oocytes for Fertility Preservation in a Patient with Bilateral Borderline Ovarian Tumor

We report a case of ultrasound-guided ex vivo oocyte retrieval for fertility preservation in a woman with bilateral borderline ovarian tumor, for whom conventional transvaginal oocyte retrieval was deemed unsafe because of the increased risk of malignant cell spillage. Ovarian stimulation with gonadotropins was performed. Surgery was scheduled according to the ovarian response to exogenous gonadotropic stimulation; oophorectomized specimens were obtained by laparoscopy, and oocyte retrieval was performed ∼ 37 hours after the ovulatory trigger. The sum of 20 ovarian follicles were aspirated, and 16 oocytes were obtained. We performed vitrification of 12 metaphase II oocytes and 3 oocytes matured in vitro. Our result emphasizes the viability of ex vivo mature oocyte retrieval after controlled ovarian stimulation for those with high risk of malignant dissemination by conventional approach.

Involvement of early embryonic miR-409-3p in the establishment of anxiety levels in female mice

Small RNA molecules in early embryos, delivered from sperm to zygotes upon fertilization, are required for normal mouse embryonic development. Even modest changes in the levels of sperm-derived miRNAs appear to influence early embryos and subsequent development. For example, stress-associated behaviors develop in mice after injection into normal zygotes sets of sperm miRNAs elevated in stressed male mice. Here, we implicate early embryonic miR-409-3p in establishing anxiety levels in adult female, but not male mice. First, we found that exposure of male mice to chronic social instability stress, which leads to elevated anxiety in their female offspring across at least three generations through the paternal lineage, elevates sperm miR-409-3p levels not only in exposed males, but also in sperm of their F1 and F2 male offspring. Second, we observed that while injection of a mimic of miR-409-3p into zygotes from mating control males was incapable of mimicking this effect in offspring derived from them, injection of a specific inhibitor of this miRNA led to the opposite, anxiolytic effect in female, but not male, and offspring. These findings imply that baseline miR-409-3p activity in early female embryos is necessary for the expression of normal anxiety levels when they develop into adult females. In addition, elevated embryo miR-409-3p activity, possibly as a consequence of stress-induced elevation of its expression in sperm, may participate in, but may not be sufficient for, the induction of enhanced anxiety.

The 5.8S pre-rRNA maturation factor, M-phase phosphoprotein 6, is a female fertility factor required for oocyte quality and meiosis

Objectives

M‐phase phosphoprotein 6 (MPP6) is important for 5.8S pre‐rRNA maturation in somatic cells and was screened as a female fertility factor. However, whether MPP6 functions in oocyte meiosis and fertility is not yet known. We aimed to address this.

Materials and Methods

Mouse oocytes with surrounded nucleus (SN) or non‐surrounded nucleus (NSN) were used for all experiments. Peptide nanoparticle‐mediated antibody transfection was used to deplete MPP6. Immunofluorescence staining, immunohistochemistry and live tracker staining were used to examine MPP6 localization and characterize phenotypes after control or MPP6 depletion. High‐fidelity PCR and fluorescence in situ hybridization (FISH) were used to examine the localization and level of 5.8S rRNAs. Western blot was used to examine the protein level. MPP6‐EGFP mRNA microinjection was used to do the rescue.

Results

MPP6 was enriched within ovaries and oocytes. MPP6 depletion significantly impeded oocyte meiosis. MPP6 depletion increased 5.8S pre‐rRNA. The mRNA levels of MPP6 and 5.8S rRNA decreased within ageing oocytes, and MPP6 mRNA injection partially increased 5.8S rRNA maturation and improved oocyte quality.

Conclusions

MPP6 is required for 5.8S rRNA maturation, meiosis and quality control in mouse oocytes, and MPP6 level might be a marker for oocyte quality.