Transcriptome analysis of porcine immature oocytes and surrounding cumulus cells after vitrification and in vitro maturation

Smart seq2 revealed distinct molecular responses during in vitro porcine oocyte maturation before or after the addition of mogroside V

Oocyte maturation involves both nuclear and cytoplasmic maturation. Mogroside V (MV) has been shown to enhance nuclear maturation, mitochondrial content, and developmental potential of porcine oocyte during in vitro maturation (IVM). However, the impact of MV on cytoplasmic maturation and its underlying mechanisms are not understood. This study aimed to assess the effect of MV on cytoplasmic maturation. Germinal vesicle (GV) oocytes treated with MV exhibited a noticeable increase in cortical granules (CGs) formation. Additionally, MV enhanced the expression of NNAT and improved glucose uptake in mature oocytes. Further insights were gained through Smart-seq2 analysis of RNA isolated from 100 oocytes. A total of 11,274 and 11,185 transcripts were identified in oocytes treated with and without MV, respectively. Among quantified genes, 438 differentially expressed genes (DEGs) were identified for further analysis. Gene Ontology (GO) enrichment analysis indicated that these DEGs were primarily involved in DNA repair regulation, cellular response to DNA damage, intracellular components, and organelles. Furthermore, the DEGs were significantly enriched in three KEGG pathways: fatty acid synthesis, pyruvate metabolism, and WNT signalling. To validate the results, lipid droplets (LD) and triglyceride (TG) were examined. MV led to an increase in the accumulation of LD and TG production in mature oocytes. These findings suggest that MV enhances cytoplasmic maturation by promoting lipid droplet synthesis. Overall, this study provides valuable insights into the mechanisms through which MV improves oocyte quality during IVM. The results have significant implications for research in livestock reproduction and offer guidance for future studies in this field.

Transcriptome analysis of porcine embryos derived from oocytes vitrified at the germinal vesicle stage

Vitrification of porcine immature oocytes at the germinal vesicle (GV) stage reduces subsequent embryo yield and changes at the molecular level may occur during embryonic development. Therefore, the present study used porcine parthenogenetic embryos as a model to investigate the effect of GV oocyte vitrification on the transcriptional profiles of the resultant embryos at the 4-cell and blastocyst stages using the Smart-seq2 RNA-seq technique. We identified 743 (420 up-regulated and 323 down-regulated) and 994 (554 up-regulated and 440 down-regulated) differentially expressed genes (DEGs) from 4-cell embryos and blastocysts derived from vitrified GV oocytes, respectively. Functional enrichment analysis of DEGs in 4-cell embryos showed that vitrification of GV oocytes influenced regulatory mechanisms related to transcription regulation, apoptotic process, metabolism and key pathways such as the MAPK signaling pathway. Moreover, DEGs in blastocysts produced from vitrified GV oocytes were enriched in critical biological functions including cell adhesion, cell migration, AMPK signaling pathway, GnRH signaling pathway and so on. In addition, the transcriptomic analysis and quantitative real-time PCR results were consistent. In summary, the present study revealed that the vitrification of porcine GV oocytes could alter gene expression patterns during subsequent embryonic developmental stages, potentially affecting their developmental competence.

Transcriptomics Reveal Molecular Differences in Equine Oocytes Vitrified before and after In Vitro Maturation

In the last decade, in vitro embryo production in horses has become an established clinical practice, but blastocyst rates from vitrified equine oocytes remain low. Cryopreservation impairs the oocyte developmental potential, which may be reflected in the messenger RNA (mRNA) profile. Therefore, this study aimed to compare the transcriptome profiles of metaphase II equine oocytes vitrified before and after in vitro maturation. To do so, three groups were analyzed with RNA sequencing: (1) fresh in vitro matured oocytes as a control (FR), (2) oocytes vitrified after in vitro maturation (VMAT), and (3) oocytes vitrified immature, warmed, and in vitro matured (VIM). In comparison with fresh oocytes, VIM resulted in 46 differentially expressed (DE) genes (14 upregulated and 32 downregulated), while VMAT showed 36 DE genes (18 in each category). A comparison of VIM vs. VMAT resulted in 44 DE genes (20 upregulated and 24 downregulated). Pathway analyses highlighted cytoskeleton, spindle formation, and calcium and cation ion transport and homeostasis as the main affected pathways in vitrified oocytes. The vitrification of in vitro matured oocytes presented subtle advantages in terms of the mRNA profile over the vitrification of immature oocytes. Therefore, this study provides a new perspective for understanding the impact of vitrification on equine oocytes and can be the basis for further improvements in the efficiency of equine oocyte vitrification.

Impacts of vitrification on the transcriptome of human ovarian tissue in patients with gynecological cancer

Objective: This study investigated the effects of a vitrification/warming procedure on the mRNA transcriptome of human ovarian tissues.

Design: Human ovarian tissues were collected and processed through vitrification (T-group) and then subjected to RNA sequencing (RNA-seq) analysis, HE, TdT-mediated dUTP nick-end labeling (TUNEL), and real-time quantitative PCR, and the results were compared to those of the fresh group (CK).

Results: A total of 12 patients, aged 15–36 years old, with a mean anti-Müllerian hormone level of 4.57 ± 3.31 ng/mL were enrolled in this study. According to the HE and TUNEL results, vitrification effectively preserved human ovarian tissue. A total of 452 significantly dysregulated genes (|log2FoldChange| > 1 and p < 0.05) were identified between the CK and T groups. Among these, 329 were upregulated and 123 were downregulated. A total of 372 genes were highly enriched for 43 pathways (p < 0.05), which were mainly related to systemic lupus erythematous, cytokine–cytokine receptor interaction, the TNF signaling pathway, and the MAPK signaling pathway. IL10, AQP7, CCL2, FSTL3, and IRF7 were significantly upregulated (p < 0.01), while IL1RN, FCGBP, VEGFA, ACTA2, and ASPN were significantly downregulated in the T-group (p < 0.05) compared to the CK group, which agreed with the results of the RNA-seq analysis.

Conclusion: These results showed (for the first time to the authors’ knowledge) that vitrification can induce changes in mRNA expression in human ovarian tissues. Further molecular studies on human ovarian tissues are required to determine whether altered gene expression could result in any downstream consequences.

Effects of oocyte vitrification on gene expression in the liver and kidney tissues of adult offspring

Oocyte vitrification is an important assisted reproductive technology (ART) that preserves the fertility of unmarried patients with malignant tumors, and promotes the development of the oocyte donation program. In recent years, the effects of ART, including the vitrification of oocytes and embryos on the health of offspring, have attracted much attention; however, it is difficult to conduct long-term follow-up and biochemical evaluation in humans. In this study, we detected the effect of oocyte vitrification on gene expression in the organs of adult mice offspring by RNA sequencing for the first time. Our results showed that only a small amount of gene expression was significantly affected. Seven genes (Tpm3, Hspe1-rs1, Ntrk2, Cyp4a31, Asic5, Cyp4a14, Retsat) were abnormally expressed in the liver, and ten genes (Lbp, Hspe1-rs1, Prxl2b, Pfn3, Gm9008, Bglap3, Col8a1, Hmgcr, Ero1lb, Ifi44l) were abnormal in the kidney. Several genes were related to metabolism and disease occurrence in the liver or kidney. Besides, we paid special attention to the expression of known imprinted genes and DNA methylation-related genes in adult organs, which are susceptible to oocyte cryopreservation in the preimplantation stage. As a result, some of these transcripts were detected in adult organs, but they were not affected by oocyte vitrification. In conclusion, we first report that oocyte vitrification did not significantly change the global gene expression in offspring organs; nonetheless, it can still influence the transcription of a few functional genes. The potential adverse effects caused by oocyte vitrification need attention and further study.

Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

Biodiversity is defined as the presence of a variety of living organisms on the Earth that is essential for human survival. However, anthropogenic activities are causing the sixth mass extinction, threatening even our own species. For many animals, dwindling numbers are becoming fragmented populations with low genetic diversity, threatening long-term species viability. With extinction rates 1000–10,000 times greater than natural, ex situ and in situ conservation programmes need additional support to save species. The indefinite storage of cryopreserved (−196°C) viable cells and tissues (cryobanking), followed by assisted or advanced assisted reproductive technology (ART: utilisation of oocytes and spermatozoa to generate offspring; aART: utilisation of somatic cell genetic material to generate offspring), may be the only hope for species’ long-term survival. As such, cryobanking should be considered a necessity for all future conservation strategies. Following cryopreservation, ART/aART can be used to reinstate lost genetics back into a population, resurrecting biodiversity. However, for this to be successful, species-specific protocol optimisation and increased knowledge of basic biology for many taxa are required. Current ART/aART is primarily focused on mammalian taxa; however, this needs to be extended to all, including to some of the most endangered species: amphibians. Gamete, reproductive tissue and somatic cell cryobanking can fill the gap between losing genetic diversity today and future technological developments. This review explores species prioritisation for cryobanking and the successes and challenges of cryopreservation and multiple ARTs/aARTs. We here discuss the value of cryobanking before more species are lost and the potential of advanced reproductive technologies not only to halt but also to reverse biodiversity loss.

Transcriptome Analysis of mRNAs and Long Non-Coding RNAs During Subsequent Embryo Development of Porcine Cloned Zygotes After Vitrification

Cryopreservation of porcine cloned zygotes has important implications for biotechnology and biomedicine research; however, lower embryo developmental potential remains an urgent problem to be resolved. For exploring the sublethal cryodamages during embryo development, this study was designed to acquire the mRNA and long non-coding RNA (lncRNA) profiles of 2-cells, 4-cells and blastocysts derived from vitrified porcine cloned zygotes using transcriptome sequencing. We identified 167 differentially expressed (DE) mRNAs and 516 DE lncRNAs in 2-cell stage, 469 DE mRNAs and 565 lncRNAs in 4-cell stage, and 389 DE mRNAs and 816 DE lncRNAs in blastocyst stage. Functional enrichment analysis revealed that the DE mRNAs during embryo development were involved in many regulatory mechanisms related to cell cycle, cell proliferation, apoptosis, metabolism and others. Moreover, the target genes of DE lncRNAs in the three embryonic stages were also enriched in many key GO terms or pathways such as “defense response”, “linoleic acid metabolic process”, “embryonic axis specification”, “negative regulation of protein neddylation”, etc., In conclusion, the present study provided comprehensive transcriptomic data about mRNAs and lncRNAs for the vitrified porcine cloned zygotes during different developmental stages, which contributed to further understand the potential cryodamage mechanisms responsible for impaired embryo development.

WGBS combined with RNA-seq analysis revealed that Dnmt1 affects the methylation modification and gene expression changes during mouse oocyte vitrification

Understanding the molecular level changes of oocyte cryopreservation and the subsequent warming process is essential for improving the oocyte cryopreservation technologies. Here, we collected the mature metaphase II (MII) oocytes from mice and vitrified. After thawing, single-cell whole-genome bisulphite sequencing (scWGBS) and single-cell RNA sequencing (scRNA-seq) were used to investigate the molecular attributes of this process. Compared to the fresh oocytes, the vitrified oocytes had lower global methylation and gene expression levels, and 1426 genes up-regulated and 3321 genes down-regulated. The 1426 up-regulated differentially expressed genes (DEGs) in the vitrified oocytes were mainly associated with the histone ubiquitination, while the 3321 down-regulated genes were mainly enriched in the mitochondrion organisation and ATP metabolism processes. The differentially methylated regions (DMRs) were mainly located in promoter, intron and exon region of genes, and the length of DMRs in the vitrified oocytes were also significantly lower than that of the fresh oocytes. Notably, there were no significant difference in the expression levels of DNA demethylases (Tet1, Tet2 and Tet3) and methyltransferases (Dnmt3a and Dnmt3b) between two treatments of oocytes. However, Dnmt1 and kcnq1ot1, which are responsible for maintaining DNA methylation, were significantly down regulated in the vitrified oocytes. Gene regulatory network (GRN) analysis showed the Dnmt1 and kcnq1ot1 play a core role in regulating methylation and expression levels of downstream genes. Moreover, some genes associated with oocyte quality were significantly down-regulated in the vitrified oocytes. The present data provides a new perspective for understanding the impact of vitrification on oocytes.

Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

Oocyte cryopreservation plays important roles in basic research and the application of models for genetic preservation and in clinical situations. This technology provides long-term storage of gametes for genetic banking and subsequent use with other assisted reproductive technologies. Until recently, oocytes have remained the most difficult cell type to freeze, as the oocytes per se are large with limited surface area to cytoplasm ratio. They are also highly sensitive to damage during cryopreservation, and therefore the success rate of oocyte cryopreservation is generally poor when compared to noncryopreserved oocytes. Although advancement in oocyte cryopreservation has progressed rapidly for decades, the improvement of cryosurvival and clinical outcomes is still required. This review focuses on the principles, techniques, outcomes and prospects of oocyte cryopreservation in domestic animals and humans.

Role of astaxanthin as an efficient antioxidant on the in vitro maturation and vitrification of porcine oocytes

As one of the most powerful natural antioxidants, astaxanthin (Ax) has begun to be applied to the field of reproductive biology. Here we used porcine oocyte as a model to explore how Ax improves the oocyte potential during in vitro maturation (IVM), and we also investigated the cytoprotective effects of Ax on the vitrified oocytes. Ax supplementation (final concentration of 2.5 μM) was subjected for immature oocytes during vitrification and subsequent IVM; fresh oocytes were also matured in vitro in the presence or absence of 2.5 μM Ax. Our results showed that Ax significantly increased the survival rate of vitrified oocytes, and promoted the blastocyst yield of both fresh and vitrified oocytes after parthenogenetic activation and somatic cell nuclear transfer. The oocytes treated with Ax displayed significantly lower reactive oxygen species generation and higher glutathione level. Vitrification of oocytes had no impact on caspase-3, cathepsin B and autophagic activities; Ax significantly decreased the cathepsin B activity in both fresh and vitrified oocytes. Moreover, the relative fluorescence intensity of lysosomes was significantly increased in vitrified oocytes, which was recovered by Ax treatment. The mitochondrial activity did not differ between fresh and vitrified oocytes, and was significantly enhanced in Ax-treated oocytes. Furthermore, Ax significantly restored the decreased expression of BMP15, ZAR1, POU5F1, GPX4 and LAMP2 genes in vitrified oocytes. Both fresh and vitrified oocytes treated with Ax showed significantly higher mRNA levels of GDF9, POU5F1, SOD2, NRF2 and ATG5. Taken together, this study provides new perspectives in understanding the mechanisms by which Ax improves the developmental competence of both fresh and vitrified porcine oocytes.

Cryopreservation of Porcine Embryos: Recent Updates and Progress

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Cryopreservation and oxidative stress in porcine oocytes

Several vitrification protocols have been established for porcine oocytes so as to facilitate gene banking of female germplasm. Although live piglets have been successfully produced from pig oocytes vitrified at the germinal vesicle (GV) stage, the competence of vitrified oocytes to develop into the blastocyst stage is greatly compromised following cryopreservation. The focus of this review is to elucidate the impact of cryopreservation on the redox balance of pig oocytes, making special reference to the relevance of non-enzymatic and enzymatic antioxidant defences. Besides, the regulation of gene expression in response to oxidative stress is also considered. Finally, we discuss the effects of supplementing maturation and vitrification media with the exogenous non-enzymatic antioxidants that have hitherto yielded the most relevant results.

Proteomic Changes of Porcine Oocytes After Vitrification and Subsequent in vitro Maturation: A Tandem Mass Tag-Based Quantitative Analysis

Cryopreservation of immature germinal vesicle (GV) oocytes is a promising strategy in pigs but still results in reduced oocyte quality due to inevitable cryodamages. Recently, there has been more focus on the molecular changes of oocytes after vitrification, but the alteration in the proteome level remains elusive. The aim of this study therefore was to decipher the proteomic characteristics of porcine GV oocytes following vitrification and in vitro maturation (IVM) by using tandem mass tag (TMT)-based quantitative approach and bioinformatics analysis. A total of 4,499 proteins were identified, out of which 153 presented significant difference. There were 94 up-regulated and 59 down-regulated proteins expressed differentially in the vitrified oocytes. Functional classification and enrichment analyses revealed that many of these proteins were involved in metabolism, signal transduction, response to stimulus, immune response, complement, coagulation cascades, and so on. Moreover, a parallel reaction monitoring technique validated the reliability of TMT data through quantitative analysis for 10 candidate proteins. In conclusion, our results provided a novel perspective of proteomics to comprehend the quality change in the vitrified porcine GV oocytes after IVM.

Initial response of ovarian tissue transcriptome to vitrification or microwave-assisted dehydration in the domestic cat model

Background

Long term preservation of living ovarian tissues is a critical approach in human reproductive medicine as well as in the conservation of rare animal genotypes. Compared to single cell preservation, optimization of protocols for tissues is highly complex because of the diversity of cells responding differently to non-physiological conditions. Using the prepubertal domestic cat as a model, the objective was to study immediate effects of vitrification or microwave-assisted dehydration on the global transcriptome dynamics in the ovarian cortex. RNA sequencing was performed on ovarian tissues (n = 6 individuals) from different conditions: fresh tissue after dissection (F), vitrified/warmed tissue (V), tissue dehydrated for 5 min (D5) or 10 min (D10) followed by rehydration. Differential gene expression analysis was performed for comparison pairs V vs. F, D10 vs. F, D5 vs. F and D10 vs. D5, and networks were built based on results of functional enrichment and in silico protein-protein interactions.

Results

The impact of the vitrification protocol was already measurable within 20 min after warming and involved upregulation of the expression of seven mitochondrial DNA genes related to mitochondrial respiration. The analysis of D10 vs. F revealed, 30 min after rehydration, major downregulation of gene expression with enrichment of in silico interacting genes in Ras, Rap1, PI3K-Akt and MAPK signaling pathways. However, comparison of D5 vs. F showed negligible effects of the shorter dehydration protocol with two genes enriched in Ras signaling. Comparison of D10 vs. D5 showed downregulation of only seven genes. Vitrification and dehydration protocols mainly changed the expression of different genes and functional terms, but some of the differentially expressed genes formed a major in silico protein-protein interaction cluster enriched for mitochondrial respiration and Ras/MAPK signaling pathways.

Conclusions

Our results showed, for the first time, different effects of vitrification and microwave-assisted dehydration protocols on the global transcriptome of the ovarian cortex (using the domestic cat as a biomedical model). Acquired data and networks built on the basis of differentially expressed genes (1) can help to better understand stress responses to non-physiological stresses and (2) can be used as directions for future preservation protocol optimizations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07236-z.

The effect of vitrification after warming on the expressions of p38, CDK1, and cyclin B in immature goat oocytes followed by in vitro maturation

Background and Aim

The combination of vitrification techniques and in vitro maturation can reduce oocyte competence. Mitogen-activated protein kinase and maturation-promoting factor are significant in oocyte meiotic maturation regulation. This study aimed to analyze vitrification's effect, after warming followed by in vitro maturation, on the expressions of protein 38 (p38), cyclin-dependent kinase 1 (CDK1), and cyclin B and oocyte maturation level.

Materials and Methods

Immature goat oocytes were soaked in vitrification and warming solutions. The procedure was followed by in vitro maturation and in vitro maturation without post-warming vitrification as a control. These oocytes, along with their cumulus, were vitrified using hemistraw in liquid nitrogen. Oocyte maturation was carried out in a maturation medium that was added with 10 μg/mL of FSH, 10 μg/mL of LH, and 1 μg/mL E₂ for 22 h. The expressions of p38, CDK1, and cyclin B were observed using immunocytochemical methods, which were assessed semiquantitatively according to the modified Remmele method. The oocyte maturation level was observed using the aceto-orcein staining method based on the achievement of chromosomes up to the metaphase II stage and/or the formation of the polar body I.

Results

p38 expression in vitrified oocytes after warming, followed by in vitro maturation, increased insignificantly (p≥0.05), with the acquisition of 3.91±2.69 and 2.69±0.50 in the control oocytes. CDK1 expression in vitrified oocytes decreased significantly (p≤0.05) after warming, followed by in vitro maturation, with the acquisition of 2.73±1.24 and 7.27±4.39 in the control oocytes. Cyclin B expression in vitrified oocytes decreased insignificantly (p≥0.05) after warming, followed by in vitro maturation, with the acquisition of 3.09±1.4 and 4.18±2.61 in the control oocytes. The proportion of vitrified oocyte maturation levels after warming, followed by in vitro maturation, decreased significantly (p≤0.05), with the acquisition of 45.45% and 77.27% in the control oocytes.

Conclusion

This study concluded that vitrification after warming resulted in an insignificant increase in p38 expression, a significant decrease in CDK1 expression, an insignificant decrease in cyclin B expression, and a significant reduction in oocyte maturation levels.

What impact does oocyte vitrification have on epigenetics and gene expression?

Children conceived by assisted reproductive technologies (ART) have a moderate risk for a number of adverse events and conditions. The question whether this additional risk is associated with specific procedures used in ART or whether it is related to the intrinsic biological factors associated with infertility remains unresolved. One of the main hypotheses is that laboratory procedures could have an effect on the epigenome of gametes and embryos. This suspicion is linked to the fact that ART procedures occur precisely during the period when there are major changes in the organization of the epigenome. Oocyte freezing protocols are generally considered safe; however, some evidence suggests that vitrification may be associated with modifications of the epigenetic marks. In this manuscript, after describing the main changes that occur during epigenetic reprogramming, we will provide current information regarding the impact of oocyte vitrification on epigenetic regulation and the consequences on gene expression, both in animals and humans. Overall, the literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by oocyte vitrification, and it also underlines the need to improve our knowledge in this field.

TMT-based quantitative proteomic analysis of cumulus cells derived from vitrified porcine immature oocytes following in vitro maturation

As the immature oocytes are submitted to cryopreservation, their surrounding cumulus cells (CCs) will inevitably suffer, which may have some adverse effects on subsequent oocyte maturation and development. So far, little is known about the molecular differences in CCs of immature oocytes after vitrification. The aim of this study therefore was to analyze the protein profile of CCs derived from vitrified porcine immature oocytes following in vitro maturation, using TMT-based quantitative proteomic approach. A total of 5910 proteins were identified, and 88 of them presented significant difference, with 46 up-regulated and 42 down-regulated proteins. Gene Ontology enrichment analysis revealed that cell cycle phase transition, mitotic cell cycle phase transition, positive regulation of cell differentiation and regulation of oogenesis were significantly down-regulated within the biological process. After Kyoto Encyclopedia of Genes and Genomes pathway analysis, some up-regulated proteins were significantly enriched in TGF-beta signaling pathway and 4 pathways related to steroid hormones. Furthermore, 10 selected proteins were quantified and verified by a parallel reaction monitoring technique, indicating a high reliability of the TMT results. In conclusion, vitrification affects protein profile of CCs as well as their biological functions, which will offer a new perspective to understand the reasons for decline in maturation quality of vitrified immature oocytes.