Effects of cryopreservation on the developmental competence, ultrastructure and cytoskeletal structure of porcine oocytes

Effects of intracellular Ca2+ on developmental potential and ultrastructure of cryopreserved-warmed oocyte in mouse

Maintaining appropriate intracellular calcium of oocytes is necessary to prevent ultrastructure and organelle damage caused by freezing and cryoprotectants. The present study aimed to investigate whether cryoprotectant-induced changes in the calcium concentrations of oocytes can be regulated to reduce damage to developmental potential and ultrastructure. A total of 33 mice and 1381 oocytes were used to explore the effects of intracellular calcium on the development and ultrastructures of oocytes subjected to 2-aminoethoxydiphenyl borate (2-APB) inhibition or thapsigargin (TG) stimulation. Results suggested that high levels intracellular calcium interfered with TG compromised oocyte survival (84.4 % vs. 93.4 %, p < 0.01) and blastocyst formation in fresh and cryopreservation oocytes (78.1 % vs. 86.4 %, and 60.5 % vs. 72.5 %, p < 0.05) compared with that of 2-APB pretreated oocytes in which Ca2+ was stabilized even though no differences in fertilization and cleavage was detected (p > 0.05). Examination by transmission electron microscopy indicated that the microvilli decreased and shortened, cortical granules considerably decreased in the cortex area, mitochondrial vesicles and vacuoles increased, and the proportion of vacuole mitochondria increased after oocytes were exposed to cryoprotectants. The cryopreservation-warming process deteriorated the negative effects on organelles of survival oocytes. By contrast, a low level of intracellular calcium mediated with 2-APB was supposed to contribute to the protection of organelles. These findings suggested oocyte injuries induced by cryoprotectants and low temperatures can be alleviated. More studies are necessary to confirm the relationship among Ca2+ concentration of the cytoplasm, ultrastructural injuries, and disrupted developmental potential in oocytes subjected to cryopreservation and warming.

Vitrification of immature oocytes in pigs

Cryopreservation of oocytes is an important technology for the in vitro gene banking of female germplasm. Although slow freezing is not feasible, porcine oocytes survive vitrification at high rates. Cryopreservation at the germinal vesicle stage appears to be more advantageous than that at the metaphase-II stage. Several factors are considered to affect the success of vitrification and subsequent utilization of immature porcine oocytes such as the device, the protocols for cryoprotectant application, warming, and the post-warming culture. Although live piglets could be obtained from vitrified immature oocytes, their competence to develop to the blastocyst stage is still reduced compared to their non-vitrified counterparts, indicating that there is room for further improvement. Vitrified oocytes suffer various types of damage and alteration which may reduce their developmental ability. Some of these can recover to some extent during subsequent culture, such as the damage of the cytoskeleton and mitochondria. Others such as premature nuclear progression, DNA damage and epigenetic alterations will require further research to be clarified and addressed. To date, the practical application of oocyte vitrification in pigs has been confined to the gene banking of a few native breeds.

Vitrification induces a focused spindle pole in mouse MI oocytes

Immature oocyte (germinal vesicle stage, GV) vitrification can avoid a cycle of ovarian stimulation, which is friendly to patients with hormone-sensitive tumors. However, the in vitro maturation of vitrification-thawed GV oocyte usually results in aneuploidy, and the underlying mechanism remains unclear. Stable spindle poles are important for accurate chromosome segregation. Acentriolar microtubule-organizing centers (aMTOCs) undergo fragmentation and reaggregation to form spindle poles. Microtubule nucleation is facilitated via the perichromosome Ran after GVBD, which plays an important role in aMTOCs fragmentation. This study showed that vitrification may reduce microtubule density by decreasing perichromosomal Ran levels, which reduced the localization of pKIF11, thereby decreased the fragmentation of aMTOCs and formed a more focused spindle pole, ultimately resulted in aneuploidy. This study revealed the mechanism of abnormal spindle pole formation in vitrified oocytes and offered a theoretical support to further improve the quality of vitrified oocytes.

Comparing the effects of vitrification, before and after mouse oocyte in vitro maturation on developmental competence, changes in epigenetic regulators and stress oxidative response

Since the developmental stage of oocyte is a challenging issue in the success of vitrification, this study investigated the effects of vitrification, before and after in vitro maturation, on the survival and maturation rates, developmental competence and the expression levels of genes involved in apoptosis, oxidative stress and epigenetic modifications. Mouse germinal vesicle (GV) oocytes were divided into four groups: fresh in vitro matured oocytes without vitrification (fIVM), in vitro matured oocytes after vitrification (vIVM), in vitro matured oocytes before vitrification (IVMv). In addition, in vivo matured oocytes (MII) were used as control. After oocytes collection, maturation and survival rates as well as the intracellular reactive oxygen species (ROS) level were evaluated. Also, the expression level of various genes was analyzed by qRT-PCR. In addition, following artificial activation (parthenogenesis), the developmental competence of oocytes to the blastocyst stage was evaluated. A significant decrease in maturation rate and survival of vIVM oocytes was observed compared to fIVM and IVMv oocytes. Intracellular ROS levels were significantly increased in both vitrified groups compared to the fIVM group, and no significant difference between vitrified groups. Pro-apoptotic genes; BAX and Bcl2 as well as genes related to oxidative stress response Hsp1a, Hsp1b and SOD1were significantly increased in the vIVM group compared to the IVMv group. Interestingly, epigenetic regulators genes DNMT1, DNMT3a and DNMT3b were highly expressed in IVMv oocytes along with a decrease in the artificial activation rate compared to the vIVM oocytes. Our results indicated that despite observing more negative effects of vitrification before IVM on the survival rate and maturation as well as apoptosis status, less epigenetic changes in vIVM oocytes can make this process a better option in the treatment of infertility than IVM of oocytes followed by vitrification, a hypothesis that needs to be investigation in human oocytes.

Cumulus cell co-culture in media drops does not improve rescue in vitro maturation of vitrified-warmed immature oocytes

OBJECTIVE

To assess whether co-culture with vitrified-warmed cumulus cells (CCs) in media drops improves rescue in vitro maturation (IVM) of previously vitrified immature oocytes. Previous studies have shown improved rescue IVM of fresh immature oocytes when cocultured with CCs in a three-dimensional matrix. However, the scheduling and workload of embryologists would benefit from a simpler IVM approach, particularly in the setting of time-sensitive oncofertility oocyte cryopreservation (OC) cases. Although the yield of developmentally competent mature metaphase II (MII) oocytes is increased when rescue IVM is performed before cryopreservation, it is unknown whether maturation of previously vitrified immature oocytes is improved after coculture with CCs in a simple system not involving a three-dimensional matrix.

DESIGN

Randomized controlled trial.

SETTING

Academic hospital.

PATIENTS

A total of 320 (160 germinal vesicles [GVs] and 160 metaphase I [MI]) immature oocytes and autologous CC clumps were vitrified from patients who were undergoing planned OC or intracytoplasmic sperm injection from July 2020 until September 2021.

INTERVENTIONS

On warming, the oocytes were randomized to culture in IVM media with CCs (+CC) or without CCs (-CC). Germinal vesicles and MI oocytes were cultured in 25 μL (SAGE IVM medium) for 32 hours and 20-22 hours, respectively.

MAIN OUTCOME MEASURES

Oocytes with a polar body (MII) were randomized to confocal microscopy for analysis of spindle integrity and chromosomal alignment to assess nuclear maturity or to parthenogenetic activation to assess cytoplasmic maturity. Wilcoxon rank sum tests for continuous variables and the chi square or Fisher's exact test for categorical variables assessed statistical significance. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated.

RESULTS

Patient demographic characteristics were similar for both the GV and MI groups after randomization to +CC vs. -CC. No statistically significant differences were observed between +CC vs. -CC groups regarding the percentage of MII from either GV (42.5% [34/80] vs. 52.5% [42/80]; RR 0.81; 95% CI: 0.57-1.15]) or MI (76.3% [61/80]; vs. 72.5% [58/80]; RR 1.05; 95% CI: 0.88-1.26]) oocytes. An increased percentage of GV-matured MIIs underwent parthenogenetic activation in the +CC group (92.3% [12/13] vs. 70.8% [17/24]), but the difference was not statistically significant (RR 1.30; 95% CI: 0.97-1.75), whereas the activation rate was identical for MI-matured oocytes (74.3% [26/35] vs. 75.0% [18/24], CC+ vs. CC-; RR 0.99; 95% CI: 0.74-1.32). No significant differences were observed between +CC vs. -CC groups for cleavage of parthenotes from GV-matured oocytes (91.7% [11/12] vs. 82.4% [14/17]) or blastulation (0 for both) or for MI-matured oocytes (cleavage: 80.8% [21/26] vs. 94.4% [17/18]; blastulation: 0 [0/26] vs. 16.7% [3/18]). Further, no significant differences were observed between +CC vs. -CC for GV-matured oocytes regarding incidence of bipolar spindles (38.9% [7/18] vs. 33.3% [5/15]) or aligned chromosomes (22.2% [4/18] vs. 0.0 [0/15]); or for MI-matured oocytes (bipolar spindle: 38.9% [7/18] vs. 42.9% [2/28]); aligned chromosomes (35.3% [6/17] vs. 24.1% [7/29]).

CONCLUSIONS

Cumulus cell co-culture in this simple two-dimensional system does not improve rescue IVM of vitrified, warmed immature oocytes, at least by the markers assessed here. Further work is required to assess the efficacy of this system given its potential to provide flexibility in a busy, in vitro fertilization clinic.

Detrimental effects of vitrification on integrin genes (α9 and β1) and in vitro fertilization in mouse oocytes

OBJECTIVE

Integrins are known as key molecules that importantly involve in fertilization. This study aimed to evaluate effects of vitrification on fertilization rate and expression of integrin genes, α9 and β1, on mice oocytes in GV and MІІ stages.

MATERIALS AND METHODS

From the ovarian tissue and fallopian tube of NMRI mice, germinal vesicle (GV, n = 200) and metaphase II (MII, n = 200) oocytes were obtained. Then, oocytes were distributed into 4 groups including non-vitrified GV, non-vitrified MII, vitrified GV, and vitrified MII. Cryotop method was used for vitrification and oocytes (for 4 weeks) were kept in liquid nitrogen. After that, by using an inverted microscope, the rate of survived oocytes was assessed. Also, in vitro fertilization (IVF) for oocytes, obtained from in vitro maturated MII and mice ovaries (ovulated MII), was done to assess embryos at differenced stages (2-cells, morula, and hatched). Finally, RT-qPCR was performed to investigate the mRNA expression of integrin genes (α9 and β1).

RESULTS

After vitrification, the rate of survived oocytes, 68.65%for GV and 65.07% % for MII, did not show a remarkable difference related to non-vitrified groups, while the fertilization rate in vitrified groups remarkably decrease compared to non-vitrified groups (p < 0.05). Also, the expression of α9 and β1 genes was significantly altered in vitrified groups when compared to non-vitrified groups (p < 0.05). There was no significant difference in embryo developmental rates for non-vitrified and vitrified groups.

CONCLUSION

Cryotop method for vitrification caused an alternation in oocyte quality by reducing fertilization rate and integrin gene expression.

Potential use of immature oocyte to improve fertility preservation outcome: A narrative review

Fertility preservation through gamete vitrification has become one of the critical strategies to secure a childbearing potential in patients who are diagnosed with cancer or risks of infertility. Preserving the gametes would prevent the deleterious effects of cancer drugs or radiotherapy exposure on the quality of the gametes. Furthermore, in vitro fertilisation of vitrified mature human oocytes has lately demonstrated promising results that are reflected in the increased survival rate of thawed oocytes and the resultant clinical pregnancy rate. However, limitations in the cryopreservation of mature oocytes of cancer patients persist. Ovarian stimulation protocols which comprise administering gonadotrophin-releasing hormones could aggravate cancer or delay essential cancer therapy. Considering such circumstances, vitrification of immature oocytes would become a rational option. While the vitrification procedure of mature oocytes has been established, the vitrification of immature oocytes remains controversial due to a low post-thaw in vitro maturation and fertilisation rate. Apparent cryoinjuries to the immature oocytes post thawing or warming have been observed in both human and animal model oocytes. An alternative strategy was therefore proposed to improve the effectiveness of utilising immature oocytes for fertility preservation by conducting the in vitro oocyte maturation process first before vitrification. This method has prevailed, especially in oncofertility patients. Although the success rate of the clinical outcomes remains low, this approach, in conjugation with proper counselling, might provide oncofertility patients with an opportunity to preserve their reproductive potential.

Effects of Porcine Immature Oocyte Vitrification on Actin Microfilament Distribution and Chromatin Integrity During Early Embryo Development in vitro

Vitrification is mainly used to cryopreserve female gametes. This technique allows maintaining cell viability, functionality, and developmental potential at low temperatures into liquid nitrogen at −196°C. For this, the addition of cryoprotectant agents, which are substances that provide cell protection during cooling and warming, is required. However, they have been reported to be toxic, reducing oocyte viability, maturation, fertilization, and embryo development, possibly by altering cell cytoskeleton structure and chromatin. Previous studies have evaluated the effects of vitrification in the germinal vesicle, metaphase II oocytes, zygotes, and blastocysts, but the knowledge of its impact on their further embryo development is limited. Other studies have evaluated the role of actin microfilaments and chromatin, based on the fertilization and embryo development rates obtained, but not the direct evaluation of these structures in embryos produced from vitrified immature oocytes. Therefore, this study was designed to evaluate how the vitrification of porcine immature oocytes affects early embryo development by the evaluation of actin microfilament distribution and chromatin integrity. Results demonstrate that the damage generated by the vitrification of immature oocytes affects viability, maturation, and the distribution of actin microfilaments and chromatin integrity, observed in early embryos. Therefore, it is suggested that vitrification could affect oocyte repair mechanisms in those structures, being one of the mechanisms that explain the low embryo development rates after vitrification.

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.

Effect of porcine immature oocyte vitrification on oocyte-cumulus cell gap junctional intercellular communication

Vitrification may severely affect cumulus cells and oocyte morphology and viability, limiting their maturation and developmental potential. The aim of this study was to evaluate the gap junction intercellular communication (GJIC) integrity after the vitrification of porcine immature cumulus-oocyte complexes (COCs). Fresh COCs were randomly distributed in three groups: untreated (control), toxicity (cryoprotectants exposure), and vitrification, then subjected to in vitro maturation (IVM). Oocyte viability and IVM were measured in all groups. The evaluation of GJIC was expressed as relative fluorescence intensity (RFI). Vitrification significantly decreased oocyte viability and maturation after 44 h of culture compared to control. Also, significantly reduced RFI was observed in vitrified COCs during the first hours of culture (4-8 h) compared to control. This study demonstrates that porcine oocyte viability and maturation after 44 h of culture decreased after vitrification. GJIC was also affected during the first hours of culture after the vitrification of immature oocytes, being one of the possible mechanisms by which oocyte maturation decreased.

Ultrastructural Characterization of Porcine Growing and In Vitro Matured Oocytes

Simple Summary

During oocyte growth and maturation, the organelle’s morphology of porcine oocytes changed and populated different compartments depending on the differentiation status. Changes in ultrastructural or subcellular level of porcine oocytes during oogenesis/folliculogenesis were observed, potentially leading to future mitochondrion replacement therapies of oocytes.

Abstract

This study aimed to investigate ultrastructural changes of growing porcine oocytes and in vitro maturated oocytes. Light microscopy was used to characterize and localize the primordial, primary, secondary, and tertiary follicles. During oocyte growth and maturation, the morphology of mitochondria was roundish or ovoid in shape depending on the differentiation state, whereas their mean diameters oscillated between 0.5 and 0.7 µm, respectively, from primary and secondary follicles. Hooded mitochondria were found in the growing oocytes of the tertiary follicles. In addition to the pleomorphism of mitochondria, changes in the appearance of lipid droplets were also observed, along with the alignment of a single layer of cortical granules beneath the oolemma. In conclusion, our study is apparently the first report to portray morphological alterations of mitochondria that possess the hooded structure during the growth phase of porcine oocytes. The spatiotemporal and intrinsic changes during oogenesis/folliculogenesis are phenomena at the ultrastructural or subcellular level of porcine oocytes, highlighting an in-depth understanding of oocyte biology and impetus for future studies on practical mitochondrion replacement therapies for oocytes.

Novel ultrastructural findings in bovine oocytes matured in vitro

The ultrastructural morphology of the bovine oocyte at different maturation stages has been previously analyzed but without detailed structural observations at the mature stage. The objective of the present study was thus to establish the ultrastructural characteristics of the mature bovine oocyte in full detail. Oocytes from Bos taurus (Holstein-Friesian) cows were aspirated from ovaries collected after being slaughtered at a local abattoir. After in vitro culture for 24 h, some of them were processed for electron microscopy. We described the ultrastructure of the zona pellucida, which presented three different regions, and novel cytoplasmic findings. There were two types of electron-lucent vesicles (heterogeneous and striated), which were suggested to give rise to lipid droplets, and presence of receptor-mediated endocytosis. In conclusion, our results indicate that although the mature bovine oocyte is devoid of evident yolk, it might be filled with an extensive lipid factory. In addition, even before fertilization, the mature oocyte seemed to absorb nutrients through receptor-mediated endocytosis, indicating active energy use or storage.

Vitrification of Human In-Vitro Matured Oocytes: Effects on Mitochondrial Ultrastructure and Oxygen Consumption

Background: This study was conducted to evaluate the impact of vitrification on mitochondrial of human IVM oocytes.

Methods: A total of 401 immature oocytes were obtained from ovarian stimulated cycles, which were randomly divided into fresh and vitrification groups after IVM. According to the cultured time after thawing, the vitrification groups were divided into 0 hours (0 h), 2 hours (2 h), or 4 hours (4 h) subgroups. Mitochondrial morphology and oxygen consumption were compared among the four groups. After fertilization by ICSI, normal fertilization, cleaved embryos, and blastocyst formation rate were also calculated.

Results: The mean gray value of mitochondria structure was significantly decreased in 0 h and 2 h groups when compared to control group (0.48 ± 0.09, 0.50 ± 0.36 vs. 0.61 ± 0.12, respectively; P [Formula: see text] 0.05), and recovered (0.61 ± 0.24 vs. 0.61 ± 0.12, P [Formula: see text] 0.05) in 4 h group. In addition, oxygen consumption was also significantly decreased in 0 h and 2 h groups compared to fresh (2.91 ± 0.77 fmol/s, 3.26 ± 1.34 fmol/s vs. 3.96 ± 1.44 fmol/s, respectively; P [Formula: see text] 0.05), and recovered after 4 h culture (3.96 ± 1.44 fmol/s vs. 4.41 ± 1.38 fmol/s, respectively; P [Formula: see text] 0.05). The percentage of normal fertilization and cleaved embryos were no differences among the four groups, however, blastocyst development rate was significantly lower in 0 h group.

Conclusion: These results indicate that during the vitrification process, the oxygen consumption and mitochondrial structure of oocytes may undergo temporary dynamic changes, but appear to recover by 4 hours.

Melatonin Improves In Vitro Development of Vitrified-Warmed Mouse Germinal Vesicle Oocytes Potentially via Modulation of Spindle Assembly Checkpoint-Related Genes

The present study aimed to investigate the effect of melatonin (MT) supplementation on in vitro maturation of vitrified mouse germinal vesicle (GV) oocytes. The fresh oocytes were randomly divided into three groups: untreated (control), or vitrified by open-pulled straw method without (vitrification group) or with MT supplementation (vitrification + MT group). After warming, oocytes were cultured in vitro, then the reactive oxygen species (ROS) and glutathione (GSH) levels, mitochondrial membrane potential, ATP levels, spindle morphology, mRNA expression of spindle assembly checkpoint (SAC)-related genes (Mps1, BubR1, Mad1, Mad2), and their subsequent developmental potential in vitro were evaluated. The results showed that vitrification/warming procedures significantly decreased the percentage of GV oocytes developed to metaphase II (MII) stage, the mitochondrial membrane potential, ATP content, and GSH levels, remarkably increased the ROS levels, and significantly impaired the spindle morphology. The expressions of SAC-related genes were also altered in vitrified oocytes. However, when 10-7 mol/L MT was administered during the whole length of the experiment, the percentage of GV oocytes matured to MII stage was significantly increased, and the other indicators were also significantly improved and almost recovered to the normal levels relative to the control. Thus, we speculate that MT might regulate the mitochondrial membrane potential, ATP content, ROS, GSH, and expression of SAC-related genes, potentially increasing the in vitro maturation of vitrified-warmed mouse GV oocytes.

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

Cryopreservation impairs oocyte quality, which may be associated with abnormal gene expression. Currently, alteration of mRNA levels in vitrified porcine oocytes has not been well characterized. The aim of this study was to analyze transcriptome profiles with RNA sequencing (RNA-seq) in porcine immature oocytes and their surrounding cumulus cells (CCs) after vitrification and in vitro maturation (IVM). There were 19 upregulated and 18 downregulated genes differentially expressed in vitrified oocytes, with no significant GO enrichment or KEGG pathway identified for these genes. In addition, CCs derived from vitrified oocytes had 40 significantly upregulated and 100 significantly downregulated genes. In total, 7 GO terms were significantly enriched in molecular function and biological process, and only MAPK signaling pathway reached significant enrichment based on KEGG analysis. Moreover, selected differentially expressed genes had similar expression patterns through comparison between results from qRT-PCR and RNA-Seq. In conclusion, our data provided detailed information on mRNA transcriptomes in porcine immature oocytes and CCs after vitrification and IVM, which offered now insights regarding reduced developmental potential of the vitrified oocytes.

An efficiency comparison of different in vitro fertilization methods: IVF, ICSI, and PICSI for embryo development to the blastocyst stage from vitrified porcine immature oocytes

Background

Most studies carried out to evaluate recovery and development after porcine oocyte vitrification, reported better rates when cryopreserved in embryonic development stages or zygotes, but not in immature oocytes. For this reason, many studies are performed to improve immature oocyte vitrification protocols testing the use of different cryoprotectant concentrations, cooling devices, incubation times; but only a few of them have evaluated which fertilization procedure enhances blastocyst rates in vitrified oocytes. Therefore, this study was aimed to evaluate: 1) if the sperm selection with hyaluronic acid (HA) or polyvinylpyrrolidone (PVP) before injection could play a key role in increasing fertilization and blastocyst formation and 2) the embryo developmental ability and blastocyst production of porcine immature oocytes retrieved after vitrification-warming and co-cultured with granulosa cells during IVM, using different fertilization techniques: in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and conventional ICSI with hyaluronic acid (HA) sperm selection, known as physiological intracytoplasmic sperm injection (PICSI) and.

Results

Sperm selected with HA-PICSI displayed a higher percentage of live/acrosome reacted status compared to those in control and exposed to PVP. Higher dead/acrosome reacted rates were obtained after PVP exposure compared to control and HA. In oocytes, viability significantly decreased after IVM in vitrified oocytes. Besides, IVM rates were not different between control denuded oocytes cultured with granulosa cells (DO-GC) and vitrified oocytes. Regarding fertilization parameters, IVF showed higher percentages of total fertilization rate than those obtained by ICSI and PICSI. However, results demonstrate that PICSI fertilization increased the blastocysts formation rate in control DO-GC and vitrified oocytes compared to IVF and ICSI.

Conclusions

To achieve high blastocyst formation rates from vitrified GV oocytes, it is recommended that sperm should be selected with HA instead of PVP before injection since high viability and acrosome reaction rates were obtained. Also, PICSI fertilization was the best method to produce higher blastocyst rates compared to the IVF and ICSI procedures.

Human cumulus cell sensitivity to vitrification, an ultrastructural study

SummaryCumulus cells (CCs) play an important role in the regulation of female gamete development, meiotic maturation, oocyte-sperm interaction, capacitation and acrosome reaction. However, their role in maintaining oocyte competence after vitrification is unclear as controversial data on their protecting action against oocyte cryoinjuries are available. Here we described the effects of vitrification on the ultrastructure of human CCs collected from women undergoing assisted reproductive technologies (ARTs). In total, 50 patches of CCs, sampled from high-quality human cumulus-oocyte complexes, were randomly allocated into two groups after patient informed consent: 1, fresh CCs (controls, n = 25); 2, vitrified CCs (n = 25). Samples were then prepared and observed by transmission electron microscopy. In fresh CCs, in which small cell clusters were visible, cell membranes were joined by focal gap junctions. Microvilli were rare and short. Nuclei, mitochondria, smooth endoplasmic reticulum (SER), Golgi apparatus and lipid droplets appeared well preserved; vacuoles were scarce. After vitrification, we observed two populations of CCs: light CCs, with a smooth appearance and few short microvilli; and dark CCs, with numerous and long microvilli. In both, most of the organelles appeared similar to those of fresh CCs. Lipid droplets were denser and more numerous, with respect to fresh CCs. They were mainly located in the peri-nuclear and sub-plasmalemmal regions. Numerous packed electron-negative vacuoles were visible. The vitrification procedure did not cause alterations in the fine structure of major organelles, except for an increased amount of lipid droplets and vacuoles. This specific sensitivity of human CCs to vitrification should be considered during ARTs.

Preincubation with glutathione ethyl ester improves the developmental competence of vitrified mouse oocytes

PURPOSE

Oocyte vitrification is currently used for human fertility preservation. However, vitrification damage is a problem caused by decreasing ooplasmic levels of glutathione (GSH). The GSH donor glutathione ethyl ester (GSH-OEt) can significantly increase the GSH content in oocytes. However, it is difficult to obtain oocyte from woman. To overcome this, we used mouse oocytes to replace human oocytes as a model of study.

METHODS

Oocytes from B6D2F1 mice were preincubated for 30 min with 2.5 mmol/L GSH-OEt (GSH-OEt group), without GSH-OEt preincubation before vitrification (control vitrification group) or in nonvitrified oocytes (fresh group). After thawing, oocytes were fertilized for evaluating the developmental competence of embryos in vitro and in vivo. Immunofluorescence, Polscope equipment and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to analyze damage, including mitochondrial distribution, reactive oxygen species (ROS) levels, spindle morphology, and gene expression levels (Bcl-2, BAX, and MnSOD).

RESULTS

The rates of fertilization, 3-4 cell, blastocyst formation and expanded blastocysts were significantly higher (p < 0.05) in the GSH-OEt group (90.4%; 91.1%; 88.9% and 63.0%) than in the control (80.0%; 81.4%; 77.7% and 50.5%). Provided embryos overcame the 2-cell block and developed to the blastocyst stage, birth rates of all groups were similar. Vitrification altered mitochondrial distribution, increased ROS levels, and caused abnormal spindle morphology; GSH-OEt preincubation could improve such damage. RT-qPCR showed that the expression of Bcl-2 was lower in the control group compared with the GSH-OEt group; BAX and MnSoD expression levels were higher in the control group than in the GSH-OEt group (p < 0.05).

CONCLUSIONS

The beneficial effect of GSH-OEt preincubation occurred before the 2-cell stage.

Vitrification of human immature oocytes before and after in vitro maturation: a review

The use of immature oocytes subjected to in vitro maturation (IVM) opens interesting perspectives for fertility preservation where ovarian reserves are damaged by pathologies or therapies, as in PCO/PCOS and cancer patients. Human oocyte cryopreservation may offer some advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation and postponing childbirth. It also eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In addition, a successful oocyte cryopreservation program could eliminate the need for donor and recipient menstrual cycle synchronization. Recent advances in vitrification technology have markedly improved the oocyte survival rate after warming, with fertilization and implantation rates comparable with those of fresh oocytes. Healthy live births can be achieved from the combination of IVM and vitrification, even if vitrification of in vivo matured oocytes is still more effective. Recently, attention is given to highlight whether vitrification procedures are more successful when performed before or after IVM, on immature GV-stage oocytes, or on in vitro matured MII-stage oocytes. In this review, we emphasize that, even if there are no differences in survival rates between oocytes vitrified prior to or post-IVM, reduced maturation rates of immature oocytes vitrified prior to IVM can be, at least in part, explained by underlying ultrastructural and biomolecular alterations.

Gene expression profile in heat-shocked Holstein and Nelore oocytes and cumulus cells

The present study determined the transcriptome profile in Nelore and Holstein oocytes subjected to heat shock during IVM and the mRNA abundance of selected candidate genes in Nelore and Holstein heat-shocked oocytes and cumulus cells (CC). Holstein and Nelore cows were subjected to in vivo follicle aspiration. Cumulus–oocyte complexes were assigned to control (38.5°C, 22 h) or heat shock (41°C for 12 h, followed by 38.5°C for 10 h) treatment during IVM. Denuded oocytes were subjected to bovine microarray analysis. Transcriptome analysis demonstrated 127, nine and six genes were differentially expressed between breed, temperature and the breed × temperature interaction respectively. Selected differentially expressed genes were evaluated by real-time polymerase chain reaction in oocytes and respective CC. The molecular motor kinesin family member 3A (KIF3A) was upregulated in Holstein oocytes, whereas the pro-apoptotic gene death-associated protein (DAP) and the membrane trafficking gene DENN/MADD domain containing 3 (DENND3) were downregulated in Holstein oocytes. Nelore CC showed increased transcript abundance for tight junction claudin 11 (CLDN11), whereas Holstein CC showed increased transcript abundance for antioxidant metallothionein 1E (MT1E) . Moreover, heat shock downregulated antioxidant MT1E mRNA expression in CC. In conclusion, oocyte transcriptome analysis indicated a strong difference between breeds involving organisation and cell death. In CC, both breed and temperature affected mRNA abundance, involving cellular organisation and oxidative stress.

Glycine increases preimplantation development of mouse oocytes following vitrification at the germinal vesicle stage

Ice-free cryopreservation, referred to as vitrification, is receiving increased attention in the human and animal assisted reproduction. However, it introduces the detrimental osmotic stress by adding and removing high contents of cryoprotectants. In this study, we evaluated the effects of normalizing cell volume regulation by adding glycine, an organic osmolyte, during vitrification of mouse germinal vesicle stage oocyte and/or subsequent maturation on its development. The data showed that glycine supplementation in either vitrification/thawing or maturation medium significantly improved the cytoplasmic maturation of MII oocytes manifested by spindle assembly, chromosomal alignment, mitochondrial distribution, euploidy rate, and blastocyst development following fertilization in vitro, compared to the control without glycine treatment. Furthermore, glycine addition during both vitrification/thawing and maturation further enhanced the oocyte quality demonstrated by various markers, including ATP contents and embryo development. Lastly, the effect of anti-apoptosis was also observed when glycine was added during vitrification. Our result suggests that reducing osmotic stress induced by vitrification could improve the development of vitrified mouse oocyte.

Incidence of methylated histones H3K4 and H3K79 in cat germinal vesicles is regulated by specific nuclear factors at the acquisition of developmental competence during the folliculogenesis

PURPOSE

This study aims to characterize the regulations of histone methylations, key epigenetic markers of oocyte competence, in germinal vesicle (GV) from different follicles (preantral, early, small, or large antral stage) using the domestic cat model.

METHODS

In Experiment 1, the incidence of H3K4me3 or H3K79me2 was determined in GVs from the diverse follicle stages directly or after exposure to (1) a methyltransferase inhibitor, (2) sonication to fracture the cytoplasmic membranes and wash away the cytoplasmic content, or (3) methyltransferase inhibitor followed by sonication. In Experiment 2, the presence and maintenance of nuclear methyltransferases SMYD3 and DOT1L (regulating H3K4me3 and H3K79me2, respectively) was characterized in separate GV stages before and after sonication. Functionality of GVs from the various follicle stages (with or without transient isolation from the cytoplasm) then was assessed in Experiment 3 by transfer into recipient competent oocytes.

RESULTS

The incidence of histones H3K4me3 and H3K79me2 within the GV were influenced by the cytoplasmic environment at all stages except at the transition to the early antral stage where nuclear regulating factors appeared to be mainly involved. The methyltransferase SMYD3 and DOT1L also appeared tightly bound to the nucleus at that transition. Interestingly, oocytes reconstructed with a GV isolated from the cytoplasm for a prolonged period had the capacity to form an embryo after fertilization which proved that communication between the donor GV and the host cytoplasm (likely including the regulation of epigenetic factors) could be restored.

CONCLUSIONS

Histone methylation apparently becomes regulated by specific nuclear factors at the acquisition of competence during the folliculogenesis and does not seem to be disrupted by prolonged isolation from the surrounding cytoplasm.

Morphometric and Ultrastructure studies of Primordial Follicles and Expression of Estrogen-dependent Genes in the Ovaries of Domestic Cats

The aim of this study was to compare and estimate the population of the primordial follicle morphometrically and ultrastructurally in the left and right side ovaries of 10 ovariohysterectomied healthy domestic shorthair cats. The ovaries were processed for light microscopy, electron microscopy, and estrogen-dependent gene expression for assessments. A total of 15,092 primordial follicles with and without a nucleus were examined and counted. A total of 6842 primordial follicles with a nucleus were examined and counted. The light-microscopy numerical data were collected from two histological sections per ovary for a total of 20 sections from the left ovary and 20 sections from the right ovary. The average surface area of the histological sections was 645.99 mm². The number of tertiary follicles was found to be higher in the left ovaries than in the right ovaries. The primordial follicles are under the tunica albuginea at various levels. Some are crowded or scattered in one or two rows, although at times, there were areas without any primordial follicles. The primordial follicles varied in size, and were surrounded by 4–10 squamous granulosa cells. Some primordial follicles shared their ooplasm with one or two neighboring primordial follicles, forming a giant primordial follicle with two or three nuclei. The ultrastructure of the primordial follicles showed rounded nuclei with distinct nucleoli, rounded and elongated mitochondria, and a considerably thick basement membrane under the granulosa cells. The squamous granulosa cells showed well-developed microvilli intermingled with the microvilli of the oocyte oolemma. Elongated mitochondria, coated pits, multicytoplasmic vesicles, ribosomes, and Golgi apparatuses were obvious in the oocyte ooplasm. Large vesicles contain small multivesicles and some scattered lipid globules in the ooplasm. There were estrogen-dependent gene-expression differences between the right and left ovaries. Further gene research is in the plan, using a larger pool of cats, with a focus on age differences.

Vitrification by Cryotop and the Maturation, Fertilization, and Developmental Rates of Mouse Oocytes

Background:

Oocyte cryopreservation is an important part of modern fertility treatment. The effect of vitrification on the fertilization and developmental rates of embryo is still a matter of debate.

Objectives:

This study aimed to investigate the effect of vitrification on the success of mouse oocyte maturation, fertilization, and preimplantation development in vitro.

Materials and Methods:

In this experimental study, a total of 200 germinal vesicle (GV) and 200 metaphase II (MII) oocytes were obtained from ovaries and fallopian tubes of NMRI mice, respectively and divided into two control and experimental (vitrified) groups. Oocytes in the experimental group were vitrified by Cryotop using vitrification medium (Origio, Denmark) and kept in liquid nitrogen for one month. Then, they were cultured in maturation medium for 24 hours. In vitro maturated metaphase 2 (IVM-MII) and ovulated metaphase 2 (OV-MII) oocytes were inseminated and the fertilized embryos assessed until the hatching blastocyst stage. Outcomes were assessed for statistical significance by Chi-square test using SPSS software.

Results:

Vitrification caused a significant reduction in the maturation rate of oocytes. Of those that matured, the fertilization rate of vitrified IVM-MII (44.1%) and OV-MII oocytes (50%) was not significantly different from each other but both were significantly lower than the control group (P < 0.05). There was no significant difference in developmental rates of both vitrified groups and the control group.

Conclusions:

The present study showed that vitrification using Cryotop and freezing medium can damage oocytes by reducing the maturation and fertilization rates in both developmental stages.

Changes in mitochondrial function in porcine vitrified MII-stage oocytes and their impacts on apoptosis and developmental ability

The purpose of this study was to investigate the changes in mitochondria in porcine MII-stage oocytes after open pulled straw (OPS) vitrification and to determine their roles in apoptosis and in vitro developmental ability. The mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS) level, adenosine-5'-triphosphate (ATP) concentration, mitochondrial distribution, mitochondrial ultrastructure, early-stage apoptosis with Annexin V-FITC staining, survival rate, parthenogenetic developmental ability and related gene expression were measured in the present experiments. The results showed that: (1) the mitochondrial ΔΨm of vitrified-thawed oocytes (1.05) was lower than that of fresh oocytes 1.24 (P<0.05). (2) ROS level in the OPS vitrification group was much higher than that of the fresh group, while the ATP concentration was much lower than that of fresh group (P<0.05). (3) Early-stage apoptosis rate from the OPS vitrification group (57.6%) was much higher than that of fresh group (8.53%) (P<0.05), and the survival rate and parthenogenetic cleavage rate of OPS vitrified oocytes were much lower than those from fresh ones (P<0.05). (4) Vitrification not only disrupted the mitochondrial distribution of porcine MII-stage oocytes, but also damaged the mitochondrial ultrastructure. (5) After vitrification, the gene expression level of Dnm1 was up-regulated, and other four genes (SOD1, Mfn2, BAX and Bcl2) were down-regulated. The present study suggested that not only the morphology and function of mitochondria were damaged greatly during the vitrification process, but also early-stage apoptosis was observed after vitrification. Intrinsic mitochondrial pathway could be in involved in the occurrence of apoptosis in vitrified-thawed porcine oocytes.

Evaluation of the impact of vitrification on the actin cytoskeleton of in vitro matured ovine oocytes by means of Raman microspectroscopy

PURPOSE

Investigation of the changes induced by vitrification on the cortical F-actin of in vitro matured ovine oocytes by Raman microspectroscopy (RMS).

METHODS

Cumulus-oocyte complexes, recovered from the ovaries of slaughtered sheep, were matured in vitro and vitrified following the Minimum Essential Volume method using cryotops. The cortical region of metaphase II (MII) oocytes (1) exposed to vitrification solutions but not cryopreserved (CPA-exp), (2) vitrified/warmed (VITRI), and (3) untreated (CTR) was analyzed by RMS. A chemical map of one quadrant of single CPA-exp, VITRI and CTR oocytes was, also, performed. In order to identify the region of Raman spectra representative of the cortical F-actin modification, a group of in vitro matured oocytes were incubated with latrunculin-A (LATA), a specific F-actin destabilizing drug, and processed for RMS analysis. Thereafter, all the oocytes were stained with rhodamine phalloidin and evaluated by fluorescence confocal microscopy. Raman spectra of the oocytes were, statistically, analyzed using Principal Component Analysis (PCA).

RESULTS

The PCA score plots showed a marked discrimination between CTR oocytes and CPA-exp/ VITRI groups. The main differences, highlighted by PCA loadings, were referable to proteins (1657, 1440 and 1300 cm(-1)) and, as indicated by LATA experiments, also included the changes of the F-actin. Analysis by confocal microscopy revealed a clear alteration of the cortical F-actin of CPA-exp and VITRI oocytes confirming RMS results.

CONCLUSIONS

Raman microspectroscopy may represent an alternative analytical tool for investigating the biochemical modification of the oocyte cortex, including the F-actin cytoskeleton, during vitrification of in vitro matured ovine oocytes.

Effects of histone acetylation status on the early development of in vitro porcine transgenic cloned embryos

The purpose of this study was to investigate the effects of the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) on transgene expression and development of porcine transgenic cloned embryos, specifically focusing on effects derived from TSA-treated donor cells or TSA-treated reconstructed embryos. The results showed that TSA treatment on reconstructed embryos modified the acetylation status, which significantly improved the development of porcine somatic cell nuclear transfer (SCNT) embryos in vitro, but not donor cells. Furthermore, the treatment of reconstructed embryos with TSA enhanced expression of the pluripotency-related gene POU5F1 and stimulated expression of the anti-apoptotic gene BCL-2. Enhanced green fluorescent protein (EGFP) mRNA expression of every group dropped drastically from donor cells to blastocysts. Interestingly, TSA is likely to prevent a decline in EGFP expression in nuclear reprogramming of porcine SCNT embryos. However DNA hypomethylation induced by modified histone acetylation of donor cells treated with TSA was significantly more effective in increasing EGFP expression in SCNT blastocysts. In conclusion, the acetylation status of both donor cells and reconstructed embryos modified by TSA treatment increased transgene expression and improved nuclear reprogramming and the developmental potential of porcine transgenic SCNT embryos.

Optimizing electrical activation of porcine oocytes by adjusting pre- and post-activation mannitol exposure times

Modifying electrical activation conditions have been used to improve in vitro embryo production and development in pigs. However, there is insufficient information about correlations of porcine embryo development with oocyte pre- and post-activation conditions. The purpose of this study was to compare the developmental rates of porcine oocytes subjected to different mannitol exposure times, either pre- or post-electrical activation, and to elucidate the reason for the optimal mannitol exposure time. Mannitol exposure times around activation were adjusted as 0, 1, 2 or 3 min. Blastocyst development were checked on day 7. Exposure of oocytes to mannitol for 1 or 2 min before electrical activation produced significantly higher blastocyst rates than exposure for 0 or 3 min. There was no significant difference in blastocyst rates when activated oocytes were exposed to mannitol for 0, 1, 2 or 3 min after electrical activation. While exposure of oocytes to mannitol for 1 min pre- and 3 min post-activation showed significantly higher blastocyst development than 0 min pre- and 0 min post-activation. It also showed higher maintenance of normal oocyte morphology than exposure for 0 min pre- and 0 min post-activation. In conclusion, exposure of oocytes to mannitol for 1 min pre- and 3 min post-activation seems to be optimal for producing higher in vitro blastocyst development of porcine parthenogenetic embryos. The higher blastocyst development is correlated with higher maintenance of normal morphology in oocytes exposed to mannitol for 1 min pre- and 3 min post-activation.

Ultrastructure of immature and mature human oocytes after cryotop vitrification

In vitro maturation of vitrified immature germinal vesicle (GV) oocytes is a promising fertility preservation option. We analyzed the ultrastructure of human GV oocytes after Cryotop vitrification (GVv) and compared it with fresh GV (GVc), fresh mature metaphase II (MIIc) and Cryotop-vitrified mature (MIIv) oocytes. By phase contrast microscopy and light microscopy, the oolemmal and cytoplasmic organization of fresh and vitrified oocytes did not show significant changes. GVv oocytes showed significant ultrastructural alterations of the microvilli in 40% of the samples; small vacuoles and occasional large/isolated vacuoles were abnormally present in the ooplasm periphery of 50% of samples. The ultrastructure of nuclei and mitochondria-vesicle (MV) complexes, as well as the distribution and characteristics of cortical granules (CGs), were comparable with those of GVc oocytes. MIIv oocytes showed an abnormal ultrastructure of microvilli in 30% of the samples and isolated large vacuoles in 70% of the samples. MV complexes were normal, but mitochondria-smooth endoplasmic reticulum aggregates appeared to be of reduced size. CGs were normally located under the oolemma but presented abnormalities in distribution and matrix electron density. In conclusion, Cryotop vitrification preserved main oocyte characteristics in the GV and MII stages, even if peculiar ultrastructural alterations appeared in both stages. This study also showed that the GV stage appears more suitable for vitrification than the MII stage, as indicated by the good ultrastructural preservation of important structures that are present only in immature oocytes, like the nucleus and migrating CGs.

The effect of vitrification on mouse oocyte apoptosis by cryotop method

BACKGROUND

Oocyte cryopreservation is one of the most important topics in the field of assisted reproductive technology to preserve women fertility, but relationship between cryopreservation and apoptosis is still a matter of debate. The present study was aimed to investigate the effects of vitrification on apoptosis in mouse oocytes by Cryotop method.

METHOD

A total of 200 germinal vesicle (GV) and 200 metaphase II (MII) oocytes were obtained from ovaries and fallopian tubes of NMRI mice, respectively and divided into control and experimental groups. Oocytes in experimental group were vitrified by Cryotop using vitrification medium and were kept in liquid nitrogen for one month. The survival rate of oocytes was evaluated after 2 hour incubation time. Then, the oocyte apoptosis was evaluated by TUNEL technique and compared with those in control group. The data was compared statistically using SPSS software and chi-square test.

RESULTS

The survival rates of vitrified GV (93%) and MII oocytes (88%) showed a significant decrease compared with the control group (P<0.05), but there was no significant difference in survival rate of both vitrified oocyte groups. The incidence of apoptosis in vitrified and control GV oocytes showed no significant difference (13% vs. 7%), but the rate of apoptosis in vitrified MII oocytes increased significantly not only in comparison with MII control group (25% vs. 5%) but also with vitrified GV oocytes (P<0.05).

CONCLUSION

The results indicate that vitrification increases apoptosis in mouse MII oocytes and apoptosis may play a role in MII oocyte injury after vitrification.

The impact of vitrification on immature oocyte cell cycle and cytoskeletal integrity in a rat model

PURPOSE

To test the effects of varying vitrification protocols on the cell cycle status and chromosomal integrity in cumulus-enclosed GV stage rat oocytes.

METHODS

Vitrified and thawed rat oocytes were labeled with fluorescent markers for chromatin, cell cycle activation, and f-actin and analyzed by conventional and laser scanning confocal microscopy.

RESULTS

In all vitrification groups, significant alterations in cumulus cell connectivity, cell cycle status, and cytoplasmic actin integrity were observed following warming compared to fresh control oocytes. Based on the protein phosphorylation marker MPM-2, it is clear that warmed oocytes rapidly enter M-phase but are unable to maintain chromosome integrity as a result of multiple chromatin fusions. A prominent reduction in f-actin is evident in both the ooplasm and at the cortex of vitrified oocytes. Finally, an irreversible but irregular retraction of TZPs occurs on the majority of oocytes subjected to any of the vitrification protocols.

CONCLUSIONS

These findings draw attention to undesirable consequences of immature oocyte vitrification that compromise cell cycle status and chromatin and cytoskeleton integrity that may not be evident until after fertilization.

Increase in histone methylation in the cat germinal vesicle related to acquisition of meiotic and developmental competence

This study identified specific changes in histone lysine methylation patterns of the feline germinal vesicle (GV) during pre-antral-to-antral follicle transition, the latter being a key interval for competence acquisition. Oocytes from adult cats were isolated from pre-antral, early (≤ 0.5 mm diameter), small (0.6-1 mm) or large (1-3.5 mm) antral follicles and immuno-stained with anti-histones H3 trimethylated at lysine 9 (H3K9me3), lysine 4 (H3K4me3), lysine 27 (H3K27me3) or H3 dimethylated at lysine 79 (H3K79me2). The vast majority of oocytes (range, 72.2-85.4%; p > 0.05) contained a GV with H3K9me3 or H3K27me3, regardless of follicular stage/size. However, the proportion of GVs with H3K4me3 or H3K79me2 was higher in early antral follicles (42.6%; p < 0.05) compared with other stages (range, 12.1-15.2%). Therefore, H3K4me3 and H3K79me2 (both known to be associated with selective gene activation) appear to be reliable markers of onset of GV competence during the pre-antral-to-antral transition phase. By contrast, H3K9me3 and H3K27me3 (both known to be related to selective gene repression) seem more linked to expression patterns during the GV stage and are less useful indicators during the entire folliculogenesis interval.

Nuclear maturation and embryo development of porcine oocytes vitrified by cryotop: effect of different stages of in vitro maturation

The present study was designed to evaluate the viability, meiotic competence and subsequent development of porcine oocytes vitrified using the cryotop method at different stages of in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were cultured in IVM medium supplemented with 1mM dibutyryl cAMP (dbcAMP) for 22 h and then for an additional 22 h without dbcAMP in the medium. Germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I (MI), anaphase I/telophase I (AI/TI) and metaphase II (MII) were found to occur predominantly at 0-22, 26, 32, 38 and 44 h of IVM, respectively. Oocytes were exposed to cryoprotectant (CPA) or vitrified after different durations of IVM (0, 22, 26, 32, 38 and 44 h). After CPA exposure and vitrification, surviving oocytes that were treated before completion of the 44 h maturation period were placed back into IVM medium for the remaining maturation period, and matured oocytes were incubated for 2h. CPA treatment did not affect the viability of oocytes matured for 26, 32, 38 or 44 h, but significantly decreased survival rate of oocytes matured for 0 or 22 h. CPA treatment had no effect on the ability of surviving oocytes to develop to the MII stage regardless of the stage during IVM; however, blastocyst formation following PA was severely lower (P<0.05) than that in the control. At 2h post-warming, the survival rates of oocytes vitrified at 26, 32, 38 and 44 h of IVM were similar but were higher (P<0.05) than those of oocytes vitrified at 0 or 22 h of IVM. The MII rates of surviving oocytes vitrified at 0 and 38 h of IVM did not differ from the control and were higher (P<0.05) than those of oocytes vitrified at 22, 26 or 32 h of IVM. After parthenogenetic activation (PA), both cleavage and blastocyst rates of vitrified oocytes matured for 22, 26, 32, 38 and 44 h did not differ, but all were lower (P<0.05) than those matured 0 h. In conclusion, our data indicate that survival, nuclear maturation and subsequent development of porcine oocytes may be affected by their stage of maturation at the time of vitrification; a higher percentage of blastocyst formation can be obtained from GV oocytes vitrified before the onset of maturation.

A possible strategy to produce pigs resistant to porcine reproductive and respiratory syndrome virus

The purpose of this study was to enhance the production of transgenic cloned embryos with porcine reproductive and respiratory syndrome virus (PRRSV) shRNA expression cassettes. To construct transgenic vector with expression targeting against PRRSV, PRRSV shRNA expression cassettes were inserted into pEGFP-N1 and the ability of resulting recombinant plasmid pEGFP-G1 inhibiting virus replication was examined in Marc-145 cells. Results showed that PRRSV replication could be significantly inhibited by pEGFP-G1 in Marc-145 cells compared with the control. The pEGFP-G1 plasmid was used to deliver a transgene expressing EGFP and the PRRSV shRNA into porcine fetal fibroblasts (PFF). Fluorescent-positive cells were used as nuclear donors for somatic cell nuclear transfer (SCNT) to produce shRNA-EGFP transgenic cloned embryos. The effects of trichostatin A (TSA) on production of transgenic cloned embryos were investigated. Reconstructed embryos were designed into 4 groups: Donor cells of Group A were treated with 50nM TSA for 24h before SCNT. Reconstructed embryos of Group B were treated with 50nM TSA for 24h after activation. Both donor cells and reconstructed embryos in Group C were treated with TSA and Group D were the control without TSA treatment. The results showed no difference (p>0.05) in cleavage rates among the 4 groups; however, blastocyst developmental rates of Group B and C (30.9% and 42.0%, respectively) were higher than for Group A and D (21.2% and 22.1%, respectively) with Group C highest among groups (p<0.05). Interestingly, EGFP expression intensity of transgenic cloned blastocysts of Group A was the highest. Our results provide promising evidence toward a new approach for production of transgenic cloned pigs with resistance to PRRSV and possibly a wide variety of other porcine diseases.

Vitrification procedure decreases inositol 1,4,5-trisphophate receptor expression, resulting in low fertility of pig oocytes

Although cryopreservation of mammalian oocytes is an important technology, it is well known that unfertilized oocytes, especially in pigs, are highly sensitive to low temperature and that cryopreserved oocytes show low fertility and developmental ability. The aim of the present study was to clarify why porcine in vitro matured (IVM) oocytes at the metaphase II (MII) stage showed low fertility and developmental ability after vitrification. In vitro matured cumulus oocyte complexes (COCs) were vitrified with Cryotop and then evaluated for fertility through in vitro fertilization (IVF). Although sperm-penetrated oocytes were observed to some extent (30-40%), the rate of pronuclear formation was low (9%) and none of them progressed to the two-cell stage. The results suggest that activation ability of cryopreserved oocytes was decreased by vitrification. We examined the localization and expression level of the type 1 inositol 1,4,5 trisphosphate receptor (IP3 R1), the channel responsible for Ca(2+) release during IVF in porcine oocytes. Localization of IP3 R1 close to the plasma membrane and total expression level of IP3 R1 protein were both decreased by vitrification. In conclusion, our present study indicates that vitrified-warmed porcine COCs showed a high survival rate but low fertility after IVF. This low fertility seems to be due to the decrease in IP3 R1 by the vitrification procedure.

Preparation of mammalian oocytes for transmission electron microscopy

The visualization of subcellular organelles and structures is a valuable tool for understanding cellular changes that occur in oocytes and early embryos as a result of genetic alterations, incubation conditions, drug treatments, and many other manipulations. Preparing oocytes for transmission electron microscopic analysis can be challenging as these cells cannot be visualized without a microscope and they are more susceptible to mechanical disruption during manipulation. Here we describe methods for immobilizing oocytes on either a solid surface or within a matrix and then document our embedding techniques which work well for preserving the ultrastructure of the mouse oocyte.

Supplementation of maturation medium with L-carnitine improves cryo-tolerance of bovine in vitro matured oocytes

The objective was to determine the effects of adding L-carnitine (an enhancer of lipid metabolism) during IVM, on cryotolerance and developmental competence of bovine oocytes. Oocytes matured in the absence (control) or presence (0.6 mg/mL) of L-carnitine were subjected to IVF and embryo culture after Cryotop vitrification or nonvitrification at the metaphase stage of the second meiotic cell division. Cleavage and blastocyst formation rates, and inner cell mass and trophectoderm cell numbers were determined. Also, ATP content in IVM oocytes was measured and intracellular lipid droplets were observed (Nile red staining and confocal microscopy). L-carnitine had no significant effect on the rate of matured oocytes. Vitrification reduced (P < 0.05) mean (±SEM) rates of live oocytes both in control (80.6 ± 1.9%) and L-carnitine groups (82.7 ± 5.1%) compared with nonvitrified oocytes (100%). After IVF, cleavage rates of vitrified control and L-carnitine groups (56.5 ± 3.9% and 62.8 ± 5.1%, respectively) were significantly lower than those in nonvitrified control and L-carnitine groups (83.9 ± 4.2% and 84.3 ± 1.3%). After vitrification, blastocyst formation rate in the L-carnitine group (54.4 ± 5.2%) was significantly higher compared with the control (34.9 ± 4.4%), and did not significantly differ from those in nonvitrified control and L-carnitine groups (52.1 ± 4.2% and 52.8 ± 3.0%). The numbers and ratio of inner cell mass and trophectoderm cells in blastocysts did not differ significantly among groups. The ATP content in L-carnitine-treated oocytes tended to be higher compared with the control. Vitrification did not reduce ATP content in oocytes, irrespective of L-carnitine treatment. Treatment with L-carnitine dislocated lipid droplets from the peripheral area to the inner cytoplasm. In conclusion, L-carnitine supplementation during IVM redistributed lipid droplets in oocytes; if they survived vitrification, their developmental competence was similar to that of nonvitrified oocytes.