The dynamics of in vitro maturation of germinal vesicle oocytes

Usable blastocysts developed from in-vitro-matured metaphase I oocytes in preimplantation genetic testing cycles

RESEARCH QUESTION

Are blastocysts derived from in-vitro-matured metaphase I (MI) oocytes less likely to produce usable embryos for transfer compared with those derived from in-vivo-matured oocytes in cycles undergoing preimplantation genetic testing (PGT)?

DESIGN

The primary outcome was usable blastocyst rate, which was compared between blastocysts derived from in-vitro-matured MI oocytes after ovarian stimulation and from in-vivo-matured oocytes. Logistic regression analysis using generalized estimating equations was used to control for confounders in the analysis of factors that may influence the chance of a blastocyst being usable and in the comparison of embryological outcomes. Student's t-test, Mann-Whitney U test, chi-squared tests or Fisher's exact tests were used to compare clinical and pregnancy outcomes.

RESULTS

A total of 1810 injected metaphase II (MII) oocytes from 154 PGT cycles involving 154 couples were included in this study. A total of 1577 MII oocytes were in-vivo-matured and 233 were in-vitro-matured MI oocytes. The usable blastocyst rate was similar between the in-vitro-matured MI oocyte group and the in-vivo-matured oocyte group (adjusted RR 0.97, 95% CI 0.40 to 2.34). Three live births were achieved using usable blastocysts derived from in-vitro-matured MI oocytes.

CONCLUSIONS

If in-vitro-matured MI oocytes can be fertilized and develop into blastocysts, their ability to provide usable embryos for transfer is similar compared with those developed from in-vivo-matured oocytes. These blastocysts could be considered valuable for women with few viable embryos in assisted reproductive technology cycles.

Regulation of proteolysis in bovine cumulus cells with possible inclusion of proton pump activators

PURPOSE

To reveal the effects of V-ATPase proton pump activation on lysosomal acidity and protein degradation in cultured cumulus cells.

METHODS

Cumulus cells from bovine ovaries were cultured in the presence of 10 and 50 μM doses of V-ATPase proton pump activators PIP2, PMA, and DOG for 12 and 24 hours. At the end of the culture period, the level of protein degradation was evaluated through DQ-Red-BSA analysis and the lysosomes were detected through a fluorescent probe. In addition, total and phosphorylated MAPK1/3 and AKT protein levels of cumulus cells were determined through western blotting.

RESULTS

PIP2 and PMA were shown to increase protein degradation and lysosomal acidity in cultured bovine cumulus cells, whereas DOG did not have any significant effects on these cells. Total and phosphorylated MAPK and AKT protein levels were higher in PIP2 and PMA groups compared to the control and DOG.

CONCLUSION

Particular proton pump activators can enhance protein degradation and lysosomal acidification in cultured bovine cumulus cells without having detrimental effects on cell signaling members required for cell viability and proper functioning. Due to the cellular interactions, increasing the lysosomal activity in cumulus cells in the culture environment could also affect the removal of protein aggregates in the oocytes. This strategy could be effective for improving in vitro maturation of the oocytes by providing proteostasis.

Potential Development of Vitrified Immature Human Oocytes: Influence of the Culture Medium and the Timing of Vitrification

How does the in vitro maturation (IVM) medium and the vitrification procedure affect the survival of germinal vesicle (GV) oocytes obtained from stimulated cycles and their development to the blastocyst stage? In total, 1085 GV human oocytes were obtained after women underwent a cycle of controlled ovarian stimulation, and these oocytes were subjected to IVM before or after their vitrification. IVM was carried out in two commercial culture media not specifically designed for maturation. MII oocytes were then activated and embryo development until day 6 was evaluated. According to the results, a higher percentage of oocytes reach the MII stage if they are vitrified before they undergo IVM. Nevertheless, the medium used and the sample size determine whether these differences become significant or not. Similar survival rates and development to blastocysts were observed in all the conditions studied.

Comparative single-cell transcriptomic profiles of human androgenotes and parthenogenotes during early development

OBJECTIVE

To unravel the differential transcriptomic behavior of human androgenotes (AGs) and parthenogenotes (PGs) throughout the first cell cycles, analyze the differential expression of genes related to key biologic processes, and determine the time frame for embryonic genome activation (EGA) in AGs and PGs.

DESIGN

Laboratory study.

SETTING

Private fertility clinic.

PATIENT(S)

Mature oocytes were retrieved from healthy donors and subjected to artificial oocyte activation using calcium ionophore and puromycin to generate PGs (n = 6) or enucleated and subjected to intracytoplasmic sperm injection to generate AGs (n = 10).

INTERVENTION(S)

Uniparental constructs at different early stages of development were disaggregated into constituent single cells (we suggest the terms parthenocytes and androcytes) to characterize the single-cell transcriptional landscape using next-generation sequencing.

MAIN OUTCOMES MEASURE(S)

Transcriptomic profiles comparison between different stages of early development in AGs and PGs.

RESULT(S)

The uniparental transcriptomic profiles at the first cell cycle showed 68 down-regulated and 26 up-regulated differentially expressed genes (DEGs) in PGs compared with AGs. During the third cell cycle, we found 60 up-regulated and 504 down-regulated DEGs in PGs compared with AGs. In the fourth cell cycle, 1,771 up-regulated and 1,171 down-regulated DEGs were found in PGs compared with AGs. The AGs and PGs had reduced EGA profiles during the first 3 cell cycles, and a spike of EGA at the fourth cell cycle was observed in PGs.

CONCLUSION(S)

Transcriptomic analysis of AGs and PGs revealed their complementary behavior until the fourth cell cycle. Androgenotes undergo a low wave of transcription during the first cell cycle, which reflects the paternal contribution to cell cycle coordination, mechanics of cell division, and novel transcription regulation. Maternal transcripts are most prominent in the third and fourth cell cycles, with amplification of transcription related to morphogenic progression and embryonic developmental competence acquisition. Regarding EGA, in PGs, a primitive EGA begins at the 1-cell stage and gradually progresses until the 4-cell stage, when crucial epigenetic reprogramming (through methylation) is up-regulated. In addition, our longitudinal single-cell transcriptomic analysis challenges that the zygote and early cleavage stages are the only totipotent entities, by revealing potential totipotency in cleavage-stage AGs and implications of paternal transcripts.

Single-cell transcriptome and translatome dual-omics reveals potential mechanisms of human oocyte maturation

The combined use of transcriptome and translatome as indicators of gene expression profiles is usually more accurate than the use of transcriptomes alone, especially in cell types governed by translational regulation, such as mammalian oocytes. Here, we developed a dual-omics methodology that includes both transcriptome and translatome sequencing (T&T-seq) of single-cell oocyte samples, and we used it to characterize the transcriptomes and translatomes during mouse and human oocyte maturation. T&T-seq analysis revealed distinct translational expression patterns between mouse and human oocytes and delineated a sequential gene expression regulation from the cytoplasm to the nucleus during human oocyte maturation. By these means, we also identified a functional role of OOSP2 inducing factor in human oocyte maturation, as human recombinant OOSP2 induced in vitro maturation of human oocytes, which was blocked by anti-OOSP2. Single-oocyte T&T-seq analyses further elucidated that OOSP2 induces specific signaling pathways, including small GTPases, through translational regulation.

Development of methods for simultaneous single cell analysis of transcription and translation is still underway. Here, Hu et al. develop single-cell transcriptome and translatome dual-omics on human oocytes, which enables them to identify OOSP2 as an induction factor during human oocyte maturation.

Ultrastructural Evaluation of the Human Oocyte at the Germinal Vesicle Stage during the Application of Assisted Reproductive Technologies

After its discovery in 1825 by the physiologist J.E. Purkinje, the human germinal vesicle (GV) attracted the interest of scientists. Discarded after laparotomy or laparoscopic ovum pick up from the pool of retrieved mature oocytes, the leftover GV was mainly used for research purposes. After the discovery of Assisted Reproductive Technologies (ARTs) such as in vitro maturation (IVM), in vitro fertilization and embryo transfer (IVF-ET) and intracytoplasmic sperm injection (ICSI), its developing potential was explored, and recognized as an important source of germ cells, especially in the case of scarce availability of mature oocytes for pathological/clinical conditions or in the case of previous recurrent implantation failure. We here review the ultrastructural data available on GV-stage human oocytes and their application to ARTs.

Analysis of maturation dynamics and developmental competence of in vitro matured oocytes under time-lapse monitoring

BACKGROUND

To improve the developmental competence of in vitro cultured oocytes, extensive literature focused on maturation rate improvement with different additives in culture medium, while studies investigating the maturation dynamics of oocytes during in vitro maturation (IVM) and the influencing factors on oocyte viability are scarce.

METHODS

The study involved a retrospective observation by time-lapse monitoring of the IVM process of 157 donated GV oocytes from 59 infertile couples receiving ICSI in 2019, in Tongji Hospital, Wuhan, China. The GV oocytes derived from controlled ovarian hyperstimulation (COH) cycles underwent rescue IVM (R-IVM), and the maturation dynamics, including GVBD time (GV-MI), time from GVBD to maturation (MI-MII), maturation time (GV-MII), and MII arrest duration (MII-ICSI), were recorded by time-lapse monitoring. The matured oocytes were inseminated at different MII arrest points and subsequent embryo developments were assessed. The effects of baseline clinical characteristics, oocyte diameters, and maturation dynamics on the developmental competence of the oocytes were also analyzed.

RESULTS

Totally, 157 GV oocytes were collected. GVBD happened in 111 oocytes, with a median GV-MI duration of 3.7 h. The median MI-MII duration was 15.6 h and the median GV-MII duration was 19.5 h. The maturation rate reached 56.7% at 24 h and 66.9% at 48 h, and the clinical factors, including patient age, FSH level, AMH level, ovarian stimulation protocol, and serum estradiol and progesterone levels on hCG trigger day, showed no effects on the 24-h maturation rate. The normal fertilization rate of oocytes resuming meiosis within 8 h and matured within 24 h was significantly higher than that of oocytes resuming meiosis after 8 h and matured after 24 h. Furthermore, among those oocytes matured within 24 h, the high-quality embryo formation rate of oocytes resuming meiosis within 4.5 h and matured within 19 h was significantly higher. All stated time was measured from the start point of IVM. Additionally, for oocytes from patients with serum progesterone levels less than 1 ng/ml on hCG trigger day, the high-quality embryo formation rate was significantly increased.

CONCLUSION

R-IVM technology could increase the available embryos for patients in routine COH cycles, but excessive culture beyond 24 h is not recommended. GV-MI duration of the oocyte, recorded by time-lapse system, and serum progesterone levels of patients on hCG trigger day can significantly affect the developmental potential of the IVM oocytes.

A Study to Find Optimal Intra-cytoplasmic Sperm Injection Timing of Oocytes Matured from Germinal Vesicle in in Vitro Maturation Cycles Using a Time Lapse System

BACKGROUND

The use of in vitro maturation (IVM) has allowed patients with polycystic ovary syndrome (PCOS) to have a positive fertility outcome, as it allows utilisation of immature oocytes to mature in vitro.

AIM

The aim of the study is to establish an optimum intra-cytoplasmic sperm injection (ICSI) timing for IVM oocytes (germinal vesicles [GV] →, metaphase I [MI]→ and metaphase II [MII]) using time lapse system (TLS) for patients with PCOS.

SETTING AND DESIGN

Patients included in this study were diagnosed with PCOS, ≤35 years of age, anti-Müllerian hormone levels >6 ng/ml and antral follicle counts <40. Furthermore, we included only GV oocytes at the time of denudation in our study.

MATERIALS AND METHODS

Patients were minimally stimulated and their oocytes were retrieved. In vitro maturated oocytes were monitored using TLS to a maximum of 30 h. MII oocytes were further cultured and injected at five different time intervals (1-2 h, 3-4 h, 5-6 h, 7-8 h and >8 h) to observe for fertilisation, cleavage and utilisation rate.

STATISTICAL ANALYSIS

Chi-square test was applied to compared the treatment groups.

RESULTS

Amongst 328 oocytes retrieved from 27 female patients, 162 oocytes were in the time-monitored cohort and 162 oocytes were grouped as the control cohort. Maturation rate between GV→ MII was highest at 18 h in the time-monitored cohort MII (n = 57). Utilisation rate was highest when ICSI was performed between 5 and 6 h after the first polar body extrusion, n = 17 (63%).

CONCLUSION

This study provides valuable insight into the optimal maturation timing using a TLS to yield the good number of oocytes. In addition, optimising ICSI timing is important to provide the best utilisation rate in an IVM cycle to achieve synchrony between nuclear and cytoplasmic maturation.

Developmental potential of immature human oocytes aspirated after controlled ovarian stimulation

PURPOSE

Intracytoplasmic sperm injection (ICSI) for initially immature oocytes that mature in vitro is controversial and practice varies widely. While it may increase the number of usable embryos, it may also be time-intensive and potentially low-yield. This study sought to elucidate which patients may benefit from ICSI of initially immature oocytes that matured in vitro.

METHODS

A retrospective study comparing fertilization, cleavage, blastulation, and embryo usage rates between sibling initially immature and mature oocytes that underwent ICSI between 2015 and 2019 was performed. Outcomes of initially immature oocytes were stratified by initial maturation stage, timing of progression to metaphase II (MII) in vitro, percentage of mature oocytes in the cycle, and female age.

RESULTS

Ten thousand eight hundred seventeen oocytes from 889 cycles were included. Of 3137 (29.0%) initially immature oocytes, 418 (13.3%) reached MII later on the day of retrieval (day 0) and 1493 (47.6%) on day 1. Overall, embryos originating from initially immature oocytes had lower cleavage and blastulation rates compared to those from initially mature oocytes (P<0.05, all groups). However, embryos from oocytes that matured later on day 0 comprised a unique subset that had clinically similar cleavage (75% vs 80%, RR 0.93, P=0.047) and blastulation rates (41% vs 50%, RR 0.81, P=0.024) compared to initially mature oocytes. Women with low percentages of mature oocytes in the cycle overall and women ≥40 in cleavage cycles derived the highest relative benefit from the use of immature oocytes.

CONCLUSION

ICSI of immature oocytes, particularly those that mature later on the day of retrieval, may improve numbers of usable embryos. This study supports routine reassessment of immature oocytes for progression to MII and ICSI on day 0. An additional reassessment on day 1 may also be of use in older women or those with low percentage of mature oocytes.

Zinc exocytosis is sensitive to myosin light chain kinase inhibition in mouse and human eggs

Zinc dynamics are essential for oocyte meiotic maturation, egg activation, and preimplantation embryo development. During fertilisation and egg activation, the egg releases billions of zinc atoms (Zn2+) in an exocytotic event termed the 'zinc spark'. We hypothesised that this zinc transport and exocytosis is dependent upon the intracellular trafficking of cortical granules (CG) which requires myosin-actin-dependent motors. Treatment of mature mouse and human eggs with ML-7, a myosin light chain kinase inhibitor (MLCK), resulted in an 80% reduction in zinc spark intensity compared to untreated controls when activated with ionomycin. Moreover, CG migration towards the plasma membrane was significantly decreased in ML-7-treated eggs compared with controls when activated parthenogenetically with ionomycin. In sperm-induced fertilisation via intracytoplasmic sperm injection (ICSI), ML-7-treated mouse eggs exhibited decreased labile zinc intensity and cortical CG staining. Collectively, these data demonstrate that ML-7 treatment impairs zinc release from both murine and human eggs after activation, demonstrating that zinc exocytosis requires myosin light chain kinase activity. Further, these results provide additional support that zinc is likely stored and released from CGs. These data underscore the importance of intracellular zinc trafficking as a crucial component of egg maturation necessary for egg activation and early embryo development.

Lysophosphatidic acid improves oocyte quality during IVM by activating the ERK1/2 pathway in cumulus cells and oocytes

Oocyte IVM technology is an option for fertility preservation in some groups of patients, such as those with polycystic ovary syndrome, patients with ovarian hyperstimulation syndrome, and for patients with cancer. However, the developmental potential of oocytes from IVM still needs to improve. Several previous studies have reported that lysophosphatidic acid (LPA) promotes glucose metabolism, cumulus cell (CC) expansion, and oocyte nuclear maturation. However, the effect of LPA on oocyte cytoplasmic maturation, particularly mitochondrial function, has rarely been studied and the underlying mechanism is largely unknown, which impedes (pre)clinical applications of LPA. In this study, cumulus-oocyte complexes (COCs) and cumulus-denuded germinal vesicle oocytes (DOs) were treated with various concentrations of LPA during IVM, in the presence or absence of the oxidative stressor cyclophosphamide (CTX). In both normal and CTX-damaged COCs, the 25 μM LPA group exhibited improved CC expansion capacity, a higher nuclear maturation rate, and superior mitochondrial function, compared to no LPA treatment. When the concentration of LPA was over 40 μM, detrimental effects of LPA on oocyte maturation occurred. Compared with COCs, the addition of LPA slightly improved oocyte nuclear and cytoplasmic maturation of DOs, but this was not statistically significant. We observed that LPA promotes the activation of extracellular signal-regulated kinase (ERK)1/2, although this was not statistically significant in DOs. Furthermore, LPA could not reverse the negative effect of CC expansion and mitochondrial function after inactivation of ERK1/2 by U0126. RNA-sequencing and RT-PCR results showed that LPA upregulated several ERK1/2 downstream genes related to CC expansion, such as Areg, Cited4, and Ptgs2. This study demonstrates that LPA improves oocyte quality during IVM through the activation of ERK1/2 pathway CCs and oocytes, which provides evidence for the potential addition of LPA to IVM medium.

Impact of Maturation and Vitrification Time of Human GV Oocytes on the Metaphase Plate Configuration

The combination of in vitro maturation (IVM) techniques and oocyte vitrification (OV) could increase the number of useful oocytes in different types of patients. IVM and subsequent OV is the most widely used clinical strategy. Would the results improve if we reverse the order of the techniques? Here, we evaluated survival, in vitro maturation, time to extrude the first polar body (PB), and the metaphase plate configuration of human prophase I (GV) oocytes before or after their vitrification. Specific, 195 GV oocytes from 104 patients subjected to controlled ovarian stimulation cycles were included. We stablished three experimental groups: GV oocytes vitrified and IVM (Group GV-Vit), GV oocytes IVM and vitrified at MII stage (Group MII-Vit), and GV oocytes IVM (Group not-Vit). All of them were in vitro matured for a maximum of 48 h and fixed to study the metaphase plate by confocal microscopy. According to our results, the vitrification of immature oocytes and their subsequent maturation presented similar survival, maturation, and metaphase plate conformation rates, but a significantly higher percentage of normal spindle than the standard strategy. Additionally, the extension of IVM time to 48 h did not seem to negatively affect the oocyte metaphase plate configuration.

Fertilisation and early embryonic development of immature and rescue in vitro-matured sibling oocytes

The objective of this study was to assess the effect of rescue in vitro maturation and immediate intracytoplasmic sperm injection (ICSI) application on fertilisation success and early embryonic development of metaphase I (MI) oocytes. This was a retrospective cohort study including 2425 sibling oocytes in 259 ICSI cycles. ICSI was performed on 104 GV (germinal vesicle) oocytes which had reached the metaphase II (MII) stage (Group 1) and 231 MI oocytes which had reached the MII stage (Group 2) following IVM (in vitro maturation). Immediate ICSI was applied following oocyte aspiration on 292 MI stage (Group 3) and 1798 MII stage oocytes (Group 4). Normal fertilisation rates in Groups 1, 2, 3 and 4 were 51.9%, 39%, 30.1% and 59.5%, respectively. The rates of blastocyst development per oocyte and per zygote were calculated as 3.8%, 3.0%, 6.8%, 14.1% and 7.4%, 7.7%, 22.7%, 23.6% for Groups 1, 2, 3 and 4, respectively. The blastocyst development rate was significantly higher in the MI-ICSI group compared with other immature oocytes. Even though performing ICSI on the oocytes at the MI stage on the day of oocyte aspiration resulted in lower fertilisation rates, it was associated with significantly higher rates of blastocyst development.

Chromosome errors in human eggs shape natural fertility over reproductive life span

Chromosome errors, or aneuploidy, affect an exceptionally high number of human conceptions, causing pregnancy loss and congenital disorders. Here, we have followed chromosome segregation in human oocytes from females aged 9 to 43 years and report that aneuploidy follows a U-curve. Specific segregation error types show different age dependencies, providing a quantitative explanation for the U-curve. Whole-chromosome nondisjunction events are preferentially associated with increased aneuploidy in young girls, whereas centromeric and more extensive cohesion loss limit fertility as women age. Our findings suggest that chromosomal errors originating in oocytes determine the curve of natural fertility in humans.

Do immature and mature sibling oocytes recovered from stimulated cycles have the same reproductive potential?

RESEARCH QUESTION

How can laboratory and clinical outcomes of spontaneously, early maturing germinal-vesicle oocytes and sibling in-vivo-matured (metaphase II [MII]) oocytes be quantified and compared?

DESIGN

A prospective, non-randomized intra-cohort study of oocytes from women aged 38 years or younger, with six or fewer MII oocytes and four or more germinal vesicles retrieved. No indication was identified for genetic tests or oocyte or embryo cryopreservation. The study was carried out at IVIRMA-Valencia. Early maturing germinal vesicles were selected for reproductive purposes. In vitro- and in-vivo MII oocytes were fertilized. After time-lapse culture, hatching blastocysts from germinal vesicles were biopsied for aneuploidy screening and vitrified. Laboratory and clinical outcomes were compared according to oocyte origin.

RESULTS

Almost 70% of germinal vesicles had matured early and spontaneously, and had comparable in vitro-outcomes and morphokinetics to sibling in vivo-matured oocytes. Fifty per cent of biopsied blastocysts were euploid. Germinal-vesicle rescue increased the number of MII oocytes per cycle to 3.9, finally adding one extra-blastocyst per cycle. A live birth confirmed the feasibility of this approach. Further data, however, are needed to quantify its real contribution to standard intracytoplasmic sperm injection cycles. Nevertheless, 40% of patients obtained either an immediate advantage (reduction of cancellation rate) or long-term benefit (availability of extra blastocysts of attempts).

CONCLUSIONS

Germinal-vesicle rescue can be considered as a complementary approach when folliculometry (expected) and number of MII (observed) are unequal.

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

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

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Infertility affects ~7% of couples of reproductive age with little change in incidence in the last two decades. ART, as well as other interventions, have made major strides in correcting this condition. However, and in spite of advancements in the field, the age of the female partner remains a main factor for a successful outcome. A better understanding of the final stages of gamete maturation yielding an egg that can sustain embryo development and a pregnancy to term remains a major area for improvement in the field. This review will summarize the major cellular and molecular events unfolding at the oocyte-to-embryo transition. We will provide an update on the most important processes/pathways currently understood as the basis of developmental competence, including the molecular processes involved in mRNA storage, its recruitment to the translational machinery, and its degradation. We will discuss the hypothesis that the translational programme of maternal mRNAs plays a key role in establishing developmental competence. These regulations are essential to assemble the machinery that is used to establish a totipotent zygote. This hypothesis further supports the view that embryogenesis begins during oogenesis. A better understanding of the events required for developmental competence will guide the development of novel strategies to monitor and improve the success rate of IVF. Using this information, it will be possible to develop new biomarkers that may be used to better predict oocyte quality and in selection of the best egg for IVF.

Cytoplasmic movement profiles of mouse surrounding nucleolus and not-surrounding nucleolus antral oocytes during meiotic resumption

Full-grown mouse antral oocytes are classified as surrounding nucleolus (SN) or not-surrounding nucleolus (NSN), depending on the respective presence or absence of a ring of Hoechst-positive chromatin surrounding the nucleolus. In culture, both types of oocytes resume meiosis and reach the metaphase II (MII) stage, but following insemination, NSN oocytes arrest at the two-cell stage whereas SN oocytes may develop to term. By coupling time-lapse bright-field microscopy with image analysis based on particle image velocimetry, we provide the first systematic measure of the changes to the cytoplasmic movement velocity (CMV) occurring during the germinal vesicle-to-MII (GV-to-MII) transition of these two types of oocytes. Compared to SN oocytes, NSN oocytes display a delayed GV-to-MII transition, which can be mostly explained by retarded germinal vesicle break down and first polar body extrusion. SN and NSN oocytes also exhibit significantly different CMV profiles at four main time-lapse intervals, although this difference was not predictive of SN or NSN oocyte origin because of the high variability in CMV. When CMV profile was analyzed through a trained artificial neural network, however, each single SN or NSN oocyte was blindly identified with a probability of 92.2% and 88.7%, respectively. Thus, the CMV profile recorded during meiotic resumption may be exploited as a cytological signature for the non-invasive assessment of the oocyte developmental potential, and could be informative for the analysis of the GV-to-MII transition of oocytes of other species.

Involvement of blood mononuclear cells in the infertility, age-associated diseases and cancer treatment

Blood mononuclear cells consist of T cells and monocyte derived cells. Beside immunity, the blood mononuclear cells belong to the complex tissue control system (TCS), where they exhibit morphostatic function by stimulating proliferation of tissue stem cells followed by cellular differentiation, that is stopped after attaining the proper functional stage, which differs among various tissue types. Therefore, the term immune and morphostatic system (IMS) should be implied. The TCS-mediated morphostasis also consists of vascular pericytes controlled by autonomic innervation, which is regulating the quantity of distinct tissues in vivo. Lack of proper differentiation of tissue cells by TCS causes either tissue underdevelopment, e.g., muscular dystrophy, or degenerative functional failures, e.g., type 1 diabetes and age-associated diseases. With the gradual IMS regression after 35 years of age the gonadal infertility develops, followed by a growing incidence of age-associated diseases and cancers. Without restoring an altered TCS function in a degenerative disease, the implantation of tissue-specific stem cells alone by regenerative medicine can not be successful. Transfused young blood could temporarily restore fertility to enable parenthood. The young blood could also temporarily alleviate aging diseases, and this can be extended by substances inducing IMS regeneration, like the honey bee propolis. The local and/or systemic use of honey bee propolis stopped hair and teeth loss, regressed varicose veins, improved altered hearing, and lowered high blood pressure and sugar levels. Complete regression of stage IV ovarian cancer with liver metastases after a simple elaborated immunotherapy is also reported.

Impact of vitrification on the mitochondrial activity and redox homeostasis of human oocyte

STUDY QUESTION

Do the extreme conditions of vitrification affect mitochondrial health and reactive oxygen species (ROS) levels of human oocytes?

SUMMARY ANSWER

Vitrification of discarded human oocytes shifts the intracellular redox potential towards oxidation but does not alter the mitochondrial potential or intracellular ROS levels.

WHAT IS KNOWN ALREADY

Recent studies have reflected increased ROS levels in warmed young oocytes and have highlighted the temporal dynamic loss of mitochondrial potential that could, therefore, lead to a decrease in ATP production, impairing embryo development. Mitochondrial function can also be evaluated in vivo by the FAD/NAD(P)H autofluorescence ratio, which reflects the respiratory chain activity and is considered as a marker of the intracellular redox state.

STUDY DESIGN, SIZE, DURATION

A total of 629 discarded Metaphase II (MII) oocytes collected from June 2013 to April 2014 were included in this control (fresh oocytes, n= 270) versus treatment (vitrified oocytes, n= 359) study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Discarded MII oocytes were donated to research by young (<27 years old) and reproductively aged (>36 years old) women who underwent ovarian stimulation for IVF at a university-affiliated private fertility clinic. Redox state was assessed by measuring the FAD/NAD(P)H autofluorescence ratio, while ROS and mitochondrial activity were reported by in vivo labelling with carboxy-H2DCFDA and JC-1, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

Young and aged oocytes showed high and similar survival rates (81.8 versus 83.1%, not significant). Confocal microscopy revealed that the FAD/NAD(P)H ratio was significantly higher in vitrified oocytes than in fresh oocytes, suggesting a significant shift towards the oxidized state in oocytes after vitrification, regardless of the maternal age. Mitochondrial distribution was not affected by vitrification. Furthermore, it was not possible to resolve any difference in mitochondrial potential using JC-1 potentiometric dye or in reactive oxygen species (ROS) production (assessed with H2-DCFDA staining) between fresh and vitrified oocytes. Therefore, measurement of intracellular redox potential by autofluorescence imaging may be a more sensitive method to assess oxidative stress or mitochondrial demise in human oocytes because it showed a higher resolving power than JC-1 staining and displayed less variability than H2-DCFDA staining.

LIMITATIONS, REASONS FOR CAUTION

Owing to sample availability, MII discarded oocytes (in vitro matured oocytes and unfertilized oocytes 20 h after ICSI) were included in the study. These discarded oocytes do not necessarily reflect the physiological condition of the MII human oocyte.

WIDER IMPLICATIONS OF THE FINDINGS

Although vitrified oocytes yield comparable clinical outcomes compared with fresh oocytes, lower cleavage and blastocyst rates can be observed during in vitro culture. Data here obtained suggest that the redox state of human oocytes could be affected by vitrification. Therefore, the importance of adding protective antioxidant molecules to the vitrification solution and to the post-warming culture medium to improve embryo cleavage deserves some research.

STUDY FUNDING/COMPETING INTERESTS

This research project was supported by the Valencian Government (Val+i+D program, M.N.-C.), INCLIVA Foundation for health research (G.S.-A.) and by the University of L'Aquila and Regione Abruzzo ('Reti per l'Alta Formazione' - P.O.F.S.E. Abruzzo 2007-2013 G.D.E.). No conflicts of interest were declared.

Differences in the Kinetic of the First Meiotic Division and in Active Mitochondrial Distribution between Prepubertal and Adult Oocytes Mirror Differences in their Developmental Competence in a Sheep Model

Our aim is to verify if oocyte developmental potential is related to the timing of meiotic progression and to mitochondrial distribution and activity using prepubertal and adult oocytes as models of low and high developmental capacity respectively. Prepubertal and adult oocytes were incorporated in an in vitro maturation system to determine meiotic and developmental competence and to assess at different time points kinetic of meiotic maturation, 2D protein electrophoresis patterns, ATP content and mitochondria distribution. Maturation and fertilization rates did not differ between prepubertal and adult oocytes (95.1% vs 96.7% and 66.73% vs 70.62% respectively for prepubertal and adult oocytes). Compared to adults, prepubertal oocytes showed higher parthenogenesis (17.38% vs 2.08% respectively in prepubertals and adults; P<0.01) and polispermy (14.30% vs 2.21% respectively in prepubertals and adults; P<0.01), lower cleavage rates (60.00% vs 67.08% respectively in prepubertals and adults; P<0.05) and blastocyst output (11.94% vs 34.% respectively in prepubertals and adults; P<0.01). Prepubertal oocytes reached MI stage 1 hr later than adults and this delay grows as the first meiotic division proceeds. Simultaneously, the protein pattern was altered since in prepubertal oocytes it fluctuates, dropping and rising to levels similar to adults only at 24 hrs. In prepubertal oocytes ATP rise is delayed and did not reach levels comparable to adult ones. CLSM observations revealed that at MII, in the majority of prepubertal oocytes, the active mitochondria are homogenously distributed, while in adults they are aggregated in big clusters. Our work demonstrates that mitochondria and their functional aggregation during maturation play an active role to provide energy in terms of ATP. The oocyte ATP content determines the timing of the meiotic cycle and the acquisition of developmental competence. Taken together our data suggest that oocytes with low developmental competence have a slowed down energetic metabolism which delays later development.

Impaired oocyte quality induced by dehydroepiandrosterone is partially rescued by metformin treatment

The present study evaluated the influence of hyperandrogenism on oocyte quality using a murine PCOS model induced by dehydroepiandrosterone (DHEA) and further explored the effect of metformin treatment. Female BALB/c mice were treated with a vehicle control or DHEA (6 mg /100 g body weight) or DHEA plus metformin (50 mg /100 g body weight) for 20 consecutive days. DHEA-induced mice resembled some characters of human PCOS, such as irregular sexual cycles and polycystic ovaries. After the model validation was completed, metaphase II (MII) oocytes were retrieved and subsequent analyses of oocyte quality were performed. DHEA-treated mice yielded fewer MII oocytes, which displayed decreased mtDNA copy number, ATP content, inner mitochondrial membrane potential, excessive oxidative stress and impaired embryo development competence compared with those in control mice. Metformin treatment partially attenuated those damages, as evidenced by the increased fertilization and blastocyst rate, ATP content, GSH concentration and GSH/GSSG ratio, and decreased reactive oxygen species levels. No significant difference in normal spindle assembly was observed among the three groups. During in vitro maturation (IVM), the periods of germinal vesicle breakdown (GVBD) and the first polar body (PB1) extrusion were extended and the maturation rate of GVBD oocytes was decreased in DHEA mice compared with controls. Metformin treatment decreased the time elapsed of GVBD while had no effect on PB1 extrusion. These results indicated that excessive androgen is detrimental to oocyte quality while metformin treatment is, directly or indirectly, beneficial for oocyte quality improvement.