Meiotic spindle location and identification and its effect on embryonic cleavage plane and early development

Clinical effectiveness of spindle-view intracytoplasmic sperm injection compared to conventional intracytoplasmic sperm injection in patients with poor ovarian response and previous implantation failure

OBJECTIVE

This study aimed to determine the clinical advantage of spindle-view intracytoplasmic sperm injection (SVICSI; a novel technology) over conventional intracytoplasmic sperm injection (cICSI) in patients with poor ovarian response (POR) and previous implantation failure.

METHODS

The study included 37 patients who underwent SVICSI followed by fresh embryo transfer (FET) at a single fertility clinic from January to December 2022, 58 patients who underwent cICSI followed by FET at the same fertility clinic from January to December 2021 as a control group. All study participants met the Bologna criteria for POR and had at least three or more previous failed embryo transfers.

RESULTS

The number of blastocyst transfers was significantly higher in the SVICSI group than in the cICSI group. A good-quality cleavage embryo rate, blastocyst rate, and good-quality blastocyst rate were also significantly higher in the SVICSI group than in the cICSI group. There were no significant differences in the rates of fertilization, implantation, clinical pregnancy, or clinical abortion between the two groups.

CONCLUSION

In patients with POR, those who underwent SVICSI appeared to have better embryos than those who underwent cICSI. However, whether SVICSI improved clinical outcomes such as implantation and pregnancy rates cannot be proven.

Perfluorooctanoic acid (PFOA) exposure affects early embryonic development and offspring oocyte quality via inducing mitochondrial dysfunction

Perfluorooctanoic acid (PFOA) is a synthetic perfluorinated compound that is extensively used as an integral surfactant in commercial production. Owing to its hydrophilicity and persistence, PFOA can accumulate in living organisms and induce severe disease in animals and humans. It has been reported that PFOA exposure can affect ovarian function and induce reproductive toxicity; however, the effects and potential mechanism of PFOA exposure during gestation on early embryonic development and offspring remain unclear. This study found that PFOA exposure in vitro disrupted spindle assembly and chromosome alignment during the first cleavage of early mouse embryos, which impacted early embryonic cleavage and blastocyst formation. Moreover, PFOA exposure caused mitochondrial dysfunction and oxidative stress by inducing aberrant Ca²⁺ levels, liquid drops(LDs), and mitochondrial membrane potential in the 2-cell stage. Furthermore, we found that PFOA exposure resulted in DNA damage, autophagy, and apoptosis in 2-cell stage by inhibiting SOD2 function. Gestational exposure to PFOA significantly increased ovarian apoptosis and disrupted follicle development in F1 offspring. In addition, oocyte maturation competence was decreased in F1 offspring. Finally, single-cell transcriptome analysis revealed that PFOA-induced oocyte deterioration was caused by mitochondrial dysfunction and apoptosis in the F1 offspring. In summary, our results indicated that gestational exposure to PFOA had potential toxic effects on ovarian function and led to a higher incidence of meiotic defects in F1 female offspring.

Tea polyphenols alleviate the adverse effects of diabetes on oocyte quality

Maternal diabetes mellitus reduces oocyte quality, such as abnormalities of spindle assembly and chromosome segregation, mitochondrial dysfunction, decrease of fertilization rate, increase of ROS, and so on. So, it is important to research how to restore the decreased oocyte quality induced by maternal diabetes mellitus. Polyphenols are the most abundant bioactive components of green tea. It is reported that tea polyphenols have many health functions, for instance anti-oxidation, anti-inflammation, anti-obesity, and anti-diabetes. Thus, we hypothesize that tea polyphenols may play a crucial role in alleviating adverse effects of diabetes on oocyte quality. In the present study, we researched the effects of tea polyphenols on diabetic oocyte maturation in vitro. Compared with the control, oocytes from diabetic mice displayed a lower maturation rate and a higher frequency of spindle defects and chromosome misalignment. However, tea polyphenols significantly increased the oocyte maturation rate, and reduced the incidence of abnormal spindle assembly and chromosome segregation. Tea polyphenols also obviously decreased the reactive oxygen species (ROS) levels in diabetic oocytes, and increased the expression of antioxidant genes (Sod1 and Sod2). Abnormal mitochondrial membrane potential was also alleviated in diabetic oocytes, and the expression of genes regulating mitochondrial fusion (Opa1, Mfn1 and Mfn2) and fission (Drp1) was significantly increased while tea polyphenols were added. Meanwhile, tea polyphenols reduced DNA damage in diabetic oocytes which may be mediated by the increased expression of Rad51, related to DNA damage repair. Our results suggest that tea polyphenols would, at least partially, restore the adverse effects of diabetes mellitus on oocyte quality.

Non-contact ultrasound oocyte denudation

Cumulus removal (CR) is a central prerequisite step for many protocols involved in the assisted reproductive technology (ART) such as intracytoplasmic sperm injection (ICSI) and preimplantation genetic testing (PGT). The most prevalent CR technique is based upon laborious manual pipetting, which suffers from inter-operator variability and therefore a lack of standardization. Automating CR procedures would alleviate many of these challenges, improving the odds of a successful ART or PGT outcome. In this study, a chip-scale ultrasonic device consisting of four interdigitated transducers (IDT) on a lithium niobate substrate has been engineered to deliver megahertz (MHz) range ultrasound to perform denudation. The acoustic streaming and acoustic radiation force agitate COCs inside a microwell placed on top of the LiNbO₃ substrate to remove the cumulus cells from the oocytes. This paper demonstrates the capability and safety of the denudation procedure utilizing surface acoustic wave (SAW), achieving automation of this delicate manual procedure and paving the steps toward improved and standardized oocyte manipulation.

Paraquat Reduces the Female Fertility by Impairing the Oocyte Maturation in Mice

Paraquat (PQ) is a widely used non-selective and oxidizing herbicide in farmland, orchards, flower nursery, and grassland. Overuse of PQ will accumulate in the body and affect the reproduction in mammals. In this study, we found that PQ could reduce the female fertility by oral administration for 21 days in mice. PQ exposure could impair the nuclear maturation by perturbing the spindle assembly and kinetochore–microtubule attachment to cause the misaligned chromosomes during meiosis. In the meantime, PQ exposure disturbed the mitochondrial distribution and enhanced the level of reactive oxygen species and early apoptosis, which thereby deteriorated the early embryo development. Also, PQ administration could cause some changes in epigenetic modifications such as the level of H3K9me2 and H3K27me3. Therefore, PQ administration reduces the female fertility by impairing the nuclear and cytoplasmic maturation of oocytes in mice.

Selection of competent oocytes by morphological criteria for assisted reproductive technologies

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

In Vitro Maturation of Fully Grown Mouse Antral Follicles in the Presence of 1 nM 2-Hydroxyestradiol Improves Oocytes' Developmental Competence

Cathecolestrogens are estradiol metabolites produced during folliculogenesis in the mammalian ovary. 2-Hydroxyestradiol (2-OHE₂) is one of the most abundant although its role remains unknown. The aim of this study is to investigate whether the presence of 2-OHE₂ during the germinal vesicle-to-metaphase II transition affects oocyte meiotic and preimplantation developmental competence. Mouse cumulus-oocyte complexes (COCs), isolated from fully grown antral follicles, were in vitro–matured (IVM) in the presence of 2-OHE₂ (0.1, 1, 10 or 100 nM) for 6 or 15 h; then, their meiotic and developmental competence was evaluated using a number of cytological quality markers. With the exception of the highest dose (100 nM), the addition of 2-OHE₂ to the IVM medium, did not alter, compared with untreated control, the frequency of oocytes that reached the MII stage. Instead, IVM in the presence of 1 nM 2-OHE₂ highly increased the rate of preimplantation development and blastocyst quality. To understand whether this positive effect could be attributed to the events occurring during meiosis resumption, we analysed a number of specific cytological quality markers of the asymmetric division, such as PB-I volume and position, presence and extension of the cortical F-actin cap, meiotic spindle shape and area, and microtubule organisation centre localisation. The results highlighted how the presence of 1 nM 2-OHE₂ significantly improved the overall cytological organisation required for a correct asymmetric division. Our results contribute a first step to acknowledge a potential role of this estradiol metabolite during the GV-to-MII transition, contributing to the acquisition of oocytes developmental competence.

Hfm1 participates in Golgi-associated spindle assembly and division in mouse oocyte meiosis

HFM1 (helicase for meiosis 1) is widely recognized as an ATP-dependent DNA helicase and is expressed mainly in germ-line cells. HFM1 is a candidate gene of premature ovarian failure (POF), hence it is also known as POF9. However, the roles of HFM1 in mammalian oocytes remain uncertain. To investigate the functions of HFM1, we established a conditional knockout (cKO) mouse model. Specific knockout of Hfm1 in mouse oocytes from the primordial follicle stage resulted in depletion of ovarian follicular reserve and subfertility of mice. In particular, abnormal spindle, misaligned chromosomes, loss of cortical actin cap, and failing polar body extrusion were readily observed in Hfm1-cKO oocytes. Further studies indicated that in addition to its cytoplasmic distribution, Hfm1 accumulated at the spindle poles, colocalized with the Golgi marker protein, GM130. Generally, GM130 signals overlapped with p-Mapk at the two spindle poles to regulate meiotic spindle assembly and asymmetric division. In this research, centrosome associated proteins, such as GM130 and p-Mapk, detached from the spindle poles in Hfm1-cKO oocytes. In conclusion, our data suggest that Hfm1 participates in Golgi-associated spindle assembly and division in mouse oocyte meiosis. These findings provide clues for pathogenesis of POF.

NQO2 inhibition relieves reactive oxygen species effects on mouse oocyte meiotic maturation and embryo development

NRH: quinone oxidoreductase 2 (NQO2) is a cytosolic and ubiquitously expressed flavoprotein that catalyzes the two-electron reduction of quinone to hydroquinones. Herein, we assessed the protein expression, subcellular localization, and possible functions of NQO2 in mouse oocyte meiotic maturation and embryo development. Western blot analysis detected high and stable protein expression of NQO2 in mouse oocytes during meiotic progression. Immunofluorescence illustrated NQO2 distribution on nuclear membrane, chromosomes, and meiotic spindles. Microtubule poisons treatment (nocodazole and taxol) showed that filamentous assembly of NQO2 and its co-localization with microtubules require microtubule integrity and normal dynamics. Increased levels of NQO2, reactive oxygen species (ROS), malondialdehyde (MDA), and autophagy protein Beclin1 expression were detected in oocytes cultured with ROS stimulator vitamin K3 (VK3), combined with decreased antioxidant glutathione (GSH). These oocytes were arrested at metaphase I with abnormal spindle structure and chromosome configuration. However, this impact was counteracted by melatonin or NQO2 inhibitor S29434, and the spindle configuration and first polar body extrusion were restored. Similarly, morpholino oligo-induced NQO2 knockdown suppressed ROS, MDA, and Beclin1, instead increased GSH in oocytes under VK3. Supplementary S29434 or melatonin limited changes in NQO2, ROS, MDA, Beclin1, and GSH during in vitro aging of ovulated oocytes, thereby maintaining spindle structure, as well as ordered chromosome separation and embryo development potential after parthenogenetic activation with SrCl2. Taken together, NQO2 is involved in ROS generation and subsequent cytotoxicity in oocytes, and its inhibition can restore oocyte maturation and embryo development, suggesting NQO2 as a pharmacological target for infertility cure.

Meiotic spindle size is a strong indicator of human oocyte quality

PURPOSE

To investigate the relationship between the meiotic spindle size in human metaphase II oocytes and embryo developmental potential after intracytoplasmic sperm injection (ICSI).

METHODS

Analyzed were 1302 oocytes with a visible meiotic spindle from 281 patients aged under 40 years undergoing ICSI cycles. The meiotic spindle was imaged by using PolScope before ICSI. The oocytes were classified into three groups, according to spindle size: group A (<90 μm2), group B (90-120 μm2), and group C (>120 μm2).

RESULTS

Overall, 389 (29.9%) oocytes were classified into group A, 662 (50.8%) into group B, and 251 (19.3%) into group C. The fertilization rate of the group B oocytes was significantly higher than for the A and C oocytes. The blastocyst formation rate in group B was significantly higher than in group A. In addition, the pregnancy rate in group B was significantly higher than in the other two groups.

CONCLUSION

The oocytes with a spindle size of 90-120 μm2 showed higher fertilization, blastocyst formation, and clinical pregnancy rates than those with larger or smaller spindles. The measurement of the meiotic spindle size thus has a positive predictive value for identifying human embryo developmental potential clinically.

Double Strand Break DNA Repair occurs via Non-Homologous End-Joining in Mouse MII Oocytes

The unique biology of the oocyte means that accepted paradigms for DNA repair and protection are not of direct relevance to the female gamete. Instead, preservation of the integrity of the maternal genome depends on endogenous protein stores and/or mRNA transcripts accumulated during oogenesis. The aim of this study was to determine whether mature (MII) oocytes have the capacity to detect DNA damage and subsequently mount effective repair. For this purpose, DNA double strand breaks (DSB) were elicited using the topoisomerase II inhibitor, etoposide (ETP). ETP challenge led to a rapid and significant increase in DSB (P = 0.0002) and the consequential incidence of metaphase plate abnormalities (P = 0.0031). Despite this, ETP-treated MII oocytes retained their ability to participate in in vitro fertilisation, though displayed reduced developmental competence beyond the 2-cell stage (P = 0.02). To account for these findings, we analysed the efficacy of DSB resolution, revealing a significant reduction in DSB lesions 4 h post-ETP treatment. Notably, this response was completely abrogated by pharmacological inhibition of key elements (DNA-PKcs and DNA ligase IV) of the canonical non-homologous end joining DNA repair pathway, thus providing the first evidence implicating this reparative cascade in the protection of the maternal genome.

Relationship between meiotic spindles visualization and intracytoplasmic sperm injection outcomes in human oocytes

In assisted reproductive techniques, the operator attempts to select morphologically best embryos to predict embryo viability. Development of polarized light microscope, which evaluates the oocytes' spindles according to birefringence of living cells, had been helpful in oocyte selection. The aim of this study is evaluating the relationship between meiotic spindles visualization and intracytoplasmic sperm injection (ICSI) outcomes in human oocytes. In this study, 264 oocytes from 24 patients with an average age of 30.5±7.5 years with infertility duration of 1 to 10 years were collected. The oocytes were randomly allocated to the control injection group (n=126) and the oocyte imaging group (spindle-aligned group) (n=138). In the spindle-aligned group, the meiotic spindle was identified by means of polarized light microscope to align the spindle at 6 or 12 o'clock. Then the spindle-aligned group was divided into three sub-groups based on spindle morphology: fine, average, and (poor). After ICSI, embryos were checked every 24 hours and scored; 72 hours later, high-grade embryos were transferred intravaginally to uterus. This study showed that the fertilization rate in the spindle-aligned group was higher than the control group (P<0.05). After cleavage, a positive correlation was observed between spindle morphology and embryo morphology. Among the sub-groups of spindle-aligned group, the embryos' morphology of the fine group was better than the other subgroups and embryos of the poor group had lower quality and more fragmentation. The results revealed that the selection of oocytes based on meiotic spindle imaging can significantly improve the rate of fertilization and embryo cleavage and certainly increase the rate of implantation.

Evaluation of equine oocyte developmental competence using polarized light microscopy

The purpose of this study was to observe in vitro-matured equine oocytes with an objective computerized technique that involves the use of a polarized light microscope (PLM) in addition to the subjective morphological evaluation obtained using a classic light microscope (LM). Equine cumulus-oocyte complexes (COCs, n = 922) were subjected to different in vitro maturation times (24, 36 or 45 h), however, only 36-h matured oocytes were analyzed using CLM. The 36-h matured oocytes that reached maturity were parthenogenetically activated to evaluate the quality and meiotic competence. Average maturation percentages per session in groups 1, 2 and 3 (24-, 36- and 45-h matured oocytes respectively) were 29.31 ± 13.85, 47.01 ± 9.90 and 36.62 ± 5.28%, whereas the average percentages of immature oocytes per session were 28.78 ± 20.17, 7.83 ± 5.51 and 22.36 ± 8.39% respectively. The zona pellucida (ZP) birefringent properties were estimated and correlated with activation outcome. ZP thickness and retardance of the inner layer of the zona pellucida (IL-ZP) were significantly increased in immature oocytes compared with mature oocytes (P < 0.001 and P < 0.01 respectively). The comparison between parthenogenetically activated and non-activated oocytes showed a significant increase in the area and thickness of the IL-ZP in parthenogenetically activated oocytes (P < 0.01). These results show that the 36-h in vitro maturation (IVM) protocol allowed equine oocytes to reach maturity, and PLM observation of ZP can be used to distinguish mature and immature oocytes as well as activated and non-activated oocytes.

Relationship between pre-ICSI meiotic spindle angle, ovarian reserve, gonadotropin stimulation, and pregnancy outcomes

PURPOSE

The goals of this study are to analyze the clinical pregnancy rate as a function of the pre-intracytoplasmic sperm injection (ICSI) oocyte spindle angle and determine factors which can be associated with different spindle angles, if clinically relevant.

METHODS

Fifty-eight patients, who underwent their first ICSI cycle from January to December 2013, were included. Eight hundred thirty oocytes were collected, and 648 were metaphase II (MII) on retrieval day. Spindles were characterized in terms of visibility and position in relation to the first polar body (PB). Oocytes were separated into four groups based on angle: (group 1, n = 297) 0°-29°; (group 2 n = 212) 30°-89°; (group 3, n = 72) ≥90°; and those with no visible spindle (group 4, n = 67).

RESULTS

The rate of blastocyst development was associated with the spindle angle (p = 0.002). The rate of good quality blastocysts were as follows: group 1 (42%), group 2 (30%), group 3 (35%), and group 4 (19%) (p = 0.02). Pregnancy and live birth rates were also affected (p = 0.007 and p = 0.046, respectively). Antral follicle count (AFC) (p = 0.001), total FSH stimulating dose (p = 0.0001), and peak serum estradiol level (p = 0.0001) were associated with spindle angle grouping. Miscarriage rates trended different (p = 0.07). On the other hand, day 3 follicle-stimulating hormone (FSH) levels and female and male age were not associated with spindle angle grouping.

CONCLUSIONS

Embryos resulting from oocytes with pre-ICSI spindle angles between 0° and 29° were associated with better blastocyst, pregnancy, live birth, and miscarriage rates when compared to oocytes that had no visible spindle. Low ovarian reserve and excessive stimulation were also associated with lack of spindle and therefore lower pregnancy outcomes.

Is oocyte meiotic spindle morphology associated with embryo ploidy? A prospective cohort study

OBJECTIVE

To explore whether an association exists between oocyte meiotic spindle morphology visualized by polarized light microscopy at the time of intracytoplasmic sperm injection and the ploidy of the resulting embryo.

DESIGN

Prospective cohort study.

SETTING

Private IVF clinic.

PATIENT(S)

Patients undergoing preimplantation genetic screening/diagnosis (n = 113 patients).

INTERVENTION(S)

Oocyte meiotic spindles were assessed by polarized light microscopy and classified at the time of intracytoplasmic sperm injection as normal, dysmorphic, translucent, telophase, or no visible spindle. Single blastomere biopsy was performed on day 3 of culture for analysis by array comparative genomic hybridization.

MAIN OUTCOME MEASURE(S)

Spindle morphology and embryo ploidy association was evaluated by regression methods accounting for non-independence of data.

RESULT(S)

The frequency of euploidy in embryos derived from oocytes with normal spindle morphology was significantly higher than all other spindle classifications combined (odds ratio [OR] 1.93, 95% confidence interval [CI] 1.33-2.79). Oocytes with translucent (OR 0.25, 95% CI 0.13-0.46) and no visible spindle morphology (OR 0.35, 95% CI 0.19-0.63) were significantly less likely to result in euploid embryos when compared with oocytes with normal spindle morphology. There was no significant difference between normal and dysmorphic spindle morphology (OR 0.73, 95% CI 0.49-1.08), whereas no telophase spindles resulted in euploid embryos (n = 11). Assessment of spindle morphology was found to be independently associated with embryo euploidy after controlling for embryo quality (OR 1.73, 95% CI 1.16-2.60).

CONCLUSION(S)

Oocyte spindle morphology is associated with the resulting embryo's ploidy. Oocytes with normal spindle morphology are significantly more likely to produce euploid embryos compared with oocytes with meiotic spindles that are translucent or not visible.

Sperm DNA oxidative damage and DNA adducts

The objective of this study was to investigate DNA damage and adducts in sperm from coke oven workers who have been exposed to polycyclic aromatic hydrocarbons. A longitudinal study was conducted with repeated measurements during spermatogenesis. Coke-oven workers (n=112) from a coke-oven plant served the PAH-exposed group, while administrators and security personnel (n=67) served the control. Routine semen parameters (concentration, motility, vitality, and morphology) were analyzed simultaneously; the assessment of sperm DNA integrity endpoints included DNA fragmentation, bulky DNA adducts, and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo). The degree of sperm DNA fragmentation was measured using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and sperm chromatin structure assay (SCSA). The PAH-exposed group had a significant increase in bulky DNA adducts and 8-oxo-dGuo compared to the control subjects (Ps=0.002 and 0.045, respectively). Coke oven workers' percentages of DNA fragmentation and denaturation from the PAH-exposed group were not significantly different from those of the control subjects (Ps=0.232 and 0.245, respectively). Routine semen parameters and DNA integrity endpoints were not correlated. Concentrations of 8-oxo-dGuo were positively correlated with percentages of DNA fragmentation measured by both TUNEL and SCSA (Ps=0.045 and 0.034, respectively). However, the concentrations of 8-oxo-dGuo and percentages of DNA fragmentation did not correlate with concentrations of bulky DNA adducts. In summary, coke oven workers with chronic exposure to PAHs experienced decreased sperm DNA integrity. Oxidative stress could contribute to the degree of DNA fragmentation. Bulky DNA adducts may be independent of the formation of DNA fragmentation and oxidative adducts in sperm. Monitoring sperm DNA integrity is recommended as a part of the process of assessing the impact of occupational and environmental toxins on sperm.

Pre-implantation developmental potential from in vivo and in vitro matured mouse oocytes: a cytoskeletal perspective on oocyte quality

Purpose

In the present study, fertilization and developmental potential of mouse oocytes matured in different conditions were tested. The efficiency of in vitro fertilization (IVF), pre-implantation development and some important aspects of cytokinesis during early cleavages are discussed.

Methods

In vivo matured (IVO), in vitro matured (IVM) and roscovitine-treated (IVM-Rosco) mouse oocytes were subjected to IVF under identical conditions. Three replicates per group were analyzed. Fertilization was identified by the presence of two pronuclei at 6–8 h post-fertilization. Evaluation of pre-implantation embryonic development was done daily from day 2 to day 5 and embryos were processed for analyses of chromatin, nuclear lamina, microtubules and centrosomal proteins by conventional and confocal fluorescence microscopy.

Results

Both IVM groups displayed lower fertilization rates when compared to in vivo controls. While IVO-derived embryos exhibit efficient and synchronous progression to the blastocyst stage, both IVM-derived embryos exhibit a delay in embryonic progression, and a lower blastocyst rate. Interestingly, IVM-Rosco M-II oocytes exhibited more blastomere symmetries and higher number of cells at the blastocyst stage than the IVM group with the most notable influence being on the centrosome-microtubule complex of blastomeres.

Conclusion

Our study strongly indicates that when compared to spontaneously in vitro matured oocytes, treatment with roscovitine may partially enhance developmental competence by maintaining coordination between nuclear and cytoplasmic events. Further evidence is given of cytoskeletal biomarkers that can be identified during in vitro oocyte maturation conditions.

Molecular signatures of bovine embryo developmental competence

Assessment of the developmental capacity of early bovine embryos is still an obstacle. Therefore, the present paper reviews all current knowledge with respect to morphological criteria and environmental factors that affect embryo quality. The molecular signature of an oocyte or embryo is considered to reflect its quality and to predict its subsequent developmental capacity. Therefore, the primary aim of the present review is to provide an overview of reported correlations between molecular signatures and developmental competence. A secondary aim of this paper is to present some new strategies to enable concomitant evaluation of the molecular signatures of specific embryos and individual developmental capacity.

The impact of examining the meiotic spindle by polarization microscopy on assisted reproduction outcomes

OBJECTIVE

To examine the effect of submitting oocytes to polarization microscopy (PM) before intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective observational study.

SETTING

University hospital in Brazil.

PATIENT(S)

Couples undergoing ICSI.

INTERVENTION(S)

PM before ICSI (PM group) compared with no PM before ICSI (No-PM group)

MAIN OUTCOMES MEASURE(S)

Fertilization and cleavage rates, formation of top-quality embryos (TQEs), and implantation, clinical pregnancy, miscarriage, and live-birth rates.

RESULT(S)

The PM group consisted of 1,000 consecutive oocytes from 201 couples submitted to PM during the year of 2008. The No-PM group consisted of 1,400 oocytes from 249 couples: 700 consecutive oocytes were retrieved before we started using PM and 700 consecutive oocytes were retrieved after we stopped using PM. In the PM group, we observed an increased fertilization rate (79.7% vs. 72.5%, PM group vs. No-PM group, respectively) but reduced cleavage rate (86.2% vs. 92.5%) and TQE formation (33.1% vs. 49.9%). Implantation (18.7% vs. 20.6%), clinical pregnancy (31.8% vs. 33.3%), miscarriage (21.9% vs. 15.7%), and live-birth (24.9% vs. 28.1%) rates were not significantly different between groups.

CONCLUSION(S)

Use of PM was associated with increased fertilization rate but reduced cleavage rate and TQE formation; no significant difference was observed for implantation, clinical pregnancy, or live-birth rates.

Behaviour of cytoplasmic organelles and cytoskeleton during oocyte maturation

Assisted reproduction technology (ART) has become an attractive option for infertility treatment and holds tremendous promise. However, at present, there is still room for improvement in its success rates. Oocyte maturation is a process by which the oocyte becomes competent for fertilization and subsequent embryo development. To better understand the mechanism underlying oocyte maturation and for the future improvement of assisted reproduction technology, this review focuses on the complex processes of cytoplasmic organelles and the dynamic alterations of the cytoskeleton that occur during oocyte maturation. Ovarian stimulation and in-vitro maturation are the major techniques used in assisted reproduction technology and their influence on the organelles of oocytes is also discussed. Since the first birth by assisted reproduction treatment was achieved in 1978, numerous techniques involved in assisted reproduction have been developed and have become attractive options for infertility treatment. However, the unsatisfactory success rate remains as a main challenge. Oocyte maturation is a process by which the oocyte becomes competent for fertilization and subsequent embryo development. Oocyte maturation includes both nuclear and cytoplasmic maturation. Nuclear maturation primarily involves chromosomal segregation, which has been well studied, whereas cytoplasmic maturation involves a series of complicated processes, and there are still many parts of this process that remain controversial. Ovarian stimulation and in-vitro maturation (IVM) are the major techniques of assisted reproduction. The effect of ovarian stimulation or IVM on the behaviour of cell organelles of the oocyte has been postulated as the reason for the reduced developmental potential of in-vitro-produced embryos. To further understanding of the mechanism of oocyte maturation and future improvement of assisted reproduction treatment, the complex events of cytoplasmic organelles and the cytoskeleton that occur during oocyte maturation and the influence of ovarian stimulation and IVM on these organelles are described in this review.

Effects of frozen timing on the spindle density, the angle between the polar body and spindle, and embryo development of intracytoplasmic sperm injection in mouse mature oocytes

Better pregnancy outcomes can be obtained by human mature oocyte vitrification, but many problems remain to be resolved in human mature oocyte vitrification. Since mature oocyte development possesses its own maturity cycle, there should be the optimal timing for mature oocyte vitrification. The purpose of this study was to observe the effects of frozen timing on the spindle density, the angle between the polar body and spindle, and embryo development of intracytoplasmic sperm injection (ICSI) in vitrified mouse mature oocytes and explore its possible mechanism. Mouse oocytes were randomly divided into three groups according to different frozen timing including Groups A, B, and C in which oocytes were vitrified within 2 h after ovum pick-up, and 3-4 and 5-6 h after ovum pick-up, respectively. Spindle-related parameters were measured, ICSI was performed. The spindle occurrence rate of vitrified-thawed oocytes was 98.4% in Group A, 82.3% in Group B, and 75.8% in Group C, without statistical differences between pre-vitrification and post-thawing and among the three groups (P > 0.05). The angles between the polar body and spindle were larger after thawing than before vitrification (P < 0.01). The spindle retardance values were lower after thawing than before vitrification in Groups B and C (P < 0.05), but higher in Group A (P < 0.05). The spindle retardance values before vitrification were higher in Group B than in Groups A and C (P < 0.05), but the spindle retardance value, oocyte survival and two-cell rate after thawing were higher in Group A than in Groups B and C (P < 0.05). There were no statistical differences in ICSI fertility rate between the three groups (P > 0.05). The damage on the spindle is the slightest and embryo quality is the highest in the mouse oocytes vitrified within 2 h after ovum pick-up. The spindle retardance value is more valuable than the spindle occurrence rate in the evaluation of vitrified-thawed oocyte quality, and is positively correlated with embryo quality.

Predicting live birth chances for women with multiple consecutive failing IVF cycles: a simple and accurate prediction for routine medical practice

BACKGROUND

Women having experienced several consecutive failing IVF cycles constitute a critical and particular subset of patients, for which growing perception of irremediable failure, increasing costs and IVF treatment related risks necessitate appropriate decision making when starting or not a new cycle. Predicting chances of LB might constitute a useful tool for discussion between the patient and the clinician. Our essential objective was to dispose of a simple and accurate prediction model for use in routine medical practice. The currently available predictive models applicable to general populations cannot be considered as accurate enough for this purpose.

METHODS

Patients with at least four consecutive Failing cycles (CFCs) were selected. We constructed a predictive model of LB occurrence during the last cycle, by using a stepwise logistic regression, using all the baseline patient characteristics and intermediate stage variables during the four first cycles.

RESULTS

On as set of 151 patients, we identified five determinant predictors: the number of previous cycles with at least one gestational sac (NGS), the mean number of good-quality embryos, age, male infertility (MI) aetiology and basal FSH. Our model was characterized by a much higher discrimination as the existing models (C-statistics=0.76), and an excellent calibration.

CONCLUSIONS

Couples having experienced multiple IVF failures need precise and appropriate information to decide to resume or interrupt their fertility project. Our essential objective was to dispose of a simple and accurate prediction model to allow a routine practice use. Our model is adapted to this purpose: It is very simple, combines five easily collected variables in a short calculation; it is more accurate than existing models, with a fair discrimination and a well calibrated prediction.

Folic acid facilitates in vitro maturation of mouse and Xenopus laevis oocytes

The water-soluble B vitamins, folate and folic acid, play an important role in reproductive health, but little is known about the effects of folic acid on infertility. The present study tested the hypothesis that folic acid affects oocyte maturation, a possible cause of female infertility. We have studied the in vitro maturation of mouse and Xenopus oocytes. Hypoxanthine (Hx) was used as an inhibitor of mouse oocyte maturation to mimic in vivo conditions by maintaining high levels of cyclic-AMP. The frequency of first polar body (PB1) formation and germinal vesicle breakdown (GVBD) in mouse oocytes was decreased by Hx. This effect was counteracted by folic acid added to the medium. PB1 extrusion and GVBD percentages rose to 27·7 and 40·0% from 12·8 and 19·9%, respectively, by exposure to 500 μM-folic acid. Folic acid also restored the spindle configuration, which had been elongated by Hx, as well as normalising the distribution of cortical granules (CG). In folic acid-treated Xenopus eggs, extracellular signal-regulated kinase 1 was phosphorylated, cyclin B2 and Mos were up-regulated and the frequency of GVBD was accelerated. Taken together, the findings suggest that folic acid facilitates oocyte maturation by altering the expression and phosphorylation of proteins involved in M-phase-promoting factor and mitogen-activated protein kinase pathways, as well as causing changes in spindle configuration and CG migration.

Kinesin-1 prevents capture of the oocyte meiotic spindle by the sperm aster

Centrioles are lost during oogenesis and inherited from the sperm at fertilization. In the zygote, the centrioles recruit pericentriolar proteins from the egg to form a mature centrosome that nucleates a sperm aster. The sperm aster then captures the female pronucleus to join the maternal and paternal genomes. Because fertilization occurs before completion of female meiosis, some mechanism must prevent capture of the meiotic spindle by the sperm aster. Here we show that in wild-type Caenorhabditis elegans zygotes, maternal pericentriolar proteins are not recruited to the sperm centrioles until after completion of meiosis. Depletion of kinesin-1 heavy chain or its binding partner resulted in premature centrosome maturation during meiosis and growth of a sperm aster that could capture the oocyte meiotic spindle. Kinesin prevents recruitment of pericentriolar proteins by coating the sperm DNA and centrioles and thus prevents triploidy by a nonmotor mechanism.

Relationship between meiotic spindle characteristics in human oocytes and the timing of the first zygotic cleavage after intracytoplasmic sperm injection

PURPOSE

To investigate the relationship between meiotic spindle characteristics in human oocytes and the timing of the first zygotic cleavage after intracytoplasmic sperm injection (ICSI).

METHODS

Zygotes that had cleaved to two-cell stage by 27 h post-ICSI were classified as early cleaving and the remainder as late cleaving. Meiotic spindle parameters previously imaged using the PolScope were compared between the two groups.

RESULTS

Of 384 embryos, 163 were classed as early cleaving and 221 as late cleaving. The rate of blastocyst formation or pregnancy by Day 2 embryo transfer was significantly higher following early cleavage than after late cleavage (52.4% vs. 24.4% or 32.6% vs. 11.4%). Spindle areas (108.0 vs. 89.8 μm(2)), lengths (14.7 vs. 13.4 μm) and PolScope retardance were also significantly greater in the early cleaving group.

CONCLUSIONS

Meiotic spindle parameters determine the timing of the first zygotic cleavage and are strong indicators of human embryo developmental potential.

Relevance and Methodology for the Morphological Analysis of Oocyte Quality in IVF and ICSI

Oocytes collected from patients following ovarian stimulation exhibit varying qualities. The quality of oocytes has an effect on its subsequent fertilization, developmental competence post-fertilization and the viability of resultant embryos. The aim of this article was to review the morphological criteria devised for assessment of oocyte quality by ordinary light and polarized light microscopy before IVF or ICSI. The parameters employed in the evaluation of oocyte morphology include the appearance of: structure of the cumulus–oocyte complex, oocyte cytoplasm, perivitelline space, zona pellucida, polar body and meiotic spindle.

Predictive value of oocyte morphology in human IVF: a systematic review of the literature

BACKGROUND

Non-invasive selection of developmentally competent human oocytes may increase the overall efficiency of human assisted reproduction and is regarded as crucial in countries where legal, social or religious factors restrict the production of supernumerary embryos. The purpose of this study was to summarize the predictive value for IVF success of morphological features of the oocyte that can be obtained by light or polarized microscopic investigations.

METHODS

Studies about oocyte morphology and IVF/ICSI outcomes were identified by using a systematic literature search.

RESULTS

Fifty relevant articles were identified: 33 analysed a single feature, 9 observed multiple features and investigated the effect of these features individually, 8 summarized the effect of individual features. Investigated structures were the following: meiotic spindle (15 papers), zona pellucida (15 papers), vacuoles or refractile bodies (14 papers), polar body shape (12 papers), oocyte shape (10 papers), dark cytoplasm or diffuse granulation (12 papers), perivitelline space (11 papers), central cytoplasmic granulation (8 papers), cumulus–oocyte complex (6 papers) and cytoplasm viscosity and membrane resistance characteristics (2 papers). None of these features were unanimously evaluated to have prognostic value for further developmental competence of oocytes.

CONCLUSIONS

No clear tendency in recent publications to a general increase in predictive value of morphological features was found. These contradicting data underline the importance of more intensive and coordinated research to reach a consensus and fully exploit the predictive potential of morphological examination of human oocytes.

Time course of meiotic spindle development in MII oocytes

The aim of this study was to examine changes in meiotic spindle morphology over time to potentially optimize timing for ICSI. Using polarized light microscopy, images of MII oocytes were captured after retrieval of oocytes in stimulated cycles at six time intervals in culture: 36–36.5 h, 36.5–37.0 h, 38–38.5 h, 39–39.5 h, 40–40.5 h and 40.5–41 h post hCG. Captured images were analysed for spindle presence and their retardance. Results showed that spindles were detected in 58% (45/78) of oocytes at 36–36.5 h. This percentage rose to a peak (96% vs. 58%, p < 0.001) at 39–39.5 h and stabilized between 39–40.5 h post trigger then significantly declined at 40.5–41 h post hCG (96% vs. 77%, p < 0.001). Average spindle retardance increased from 36–36.5 h (1.8 ± 0.7 nm) until it peaked at 39–40.5 h (3.8 ± 0.8 nm, p < 0.0001) and then declined significantly after 40.5–41 h (3.2 ± 0.9 nm, p = 0.0001). These results show that the meiotic spindle appearance is time dependent with the majority of oocytes having detectable spindles and highest retardance between 39–40.5 h post hCG under currently used stimulation protocol after which they start to disaggregate. 39–40.5 h post hCG may be the optimal time for ICSI.

Vacuolated oocytes: fertilization and embryonic arrest following intra-cytoplasmic sperm injection in a patient exhibiting persistent oocyte macro vacuolization--case report

PURPOSE

To describe a case of homogeneous macro vacuolar formation in oocytes from a patient undergoing IVF/ICSI over 3 cycles and implications thereof.

METHODS

Case report and analysis of cycle outcomes including spindle visualization to determine severity of internal disruption caused.

RESULTS

Characteristic macro vacuoles (>25 microm diameter) were identified in the vast majority of oocytes. Spindle visualization identified that macro vacuoles were not associated with spindle displacement. IVF resulted in failed fertilization. Low numbers of fertilized oocytes were obtained through ICSI. The vast majority of embryos exhibited maturation arrest on day 2.

CONCLUSIONS

It is likely that persistent Oocyte Macro Vacuolization is the cause of infertility in this patient. It probably has a biological basis and possibly a genetic cause, resulting in either uncontrollable endocytosis or poor exocytosis and consequent vacuolar formation.

A PolScope evaluation of meiotic spindle dynamics in frozen-thawed oocytes

In mature human oocytes, the metaphase II (MII) spindle presence and birefringence signal detected through the PolScope may vary before and after freezing. In particular, spindle dynamics during the first few hours after thawing is still under study. In this study, oocytes from stimulated ovaries were cryopreserved in 1.5 mol/l 1,2-propanediol with 0.3 mol/l sucrose using a slow freezing-rapid thawing method. Oocytes were examined with the PolScope for the presence, intensity of signal birefringence and size of the meiotic spindle before freezing and at 0, 1 and 2 h post-thaw (where 0 h = the time of the end of the thawing procedure). Of the 173 surviving oocytes exhibiting a spindle before freezing, 82.7% (143/173) showed spindle birefringence within 1 h of thawing. However, at the end of the thawing procedure the intensity of spindle birefringence (retardance) and the spindle length were smaller in comparison to the pre-freezing condition. These parameters increased after 1 h, although were not restored to the value observed before freezing. No significant changes were observed by extending the culture to 2 h.

Are there non-invasive markers in human oocytes that can predict pregnancy outcome?

Predictive criteria for selection of the best embryo for single embryo transfer remain elusive. This study aimed to determine if non-invasive markers in human oocytes, detectable using polarized light microscopy, can predict pregnancy outcome. Twenty-two pregnancy-producing oocytes from 19 patients had their morphological features compared with 30 oocytes from 19 age-matched patients whose transfer did not result in a pregnancy. Both pregnant and non-pregnant patients had similar numbers of oocytes collected (average: 11.9 +/- 2.8 versus 11.3 +/- 2.9) and similar fertilization rates (70.1% versus 69.6%). All embryos transferred were 4-cell cleavage-stage on day 2 with <10% fragmentation. Meiotic spindles were examined at 39-40 h following human chorionic gonadotrophin administration for spindle normality, length, density and angle from first polar body. There was a significant difference in spindle normality in oocytes in the pregnant patients compared with oocytes in the non-pregnant patients (100% versus 33%, P < 0.001). Spindle density was significantly higher in those oocytes resulting in pregnancy (3.0 +/- 1.23 nm versus 2.5 +/- 0.7 nm, P = 0.02). These oocyte markers may provide a useful non-invasive tool in the selection of the embryo most likely to produce a pregnancy.

Human embryos derived by somatic cell nuclear transfer using an alternative enucleation approach

Somatic cell nuclear transfer (SCNT) was used to generate patient-specific embryonic stem cells (ESCs) from blastocysts cloned by nuclear transfer (ntESCs). In this study, a total of 135 oocytes were obtained from 12 healthy donors (30-35 years). Human oocytes, obtained within 2 h following transvaginal aspiration, were enucleated using a Spindle Imaging System to position the spindle and chromosomes that lay on the metaphase plate, and a Zona Infrared Laser Optical System was used to open a single hole in the zona pellucida at the ~ 2 o'clock position. Human fibroblasts and lymphocytes were used to construct SCNT embryos. Nearly half (26 of 58) of the oocytes were fused after electrofusion and embryo development rates were 96.2% (two-cell, 25 of 26), 92.3% (four-cell, 24 of 26), 61.5% (eight-cell, 16 of 26), 34.6% (16-cell, 9 of 26), 26.9% (morula, 7 of 26), and 19.2% (blastocyst, 5 of 26), respectively, following incubation in improved G-series sequential medium. One cloned blastocyst was used for STR-DNA identification and genetic polymorphism analysis of mtDNA, and STR-DNA analysis of all cloned blastocysts indicated they were derived from SCNT. Quantitative analysis showed that mtDNA of cloned embryos reflected the change tendency of those observed in human IVF embryos. Our research provides an alternative enucleation approach for producing human SCNT-derived blastocysts, and may aid in providing a new method for human therapeutic cloning.

Assisted fertilization and embryonic axis formation in higher primates

In naturally fertilized embryos of various organisms, the spermatozoon provides a localized cue to initiate early embryonic patterning. In mice, the sperm entry point (SEP) may reorient the first cleavage division, which separates the zygote into two halves that follow distinct fates. However, it is unknown whether the mechanical injection of spermatozoa into an oocyte by intracytoplasmic sperm injection (ICSI), a technique commonly used in human assisted reproduction, possesses such a role. Rhesus macaque embryos fertilized by ICSI were examined in order to determine the consequences of placing the spermatozoon at specific positions in the ooplasm and whether this can provide new information about patterning in mammalian eggs. The SEP specified by the injected spermatozoa was most often localized near the first cleavage plane and was mainly distributed along the boundary zone that separates the embryonic and abembryonic parts of the monkey blastocyst. Moreover, the ICSI data, when compared with naturally fertilized mouse embryos, showed a similar outcome in terms of cleavage axes and first embryonic axis specification. As there are no studies to date regarding sperm entry in human oocytes and its influence on embryonic development, this investigation using the rhesus macaque as a clinical model is noteworthy.

Relationship between visualization of meiotic spindle in human oocytes and ICSI outcomes: a meta-analysis

The objective of this meta-analysis was to investigate the influence of meiotic spindle visualization in human oocytes on intracytoplasmic sperm injection (ICSI) outcomes. Search strategies included on-line surveys of databases (MEDLINE, EMBASE, Science Citation Index, Cochrane Controlled Trials Register and Ovid). The fixed effect was used for odds ratio. Ten trials fulfilled the inclusion criteria comparing in-vitro and clinical ICSI outcomes with or without visualization of meiotic spindle in fresh and in-vivo matured oocytes. According to the meta-analysis, the results showed statistically significant higher fertilization rate (P < 0.0001) when the meiotic spindle was viewed than when it was not. Moreover, the percentage of pro-nuclear-stage embryos with good morphology (P = 0.003), cleavage rate (P < 0.0001), percentage of day-3 top-quality embryos (P = 0.003) and percentage of embryos that reached the blastocyst stage (P < 0.0001) were statistically significantly better among embryos derived from oocytes in which meiotic spindle was viewed compared with those in which meiotic spindle was not observed. However, these differences were not observed in the clinical pregnancy or implantation rates. This observation has clinical relevance mainly in countries where there is a legal limit on the number of oocytes to be fertilized. However, additional controlled trials are needed to further confirm these results.

Effect of denuding on polar body position in in-vitro matured oocytes

The aim of this study was to determine whether the denuding procedure causes the polar body to move within the perivitelline space. Only those patients undergoing IVF who had unused in-vitro matured (IVM) oocytes were included in this study. IVM oocytes were initially viewed under a non-invasive, polarized light microscope. A laser was used to mark the location of the polar body on the zona. Oocytes were subjected to the denuding procedure with a 150 microm, 135 microm and 125 mum diameter pipette. After each pipetting, the oocytes were viewed again to determine whether the polar body had moved. After denuding, the oocyte was left to culture overnight and viewed 24 h later. After denuding with the 150 microm, 135 microm and 125 microm pipettes and after 24 h in culture, the average angle between the spindle and polar body was 15.4 +/- 10.4 degrees , 16.1 +/- 10.1 degrees , 20.9 +/- 11.7 degrees , and 26.7 +/- 18.2 degrees , respectively (P = 0.0021). Slight changes in angles were noted between denuding with the different diameter pipettes. The largest changes in angles were seen after 24 h in culture.