Enhanced polarizing microscopy as a new tool in aneuploidy research in oocytes

Picrosirius-Polarization Method for Collagen Fiber Detection in Tendons: A Mini-Review

Although the structure and composition of collagen have been studied by polarized light microscopy since the early 19th century, many studies and reviews have paid little or no attention to the morphological problems of histopathological diagnosis. The morphology of collagen fibers is critical in guiding mechanical and biological properties in both normal and pathological tendons. Highlighting the organization and spatial distribution of tendon‐containing collagen fibers can be very useful for visualizing a tendon's ultrastructure, biochemical and indirect mechanical properties, which benefits other researchers and clinicians. Picrosirius red (PSR) staining, relying on the birefringence of collagen fibers, is one of the best understood histochemical methods that can highly and specifically underline fibers better than other common staining techniques when combined with polarized light microscopy (PLM). Polarized light microscopy provides complementary information about collagen fibers, such as orientation, type and spatial distribution, which is important for a comprehensive assessment of collagen alteration in a tendon. Here, this brief review serves as a simplistic and important primer to research developments in which differential staining of collagen types by the Picrosirius‐polarization method is increasing in diverse studies of the medical field, mainly in the assessment of the morphology, spatial distribution, and content of collagen in tendons.

Loss of heterozygosity by SCRaMbLEing

Genetic variation drives phenotypic evolution within populations. Genetic variation can be divided into different forms according to the size of genomic changes. However, study of large-scale genomic variation such as structural variation and aneuploidy is still limited and mainly based on the static, predetermined feature of individual genomes. Here, using SCRaMbLE, different levels of loss of heterozygosity (LOH) events including short-range LOH, long-range LOH and whole chromosome LOH were detected in evolved strains. By contrast, using rapid adaptive evolution, aneuploidy was detected in the adaptive strains. It was further found that deletion of gene GLN3, long-range LOH in the left arm of synthetic chromosome X, whole chromosome LOH of synthetic chromosome X, and duplication of chromosome VIII (trisomy) lead to increased rapamycin resistance in synthetic yeast. Comparative analysis of genome stability of evolved strains indicates that the aneuploid strain has a higher frequency of degeneration than the SCRaMbLEd strain. These findings enrich our understanding of genetic mechanism of rapamycin resistance in yeast, and provide valuable insights into yeast genome architecture and function.

Regulation of the meiotic divisions of mammalian oocytes and eggs

Initiated by luteinizing hormone and finalized by the fertilizing sperm, the mammalian oocyte completes its two meiotic divisions. The first division occurs in the mature Graafian follicle during the hours preceding ovulation and culminates in an extreme asymmetric cell division and the segregation of the two pairs of homologous chromosomes. The newly created mature egg rearrests at metaphase of the second meiotic division prior to ovulation and only completes meiosis following a Ca²⁺ signal initiated by the sperm at gamete fusion. Here, we review the cellular events that govern the passage of the oocyte through meiosis I with a focus on the role of the spindle assembly checkpoint in regulating its timing. In meiosis II, we examine how the egg achieves its arrest and how the fertilization Ca²⁺ signal allows the initiation of embryo development.

Regulation of chromosome segregation in oocytes and the cellular basis for female meiotic errors

BACKGROUND

Meiotic chromosome segregation in human oocytes is notoriously error-prone, especially with ageing. Such errors markedly reduce the reproductive chances of increasing numbers of women embarking on pregnancy later in life. However, understanding the basis for these errors is hampered by limited access to human oocytes.

OBJECTIVE AND RATIONALE

Important new discoveries have arisen from molecular analyses of human female recombination and aneuploidy along with high-resolution analyses of human oocyte maturation and mouse models. Here, we review these findings to provide a contemporary picture of the key players choreographing chromosome segregation in mammalian oocytes and the cellular basis for errors.

SEARCH METHODS

A search of PubMed was conducted using keywords including meiosis, oocytes, recombination, cohesion, cohesin complex, chromosome segregation, kinetochores, spindle, aneuploidy, meiotic cell cycle, spindle assembly checkpoint, anaphase-promoting complex, DNA damage, telomeres, mitochondria, female ageing and female fertility. We extracted papers focusing on mouse and human oocytes that best aligned with the themes of this review and that reported transformative and novel discoveries.

OUTCOMES

Meiosis incorporates two sequential rounds of chromosome segregation executed by a spindle whose component microtubules bind chromosomes via kinetochores. Cohesion mediated by the cohesin complex holds chromosomes together and should be resolved at the appropriate time, in a specific step-wise manner and in conjunction with meiotically programmed kinetochore behaviour. In women, the stage is set for meiotic error even before birth when female-specific crossover maturation inefficiency leads to the formation of at-risk recombination patterns. In adult life, multiple co-conspiring factors interact with at-risk crossovers to increase the likelihood of mis-segregation. Available evidence support that these factors include, but are not limited to, cohesion deterioration, uncoordinated sister kinetochore behaviour, erroneous microtubule attachments, spindle instability and structural chromosomal defects that impact centromeres and telomeres. Data from mice indicate that cohesin and centromere-specific histones are long-lived proteins in oocytes. Since these proteins are pivotal for chromosome segregation, but lack any obvious renewal pathway, their deterioration with age provides an appealing explanation for at least some of the problems in older oocytes.

WIDER IMPLICATIONS

Research in the mouse model has identified a number of candidate genes and pathways that are important for chromosome segregation in this species. However, many of these have not yet been investigated in human oocytes so it is uncertain at this stage to what extent they apply to women. The challenge for the future involves applying emerging knowledge of female meiotic molecular regulation towards improving clinical fertility management.

The lipid peroxidation product 4-hydroxynonenal contributes to oxidative stress-mediated deterioration of the ageing oocyte

An increase in intraovarian reactive oxygen species (ROS) has long been implicated in the decline in oocyte quality associated with maternal ageing. Oxidative stress (OS)-induced lipid peroxidation and the consequent generation of highly electrophilic aldehydes, such as 4-hydroxynonenal (4-HNE), represents a potential mechanism by which ROS can inflict damage in the ageing oocyte. In this study, we have established that aged oocytes are vulnerable to damage by 4-HNE resulting from increased cytosolic ROS production within the oocyte itself. Further, we demonstrated that the age-related induction of OS can be recapitulated by exposure of germinal vesicle (GV) oocytes to exogenous H₂O₂. Such treatments stimulated an increase in 4-HNE generation, which remained elevated during in vitro oocyte maturation to metaphase II. Additionally, exposure of GV oocytes to either H₂O₂ or 4-HNE resulted in decreased meiotic completion, increased spindle abnormalities, chromosome misalignments and aneuploidy. In seeking to account for these data, we revealed that proteins essential for oocyte health and meiotic development, namely α-, β-, and γ-tubulin are vulnerable to adduction via 4-HNE. Importantly, 4-HNE-tubulin adduction, as well as increased aneuploidy rates, were resolved by co-treatment with the antioxidant penicillamine, demonstrating a possible therapeutic mechanism to improve oocyte quality in older females.

Optical coherence microscopy as a novel, non-invasive method for the 4D live imaging of early mammalian embryos

Imaging of living cells based on traditional fluorescence and confocal laser scanning microscopy has delivered an enormous amount of information critical for understanding biological processes in single cells. However, the requirement for a high numerical aperture and fluorescent markers still limits researchers’ ability to visualize the cellular architecture without causing short- and long-term photodamage. Optical coherence microscopy (OCM) is a promising alternative that circumvents the technical limitations of fluorescence imaging techniques and provides unique access to fundamental aspects of early embryonic development, without the requirement for sample pre-processing or labeling. In the present paper, we utilized the internal motion of cytoplasm, as well as custom scanning and signal processing protocols, to effectively reduce the speckle noise typical for standard OCM and enable high-resolution intracellular time-lapse imaging. To test our imaging system we used mouse and pig oocytes and embryos and visualized them through fertilization and the first embryonic division, as well as at selected stages of oogenesis and preimplantation development. Because all morphological and morphokinetic properties recorded by OCM are believed to be biomarkers of oocyte/embryo quality, OCM may represent a new chapter in imaging-based preimplantation embryo diagnostics.

Polarization resolved second harmonic microscopy

Second harmonic (SH) microscopy has proven to be a powerful imaging modality over the past years due to its intrinsic advantages as a multiphoton process with endogenous contrast specificity, which allows pinhole-less optical sectioning, non-invasive observation, deep tissue penetration, and the possibility of easier signal detection at visible wavelengths. Depending on the relative orientation between the polarization of the incoming light and the second-order susceptibility of non-centrosymmetric structures, SH microscopy provides the unique capacity to probe the absolute molecular structure of a broad variety of biological tissues without the necessity for additional labeling. In addition, SH microscopy, when working with polarimetry, provides clear and in-depth insights on the details of molecular orientation and structural symmetry. In this review, the working principles of the polarization resolving techniques and the corresponding implements of SH microscopy are elucidated, with focus on Stokes vector based polarimetry. An overview of the advancements on SH anisotropy measurements are also presented. Specifically, the recent progresses on the following three topics in polarization resolved SH microscopy will be elucidated, which include Stokes vector resolving for imaging molecular structure and orientation, 3-D structural chirality by SH circular dichroism, and correlation with fluorescence lifetime imaging (FLIM) for in vivo wound healing diagnosis. The potentials and challenges for future researches in exploring complex biological tissues are also discussed.

Predictive value of spindle retardance in embryo implantation rate

PURPOSE

We evaluated the relationship between meiotic spindle characteristics and in vitro fertilization cycle outcome.

METHODS

Five hundred sixty-nine oocytes from 86 in vitro fertilization cycles were analyzed for fertilization and subsequent implantation rates. Oocytes were assessed for maturation status. The oocytes and embryos were cultured in sequential and nonsequential media (G Series, Vitrolife, Sweden) and incubated in 6% CO₂, 5% O₂ at 37 °C. Two hours following oocyte decumulation (38-39 h post-hCG/GnRH administration) and prior to microinjection, the structure of the meiotic spindle was assessed using the Oosight Imaging System (CRI, UK).

RESULTS

Four hundred fifty-six oocytes (80.5%) had a visible meiotic spindle, 82 (14.7%) had no meiotic spindle, and 31 (5.5%) were in telophase I. Oocytes exhibiting a meiotic spindle had a significantly higher fertilization rate and a lower rate of abnormal fertilization. Implantation data were obtained for 195 of the embryos transferred. The implantation rate for embryos derived from oocytes with a meiotic spindle was 32.9%, while in embryos originating from oocytes without a meiotic spindle and oocytes in telophase, this value dropped significantly (8.8 and 0%, respectively). To determine the correlation between retardance values and implantation rate for each oocyte, we established four groups, finding a range of retardance values with significantly higher implantation rates (27.5, 21, 29.3, and 53.8%, respectively).

CONCLUSION

Meiotic spindle imaging may be a valuable tool for prediction of oocyte quality, and retardance values of meiotic spindles, together with classical morphological classification, can be useful to select embryos with a higher implantation potential.

Improved cryotolerance and developmental potential of in vitro and in vivo matured mouse oocytes by supplementing with a glutathione donor prior to vitrification

STUDY QUESTION

Can supplementation of media with a glutathione (GSH) donor, glutathione ethyl ester (GEE), prior to vitrification protect the mouse oocyte from oxidative damage and critical changes in redox homeostasis, and thereby improve cryotolerance?

SUMMARY ANSWER

GEE supplementation supported redox regulation, rapid recovery of spindle and chromosome alignment after vitrification/warming and improved preimplantation development of mouse metaphase II (MII) oocytes.

WHAT IS KNOWN ALREADY

Cryopreservation may affect mitochondrial functionality, induce oxidative stress, and thereby affect spindle integrity, chromosome segregation and the quality of mammalian oocytes. GEE is a membrane permeable GSH donor that promoted fertilization and early embryonic development of macaque and bovine oocytes after IVM.

STUDY DESIGN, SIZE, DURATION

Two experimental groups consisted of (i) denuded mouse germinal vesicle (GV) oocytes that were matured in vitro in the presence or absence of 1 mM GEE (IVM group 1) and (ii) in vivo ovulated (IVO) MII oocytes that were isolated from the ampullae and exposed to 1 mM GEE for 1 h prior to vitrification (IVO group 2). Recovery of oocytes from both groups was followed after CryoTop vitrification/warming for up to 2 h and parthenogenetic activation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Reactive oxygen species (ROS), spindle morphology and chromosome alignment were analyzed by confocal laser scanning microscopy (CLSM) and polarization microscopy in control and GEE-supplemented MII oocytes. The relative overall intra-oocyte GSH content was assessed by analysis of monochlorobimane (MBC)-GSH adduct fluorescence in IVM MII oocytes. The GSH-dependent intra-mitochondrial redox potential (E^m_GSH) of IVM MII oocytes was determined after microinjection with specific mRNA at the GV stage to express a redox-sensitive probe within mitochondria (mito-Grx1-roGFP2). The absolute negative redox capacity (in millivolts) was determined by analysis of fluorescence of the oxidized versus the reduced form of sensor by CLSM and quantification according to Nernst equation. Proteome analysis was performed by quantitative 2D saturation gel electrophoresis (2D DIGE). Since microinjection and expression of redox sensor mRNA required removal of cumulus cells, and IVM of denuded mouse oocytes in group 1 induces zona hardening, the development to blastocysts was not assessed after IVF but instead after parthenogenetic activation of vitrified/warmed MII oocytes from both experimental groups.

MAIN RESULTS AND ROLE OF CHANCE

IVM of denuded mouse oocytes in the presence of 1 mM GEE significantly increased intra-oocyte GSH content. ROS was not increased by CryoTop vitrification but was significantly lower in the IVM GEE group compared to IVM without GEE before vitrification and after recovery from vitrification/warming (P < 0.001). Vitrification alone significantly increased the GSH-dependent intra-mitochondrial redox capacity after warming (E^m_GSH, P < 0.001) in IVM oocytes, presumably by diffusion/uptake of cytoplasmic GSH into mitochondria. The presence of 1 mM GEE during IVM increased the redox capacity before vitrification and there was no further increase after vitrification/warming. None of the reproducibly detected 1492 spots of 2D DIGE separated proteins were significantly altered by vitrification or GEE supplementation. However, IVM of denuded oocytes significantly affected spindle integrity and chromosome alignment right after warming from vitrification (0 h) in group 1 and spindle integrity in group 2 (P < 0.05). GEE improved recovery in IVM group as numbers of oocytes with unaligned chromosomes and aberrant spindles was not significantly increased compared to unvitrified controls. The supplementation with GEE for 1 h before vitrification also supported more rapid recovery of spindle birefringence. GEE improved significantly development to the 2-cell stage for MII oocytes that were activated directly after vitrification/warming in both experimental groups, and also the blastocyst rate in the IVO GEE-supplemented group compared to the controls (P < 0.05).

LARGE SCALE DATA

None LIMITATIONS, REASONS FOR CAUTION: The studies were carried out in a mouse model, in IVM denuded rather than cumulus-enclosed oocytes, and in activated rather than IVF MII oocytes. Whether the increased GSH-dependent intra-mitochondrial redox capacity also improves male pronuclear formation needs to be studied further experimentally. The influence of GEE supplementation requires also further examination and optimization in human oocytes before it can be considered for clinical ART.

WIDER IMPLICATIONS OF THE FINDINGS

Although GEE supplementation did not alter the proteome at MII, the GSH donor may support cellular homeostasis and redox regulation and, thus, increase developmental competence. While human MII oocyte vitrification is an established procedure, GEE might be particularly beneficial for oocytes that suffer from oxidative stress and reduced redox capacity (e.g. aged oocytes) or possess low GSH due to a reduced supply of GSH from cumulus. It might also be of relevance for immature human oocytes that develop without cumulus to MII in vitro (e.g. in ICSI cycles) for ART.

STUDY FUNDING AND COMPETING INTERESTS

The study has been supported by the German Research Foundation (DFG FOR 1041; EI 199/3-2). There are no conflict of interests.

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

Background:

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

Objectives:

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

Materials and Methods:

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

Results:

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

Conclusions:

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

Developmental competence of equine oocytes: impacts of zona pellucida birefringence and maternally derived transcript expression

In the present study, equine oocytes were classified into groups of presumably high and low developmental competence according to cumulus morphology, as well as oocyte ability to metabolise brilliant cresyl blue (BCB) stain. All oocytes were evaluated individually in terms of morphometry, zona pellucida birefringence (ZPB) and relative abundance of selected candidate genes. Oocytes with an expanded cumulus (Ex), representing those with presumably high developmental competence, had a significantly thicker zona (18.2 vs 17.3µm) and a significantly higher ZPB (64.6 vs 62.1) than oocytes with a compacted cumulus (Cp). Concurrently, oocytes classified as highly developmentally competent (BCB+) had a significantly thicker zona (18.8 vs 16.1µm) and significantly higher ZPB (63.1 vs 61.3) compared with oocytes classified as having low developmental competence. Expression of TFAM, STAT3 and CKS2 was significantly higher in Ex compared with Cp oocytes, whereas expression of COX1, ATPV6E and DNMT1 was lower. Together, the data reveal that developmentally competent equine oocytes are larger in size, have higher ZPB values and exhibit a typical genetic signature of maternally derived transcripts compared with oocytes with lower in vitro developmental competence.

Zona pellucida birefringence correlates with developmental capacity of bovine oocytes classified by maturational environment, COC morphology and G6PDH activity

In the present study we aimed to analyse structural changes during in vitro maturation of the bovine zona pellucida (ZP) by scanning electron microscopy (SEM) ands zona pellucida birefringence (ZPB). Here we show that alterations during in vitro maturation invasively analysed by SEM are reflected in ZPB. In vivo-matured oocytes displayed significantly lower birefringence parameters and significantly higher blastocyst rates compared with in vitro-derived oocytes (39.1% vs 21.6%). The same was observed for in vitro-matured oocytes with cumulus-oocyte complex (COC) Quality 1 (Q1) compared with Q3-COCs with respect to zona birefringence and developmental capacity. Immature oocytes with Q1-COCs displayed higher ZPB values and a higher developmental capacity to the blastocyst stage (27.7% vs 16.9%) compared with immature Q3-COCs. Considering in vitro-matured oocytes, only those with Q1-COC showed a trend for ZPB similar to in vivo-matured oocytes. Therefore, a decreasing trend for ZPB during in vitro maturation seems to be typical for high-quality oocytes and successful cytoplasmic maturation. In accordance, fully-grown immature oocytes reached significantly higher blastocyst rates (32.0% vs 11.5%) and lower ZPB values compared with still-growing ones. In conclusion, we successfully evaluated the applicability of zona imaging to bovine oocytes: alterations during in vitro maturation invasively analysed by scanning electron microscopy were reflected in the birefringence of the zona pellucida of bovine oocytes affecting developmental capacity at the same value. Therefore ZPB measurement by live zona imaging has potential to become a new tool to assess correctness of in vitro maturation and to predict developmental competence.

Utility of animal models for human embryo culture: nonhuman primates

Nonhuman primates are the closest relatives to humans and therefore our most evolutionary close cousins. While marvelous insights are gleaned from studying rodents and other systems, it is impossible to envision how those mechanistic findings can be responsibly translated to the clinic without the appropriate use of nonhuman primates. Thankfully, noninvasive technologies now permit nonhuman primate studies without endangering the model itself. Work with primates is predicted to continue to lead the fields of reproductive and regenerative medicine for the rest of the twenty-first century.

The relationship between meiotic spindle imaging and outcome of intracytoplasmic sperm injection: a retrospective study

Meiotic spindle analysis with a non-invasive technique, the PolScope, is used to protect the meiotic spindle from damage during microinjection. To evaluate the predictive feature of PolScope, we have designed a retrospective study to analyse the correlation between the meiotic spindle visualisation with regard to spindle location and outcomes of assisted reproductive technologies (ART), including patient age, previous cycles, the number of the collected oocytes, fertilisation rates (FR), pronuclear scoring (PNS) and embryo scoring of the days from two to five. All of the data belonging to 1496 oocytes from 190 patients were statistically analysed. We found that the oocytes having PolScope visualised spindle have higher FR, and also observed that when the spindle located at 0°-30° according to the first polar body, gave the highest FR. PNS gave higher scores in the spindle visualised group, but spindle angle did not affect PNS outcomes. Although a correlation was found between spindle visualisation and developed embryo qualities, particularly at day 2 and 3, spindle angles did not affect embryo quality. We conclude that PolScope microscopy has an efficiency to estimate FR, and cleavage stage embryo development.

Evidence that carbonyl stress by methylglyoxal exposure induces DNA damage and spindle aberrations, affects mitochondrial integrity in mammalian oocytes and contributes to oocyte ageing

BACKGROUND

Highly reactive carbonyl compounds formed during glycolysis, such as methylglyoxal (MG), can lead to the formation of 'advanced glycation end products' (AGE) and carbonyl stress. Toxic AGEs are suspected to accumulate and play a role in reducing quality and developmental potential of mammalian oocytes of aged females and in PCOS and diabetic patients. Whether and how MG and AGE affect young and aged oocytes at the cellular level is unknown.

METHODS

The study consists of three parts. In Part A expression of MG-detoxifying enzymes glyoxalases 1 and 2 was analysed by RT-PCR at different stages of maturation in denuded oocytes (DO), cumulus-enclosed oocytes (CEO) and metaphase (M)II oocytes of the CD-1 mouse to obtain information on stage-specific susceptibility to carbonyl stress. DO and CEO from young and aged females and from stimulated cycles were exposed to MG during maturation in vitro to assess also age-related changes in sensitivity to carbonyl stress induced by MG. Induction of apoptosis by MG on in vitro maturing DO was assessed by terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling test. In Part B of the study, DO from large antral follicles of ovaries of adult, young MF-1 mice in late diestrous were exposed to MG to assess direct influences of MG and AGEs formed during continuous exposure to MG on rate and kinetics of maturation to MII, on DNA integrity (by γ-H2AX staining) in the germinal vesicle (GV) stage, and on spindle formation and chromosome alignment (by tubulin and pericentrin immunofluorescence and polarization microscopy), and chromosome segregation (by C-banding) during in vitro maturation. Since MG and AGEs can affect functionality of mitochondria in Part C, mitochondrial distribution and membrane potential was studied using JC-1 probe. Expression of a redox-sensitive mito-Grx1-roGFP2 protein in mitochondria of maturing oocytes by confocal laser scanning microscopy was employed to determine the inner mitochondrial glutathion (GSH)/glutathion disulfide (GSSG)-dependent redox potential.

RESULTS

Part A revealed that mRNA for glyoxalases decreases during meiotic maturation. Importantly, cumulus from aged mice in CEO obtained from stimulated cycles does not protect oocytes efficiently from MG-induced meiotic arrest during in vitro maturation. Part B showed that the MG-induced meiotic delay or arrest is associated with significant rises in spindle aberrations, chromosome congression failure and aberrant telophase I in oocytes. MG exposure of meiotically arrested GV-stage oocytes significantly increases the numbers of γ-H2AX spots in the nucleus suggesting increased DNA damage, while MG exposure during maturation affects chromatin condensation and induces chromosome lagging at anaphase I. Moreover, Part C revealed that carbonyl stress by chronic exposure to MG is associated with delays in changes in mitochondrial distribution and altered inner-mitochondrial GSH/GSSG redox potential, which might be particularly relevant for cytoskeletal dynamics as well as processes after fertilization. Sensitivity to a meiotic block by MG appears dependent on the genetic background.

CONCLUSIONS

The sensitivity to carbonyl stress by MG appears to increase with maternal age. Since MG-exposure induces DNA damage, meiotic delay, spindle aberrations, anaphase I lagging and epimutation, aged oocytes are particularly at risk for such disturbances in the absence of efficient protection by cumulus. Furthermore, disturbances in mitochondrial distribution and redox regulation may be especially critical for fertilization and developmental competence of oocytes exposed to MG and carbonyl stress before or during maturation, for instance, in aged females, or in PCOS or diabetic patients, in agreement with recent suggestions of correlations between poor follicular and embryonic development, lower pregnancy rate and presence of toxic AGEs in serum, irrespective of age.

Laboratory evaluation in oocyte cryopreservation suggests retrieved oocytes are comparable whether frozen for medical indications, deferred reproduction or oocyte donation

PURPOSE

to compare pre-cryo data from oocyte cryopreservation (OC) cycles performed for malignancy (MED) vs. elective deferment of reproduction (DR) or oocyte donation (OD).

METHODS

all patients were ≤40 y and underwent standard ovarian stimulation and retrieval. Prior to OC, meiotic spindle (MS) and zona pellucida (ZP) retardance was measured using digital polarized light microscopy (DPLM).

RESULTS

of 130 OC cycles, 49 were for MED, 73 for DR, and 8 for OD. Cycles completed for MED had an average of 9 ±1 spindle-positive oocytes with a mean MS retardance of 1.2  ± 02 nm and ZP retardance of 2.1 ± .06 nm, which was clinically comparable to the other groups.

CONCLUSIONS

women with malignancy can achieve adequate ovarian response and similar oocyte parameters to those of women undergoing fertility preservation for non-cancer indications. Such information, coupled with the ability to noninvasively study oocyte dynamics, may improve the counseling of cancer patients seeking fertility preservation.

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.

MCAK is present at centromeres, midspindle and chiasmata and involved in silencing of the spindle assembly checkpoint in mammalian oocytes

Mitotic centromere-associated kinesin (MCAK) is an ATP-dependent microtubule (MT) depolymerase regulated by Aurora kinase (AURK) phosphorylation and implicated in resolution of improper MT attachments in mitosis. Distribution of MCAK was studied in oocyte maturation by anti-MCAK antibody, anti-tubulin antibody, anti-AURKB antibody and anti-centromere antibody (ACA) and by the expression of MCAK-enhanced green fluorescent protein fusion protein in maturing mouse oocytes. Function was assessed by knockdown of MCAK and Mad2, by inhibiting AURK or the proteasome, by live imaging with polarization microscope and by chromosomal analysis. The results show that MCAK is transiently recruited to the nucleus and transits to spindle poles, ACA-positive domains and chiasmata at prometaphase I. At metaphase I and II, it is present at centrosomes and centromeres next to AURKB and checkpoint proteins Mad2 and BubR1. It is retained at centromeres at telophase I and also at the midbody. Knockdown of MCAK causes a delay in chromosome congression but does not prevent bipolar spindle assembly. MCAK knockdown also induces a meiosis I arrest, which is overcome by knockdown of Mad2 resulting in chiasma resolution, chromosome separation, formation of aberrant meiosis II spindles and increased hypoploidy. In conclusion, MCAK appears to possess a unique distribution and function in oocyte maturation. It is required for meiotic progression from meiosis I to meiosis II associated with silencing of the spindle assembly checkpoint. Alterations in abundance and activity of MCAK, as implicated in aged oocytes, may therefore contribute to the loss of control of cell cycle and chromosome behaviour, thus increasing risk for errors in chromosome segregation and aneuploidy.

Spindle and chromosome configurations of human oocytes matured in vitro in two different culture media

In-vitro maturation can have deleterious effects on spindle formation and proper chromosome alignment in human oocytes and can be profoundly affected by culture conditions. This study compared the spindle presence and location with the maturation rate of germinal vesicle (GV) oocytes cultured in two different media: G1.2 and G1.2 supplemented with follicle-stimulating hormone, human chorionic gonadotrophin and 17beta-oestradiol. A total of 304 oocytes were retrieved from 101 women undergoing IVF treatment with intracytoplasmic sperm injection. Spindle presence was recorded using the Polscope. Spindle morphology was evaluated with immunocytological staining for alpha-tubulin and chromatin. Twenty-one in-vitro matured oocytes with the presence of spindle and ten of their corresponding polar bodies (PB) were also assessed for aneuploidy. A significantly increased maturation rate (69.7%) was observed after 24h in the supplemented culture media compared with the G1.2 media (56.6%; P<0.05). The proportions of metaphase II (MII) oocytes with spindle presence and abnormal spindle morphology were similar in the two culture media. Also, 76.9% of MII and 70% of PB had chromosomal abnormalities. In conclusion, supplementing culture media may increase the oocyte maturation rate in vitro, but does not necessarily indicate the presence of a birefringent spindle, or normal spindle and chromosomal alignment.

Rhesus macaque embryos derived from MI oocytes maturing after retrieval display high rates of chromosomal anomalies

BACKGROUND

Rhesus macaque and human preimplantation embryos display similar rates of chromosomal abnormalities. The aim of this study was to determine whether embryos developing from MI oocytes that mature post-retrieval display more chromosomal anomalies than those embryos that are generated from oocytes that are at MII at the time of retrieval.

METHODS

Rhesus macaque oocytes were obtained after hormonal ovarian stimulation. Immediately after retrieval, the oocytes were classified according to their maturational status. Following in vitro fertilization, Day 3 embryos with good morphology and development derived from oocytes maturing post-retrieval and those from oocytes that were mature at the time of retrieval were cytogenetically assessed using a five-color fluorescent in situ fluorescent hybridization assay developed for rhesus macaque chromosomes homologous to human chromosomes 13, 16, 18, X and Y.

RESULTS

Blastomeres from 53 embryos were analyzed. Of the 27 embryos that developed from oocytes that were mature at collection, 18 embryos were chromosomally normal (66.7%), while from the 26 embryos that developed from oocytes that matured post-retrieval, only 9 embryos were chromosomally normal (34.6%).

CONCLUSIONS

These results indicate that embryos developing from oocytes maturing post-retrieval display high rates of chromosomal abnormalities and have therefore a reduced developmental competence. As a result, the clinical relevance of using immature oocytes that are retrieved after stimulated cycles in human IVF warrants further investigation.