Cytoplasmic microtubular dynamics and chromatin organization during mammalian oogenesis and oocyte maturation

The spectrum of in vitro maturation in clinical practice: the current insight

In vitro oocyte maturation (IVM) has been used worldwide. Despite the long-term implementation, the uptake of this procedure to complement current in vitro fertilization (IVF) remains low. The main reason is likely due to the non-synchronization of protocol and definition criteria, leading to difficulty in collective proper outcome data worldwide and, thus, lack of understanding of the exact IVM procedure. The review aims to consolidate the current clinical practice of IVM by dissecting relevant publications to be tailored for a current spectrum of clinical practice. Nevertheless, the background theories of oocyte maturation were also explored to provide a comprehensive understanding of the basis of IVM theories. Additional discussion of other potential uses of IVM in the future, such as in ovarian tissue cryopreservation known as OTO-IVM for fertility preservation and among women with diminished ovarian reserve, was also explored. Otherwise, future collaboration among all IVM centers is paramount for better collection of clinical data to provide valid recommendations for IVM in clinical practice, especially in molecular integrity and possible DNA alteration if present for IVM offspring outcome safety purposes.

Proteomics Recapitulates Ovarian Proteins Relevant to Puberty and Fertility in Brahman Heifers (Bos indicus L.)

High fertility and early puberty in Bos indicus heifers are desirable and genetically correlated traits in beef production. The hypothalamus-pituitary-ovarian (HPO) axis synthesizes steroid hormones, which contribute to the shift from the pre-pubertal state into the post-pubertal state and influence subsequent fertility. Understanding variations in abundance of proteins that govern steroid synthesis and ovarian signaling pathways remains crucial to understanding puberty and fertility. We used whole ovaries of six pre-pubertal and six post-pubertal Brahman heifers to conduct differential abundance analyses of protein profiles between the two physiological states. Extracted proteins were digested into peptides followed by identification and quantification with massspectrometry (MS) by sequential window acquisition of all instances of theoretical fragment ion mass spectrometry (SWATH-MS). MS and statistical analysis identified 566 significantly differentially abundant (DA) proteins (adjusted p < 0.05), which were then analyzed for gene ontology and pathway enrichment. Our data indicated an up-regulation of steroidogenic proteins contributing to progesterone synthesis at luteal phase post-puberty. Proteins related to progesterone signaling, TGF-β, retinoic acid, extracellular matrix, cytoskeleton, and pleiotrophin signaling were DA in this study. The DA proteins probably relate to the formation and function of the corpus luteum, which is only present after ovulation, post-puberty. Some DA proteins might also be related to granulosa cells signaling, which regulates oocyte maturation or arrest in ovaries prior to ovulation. Ten DA proteins were coded by genes previously associated with reproductive traits according to the animal quantitative trait loci (QTL) database. In conclusion, the DA proteins and their pathways were related to ovarian activity in Bos indicus cattle. The genes that code for these proteins may explain some known QTLs and could be targeted in future genetic studies.

Effects of resveratrol on in vitro maturation of porcine oocytes and subsequent early embryonic development following somatic cell nuclear transfer

As a natural plant-derived antitoxin, resveratrol possesses several pharmacological activities. This study aimed to evaluate the effects of resveratrol addition on nuclear maturation, oocyte quality during in vitro maturation (IVM) of porcine oocytes and subsequent early embryonic development following somatic cell nuclear transfer (SCNT). Our experiments showed that the treatment of porcine oocytes with 5 µM resveratrol during IVM resulted in the highest rate of the first polar body extrusion. Treatment of oocytes with resveratrol had no influence on cytoskeletal dynamics, whereas it significantly increased glucose uptake ability compared to the control oocytes. Oocytes matured with 5 μM resveratrol displayed significantly lower intracellular reactive oxygen species (ROS) levels and higher relative mRNA expression levels of the genes encoding such antioxidant enzymes as catalase (CAT) and superoxide dismutase 1 (SOD1). In addition, resveratrol also prevented onset and progression of programmed cell death in porcine oocytes, which was confirmed by significant upregulation of the anti-apoptotic B-cell lymphoma 2 (BCL-2) gene and significant downregulation of the pro-apoptotic BCL2-associated X (BAX) gene. Furthermore, the blastocyst rates and the blastocyst cell numbers in cloned embryos derived from the oocytes that had matured in the presence of 5 μM resveratrol were significantly increased. In conclusion, supplementation of IVM medium with 5 μM resveratrol improves the quality of porcine oocytes by protecting them from oxidative damage and apoptosis, which leads to the production of meiotically matured oocytes exhibiting enhanced developmental potential following SCNT.

The Effect of Epigenetic Changes on the Extrusion of the First Polar Body in Pig Oocytes During In Vitro Maturation

The present study was designed to investigate the comprehensive function of maternal factors of primordial germ cell 7 (PGC7) and POU5F1-POU class 5 homeobox 1 (OCT4), as well as the epigenetic modification roles on the mitosis for the extrusion of first polar body (PB1) in pig maturated oocytes. First, the common distribution of histone modifications, including H3K4me2, H3K27me3, H3K9me2, and H4K12ac and DNA methylation, were detected at the high level in the nucleus. However, only one part of the chromosome was higher methylated or acetylated when the mitosis happened to extrude the PB1. When the mitosis was inhibited by the cytochalasin B (CB) treatment, the expression of PGC7, OCT4, DNA methyltransferase1 (DNMT1), DNA methyltransferase3b (DNMT3b), tet methylcytosine dioxygenase 1 (TET1), tet methylcytosine dioxygenase 2 (TET2), and tet methylcytosine dioxygenase 3 (TET3) could be inhibited (p < 0.01), and no concentrated expression of the PGC7 and OCT4 was observed on the chromosome, but the levels of H3K9me2 and H4K12ac were higher. In addition, when the trichostatin A was performed on the in vitro maturation, the extrusion of the PB1 was inhibited too. And the histone methylation (H3K9me2 and H3K27me3) could be detected all the time with relative higher level and no demethylation could be observed. However, the expression of PGC7 and OCT4 was lower in the chromosome. It might indicate that the maternal factor of PGC7 and histone modification that included H4K12ac and H3K9me2 could regulate the extrusion of the PB1 and play an important role in the maturation of pig oocytes.

Structure of preantral follicles, oxidative status and developmental competence of in vitro matured oocytes after ovary storage at 4 °C in the domestic cat model

BACKGROUND

Storage conditions during transportation of explanted ovaries are a critical step in setting up fertility preservation protocols in both animal and human fields. Here, we evaluated the effects of ovary storage at 4 °C on the preservation of preantral follicles and oocytes retrieved from antral follicles using the domestic cat as model.

METHODS

Ovaries were harvested from fifty-five healthy domestic queens during ovariectomy and stored at 4 °C for 0 (control), 24, 48, 72 and 96 h. In Experiment 1, the effects of the storage period at 4 °C on the morphology, cytoskeleton (α/β tubulin) and DNA integrity (phosphorylation of histone H2AX) of preantral follicles were investigated. In Experiment 2, oocytes recovered from antral follicles were matured and fertilized in vitro to evaluate their meiotic and developmental competence. Reactive oxygen species (ROS), glutathione (GSH) and lipid peroxidation were measured in matured oocytes.

RESULTS

The results showed that: a) storage up to 24 h did not affect the morphology and the DNA integrity of preantral follicles; b) extended storage times caused progressive morphological abnormalities, disassembling of microtubules and DNA damage; c) storage up to 48 h did not influence in vitro meiotic maturation of oocytes nor cleavage after in vitro fertilization. However, only oocytes stored within the ovary for 24 h produced blastocysts in a percentage similar to control oocytes; d) GSH levels of in vitro matured oocytes did not change at any time during ovary storage; a progressive increase in ROS levels was detected from 48 h associated with elevated lipid peroxidation at 72 and 96 h of storage.

CONCLUSIONS

Storage of cat ovaries for up to 24 h caused minimal alteration of preantral follicles and oocytes. The extension of the storage period beyond 24 h progressively impaired the structure of follicles, and modified the oxidative status of in vitro matured oocytes and their developmental competence after in vitro fertilization. This information may help when setting up programs for fertility conservation, especially for wild feline species which die in geographic areas located far away from ARTs centers.

Advanced oxidation protein products from the follicular microenvironment and their role in infertile women with endometriosis

Endometriosis (EM) is associated with oxidative stress. Advanced oxidation protein products (AOPPs) are novel markers of oxidative stress, which serve an important role as an inflammatory mediator in various chronic diseases. In order to examine the role of AOPPs in infertile women with EM, the present study analyzed the levels of AOPPs, estradiol (E₂) and progesterone (P₄) in the follicular fluid (FF) of 89 women with or without EM undergoing in vitro fertilization (IVF). The AOPP concentration in the FF of the EM group was significantly higher when compared with that of the control group (51.5±22.4 vs. 41.8±18.3 µmol/l; P<0.05). However, the FF P₄ levels and blastocyst rate were significantly lower in the EM group compared with the control group (P₄:1,249.6±465.4 vs. 1,752.7±565.4 ng/ml, P<0.05; blastocyst rate: 0.511±0.322 vs. 0.662±0.278; P<0.05). The AOPP concentration and P₄ level in the FF presented a significant negative correlation in the EM and control groups, as well as in the total cohort of patients (EM group: r=-0.406, P=0.006; control group: r=-0.315, P=0.035; total: r=-0.421, P<0.001). In addition, there was a significant negative correlation between the FF AOPP concentrations and blastocyst rate in the EM group and in the total cohort (EM group: r=-0.376, P=0.012; total: r=-0.367, P<0.001). In conclusion, these results suggested that AOPPs may be a potentially effective marker for predicting the oocyte quality and outcomes of IVF in infertile women with EM.

Differences in cumulus cell gene expression indicate the benefit of a pre-maturation step to improve in-vitro bovine embryo production

STUDY QUESTION

Does the gene expression profile of cumulus cells (CC) accompanying oocytes with different degrees of chromatin compaction within the germinal vesicle (GV) reflect the oocyte's quality and response in culture during in-vitro embryo production (IVP).

SUMMARY ANSWER

The transcriptomic profile of the CC is related to oocyte competence, setting the stage for the development of customized pre-maturation strategies to improve IVP.

WHAT IS KNOWN ALREADY

Oocytes complete the acquisition of their competence during antral follicle development. During this period, the chromatin configuration within the GV changes dynamically and is indicative of oocyte's developmental potential. The interactions between somatic and germ cells modulate chromatin morphology and function and are critical for acquisition of oocyte competence.

STUDY DESIGN, SIZE, DURATION

Bovine cumulus-oocyte complexes (COC) were isolated from 0.5 to 6 mm antral follicles. Surrounding CC were separated from the oocyte and classified as GV0, GV1, GV2 and GV3 according to the degree of the oocyte's chromatin compaction.

PARTICIPANTS/MATERIALS, SETTING, METHOD

RNA extracted from CC of each group was amplified and hybridized on a bovine embryo-specific 44 K Agilent slide. The CC_GV1, CC_GV2 and CC_GV3 classes were each hybridized against the CC_GV0 class, representing an early oocyte differentiation stage with poor development competence. The data were normalized and fold changes of the differentially expressed genes were determined. Microarray data were validated using quantitative RT-PCR on selected targets. Microarray data were further analyzed through: (i) between-group analysis (BGA), which classifies the samples according to their transcriptomic profiles; (ii) cluster analysis according to the expression profile of each gene; and (iii) Ingenuity Pathway Analysis (IPA) to study gene regulation patterns and predicted functions. Furthermore, CC of each GV group were cultured and apoptotic cells were assessed after 3 h by caspase analysis. Finally, based on the analysis of CC transcriptomic profiles and the relationship between morphological features of the COC and the oocyte chromatin configuration, a customized, stage-dependent oocyte pre-maturation (pre-IVM) system was used to improve oocyte developmental potential before IVM. For this, the blastocyst rate and quality were assessed after in-vitro maturation and fertilization of pre-matured oocytes.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, quantitative RT-PCR results of a subset of five selected genes were consistent with the microarray data. Clustering analysis generated 16 clusters representing the main profiles of transcription modulation. Of the 5571 significantly differentially expressed probes, the majority (25.49%) best fitted with cluster #6 (downregulation between CC_GV0 and CC_GV1 and stable low levels in successive groups). IPA identified the most relevant functions associated with each cluster. Genes included in cluster #1 were mostly related to biological processes such as 'cell cycle' and 'cell death and survival', whereas genes included in cluster #5 were mostly related to 'gene expression'. Interestingly, 'lipid metabolism' was the most significant function identified in clusters #6, #9 and #12. IPA of gene lists obtained from each contrast (i.e., CC_GV0 vs. CC_GV1; CC_GV0 vs. CC_GV2; CC_GV0 vs. CC_GV3) revealed that the main affected function in each contrast was 'cell death and survival'. Importantly, apoptosis was predicted to be inhibited in CC_GV1 and CC_GV2, but activated in CC_GV3. Caspase analysis indicated that a low percentage of CC_GV0 was prone to undergo apoptosis but apoptosis increased significantly in CC from oocytes with condensed chromatin, reaching a peak in CC_GV3 (P < 0.05). Finally, the tailored oocyte pre-maturation strategy, based on morphological features of the COC and the oocyte chromatin configuration, demonstrated that pre-IVM improved the developmental capability of oocytes at early stages of differentiation (GV1-enriched COC) but was detrimental for oocytes at more advanced stages of development (GV2 and GV3-enriched COC).

LARGE SCALE DATA

The data are available through the GEO series accession number GSE79886.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted with bovine samples. Whether or not the results are applicable to human oocytes requests further elucidation. Embryo transfer experiments are required to determine whether the improvement in blastocyst rates in the tailored system leads to increased live birth rates.

WIDER IMPLICATIONS OF THE FINDINGS

The identification of multiple non-invasive biomarkers predictive of oocyte quality can greatly strengthen the pre-IVM approach aimed to improve IVM outcomes. These results have potentially important implications in treating human infertility and in developing breeding schemes for domestic mammals.

STUDY FUNDING/COMPETING INTERESTS

This work was supported in part by NSERC Strategic Network EmbryoGENE, Canada and in part by CIG-Marie Curie Actions-Reintegration Grants within the EU 7FP (n. 303640, 'Pro-Ovum'). The authors declare no potential conflict of interest.

Microtubule assembly crucial to bovine embryonic development in assisted reproductive technologies

Centrosome integrity and microtubule network are crucial to the events around fertilization, including pronuclear development, migration and fusion, and the first mitotic division. The present review highlights the importance of bull spermatozoal centrosomes to function as a microtubule‐organizing center for successful fertilization and the subsequent embryonic development. Spermatozoal centrosomes need to be blended with ooplasmic pericentriolar materials accurately to nucleate and organize the sperm aster. Dysfunction of the spermatozoal centrosomes is associated with fertilization failure, which has been overcome with supplemental stimuli for oocyte activation following intracytoplasmic sperm injection in humans. Even though the spermatozoal centrosomes are functionally intact, abnormal sperm aster formation was frequently observed in vitrified‐warmed bovine oocytes, with delayed pronuclear development and migration. Treatment of the post‐warm oocytes with Rho‐associated coiled‐coil kinase inhibitor or α‐tocopherol inhibited the incidence of the abnormal aster formation, resulting in higher blastocyst yields following in vitro fertilization and culture. Thus, understanding of centrosomal function made it possible to improve the performance of advanced reproductive technologies.

Peroxynitrite deteriorates oocyte quality through disassembly of microtubule organizing centers

Previous theoretical studies have suggested that utilization of 3-D imaging to acquire morphologic parameters of meiotic spindles may be useful in infertility related procedures as an assessment of oocyte quality. However, our results show that treatment of oocytes with increasing concentrations of peroxynitrite (ONOO(-)) caused a dramatic alteration in spindle shape in which morphologic parameters are not measurable or are uninformative in terms of oocyte quality. Metaphase II mouse oocytes (n=520) were treated with increasing concentrations of ONOO(-), after which all oocytes were fixed and subjected to indirect immunofluorescence. Oocyte quality was assessed by alterations in the microtubule-organizing center (MTOC), pericentrin location, microtubule morphology, and chromosomal alignment. In untreated oocytes, pericentrin is primarily assembled utilizing the acentrosomal MTOC, which appears as a condensation at both spindle poles. The spindle has a symmetrical pointed barrel shape, assembled around the chromosomal plate at the spindle equator. Oocytes treated with low concentrations of ONOO(-) (<2.5 μM) showed shortening of the spindle apparatus, while pericentrin scatters from a tight condensation to a dispersed cluster around each spindle pole. At higher ONOO(-) concentrations (>2.5μM) the central attachments between microtubules are strained and bend or unevenly break, and the MTOC proteins are further dispersed or undetectable. Peroxynitrite mediated MTOC damage, which deranges the chromosomal scaffold at the time of assembly and separation, caused the deterioration in oocyte quality. These results provide a link between reactive oxygen species and poor reproductive outcomes and elucidate the underlying etiology, which could be used as a superior biomarker for oocyte quality compared to existing assessment tools.

N-Acetyl-Cysteine and l-Carnitine Prevent Meiotic Oocyte Damage Induced by Follicular Fluid From Infertile Women With Mild Endometriosis

This study evaluated the potential protective effect of the antioxidants, l-carnitine (LC) and N-acetyl-cysteine (NAC), in preventing meiotic oocyte damage induced by follicular fluid (FF) from infertile women with mild endometriosis (ME). We performed an experimental study. The FF samples were obtained from 22 infertile women undergoing stimulated cycles for intracytoplasmic sperm injection (11 with ME and 11 without endometriosis). Immature bovine oocytes were submitted to in vitro maturation (IVM) divided into 9 groups: no-FF (No-FF); with FF from control (CFF) or ME (EFF) groups; and with LC (C + LC and E + LC), NAC (C + NAC and E + NAC), or both antioxidants (C + 2Ao and E + 2Ao). After IVM, oocytes were immunostained for visualization of microtubules and chromatin by confocal microscopy. The percentage of meiotically normal metaphase II (MII) oocytes was significantly lower in the EFF group (51.35%) compared to No-FF (86.36%) and CFF (83.52%) groups. The E + NAC (62.22%), E + LC (80.61%), and E + 2Ao (61.40%) groups showed higher percentage of normal MII than EFF group. The E + LC group showed higher percentage of normal MII than E + NAC and E + 2Ao groups and a similar percentage to No-FF and CFF groups. Therefore, FF from infertile women with ME causes meiotic abnormalities in bovine oocytes, and, for the first time, we demonstrated that the use of NAC and LC prevents these damages. Our findings elucidate part of the pathogenic mechanisms involved in infertility associated with ME and open perspectives for further studies investigating whether the use of LC could improve the natural fertility and/or the results of in vitro fertilization of women with ME.

Chromosomal aberrations in in-vitro matured oocytes influence implantation and ongoing pregnancy rates in a mouse model undergoing intracytoplasmic sperm injection

Implantation failure and early pregnancy loss have been reported to be closely related to the quality of mammalian oocytes; however, the pregnant outcome of embryos from in-vitro matured (IVM) oocytes remains unknown. In this study we examined spindle assembly and chromosome segregation during differentiation, and the duration of IVM of mouse oocytes. The resulting implantation and pregnancy outcomes were analyzed to clarify the relationship between the spindle and chromosomes of IVM oocytes and implantation and early pregnancy. Cumulus-enclosed germinal vesicle oocytes were collected and randomly cultured in IVM medium with different IVM durations. One part of IVM oocytes were analyzed the spindle and chromosome morphology by immunofluorescence method, and the other part of them were fertilized by intracytoplasmic sperm injection. The resulting embryos were transferred into pseudo-pregnant female mice, and the post-implantation and full term development was observed. The chromosome aberrations and incorrect spindle assembly seems not affect the early development and blastocyst cell number derived from IVM oocytes, however the development potential of the resulting embryos after implantation were significant decreased with the ratio increasing of chromosome aberrations and incorrect spindle assembly. Accordingly, the full-term development was also decreased. In conclusion, the present study showed the spindle assembly of in vitro-matured oocytes was one of the most important factors that affected the implantation and ongoing pregnancy rates of IVM oocytes, and the improvement by an appropriate duration of maturation in vitro will enhance the post-implantation development potential of the resulting embryos, and decrease implantation failure and early pregnancy loss.

Membrane lipid phase transition behavior of oocytes from three gorgonian corals in relation to chilling injury

The lipid phase transition (LPT) from the fluid liquid crystalline phase to the more rigid gel structure phase that occurs upon exposure to low temperatures can affect physical structure and function of cellular membranes. This study set out to investigate the membrane phase behavior of oocytes of three gorgonian corals; Junceela fragilis, J. juncea and Ellisella robusta,at different developmental stages after exposure to reduced temperatures. Oocytes were chilled to 5°C for 48, 96 or 144 h, and the LPT temperature (LPTT) was determined with Fourier Transform Infrared (FTIR) spectroscopy. The J. fragilis oocytes had a higher LPTT (∼23.0–23.7°C) than those of J. juncea and E. robusta oocytes (approximately 18.3–20.3°C). Upon chilling for 96 h at 5°C, the LPTTs of J. juncea and E. robusta oocytes in the early (18.0±1.0 and 18.3±0.6°C, respectively) and late (17.3±0.6 and 17.7±1.2°C, respectively) stages were significantly lower than those of J. fragilis oocytes (20.3±2.1 and 19.3±1.5°C for the early and late stages, respectively). The LPTTs of early stage gorgonian oocytes was significantly lower than those of late stage oocytes. These results suggest that the LPT of three gorgonian oocytes at different developmental stages may have been influenced by the phospholipid composition of their plasma membranes, which could have implications for their low temperature resistance.

Follicular fluid from infertile women with mild endometriosis may compromise the meiotic spindles of bovine metaphase II oocytes

STUDY QUESTION

What is the potential impact of follicular fluid (FF) from infertile women with mild endometriosis (ME) on oocyte quality, especially on nuclear maturation and the meiotic spindle?

SUMMARY ANSWER

FF from infertile women with ME may compromise nuclear maturation and the meiotic spindles of in vitro matured bovine oocytes.

WHAT IS KNOWN ALREADY

Controversial studies have suggested that impaired oocyte quality may be involved in the pathogenesis of endometriosis-related infertility. Moreover, some studies have demonstrated alterations in the composition of FF from infertile women with endometriosis. However, to date no study has evaluated the effect of FF from infertile women with ME on the genesis of meiotic oocyte anomalies.

STUDY DESIGN, SIZE, DURATION

We performed an experimental study. Samples of FF were obtained from February 2009 to February 2011 from 22 infertile women, 11 with ME and 11 with tubal or male factors of infertility (control group), who underwent ovarian stimulation for ICSI at our university IVF Unit. From March 2011 to February 2012 we performed in vitro maturation (IVM) experiments using immature bovine oocytes as described below.

PARTICIPANTS/MATERIALS, SETTING, METHODS

FF free of blood and containing a mature oocyte was obtained from 22 infertile women during oocyte retrieval for ICSI. Immature bovine oocytes underwent IVM in the absence of FF (No-FF) and in the presence of four concentrations (1, 5, 10 and 15%) of FF from infertile women without endometriosis (C-FF) and with ME (ME-FF). Eleven replicates were performed, each one using FF from a control patient and a patient with ME. Each FF sample was used in only one experiment. After 22-24 h of IVM, oocytes were denuded, fixed and immunostained for morphological visualization of microtubules and chromatin by confocal microscopy.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1324 cumulus-oocyte complexes were matured in vitro. Of these, 1128 were fixed and 1048 were analyzed by confocal microscopy. The percentage of meiotically normal oocytes was significantly higher for oocytes that underwent IVM in the absence of FF (No-FF; 76.5%) and in the presence of 1% (80.9%), 5% (76.6%), 10% (75%) and 15% (76.2%) C-FF than in oocytes that underwent IVM in the presence of 1% (44.4%), 5% (36.7%), 10% (45.5%) and 15% (51.2%) ME-FF (P < 0.01). No differences were observed among FF concentrations within each group. When the four concentrations from each group were pooled, the number of oocytes in metaphase I stage was significantly higher in the ME-FF (50 oocytes) than in the C-FF (29 oocytes) group and the percentage of meiotic abnormalities was significantly higher when oocytes were matured with ME-FF (55.8%) than with C-FF (23.1%), P < 0.01.

LIMITATIONS, REASONS FOR CAUTION

Owing to the strict selection criteria for FF donors, this study had a small sample size (11 cases and 11 controls), and thus further investigations using a large cohort of patients are needed to confirm these results. In addition, data obtained from studies using animal models may not necessarily be extrapolated to humans and studies evaluating in vivo matured oocytes from infertile women with ME are important to confirm our results.

WIDER IMPLICATIONS OF THE FINDINGS

Our results open new insights into the pathogenic mechanisms of infertility related to mild endometriosis, suggesting that FF from infertile women with mild endometriosis may be involved in the worsening of oocyte quality of these women.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Council for Scientific and Technological Development (CNPq), Brazil. The authors declare no conflicts of interest.

Recent insights into spindle function in mammalian oocytes and early embryos

Errors in chromosome segregation in oocytes and early embryos lead to embryo aneuploidy, which contributes to early pregnancy loss. At the heart of chromosome segregation is the spindle, a dynamic biomechanical machine fashioned from microtubules, which is tasked with gathering and sorting chromosomes and dispatching them to the daughter cells at the time of cell division. Understanding the causes of segregation error in the oocyte and early embryo will undoubtedly hinge on a thorough understanding of the mechanism of spindle assembly and function in these highly specialized cellular environments. The recent advent of live imaging approaches to observe chromosome segregation in real-time in oocytes and embryos, paired with gene-silencing techniques and specific inhibition for assessing the function of a protein of interest, has led to a substantial advance in our understanding of chromosome segregation in early mammalian development. These studies have uncovered numerous mechanistic differences between oocytes, embryos, and traditional model systems. In addition, a flurry of recent studies using naturally aged mice as the model for human aging have begun to shed light on the increased levels of aneuploidy seen in embryos from older mothers. Here we review these recent developments and consider what has been learned about the causes of chromosome missegregation in early development.

Treatment with the proteasome inhibitor MG132 during the end of oocyte maturation improves oocyte competence for development after fertilization in cattle

Maturation of the oocyte involves nuclear and cytoplasmic changes that include post-translational processing of proteins. The objective was to investigate whether inhibition of proteasomes during maturation would alter competence of the bovine oocyte for fertilization and subsequent development. Cumulus-oocyte complexes were cultured in the presence or absence of the proteasomal inhibitor MG132 from either 0-6 h or 16-22 h after initiation of maturation. Treatment with MG132 early in maturation prevented progression to meiosis II and reduced fertilization rate and the proportion of oocytes and cleaved embryos that became blastocysts. Conversely, treatment with MG132 late in maturation improved the percentage of oocytes and cleaved embryos that became blastocysts without affecting nuclear maturation or fertilization rate. Optimal results with MG132 were achieved at a concentration of 10 µM - effects were generally not observed at lower or higher concentrations. Using proteomic analysis, it was found that MG132 at the end of maturation increased relative expression of 6 proteins and decreased relative expression of 23. Among those increased by MG132 that are potentially important for oocyte competence are GAPDH, involved in glycolysis, TUBA1C, needed for organellar movement, and two proteins involved in protein folding (P4HB and HYOU1). MG132 decreased amounts of several proteins that exert anti-apoptotic actions including ASNS, HSP90B1, PDIA3 and VCP. Another protein decreased by MG132, CDK5, can lead to apoptosis if aberrantly activated and one protein increased by MG132, P4HB, is anti-apoptotic. Finally, the pregnancy rate of cows receiving embryos produced from oocytes treated with MG132 from 16-22 h of maturation was similar to that for control embryos, suggesting that use of MG132 for production of embryos in vitro does not cause a substantial decrease in embryo quality.

Detection of DNA damage in oocytes of small ovarian follicles following phosphoramide mustard exposures of cultured rodent ovaries in vitro

Healthy oocytes are critical for producing healthy children, but little is known about whether or not oocytes have the capacity to identify and recover from injury. Using a model ovotoxic alkylating drug, cyclophosphamide (CPA), and its active metabolite, phosphoramide mustard (PM), we previously showed that PM (≥3μM) caused significant follicle loss in postnatal day 4 (PND4) mouse ovaries in vitro. We now investigate whether PM induces DNA damage in oocytes, examining histone H2AX phosphorylation (γH2AX), a marker of DNA double-strand breaks (DSBs). Exposure of cultured PND4 mouse ovaries to 3 and 0.1μM PM induced significant losses of primordial and small primary follicles, respectively. PM-induced γH2AX was observed predominantly in oocytes, in which foci of γH2AX staining increased in a concentration-dependent manner and peaked 18-24h after exposure to 3-10μMPM. Numbers of oocytes with ≥5 γH2AX foci were significantly increased both 1 and 8days after exposure to ≥1μMPM compared to controls. Inhibiting the kinases that phosphorylate H2AX significantly increased follicle loss relative to PM alone. In adult mice, CPA also induced follicle loss in vivo. PM also significantly decreased primordial follicle numbers (≥30μM) and increased γH2AX foci (≥3μM) in cultured PND4 Sprague-Dawley rat ovaries. Results suggest oocytes can detect PM-induced damage at or below concentrations which cause significant follicle loss, and there are quantitative species-specific differences in sensitivity. Surviving oocytes with DNA damage may represent an increased risk for fertility problems or unhealthy offspring.

Biomarkers of human oocyte developmental competence expressed in cumulus cells before ICSI: a preliminary study

PURPOSE

To identify reliable genomic biomarkers expressed in cumulus cells that accurately and non-invasively predict the oocyte developmental competence and reinforce the already used morphological criteria.

METHODS

Eight consenting patients were selected for ovarian stimulation and ICSI procedures. Cumulus-oocyte complexes were transvaginally punctured and individually selected based on both good morphological criteria and high zona pellucida birefringence. Following ICSI, two 3-day embryos per patient were transferred. Pregnancy outcome was recorded and proven implantation was thereafter confirmed. Differential gene expression was assessed using two microarray platforms. Further real-time PCR validation, Ingenuity pathways analysis and intra-patient analysis were performed on 17 selected candidates.

RESULTS

Seven genes were differentially (p ≤ 0.05) associated to successful pregnancy and implantation. These biomarkers could be used to predict the oocyte developmental competence.

CONCLUSIONS

These genomic markers are a powerful reinforcement of morphological approaches of oocyte selection. Their large-scale validation could increase pregnancy outcome and single embryo transfer efficiency.

In vitro developmental potential of macaque oocytes, derived from unstimulated ovaries, following maturation in the presence of glutathione ethyl ester

BACKGROUND

The inadequacies of oocyte in vitro maturation (IVM) systems for both non-human primates and humans are evidenced by reduced fertilization and poor embryonic development, and may be partly explained by significantly lower glutathione (GSH) contents compared with in vivo matured (IVO) oocytes. As this influence has not been fully explored, this study investigated the effect of the GSH donor, glutathione ethyl ester (GSH-OEt), on the IVM and development of macaque oocytes as a model of human oocyte IVM.

METHODS

Macaque oocytes derived from unstimulated ovaries were cultured in mCMRL-1066 alone or supplemented with 3 or 5 mM GSH-OEt. In vitro matured oocytes were subjected to the GSH assay, fixed for the assessment of spindle morphology or prepared ICSI. Embryo development of zygotes cultured in mHECM-9 was assessed up to Day 9 post-ICSI. RESULTS Supplementation of the maturation medium with GSH-OEt significantly increased oocyte maturation and normal fertilization rates compared with control oocytes, but only 5 mM GSH-OEt significantly increased the oocyte and cumulus cell GSH content. Confocal microscopy revealed significant differences in the spindle morphology between IVO and control in vitro matured metaphase II oocytes. Oocytes matured with 5 mM GSH-OEt exhibited spindle area and spindle pole width similar to that seen in the IVO oocyte. While no significant differences were observed in blastocyst rates, addition of 3 mM GSH-OEt during IVM significantly increased the proportion of embryos developing to the 5-8 cell stage while 5 mM GSH-OEt significantly increased the proportion of morula-stage embryos compared with controls.

CONCLUSIONS

Supplementation of the IVM medium with GSH-OEt promotes better maturation and normal fertilization of macaque oocytes compared with non-supplemented medium. However, further improvement of the primate oocyte IVM culture system is required to support better blastocyst development of oocytes derived from unstimulated ovaries.

Effects of in vitro maturation and age on oocyte quality in the rhesus macaque Macaca mulatta

OBJECTIVE

To evaluate oocyte quality in a primate model.

DESIGN

Analysis of oocyte karyotype by chromosome spreading and oocyte spindles by confocal microscopy.

SETTING

Research laboratory, Caribbean Primate Research Center.

ANIMAL(S)

Rhesus macaques aged 6-22 years.

INTERVENTION(S)

Fourteen females underwent both Regimen A (FSH + hCG) and Regimen B (FSH only) stimulation cycles to facilitate collection of mature and immature oocytes. Immature oocytes from Regimens A and B underwent in vitro maturation (IVM) to produce metaphase II oocytes. All metaphase II oocytes underwent gradual fixation to spread chromosomes or were fixed and stained with probes specific to alpha-tubulin, actin, and DNA for visualization of the meiotic spindle using confocal microscopy.

MAIN OUTCOME MEASURE(S)

Karyotype and meiotic spindle architecture differences among in vivo matured (IVO) and IVM oocytes from young and old rhesus macaques.

RESULT(S)

In all, 4.7% of IVO oocytes (Regimen A) from young females were hyperhaploid versus 25.0% of IVM oocytes (Regimen B) from old females; 4.5% of IVO oocytes (Regimen A) from young females versus 51.5% of IVM oocytes (Regimen B) from old females displayed abnormal chromosome alignment on the metaphase spindle.

CONCLUSION(S)

IVM can induce meiotic anomalies in macaque oocytes, especially those obtained from older females. Results from this study provide possible explanations for the reported reduction in developmental competence of IVM primate oocytes.

Studies on chilling sensitivity of early stage zebrafish (Danio rerio) ovarian follicles

Cryopreservation of fish gametes is of great importance in aquaculture, conservation and human genomic research. The creation of gamete cryobanks allows the storage of genetic material of targeted species for almost unlimited time periods. Cryopreservation has been successfully applied to fish sperm of many species, but there has been no success with fish embryos and oocytes. One of the obstacles to fish oocyte cryopreservation is their high chilling sensitivity and especially at subzero temperatures. Although studies on late stage oocyte cryopreservation has been carried out, there have been no reported studies on cryopreservation of early stage ovarian follicles. The aim of this study is to investigate the chilling sensitivity of early stage zebrafish ovarian follicles before developing protocols for their cryopreservation. Experiments were conducted with stage I (primary growth), stage II (cortical alveolus) and stage III (vetillogenesis) ovarian follicles, which were chilled in KCl buffer and L-15 medium for up to 144h at -1 degrees C in a low temperature bath. Ovarian follicles were also exposed to 2M methanol or 2M DMSO in L-15 medium for up to 168h at -1 and -5 degrees C, respectively. Control follicles were kept at 28 degrees C. Ovarian follicle viability was assessed using trypan blue staining. The results showed that stage I and II ovarian follicles are less sensitive to chilling than stage III follicles. These results were also confirmed following in vitro maturation of the chilled ovarian follicles. The results also showed that L-15 medium is more beneficial than KCl buffer for ovarian follicles at all stages. The presence of both methanol and DMSO reduced chilling sensitivity of ovarian follicles at all stages with methanol being the most effective. The study indicated that stage I and II follicles are less sensitive to chilling than stage III follicles, and that early stage zebrafish ovarian follicles may be better candidates for cryopreservation.

The current knowledge on radiosensitivity of ovarian follicle development stages

BACKGROUND

The aim of this paper is to review the available information on ovarian radiation sensitivity and the genetic hazard of ionizing radiation in female mammals including humans.

METHODS

The literature present in the author's laboratories (international papers from the 1970s) was complemented by a Medline literature search using the keywords 'ionizing radiation genetic effects', 'oocyte radiosensitivity' and 'oocyte DNA repair' (1990-2008). Further articles were acquired from citations in the research papers and reports.

RESULTS

Animal data show that oocyte radiosensitivity varies widely according to the follicle/oocyte stage and the species. Oocytes near ovulation show the highest susceptibility to radiation induction of mutational events. Congenital anomalies have been observed after exposure to high doses (1-5 Gy), but extrapolation of these data to humans requires caution. In humans, the dose required to induce permanent ovarian failure would vary from 20.3 Gy at birth to 14.3 Gy at 30 years. Most epidemiological studies found little evidence of genetic diseases at the doses at which medical, occupational or accidental exposure occurred.

CONCLUSIONS

The fact that genetic effects were observed in irradiated animals suggests that these could also occur in humans. The probability of such events remains low compared with the 'spontaneous' risks of genetic effects.

Evolution of "determinants" in sex-determination: a novel hypothesis for the origin of environmental contingencies in avian sex-bias

Sex-determination is commonly categorized as either "genetic" or "environmental"-a classification that obscures the origin of this dichotomy and the evolution of sex-determining factors. The current focus on static outcomes of sex-determination provides little insight into the dynamic developmental processes by which some mechanisms acquire the role of sex determinants. Systems that combine "genetic" pathways of sex-determination (i.e., sex chromosomes) with "environmental" pathways (e.g., epigenetically induced segregation distortion) provide an opportunity to examine the evolutionary relationships between the two classes of processes and, ultimately, illuminate the evolution of sex-determining systems. Taxa with sex chromosomes typically undergo an evolutionary reduction in size of one of the sex chromosomes due to suppressed recombination, resulting in pronounced dimorphism of the sex chromosomes, and setting the stage for emergence of epigenetic compensatory mechanisms regulating meiotic segregation of heteromorphic sex chromosomes. Here we propose that these dispersed and redundant regulatory mechanisms enable environmental contingency in genetic sex-determination in birds and account for frequently documented context-dependence in avian sex-determination. We examine the evolution of directionality in such sex-determination as a result of exposure of epigenetic regulators of meiosis to natural selection and identify a central role of hormones in integrating female reproductive homeostasis, resource allocation to oocytes, and offspring sex. This approach clarifies the evolutionary relationship between sex-specific molecular genetic mechanisms of sex-determination and non-sex-specific epigenetic regulators of meiosis and demonstrates that both can determine sex. Our perspective shows how non-sex-specific mechanisms can acquire sex-determining function and, by establishing the explicit link between physiological integration of oogenesis and sex-determination, opens new avenues to the studies of adaptive sex-bias and sex-specific resource allocation in species with genetic sex-determination.

Cytogenetic analysis of in vivo and in vitro matured oocytes derived from naturally cycling and stimulated mice

The objective of the study was to analyze the potential role of follicle stimulating hormone (FSH) in cytogenetic changes of in vivo and in vitro matured mouse oocytes and to determine whether the lower developmental potential of immature oocytes is due to a higher incidence of abnormalities in meiotic spindle organization and chromosome alignment as well as aneuploidy. In vivo matured oocytes were collected from naturally ovulated and superovulated (5.0 I U of recombinant follicle-stimulating hormone [rec-FSH] + recombinant human chorionic gonadotropin [rec-HCG]) mice. Immature oocytes were retrieved from naturally cycling mice and from mice primed with rec-FSH for 48 h. The immature oocytes were cultured 18 h for in vitro maturation (IVM). In vivo and in vitro matured oocytes were assessed for the meiotic spindle organization and chromosome alignment as well as aneuploidy. There was no significant difference of meiotic spindle organization, chromosomal alignment and aneuploidy between in vivo and in vitro matured oocytes derived from naturally cycling and stimulated mice. Therefore, the lower developmental potential of immature oocytes does not appear to be directly related to the incidence of abnormal meiotic spindle organization and chromosome alignment or to aneuploidy.

Gene expression profiling of human oocytes at different maturational stages and after in vitro maturation

OBJECTIVE

The purpose of this study was to catalog genes expressed in human oocytes at germinal vesicle (GV) or metaphase II (MII) stage and to compare gene profiles between oocytes matured in vivo (in vivo-MII) and in vitro (IVM-MII).

STUDY DESIGN

University-based research utilizing unfertilized oocytes analyzed for > 29,000 genes with RNA amplification and microarray.

RESULTS

GV, in vivo-MII, and IVM-MII oocytes expressed 12,219, 9735, and 8510 genes, respectively. There was extensive overlap among the 3 groups, but also some significant differences. In particular, in vivo-MII and IVM-MII oocytes shared very similar patterns of gene expression. However, some immature patterns of expression, reminiscent of GVs, persisted in IVM-MIIs.

CONCLUSION

In vitro maturation is an attractive strategy for IVF treatment; however, current IVM methods produce oocytes that perform poorly in the context of IVF. Data from the current study suggest that although IVM-MII oocytes closely resemble in vivo-MII oocytes for cellular pathways related to nuclear maturity, several pathways associated with cytoplasmic functions continue to be expressed in an immature manner. Additionally, IVM-MII oocytes have differences in the expression of genes related to cellular storage and homeostasis. Differentially expressed genes/pathways provide clues for the optimization of IVM techniques.

Bovine in vitro oocyte maturation as a model for manipulation of the γ-glutamyl cycle and intraoocyte glutathione

Glutathione (GSH) is the main non-enzymatic defence against oxidative stress and is a critical intracellular component required for oocyte maturation. In the present study, several modulators of intracellular GSH were assessed for their effect on the in vitro maturation (IVM) and intracellular GSH content of bovine metaphase (MII) oocytes. Of the five GSH modulators tested, only the cell-permeable GSH donor glutathione ethyl ester (GSH-OEt) significantly increased the GSH content of IVM MII oocytes in a concentration-dependent manner without adversely affecting oocyte maturation rate. The GSH level in IVM MII oocytes was greatly influenced by the presence or absence of cumulus cells and severely restricted when oocytes were cultured in the presence of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis. The addition of GSH-OEt to cumulus-denuded or BSO-treated oocytes increased the GSH content of bovine MII oocytes. Supplementation of the maturation medium with bovine serum albumin (BSA) or fetal calf serum (FCS) affected the GSH content of IVM MII oocytes, with greater levels attained under BSA culture conditions. The addition of GSH-OEt to the maturation medium increased the GSH content of IVM MII oocytes, irrespective of protein source. Spindle morphology, as assessed by immunocytochemistry and confocal microscopy, displayed distinct alterations in response to changes in oocyte GSH levels. GSH depletion caused by BSO treatment tended to widen spindle poles and significantly increased spindle area. Supplementation of the IVM medium with GSH-OEt increased spindle length, but did not significantly alter spindle area or spindle morphology. GSH-OEt represents a novel oocyte-permeable and cumulus cell-independent approach for effective elevation of mammalian oocyte GSH levels.

Spindle formation, chromosome segregation and the spindle checkpoint in mammalian oocytes and susceptibility to meiotic error

The spindle assembly checkpoint (SAC) monitors attachment to microtubules and tension on chromosomes in mitosis and meiosis. It represents a surveillance mechanism that halts cells in M-phase in the presence of unattached chromosomes, associated with accumulation of checkpoint components, in particular, Mad2, at the kinetochores. A complex between the anaphase promoting factor/cylosome (APC/C), its accessory protein Cdc20 and proteins of the SAC renders APC/C inactive, usually until all chromosomes are properly assembled at the spindle equator (chromosome congression) and under tension from spindle fibres. Upon release from the SAC the APC/C can target proteins like cyclin B and securin for degradation by the proteasome. Securin degradation causes activation of separase proteolytic enzyme, and in mitosis cleavage of cohesin proteins at the centromeres and arms of sister chromatids. In meiosis I only the cohesin proteins at the sister chromatid arms are cleaved. This requires meiosis specific components and tight regulation by kinase and phosphatase activities. There is no S-phase between meiotic divisions. Second meiosis resembles mitosis. Mammalian oocytes arrest constitutively at metaphase II in presence of aligned chromosomes, which is due to the activity of the cytostatic factor (CSF). The SAC has been identified in spermatogenesis and oogenesis, but gender-differences may contribute to sex-specific differential responses to aneugens. The age-related reduction in expression of components of the SAC in mammalian oocytes may act synergistically with spindle and other cell organelles' dysfunction, and a partial loss of cohesion between sister chromatids to predispose oocytes to errors in chromosome segregation. This might affect dose-response to aneugens. In view of the tendency to have children at advanced maternal ages it appears relevant to pursue studies on consequences of ageing on the susceptibility of human oocytes to the induction of meiotic error by aneugens and establish models to assess risks to human health by environmental exposures.

Nuclear and cytoplasmic maturation of in vitro matured human oocytes after temporary nuclear arrest by phosphodiesterase 3-inhibitor

BACKGROUND

The use of hormones for controlled ovarian stimulation results in follicular heterogeneity, with oocytes at diverse stages of nuclear and cytoplasmic development. This study evaluated the impact of temporary nuclear arrest by a specific phosphodiesterase 3-inhibitor (PDE3-I), cilostamide, on nuclear and cytoplasmic maturation of cumulus-free germinal vesicle (GV) human oocytes from controlled ovarian stimulated cycles.

METHODS

GV oocytes (n = 234) were cultured in: (i) medium without the inhibitor (control); (ii) medium supplemented with 1 microM cilostamide and (iii) medium supplemented with 10 microM cilostamide. Oocytes in groups (ii) and (iii) were exposed to cilostamide for 24 h. The PDE3-I was subsequently removed by transfer of oocytes to fresh in vitro maturation (IVM) medium and the reversibility of GV arrest was assessed during IVM culture for maximum 48 h.

RESULTS

Cilostamide (1 and 10 microM) could maintain >80% of the oocytes at the GV stage, without affecting subsequent maturation to metaphase II. Oocytes exposed to 1 microM cilostamide were more likely to have normal bipolar spindles with aligned chromosomes than control oocytes (P < 0.05). When GV chromatin configurations before and after arrest were compared, a significantly higher proportion of oocytes had acquired a nucleolus completely surrounded by a rim of highly condensed chromatin (P < 0.05).

CONCLUSIONS

Temporary nuclear arrest of human GV oocytes with PDE3-I proved to be beneficial for obtaining normal spindle and chromosome configurations after IVM. It resulted also in synchronization within the population of GV oocytes.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

Genetic strain variations in the metaphase-II phenotype of mouse oocytes matured in vivo or in vitro

The interplay between genetic and epigenetic factors plays a central role in mammalian embryo production strategies that superimposeex vivoorin vivomanipulations upon strain background characteristics. In this study, we examined the relationship between genetic background and the phenotypic properties of mouse metaphase-II (M-II) oocytes that were matured underin vivo(IVO) orin vitroconditions, either in a basal (IVM) or a supplemented (IVM + ) medium. Differences existed amongst inbred (C57BL/6), outbred (CF-1, Black Swiss, NU/NU) and hybrid lines (B6D2F1) induced to superovulate with regard to cytoplasmic microtubule organizing center (MTOC) number but not spindle size or shape, except for larger and asymmetrical spindles in Black Swiss oocytes. When oocytes were matured in culture, meiotic spindle and cytoplasmic phenotypic properties of M-II oocytes were affected relative toin vivoconditions and between strains. Specifically, measures of meiotic spindle size, shape, polar pericentrin distribution and cytoplasmic MTOC number all revealed characteristic variations. Interestingly, the overall reduction in cytoplasmic MTOC number noted upon IVM was concomitant with an overall increase in spindle and polar body size. Maturation under IVM + conditions resulted in a further decrease in cytoplasmic MTOC number, but spindle and polar body characteristics were intermediate between IVO and IVM. How these oocyte phenotypic properties of maternal origin may be linked to predictive assessments of fecundity remains to be established.

Bisphenol-A induces cell cycle delay and alters centrosome and spindle microtubular organization in oocytes during meiosis

Bisphenol-A (BPA) is a widely used environmental estrogen-like chemical that has a weak estrogenic activity. This study aimed to test the potential inhibitory effects of BPA on meiotic cell cycle progression, centrosomes and spindle integrity in mouse cumulus-oocyte complexes (COCs). They were exposed to BPA (10-30 microM; 2.3-6.8 ppm) during meiosis-I and the formation of metaphase-II (M-II) spindle. Exposure to BPA during meiosis-I caused a dose-dependent retardation/inhibition of cell cycle progression; 74 and 61% of cells reached metaphase-I (M-I) in the presence of 10 and 30 microM BPA, respectively, (81% in controls, P<0.001). A more striking delay was noted when oocytes were exposed to BPA during the formation of M-II spindle, i.e. 61 and 41% of cells (94% in controls, P<0.001) reached M-II while the remaining cells remained at M-I. Depending on dose, both (i) loosening and elongation of meiotic spindles and (ii) compaction and dispersion of pericentriolar material (PCM) were noted in all samples, all of which resulted in a series of spindle abnormalities. Interestingly, no chromosome was detected in the first polar body after the 10 and 30 microM BPA treatments. When the cells were freed from BPA exposure at 10 and 30 microM, 70 and 61%, of the cells succeeded in reaching M-II (93% in controls, P<0.001), respectively. In conclusion, one mode of action of BPA is a moderately severe yet reversible delay in the meiotic cell cycle, possibly by a mechanism that degrades centrosomal proteins and thus perturbs the spindle microtubule organization and chromosome segregation.

Identification of a Spindlin homolog in gibel carp (Carassius auratus gibelio)

Spindlin has been suggested to play an important role during the transition from oocyte maturation to embryo development in mouse, but its homolog similar to the mouse Spindlin in molecular and expression characterization has not been identified up to now in other vertebrates. In this study, a full length of cDNA sequence is cloned and sequenced from the gibel carp (Carassius auratus gibelio). It contains 1240 nucleotides with an open reading frame of 771 nt encoding 257 amino acids. Based on its amino acid sequence alignment and comparison analysis with the known Spin family proteins, the newly cloned Spin is named Carassius auratus gibelio Spindlin (CagSpin). Its product could be detected from mature eggs to blastula embryos, but its content decreased from the two-cell stage, and could not be detected after the gastrula stage. It suggests that the CagSpin should be a maternal protein that is expressed during oocyte maturation, and plays a crucial role in early cleavage of embryogenesis. CagSpin is the first homolog similar to mouse spindlin identified in fish, and also in other vertebrates. GST pull-down assay reveals the first biochemical evidence for the association of CagSpin and beta-tubulin, the microtubule component. Therefore, CagSpin may play important functions by interacting with beta-tubulin and other spindle proteins during oocyte maturation and egg fertilization.

The developmental origins of mammalian oocyte polarity

Drosophila has been an excellent model system to study the cell and molecular determinants of oocyte axis specification, a problem which is little known in mammalian species. Recent evidence supports the notion that mammalian oocytes utilize axis-orienting properties during the course of oogenesis. Among these, axis specification in relation to the oocyte cortex, germinal vesicle (GV) position, anchoring of GV and spindle, and patterning of follicle cell/oocyte attachments are proposed as conserved features of oogenesis in mammals that may be important to the survival and development of the preimplantation embryo.

Follicle-Stimulating Hormone Affects Metaphase I Chromosome Alignment and Increases Aneuploidy in Mouse Oocytes Matured in Vitro1

Follicle-Stimulating Hormone (FSH) at a wide range of doses is routinely added to culture media during in vitro maturation (IVM) of oocytes, but the effects on oocyte health are unclear. The suggestion that superovulation may cause aneuploidy and fetal abnormalities prompted us to study the potential role of FSH in the genesis of chromosomal abnormalities during meiosis I. Mouse cumulus-oocyte complexes (COCs) isolated from the antral follicles of unprimed, sexually immature B6CBF1 mice were cultured in increasing concentrations of FSH. Following culture, matured oocytes were isolated, spread, stained with DAPI, and the numbers of chromosomes counted. Significantly increased aneuploidy, arising during the first meiotic division, was observed in metaphase II oocytes matured in higher concentrations of FSH (> or =20 ng/ml). The effect of FSH on spindle morphology and chromosome alignment during metaphase I was then explored using immunocytochemistry and three-dimensional reconstruction of confocal sections. High FSH had no effect on gross spindle morphology but did alter chromosome congression during prometaphase and metaphase, with the spread of chromosomes across the spindle at this time being significantly greater in oocytes cultured in 2000 ng/ml compared with 2 ng/ml FSH. Analysis of three-dimensional reconstructions of spindles in oocytes matured in 2000 ng/ml FSH shows that chromosomes are more scattered and farther apart than they are following maturation in 2 ng/ml FSH. These results demonstrate that exposure to high levels of FSH during IVM can accelerate nuclear maturation and induce chromosomal abnormalities and highlights the importance of the judicious use of FSH during IVM.

Estradiol and Its Membrane-Impermeable Conjugate (Estradiol-Bovine Serum Albumin) During In Vitro Maturation of Bovine Oocytes: Effects on Nuclear and Cytoplasmic Maturation, Cytoskeleton, and Embryo Quality

In various cell types, there is increasing evidence for nongenomic steroid effects, i.e., effects that are not mediated via the classical steroid receptors. However, little is known about the involvement of the nongenomic pathway of estradiol (E2) on mammalian oocyte in vitro maturation (IVM). The aim of this study was to investigate whether the effects of E2 on bovine oocyte IVM are mediated via a plasma membrane receptor (nongenomic). First, we investigated the expression of estradiol (classical) receptor alpha (ERalpha) and beta (ERbeta) mRNA in oocytes and cumulus cells (CC). We also studied the effects of different exposure times to E2 (before and after germinal vesicle breakdown, GVBD) on nuclear maturation. To study the possible involvement of the putative estradiol plasma membrane receptor on the IVM of oocytes, we used E2 conjugated with bovine serum albumin (E2-BSA), which cannot cross the plasma membranes. Our results demonstrate that oocytes expressed ERbeta mRNA, while CC expressed both ERalpha and ERbeta mRNA. Exposure to E2 during the first 8 h of culture (before GVBD) induced a block at the metaphase I stage (MI). However, the presence of E2 after GVBD induced an increase of oocytes with nuclear aberrations. Meiotic spindle organization was severely affected by E2 during IVM and multipolar spindle was the most frequently observed aberration. Exposure of oocytes to E2-BSA did not affect nuclear maturation, blastocyst formation rate, nor embryo quality. Our results suggest that the detrimental effects of E2 on in vitro nuclear maturation of bovine oocyte are not exerted via a plasma membrane receptor.

Effects of chilling on structural aspects of early preantral mouse follicles

Chilling injury is one of the major limiting factors for achieving optimal cryopreservation of gametes. This study aimed to determine potential chilling-induced damage on several structural aspects of early preantral mouse follicles. Mechanically isolated intact early preantral follicles (type 3b-4) were exposed to 0 degrees C for 1, 5, 10, or 30 min. Control and chilled follicles were analyzed by confocal microscopy after staining for tubulin, F-actin, and chromatin, and by electron microscopy. Chilling for only 1 min was sufficient to cause depolymerization of microtubules in the oocyte and the surrounding granulosa cell layer as evidenced by a substantial decrease in fluorescence intensity after antitubulin labeling. Cooling for longer periods caused alterations in microtubule organization in the follicle-enclosed oocyte. These alterations included the loss of interphase microtubules, concomitant with the formation of perinuclear or cortical microtubule asters and sometimes a complete disappearance of microtubules. The extent of microtubule modification was related to the time of chilling, but was fully reversible after rewarming follicles at 37 degrees C for 1 h. Chilling had only minor effects on the actin-containing elements located predominantly in the oocyte cortex and the transzonal projections. Ultrastructural analysis confirmed that oocyte-somatic cell interactions were present. There was no influence on the chromatin configuration within the follicle-enclosed oocyte. These results indicate that mouse follicles are relatively tolerant to direct chilling injury and, as a consequence, are able to withstand the cooling-warming steps during conventional cryopreservation procedures.

Golgi dynamics during meiosis are distinct from mitosis and are coupled to endoplasmic reticulum dynamics until fertilization

One current theory of the Golgi apparatus views its organization as containing both a matrix fraction of structural proteins and a reservoir of cycling enzymes. During mitosis, the putative matrix protein GM130 is phosphorylated and relocalized to spindle poles. When the secretory pathway is inhibited during interphase, GM130 redistributes to regions adjacent to vesicle export sites on the endoplasmic reticulum (ER). Strikingly, meiotic maturation and fertilization in nonrodent mammalian eggs presents a unique experimental environment for the Golgi apparatus, because secretion is inhibited until after fertilization, and because the centrosome is absent until introduced by the sperm. Here, we test the hypothesis that phosphorylated GM130 associates not with meiotic spindle poles, but with ER clusters in the mature bovine oocyte. At the germinal vesicle stage, phosphorylated GM130 is observed as fragments dispersed throughout the cytoplasm. During meiotic maturation, GM130 reorganizes into punctate foci that associate near the ER-resident protein calreticulin and is notably absent from the meiotic spindle. GM130 colocalizes with Sec23, a marker for ER vesicle export sites, but not with Lens culinaris agglutinin, a marker for cortical granules. Because disruption of vesicle transport has been shown to block meiotic maturation and embryonic cleavage in some species, we also test the hypothesis that fertilization and cytokinesis are inhibited with membrane trafficking disruptor brefeldin A (BFA). Despite Golgi fragmentation after BFA treatment, pronuclei form and unite, and embryos cleave and develop through the eight-cell stage. We conclude that, while the meiotic phosphorylation cycle of GM130 mirrors that of mitosis, absence of a maternal centrosome precludes Golgi association with the meiotic spindle. Fertilization introduces the sperm centrosome that can reorganize Golgi proteins, but neither fertilization nor cytokinesis prior to compaction requires a functional Golgi apparatus.

Asynchronous cytoplast and karyoplast transplantation reveals that the cytoplasm determines the developmental fate of the nucleus in mouse oocytes

The relationship between nucleus and cytoplasm can be well revealed by nuclear transplantation. Here, we have investigated the behavior changes of the reconstructed oocytes after transferring the karyoplasts from mouse GV, MI, and MII oocytes into the cytoplasts at the different developmental stages. When the GV cytoplast was used as recipient and MI or MII karyoplast was used as donor (MI-GV pair and MII-GV pair), the reconstructed pairs extruded a polar body after electrofusion and culture. Both the cytoplasm and the polar body had a metaphase spindle in the MI-GV pair, while only a clutch of condensed chromatin was observed in the cytoplasm and polar body of the MII-GV pair. When the MI cytoplast was used as recipient and GV or MII karyoplast was used as donor (GV-MI pair and MII-MI pair), the reconstructed pairs also extruded a polar body. Each had one spindle and a group of metaphase chromosomes in the cytoplasm and polar body, respectively. When the MII cytoplast was used as recipient and GV or MI karyoplast was used as donor (GV-MII pair and MI-MII pair), the reconstructed pairs were activated, became parthenogenetic embryos and even developed to hatching blastocysts after electrofusion. The result from immunoblotting showed that MAP kinase activity was high in the MI and MII cytoplasts, while not detected in GV cytoplast. The results demonstrate that the cytoplasmic environment determines the behavior of asynchronous donors.

Rotation of meiotic spindle is controlled by microfilaments in mouse oocytes

The completion of meiosis requires the spatial and temporal coordination of cytokinesis and karyokinesis. During meiotic maturation, many events, such as formation, location, and rotation of the meiotic spindle as well as chromosomal movement, polar body extrusion, and pronuclear migration, are dependent on regulation of the cytoskeleton system. To study functions of microfilaments in meiosis, we induced metaphase II (MII) mouse oocytes to resume meiosis by in vitro fertilization or parthenogenetic activation, and we treated such oocytes with cytochalasin B (CB). The changes of the meiotic spindle, as visualized in preparations stained for beta-tubulin and chromatin, were observed by fluorescent confocal microscopy. The meiotic spindle of MII oocytes was observed to be parallel to the plasmalemma. After meiosis had resumed, the spindle rotated to the vertical position so that the second polar body could be extruded into the perivitelline space. When meiosis resumed and oocytes were treated with 10 micro g/ml of CB, the spindle rotation was inhibited. Consequently, the oocyte formed an extra pronucleus instead of extruding a second polar body. These results indicate that spindle rotation is essential for polar body extrusion; it is the microfilaments that play a crucial role in regulating rotation of the meiotic spindle.

Nuclear transfer in practice

The technique of nuclear transfer (NT) allows the production of embryos, fetuses, and offspring from a range of embryonic, fetal, and adult derived cell types in a range of species. Successful development is dependent upon numerous factors, including type of recipient cell, source of recipient cell, method of reconstruction, activation, embryo culture, donor cell type, and donor and recipient cell cycle stages. The present review will discuss the uses of NT, the techniques presently available, and the factors affecting subsequent development.