Culture conditions affect meiotic regulation in cumulus cell-enclosed mouse oocytes

Effect of heat exposure on the growth and developmental competence of bovine oocytes derived from early antral follicles

In dairy cows, low fertility caused by summer heat stress continues into the cooler autumn season. This can be caused by impaired oocyte quality in small growing follicles during summer. Here, we subjected oocyte-cumulus-granulosa complexes (OCGCs) derived from early antral follicles (0.5-1 mm) to in vitro growth (IVG) culture under two different temperature settings (the control and heat shock groups), and evaluated effects of heat exposure on growth and developmental competence of oocytes, factors affecting the developmental competence of oocytes (steroidogenesis of granulosa cells, oxidative stress in oocytes, and cell-to-cell communication between oocytes and somatic cells). Oocyte diameters after culture were smaller in the heat shock group. Although nuclear maturation and cleavage rates were similar between the groups, blastocyst rates were lower in the heat shock group (0.0%) than in the control group (27.7%), and reduced glutathione (GSH) levels in oocytes were lower in the heat shock group. Supplementation of cysteine, which stimulates GSH synthesis, increased GSH level and improved blastocyst rate of heat shocked oocytes (27.9%). These results suggest that heat exposure impairs the growth and developmental competence of oocytes in early antral follicles through GSH depletion, which can induce low fertility during summer and the following autumn.

Improved conditions of a whole testis organ culture system in terms of spermatogonial proliferation levels in marine medaka (Oryzias dancena)

In vitro spermatogenesis can be performed for marine medaka (Oryzias dancena) via whole testis organ cultures, but spermatogenesis could only be maintained during the early phase of culturing, suggesting that the culture conditions can be further optimized. To improve the culture conditions, we examined the effects of culture temperature, basal media, and medium supplements on spermatogonial proliferation levels during whole testis organ culturing by BrdU incorporation assays. Our results show that a 30°C culture temperature negatively affected spermatogonial proliferation compared to 26°C and 28°C and that the use of Dulbecco's Modified Eagle Medium and Minimum Essential Medium α (α-MEM) was more effective for spermatogonial proliferation than the use of Leibovitz's L-15 Medium (L15). When fetal bovine serum (FBS) was replaced with KnockOut Serum Replacement (KSR), a significantly positive effect was observed for the maintenance of spermatogonial proliferation. However, supplementation of the medium with 17α, 20β-dihydroxy-4-pregnen-3-one did not show any significant effect. Gene expression analyses of four genes, including Nanos2, SCP3, AMH, and StAR, indicated that the optimized culture conditions consisting of α-MEM and KSR had the most positive influence on the maintenance of spermatogonial proliferation levels in whole testis organ cultures compared to the original culture conditions consisting of L15 and FBS by maintaining the function of Sertoli and Leydig cells. The results from this study will provide useful information for the study of in vitro spermatogenesis in fish.

Granulosa cells affect in vitro maturation and subsequent parthenogenetic development of buffalo (Bubalus bubalis) oocytes

Granulosa cells (GCs) play a crucial role in follicular development and atresia. Previous studies have showed that GCs in the form of monolayer influenced in vitro maturation (IVM) of oocytes. However, the effects of GCs in the form of conditioned medium and monolayer on IVM and development competence of buffalo oocytes remain unclear. In the present study, we examined the impacts of GC-conditioned medium (GCCM) and monolayer GC on maturation efficiency and embryo development of buffalo oocytes after parthenogenetic activation (PA). Our results showed that GCCM that was collected on day 2 and added to IVM medium at a 20% proportional level (2 days and 20%) exerted significant negative effects on IVM rate (41.6% vs. 44.5%), but significantly enhanced embryo development (oocyte cleavage, 81.3% vs. 69.3%; blastocyst formation, 36.3% vs. 29.3%) of buffalo oocytes after PA compared with the control group. Furthermore, monolayer GC significantly reduced both maturation efficiency (40.2% vs. 44.5%) and embryo development (oocyte cleavage, 60.6% vs. 69.3%; blastocyst formation, 20.6% vs. 29.3%) of buffalo oocytes after PA compared to the control group. Our study indicated that GCs in the form of GCCM (2 days and 20%) and monolayer GC had different effects on IVM and subsequent parthenogenetic development of buffalo oocytes.

Validation of the blood gas analyzer for pH measurements in IVF culture medium: Prevent suboptimal culture conditions

Measurement of pH in IVF-media using the blood gas analyzer (BGA) requires validation, because IVF-media is outside the intended scope of the BGA. To determine whether the Siemens Rapidpoint 500 BGA is suitable for pH measurements in IVF-media this study will validate the BGA and assess its accuracy. In this method comparison study, the pH of over three hundred IVF-media samples was measured with the BGA and a pH electrode (Hanna pH checker). The precision of both the BGA and the pH electrode were excellent (coefficient variation <1.4%). However, the closeness of agreement between measured values of both devices were not equivalent to each other in the tested IVF-media, showing 15% to 85% accordance between devices. The pH measured with the blood gas analyzer was also significantly higher in the tested media, compared to that measured by the pH electrode. One of the tested media did not reach its target pH when it was measured with the BGA, even at 9% CO₂. The results show that the validated blood gas analyzer produces excellent results in terms of precision but not in terms of accuracy. Inaccurate measurement may lead to misinterpretation of results and consequently to suboptimal culture conditions. Therefore, each laboratory is encouraged to perform a validation of their BGA.

In vivo oxygen, temperature and pH dynamics in the female reproductive tract and their importance in human conception: a systematic review

BACKGROUND

Despite advances in ART, implantation and pregnancy rates per embryo transfer still remain low. IVF laboratories strive to ensure that the process of handling gametes in vitro closely mimics the in vivo environment. However, there remains a lack of knowledge regarding the in vivo regulation and dynamic variation in biophysical parameters such as oxygen concentration, pH and temperature within the reproductive tract.

OBJECTIVE AND RATIONALE

To undertake a systematic review of the current understanding of the physico-chemical parameters of oxygen tension (pO2), pH and temperature within the female reproductive tract, and their potential implications in clinical and pathological processes related to fertility and those pertaining to limited reproductive capacity.

SEARCH METHODS

A comprehensive literature search was performed using electronic databases including Medline, Embase, Cochrane Library and Pubmed to identify original and review articles addressing the biophysical parameters (pO2, pH and temperature) in the female reproductive tract of any species. The search included all studies published between 1946 and November 2015. Search terms included 'oxygen', 'pH', 'hydrogen ion concentration', 'acid base' and others terms. We also used special features and truncations to identify synonyms and broaden the search. Studies were excluded if they only assessed embryo culture conditions, fetal acid-base status, oxidative stress, outcomes of pregnancy and measurements of these parameters in non-reproductive organs.

OUTCOMES

Our search generated 18 685 records and 60 articles were included. pO2 within the female reproductive tract shows cyclical variation and minute-to-minute oscillations, which may be influenced by uterine contractility, hormones, the autonomic system, cardiac pulsatility, and myometrial and smooth muscle integrity. Fine balanced control of pO2 and avoidance of overwhelming oxidative stress is crucial for embryogenesis and implantation. The pH in the female reproductive tract is graduated, with lowest pH in the vagina (~pH 4.42) increasing toward the Fallopian tubes (FTs) (~pH 7.94), reflecting variation in the site-specific microbiome and acid-base buffering at the tissue/cellular level. The temperature variation in humans is cyclical by day and month. In humans, it is biphasic, increasing in the luteal phase; with the caudal region of the oviduct 1-2 degrees cooler than the cranial portion. Temperature variation is influenced by hormones, density of pelvic/uterine vascular beds and effectiveness of heat exchange locally, crucial for sperm motility and embryo development. We have identified significant deficiencies and inconsistencies in the methods used to assess these biophysical factors within the reproductive tract. We have suggested that the technological solutions including the development of methods and models for real time, in vivo recordings of biophysical parameters.

WIDER IMPLICATIONS

The notion of 'back to nature' in assisted conception suggested 20 years ago has yet to be translated into clinical practice. While the findings from this systematic review do not provide evidence to change current in vitro protocols, it highlights our current inability to assess the in vivo reproductive tract environment in real time. Data made available through future development of sensing technology in utero may help to provide new insights into how best to optimize the in vitro embryo environment and allow for more precise and personalized fertility treatment.

Strategies to improve fertilisation rates with assisted conception: a systematic review

Successful fertilisation is one of the key steps determining success of assisted conception. Various factors including sperm or oocyte pathology and environmental factors have a significant impact on fertilisation rates. This systematic review is aimed to evaluate the existing evidence about factors affecting fertilisation and strategies to improve fertilisation rates. A literature search was performed using Ovid MEDLINE ® (Jan 1950-April 2016), EMBASE (Jan 1950-April 2016), Ovid OLDMEDLINE ®, Pre-MEDLINE (Jan 1950-April 2016) and the Cochrane Library. Relevant key words were used to combine sets of results and a total 243 papers were screened. Only qualitative analysis was performed, as there was major heterogeneity in study design and methodology for quantitative synthesis. Factors affecting fertilisation were divided into sperm- and oocyte-related factors. The methods to improve fertilisation rates were grouped together based on the approach used to improve fertilisation rates. Optimising laboratory condition and procedural effects in techniques is associated with improved fertilisation rates. Various techniques are described to improve fertilisation rates including assisted oocyte activation, physiological intracytoplasmic sperm injection (PICSI) and intracytoplasmic morphologically selected sperm injection (IMSI). This review highlights the promising strategies under research to enhance fertilisation rates. Adequately powered multicentre randomised trials are required to evaluate these techniques before considering clinical application.

The potential role of granulosa cells in the maturation rate of immature human oocytes and embryo development: A co-culture study

Objective

In order to increase the number of mature oocytes usable for intracytoplasmic sperm injection (ICSI), we aimed to investigate the effect of co-culturing granulosa cells (GCs) on human oocyte maturation in vitro, the fertilization rate, and embryo development.

Methods

A total of 133 immature oocytes were retrieved and were randomly divided into two groups; oocytes that were cultured with GCs (group A) and oocytes that were cultured without GCs (group B). After in vitro maturation, only oocytes that displayed metaphase II (MII) underwent the ICSI procedure. The maturation and fertilization rates were analyzed, as well as the frequency of embryo development.

Results

The mean age of the patients, their basal levels of follicle-stimulating hormone, and the number of oocytes recovered from the patients were all comparable between the two study groups. The number of oocytes that reached MII (mature oocytes) was 59 out of 70 (84.28%) in group A, compared to 41 out of 63 (65.07%) in group B (p=0.011). No significant difference between fertilization rates was found between the two study groups (p=0.702). The embryo development rate was higher in group A (33/59, 75%) than in group B (12/41, 42.85%; p=0.006). The proportion of highest-quality embryos and the blastocyst formation rate were significantly lower in group B than in group A (p=0.003 and p<0.001, respectively).

Conclusion

The findings of the current study demonstrate that culturing immature human oocytes with GCs prior to ICSI improves the maturation rate and the likelihood of embryo development.

Nutrient pathways regulating the nuclear maturation of mammalian oocytes

Oocyte maturation is defined as that phase of development whereby a fully grown oocyte reinitiates meiotic maturation, completes one meiotic division with extrusion of a polar body, then arrests at MII until fertilisation. Completion of maturation depends on many different factors, not the least of which is the proper provision of energy substrates to fuel the process. Interaction of the oocyte and somatic compartment of the follicle is critical and involves numerous signals exchanged between the two cell types in both directions. One of the prominent functions of the cumulus cells is the channelling of metabolites and nutrients to the oocyte to help stimulate germinal vesicle breakdown and direct development to MII. This entails the careful integration and coordination of numerous metabolic pathways, as well as oocyte paracrine signals that direct certain aspects of cumulus cell metabolism. These forces collaborate to produce a mature oocyte that, along with accompanying physiological changes called cytoplasmic maturation, which impart subsequent developmental competence to the oocyte, can be fertilised and develop to term. This review focuses on nuclear maturation and the metabolic interplay that regulates it, with special emphasis on data generated in the mouse.

TUNEL analysis of DNA fragmentation in mouse unfertilized oocytes: the effect of microorganisms within human follicular fluid collected during IVF cycles

Recently we reported the presence of bacteria within follicular fluid. Previous studies have reported that DNA fragmentation in human spermatozoa after in vivo or in vitro incubation with bacteria results in early embryo demise and a reduced rate of ongoing pregnancy, but the effect of bacteria on oocytes is unknown. This study examined the DNA within mouse oocytes after 12 hours' incubation within human follicular fluids (n=5), which were collected from women undergoing in vitro fertilization (IVF) treatment. Each follicular fluid sample was cultured to detect the presence of bacteria. Terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) was used to label DNA fragmentation in ovulated, non-fertilized mouse oocytes following in vitro incubation in human follicular fluid. The bacteria Streptococcus anginosus and Peptoniphilus spp., Lactobacillus gasseri (low-dose), L. gasseri (high-dose), Enterococcus faecalis, or Propionibacterium acnes were detected within the follicular fluids. The most severe DNA fragmentation was observed in oocytes incubated in the follicular fluids containing P. acnes or L. gasseri (high-dose). No DNA fragmentation was observed in the mouse oocytes incubated in the follicular fluid containing low-dose L. gasseri or E. faecalis. Low human oocyte fertilization rates (<29%) were associated with extensive fragmentation in mouse oocytes (80-100%). Bacteria colonizing human follicular fluid in vivo may cause DNA fragmentation in mouse oocytes following 12h of in vitro incubation. Follicular fluid bacteria may result in poor quality oocytes and/or embryos, leading to poor IVF outcomes.

The effect of human cumulus cells on the maturation and developmental potential of immature oocytes in ICSI cycles

PURPOSE

To investigate the effect of human cumulus cells on the maturation and developmental potential of immature oocytes in ICSI cycles.

METHODS

Immature oocytes were randomly divided into two groups: the cumulus-denuded oocyte group (group A) and the cumulus-intact oocyte group (group B). Only oocytes that reached metaphase II (MII) stage after in vitro maturation were used in the ICSI procedure. In vivo mature sibling MII oocytes served as the control group. Maturation rate, fertilization rate, embryo quality and developmental potential were examined.

RESULTS

There was no significant difference in maturation rate between group A (68.16%) and group B (70.49%; P > 0.05). The total fertilization rate among the three groups was comparable (P > 0.05), while the zygotes with two pronuclei in group A (74.59%) or group B (75.97%) were significantly lower than those in control group (84.29%; P < 0.05). The available embryo rate in group A (11.49%) was markedly lower than that in group B (27.66%; P < 0.05), and both of them were significantly lower than that in control group (62.38%; P < 0.05). The proportion of ≥6-cell embryos in group B (45.74%) was notably higher than in group A (26.44%; P < 0.05), and both were markedly lower than in control group (65.92%; P < 0.05). The proportion of embryos with <10% fragmentation in group A (13.79%) was significantly lower than in group B (29.79%; P < 0.05), and both were notably lower than in control group (42.98%; P < 0.05).

CONCLUSIONS

The presence of cumulus cells surrounding the immature oocytes during IVM before ICSI had no influence on nuclear maturation and fertilization, but leads to better subsequent embryonic development. This is perhaps mediated by an improvement in cytoplasmic maturation.

Mouse versus rat: Profound differences in meiotic regulation at the level of the isolated oocyte

Cumulus cell-enclosed oocytes (CEO), denuded oocytes (DO), or dissected follicles were obtained 44-48 hr after priming immature mice (20-23 days old) with 5 IU or immature rats (25-27 days old) with 12.5 IU of equine chorionic gonadotropin, and exposed to a variety of culture conditions. Mouse oocytes were more effectively maintained in meiotic arrest by hypoxanthine, dbcAMP, IBMX, milrinone, and 8-Br-cGMP. Atrial natriuretic peptide, a guanylate cyclase activator, suppressed maturation in CEO from both species, but mycophenolic acid reversed IBMX-maintained meiotic arrest in mouse CEO with little activity in rat CEO. IBMX-arrested mouse, but not rat, CEO were induced to undergo germinal vesicle breakdown (GVB) by follicle-stimulating hormone (FSH) and amphiregulin, while human chorionic gonadotropin (hCG) was ineffective in both species. Nevertheless, FSH and amphiregulin stimulated cumulus expansion in both species. FSH and hCG were both effective inducers of GVB in cultured mouse and rat follicles while amphiregulin was stimulatory only in mouse follicles. Changing the culture medium or altering macromolecular supplementation had no effect on FSH-induced maturation in rat CEO. The AMP-activated protein kinase (AMPK) activator, AICAR, was a potent stimulator of maturation in mouse CEO and DO, but only marginally stimulatory in rat CEO and ineffective in rat DO. The AMPK inhibitor, compound C, blocked meiotic induction more effectively in hCG-treated mouse follicles and heat-treated mouse CEO. Both agents produced contrasting results on polar body formation in cultured CEO in the two species. Active AMPK was detected in germinal vesicles of immature mouse, but not rat, oocytes prior to hCG-induced maturation in vivo; it colocalized with chromatin after GVB in rat and mouse oocytes, but did not appear at the spindle poles in rat oocytes as it did in mouse oocytes. Finally, cultured mouse and rat CEO displayed disparate maturation responses to energy substrate manipulation. These data highlight significant differences in meiotic regulation between the two species, and demonstrate a greater potential in mice for control at the level of the cumulus CEO.

Effect of lanosterol on the in vitro maturation in semi-defined culture system of prepubertal ewe oocytes

The choice of medium and supplements can affect meiotic regulation and may have an impact on the regulation of mammalian oocyte growth and embryonic cell function. The aim of the present study was to assess the effects of oxygen concentration and endogenous lanosterol on the in vitro maturation (IVM) media without serum and based on recombinant human chorionic gonadotrophin in prepubertal ewe oocytes. Firstly, the effect of varying oxygen concentrations (5% and 20%) during IVM in TCM-199 supplemented (4 mg/ml bovine serum albumin (BSA), 100 μM cysteamine, 0.3 mM sodium pyruvate, 0.1 UI/ml recombinant follicle-stimulating hormone (r-FSH; Gonal-F® 75 UI, Serono, Italy), 0.1 UI/ml recombinant leuteinizing hormone (r-LH; Lhadi® 75 UI, Serono, Italy) and 1 μg/ml estradiol-17β) on subsequent nuclear maturation of oocytes examined under ultraviolet light following staining with bisbenzimide (Hoechst 33342) was investigated. Secondly, two concentrations of lanosterol (0, 10 and 50 μM) were added to the IVM medium. Nuclear maturation of oocytes was examined as previously. Lipid content in oocytes, an important indicator of cytoplasmic maturity, was also measured using Nile red fluorescent stain. The results showed that low oxygen concentration affected the nuclear maturation. Similarly, a significantly higher rate of meiosis resumption was observed with 10 μM (72.3%) of lanosterol compared with the control (51.8%) or 50 μM of lanosterol (59.4%). A significantly higher content of lipids was also observed with 10 and 50 μM of lanosterol (7.3 ± 0.2 × 106 and 7.4 ± 0.2 × 106 arbitrary units of fluorescence) compared with the control (6.7 ± 0.2 × 106 arbitrary units of fluorescence). The results indicate that 10 μM lanosterol during IVM in medium without serum and based on recombinant human chorionic gonadotrophin has a positive effect on maturation of prepubertal ewe oocytes.

Cows are not mice: the role of cyclic AMP, phosphodiesterases, and adenosine monophosphate-activated protein kinase in the maintenance of meiotic arrest in bovine oocytes

Meiotic maturation in mammalian oocytes is initiated during fetal development, and is then arrested at the dictyate stage - possibly for several years. Oocyte meiosis resumes in preovulatory follicles in response to the lutenizing hormone (LH) surge or spontaneously when competent oocytes are removed from follicles and cultured. The mechanisms involved in meiotic arrest and resumption in bovine oocytes are not fully understood, and several studies point to important differences between oocytes from rodent and livestock species. This paper reviews earlier and contemporary studies on the effects of cAMP-elevating agents and phosphodiesterase (PDE) enzyme inhibitors on the maintenance of meiotic arrest in bovine oocytes in vitro. Contrary to results obtained with mouse oocytes, bovine oocyte meiosis is inhibited by activators of the energy sensor adenosine monophosphate-activated protein kinase (AMPK, mammalian gene PRKA), which is activated by AMP, the degradation product of cAMP. It is not clear whether or not the effects were due to AMPK activation, and they may depend on culture conditions. Evidence suggests that other signaling pathways (for example, the cGMP/nitric oxide pathway) are involved in bovine oocyte meiotic arrest, but further studies are needed to understand the interactions between the signaling pathways that lead to maturation promoting factor (MPF) being inactive or active. An improved understanding of the mechanisms involved in the control of bovine oocyte meiosis will facilitate better control of the process in vitro, resulting in increased developmental competence and increased efficiency of in vitro embryo production procedures.

Biological pH buffers in IVF: help or hindrance to success

PURPOSE

Minimizing environmental stress helps maintain cellular homeostasis and is a crucial component in optimizing embryo development in vitro and resulting ART success. One stressor of particular interest is pH. Biologic buffers, such as HEPES and MOPS, are valuable tools for stabilizing pH. The objective of this manuscript is to summarize efficacy and impact of various pH buffers used during IVF lab procedures

METHODS

Keyword searches were performed using Pubmed and Medline and relevant literature reviewed.

RESULTS

Various pH buffers have been used with varying degrees of success for gamete and embryo processing in a variety of animal species, as well as in human.

CONCLUSION

Though biologic buffers off a means to improve pH stability, not all buffers may be appropriate for use with gametes and embryos. Specific buffers may have undesired effects, and these may be buffer, species, cell type or concentration dependent. Continued research is needed to further refine and improve the use of biologic buffers for use in human ART.

Optimizing the culture environment in the IVF laboratory: impact of pH and buffer capacity on gamete and embryo quality

Supplying and maintaining appropriate culture conditions is critical to minimize stress imposed upon gametes and embryos and to optimize the in-vitro environment. One parameter that requires close scrutiny in this endeavour is pH. Though embryos have a limited ability to regulate their internal pH (pH(i)), oocytes lack robust mechanisms. Thus, careful attention to external pH (pH(e)) of culture media is imperative in IVF. Ability to withstand deviations in hydrogen ion concentration varies depending on culture conditions, as well as laboratory procedures. Cryopreserved--thaw--thawed embryos, as well as denuded oocytes, are especially susceptible to perturbations in pH(e). Therefore, proper setting, monitoring and stabilizing of pH(e) during IVF laboratory procedures is a crucial component of a rigorous quality control programme. Here, importance of both pH(i) and pH(e) in respect to gamete and embryo quality are discussed. Furthermore, factors influencing selection of pH(e), as well as emerging methods to stabilize pH(e) in the IVF laboratory are detailed.

In vitro maturation of dromedary (Camelus dromedarius) oocytes: effect of different protein supplementations and epidermal growth factor*

The present experiment was aimed to compare the effect of different protein supplementation sources, foetal calf serum (FCS), oestrous dromedary serum (EDS) and BSA, in experiment 1, and the effect of different concentrations of epidermal growth factor (EGF), in experiment 2, on in vitro nuclear maturation of the dromedary oocytes. Cumulus oocyte complexes (COCs) were harvested from the ovaries collected from a local slaughterhouse by aspirating the visible follicles in PBS supplemented with 5% FCS. Pooled COCs were randomly distributed to 4-well culture plates containing 500 μl of the maturation medium and cultured at 38.5 °C in an atmosphere of 5% CO(2) in air for 32-36 h. The basic maturation medium consisted of TCM-199 supplemented with 0.1 mg/ml L-glutamine, 0.8 mg/ml sodium bicarbonate, 0.25 mg/ml pyruvate, 50 μg/ml gentamicin, 10 μg/ml bFSH, 10 μg/ml bLH and 1 μg/ml estradiol. In experiment 1, this medium was supplemented with 10% FCS, 10% EDS or 0.4% BSA, whereas in experiment 2, it was supplemented with 0.4% BSA and 0, 10, 20 or 50 ng/ml of EGF. The oocytes were fixed, stained with 1% aceto-orcein stain and their nuclear status was evaluated. Oocytes were classified as germinal vesicle, diakinesis, metaphase-I, anaphase-I (A-I), metaphase-II (M-II) and those with degenerated, fragmented, scattered, activated or without visible chromatin as others. There was no difference (p > 0.05) observed in the proportion of oocytes reaching M-II stage between the media supplemented with FCS (71.5 ± 4.8), EDS (72.8 ± 2.9) and BSA (72.7 ± 6.2). In experiment 2, a higher proportion (p < 0.05) of oocytes reached M-II stage when the medium was supplemented with 20 ng/ml of EGF (81.4 ± 3.2) when compared with the media supplemented with 10 ng/ml (66.9 ± 4.1) and control (67.2 ± 7.1) groups. It may be concluded that the maturation media for dromedary camel oocytes can be supplemented with any of the three protein sources, i.e. FCS, EDS and BSA without any significant differences on the maturation rates. Also, a supplementation of 20 ng/ml of EGF in the maturation medium seems to be optimal and improves the nuclear maturation of dromedary camel oocytes.

Akt expression in mouse oocytes matured in vivo and in vitro

To improve developmental competence of in vitro matured oocytes, culture medium can be supplemented with hypoxanthine (Hx) and FSH or epidermal growth factor (EGF) to trigger the activation of essential signalling pathways regulating meiotic resumption and progression. Since the serine/threonine kinase, Akt, contributes to the regulation of the meiotic cell cycle, this study analysed its expression level and localization at the meiotic spindle in oocytes matured in vivo or in vitro in the presence of Hx-FSH or Hx-EGF. Independently of culture conditions adopted, Akt mRNA concentration did not vary from germinal vesicle to metaphase I (MI), while at MII a significant decrease in Akt1 mRNA concentration was recorded in oocytes matured in vivo and in those stimulated by Hx-EGF (P < 0.05). Phoshorylated Akt protein content was similar in the different groups of MI oocytes, but it decreased at MII in oocytes matured either in vivo or in vitro with Hx-EGF. Ser-473-phosphorylated Akt was localized uniformly to the meiotic spindle in more than 90% of oocytes. These results indicate that, in mouse oocytes, Akt expression is differentially regulated during in vivo and in vitro maturation and suggest that EGF could be a positive modulator, even stronger than FSH, of oocyte meiotic maturation.

New pH-buffering system for media utilized during gamete and embryo manipulations for assisted reproduction

Maintenance of stable pH is important for optimizing gamete and embryo culture. One method to stabilize pH entails using zwitterionic buffers in IVF handling media used outside the laboratory incubator. Current handling media utilize single buffers, such as MOPS or HEPES. However, the use of a single buffer limits the ability to adjust the range of buffering capacity. Furthermore, changes in temperature alter buffering of these compounds. Therefore, traditional IVF handling media utilizing a single buffer may not provide ideal pH buffering. This study reports that combining multiple buffers, such as HEPES, MOPS and DIPSO, into a single medium in various ratios gives the ability to shift the effective buffering range to cover a specific pH. Additionally, by combining various buffers, it is possible to expand pH buffering over a range of temperatures, while simultaneously reducing the absolute concentration of individual buffers, thereby reducing or alleviating toxicity concerns. This report verifies that DIPSO, MOPS and HEPES, and their combinations, support embryo development. Therefore, utilization of bi- and tri-buffered media, containing a mixture of HEPES, MOPS or DIPSO, offers advantages compared with media containing HEPES or MOPS alone, and may be used for procedures such as oocyte retrieval, intracytoplasmic sperm injection, embryo transfer and cryopreservation.

The effect of different zwitterionic buffers and PBS used for out-of-incubator procedures during standard in vitro embryo production on development, morphology and gene expression of bovine embryos

The effect of the zwitterionic buffers HEPES, TES and MOPS and of PBS used for out-of-incubator procedures during standard in vitro embryo production on bovine oocytes and embryo development, morphology and on the expression patterns of eight selected genes: Fgf-4, Lama1, Ube2a, Gsta4, Il6, Sod1, Prss11 and Hspb1, was evaluated. All buffers were prepared at a concentration of 10 mM in TALP medium, with the exception of PBS. The total time of oocyte/embryo exposure to each buffer was approximately 41 min. The cleavage rates and number of embryos that developed to > or =8 cells at day 4 were no different among the buffers tested, however, more blastocysts developed at day 7, 8 and 9 in HEPES and MOPS treatments than in PBS and TES (P<0.05). No difference between buffers in total and apoptotic cell number was found. Except for Hspb1 and Ube2a genes, the levels of expression of the six remaining transcripts were higher in in vivo than in in vitro embryos irrespective of buffer used (P<0.05). In addition, higher expression of Hspb1 and lower expression of Ube2a and Lama1 were observed in PBS and TES than in MOPS and HEPES treatments (P<0.05). Expression of Fgf-4 and Gsta4 in the in vitro embryos was lower in PBS than in the remaining three buffers (P<0.05) and the level of expression of the Il6 gene was not affected by any buffer tested but was lower in in vitro than in in vivo derived embryos. Expression of both Sod1 and Prss11 genes in MOPS were at the level of the in vivo embryos. These results showed that the choice of buffer and short exposure time of approximately 41 min, affects mRNA expression of in vitro produced bovine embryos.

Decreased oocyte-granulosa cell gap junction communication and connexin expression in a type 1 diabetic mouse model

In women, type 1 diabetes is associated with an increased risk of poor prenatal outcomes such as congenital anomalies and early miscarriage. In murine models of type 1 diabetes, impaired oocyte meiotic maturation, abnormal oocyte metabolism, and increased granulosa cell apoptosis have been noted. because gap junction communication is critical for the regulation of oocyte growth and meiotic maturation, we investigated the level of communication between the oocyte and surrounding cumulus cells in a streptozotocin-induced type 1 diabetic B6SJL/F1 mouse model and the expression of gap junction proteins known as connexins. Fluorescence recovery after photobleaching analyses of cumulus cell-enclosed oocytes (CEOs) from diabetic mice showed a 60% decrease in communication as compared with CEOs from nondiabetic mice. Real-time RT-PCR analyses confirmed the presence of Cx26, Cx37, and Cx57 mRNA and revealed a significant decrease in Cx37 mRNA expression in oocytes from diabetic mice compared with nondiabetic mice. Western analyses detected Cx26 expression in CEO but not denuded oocyte (DO) samples, and Cx37 in DO samples. Cx26 protein levels were decreased by 78% in CEOs from diabetic mice, and Cx37 protein levels were decreased 36% in DOs from diabetic mice. This decrease in connexin expression and gap junction communication in CEOs from diabetic mice may be responsible for the impaired oocyte meiotic maturation and poor pregnancy outcomes.

Principal findings from a multicenter trial investigating the safety of follicular-fluid meiosis-activating sterol for in vitro maturation of human cumulus-enclosed oocytes

OBJECTIVE

To evaluate the safety of applying follicular-fluid meiosis-activating sterol (FF-MAS) in vitro to immature human oocytes.

DESIGN

Phase I bicenter, randomized, parallel-group, controlled, partially blinded trial.

SETTING

Third-level referral academic centers, including reproductive biology and genetics laboratories.

PATIENTS

Endocrinologically normal women with a medical indication for IVF or intracytoplasmic sperm injection, or healthy volunteers.

INTERVENTION(S)

Subjects were randomized at a ratio 1 to 6 into either conventional GnRH-agonist and recombinant FSH stimulation (IVO) for oocyte retrieval, or minimally stimulated in vitro maturation (IVM) with the use of recombinant FSH. Retrieved immature oocyte cumulus complexes were cultured for 30 or 36 hours in one of six IVM culture conditions containing FF-MAS (range, 0.1-20 microM). Polar body-extruded oocytes from the IVO and IVM groups were processed for chromosomal analysis.

MAIN OUTCOME MEASURE(S)

The primary endpoint was the incidence of metaphase II stage oocytes with numeric chromosomal abnormalities, using full (spectral karyotyping) or partial (fluorescent in situ hybridization with seven probes) karyotyping or Giemsa count. A secondary objective was to document the frequency of metaphase II oocytes after IVM with FF-MAS supplements.

RESULT(S)

Oocyte cumulus complexes obtained from the IVO (mean, 8.9) and IVM (mean, 6.2) groups had equal maturation rates. Compared to IVO, exposure of germinal-vesicle oocytes for a maturation period of 30 hours did not increase aneuploidy. An exposure period of 36 hours doubled the aneuploidy rate, but this was significant only for the 20-muM dose of FF-MAS.

CONCLUSION

Inclusion of 1-10 microM FF-MAS in a 30-hour IVM protocol is safe.

The PKC pathway and in particular its β1 isoform is clearly involved in meiotic arrest maintenance but poorly in FSH-induced meiosis resumption of the mouse cumulus cell enclosed oocyte

PKC modulators were used to investigate the role of the PKC pathway either on the maintenance of meiotic arrest or on FSH-induced maturation of mouse cumulus cell enclosed oocytes (CEOs). (1) Whereas PKC activation (PMA 8 microM) overcomed clearly the HX-maintained meiotic arrest (83.7 +/- 3.6% vs. 16.1 +/- 10.6% GVBD oocytes), PKC inhibition (Calphostin C 100 nM) did not. On the contrary, it better maintained the meiotic arrest than HX alone. (2) No significant effect of PKC activation or inhibition was observed. (3) HX alone maintained PKCbeta1 in the cytoplasm, whereas FSH and PKC activation induced partly its translocation into the nucleus. The results show that whereas the PKC pathway is clearly involved in maintenance of the meiotic arrest through PKCbeta1, it is not involved in FSH-induced meiosis of CEOs.

Meiotic induction by heat stress in mouse oocytes: involvement of AMP-activated protein kinase and MAPK family members

In this study, we examined the effect of heat pulsing on oocyte maturation and assessed the possible role of stress-activated enzymes during heat stress-induced meiotic maturation. Denuded oocytes from immature eCG-primed mice were pulsed for 30 min at increasing temperatures from 40 degrees C to 43 degrees C in dibutyryl cAMP-containing medium and were subsequently cultured at 37 degrees C for a total incubation time of 17-18 h. Oocytes exposed to 42 degrees C showed the greatest stimulation of maturation, with no effect at 43 degrees C. A heat pulse did not compromise progression to metaphase II as observed by polar body (PB) formation. The AMP-activated protein kinase (PRKA) inhibitors compound C and Ara-A each blocked the meiosis-stimulating effects of heat. Western blots showed that acetyl-CoA carboxylase, an important substrate of PRKA, was phosphorylated in heat-treated germinal vesicle-stage oocytes, indicating activation of PRKA before maturation. The mitogen-activated protein 2 kinase (MAP2K1) inhibitor PD98059 also prevented heat-induced maturation, but this effect was unrelated to MAPK1/3 activation, which was not observed until after germinal vesicle breakdown (GVB). Phosphorylated MAPK14 was not detected in the oocyte under any experimental condition, and only high concentrations of the MAPK14 inhibitor SB203580 blocked heat-stimulated maturation, suggesting that MAPK14 is not involved in meiotic induction. MAPK8/9 was activated by heat, and the MAPK8/9 inhibitor SP600125, but not JUN N-terminal kinase I, blocked heat-induced maturation. Heat treatment transiently suppressed GVB and PB formation in spontaneously maturing oocytes by a mechanism that is apparently different from its meiosis-inducing action. Collectively, these data show that an acute heat pulse stimulates GVB in meiotically arrested oocytes and suggest that this effect is mediated through the activation of PRKA.

Differential response of cumulus cell-enclosed and denuded mouse oocytes in a meiotic induction model system

In this study we have examined the effects of denuded oocyte coculture with dissociated cumulus cells (CC) or intact oocyte-CC complexes on meiotic resumption. When denuded oocytes (DO) or cumulus cell-enclosed oocytes (CEO) were cultured in 40-microl drops of medium under oil, and held in meiotic arrest with 4 mM hypoxanthine plus 25 microM dbcAMP, they underwent germinal vesicle breakdown (GVB) at similar frequencies (34%-35%). Coculture of DO with complexes or dissociated CCs stimulated maturation (50% and 61% GVB, respectively), with no effect of DO on maturation of cocultured CEO (32% GVB). This coculture effect was increased with the number of CCs added to the culture drop. When either glucose or glutamine was eliminated from the medium, no meiotic induction resulted from cocultured CCs. When CEO were cultured alone in microdrops, increasing their number from 10 to 50 significantly lowered the percentage resuming maturation, an effect also reduced by removing glucose and/or glutamine from the medium. This effect was not observed with DO. When inhibitory medium was conditioned overnight with complexes, subsequent culture with DO led to higher maturation percentages than culture in unconditioned medium; however, when CEO were cultured in conditioned medium, there was either no effect or increased inhibition of maturation. Assay of glucose and pyruvate in spent medium showed that DO cultured alone consumed glucose and pyruvate, but under CC coculture conditions more glucose was consumed and significant amounts of pyruvate accumulated in the medium, changes that led to an increase in the maturation of DO. Further experiments showed that DO were more sensitive than CEO to the meiosis-inducing effect of pyruvate. These results demonstrate different responsiveness of DO and CEO to coculture conditions and question the physiological relevance of denuded oocyte/CC coculture to study meiotic induction.

Use of a medium buffered with N-hydroxyethylpiperazine-N-ethanesulfonate (HEPES) in intracytoplasmic sperm injection procedures is detrimental to the outcome of in vitro fertilization

OBJECTIVE

This study was conducted to determine whether N-hydroxyethylpiperazine-N-ethanesulfonate (HEPES)-buffered medium used for the microinjection of sperm into oocytes may be detrimental for the embryo.

DESIGN

Controlled randomized study.

SETTING

Private IVF center.

PATIENT(S)

Women (n = 708) undergoing ICSI.

INTERVENTION(S)

The women were randomized into two study groups: 2,204 oocytes from 357 women were treated using a medium buffered with bicarbonate without HEPES during the ICSI procedure, and 2,168 oocytes from 351 women were treated using a medium buffered with HEPES during the ICSI procedure.

MAIN OUTCOME MEASURE(S)

Fertilization rate, degeneration rate, triploid rate, cleavage rate, embryo quality, pregnancy rate, implantation rate, and abortion rate.

RESULT(S)

Oocytes treated with a HEPES-buffered medium showed a statistically significant higher rate of triploid and degenerated oocytes after fertilization with ICSI compared with oocytes treated with a medium without HEPES. The embryos obtained from oocytes microinjected with a HEPES-buffered medium showed a statistically significant higher rate of highly fragmented embryos compared with the controls. Pregnancy rate and implantation rate were statistically significantly lower in the patient group with oocytes treated with the HEPES-buffered medium. The other parameters evaluated did not show any statistically significant differences.

CONCLUSION(S)

Our study showed that the use of media buffered with HEPES, during the microinjection of sperm into the oocytes, is detrimental for IVF outcome and should be avoided.

Effects of culture media and energy sources on the inhibition of nuclear maturation in bovine oocytes

The influence of the culture medium and energy sources on spontaneous nuclear maturation and inhibition of maturation in bovine cumulus-enclosed oocytes (CEO) was examined. CEO were cultured in Medium 199, minimum essential medium, M16, or synthetic oviduct fluid (SOF), all containing 3 mg/mL bovine serum albumin (BSA), and SOF without BSA, alone or supplemented with hypoxanthine (HYPO, 4 mM) or forskolin (FSK, 100 microM) for 21 h. More CEO remained at the GV stage in M16 compared to other media (P < 0.05). Supplementation with HYPO increased and FSK reduced the percentage of CEO remaining at the GV stage (P < 0.05) only in M16. The effects of energy sources, in the absence or presence of HYPO or FSK, were examined in CEO cultured in M16 salts+PVA. Glucose (0.5 and 5.5 mM), pyruvate (0.32 and 3.2 mM), lactate (3.3 mM) and glutamine (1.3 mM) significantly reduced the percentage of CEO remaining at the GV stage compared to M16 salts alone; only glutamine significantly increased the percentage of CEO at the MII stage compared to M16 salts. In M16 salts+HYPO, glucose (0.5 mM), pyruvate (0.32 mM), lactate (3.3 mM) and glutamine (1.3 mM) significantly reduced the percentage of GV and degenerate oocytes and increased the percentage of CEO at the MI stage. In M16 salts+FSK, the energy sources significantly decreased the percentage of oocytes with condensed chromosomes and increased the percentage of CEO reaching metaphase I. In conclusion, meiotic inhibitors had different effects in different culture media and glucose, pyruvate, lactate and glutamine were stimulatory to nuclear maturation. It was noteworthy that some of the results obtained were contrary to previous findings in mouse oocytes.

Stress stimulates AMP-activated protein kinase and meiotic resumption in mouse oocytes

This study examined the effects of three different cellular stresses on oocyte maturation in meiotically arrested mouse oocytes. Cumulus-cell enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured for 17-18 h in dbcAMP-containing medium plus increasing concentrations of the metabolic poison, sodium arsenite, or the free radical-generating agent, menadione. Alternatively, oocytes were exposed to osmotic stress by pulsing with sorbitol and returned to control inhibitory conditions for the duration of culture. Arsenite and menadione each dose-dependently induced germinal vesicle breakdown (GVB) in both DO and CEO. DO, but not CEO, pulsed for 60 min with 500 mM sorbitol were stimulated to resume maturation. The lack of effect in CEO suggests that the cumulus cells may be playing a protective role in osmotic stress-induced GVB. The AMP-activated protein kinase (PRKA; formerly known as AMPK) inhibitors, compound C and araA, completely blocked the meiosis-stimulating effects of all the tested stresses. Western blots showed that acetyl-CoA carboxylase, an important substrate of PRKA, was phosphorylated before GVB, supporting a role for PRKA in stress-induced maturation. Together, these data show that a variety of stresses stimulate GVB in meiotically arrested mouse oocytes in vitro and suggest that this effect is mediated through activation of PRKA.

Nutrient concentrations in murine follicular fluid and the female reproductive tract

The culture of murine oocytes and preimplantation embryos in vitro has been used successfully for many years. However, this practice can result in cellular stress and reduced viability. Since this phenomenon is partly attributable to differences in nutrient composition between culture media and maternal tract fluids, we determined the concentrations of glucose, pyruvate, lactate and 19 amino acids in murine preovulatory follicles and oestrous oviductal and uterine fluids. Follicular fluids were aspirated from hyperstimulated ovaries, whereas oviductal fluids (with/without oocyte-cumulus complexes) and uterine fluids were collected from naturally cycling animals. Glucose, pyruvate and lactate concentrations were analysed using ultramicrofluorometric methods, whilst amino acid profiles were determined by reverse-phase high performance liquid chromatography. Mean glucose concentrations in follicular, oviduct (with/without cumulus cells) and uterine fluids were 0.46, 1.09/1.65 and 0.61 mmol l(-1), respectively. Pyruvate concentrations were 0.38, 0.37/0.17 and 0.25 mmol l(-1), respectively, and lactate concentrations were 17.34, 10.92/11.68 and 9.41 mmol l(-1), respectively. Oviductal pyruvate concentration was significantly higher, and glucose significantly lower, in the presence of cumulus cells. Taurine, glycine, alanine, glutamine and glutamate were the major amino acids detected. Concentrations of amino acids differed among fluids, with highest levels being found in the oviduct. The follicular fluid and tract nutrient profiles differed from those of murine maturation, fertilisation and embryo culture media. These data extend our understanding of cellular metabolism and of nutritional environments of the oocyte and early embryo as they progress along the reproductive tract in vivo. These results may also contribute to the formulation of nutritionally more physiological media for mouse oocyte maturation and embryo culture.

MEK inhibitors block AICAR-induced maturation in mouse oocytes by a MAPK-independent mechanism

The present study was carried out to assess the possible role of mitogen-activated protein kinase (MAPK) in the meiosis-inducing action of the AMP-activated protein kinase (AMPK) activator, 5-aminoimidazole-4-carboxamide 1-beta-ribofuranoside (AICAR). Cumulus cell-enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured 4 hr in Eagle's minimum essential medium containing dbcAMP plus increasing concentrations of AICAR or okadaic acid (OA). OA is a phosphatase inhibitor known to stimulate both meiotic maturation and MAPK activation and served as a positive control. Both OA and AICAR were potent inducers of meiotic resumption in mouse oocytes and brought about the phosphorylation (and thus, activation) of MAPK, but by different kinetics: MAPK phosphorylation preceded GVB in OA-treated oocytes, while that resulting from AICAR treatment appeared only after GVB. The MEK inhibitors, PD98059 and U0126, blocked the meiotic resumption induced by AICAR but not that induced by OA. Although the MEK inhibitors suppressed MAPK phosphorylation in both OA- and AICAR-treated oocytes, meiotic resumption was not causally linked to MAPK phosphorylation in either group. Furthermore, AICAR-induced meiotic resumption in Mos-null oocytes (which are unable to stimulate MAPK) was also abrogated by PD98059 treatment. A non-specific effect of the MEK inhibitors on AICAR accessibility to the oocyte was discounted by showing that they failed to suppress either nucleoside uptake or AICAR-stimulated phosphorylation of acetyl CoA carboxylase (ACC), a substrate of AMPK. The suppression of AICAR-induced maturation by MEK inhibitors must, therefore, be occurring by actions unrelated to MEK stimulation of MAPK; consequently, it would be prudent to consider this possible non-specific action of the inhibitors when they are used to block MAPK activation in mouse oocytes.

The effect of harvesting technique on efficiency of oocyte collection and different maturation media on the nuclear maturation of oocytes in camels (Camelus dromedarius)

The purpose of this investigation was to develop an efficient method for harvesting oocytes from dromedary camel ovaries and to examine the effect of different maturation media on their subsequent maturation in vitro. Oocytes were collected by aspirating the follicular contents using a needle attached to a syringe (Method I, n=163 ovaries) or to a constant aspirating pressure, applied by a vacuum pump (Method II, n=117 ovaries). Individual follicles were excised from ovaries and follicles were punctured with two needles (Method III, n=117). Oocytes were matured in vitro for 40-42 h. At the end of maturation period, oocytes were denuded of cumulus cells and the proportion of oocytes in metaphase-II (MII) stage was determined. In the second experiment, oocytes collected by the dissection method were matured in Tissue Culture Medium199 (TCM), CR1 or modified Connaught Medical Research Laboratories medium-1066 (CMRL) and their nuclear maturation was evaluated after 40-42 h. The recovery rate of oocytes was higher (P<0.01) with Method III compared with Method I or II (94, 31 and 33%, respectively). A higher proportions of oocytes collected with Method I or II were either completely or partially denuded compared with Method III (31, 14% versus 1%). The proportions of viable oocytes (78, 60 and 70%, respectively) and those showing metaphase II was not different (39, 50 and 46%, respectively, P>0.05) among the three treatment groups. Oocyte maturation rate was higher (P<0.05) when TCM was used compared with CMRL or CR1 medium. There was, however, no difference in the maturation rate for oocytes cultured in CMRL or CR1 medium. It may be concluded that a higher proportion of cumulus enclosed oocytes may be recovered by follicle dissection method compared to aspiration using syringe or pump. The higher recovery rate with a comparable proportion of viable and matured oocytes resulted in the overall increase in the number of matured (MII) oocytes/ovary with follicle dissection procedure compared with aspiration procedures. For in vitro maturation of oocytes, TCM is superior to CR1 and CMRL as basic maturation medium for this species.

Fluctuations in bovine ovarian follicular fluid composition throughout the oestrous cycle

Bovine oocyte maturation in vitro frequently results in abnormal cytoplasmic maturation and failure to acquire developmental competence. This is, in part, likely to be due to the non-physiological nutritional milieu to which oocytes are exposed. Improvements in oocyte developmental potential may be achieved by modelling nutrient profiles on those of preovulatory follicular fluid (FF). However, little is known about fluctuations in FF nutrient levels according to follicle dominance and oestrous cyclicity. This study therefore characterised the carbohydrate and amino acid profile of FF according to these parameters, and compared preovulatory FF composition with that of maturation medium. Carbohydrate concentrations (n = 121) were determined enzymatically whilst amino acid profiles (n = 40) were determined by reverse-phase HPLC. Pyruvate and glucose concentrations were unaffected by follicle dominance, whereas Stage III-IV lactate profiles were higher in non-dominant FF (P < 0.01). While most dominant FF amino acid concentrations were affected by oestrous stage, only glutamate, alanine, leucine and lysine levels fluctuated in non-dominant FF. Glucose and lactate concentrations were significantly negatively correlated, whereas most amino acids were significantly positively correlated with each other. Maturation medium had higher pyruvate and lower lactate concentrations than preovulatory FF (P < 0.001), whereas glucose level was similar. All amino acid levels (except histidine, taurine, alanine and tryptophan) differed significantly between maturation medium and preovulatory FF. These data indicated that FF composition varies throughout the oestrous cycle. Preovulatory FF nutrient profile differed from that of maturation medium, perhaps accounting for the poor developmental competence of in vitro matured oocytes. These data may contribute to the formulation of a nutritionally more physiological maturation medium.

Maintenance of meiotic arrest in bovine oocytes using the S-enantiomer of roscovitine: effects on maturation, fertilization and subsequent embryo development in vitro

The overall objective was to evaluate the effectiveness of the S-enantiomer of roscovitine (inhibitor of p34cdc2/cyclin B kinase) to maintain bovine cumulus-oocyte complexes at the germinal vesicle (GV) stage for extended times after removal from antral follicles without compromising subsequent maturation, fertilization and embryo development. Oocytes were cultured in 0, 12.5, 25 or 50 micromol/l S-roscovitine for 24 h. Hoechst staining showed that 50 micromol/l S-roscovitine maintained >90% of oocytes at the GV stage and inhibited gonadotropin-induced cumulus expansion. Fewer oocytes underwent nuclear maturation after in vitro maturation (Hoechst staining) when cultured in 50 micromol/l S-roscovitine for 66 versus 21 or 42 h. Zona pellucida (ZP) hardening (pronase resistance), cortical granule types (lens culinaris agglutinin-fluorescein isothiocyanate), nuclear maturation and fertilization with frozen-thawed spermatozoa (Hoechst staining) were assessed after culture of oocytes in 50 micromol/l S-roscovitine for 0, 24 or 48 h. Neither ZP hardening, nor nuclear maturation nor fertilization were altered by roscovitine culture for 48 h. A higher proportion of oocytes had a type III cortical granule pattern (premature translocation to the oolemma) after roscovitine culture for 48 h. However, embryo development was not compromised as cleavage, development to 8-16 cell and blastocyst stages were at least comparable in control and roscovitine-treated oocytes. In conclusion, the studies have shown that S-roscovitine reversibly maintained bovine oocytes at the GV stage for 48 h. However, maintenance of oocytes in static culture for 48 h was not sufficient to improve development above non-treated controls.

Effect of EGF on in vitro maturation of domestic cat oocytes

The objective of this study was to evaluate the influence of different concentrations of epidermal growth factor (EGF) on in vitro maturation of domestic cat oocytes. A total of 444 cat oocytes were matured in MSOF (maturation synthetic oviductal fluid) in the presence of varying EGF concentrations: (1) MSOF (control); (2) MSOF+10 ng/mL EGF (EGF10); (3) MSOF+25 ng/mL EGF (EGF25); and (4) MSOF+50 ng/mL EGF (EGF50). After IVM, oocytes were in vitro fertilized to verify the effect of adding EGF on cytoplasmic maturation. Cleavage rate was recorded and noncleaving oocytes were stained with Hoechst 33258 and examined to determine nuclear maturation rate. Cleaved zygotes were cultured in vitro and embryo stages were evaluated on days 6 and 7. There was no difference among groups in the total number of oocytes reaching the metaphase II (MII) stage (P>0.05). The EGF25 group had the highest (P<0.01) blastocyst yield (37.5%) and developmental competence (60.9%). Cleavage rate and resulting morulae and blastocysts on day 6 for EGF25 group were higher (P<0.01) than control and EGF50 groups. Although EGF did not significantly enhance nuclear maturation rate, it had a dose-related positive effect on cytoplasmic maturation, since the oocyte's ability to cleave and reach the blastocyst stage was improved at 25 ng/mL, with intermediate improvement at 10 ng/mL, but 50 ng/mL had no significant benefit. In conclusion, the addition of EGF to the maturation medium enhanced cytoplasmic maturation of cat oocytes in vitro.

Effects of granulosa coculture on in-vitro oocyte meiotic maturation within a putatively less competent murine model

A less competent murine in vitro maturation (IVM) model was achieved by shortening the standard duration of in vivo PMSG stimulation from 48 to 24 h and selecting only naked/partially naked GV oocytes from a mixture of large and small follicles. Porcine granulosa coculture enhanced meiotic maturation within such a less competent model (37.3% versus 23.1%, P<0.05), while no significant enhancement was observed with macaque and murine granulosa coculture. Culture of porcine granulosa on extracellular matrix (ECM) gel resulted in a more differentiated morphology, but did not significantly further enhance the beneficial effects it already had on meiotic maturation. Increased concentrations of serum as well as the supplementation of gonadotrophins and follicular fluid within the culture milieu did not enhance IVM under both cell-free and coculture conditions. Porcine granulosa-conditioned medium also enhanced meiotic maturation (36.5% versus 26.7%, P<0.05), which was not diminished upon freeze-thawing (35.8% versus 22.6%, P<0.05). Enhancement of meiotic maturation by porcine granulosa coculture did not however translate to significant improvements in developmental competence, as assessed by in vitro fertilization (IVF) and embryo culture to the blastocyst stage, followed by total cell counts. ECM gel had a detrimental effect on fertilization and developmental competence, even though it had no detrimental effect on meiotic maturation itself.

Effect of recombinant human FSH and LH on in vitro maturation of sheep oocytes; embryo development and viability

The objective of this work was to study the effect of a preparation of human recombinant gonadotrophins (r-FSH and r-LH) on the in vitro maturation (IVM) and development of sheep oocytes. In addition, the viability of fresh and vitrified blastocysts obtained after transfer was tested. Oocytes collected from slaughtered animals were divided into five different maturation groups. All groups were matured in a medium containing TCM199 with 4 mg/ml BSA, 100 microM cysteamine and 1 microg/ml estradiol-17beta. Each group was also treated with one of the following: 0.1 UI/ml r-FSH (r-FSH group), 0.1UI/ml r-LH (r-LH group), 0.1 UI/ml r-FSH and 0.1 UI/ml r-LH (r-FSH/r-LH group), 5 microg/ml FSH and 5 microg/ml LH hypophysial gonadotrophins (h-G group) as a control, or no gonadotrophins (no-G group). After in vitro fertilization with fresh ram semen, presumptive zygotes were cultured in vitro for 6-7 days and a total of 109 blastocysts were then transferred in pairs into synchronized ewes. To determine the viability of embryos after vitrification, 36 blastocysts from the r-FSH/r-LH group and 30 from the h-G group were vitrified in 10% ethylene glycol (EG) and 10% dimethylsulphoxide (DMSO) for 5min, followed by 20% EG, 20% DMSO and 0.5M Sucrose (S) for <45 s. They were loaded into open pulled straws (OPS) and plunged into LN(2). After warming, the blastocysts were transferred in pairs into synchronized ewes. The highest maturation rate was reached in the r-FSH/r-LH group (91.9%). However, no statistical difference was found when this group was compared with the h-G group (84.0%). Likewise, the cleavage rate of the r-FSH/r-LH group (81.4%) was not significantly different from that of the h-G group (82.3%). The cleavage rates of all other groups, however, were significantly lower than the r-FSH/r-LH and h-G groups. The blastocyst rate was highest in the h-G group (53.6%), and it was statistically higher than in the r-FSH/r-LH group (41.5%). The blastocyst rate was very similar between groups r-FSH and r-FSH/r-LH (42.0 and 41.5%, respectively). The lowest lambing rate (31.8%) was in the no-G group. The highest lambing rate was achieved in the r-FSH/r-LH group (66.6%). The vitrified embryos of h-G and r-FSH/r-LH groups had a very similar lambing rate (16.6% and 19.4%). In conclusion, these data provide support for the hypothesis that sheep oocytes respond to human recombinant gonadotrophins used for in vitro embryo production.

Physiological changes in oocyte-cumulus cell complexes from diabetic mice that potentially influence meiotic regulation

We have previously shown that the type I diabetic condition significantly alters meiotic regulation in mouse oocytes. In the present study, possible physiological deficiencies underlying such meiotic dysfunction were examined in oocyte-cumulus cell complexes (OCC) from type I diabetic mice. Whereas the diabetic condition did not affect glycolysis or the tricarboxylic acid cycle, the increased flux of glucose through the pentose phosphate pathway in response to FSH treatment was suppressed. De novo purine synthesis was also compromised, and ATP levels were reduced in freshly isolated OCC. Additionally, diabetes resulted in a reduction in FSH-mediated cAMP synthesis. The responsiveness of the oocyte to cAMP was also affected; fewer oocytes were induced to resume maturation after a stimulatory pulse with cAMP analogs. Meiotic induction triggered by FSH was significantly reduced, but that stimulated by phorbol ester or epidermal growth factor was affected to a much lesser extent. In addition to metabolic deficiencies, the cell-cell communication between the oocyte and the cumulus cells was reduced in diabetic mice as determined by coupling assays. Thus, numerous physiological parameters are affected by type I diabetes, and these changes may collectively contribute to altered meiotic regulation.

Glutamine and the maintenance of meiotic arrest in mouse oocytes: influence of culture medium, glucose, and cumulus cells

The selection of culture media and supplements therein has a tremendous impact on the regulation of oocyte maturation in vitro. In the present study, we have evaluated how altering the levels of glutamine in the presence or absence of glucose affects meiotic arrest in cumulus cell-enclosed oocytes (CEO) and denuded oocytes (DO) when cultured in either the simple medium M16 or the more complex Eagle's minimum essential medium (MEM). We have also tested the effectiveness of follicle-stimulating hormone (FSH) in triggering germinal vesicle breakdown (GVB) and purine de novo synthesis in differing MEM culture conditions. When DO were cultured 17-18 hr in hypoxanthine (HX)- or dbcAMP-supplemented M16 medium, neither glucose nor glutamine had any effect on oocyte maturation, with dbcAMP the more effective inhibitor. In the absence of glutamine, cumulus cells promoted meiotic resumption, since significantly lower levels of meiotic arrest were maintained in CEO than in DO by either HX or dbcAMP, but addition of the amino acid dose-dependently decreased the maturation percentage in CEO below that observed in DO. In MEM, glutamine and glucose again had little effect on the maturation of DO, although the percentage of maturing DO in HX-supplemented medium was about 20% lower than that in M16 medium. In the absence of glucose, high levels of maturation were observed in CEO in glutamine-free medium that were dose-dependently lowered by the amino acid. However, when glucose was present, CEO were as effectively arrested as DO when glutamine was absent, with no further effect of the amino acid. This inhibitory action of glucose was dependent on the essential amino acids present in MEM. The effects of glutamine were not due to changes in metabolic coupling between the oocyte and cumulus cells. Measurement of purine de novo synthesis indicated that the maintenance of meiotic arrest as well as FSH induction of meiotic resumption were associated with increases in purine synthesis. We conclude that glucose and glutamine act cooperatively to promote the synthesis of new purine compounds within the somatic compartment and that the timing and duration of such synthesis determines whether meiotic resumption will be suppressed or promoted.

Maturation-promoting factor governs mitogen-activated protein kinase activation and interphase suppression during meiosis of rat oocytes

Meiosis is a particular example of a cell cycle, characterized by two successive divisions without an intervening interphase. Resumption of meiosis in oocytes is associated with activation of maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK). The activity of MPF declines during the transition between the two meiotic divisions, whereas the activity of MAPK is sustained. Attempts to disclose the interplay between these key regulators of meiosis in both amphibian and mammalian oocytes generated contradictory results. Furthermore, the enzyme that governs the suppression of interphase in mammals is still unidentified. To our knowledge, we provide herein the first demonstration in a mammalian system that inhibition of MPF at reinitiation of meiosis abrogated Mos expression and MAPK activation. We also show that oocytes, in which reactivation of MPF at completion of the first telophase was prevented, exhibited an interphase nucleus with decondensed chromosomes. Inhibition of MAPK did not interfere with the progression to the second meiotic metaphase but, rather, resulted in parthenogenic activation. We conclude that in rat oocytes, MPF regulates MAPK activation and its timely reactivation prevents the oocytes from entering interphase.

Altered meiotic regulation in oocytes from diabetic mice

In the present study, we have utilized a streptozotocin-induced diabetic mouse model to examine how the diabetic condition and different glucose concentrations affect several parameters of reproductive physiology. We report that oocyte maturation is altered under all experimental conditions examined. In cumulus cell-enclosed oocytes (CEO) from diabetic mice, spontaneous maturation was accelerated but the FSH-mediated delay of spontaneous maturation was suppressed. Higher glucose levels in the culture medium suppressed spontaneous maturation but did not influence the transient arrest mediated by FSH. Meiotic arrest in CEO by hypoxanthine and dibutyryl cAMP (dbcAMP) was less effective at higher glucose concentrations. In addition, both FSH-induced maturation in vitro and hCG-induced maturation in vivo were reduced by the diabetic condition. The ovulation rate was lowered by about 50% in diabetic mice and fewer ovulated ova had reached metaphase II. Despite the decreased number of ova at metaphase II, in vitro cultures showed the oocytes were capable of completing meiotic maturation at control levels. Insulin treatment reversed the detrimental effects of diabetes on meiotic induction, ovulation, and completion of meiotic maturation. Cultures of pronuclear-staged embryos confirmed a negative effect of diabetes and hyperglycemia on development to the blastocyst stage. These data suggest that defects in meiotic regulation brought about by the diabetic condition are due to decreased communication between the somatic and germ cell compartments, and it is concluded that such conditions may contribute to postfertilization developmental abnormalities.

Nuclear maturation of canine oocytes cultured in protein-free media

The objective of this study was to determine the ability of canine oocytes to complete nuclear maturation in a protein-free medium. Oocytes obtained from ovaries of bitches aged 6 months to 2 years were cultured either in TCM199 or CMRL1066 medium without protein supplementation in 5% or 20% O(2). Sixteen of 121 (13%) oocytes cultured in TCM199 reached metaphase II, but only 1 of 135 oocytes cultured in CMRL1066 did so (P < 0.05). Oxygen concentration did not affect nuclear maturation. An additional 103 oocytes were cultured in TCM199 for 48 hr, inseminated with chilled ejaculated spermatozoa, fixed in 1:3 acetic acid-ethanol and then stained with aceto-orcein; 34% of these oocytes were penetrated by spermatozoa. To determine developmental competence of oocytes cultured in a protein-free medium, 85 oocytes were cultured in TCM 199 for 48 hr, inseminated and then cultured; 7 early stage embryos were produced. The effects of growth hormone, beta-mercaptoethanol (betaME), luteinizing hormone (LH) and energy substrates, alone or in combination, on nuclear maturation of oocytes cultured in a protein-free medium were also determined. Growth hormone enhanced cumulus expansion, but did not improve nuclear maturation. beta-mercaptoethanol had no effect on nuclear maturation. However, percentages of MII oocytes significantly decreased when the oocytes were cultured for 48 hr in the medium containing LH or a high concentration of glucose (P < 0.05). In conclusion, canine oocytes are able to complete nuclear maturation in a protein-free medium. The specific type of medium and other supplements significantly influence the meiotic maturation of canine oocytes.

A potential role for AMP-activated protein kinase in meiotic induction in mouse oocytes

Cyclic adenosine monophosphate (cAMP) has been implicated as an important regulator of meiotic maturation in mammalian oocytes. A decrease in cAMP, brought about by the action of cAMP phosphodiesterase (PDE), is thought to initiate germinal vesicle breakdown (GVB) by the inactivation of cAMP-dependent protein kinase. However, the product of PDE activity, 5'-AMP, is a potent activator of an important regulatory enzyme, AMP-activated protein kinase (AMPK). The aim of this study was to evaluate a possible role for AMPK in meiotic induction, using oocytes obtained from eCG-primed, immature mice. Alpha-1 and -2 isoforms of the catalytic subunit of AMPK were detected in both oocytes and cumulus cells. When 5-aminoimidazole-4-carboxamide 1-beta-d-ribofuranoside (AICA riboside), an activator of AMPK, was tested on denuded oocytes (DO) and cumulus cell-enclosed oocytes (CEO) maintained in meiotic arrest by dbcAMP or hypoxanthine, GVB was dose-dependently induced. Meiotic induction by AICA riboside in dbcAMP-supplemented medium was initiated within 3 h in DO and 4 h in CEO and was accompanied by increased AMPK activity in the oocyte. AICA riboside also triggered GVB when meiotic arrest was maintained with hypoxanthine, 8-AHA-cAMP, guanosine, or milrinone, but was ineffective in olomoucine- or roscovitine-arrested oocytes, indicating that it acts upstream of maturation-promoting factor. Adenosine monophosphate dose-dependently stimulated GVB in DO when meiotic arrest was maintained with dbcAMP or hypoxanthine. This effect was not mimicked by other monophosphate or adenosine nucleotides and was not affected by inhibitors of ectophosphatases. Combined treatment with adenosine and deoxycoformycin, an adenosine deaminase inhibitor, stimulated GVB in dbcAMP-arrested CEO, suggesting AMPK activation due to AMP accumulation. It is concluded that phosphodiesterase-generated AMP may serve as a transducer of the meiotic induction process through activation of AMPK.

Pyruvate utilization by mouse oocytes is influenced by meiotic status and the cumulus oophorus

In this study, the effects of meiotic status on the energy substrate dynamics of mouse oocyte-cumulus cell complexes (OCCs) and denuded oocytes (DOs) have been examined. In the first series of experiments, OCCs from PMSG-primed, immature mice were cultured in minimum essential medium in 8-microl microdrops under a variety of conditions, and the medium and oocytes were sampled for pyruvate and glucose concentration and for meiotic status. Oocytes in control medium underwent germinal vesicle breakdown within 3 hr and the OCCs displayed a time-dependent increase in pyruvate consumption, but the glucose concentration changed very little. Treatment with IBMX or dbcAMP, which maintained complete meiotic arrest, suppressed pyruvate consumption, but slightly more glucose was consumed than in controls. Hypoxanthine (HX) allowed up to 10% of the oocytes to resume maturation, and pyruvate and glucose consumption resembled that of control OCCs. FSH added to HX-containing medium stimulated significant glucose consumption and pyruvate production. In general, a reciprocal relationship was observed between glucose and pyruvate consumption. When the energy substrate dynamics were compared with meiotic status of the oocytes, pyruvate consumption was associated with the maturation process. Although HX maintained oocytes in the germinal vesicle stage, the meiotic arrest was "leaky," allowing increased pyruvate consumption. Additional experiments showed that DOs at either the prophase I or metaphase II stages consumed less pyruvate than oocytes actively engaged in meiotic maturation. DOs oxidized significantly more pyruvate than OCCs, and glycolytic metabolism of glucose lowered the oxidation rate in OCCs. Furthermore, while 5-6.2 times more pyruvate was consumed by OCCs than by DOs in the absence of glucose, oxidation did not mediate the meiosis-inducing effect of pyruvate, since less of this substrate was oxidized by OCCs than by DOs. We conclude that meiotically active oocytes have a greater requirement for pyruvate than prophase I- or metaphase II-arrested oocytes and that meiotic status can influence the metabolism not only of oocytes, but also of the OCCs.

Evidence that multifunctional calcium/calmodulin-dependent protein kinase II (CaM KII) participates in the meiotic maturation of mouse oocytes

Calcium-dependent signaling pathways are thought to be involved in the regulation of mammalian oocyte meiotic maturation. However, the molecular linkages between the calcium signal and the processes driving meiotic maturation are not clearly defined. The present study was conducted to test the hypothesis that the multi-functional calcium/calmodulin-dependent protein kinase II (CaM KII) functions as one of these key linkers. Mouse oocytes were treated with a pharmacological CaM KII inhibitor, KN-93, or a peptide CaM KII inhibitor, myristoylated AIP, and assessed for the progression of meiosis. Two systems for in vitro oocyte maturation were used: (1) spontaneous gonadotropin-independent maturation and (2) follicle-stimulating hormone (FSH)-induced reversal of hypoxanthine-mediated meiotic arrest. FSH-induced, but not spontaneous germinal vesicle breakdown (GVB) was dose-dependently inhibited by both myristoylated AIP and KN-93, but not its inactive analog, KN-92. However, emission of the first polar body (PB1) was inhibited by myristoylated AIP and KN-93 in both oocyte maturation systems. Oocytes that failed to produce PB1 exhibited normal-appearing metaphase I chromosome congression and spindles indicating that CaM KII inhibitors blocked the metaphase I to anaphase I transition. Similar results were obtained when the oocytes were treated with a calmodulin antagonist, W-7, and matured spontaneously. These results suggest that CaM KII, and hence the calcium signaling pathway, is potentially involved in regulating the meiotic maturation of mouse oocytes. This kinase both participates in gonadotropin-induced resumption of meiosis, as well as promoting the metaphase I to anaphase I transition. Further evidence is therefore, provided of the critical role of calcium-dependent pathways in mammalian oocyte maturation.

Adenosine blocks hormone-induced meiotic maturation by suppressing purine de novo synthesis

We have examined adenosine (Ado) suppression of FSH-induced germinal vesicle breakdown (GVB) and its relationship to purine de novo synthesis. Oocyte-cumulus cell complexes (OCC) from PMSG-primed, immature mice were cultured 17-18 hr in medium containing 4 mM hypoxanthine (HX) or 300 microM dibutyryl cAMP (dbcAMP) to maintain meiotic arrest, and FSH was added to stimulate meiotic maturation. In the absence of FSH, Ado (1-250 microM) had no effect in dbcAMP-arrested oocytes but dose-dependently suppressed maturation in HX-treated oocytes. FSH-induced maturation was prevented by Ado, though more effectively in dbcAMP-supplemented cultures. Ado affected the magnitude, but not the kinetics pattern, of the response to FSH. Inosine also blocked meiotic induction, but only in dbcAMP-arrested oocytes. Purine de novo synthesis was nearly doubled in OCC by FSH treatment, and this response was completely prevented by Ado. FSH had no effect on HX salvage, although Ado reduced this activity by 98%. Inosine effects on metabolism were intermediate between the control and Ado groups. Experiments with radiolabeled energy substrates showed that Ado suppressed FSH activation of the pentose phosphate pathway but did not prevent significant activation of glycolysis or oxidation of pyruvate. Finally, in cultured follicles from primed mice, hCG-induced maturation was blocked by Ado as effectively as by the purine de novo synthesis inhibitor, azaserine. It is concluded that Ado has an inhibitory action on hormone-induced maturation that is due, at least in part, to suppression of glucose metabolism, leading to compromised purine de novo synthesis.

Oocyte metabolism predicts the development of cat embryos to blastocyst in vitro

Current methods for detecting complete oocyte maturation and developmental competence are inadequate. The objectives of this study were to (1) examine the relationship between cat oocyte energy metabolism and development in vitro after fertilization and (2) determine if cumulus cell metabolism could be used to predict development of individual oocytes after fertilization in vitro. The hanging drop method was used to assess metabolism of three different types of cat oocytes: immature (IMO), in vitro matured (IVM), and in vivo matured (IVOM). Stage of oocyte nuclear maturation or developmental competence was assessed after metabolic analysis. Glycolysis and oxidation of glucose, glutamine, palmitate, and lactate increased with the resumption of oocyte meiotic maturation (P<0.05). Pyruvate was the preferred substrate, but uptake was not linked to maturation. IVM oocytes had impaired glucose and palmitate metabolism compared to IVOM oocytes (P<0.05). Oocyte glycolytic activity and oocyte glucose oxidation correlated well with embryo development after insemination in vitro (P<0.05). Furthermore, oocytes that had similar glucose metabolism and that were grouped together for culture on this basis had higher (P<0.05) overall rates of development than oocytes grouped randomly. There was no correlation (P>0.05) between cumulus cell metabolism and individual oocyte development after in vitro fertilization. The data reveal that energy metabolism is linked to oocyte maturation in the cat and that glucose metabolic activity can indicate those oocytes most likely to fertilize and develop in vitro. Measuring cumulus cell metabolism does not accurately predict individual oocyte development after insemination in vitro.

Nitric oxide is essential for optimal meiotic maturation of murine cumulus-oocyte complexes in vitro

This study was conducted to determine whether endothelial-derived nitric oxide synthase (eNOS) affects meiotic maturation of mouse oocytes in vitro. Cumulus-oocyte complexes (COC) were isolated from ovarian follicles of 27-day-old PMSG-primed wildtype (WT), and eNOS-knockout (eNOS-KO) females, and cultured in drops of medium under oil at 37 degrees C for 16-18 hr. Experiment 1 was carried out to determine effects of eNOS deficiency on the ability of COC to mature in vitro. To determine whether acute synthesis of nitric oxide (NO) was required for oocyte maturation, COC collected from WT mice were cultured in medium without (control) or with different doses of N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOS (exp. 2). To assess effects of NO deficiency on the kinetics of germinal vesicle breakdown (GVBD), COC from WT and eNOS-KO females were observed for 3.5 hr. COC from WT females were also incubated in medium without or with L-NAME (exp. 3 and 4). After the culture period, cumulus cells were removed, and oocytes were counted and classified as metaphase II (M II), metaphase I (M I) or showing atypical (degenerative) morphology. To determine viability and nuclear morphology of oocytes, they were stained with fluorescein diacetate or 4,6-diamidine-2'-phenylindole dihydrochloride, respectively. There were no differences in body weights but ovarian weights were lower in eNOS-KO mice compared with WT mice (P < 0.05). Ovaries from eNOS-KO mice contained fewer COC collected relative to WT mice (P < 0.01). Maturation of COC from eNOS-KO mice or WT oocytes treated with L-NAME resulted in a lower percentage of oocytes at M II stage (P < 0.01 and P < 0.05, respectively) and a higher percentage of oocytes at M I or atypical stages compared with those from WT (P < 0.01 and P < 0.05, respectively). Many oocytes that showed either an arrest in M I stage or abnormal morphology were not viable. Several oocytes in M II stage demonstrated abnormalities in distribution of maternal chromosomes. Our data demonstrate that eNOS-derived NO is a key modulator of oocyte meiotic maturation in vitro. These results support our previous observations in vivo and indicate that eNOS/NO has independent functions in both oocyte maturation and follicular/oocyte development.