Paracrine factors from cumulus-enclosed oocytes ensure the successful maturation and fertilization in vitro of denuded oocytes in the cat model

Fighting Like Cats and Dogs: Challenges in Domestic Carnivore Oocyte Development and Promises of Innovative Culture Systems

In vitro embryo production in cats and dogs still presents some challenges, and it needs to be optimized to transfer efficient protocols to related wild, endangered species. While the chemical composition of culture media has been the focus of several studies, the importance of culture substrates for oocyte and embryo culture has often been neglected. Traditional in vitro systems, i.e., two-dimensional cultures, do not resemble the physiological environments where cells develop, and they may cause morphological and functional alterations to oocytes and embryos. More modern three-dimensional and microfluidic culture system better mimic the structure and the stimuli found in in vivo conditions, and they could better support the development of oocytes and embryos in vitro, as well as the maintenance of more physiological behaviors. This review describes the different culture systems tested for domestic carnivore reproductive cells along the years, and it summarizes their effects on cultured cells with the purpose of analyzing innovative options to improve in vitro embryo production outcomes.

IVF and the exogenous progesterone-free luteal phase

PURPOSE OF REVIEW

In a conventional IVF cycle, final oocyte maturation and ovulation is triggered with a bolus of hCG, followed by progesterone-based luteal support that spans several weeks if pregnancy is achieved. This article summarizes several approaches of the exogenous progesterone-free luteal support in IVF.

RECENT FINDINGS

Triggering ovulation with GnRH agonist may serve as an alternative to hCG, with well established advantages. In addition, the luteal phase can be individualized in order to achieve a more physiologic hormonal milieu, and a more patient friendly treatment, alleviating the burden of a lengthy exogenous progesterone therapy.

SUMMARY

GnRH agonist trigger followed by a 'freeze all' policy is undoubtedly the best approach towards the 'OHSS-free clinic'. If fresh embryo transfer is considered well tolerated after GnRH agonist trigger, rescue of the corpora lutea by LH activity supplementation is mandatory. Herein we discuss the different approaches of corpus luteum rescue.

Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

Simple Summary

Assisted reproduction techniques (ART) are crucial for preserving endangered animal species. Cryopreservation by vitrification can maintain gamete viability for a long time. Efforts to preserve endangered species within the Felidae family are focused on developing appropriate ART procedures. The domestic cat is a good biomedical model. Unfortunately, the current state of knowledge on vitrification of cat oocytes is inconclusive and the efficiency of ART procedures is low. A key example concerns how the meiotic status of the oocyte influences suitability for vitrification. This is the main question of this study. First, we conducted a toxicity test to make sure that the vitrification solution (VS) we proposed does not have a toxic effect on cat oocytes. Next, we performed vitrification on cat oocytes before (nonmature) and after in vitro maturation (IVM) and checked their developmental potential. There was no negative impact of the applied VS on oocyte maturation and fertilization, demonstrating a possibility to obtain embryos in vitro regardless of the meiotic status. There is a need for more research on vitrification of the domestic cat oocytes as a model species for wild cats.

Abstract

Cryopreservation is important for animal fertility and biodiversity. Unfortunately, cryopreservation of feline oocytes is still an experimental technique. The aims of this study were to analyze the potential toxicity of the cryoprotectants in the vitrification solution (VS) on cat oocytes and to investigate whether the meiotic status of oocytes influences their developmental potential after vitrification. Two experiments were conducted with the VS composed of 20% ethylene glycol, 20% dimethyl sulfoxide, 20% fetal calf serum, 1.5 M trehalose, and 10% Ficoll PM-70: (1) toxicity assessment of the VS on immature cumulus oocyte complexes (COCs), and subsequently in vitro maturation (IVM) and in vitro fertilization; (2) assessment of the influence of the meiotic status on vitrification effectiveness, where immature and in vitro matured COCs were vitrified on the Cryotop. After rewarming, vitrified oocytes were subjected to IVM (immature) and intracytoplasmic sperm injection (ICSI) with fresh epididymal sperm. The toxicity test revealed no negative effect of oocyte exposure to the applied VS on their developmental potential (p > 0.05). Although the vitrification procedure itself significantly reduced the meiotic competence of oocytes, their meiotic status before vitrification (immature vs. in vitro matured) did not influence fertilization and morula rates. The only parameter affected by vitrification was the rate of oocytes suitable for ICSI, which was significantly lower for immature oocytes. Regardless of the meiotic status of vitrified oocytes, morphologically normal morulae were obtained. Moreover, the two meiotic stages examined are suitable for vitrification, with mature oocytes being a better choice when a well-equipped laboratory is available.

Gonadotropin-releasing hormone agonist ovulation trigger-beyond OHSS prevention

In this review the advantages of the gonadotropin-releasing hormone agonist (GnRHa) trigger are discussed beyond those immediately associated with ovarian hyperstimulation syndrome (OHSS) prevention. The GnRHa trigger concept has sparked the development of novel protocols, enriching the assisted reproductive technology (ART) armamentarium for the benefit of present and future patients. Thus, GnRHa trigger already has a pivotal role, not only for the standard in vitro fertilisation (IVF) patient, but also for patient groups like oocyte donors, cancer patients, patients with poor ovarian reserve, and patients with immature oocyte syndrome and empty follicle syndrome. Herein, we discuss the importance of the GnRHa-elicited midcycle FSH surge and the potential improvement in oocyte yield and embryo competence.

Effect of cumulus cells of cumulus-oocyte complexes on in vitro maturation, embryonic developmental and expression pattern of apoptotic genes after in vitro fertilization in water buffalo (Bubalus bubalis)

In the present study, the potential of different grades of cumulus-oocyte complexes (COCs) for in vitro maturation (IVM) and embryonic development was assessed. Further, the association of the expression pattern of anti-apoptotic Mcl-1 and pro-apoptotic Bax genes in embryonic development was analyzed. Abattoir derived oocytes were graded into grade A and B based on surrounding cumulus rings. Out of 1050 ovaries, a total number of 770 and 1360, were of grade A and B COCs, respectively, were aspirated. After IVM, grade A COCs had a significantly higher number of polar bodies (92.04 ± 0.60%) as compared to grade B (85.88 ± 0.46%). On IVF and embryo culture, grade A COCs produced the significantly higher rate of cleavage and blastocyst (90.44 ± 0.71% and 41.55 ± 0.96%) as compared to grade B COCs (79.77 ± 0.76% and 30.44 ± 0.96%). The transcriptional analysis of apoptotic genes expression by Real-time PCR revealed a significantly higher expression of Mcl-1 gene in embryos of grade A as compared to grade B, whereas, the relative expression of Bax gene was down-regulated in grade A than grade B embryos. Thus it was concluded that the pattern of apoptotic genes expression in early-stage embryos can be used as a marker gene to predict the developmental competence of COCs.

The never-ending search of an ideal culture system for domestic cat oocytes and embryos

In the domestic cat, in vitro fertilization started 40 years ago, but an ideal culture system has yet to be achieved. The physiological microenvironments, which interact with oocytes and embryos promoting their competence, have been investigated. However, recreating in vitro follicle- and oviduct-like conditions is challenging and a matter of both chemistry and physics. This review presents an excursus of the experimental investigations focused on the improvement of feline oocytes and embryos culture through the modulation of chemical and physical factors. Medium supplementation with components of follicular and oviductal fluids, or the use of different co-cultures, supports or substrata have been considered. Innovative and sophisticated systems as "organ-on-a-chip" might lead to the creation of artificial follicles and oviducts and they may represent the ideal combination of chemical and physical factors. Will the search ever end?

An efficiency comparison of different in vitro fertilization methods: IVF, ICSI, and PICSI for embryo development to the blastocyst stage from vitrified porcine immature oocytes

Background

Most studies carried out to evaluate recovery and development after porcine oocyte vitrification, reported better rates when cryopreserved in embryonic development stages or zygotes, but not in immature oocytes. For this reason, many studies are performed to improve immature oocyte vitrification protocols testing the use of different cryoprotectant concentrations, cooling devices, incubation times; but only a few of them have evaluated which fertilization procedure enhances blastocyst rates in vitrified oocytes. Therefore, this study was aimed to evaluate: 1) if the sperm selection with hyaluronic acid (HA) or polyvinylpyrrolidone (PVP) before injection could play a key role in increasing fertilization and blastocyst formation and 2) the embryo developmental ability and blastocyst production of porcine immature oocytes retrieved after vitrification-warming and co-cultured with granulosa cells during IVM, using different fertilization techniques: in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and conventional ICSI with hyaluronic acid (HA) sperm selection, known as physiological intracytoplasmic sperm injection (PICSI) and.

Results

Sperm selected with HA-PICSI displayed a higher percentage of live/acrosome reacted status compared to those in control and exposed to PVP. Higher dead/acrosome reacted rates were obtained after PVP exposure compared to control and HA. In oocytes, viability significantly decreased after IVM in vitrified oocytes. Besides, IVM rates were not different between control denuded oocytes cultured with granulosa cells (DO-GC) and vitrified oocytes. Regarding fertilization parameters, IVF showed higher percentages of total fertilization rate than those obtained by ICSI and PICSI. However, results demonstrate that PICSI fertilization increased the blastocysts formation rate in control DO-GC and vitrified oocytes compared to IVF and ICSI.

Conclusions

To achieve high blastocyst formation rates from vitrified GV oocytes, it is recommended that sperm should be selected with HA instead of PVP before injection since high viability and acrosome reaction rates were obtained. Also, PICSI fertilization was the best method to produce higher blastocyst rates compared to the IVF and ICSI procedures.

The mutual benefits of research in wild animal species and human-assisted reproduction

Studying the reproductive biology of wild animal species produces knowledge beneficial to their management and conservation. However, wild species also share intriguing similarities in reproductive biology with humans, thereby offering alternative models for better understanding the etiology of infertility and developing innovative treatments. The purpose of this review is to raise awareness in different scientific communities about intriguing connections between wild animals and humans regarding infertility syndromes or improvement of fertility preservation. The objectives are to (1) highlight commonalities between wild species and human fertility, (2) demonstrate that research in wild species-assisted reproductive technologies can greatly enhance success in human reproductive medicine, and (3) recognize that human fertility preservation is highly inspiring and relevant to wild species conservation. In addition to having similar biological traits in some wild species and humans, the fact of sharing the same natural environment and the common needs for more options in fertility preservation are strong incentives to build more bridges that will eventually benefit both animal conservation and human reproductive medicine.

Analysis of gene expression in granulosa cells post-maturation to evaluate oocyte culture systems in the domestic cat

Maturation of oocytes is a prerequisite for successful embryo development. The fertilization competence of in vivo derived oocytes is significantly higher than that of oocytes matured in vitro. Commonly evaluated morphological criteria for oocyte maturation do not reflect the complexity and quality of maturation processes. Oocytes and granulosa cells are communicating closely in a bidirectional way during follicular growth and maturation. Assessing the mRNA expression of specific genes in granulosa cells could be a non-invasive way to evaluate the conditions of in vitro oocyte maturation. The objective of this study was to elucidate the influence of two different FSH additives on the in vitro maturation rate and gene expression of cumulus-oocytes complexes in domestic cat. Feline oocytes were matured in a medium, supplemented with LH and 0.02 IU/ml porcine FSH versus 0.02 IU or 1.06 IU/ml human FSH. Granulosa cells were separated from oocytes directly after 24 hr of maturation or after additional 12 hr of in vitro fertilization. Gene expression levels were analysed by quantitative PCR for aromatase, antimullerian hormone, follicle stimulating hormone receptor (FSHR), luteinizing hormone/choriogonadotropin receptor (LHCGR) and prostaglandin E synthase. Neither oocyte maturation rate nor gene expression levels differed after 24 or 36 hr in all three groups. However, variations were discovered in correlations of expression levels, for instance for FSHR and LHCG, indicating differences in the fine-tuning of in vitro maturation processes under varying FSH supplementations. We suppose that correlation between gene expressions of selected genes suggests a superior maturation quality of feline oocytes.

Short-term hypertonic exposure enhances in vitro follicle growth and meiotic competence of enclosed oocytes while modestly affecting mRNA expression of aquaporin and steroidogenic genes in the domestic cat model

Using the domestic cat as a non-rodent, larger animal model, the objective was to determine the impact of a brief incubation in a hypertonic microenvironment on (1) ovarian follicle and oocyte growth in vitro, (2) developmental capacity of the resident oocyte, and (3) expression of aquaporin (AQP) genes in parallel with genes involved in regulation of folliculogenesis. In Study 1: Secondary or early antral follicles encapsulated in 0.5% alginate were allocated to one of three treatment groups: 1) culture in standard medium at 290 mOsm for 15 d (Control); 2) incubation in 350 mOsm medium for 1 h followed by culture in standard medium for 15 d (Hypertonic-1h); or 3) incubation in 350 mOsm medium for 24 h followed by incubation in standard medium for additional 14 d (Hypertonic-24h). After measuring follicle and oocyte diameters on Day 15, in vitro-grown oocytes were incubated for 24 h before assessing nuclear status. In Study 2: secondary or early antral follicles were subjected to one of the three treatments: 1) culture in standard medium at 290 mOsm for 48 h; 2) incubation in 350 mOsm medium for 1 h followed by culture in standard medium for additional 47 h; or 3) incubation in 350 mOsm medium for 24 h followed by culture in standard medium for additional 24 h. At the end of the culture period, all follicles were assessed for mRNA level of Cyp17a1, Cyp19a1, Star, Aqp1, 3, 5, 7 and 8 as well as Fshr using qPCR. Freshly collected follicles also were subjected to gene expression analysis and served as the 'Non-cultured control'. Hypertonic-24h follicles grew larger (P < 0.05) than the control, whereas those in Hypertonic-1h group exhibited intermediate growth, especially when the culture started at the early antral stage. Oocytes in the Hypertonic-24h group were larger and resumed meiosis at a higher rate than in the other treatments. In vitro culture affected (P < 0.05) mRNA expression of Cyp19a1, Star, Aqp1, and Aqp7 in both the secondary and early antral stage while Fshr was only affected in the former compared to the non-cultured control. Pre-incubating follicles in 350 mOsm medium for 24 h enhanced (P < 0.05) Star and Aqp7 while decreasing (P < 0.05) Aqp1 expression compared to the control in secondary follicles, but not in the early antral stage. In summary, short-term hypertonic exposure promoted cat follicle development in vitro (including the meiotic competence of the enclosed oocyte) possibly through a mechanism that does not involve water transport genes.

The effect of cumulus cells on domestic cat (Felis catus) oocytes during in vitro maturation and fertilization

The aim of this study was to evaluate the effect of co-culture of denuded oocytes with cumulus cells (CC) or cumulus-oocyte complexes (COCs) on in vitro maturation (IVM) and in vitro fertilization (IVF). Immature oocytes were collected from ovaries of domestic cats following a routine ovariectomy. Oocytes were matured in vitro for 24 hr within four groups: (i) denuded oocytes (DO), (ii) DO co-cultured with CC, (iii) DO co-cultured with COC and (iv) COC as a control group. In further experiments, COCs were matured in vitro for 24 hr, and then, oocytes were randomly divided into four groups as previously described and fertilized in vitro. Embryos were cultured for up to 7 days. At the end of each experiment, oocytes/embryos were stained with Hoechst 33342 solution and observed under an inverted fluorescence microscope. The results of oocyte maturation showed that their meiotic competence decreased significantly in all experimental groups, compared to the control group. The maturation rates were approximately 45%, 24%, 43% and 76% in experiment 1, and 21%, 14%, 33% and 50% in experiment 2 in groups (i), (ii), (iii) and (iv), respectively. Examination of in vitro fertilization revealed that embryos developed up to the morula stage in all experimental groups. DO and oocytes cultured with COC during fertilization showed a lower cleavage rate-36% and 25% as opposed to those co-cultured with loose CC and the control group-43% and 42%, respectively. Results of this study indicate that cumulus cells connected with an oocyte into a cumulus-oocyte complex are irreplaceable for the maturation of domestic cat oocyte, but that the addition of loose CC may be beneficial for IVF.

The nuclear and developmental competence of cumulus-oocyte complexes is enhanced by three-dimensional coculture with conspecific denuded oocytes during in vitro maturation in the domestic cat model

The objective of the study was to assess the efficacy of coculture with conspecific cumulus-denuded oocytes (CDOs) during in vitro maturation in a three-dimensional system of barium alginate microcapsules on the in vitro embryo development of domestic cat cumulus-oocyte complexes (COCs). In Experiment I, COCs were cocultured with conspecific CDOs or cultured separately in a 3D system for 24 hr of in vitro maturation, before assessing the meiotic progression. In Experiment II, the in vitro fertilization of COCs and CDOs was carried out with chilled epididymal spermatozoa and the presumptive zygotes were cultured in vitro separately for 7 days in 3D microcapsules before assesment of embryonic development. The results showed that the viability was maintained and that meiosis was resumed in the 3D culture system. The presence of CDOs during in vitro maturation improved the meiotic competence of the COCs, since the proportions of telophase I/metaphase II were higher than that in the groups cultured separately. The enrichment of the maturation system by companion oocytes also enhanced the ability of COCs to develop into embryos, and increased the percentages of morula and blastoycst stages. The COCs cocultured with CDOs developed at higher rates than the COCs cultured separately and the CDOs themselves. The beneficial effects of coculture with conspecific CDOs were presumably due to the paracrine action of some secreted factors that enhanced many molecular patterns related to the complex of cumulus oophorous cells. Further investigations to understand how the 3D microenvironment can influence the features of oocytes and embryos are required.

A three-dimensional alginate system for in vitro culture of cumulus-denuded feline oocytes

In the case of high valuable individuals with very precious genetic material, widening the genetic pool including gametes with poor morphological characteristics, as cumulus-denuded oocytes (CDOs), could be an option. To improve the in vitro culture of low-competence feline CDOs, an enriched three-dimensional (3D) system in association with competent cumulus-oocyte complexes (COCs) was developed. For this purpose, domestic cat CDOs were cultured with or without companion COCs in the 3D barium alginate microcapsules. The overall viability and the meiotic progression of feline CDOs cocultured with COCs or cultured separately in 3D or in 2D (traditional microdrops) system were compared. The 3D system was able to support viability and meiotic resumption of the feline oocytes, as well as the 2D microdrops. In 3D microcapsules, the presence of COCs resulted in a higher viability of CDOs (91.1%, p < .05), than that obtained without COCs or in 2D microdrops (71.2% and 67.3%, respectively), but the percentages of meiotic resumption were similar of those of CDOs cultured separately (55.4% vs. 40.4%, p > .05). It is notable that the presence of CDOs seemed to enhance the meiotic progression of the associated COCs. In conclusion, the 3D barium alginate microcapsules are a suitable system for feline oocytes in vitro culture, but more specific enriched conditions should be developed to improve the CDOs full competence in vitro.

Incidence of methylated histones H3K4 and H3K79 in cat germinal vesicles is regulated by specific nuclear factors at the acquisition of developmental competence during the folliculogenesis

PURPOSE

This study aims to characterize the regulations of histone methylations, key epigenetic markers of oocyte competence, in germinal vesicle (GV) from different follicles (preantral, early, small, or large antral stage) using the domestic cat model.

METHODS

In Experiment 1, the incidence of H3K4me3 or H3K79me2 was determined in GVs from the diverse follicle stages directly or after exposure to (1) a methyltransferase inhibitor, (2) sonication to fracture the cytoplasmic membranes and wash away the cytoplasmic content, or (3) methyltransferase inhibitor followed by sonication. In Experiment 2, the presence and maintenance of nuclear methyltransferases SMYD3 and DOT1L (regulating H3K4me3 and H3K79me2, respectively) was characterized in separate GV stages before and after sonication. Functionality of GVs from the various follicle stages (with or without transient isolation from the cytoplasm) then was assessed in Experiment 3 by transfer into recipient competent oocytes.

RESULTS

The incidence of histones H3K4me3 and H3K79me2 within the GV were influenced by the cytoplasmic environment at all stages except at the transition to the early antral stage where nuclear regulating factors appeared to be mainly involved. The methyltransferase SMYD3 and DOT1L also appeared tightly bound to the nucleus at that transition. Interestingly, oocytes reconstructed with a GV isolated from the cytoplasm for a prolonged period had the capacity to form an embryo after fertilization which proved that communication between the donor GV and the host cytoplasm (likely including the regulation of epigenetic factors) could be restored.

CONCLUSIONS

Histone methylation apparently becomes regulated by specific nuclear factors at the acquisition of competence during the folliculogenesis and does not seem to be disrupted by prolonged isolation from the surrounding cytoplasm.

Embryo apoptosis identification: Oocyte grade or cleavage stage?

Apoptosis is a programed cell death that is vital for tissue homeostasis. However, embryo apoptosis had been known to be related to embryo fragmentation which should be avoided in in vitro fertilization (IVF). The purpose of this study was to evaluate the relationship of embryo apoptosis with the grade of immature oocytes and cleavage stage of in vitro produced (IVP) cattle embryos. This study consisted of 345 oocytes collected through ovary slicing. Immature oocytes were graded as A, B and C. This grading was based on cumulus cell thickness and compactness. All oocytes then underwent an in vitro maturation (IVM) procedure. An IVF was done 24 h after IVM culture. Prior to staining, stage of cleaved embryos was determined and classified as either 2, 4, 8 or >8-cell embryo stage. Apoptosis status of cleaved IVP embryos was determined by using annexin V-FITC staining technique at 48 and 72 h post insemination (hpi). Apoptosis status for each embryo was classified as either early or late. The result showed that there was no significant difference (p > 0.05) of apoptosis status among grade A, B and C embryos. All grades of oocytes showed embryo apoptosis where 1.5% late apoptosis for grade A, 4.5% and 10.4% of early and late apoptosis for grade B and grade C. Early apoptosis was not seen in grade A embryo. We also noted no significant difference (p > 0.05) of apoptosis status between 2, 4, 8 and >8-cell embryo stage. Early apoptosis was also not seen in >8-cell stage. Even though there were no differences in apoptosis expression between the three classes, the cleavage rate of grade A oocytes was significantly higher (p < 0.01) than grade B and grade C. In conclusion, the apoptosis expression in the embryo can occur regardless of the oocyte quality and the cleavage stage of the embryo produced.

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.

Reversible meiotic arrest in feline oocytes

Increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP) within the cumulus-oocyte complex (COC) inhibits or delays spontaneous oocyte maturation and improves the developmental competence of the oocyte in many species, but information for carnivores is limited. The objectives of the present study were to describe the effects of isobutyl methylxanthine (IBMX), which decreases cAMP degradation, and forskolin, which increases cAMP production, on spontaneous and induced maturation (by equine chorionic gonadotrophin (eCG) and epidermal growth factor (EGF)) of feline oocytes and to evaluate the reversibility of IBMX-induced arrest by measuring the resumption of meiosis and embryonic development following IVF. IBMX decreased (P<0.05) the incidence of spontaneous (6.7% vs 42.0%, metaphase II (MII)) and induced (5.6% vs 66.1% MII) maturation after 24 h of culture. In contrast, forskolin stimulated meiosis (81.7% MII; P<0.05). Following 12 h of culture with IBMX and an additional 24h with eCG and EGF in the absence of IBMX, the proportions of oocytes reaching MII (66.1%), cleaving (79.9%) and developing to the blastocyst stage (15.3%) were similar (P>0.05) to oocytes cultured continuously with eCG and EGF (70.2%, 83.0% and 18.1%, respectively). These results demonstrate that IBMX reversibly inhibits both spontaneous and eCG+EGF-induced meiosis in feline oocytes without compromising the oocyte's developmental competence.

The impact of vitrification on immature oocyte cell cycle and cytoskeletal integrity in a rat model

PURPOSE

To test the effects of varying vitrification protocols on the cell cycle status and chromosomal integrity in cumulus-enclosed GV stage rat oocytes.

METHODS

Vitrified and thawed rat oocytes were labeled with fluorescent markers for chromatin, cell cycle activation, and f-actin and analyzed by conventional and laser scanning confocal microscopy.

RESULTS

In all vitrification groups, significant alterations in cumulus cell connectivity, cell cycle status, and cytoplasmic actin integrity were observed following warming compared to fresh control oocytes. Based on the protein phosphorylation marker MPM-2, it is clear that warmed oocytes rapidly enter M-phase but are unable to maintain chromosome integrity as a result of multiple chromatin fusions. A prominent reduction in f-actin is evident in both the ooplasm and at the cortex of vitrified oocytes. Finally, an irreversible but irregular retraction of TZPs occurs on the majority of oocytes subjected to any of the vitrification protocols.

CONCLUSIONS

These findings draw attention to undesirable consequences of immature oocyte vitrification that compromise cell cycle status and chromatin and cytoskeleton integrity that may not be evident until after fertilization.

The effects of EGF and IGF-1 on FSH-mediated in vitro maturation of domestic cat oocytes derived from follicular and luteal stages

The objective of this study was to evaluate the influence of epidermal growth factor (EGF) and insulin like growth factor-I (IGF-1) on the in vitro maturation of cat oocytes recovered from follicular and luteal stage ovaries. Oocytes from follicular (n=580) and luteal (n=209) stages were harvested and divided into four groups, which were cultured in FSH-mediated maturation medium supplemented with: (1) EGF alone (25ng/mL); (2) IGF-1 alone (100ng/mL); (3) EGF+IGF-1 (25ng/mL EGF+100ng/mL IGF-I); or (4) no growth factor (control). The proportion of follicular stage oocytes reaching the metaphase II stage was significantly higher than that of oocytes obtained at the luteal stage in both control and study groups (p<0.001). The percentages of oocytes reaching the metaphase II stage during the follicular period were 62.6% in control; 70.9% in EGF; 72.8% in IGF-1, and 78.1% in EGF+IGF-1 groups, whereas the respective values for gametes collected from luteal stage ovaries were 12.5%, 17.5%, 12.5%, and 16.9%. Additionally, the differences between the study and control groups were significant in the case of follicular stage oocytes. Finally, supplementing the maturation medium with EGF and/or IGF-1 significantly enhanced the meiotic maturation of oocytes recovered from follicular stage ovaries. The present study also demonstrated that the combination of EGF and IGF-I provides an additional or synergic effect on meiotic maturation of oocytes recovered from the follicular stage.

The current challenges to efficient immature oocyte cryopreservation

Oocyte cryopreservation represents an important tool for assisted reproductive technology. It offers the opportunity to preserve fertility in women at risk of loss of the ovarian function for various pathologies. It also represents a treatment alternative for couples that cannot benefit from embryo cryopreservation because of moral, religious, or legal constrains. On the other hand, in vitro oocyte maturation has a range of applications. It can be applied in patients with a contraindication to ovarian stimulation to prevent ovarian hyperstimulation syndrome or to eliminate the risk of stimulation of hormone-sensitive tumours in cancer patients. However, while mature oocyte cryopreservation has found wide-spread application and oocyte in vitro maturation has a place for the treatment of specific clinical conditions, data on the efficiency of freezing of immature or in vitro matured oocytes are poorer. In this review we will focus on the combination of oocyte in vitro maturation with oocyte cryopreservation with particular emphasis on the biological implications of the cryopreservation of immature or in vitro matured oocytes. The two cryopreservation approaches, slow freezing and vitrification, will be discussed in relation to possible cryodamage occurring to subcellular structures of the oocyte and the functional interaction between oocyte and cumulus cells.

Retention of structure and function of the cat germinal vesicle after air-drying and storage at suprazero temperature

The study explored a novel approach for preserving the maternal genome without the entire oocyte by air-drying the cat germinal vesicle (GV) in the presence of the disaccharide trehalose. Specifically, we examined GV structure and function after desiccation, storage at 4 °C (up to 32 wk), and rehydration including the ability to resume meiosis after injection into a fresh, conspecific cytoplast. In experiment 1, DNA integrity was similar to fresh controls after 1 and 4 wk storage in the presence of trehalose, but was more fragmented at later time points (especially after 32 wk). Nuclear envelope integrity was sustained in >90% of oocytes stored for 0, 4, or 16 wk regardless of protective treatment. In experiment 2, compacted, air-dried GVs were stored for 2 or 4 wk, rehydrated, and injected into fresh cytoplasts. After culture for 24 h in vitro, up to 73% of oocytes reconstructed with desiccated GVs preserved in trehalose resumed meiosis compared to 30% of those dried in the absence of the disaccharide. At each storage time point, trehalose presence during air-drying was advantageous for resumption of meiosis, with >20% of oocytes completing nuclear maturation to metaphase II. This demonstrates a potential for preserving the female genome using the GV alone and for multiple weeks after desiccation. Trehalose enhanced the process by retaining the ability of a dried and rehydrated GV to resume communication with the surrounding cytoplasm of the recipient oocyte to permit reaching metaphase II and likely sustain subsequent embryo development.

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.

Empty follicle syndrome: successful treatment in a recurrent case and review of the literature

Empty follicle syndrome is a condition in which no oocytes are retrieved after an apparently adequate ovarian response to stimulation and meticulous follicular aspiration. It is a rare condition of obscure etiology. A patient with primary infertility who underwent seven assisted reproductive technique cycles is described. In spite of a satisfactory ovarian response, aspiration yielded no oocytes in four cycles and 1-4 low quality oocytes in three cycles. In the index treatment cycle, ovulation was triggered using GnRH agonist 40 h prior to ovum pickup and hCG was added 6 h after the first trigger. Eighteen oocytes were recovered, of which 16 were mature and were inseminated by ICSI. Two embryos were transferred 48 h after aspiration and nine embryos were cryopreserved. The patient conceived and delivered a healthy boy at 38 weeks of gestation. The literature is reviewed and possible etiologies and treatment options of this enigmatic syndrome are suggested.

The ability to achieve meiotic maturation in the dog oocyte is linked to glycolysis and glutamine oxidation

We tested the hypothesis that meiotic competence of dog oocytes is tightly linked with donor follicle size and energy metabolism. Oocytes were recovered from small (<1 mm diameter, n = 327), medium (1-<2 mm, n = 292) or large (≥2 mm, n = 102) follicles, cultured for 0, 24, or 48 hr, and then assessed for glycolysis, glucose oxidation, pyruvate uptake, glutamine oxidation, and nuclear status. More oocytes (P < 0.05) from large follicles (37%) reached the metaphase-II (MII) stage than from the small group (11%), with the medium-sized class being intermediate (18%; P > 0.05). Glycolytic rate increased (P < 0.05) as oocytes progressed from the germinal vesicle (GV) to MII stage. After 48 hr of culture, oocytes completing nuclear maturation had higher (P < 0.05) glycolytic rates than those arrested at earlier stages. GV oocytes recovered from large follicle oocytes had higher (P < 0.05) metabolism than those from smaller counterparts at culture onset. MII oocytes from large follicles oxidized more (P < 0.05) glutamine than the same stage gametes recovered from smaller counterparts. In summary, larger-sized dog follicles contain a more metabolically active oocyte with a greater chance of achieving nuclear maturation in vitro. These findings demonstrate a significant role for energy metabolism in promoting dog oocyte maturation, information that will be useful for improving culture systems for rescuing intraovarian genetic material.

The competence of germinal vesicle oocytes is unrelated to nuclear chromatin configuration and strictly depends on cytoplasmic quantity and quality in the cat model

BACKGROUND

Chromatin configuration of the germinal vesicle (GV) and quality of the cytoplasm are critical factors in achieving oocyte meiotic and developmental capacity during folliculogenesis. Besides gaining new insights into the timing and cellular mechanisms associated with the acquisition and regulation of GV oocyte competence, the domestic cat model was used to examine (i) the relation between GV chromatin configuration and oocyte functionality during folliculogenesis and (ii) the role of the cytoplasmic environment on the GV competence and stability.

METHODS

Structural and functional properties of GV oocytes were characterized after isolation from different follicle stages of non-stimulated cat ovaries. GV transfers, artificial chromatin compaction and oocyte vitrification were used to demonstrate the respective roles of GV and cytoplasm on the oocyte functionality.

RESULTS

GVs acquired the intrinsic capability to resume meiosis during the pre-antral follicle stage, whereas the capacity to support embryo development occurred while the antrum started to form. Chromatin configuration of the GV did not undergo extensive modification during the acquisition of competence or during the arrest of transcriptional activity at the large antral follicle stage. However, the quality and quantity of the cytoplasm regulated and enhanced GV functionality. This finding also held for GVs transferred from incompetent or subpar oocytes into the cytoplasm of good quality oocytes or when chromatin was artificially modified or vitrified.

CONCLUSIONS

The cat model provides a new insight into GV oocyte structure and function during folliculogenesis while challenging current concepts about oocyte quality criteria based on the GV morphology. This suggests alternative evaluative approaches for oocytes from other species too, including humans. Cat GVs also appear competent at an early follicle stage and are resilient to perturbations which designate this organelle as an attractive target for developing novel fertility preservation tactics.

Autologous embryo–cumulus cells co-culture and blastocyst transfer in repeated implantation failures: a collaborative prospective randomized study

In repeated implantation failure, the co-culture of human embryos with somatic cells has been reported to promote the improvement of embryos quality, implantation and pregnancy rate. It was reported that feeder cells can be more beneficial to the oocyte and embryo by detoxifying the culture medium and supporting embryo development via different pathways. In this study, 432 patients, each with a minimum of three repeated implantation failures, were accepted for a prospective randomized study with or without autologous cumulus cell embryo co-culture and transfer at day 3 or day 5–6. We also investigated the expression of leukaemia inhibitor factor (LIF) and platelet activating factor receptor (PAF-R) on day 3 confluent cumulus cells. The statistic analysis of the data showed significant difference of implantation and clinical pregnancy rates between classical culture and day 3 compared with co-culture and day 5–6 transfer. The molecular analysis showed that cumulus cells express the LIF and the PAF-R genes and confirmed the possible positive role of growth factors and cytokines in early embryo development. Embryo co-culture systems with autologous cells can be beneficial in routine in vitro fertilization for embryo selection and implantation improvement. More molecular investigations need to be done to improve elucidation of the complex dialogue between the embryo and feeder cells prior to implantation and to understand the involved biological function and molecular process during embryo development.