A confocal microscopy analysis of the spindle and chromosome configurations of human oocytes cryopreserved at the germinal vesicle and metaphase II stage

Oocyte cryopreservation

OBJECTIVE

To review historical and contemporary advances in oocyte-cryopreservation techniques and outcomes.

DESIGN

Publications related to oocyte cryopreservation were identified through MEDLINE and other bibliographic databases.

CONCLUSION(S)

Oocyte cryopreservation can be used as an adjunct to conventional IVF and as an option for fertile women to electively cryopreserve their gametes. Recent reports indicate pregnancy rates comparable to those for cryopreserved embryos by either slow-freeze or vitrification methods. Larger prospective trials are needed to determine the true efficacy and safety of oocyte cryopreservation. Until a sufficient number of births is reached and adequate outcome data are collected, oocyte cryopreservation should continue to be considered experimental and to be performed under the oversight of an institutional review board.

Light retardance by human oocyte spindle is positively related to pronuclear score after ICSI

Disturbed spindle assembly increases risks of chromosome mal-segregation. Non-invasive polarization microscopy (PolScope) was employed in two centres to assess spindle integrity for the first time quantitatively in human oocytes from consenting patients undergoing intracytoplasmic sperm injection (ICSI) with respect to pronuclear (PN) score after fertilization. In one centre oocytes were selected before ICSI, in another selection was after ICSI according to PN score. In both centres, mean retardance of light by birefringent spindles in oocytes forming a pre-embryo with good PN score after ICSI was significantly higher compared with spindles in oocytes developing into a lower PN score pre-embryo with limited developmental potential (P < 0.001). Transfers involving oocytes with high retardance and at least one good PN score embryo resulted more frequently in a conception than transfers from oocytes with spindles of lower mean retardance and lower PN score embryos. There was a trend for an inverse relationship between age and magnitude of retardance in a small oocyte cohort. The study suggests that quantitative evaluation of mean retardance of light by the oocyte spindle predicts oocyte health, is related to PN score of the embryo and may be especially useful to assess oocyte quality in countries with legal restrictions to select after fertilization.

Ovarian tissue cryopreservation and transplantation: a review

The review covers current options for ovarian tissue cryopreservation and transplantation and provides a systematic review of the existing literature from the last 10 years, taking into account all previously published reviews on the subject. The different cryopreservation options available for fertility preservation in cancer patients are embryo cryopreservation, oocyte cryopreservation and ovarian tissue cryopreservation. The choice depends on various parameters: the type and timing of chemotherapy, the type of cancer, the patient's age and the partner status. The different options and their results are discussed, as well as their putative indications and efficacy. The review concludes that advances in reproductive technology have made fertility preservation techniques a real possibility for patients whose gonadal function is threatened by premature menopause, or by treatments such as radiotherapy, chemotherapy or surgical castration.

Oocytes cryopreservation: state of art

In the present review article we sought to analyze, on the basis of a systematic review, the indications, rationale of oocytes cryopreservation, as well as the techniques that improved the aforementioned procedure in order to higher the pregnancy rate in women undergoing that procedure. Moreover, we pointed out the importance of oocytes cryopreservation in the research field as oocyte banking may be of utmost importance to increase the availability of oocytes for research applications such as genetic engineering or embryo cloning. Oocyte freezing has 25 year of history alternating successes and setbacks. Human oocytes have a delicate architecture but are freezable. Clinical efficiency remains low, but healthy children have been born, indicating that chromosomally normal embryos can originate from frozen oocytes. Freezing protocols are not yet optimal and it is now desirable to combine empirical and theoretical knowledge.

Progress with oocyte cryopreservation

PURPOSE OF REVIEW

This article reviews human oocyte cryopreservation, one of the most stimulating challenges of assisted reproduction technology. Since the first steps in assisted reproduction technology, researchers have pursued this goal, to greatly improve the management of infertility treatments. This present review depicts the present state of research and clinical applications of this methodology.

RECENT FINDINGS

Recent literature focuses on the possible mechanisms of oocyte damage caused by temperature and cryoprotectant injury and forecasts possible technological solutions. Several papers illustrate encouraging results in the increasing clinical application of this procedure.

SUMMARY

Findings give support to several indications of human female gamete cryostorage. Oocyte cryopreservation might replace embryo freezing. Egg freezing offers an alternative to women at risk of losing their reproductive function, caused by antineoplastic treatments, endometriosis, ovarian surgery or genetic premature ovarian failure. In addition, oocyte storage may contribute to an increase in in-vitro fertilization flexibility. Despite the early disappointing results, recent technical modifications have improved the clinical efficiency greatly, with the birth of several healthy children.

Membranous and structural damage that occur during cryopreservation of human sperm may be time-related events

OBJECTIVE

To evaluate sperm cryopreservation-induced injuries using sperm plasma membrane protein P34H and alpha-tubulin as two different subcellular compartment markers.

DESIGN

Prospective experimental study.

SETTING

Academic hospital research center and fertility clinic.

PATIENT(S)

Semen samples obtained from healthy donors attending the fertility clinic. Sperm samples were either directly processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot experiments (control group) or cryopreserved in liquid nitrogen for different periods of time before being analyzed.

INTERVENTION(S)

SDS-PAGE, Western blotting, and densitometric quantification of P34H and alpha-tubulin before and after cryopreservation.

MAIN OUTCOME MEASURE(S)

Changes in protein quantification between the different groups as a result of sperm cryopreservation.

RESULT(S)

In the 31 sperm samples processed for P34H evaluation, a 50% decrease is observed after sperm cryopreservation as compared to the control group. The alpha-tubulin immunoblotting of 41 sperm samples revealed a 200% increase in the protein detection in the group of cryopreserved sperm as compared to the control group. Contrary to the P34H detection, this change in alpha-tubulin immunodetected levels appears to be related to the cryopreservation period as it increases during storage.

CONCLUSION(S)

These findings indicate that cryopreservation of human semen induces damages at different cellular levels. Moreover, some cryoinjuries are immediate although others seem to take place over time stored in liquid nitrogen.

The interface between assisted reproductive technologies and genetics: technical, social, ethical and legal issues

The interface between assisted reproductive technologies (ART) and genetics comprises several sensitive and important issues that affect infertile couples, families with severe genetic diseases, potential children, professionals in ART and genetics, health care, researchers and the society in general. Genetic causes have a considerable involvement in infertility. Genetic conditions may also be transmitted to the offspring and hence create transgenerational infertility or other serious health problems. Several studies also suggest a slightly elevated risk of birth defects in children born following ART. Preimplantation genetic diagnosis (PGD) has become widely practiced throughout the world for various medical indications, but its limits are being debated. The attitudes towards ART and PGD vary substantially within Europe. The purpose of the present paper was to outline a framework for development of guidelines to be issued jointly by European Society of Human Genetics and European Society of Human Reproduction and Embryology for the interface between genetics and ART. Technical, social, ethical and legal issues of ART and genetics will be reviewed.

Membrane integrity and development of immature murine cumulus–oocyte complexes following slow cooling to −60°C: The effect of immediate rewarming, plunging into LN2 and two-controlled-rate-stage cooling

Cryopreservation of murine germinal vesicle (GV) stage cumulus-oocyte complexes (COCs) has been shown to result in poor development and cumulus cell damage. In an attempt to determine the stage of the cryopreservation protocol at which damage occurs, three cooling profiles were compared: slow-cooling (0.3 degrees C/min) to -60 degrees C (protocol A); slow-cooling to -60 degrees C and plunging to -196 degrees C (protocol B); or slow-cooling to -60 degrees C followed by further cooling at 10 degrees C/min to -150 degrees C, then plunging to -196 degrees C (protocol C). GV-stage COCs were collected from hormone-primed mice by repeated puncturing of ovarian follicles. COCs were exposed to 1.5 M Me(2)SO prior to cooling to -60 or -196 degrees C. Membrane integrity was assessed immediately after thawing using carboxy fluorescein and propidium iodide. A greater proportion of cumulus cells were damaged following protocol B than protocol A. Damage was less extensive following protocol C than following protocol B. For assessment of development, COCs were matured and fertilised in vitro. Morphological normality was significantly reduced following cooling to -60 or -196 degrees C compared with non-cryopreserved controls. Fertilisation of oocytes assessed as normal post-treatment was not significantly different between any of the groups. Development to blastocyst was least from oocytes exposed to protocol B, being significantly worse than for oocytes exposed to protocol A, but not significantly different to protocol C. A protocol comprising two stages of controlled-rate cooling decreased damage to the membranes of cumulus cells but did not significantly improve embryo development.

The Structural and Cellular Viability in Cryopreserved Rabbit Carotid Arteries

OBJECTIVE

We investigated the histological and mechanical changes in addition to viable cellular recovery in cryopreserved blood vessels.

MATERIALS AND METHODS

Rabbit carotids were cryopreserved in a cryoprotective medium containing 1.5 M of 1,2-propanediol (PD) and then were thawed slowly in an ice bag that had been precooled in liquid nitrogen. Fresh carotids were used as the control. The fresh and freeze-thawed arteries were cultured for the growth of vascular smooth muscle cells (VSMCs). The freeze-thawed arterial tissues were perfused in vitro for 6, 12, or 24 h, respectively, to assess the integrity of carotid walls and the mechanical properties.

RESULTS

The results showed that it took almost the same time (24 approximately 36 h) for the VSMCs of the PD-cryopreserved arteries to regenerate as those from the fresh arteries. Their growing speeds also were similar. On the contrary, Me2SO-cryopreserved (1.5 M) arteries were unable to regenerate VSMCs in culture. After freeze-thawing, the mechanical properties decreased significantly (P < 0.003 for elastic modulus and P < 0.001 for fracture strength). After in vitro perfusion of the freeze-thawed carotid arteries, all of the survived endothelial cells fell off, and some of the VSMCs denaturalized or necrosed. The internal elastic fibers and collagen showed various degrees of cracking. The mechanical properties were decreased (P < 0.05).

CONCLUSION

Our findings demonstrate that the PD-containing cryoprotective medium can preserve regenerative capacity of VSMCs, which makes it a useful technique for viable VSMC recovery. However, the freeze-thawing process and the in vitro perfusion caused serious disruption in the arterial mechanical properties, rendering the cryopreserved blood vessels less useful for vessel reconstruction.

Sucrose concentration influences the rate of human oocytes with normal spindle and chromosome configurations after slow-cooling cryopreservation

BACKGROUND

Recently described slow-cooling cryopreservation protocols involving elevated sucrose concentration have improved survival frequencies of human oocytes, potentially overcoming a major hurdle that has limited the adoption of oocyte storage. Because implantation rates of embryos from frozen oocytes remain generally low, it is still debated whether, irrespective of survival rates, this form of cryopreservation leads inevitably to the disruption or complete loss of the metaphase II (MII) spindle.

METHODS

Human oocytes with an extruded polar body I (PBI) were cryopreserved using a slow-cooling method including 1.5 mol/l propane-1,2-diol (PrOH) and alternative sucrose concentrations (either 0.1 or 0.3 mol/l) in the freezing solution. Fresh control and frozen-thawed survived oocytes were analysed by confocal microscopy to evaluate MII spindle and chromosome organizations.

RESULTS

Of the 104 oocytes included in the unfrozen group, 76 (73.1%) displayed normal bipolar spindles with equatorially aligned chromosomes. Spindle and chromatin organizations were significantly affected (50.8%) after cryopreservation involving lower sucrose concentration (61 oocytes), whereas these parameters were unchanged (69.7%) using the 0.3 mol/l sucrose protocol (152 oocytes).

CONCLUSIONS

Partial disruption of the MII spindle and associated chromosomes accompanies inadequate cryopreservation during slow cooling. However, protocols adopting higher sucrose concentration in the freezing solution promote the retention of an intact chromosome segregation apparatus comparable in incidence to freshly collected oocytes.

Effect of maturation stage at cryopreservation on post-thaw cytoskeleton quality and fertilizability of equine oocytes

Oocyte cryopreservation is a potentially valuable technique for salvaging the germ-line when a valuable mare dies, but facilities for in vitro embryo production or oocyte transfer are not immediately available. This study examined the influence of maturation stage and freezing technique on the cryopreservability of equine oocytes. Cumulus oocyte complexes were frozen at the immature stage (GV) or after maturation in vitro for 30 hr (MII), using either conventional slow freezing (CF) or open pulled straw vitrification (OPS); cryoprotectant-exposed and untreated nonfrozen oocytes served as controls. After thawing, GV oocytes were matured in vitro, and MII oocytes were incubated for 0 or 6 hr, before staining to examine meiotic spindle quality by confocal microscopy. To assess fertilizability, CF MII oocytes were subjected to intracytoplasmic sperm injection (ICSI) and cultured in vitro. At 12, 24, and 48 hr after ICSI, injected oocytes were fixed to examine their progression through fertilization. Both maturation stage and freezing technique affected oocyte survival. The meiosis resumption rate was higher for OPS than CF for GV oocytes (28% vs. 1.2%; P < 0.05), but still much lower than for controls (66%). Cryopreserving oocytes at either stage induced meiotic spindle disruption (37%-67% normal spindles vs. 99% in controls; P < 0.05). Among frozen oocytes, however, spindle quality was best for oocytes frozen by CF at the MII stage and incubated for 6 hr post-thaw (67% normal); since this combination of cryopreservation/IVM yielded the highest proportion of oocytes reaching MII with a normal spindle (35% compared to <20% for other groups), it was used when examining the effects of cryopreservation on fertilizability. In this respect, the rate of normal fertilization for CF MII oocytes after ICSI was much lower than for controls (total oocyte activation rate, 26% vs. 56%; cleavage rate at 48 hr, 8% vs. 42%: P < 0.05). Thus, although IVM followed by CF yields a respectable percentage of normal-looking MII oocytes (35%), their ability to support fertilization is severely compromised.

Simple Prediction of the Survival of Follicles in Cryopreserved Human Ovarian Tissue

This study examines the possible predictive value of the LIVE/DEAD fluorescence viability assay for evaluation of survival of cryopreserved human ovarian tissue. Ovarian tissue from ten patients was examined by LIVE/DEAD viability staining before and after cryopreservation and after freezing in a -20 C freezer (negative control). After cryopreservation with a slow freezing protocol and cryoprotectant the LIVE/DEAD assay showed 86% viable follicles (an intact oocyte and at least more than 50% of the granulosa cells alive), whereas after freezing at -20 C the survival rate was 67%. The healthy follicular loss after cryopreservation was 4%, whereas with freezing at -20 C, it was 25%. Although this assay overestimates the survival rate of cryopreserved primordial follicles, if the LIVE/DEAD assay yields greater than approximately 85% viable follicles, it can be assumed that the follicles in the cryopreserved tissue have maintained their developmental potential and that the tissue is suitable for retransplantation.

Ultrastructural Dynamics of Human Reproduction, from Ovulation to Fertilization and Early Embryo Development1

This study describes the updated, fine structure of human gametes, the human fertilization process, and human embryos, mainly derived from assisted reproductive technology (ART). As clearly shown, the ultrastructure of human reproduction is a peculiar multistep process, which differs in part from that of other mammalian models, having some unique features. Particular attention has been devoted to the (1) sperm ultrastructure, likely "Tygerberg (Kruger) strict morphology criteria"; (2) mature oocyte, in which the MII spindle is barrel shaped, anastral, and lacking centrioles; (3) three-dimensional microarchitecture of the zona pellucida with its unique supramolecular filamentous organization; (4) sperm-egg interactions with the peculiarity of the sperm centrosome that activates the egg and organizes the sperm aster and mitotic spindles of the embryo; and (5) presence of viable cumulus cells whose metabolic activity is closely related to egg and embryo behavior in in vitro as well as in vivo conditions, in a sort of extraovarian "microfollicular unit." Even if the ultrastructural morphodynamic features of human fertilization are well understood, our knowledge about in vivo fertilization is still very limited and the complex sequence of in vivo biological steps involved in human reproduction is only partially reproduced in current ART procedures.

Human oocyte cryopreservation: past, present and future

Despite inferior results in the past compared with embryo freezing, oocyte cryopreservation has made great strides in recent years. In fact, it has become a necessity in assisted reproduction technology, providing alternatives to legal, moral and religious problems originating from embryo freezing. Recent advances in freezing technology, modifications of conventional protocols used and continuing optimization of vitrification have efficiently improved the method. A historical description of the method's progression over time, and a comparison of principles, procedures and results as reported in the literature are presented in this review.

Successful pregnancy and delivery after transfer of a single blastocyst derived from a vitrified mature human oocyte

OBJECTIVE

To describe the first case of delivery after the transfer of a single blastocyst derived from a vitrified mature human oocyte.

DESIGN

Case report.

SETTING

Private assisted reproduction clinic.

PATIENT(S)

A normal 31-year-old woman.

INTERVENTION(S)

An unsuccessful attempt was made to extract sperm from the patient's nonobstructive azoospermic husband by testicular sperm extraction.

MAIN OUTCOME MEASURE(S)

Transfer of single blastocyst derived from vitrified human oocyte and donor sperm.

RESULT(S)

A healthy male neonate weighing 3000 g was born.

CONCLUSION(S)

Vitrification is a useful method of preserving mature human oocytes and has the advantage of time-effectiveness, simplicity, cost reduction, and no need for devices such as programmable freezers.

The effect of chilling on membrane lipid phase transition in human oocytes and zygotes

BACKGROUND

Chilling injury occurs when the cell membrane undergoes a transition from the liquid state to the gel state. Human oocytes and single-cell zygotes are of similar shape and size but the post-thawing survival rate of oocytes is poorer. We set out to investigate the possible difference in membrane lipid phase transition (LPT) temperature between the two cell types.

METHODS

The LPT temperature was measured with a Fourier Transform Infrared analyser, which detects the change in the vibration frequency of the CH2 bond stretches of the membrane lipid molecules during temperature change. The LPT temperatures of unfertilized human oocytes, in vitro-matured oocytes, and immature germinal vesicle (GV) stage oocytes were compared with that of abnormally fertilized human zygotes.

RESULTS

The LPT temperatures of zygotes and of mature and immature GV oocytes differ significantly from each other (10.0 +/- 1.2, 16.9 +/- 0.9 and 24.4 +/- 1.6 degrees C respectively; P < 0.05).

CONCLUSIONS

Zygotes show a higher resistance to chilling injury compared to oocytes at different developmental stages; this might explain the relatively poor survival rates of cryopreserved human oocytes and indicates the necessity to adjust the cryopreservation protocols in order to minimize cryoinjury.

Effects of roscovitine on the nuclear and cytoskeletal components of calf oocytes and their subsequent development

Roscovitine, a potent inhibitor of M-phase promoting factor kinase activity, was used to maintain calf oocytes at the germinal vesicle stage for a 24h culture period. Cumulus-oocyte complexes were first prematured for 24h in the presence of different levels of roscovitine (12.5, 25, 50 and 100 microM). Roscovitine was shown to block germinal vesicle breakdown in calf oocytes in a concentration dependent manner. Significantly greater inhibitory effect was observed at 50 and 100 microM with 64.6% and 63.2% oocytes being blocked in the germinal vesicle stage when compared to the control (0.0%) and the 12.5 microM (2.9%) and 25 microM (18.8%) groups. However, this inhibitory effect of roscovitine was fully reversible since a substantial number of the oocytes resumed meiosis and reached the metaphase II stage after a further 24h of culture in a permissive medium. Cleavage rates and blastocyst yields were not significantly different for oocytes cultured under 50 microM roscovitine inhibition compared to oocytes not subjected to prematuration culture (rates of 76.7% cleavage and 8.7% blastocysts for control oocytes compared to 69.8% and 6.3%, respectively, for oocytes pretreated with 50 microM roscovitine). The morphology of the meiotic spindle was typical of metaphase II in 75.8% and 82.1% of the oocytes reaching the metaphase II stage after pretreatment with 50 microM roscovitine compared to control, respectively. A normal distribution of actin filaments was observed in 97.0% and 98.2% of oocytes exposed to 50 microM roscovitine compared to control, respectively. These results demonstrate the feasibility of maintaining calf oocytes in artificial meiotic arrest without compromising their subsequent developmental competence.

Fertility preservation options for female patients with malignancies

PURPOSE OF REVIEW

Preservation of fertility in female patients diagnosed with cancer has recently been an area of intensive investigation. This review summarizes available options and discusses recently published data concerning experimental methods. Specific strategies for fertility preservation in women with gynecologic malignancies are also presented.

RECENT FINDINGS

Success with ovarian stimulation protocols using tamoxifen or aromatase inhibitors has recently been reported for women with breast cancer who attempt embryo cryopreservation prior to chemotherapy. The first embryo transfer using oocytes retrieved from cryopreserved ovarian tissue implanted at a heterotopic location, the first pregnancy following orthotopic transplantation of cryopreserved ovarian tissue, and increasing success with oocyte cryopreservation were also reported.

SUMMARY

Fertility preservation in female patients with cancer has become an important health issue due to increasing survival rates and delayed childbearing especially in Western countries. Radical vaginal trachelectomy for cervical cancer, conservative surgery for ovarian tumors, and progestin treatment in endometrial cancers may be considered at early stages in order to preserve fertility. Embryo cryopreservation is an established technique that is available for fertility preservation, providing a delay in the initiation of chemotherapy or radiotherapy is acceptable, and a partner or donor sperm is available. Additional techniques that could be offered after counseling the patient about their experimental nature include oocyte cryopreservation, ovarian cryopreservation, and gonadotropin-releasing hormone agonist co-treatment with chemotherapy. Improvement of these techniques as well as better characterization of their success rates and risks await further investigation.

Meiotic spindle imaging in human oocytes frozen with a slow freezing procedure involving high sucrose concentration

BACKGROUND

One of the major concerns derived from the cryopreservation of meiotically mature oocytes is possible damage to the cytoskeletal apparatus, and in particular the meiotic spindle.

METHODS

One hundred fresh oocytes showing the polar body I and high meiotic spindle birefringence (maximum retardance+/-1.5 mol/l SD = 2.58+/-0.1 nm), assessed through analysis, were included in this study. Oocytes were cryopreserved with a 1.5 mol/l 1,2-propanediol +0.3 mol/l sucrose solution. After thawing, spindles were imaged at 0, 3 and 5 h. Spindle birefringence was quantified by measuring microtubule maximum retardance. Signals of thawed oocytes were classified as absent (non-detectable), weak (1.55+/-0.3 nm) or high (2.50+/-0.2 nm).

RESULTS

Immediately after thawing, only 22.9% of oocytes showed a weak birefringence signal, while only 1.2% of oocytes displayed a high signal. Three hours after thawing, the proportion of oocytes exhibiting a weak or high intensity signal was 49.4% and 18.1%, respectively. Finally, after culture for 5 h following thawing, a weak birefringence signal was detected in 51.8% of oocytes, while 24.1% showed a high signal. There was a statistically significant increase in signal restoration after 3 h of culture (P < 0.001).

CONCLUSIONS

These results suggest that in mature oocytes stored via slow freezing, the meiotic spindle undergoes transient disappearance immediately after thawing but is reorganized in the majority of oocytes, at least to some extent, after 3-5 h of culture.

Effects of vitrification in open pulled straws on the cytology of in vitro matured prepubertal and adult bovine oocytes

This study was designed to evaluate the effects of the cryopreservation of oocytes obtained from prepubertal calves or adult cows on chromosome organization, spindle morphology, cytoskeleton structures, and the ability of fertilized oocytes to develop to the blastocyst stage. Once in vitro matured (IVM), the oocytes were divided into three groups according to whether they were: (1) left untreated (control); (2) exposed to cryoprotectant agents (CPAs); or (3) cryopreserved by the open-pulled-straw (OPS) vitrification method. After thawing, oocyte samples were fixed, stained using specific fluorescent probes and examined under a confocal microscope. The remaining oocytes were fertilized, and cleavage and blastocyst rates recorded. After vitrification or CPA exposure, significantly higher proportions of oocytes showed changes in spindle morphology compared to the control group. The spindle structure of the adult cow IVM oocytes was significantly more resistant to the OPS vitrification process. Vitrification of oocytes from calves or adult cows led to significantly increased proportions of oocytes showing discontinuous or null actin staining of the cytoskeleton compared to non-treated controls. Oocytes only exposed to the cryoprotectants showed a similar appearance to controls. A normal distribution of actin microfilaments was observed in both calf and adult cow oocytes, irrespective of the treatment. Cleavage and blastocyst rates were significantly lower for vitrified versus non-treated oocytes. Oocytes obtained from adult cows were more sensitive to CPA exposure, while the vitrification procedure seemed to have more detrimental effects on the calf oocytes.

Vitrification of calf oocytes: Effects of maturation stage and prematuration treatment on the nuclear and cytoskeletal components of oocytes and their subsequent development

This study was designed to establish the effects of the meiotic stage of bovine oocytes and of a prematuration treatment with roscovitine (ROS) on their resistance to cryopreservation. Oocytes from prepubertal calves at the stages of germinal vesicle breakdown (GVBD) or at metaphase II (MII) were vitrified by the open pulled straw (OPS) method. In another experiment, oocytes were kept under meiotic arrest with 50 microM ROS for 24 hr and vitrified at the GVBD stage. After warming, some oocyte samples were fixed, stained using specific fluorescent probes and examined under a confocal microscope. The remaining oocytes were fertilized, and cleavage and blastocyst rates recorded. Significantly lower cleavage rates were obtained for the vitrified GVBD and MII oocytes (9.9% and 12.6%, respectively) compared to control oocytes (73.9%). Significantly worse results in terms of cleavage rates were obtained when GVBD calf oocytes were exposed to cryoprotectants (CPAs: ethylene glycol plus dimethyl sulfoxide, DMSO) (13.1%) or vitrified (1.6%) after a prematuration treatment with ROS, when compared to untreated control oocytes (68.7%) or ROS-control oocytes (56.6%). None of the vitrification procedures yielded blastocysts, irrespective of the initial meiotic stage or previous prematuration treatment. Compared to the control oocytes, significantly fewer oocytes exhibited normal spindle configuration after being exposed to CPAs or after vitrification of either GVBD or MII calf oocytes. These results indicate that the vitrification protocol has a deleterious effect on the meiotic spindle organization of calf oocytes cryopreserved at both the GVBD and MII stage, which impairs the capacity for further development of the embryos derived from these vitrified oocytes. Prematuration treatment with ROS has no beneficial effect on the outcome of vitrification by the OPS method.

Cryopreservation of Isolated Mouse Germinal Vesicles

The storage of unfertilized oocytes, either immature, maturing or mature, is still unsatisfactory. Here we describe an approach in which germinal vesicles isolated as karyoplasts from immature oocytes are vitrified by open the pulled straws (OPS) method in evacuated porcine zonae pellucidae. After thawing, their survival was almost absolute. Moreover, when thawed GV-karyoplasts were fused to immature oocyte cytoplasts the maturation of reconstructed cells resulted in the production of secondary oocytes--metaphase II.

Criteria to assess human oocyte quality after cryopreservation

Oocyte cryopreservation certainly represents one of the most attractive developments in the field of assisted reproduction, with the aim of preserving female fertility and circumventing the ethical and legal drawbacks associated with embryo freezing. Despite the achievement of the first pregnancy from frozen oocytes dating back as early as 1987, since then fewer than 150 pregnancies have been reported. Over a long period of time, application of oocyte storage on a large scale has been prevented by various factors, namely poor post-thaw survival. Fertilization rates remained low even after the introduction of intracytoplasmic sperm injection. Modifications of slow-freezing protocols, mainly based on the increase of the concentration of sucrose used as non-penetrating cryoprotectant (CPA) and the replacement of sodium with choline, appear to have decisively improved survival rates to over 80%. Investigations at the cellular level on thawed oocytes are largely lacking. Fertilization rates have also benefited from protocol modifications, reaching values indistinguishable from those normally obtained with fresh material. Vitrification protocols have also been tested, giving rise to improvements whose reproducibility is still uncertain. Data on the dynamics of fertilization and preimplantation development of embryos derived from frozen oocytes are extremely scarce. At the moment, clinical efficiency of oocyte cryopreservation cannot be precisely assessed because of the lack of controlled studies, although it appears to be considerably lower than that achieved with embryo freezing. In summary, encouraging advances have been made in the field of oocyte cryopreservation, but presently no protocol can ensure standards of success and safety comparable to those guaranteed by embryo storage.

Vitrification of immature and in vitro matured pig oocytes: study of distribution of chromosomes, microtubules, and actin microfilaments

Studies were conducted to compare viability of immature and mature porcine oocytes vitrified in ethylene glycol (EG) using open-pulled straws (OPS). Oocytes that had been allowed to mature for 12 h (germinal vesicle group; GV) and 40 h (metaphase II group; MII) were divided into three treatments: (1) control; (2) treated with cytochalasin B and exposed to EG; and (3) treated with cytochalasin B and vitrified by stepwise exposure to EG in OPS. After warming, a sample of oocytes was fixed and evaluated by specific fluorescent probes before visualization using confocal microscopy. The remaining oocytes were fertilized and cleavage rate was recorded. Exposure of GV oocytes to EG or vitrification had a dramatic effect on spindle and chromosome configurations and no cleavage was obtained after in vitro fertilization. When MII oocytes were exposed to EG or were vitrified, 18 and 11% of oocytes, respectively, maintained the spindle structure and either EG exposure or vitrification resulted in substantial disruption in microfilament organization. The cleavage rates of mature oocytes after being exposed to EG or after vitrification were similar (14 and 13%, respectively) but were significantly less than that of control oocytes (69%). These results indicate that porcine oocytes at different meiotic stages respond differently to cryopreservation and MII porcine oocytes had better resistance to cryopreservation than GV stage oocytes.

Ovarian tissue and oocyte cryopreservation

Although currently investigational, ovarian tissue cryopreservation and oocyte cryopreservation hold promise for future female fertility preservation, particularly following aggressive chemotherapy and/or radiotherapy treatment protocols.

Effects of cryopreservation on the meiotic spindle of human oocytes

The microtubular meiotic spindle of most mammals, including humans, is very sensitive to cooling [Hum. Reprod. 16 (2001) 2374; Fertil. Steril. 54 (1990) 102; Fertil. Steril. 75 (2001) 769; Zygote 3 (1995) 357] and is rapidly depolymerised even after a slight reduction in temperature to 33 degrees C. Spindle disassembly is dependent on the extent of temperature decrease and its duration. After rewarming, the recovery is far from complete. Cryoprotectants themselves may alter the spindle structure, depending on the duration and temperature of exposure, the duration of recovery at 37 degrees C and the species [Hum. Reprod. Update 2 (1996) 193]. Damage to the meiotic spindle is considered to be the cause of aneuploid embryos, by inducing chromatid non-disjunction and chromosome scattering and by disturbing the sequence of events leading to the completion of meiosis and fertilisation. Nevertheless, a consensus arose from all the studies: appropriate exposure to cryoprotectants and appropriate rates of cooling and thawing allow the cryopreservation of mature oocytes without any significant changes in their second meiotic spindle organisation and without any increase in the rate of aneuploid embryos [Mol. Hum. Reprod. 2 (1996) 445; Hum. Reprod. 8 (1993) 1101; Hum. Reprod. 9 (1994) 684; Microsc. Res. Technol. 27 (1994) 165; Fertil. Steril. 75 (2001) 354]. These fundamental studies in humans, showing good preservation of cell structures after freeze-thaw procedures opened the way to new successful clinical trials with embryos derived from cryopreserved mature oocytes [Fertil. Steril. 68 (1997) 724]. Considering immature oocyte freezing at prophase I (germinal vesicle (GV) stage), a stage which was thought to be less sensitive to cryoinjury, pooled data from the literature showed no advantage in terms of survival rates, fertilisation rates of in vitro matured oocytes and developmental ability of the resulting embryos, especially in unstimulated cycles. Moreover, conflicting results are reported on the effects of freezing on the spindle-chromosome configuration of immature oocytes or in vitro matured oocytes, highlighting the need for large scale studies [Hum. Reprod. 10 (1995) 1816; Hum. Reprod. 13 (Suppl. 3) (1998) 161; Hum. Reprod. 17 (2002) 1885; Microsc. Res. Technol. 27 (1994) 165; Fertil. Steril. 68 (1997) 920]. One child has been born after the use of cryopreserved immature oocytes at GV stage, matured in vitro and fertilised by ICSI [Hum. Reprod. 13 (1998) 3156], demonstrating at least the feasibility of this technique. Improvements are required so as to make mature and immature oocyte cryopreservation an established and safe technique for ART.

Spindle organization after cryopreservation of mouse, human, and bovine oocytes

Oocyte cryopreservation would alleviate a number of ethical, social, and religious problems associated with human embryo storage. One potential problem is the effect of cryopreservation on the metaphase II spindle and chromosomes. The microtubules that make up the spindle tend to depolymerize at sub-physiological temperatures. Although there are numerous reports in the literature on this topic, discrepancies as to whether the spindle can or cannot reform persist. One of the confounding factors may be the low cryosurvival rates (around 50%) for mammalian oocytes. In recent years, a cryopreservation medium and protocol have been developed that allow oocytes of several species to be cryopreserved with high survival rates (>85%). Bovine, mouse, and human oocytes consistently reformed a morphologically normal spindle with chromosomes aligned along the metaphase plate (70% or higher) after first surviving cryopreservation (>87% survival for all species tested). Normal chromosome numbers were found in every second polar body tested by FISH (second polar bodies n = 4). It is concluded that the mammalian spindle, although depolymerized during cryopreservation, has the ability to reform, and in the mouse has been shown to function normally. Therefore, spindle reformation may not be a major cause for concern when storing mammalian MII oocytes.

Spindles, mitochondria and redox potential in ageing oocytes

Studies of human oocytes obtained from women of advanced reproductive age revealed that spindles are frequently aberrant, with chromosomes sometimes failing to align properly at the equator during meiosis I and II. Chromosomal analyses of donated and spare human oocytes and cytogenetic and molecular studies on the origin of trisomies collectively suggest that errors in chromosome segregation during oogenesis increase with advancing maternal age and as the menopause approaches. Disturbances in the fidelity of chromosome segregation, especially at anaphase I, leading to aneuploidy are prime causes of reduced developmental competence of embryos in assisted reproduction, as well as being responsible for the genesis of genetic disease. This review provides an overview of spindle formation and chromosome behaviour in mammalian oocytes. Evidence of a link between abnormal mitochondrial function in oocytes and somatic follicular cells, and finally disturbances in chromosome cohesion and segregation, and cell cycle control in aged mammalian oocytes, are also discussed.

Binucleated and micronucleated blastomeres in embryos derived from human assisted reproduction cycles

This prospective sequential, cohort study examined the two most common multinucleation phenotypes observed in the authors' clinic, binucleated (BN) and micronucleated (MN) blastomeres, and included all intracytoplasmic sperm injection (ICSI) patients <40 years of age with at least one multinucleated embryo in the cohort as observed on day 2 of development. Eighty ICSI cycles of 560 consecutive cycles had multinucleated embryos (14.3%). Of the 80 cycles, 770 embryos were derived; 183 (23.8%) were observed to be multinucleated. Blastocyst rates were significantly higher with BN than MN embryos. MN embryos were more often derived from embryos with poor pronuclear morphology (41/81 = 50.6%). Transferred mononucleated sibling embryos from the BN group had an ongoing pregnancy rate of 48% (12/25) compared with 15.4% (4/26 from the group with MN embryos (P = 0.03). The implantation rate for sibling embryos from the BN group was higher than for those from the MN group. Fluorescence in-situ hybridization (FISH) analysis showed that BN embryos had normal blastomeres significantly more frequently than MN embryos (9/28 (32.1%) versus 1/27 (3.7%), P = 0.016). Time-lapse photography showed that the nuclei of both morphologies dissolved independently before the next mitotic division and that BN blastomeres definitely have two distinct nuclei. These observations indicate two diverse morphologies and causal mechanisms. Time-lapse photography showed that both were subject to independent dissolution of their nuclear membrane suggesting an asynchrony between the nuclei and a possible interruption in proper nuclear and cell division. Multinucleation should definitely be looked for during IVF assessment. Excluding these embryos from transfer is prudent practice.

An overview of oocyte cryopreservation

The ability to cryopreserve human oocytes and store them indefinitely would be beneficial for cancer patients at risk of becoming sterile after therapy, allow women to delay reproduction, and alleviate religious concerns associated with embryo storage. In 1986, Chen was the first to report a pregnancy originating from a frozen-thawed human oocyte. Although over 100 babies have been born from oocyte storage since then, pregnancy rates remain unacceptably low. Adapting embryo cryopreservation techniques to oocyte storage has had limited success and new reproducible methods are needed. Problem areas other than intracellular ice formation and osmotic effects need to be identified. A broad approach of critical analysis should be conducted regarding the entire cryopreservation process from pre-equilibration and cooling, to thawing and stepout. All established facets deserve reanalysis in order to assess which aspects can be optimized or changed so that cellular demise can be avoided and cellular viability enhanced. New methods, including the use of choline-based media and vitrification have proven useful in increasing survival and pregnancy rates in some clinics. Other methods yet untested, such as injection of complex carbohydrates into the oocyte, deserve further studies. Vitrification research has led to the formulation of new ideas and has demonstrated the flexibility of cells to survive cryopreservation. Although successful, vitrification protocols are potentially harmful and technically challenging, due to elevated cryoprotectant concentrations and rapid cooling rates. Bovine embryo vitrification methods have been used to store human oocytes and embryos, particularly blastocysts with some success. Vitrification solutions containing high molecular weight polymers have also proved beneficial by reducing solution toxicity. In general, further advances are needed to improve human oocyte storage before widespread routine clinical use.

Developmental consequences of cryopreservation of mammalian oocytes and embryos

During the last three decades, significant advances have been made in successful cryopreservation of mammalian preimplantation embryos, and more recently oocytes. The ability to cryopreserve, thaw, and establish pregnancies with supernumerary preimplantation embryos has become an important tool in fertility treatment. Human oocyte cryopreservation has practical application in preserving fertility for individuals at risk of compromised egg quality due to cancer treatments or advanced maternal age. While oocyte/embryo cryopreservation success has increased over time, there is still room for improvement. Oocytes and embryos are susceptible to cryo-damage, which collectively entails cellular damage caused by mechanical, chemical, or thermal forces during the freeze-thaw process. Basic studies focused on understanding cellular structures, their composition, and more importantly their functions, in normal cell developments will continue to be critical in assessing, understanding, and correcting oocyte/embryo cryo-damage. This review will delineate many of the oocyte/embryo intracellular and extracellular structures that are or may be compromised during cryopreservation. A global theme presented throughout this review is that many structural components of the oocyte/embryo also have essential functional roles in development. Compromising these cellular structures, and thus their cellular homeostatic functions, can deleteriously influence initial cryo-survival or compromise subsequent normal development through effects on the oocyte and/or early embryo.

Live birth and normal 1-year follow-up of a baby born after transfer of cryopreserved embryos from rescue intracytoplasmic sperm injection of 1-day-old oocytes

OBJECTIVE

To report the birth and normal pediatric follow-up of the first baby born after transfer of embryos derived from cryopreserved rescue intracytoplasmic sperm injection (ICSI).

DESIGN

Case report.

SETTING

Academic fertility unit.

PATIENT(S)

A 36-year-old woman with unexplained infertility.

INTERVENTION(S)

Reinsemination by ICSI ("rescue" ICSI) followed by cryopreservation at the pronuclear stage was performed after partial fertilization failure.

MAIN OUTCOME MEASURE(S)

Pregnancy, birth, and 1-year follow-up of the baby born after the transfer of the cryopreserved rescue ICSI embryos.

RESULT(S) AND CONCLUSION(S)

Zygotes obtained after rescue ICSI were able to tolerate the process of cryopreservation and resulted in a viable pregnancy and delivery.

Preliminary experience of ovarian tissue cryopreservation procedure: alternatives, perspectives and feasibility

Chemotherapy and radiotherapy induce premature ovarian failure in many patients treated for oncological or benign diseases. The present paper reviews the risk of developing premature ovarian failure according to the type of treatment and the different options to preserve fertility, focusing on the cryopreservation of ovarian tissue. This technique constitutes a promising approach to preserve the fertility of young patients and offers the advantage of storing a large number of follicles that could be subsequently transplanted or cultured in vitro to obtain mature oocytes. Based on 34 requests, from which 19 were performed, the feasibility of the ovarian cryopreservation procedure is evaluated. The medical and ethical approaches of this protocol are also discussed. Cryopreservation of ovarian tissue constitutes new hope for many patients, but must still be kept for selected cases, with a significant risk of premature ovarian failure after treatments such as bone marrow transplantation.

Change of the Mitochondrial Distribution in Mouse OoplasmDuring In Vitro Maturation

Mitochondria (mt) have been reported to be closely related to the maturation of mammalian oocytes, but their function in oocyte maturation has not been elucidated. In this study, we examined the kinetics of mt and chromatin configuration during in vitro maturation of mouse oocytes to clarify the relationship between oocyte maturation and mitochondrial distribution morphologically. Oocytes were recovered from 6-to 8-wk-old ICR strain female mice. Germinal vesicle (GV) -stage oocytes were divided into 4 groups and cultured: group A, oocytes collected after pregnant mare serum gonadotropin (PMSG) injection; and group B, oocytes collected after PMSG-human chorionic gonadotropin injection. Groups A and B were subdivided into 2 groups: denuded oocytes (DO) and cumulus-enclosed-oocytes (CEO). At 0, 4, 8, 12 and 16 h from the onset of the culture, oocytes were fixed and stained to visualize alpha-tubulin, chromatin and mt using confocal laser scanning microscopy (CLSM). It was observed that mt aggregated around the nucleus from the GV-stage through progression to germinal vesicle breakdown (GVBD). With the movement of the nucleus, mt were concentrated around the nucleus and polarized. The maturation rate (the rate of the first polar body extrusion) and the fertilization rate of CEO were significantly higher than that of DO in both groups A (p<0.01) and B (p<0.05). During the GV-stage to GVBD, the rate of mitochondrial aggregation around the nucleus tended to be high in group A (CEO). The rates of mitochondrial polarization in MI and MII oocytes were 76.1% with in-vitro maturation (IVM) and 86.7% with in-vivo-maturation, respectively; the rate was significantly higher in in-vivo-maturation-oocytes than in IVM-oocytes (p<0.01). From the present results it can be considered that aggregaton of mitochondria around the nucleus was essential for maturation, fertilization and development.