Factors affecting low temperature survival of mammalian oocytes

The effect of a warmed enema during ovum pick-up on subsequent in vitro oocyte maturation in Southern white rhinoceros (Ceratotherium simum simum)

BACKGROUND

Rhinoceros are currently one of the most threatened mammal species globally. Slow population growth, increased poaching and habitat destruction have led to increased conservation efforts for each species. Assisted reproductive technologies (ART) have been implemented in an attempt to aid reproductive outputs for the conservation of these endangered species. Developing species-specific ART programmes for wildlife have been challenging. Temperature control during oocyte recovery is essential for ensuring in vitro success.

OBJECTIVE

This study is the first to investigate the effect of enema warming prior to trans-rectal ovum pick-up (OPU) on in vitro oocyte maturation in Southern white rhinoceros (Ceratotherium simum simum).

METHODS

OPUs were performed on 20 rhinoceros cows from three different game farms in South Africa; oocytes were transported to one of two in vitro fertilisation laboratories for culture. The enema fluid was either warmed to 32 °C or not warmed prior to the OPU. Location of the farm, the different laboratories, ambient temperature, season, aspiration probe temperature, media type and enema temperature were investigated as predictor variables for oocyte maturation success.

RESULTS

After considering all other potential covariates, warming of the enema fluid was the only independent predictor of in vitro oocyte maturation success during this study.

CONCLUSION

Oocytes retrieved from rhinoceros cows that received an enema warmed to 32 °C were 2.3 times more likely to mature in vitro compared to oocytes from cows that received an unwarmed enema; the findings can be implemented in other rhinoceros ART programmes and in conservation efforts of other endangered mammalian species.

Use of confocal microscopy and intracytoplasmic sperm injection (ICSI) to assess viability of equine oocytes from young and old mares after vitrification

BACKGROUND

The impact of vitrification on oocyte developmental competence as a function of donor age remains an important issue in assisted reproductive technologies (ARTs).

METHODS

Equine germinal vesicle (GV) or metaphase II (M(II) oocytes were vitrified using the Cryotop® method. Spindle organization and chromosome alignment were evaluated from confocal imaging data sets of in vivo (IVO) or in vitro (IVM) matured oocytes subjected to vitrification or not. Intracytoplasmic sperm injection (ICSI) from the same groups was used to assess developmental potential.

RESULTS

An increase in chromosome misalignment was observed in spindles from older mares when compared to those of younger mares (P < 0.05). When MII oocytes subjected to vitrification were examined following warming, there was no difference in the percentage of oocytes displaying chromosome misalignment. Next, GV oocytes, collected from the ovaries of younger and older mares, were compared between fresh IVM and IVM following vitrification and warming. For nonvitrified samples, an age difference was again noted for spindle organization and chromosome alignment, with a higher (P < 0.05) percentage of normal bipolar meiotic spindles with aligned chromosomes observed in nonvitrified oocytes from young versus older mares. Vitrification led to a reduction of spindle length (P < 0.05) for oocytes from old mares, whether vitrified at GV or MII stages, whereas this effect was not observed in oocytes from young mares except those vitrified at GV and subjected to IVM. Oocyte developmental potential after vitrification was evaluated after ICSI of vitrified and warmed MII or GV oocytes from young mares. From 25 MII oocytes, 18 oocytes were injected with sperm, and six blastocysts were produced, which, upon transfer to mares' uteri, resulted in four pregnancies. Immature (GV) oocytes collected from live mares were also vitrified, warmed, and matured in vitro before ICSI. In this group, nonvitrified, control, and vitrified oocytes did not differ (P > 0.05) with respect to the incidence of maturation to MII, cleavage after ICSI, or blastocyst development.

CONCLUSION

These findings demonstrate an effect of maternal age in an equine model at the level of meiotic spindle integrity and chromosome positioning that is influenced by both the meiotic stage at which oocytes are vitrified and whether meiotic maturation occurred in vivo or in vitro.

Effects of various freezing containers for vitrification freezing on mouse oogenesis

Background

In the present study, various freezing containers were tested for mouse embryos of respective developmental stages; embryos were vitrified and then their survival rate and developmental rate were monitored. Mouse two cell, 8 cell, and blastula stage embryos underwent vitrification freezing-thawing and then their recovery rate, survival rate, development rate, and hatching rate were investigated.

Methods

EM-grid, OPS, and cryo-loop were utilized for vitrification freezing-thawing of mouse embryos.

Results

It was found that recovery rate and survival rate were higher in the group of cryo-loop compared to those of EM-grid (p < 0.05). Embryonic development rate, two cell embryos to blastocyst, as well as hatching rate were higher in the control group compared to the EM-grid group and OPS group (p < 0.05), yet no difference was noted between the control group and cryo-loop group. Development rate and hatching rate of eight cell morulae and blastocysts were all lower in the treatment groups than the control group whilst hatching rate of blastocysts was higher in the control group compared to the groups of EM-grid and OPS (p < 0.05); although the cryo-loop group was shown to be slightly higher than other groups, it was not statistically significant.

Conclusions

In the study, we investigate effects of freezing containers on vitrified embryos of respective developmental stages; it was demonstrated that higher developmental rate was shown in more progressed (or developed) embryos with more blastomeres. There was however, no difference in embryonic development rate was shown amongst containers. Taken together, further additional studies are warranted with regards to 1) manipulation techniques of embryos for various vitrification freezing containers and 2) preventive measures against contamination via liquid nitrogen.

Ultra-Structural Alterations in In Vitro Produced Four-Cell Bovine Embryos Following Controlled Slow Freezing or Vitrification

Cryopreservation is the process of freezing and preserving cells and tissues at low temperatures. Controlled slow freezing and vitrification have successfully been used for cryopreservation of mammalian embryos. We investigated the effect of these two cryopreservation methods on in vitro produced four-cell stage bovine embryos which were classified according to their quality and separated into three groups. The first group was maintained as untreated controls (n = 350). Embryos of the second (n = 385) and the third (n = 385) groups were cryopreserved either by controlled slow freezing or by vitrification. Embryos in groups 2 and 3 were thawed after 1 day. Hundred embryos were randomly selected from the control group, and 100 morphologically intact embryos from the second and third group were thawed after 1 day and cultured to observe the development up to the blastocyst stage. The blastocyst development rate was 22% in the control group, 1% in the slow-freezing group and 3% in the vitrification group. Remaining embryos of all three groups were examined by light microscopy, transmission electron microscopy and immunofluorescence confocal microscopy with subsequent histological staining procedures. Cryopreservation caused degenerative changes at the ultra-structural level. Compared with vitrification, slow freezing caused an increased mitochondrial degeneration, cytoplasmic vacuolization, disruption of the nuclear and plasma membrane integrity, organelle disintegration, cytoskeletal damage, a reduced thickness of the zona pellucida and a formation of fractures in the zona pellucida. Further studies are required to understand and decrease the harmful effects of cryopreservation.

Changes in mitochondrial function in porcine vitrified MII-stage oocytes and their impacts on apoptosis and developmental ability

The purpose of this study was to investigate the changes in mitochondria in porcine MII-stage oocytes after open pulled straw (OPS) vitrification and to determine their roles in apoptosis and in vitro developmental ability. The mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS) level, adenosine-5'-triphosphate (ATP) concentration, mitochondrial distribution, mitochondrial ultrastructure, early-stage apoptosis with Annexin V-FITC staining, survival rate, parthenogenetic developmental ability and related gene expression were measured in the present experiments. The results showed that: (1) the mitochondrial ΔΨm of vitrified-thawed oocytes (1.05) was lower than that of fresh oocytes 1.24 (P<0.05). (2) ROS level in the OPS vitrification group was much higher than that of the fresh group, while the ATP concentration was much lower than that of fresh group (P<0.05). (3) Early-stage apoptosis rate from the OPS vitrification group (57.6%) was much higher than that of fresh group (8.53%) (P<0.05), and the survival rate and parthenogenetic cleavage rate of OPS vitrified oocytes were much lower than those from fresh ones (P<0.05). (4) Vitrification not only disrupted the mitochondrial distribution of porcine MII-stage oocytes, but also damaged the mitochondrial ultrastructure. (5) After vitrification, the gene expression level of Dnm1 was up-regulated, and other four genes (SOD1, Mfn2, BAX and Bcl2) were down-regulated. The present study suggested that not only the morphology and function of mitochondria were damaged greatly during the vitrification process, but also early-stage apoptosis was observed after vitrification. Intrinsic mitochondrial pathway could be in involved in the occurrence of apoptosis in vitrified-thawed porcine oocytes.

Development of a novel vitrification method for chondrocyte sheets

Background

There is considerable interest in using cell sheets for the treatment of various lesions as part of regenerative medicine therapy. Cell sheets can be prepared in temperature-responsive culture dishes and applied to injured tissue. For example, cartilage-derived cell sheets are currently under preclinical testing for use in treatment of knee cartilage injuries. The additional use of cryopreservation technology could increase the range and practicality of cell sheet therapies. To date, however, cryopreservation of cell sheets has proved impractical.

Results

Here we have developed a novel and effective method for cryopreserving fragile chondrocyte sheets. We modified the vitrification method previously developed for cryopreservation of mammalian embryos to vitrify a cell sheet through use of a minimum volume of vitrification solution containing 20% dimethyl sulfoxide, 20% ethylene glycol, 0.5 M sucrose, and 10% carboxylated poly-L-lysine. The principal feature of our method is the coating of the cell sheet with a viscous vitrification solution containing permeable and non-permeable cryoprotectants prior to vitrification in liquid nitrogen vapor. This method prevented fracturing of the fragile cell sheet even after vitrification and rewarming. Both the macro- and microstructures of the vitrified cell sheets were maintained without damage or loss of major components. Cell survival in the vitrified sheets was comparable to that in non-vitrified samples.

Conclusions

We have shown here that it is feasible to vitrify chondrocyte cell sheets and that these sheets retain their normal characteristics upon thawing. The availability of a practical cryopreservation method should make a significant contribution to the effectiveness and range of applications of cell sheet therapy.

Vitrification of bovine oocytes: implications of follicular size and sire on the rates of embryonic development

PURPOSE

The objectives were to test how the source of oocytes and semen impacted vitrification of large numbers of bovine oocytes and subsequent IVF and early embryo development to test procedures that may assist with assisted reproductive technologies in humans.

METHODS

Bovine oocytes were vitrified from follicles of different diameters, small (< or =4 mm) and medium (4 to 10 mm), using nylon mesh. Oocytes were exposed to the cryoprotectant composed of 40% (v/v) ethylene glycol, 18% (w/v) Ficoll-70, and 0.3 M sucrose in three stepwise dilutions. Thawing was conducted with a series of 0.5, 0.25 and 0.125 M sucrose dilutions in 20% fetal bovine serum.

RESULTS

The cleavage (39.1% vs. 58.5%) and blastocyst rates (5.1% vs. 22.9%) were significantly lower for the vitrified oocytes. Follicle size had a significant impact on the development of embryos. Sires had significant effects on embryonic developmental rates.

CONCLUSIONS

We conclude that differences in development exist due to follicle source and sire used for IVF after vitrification.

A critical evaluation of ovarian tissue cryopreservation and grafting as a strategy for preserving the human female germline

Ovarian tissue freezing has been used successfully in animals and it has recently begun to be offered clinically to young women who have medical conditions with a high risk of sterility. Although no frozen human ovarian grafts have yet been returned to the donor and resulted in a pregnancy, there are many indications that this procedure should be feasible. Although live young have been derived from frozen grafts in several species, research should aim to make further improvements to the cryopreservation and grafting procedures to optimize follicle survival, and hence minimize the amount of tissue that needs to be collected, stored and returned. Ovarian tissue freezing, particular if used in combination with egg and embryo freezing, should allow a patient to safeguard their chance of becoming a parent later (Table 1). In cases where the patient has a systemic cancer or infection and malignant cells or viruses may be present in the systemic circulation and the gonadal tissue, ovarian tissue could be collected and frozen, but grafting is not currently recommended (Table 3).

Comparison of survival and embryonic development in human oocytes cryopreserved by slow-freezing and vitrification

OBJECTIVE

To compare the survival, fertilization, early embryonic development, and meiotic spindle assembly and chromosome alignment in frozen-thawed human oocytes after slow-freezing and vitrification.

DESIGN

A randomized study.

SETTING

A university-affiliated assisted reproductive center.

PATIENT(S)

Donated extra eggs from women undergoing assisted reproduction treatment.

INTERVENTION(S)

A total of 605 mature oocytes were divided into a slow-freezing group and a vitrification group for cryopreservation.

MAIN OUTCOME MEASURE(S)

After frozen-thawing, the oocyte survival rate, spindle assembly, and chromosome alignment were compared. The surviving oocytes were inseminated by intracytoplasmic sperm injection, and the rate of fertilization and embryo development were also compared in two groups.

RESULT(S)

The oocyte survival rate was statistically significantly lower in the slow-freezing group (75 out of 123, 61.0%) than the vitrification group (268 out of 292, 91.8%). The fertilization rate was the same for both groups, but the cleavage rate of zygotes was statistically significantly different between two groups: (slow-freezing, 25/46 (54.4%) versus vitrification, 142 out of 182 (78.0%). There was a considerable difference in the percentage of high-quality embryos between slow-freezing and vitrification groups: 6 out of 25 (24.0%) versus 60 out of 142 (42.3%), respectively. The percentage of blastocyst development was statistically significantly higher in the vitrification group (47 out of 60, 33.1%) than in the slow-freezing group (3 out of 25, 12.0%). There was a much higher percentage of oocyte abnormalities in terms of spindle assembly and chromosome alignment in the slow-freezing group (25 out of 64, 39.1%) compared with the vitrification group (11 out of 62, 17.7%).

CONCLUSION(S)

Vitrification is superior to the slow-freezing method, leading to improved oocyte survival rate, fertilization, and embryonic development in vitro. These results may be related to vitrified human oocytes incurring less damage to spindle integrity and chromosome alignment.

Effect of slow freezing on morphology and developmental competence of buffalo (Bubalus bubalis) immature oocytes

The present study was conducted to evaluate the effects of three cryoprotectants, dimethyl sulphoxide (DMSO), ethylene glycol (EG) and 1,2-propanediol (PROH), each used at two concentrations (1.0 and 1.5 M) on the morphology, maturation rate and developmental capacity of usable quality immature buffalo oocytes subjected to slow freezing. The addition of the cryoprotectant before freezing and its dilution after thawing were carried out in a two- (for 1.0 M) or three-step manner (for 1.5 M). The incidence of damage was found to be significantly higher (P<0.05) with the lower concentration of 1.0 M, compared to that with 1.5 M for all the three cryoprotectants examined. The proportion of immature oocytes recovered in a morphologically normal state was significantly higher (P<0.05) for DMSO than those for EG or PROH at both 1.0 and 1.5 M concentrations. Among the six combinations evaluated, that of DMSO at 1.5 M concentration was found to be superior to others. Irrespective of the type or concentration of the cryoprotectant, partial or complete loss of the cumulus mass was the most prevalent damage. Following in vitro maturation, the nuclear maturation rate was significantly higher (P<0.05) for DMSO than those for EG or PROH at both 1.0 and 1.5 M concentrations. When the in vitro matured oocytes were subjected to in vitro fertilization after slow freezing, using 1.5 M DMSO as cryoprotectant, 4.5% and 0.6% of them were able to develop to morulae and blastocysts, respectively, on Day 9 post insemination, compared to 19.2% and 10.6%, respectively, for the controls. In conclusion, DMSO was more effective than EG or PROH for the slow freezing of immature buffalo oocytes and blastocysts could be produced from immature buffalo oocytes subjected to slow freezing in 1.5 M DMSO.

Effect of choline-supplemented sodium-depleted slow freezing versus vitrification on mouse oocyte meiotic spindles and chromosome abnormalities

OBJECTIVE

To evaluate and compare vitrification and choline-supplemented sodium-depleted slow freezing of mouse oocytes.

DESIGN

Animal study.

SETTING

University-affiliated hospital.

ANIMAL(S)

CD-1 mice.

INTERVENTION(S)

Oocyte cryopreservation by vitrification or choline-supplemented sodium-depleted slow freezing.

MAIN OUTCOME MEASURE(S)

Survival rate, fertilization and embryonic development in vitro, meiotic spindle and chromosome configuration, and aneuploidy screening after parthenogenetic activation.

RESULT(S)

A total of 564 oocytes were vitrified, and 791 oocytes were cryopreserved using the slow freezing. The survival rates were 91.8% (518/564) and 73.3% (579/791), respectively. After IVF, the cleavage and blastocyst formation rates of vitrified oocytes were significantly higher than those of slow-frozen oocytes (63.6% vs. 39.9% and 30.50% vs. 20.2%, respectively). Vitrified oocytes were more likely than slow-frozen oocytes to maintain normal meiotic spindles and chromosome alignment (86.9% vs. 70.1%). However, the incidence of aneuploidy was similar in vitrified oocytes and slow-frozen oocytes (9.30% vs. 8.7%).

CONCLUSION(S)

Vitrification is superior to choline-supplemented sodium-depleted slow freezing, leading to improved survival, fertilization, and embryonic development in vitro. Analysis of meiotic spindle integrity and chromosome alignment indicates that less damage was detected in vitrified oocytes. However, the incidence of aneuploidy is similar in both vitrified and slow-frozen oocytes.

Effects of cumulus cells, different cryoprotectants, various maturation stages and preincubation before insemination on developmental capacity of frozen-thawed bovine oocytes

To improve freezability of bovine follicular oocytes, it is necessary to minimize injury to the oocytes caused by freezing and the toxicity of cryoprotectants. The maturing ability of frozen-thawed follicular oocytes with or without cumulus complexes was tested. The proportion of frozen-thawed follicular oocytes reaching the metaphasc II (M II) stage after in vitro maturation of 24 h was significantly (P < 0.05) higher in cumulus oocyte complexes (COCs; 44%) than in denuded oocytes (30%). Oocytes were cultured for 0, 6, 12, 18 or 24 h then frozen-thawed with 1,2-propanediol (PROH) or dimethyl sulfoxide (DMSO), and cultured for 24, 18, 12, 6 or 0 h respectively. In PROH, 24:0 (67%) showed significantly (P < 0.05) higher maturation rate than 0:24 (38%), 6:18 (41%). In DMSO, 18:6 (72%) and 24:0 (61%) showed significantly (P < 0.05) higher maturation rate than 0:24 (30%), 6:18 (33%) and 12:12 (44%). In case of 18:6, DMSO (72%) showed significant (P < 0.05) higher maturation rate than PROH (52%), however in case of 0:24, 6:18, 12:12 and 24:0, there was no significant (P < 0.05) difference in the maturation rate between PROH and DMSO. The proportion of embryos developed to > or = 2 cell, > or = 8 cell, morula and blastocyst in 18:6 DMSO (35, 10, 3 and 0%) and 24:0 PROH (38, 12, 5 and 0%) was significantly (P < 0.05) lower than that of fresh oocytes (67, 38, 31 and 16%). There was no significant (P < 0.05) difference in the rate of embryos that developed to > or = 2 cells, > or = 8 cells, morulae and blastocysts between PROH and DMSO. When the frozen oocytes were grouped as rewarming culture (21:2 PROH) and control (24:0 PROH), there was no significant (P < 0.05) difference in the rate of embryos that developed to > or = 2 cells, > or = 8 cells, morulae and blastocysts between 24:0 PROH (42, 24, 11 and 1%) and 21:2 PROH (51, 29, 16 and 4%) but 21:2 PROH showed slightly higher developmental capacity than 24:0 PROH. Transferable blastocysts (4%) were obtained in 21:2 PROH when the frozen-thawed follicular oocytcs were fertilized and cultured for 8 to 9 d.

A review on reproductive biotechnologies for conservation of endangered mammalian species

This review describes the use of modern reproductive biotechnologies or assisted reproductive techniques (ART) including artificial insemination, embryo transfer/sexing, in vitro fertilization, gamete/embryo micromanipulation, semen sexing, genome resource banking, and somatic cell nuclear transfer (cloning) in conservation programs for endangered mammalian species. Such biotechnologies allow more offspring to be obtained from selected parents to ensure genetic diversity and may reduce the interval between generations. However, the application of reproductive biotechnologies for endangered free-living mammals is rarer than for endangered domestic breeds. Progress in ART for non-domestic species will continue at a slow pace due to limited resources, but also because the management and conservation of endangered species is biologically quite complex. In practice, current reproductive biotechnologies are species-specific or inefficient for many endangered animals because of insufficient knowledge on basic reproduction like estrous cycle, seasonality, structural anatomy, gamete physiology and site for semen deposition or embryo transfer of non-domestic species.

Allogeneic and autologous ovarian orthotopic transplantation without a vascular pedicle: morphological, endocrinologic and natural pregnancy assessment

BACKGROUND

To assess the natural pregnancy of rabbits submitted to bilateral oophorectomy and orthotopic allogeneic or autologous intact and sliced ovarian transplantation without a vascular pedicle, and to determine the morpho-functional aspects of the transplanted ovaries.

METHODS

Fifty-six female rabbits were studied. The ovaries were removed and orthotopically transplanted or replaced without vascular anastomoses: Group 1 (n = 8), only laparotomy and laparorrhaphy; Group 2A (n = 8), intact ovaries were transplanted on both sides; Group 2B (n = 8), both ovaries were sliced and orthotopically transplanted; Group 2C (n = 8), an intact ovary was transplanted on one side and a sliced ovary on the other side; Groups 3A-C, the ovaries were reimplanted according to the procedure and subgroups described for Group 2. Three months later, the animals were paired with males for copulation. Estradiol, progesterone, FSH and LH hormone levels were assessed. A histological study was carried out, and the number of pregnancies and litters were also determined. Chi-squared test compared the number of pregnancies and litters. One-way anova and the Tukey-Kramer tests compared the hormonal dosages.

RESULTS

Pregnancies occurred in seven rabbits of Group 1, in 37.5% of rabbits in Groups 2A and 3A, in 50% of groups 2B, 3B and 3C, and in 62.5% of group 2C. Hormone levels and histology confirmed the vitality of all ovaries.

CONCLUSIONS

Intact or sliced orthotopic allogeneic and autologous ovarian transplantation without a vascular pedicle is viable in rabbits, and preserves their hormonal and fertile functions.

Morphologic, endocrinologic and natural pregnancy assessment of allogeneic ovarian orthotopic transplantation without a vascular pedicle in rabbits

OBJECTIVE

The objective was to assess the natural pregnancy of rabbits subjected to bilateral oophorectomy and orthotopic allogeneic intact and sliced ovarian transplantation without a vascular pedicle, and to determine the morphofunctional aspects of the transplanted ovaries.

STUDY DESIGN

Thirty-two female rabbits were studied. The ovaries were removed and orthotopically transplanted without vascular anastomoses between the two breeds of rabbits. In Group 1 (n=8), only laparotomy and laparorrhaphy were performed, in Group 2A (n=8) intact ovaries were transplanted on both sides, in Group 2B (n=8) both ovaries were sliced and orthotopically transplanted, and in Group 2C (n=8) an intact ovary was transplanted on one side and a sliced ovary on the other side. Three months later, the animals were paired with males for copulation. Estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone levels were assessed. A histologic study was carried out and the numbers of pregnancies and litters were also determined.

RESULTS

Pregnancies occurred in seven rabbits in Group 1, 37.5% of rabbits in Group 2A, 50% in Group 2B, and 62.5% in Group 2C. Hormone levels and histology confirmed the vitality and function of all ovaries.

CONCLUSIONS

Intact or sliced orthotopic allogeneic ovarian transplantation without a vascular pedicle is viable in rabbits, and preserves their hormonal and fertile functions.

Subzero water transport characteristics and optimal rates of freezing rhesus monkey (Macaca mulatta) ovarian tissue

The purpose of the present study was to examine the effect of two different suprazero (room temperature +25 degrees C to +4 degrees C) cooling conditions on the measured water transport response of primate (Macaca mulatta) ovarian tissue in the presence and absence of cryoprotective agents (CPAs). Freshly collected Macaca mulatta (rhesus monkey) ovarian tissue sections were cooled at either 0.5 degrees C/min or 40 degrees C/min from 25 to 4 degrees C. A shape independent differential scanning calorimeter (DSC) technique was then used to measure the volumetric shrinkage during freezing of ovarian tissue sections at a freezing rate of 5 degrees C/min in the presence and absence of three different CPAs (0.85 M glycerol, 0.85 M dimethylsulfoxide, and 0.85 M ethylene glycol). Thus, water transport during freezing of primate ovarian tissue was obtained at eight different conditions (i.e., at four different freezing media with two different suprazero cooling conditions). The water transport response of ovarian tissue cooled rapidly from 25 to 4 degrees C was significantly different (P < 0.01) than that of slow cooled tissue, in the freezing media without CPAs and with dimethylsulfoxide. However, the differences in the measured water transport response due to the imposed suprazero cooling conditions were reduced with the addition of glycerol and ethylene glycol (statistically different with P < 0.05). By fitting a model of water transport to the experimentally obtained volumetric shrinkage data the best-fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The best-fit parameters of water transport in primate ovarian tissue sections ranged from: L(pg) = 0.7 to 0.15 microm/min-atm and E(Lp) = 22.1 to 32.1 kcal/mol (the goodness of fit parameter, R(2) > 0.96). These parameters suggest that the "optimal rates of cryopreservation" for ovarian tissue are significantly dependent upon suprazero cooling conditions and the choice of CPA.

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.

Suprazero cooling conditions significantly influence subzero permeability parameters of mammalian ovarian tissue

To model the cryobiological responses of cells and tissues, permeability characteristics are often measured at suprazero temperatures and the measured values are used to predict the responses at subzero temperatures. The purpose of the present study was to determine whether the rate of cooling from +25 to +4 degrees C influenced the measured water transport response of ovarian tissue at subzero temperatures in the presence or absence of cryoprotective agents (CPAs). Sections of freshly collected equine ovarian tissue were first cooled either at 40 degrees C/min or at 0.5 degrees C/min from 25 to 4 degrees C, and then cooled to subzero temperatures. A shape-independent differential scanning calorimeter (DSC) technique was used to measure the volumetric shrinkage during freezing of equine ovarian tissue sections. After ice was induced to form in the extracellular fluid within the specimen, the sample was frozen from the phase change temperature to -50 degrees C at 5 degrees C/min. Replicate samples were frozen in isotonic medium alone or in medium containing 0.85 M glycerol or 0.85 M dimethylsulfoxide. The water transport response of ovarian tissue samples cooled at 40 degrees C/min from 25 to 4 degrees C was significantly different (confidence level >95%) from that of tissue samples cooled at 0.5 degrees C/min, whether in the presence or absence of CPAs. We fitted a model of water transport to the experimentally-derived volumetric shrinkage data and determined the best-fit membrane permeability parameters (L(pg) and E(Lp)) of equine ovarian tissue during freezing. Subzero water transport parameters of ovarian tissue samples cooled at 0.5 degrees C/min from 25 to 4 degrees C ranged from: L(pg) = 0.06 to 0.73 microm/min.atm and E(Lp) = 6.1 to 20.5 kcal/mol. The corresponding parameters of samples cooled at 40 degrees C/min from 25 to 4 degrees C ranged from: L(pg) = 0.04 to 0.61 microm/min.atm and E(Lp) = 8.2 to 54.2 kcal/mol. Calculations made of the theoretical response of tissue at subzero temperatures suggest that the optimal cooling rates to cryopreserve ovarian tissue are significantly dependent upon suprazero cooling conditions.

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.

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 ovary storage time and temperature on DNA fragmentation and development of porcine oocytes

The present study was conducted to investigate the effects of storage time and temperature of porcine ovaries on the quality and nuclear maturation in vitro of oocytes obtained from stored ovaries and their subsequent development after in vitro fertilization. The ovaries were stored in physiological saline for 0, 3, 6, 9 and 12 h at various temperatures (4, 15, 25 and 35 C). The pH of follicular fluid obtained from the ovaries, DNA fragmentation of the oocyte nucleus and meiotic competence of oocytes were examined. Some oocytes from ovaries stored at 15, 25 and 35 C for 6 h were fertilized in vitro, and then cultured for 7 days to examine the ability of embryos to develop to the blastocyst stage. When the ovaries were stored at 35 C, the pH of follicular fluid decreased and the proportions of oocytes with DNA fragmented nuclei increased as the storage time was prolonged, and the storage of ovaries for 6, 9 and 12 h resulted in lower maturation rates of oocytes. When the ovaries were stored at 4, 15, 25 and 35 C for 6 h, the storage at higher temperatures (> or =15 C) decreased the pH of follicular fluid and induced nucleic DNA fragmentation in higher proportions of oocytes. None of the oocytes from ovaries stored at 4 C reached metaphase II. The storage of ovaries at 15 C reduced the rates of in vitro fertilized oocytes and subsequent embryo development, but there were no significant differences in the rates of fertilization and blastocyst formation between oocytes from ovaries stored at 25 C and 35 C. Our findings indicate that the storage of ovaries at 25-35 C for 6 h is effective for maintaining the developmental competence of porcine oocytes even though the development rates were lower than those of ovaries stored at 35 C for 3 h.

Extrusion and removal of lipid from the cytoplasm of porcine oocytes at the germinal vesicle stage: Centrifugation under hypertonic conditions influences vitrification

In the present study, we examined a novel lipid removal method, centrifugation in solutions made hypertonic by adding 0.27 M sugar. This allowed the lipid to be extruded and removed without the loss of active mitochondria or extra cytoplasm. The type of sugar influenced the proportion of oocytes that could be stratified by centrifugation. Glucose induced the highest extrusion rate of lipid droplets. After vitrification the rates of survival, germinal vesicle breakdown and metaphase II were 30, 26, and 7%, respectively, for lipid-removed GV oocytes; this was significantly higher (P<0.05) than for corresponding vitrified lipid-intact oocytes (2, 0, and 0%, respectively). These results indicated that this method is useful to remove whole lipid droplets without losing mitochondria and improves cryotolerance of porcine GV oocytes.

Effects of Partial Removal of Cytoplasmic Lipid on Survival of Vitrified Germinal Vesicle Stage Pig Oocytes

This study was designed to investigate whether the partial removal of cytoplasmic lipid from immature pig oocytes prior to vitrification had any positive effects on subsequent maturation, fertilization and early development. Oocytes at the germinal vesicle stage were partially freed from cumulus cells and centrifuged, and then polarized cytoplasmic lipid was removed by micromanipulation. When cultured for 44-48 h, significantly fewer of the centrifuged oocytes reached metaphase II (M-II) than did the non-centrifuged oocytes (approximately 53% vs approximately 68%, respectively); however, no further reduction in the M-II rate was observed when centrifuged oocytes were then delipated prior to culture (approximately 47%). To evaluate their sensitivity to the equilibration and vitrification solutions containing ethylene glycol, non-centrifuged, centrifuged, and delipated oocytes were cultured continuously for several minutes in those solutions, then washed and cultured further; no significant differences in the M-II rates (approximately 20-27%) were observed among the three treatment groups. When oocytes were vitrified and then warmed, significantly more delipated oocytes reached M-II in culture (approximately 15%) than did the non-delipated oocytes, whether centrifuged or not (approximately 4% in each group). When delipated, vitrified and matured oocytes were microsurgically injected with frozen-thawed spermatozoa, approximately 39% were activated and male pronucleus formation was observed in approximately 40% of activated oocytes; none developed beyond the 4-cell stage. These results show that maturation in vitro of vitrified pig oocytes can be promoted by partial removal of cytoplasmic lipid prior to vitrification and that the vitrified oocytes can be fertilized, although the embryonic development obtained in this study was limited.

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.

Effects of cooling ovaries before oocyte aspiration on meiotic competence of porcine oocytes and of exposing in vitro matured oocytes to ambient temperature on in vitro fertilization and development of the oocytes

Experiments were conducted to evaluate the effects of cooling porcine ovaries to low temperature (4 degrees C, 15 degrees C, 20 degrees C, 25 degrees C or 30 degrees C) for 1 h on the meiotic competence of their oocytes. Moreover, it was determined whether or not the exposure of in vitro matured oocytes to ambient temperature (20 degrees C, 25 degrees C or 30 degrees C) for 1 h affects the fertilization and developmental competence of the oocytes. There was no difference between the proportions of oocytes that underwent maturation to metaphase II when isolated from control ovaries held at 35 degrees C and ovaries exposed to 30 degrees C. However, the percentages of oocytes from ovaries exposed to 25 degrees C or less were significantly lower than those of oocytes from ovaries exposed to 30 degrees C and control ovaries. The proportions of total and normal fertilization of oocytes that had been exposed to 20 degrees C before in vitro fertilization (IVF) were significantly lower than those of control oocytes maintained at 38.5 degrees C. However, cooling in vitro matured oocytes had no effects on their cleavage and development to blastocysts after IVF. These data suggest that exposing porcine ovaries to a low temperature of 25 degrees C or less before aspiration of oocytes may adversely affect their subsequent in vitro maturation. It may be necessary to maintain the oocytes at a temperature of more than 25 degrees C during manipulation of oocytes for retaining the fertilizability of the oocytes.

Intracytoplasmic sperm injection of frozen-thawed bovine oocytes and subsequent embryo development

Oocyte cryopreservation and intracytoplasmic sperm injection (ICSI) are advantageous to expand their usefulness in genetic engineering. Oocytes matured for 22 hr were vitrified in droplets of cryoprotectants (3.2 M ethylene glycol (EG), 2.36 M dimethyl sulfoxide (DMSO), 0.6 M sucrose) on copper electron microscope (EM) grids. After being warmed, the oocytes were cultured in IVM medium for an additional 2 hr. Sperm treated with dithiothreitol were utilized for ICSI. Oocytes injected with sperm were activated by combination of ionomycin with cycloheximide (CHX). The ICSI oocytes were compared for the rates of pronuclear formation, development, cell number, and the ratio of ICM to those of fresh ICSI and IVF control. The proportion of 2PN formation was significantly higher in IVF control (Group 1) than those in other treated groups. Among the treated groups a significant lower 2PN formation was observed in IVF-frozen-thawed than in ICSI-fresh and frozen-thawed groups. Cleavage rates in IVF-frozen-thawed and ICSI-frozen-thawed groups were significantly lower than those of IVF control and ICSI-fresh groups. In ICSI groups, the rates of cleavage and blastocyst in fresh oocytes were significantly higher than in frozen-thawed. Development rates into blastocysts in the ICSI-fresh and frozen-thawed groups were significantly lower than that of IVF control. Total cell number was significantly lower in both frozen-thawed IVF and ICSI groups than those in IVF-control and ICSI-fresh groups. However, the rates of the remaining cells that were found in the ICM were significantly higher in both frozen-thawed IVF and ICSI than in the IVF-control and ICSI-fresh groups. The results indicated that frozen-thawed bovine oocytes were suitable for ICSI procedure.

Use of sugars in cryopreserving human oocytes

In the last 20 years, a worldwide effort to cryopreserve oocytes has resulted in 40 infants and approximately 50 ongoing pregnancies being reported. While the ability to freeze human embryos has become a standard of practice in assisted reproductive technologies, obtaining reliable techniques for oocyte cryopreservation has been more difficult. The unique properties of the mature oocyte, such as the meiotic stage with sensitive spindle structure as well as the large cell volume, are responsible for the limited success obtained to date. There have been two approaches to cryopreserving the oocyte: (i) slow freeze-rapid thaw, and (ii) vitrification protocols with rapid cooling-rapid warming. Both methods have incorporated sugars (sucrose) as a beneficial non-permeating extracellular cryoprotectant. Studies of organisms that survive extreme conditions of freezing/dehydration have demonstrated the ability to accumulate intracellular sugars to afford protection and survival. A novel technique using microinjection of sugars into the oocyte for cryopreservation has been developed as an alternative approach to external addition of sugars. Freezing the human oocyte has been a challenging goal; however, developing research and efforts will, in the near future, provide women with an important option for their reproductive health.

Gestação obtida em coelha após ooforectomia bilateral e transplante ovariano homógeno

OBJETIVO: Verificar a possibilidade de fertilização natural após ooforectomia total bilateral e transplante ovariano homógeno ortotópico sem anastomose vascular e imunossuprimidos pela ciclosporina. MÉTODO: Foram utilizadas dez coelhas da raça Nova Zelândia Branca e Califórnia. Realizou-se ooforectomia total bilateral e transplante ortotópico dos ovários entre pares de animais. De um lado, foi transplantado o ovário íntegro e de outro, o ovário fatiado. Não houve anastomose vascular. A imunossupressão se deu com a administração ciclosporina através de tubo orogástrico diariamente, durante seis meses. Três meses depois, as fêmeas foram colocadas diariamente para copular com machos sabidamente férteis da raça Nova Zelândia Branca, por outros seis meses. No final do período do experimento, foram realizadas dosagens de estradiol, progesterona, hormônio folículo estimulante e hormônio luteinizante, além de estudo histológico dos ovários, tubas e úteros. RESULTADOS: Gravidezes ocorreram em cinco coelhas, sendo que, em quatro delas, houve nascimento de filhotes. As dosagens hormonais estiveram dentro da faixa de normalidade em todos os animais. Os ovários transplantados estavam rodeados de tecido conjuntivos, bem vascularizados e com folículos ovarianos em vários estádios de desenvolvimento. CONCLUSÕES: Obteve-se, com sucesso, a fertilização natural e manutenção hormonal feminina em coelhas submetidas a transplante homógeno de tecido ovariano sem anastomose vascular e imunossuprimidos pela ciclosporina.

Cold-induced calcium elevation triggers DNA fragmentation in immature pig oocytes

Fluo-4 loaded immature oocytes were cooled from 30 degrees C to various lower temperatures between 20 and 10 degrees C and changes in intracellular calcium (Ca(2+)) levels were measured. Pig oocytes cooled to 14 degrees C exhibited a clear biphasic Ca(2+) rise. Lower temperatures produced similar responses, while higher temperatures did not exert any effect. The Ca(2+) response appeared to rely on ryanodine dependent stores as removal of extracellular Ca(2+) and intracytoplasmic injection of heparin did not modify cold-induced Ca(2+) elevation, while procaine or ruthenium red virtually eliminated the response. Confocal analysis of subcellular Ca(2+) distribution during cooling revealed that the ion rises sharply within the nucleus. As Ca(2+) imbalance may activate nuclear endonucleases, DNA integrity of cooled pig oocytes was evaluated by TUNEL and comet assays. Most cooled oocytes showed clear signs of DNA fragmentation. Oocytes injected with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetracetic acid tetrapotassium salt (BAPTA), a Ca(2+) chelator, maintained their DNA integrity thus confirming that intracellular Ca(2+) is involved in triggering DNA fragmentation. The protective effect exerted by ruthenium red and/or procaine further confirmed this hypothesis. These data show that a moderate and transient cooling is sufficient to cause an intracellular Ca(2+) rise that leads to DNA damage. The addition of inhibitors of ryanodine dependent Ca(2+) stores may represent a valuable protective treatment to reduce chilling injuries.

Effects of cooling on meiotic spindle structure and chromosome alignment within in vitro matured porcine oocytes

Meiotic spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus-oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39 degrees C, 5% CO(2) in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4 degrees C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the meiotic spindle and chromosome alignment or returned to maturation medium at 39 degrees C for 2 hr for examination of spindle recovery. Most oocytes (65-71%) cooled to 24 degrees C showed partially depolymerized spindles but 81-92% of oocytes cooled at 4 degrees C did not have a spindle after cooling for 120 min. Quicker disassembly of spindles in the oocytes was observed at 4 degrees C than at 24 degrees C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited spindle recovery was observed in the oocytes cooled to both 4 and 24 degrees C regardless of cooling time. The effect of cooling on the spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the meiotic spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled.

Cryopreservation of goat oocytes and in vivo derived 2- to 4-cell embryos using the cryoloop (CLV) and solid-surface vitrification (SSV) methods

This study evaluated the efficiency and toxicity of two cryopreservation methods, solid-surface vitrification (SSV) and cryoloop vitrification (CLV), on in vitro matured oocytes and in vivo derived early stage goat embryos. In the SSV method, oocytes were vitrified in a solution of 35% ethylene glycol (EG), 5% polyvinyl-pyrrolidone (PVP), and 0.4% trehalose. Microdrops containing the oocytes were cryopreserved by dropping them on a cold metal surface that was partially immersed in liquid nitrogen. In the cryoloop method, oocytes were transferred onto a film of the CLV solution (20% DMSO, 20% EG, 10mg/ml Ficoll and 0.65 M sucrose) suspended in the cryoloop. The cryoloop was then plunged into the liquid nitrogen. In vivo derived embryos were vitrified using the same procedures. The SSV microdrops were warmed in a solution of 0.3M trehalose and those vitrified with CLV were warmed with incubation in 0.25 and 0.125 M sucrose. Oocytes and embryos vitrified by the SSV method had a significantly lower survival rate than the control (60 and 39% versus 100%, respectively; P<0.05), while the survival rate of CLV oocytes and embryos (89 and 88%, respectively) did not differ from controls. Cleavage and blastocyst rates of the surviving vitrified oocytes (parthenogenetically activated) and embryos (cultured for 9 days) were not significantly different (P>0.05) from the control nor did they differ between vitrification methods. Embryos vitrified with the CLV method gave rise to blastocysts (2/15). Our data demonstrated that the two vitrification methods employed resulted in acceptable levels of survival and cleavage of goat oocytes and embryos.

Detection of DNA damage in bovine metaphase II oocytes resulting from cryopreservation

Developmental competence of mammalian oocytes is compromised by currently available oocyte cryopreservation protocols. Experiments were designed to examine the effect of three cryopreservation protocols on the integrity of bovine oocyte DNA. In vitro matured bovine oocytes were cryopreserved either by slow cooling, vitrification in 0.25 ml straws, or in open pulled straws. After thawing/warming, recovered oocytes were immediately subjected to morphological evaluation. Morphologically intact oocytes underwent comet assay to detect cryoinjury at DNA level. All cryopreservation protocols resulted in significant morphological damage as well as DNA damage compared to unfrozen control. Among the morphologically intact oocytes, there was no difference among protocols in the number of oocytes displaying DNA damage. However, oocytes that had been cryopreserved by slow cooling or by vitrification in open pulled straws exhibited more damage than those vitrified in 0.25 ml straws in the extent of DNA damage. If we combine the number of oocytes with morphological damage and oocytes with DNA damage, oocytes cooled by slow cooling resulted in the most damage. This experiment demonstrated that oocyte DNA is a target of cryoinjury and different protocols result in different degrees of damage.

Potential importance of vitrification in reproductive medicine

As early as 1985, ice-free cryopreservation of mouse embryos at -196 degrees C by vitrification was reported in an attempted alternative approach to cryostorage. Since then, vitrification techniques have entered more and more the mainstream of animal reproduction as an alternative cryopreservation method to traditional slow-cooling/rapid-thaw protocols. In addition, the last few years have seen a significant resurgence of interest in the potential benefits of vitrification protocols and techniques in human-assisted reproductive technologies. The radical strategy of vitrification results in the total elimination of ice crystal formation, both within the cells being vitrified (intracellular) and in the surrounding solution (extracellular). The protocols for vitrification are very simple. They allow cells and tissue to be placed directly into the cryoprotectant and then plunged directly into liquid nitrogen. To date, however, vitrification as a cryopreservation method has had very little practical impact on human-assisted reproduction, and human preimplantation embryo vitrification is still considered to be largely experimental. Besides the inconsistent survival rates that have been reported, another problem is the wide variety of different carriers and vessels that have been used for vitrification. Second, many different vitrification solutions have been formulated, which has not helped to focus efforts on perfecting a single approach. On the other hand, the reports of successfully completed pregnancies following vitrification at all preimplantation stages is encouraging for further research and clinical implementation. Clearly, however, attention needs to be paid to the inconsistent survival rates following vitrification.

Microtubulin configuration and mitochondrial distribution after ultra-rapid cooling of bovine oocytes

Considerable attention has been focused on the cryopreservation of mammalian oocytes, as a consequence of poor development of cryopreserved bovine oocytes in vitro, in order to enhance the application of genetic engineering. Experiments were carried out to evaluate the viability and ultra-structural changes of bovine oocytes cryopreserved by ultra rapid cooling methods. Oocytes that had been allowed to mature for 22 hr were exposed to a mixture of cryoprotectants (3.2 M ethylene glycol, 2.36 M dimethyl sulfoxide (DMSO), 0.6 M sucrose), and were cryopreserved by very rapid cooling either within glass capillaries or as droplets on copper electron microscope grids. After being warmed, the oocytes were cultured in in vitro maturation (IVM) medium for an additional 2 hr. Viability was assessed by determining the development rate after fertilization with frozen-thawed semen from which motile sperm had been recovered using a Percoll density gradient, and by immunochemical evaluation of microtubule and mitochondrial morphology. Cleavage and development rates were significantly (P < 0.05) lower in oocytes cryopreserved by vitrification than in in vitro fertilization (IVF) control group, but did not differ in the open-pulled glass (OPG) or copper grid (CG) groups. In most oocytes cryopreserved by vitrification, the microtubules were partially or completely broken. Similarly mitochondria appeared to be abnormal compared to that of unfrozen oocytes. Oocytes cultured in IVM medium supplemented with both cytochalasin B (a protein synthesis inhibitor) and 2-mercaptoethanol (an antioxidant) showed less damage to microtubules, but not to mitochondria after cryopreservation. In conclusion, this study showed that bovine oocytes can be cryopreserved by vitrification within small droplets using CGs. While damage to microtubules and mitochondria may be involved in reduced viability, supplementation of IVM medium with cytochalasin B appears to enhance stabilization of microtubules during oocyte cryopreservation.

Vitrification of Yunnan Yellow Cattle oocytes: work in progress

The objective of this study was to provide a simple cryopreservation method for oocytes from Yunnan Yellow Cattle and facilitate preservation efforts in this native Chinese breed, which is threatened by agricultural modernization. Cumulus-oocyte complexes (COCs) were collected from slaughterhouse ovaries and matured in vitro for 22-24 h, then selected for cryopreservation. Vitrification in open pulled straws (OPS) or in microdrops on a cooled metal surface (solid surface vitrification, SSV) was compared. The OPS vitrification solution consisted of 20% ethylene glycol (EG) and 20% DMSO. The SSV solution was a mixture of 35% EG, 5% polyvinyl-pyrrolidon (PVP) and 0.4 M trehalose. Vitrified and warmed oocytes were either fertilized in vitro or parthenogenetically activated. The rates of cleavage and development to blastocysts of fertilized oocytes following OPS versus SSV were not statistically different (38.3 and 12.5% versus 35.8 and 6.0%, respectively). The corresponding rates of parthenogenetic development to blastocysts were also not different (8.2 versus 3.5%, respectively). Development to blastocysts of non-vitrified controls following fertilization was significantly higher than that of the vitrified oocytes (22.6%, P < 0.05). These results demonstrate for the first time, that although both OPS and SSV procedures reduced embryonic development, Yunnan Yellow Cattle oocytes are capable of developing to blastocysts following cryopreservation.

Advances in the cryopreservation of mammalian oocytes and embryos: Development of ultrarapid vitrification

The cryopreservation of embryos has become a powerful tool in assisted reproduction in several mammalian species. Embryos are cryopreserved by slow freezing or by vitrification. However, consistently high survival has not been obtained in most oocytes and in some embryos. The main reasons for the low survival would be sensitivity to low temperatures, which leads to chilling injury, and low permeability of the cell membrane, which leads to the formation of intracellular ice. As a strategy aiming to overcome these injuries, modified vitrification methods have been devised in which the cooling and warming rate is markedly increased by minimizing the volume of the solution and the container. The modified methods use electron microscope grids, open-pulled straws, cryoloops, or container-less microdrops. In this article, recent developments in the ultrarapid vitrification of mammalian oocytes and embryos are reviewed based on the understanding of the mechanisms of cell injury in cryopreservation. (Reprod Med Biol 2002; 1: 1-9).

Effect of chilling on the organization of tubulin and chromosomes in rhesus monkey oocytes

OBJECTIVE

To determine the effects of chilling on the organization and distribution of tubulin and chromosomes in rhesus monkey oocytes.

DESIGN

Comparative laboratory study.

SETTING

Academic research laboratory.

ANIMAL(S)

Eight adult female rhesus monkeys (Macaca mulatta) aged 6-16 years.

INTERVENTION(S)

A total of 171 oocytes retrieved from eight rhesus monkeys were separated into nine groups. One group of control oocytes was held at 37 degrees C during the experiment. Four groups of oocytes were rapidly cooled to 0 degrees C and held for 1, 5, 10, or 30 minutes and then fixed and stained. Four other groups of oocytes were cooled to 0 degrees C, held for 1, 5, 10, or 30 minutes, warmed and incubated at 37 degrees C for 60 minutes, and then fixed and stained.

MAIN OUTCOME MEASURE(S)

Organization of cytoskeleton and chromosomes.

RESULT(S)

Exposure of rhesus oocytes to 0 degrees C for only 1 minute resulted in complete depolymerization of tubulin. Incubation of chilled oocytes at 37 degrees C for 60 minutes caused partial restoration of tubulin, although most oocytes exhibited abnormal alignment of chromosomes and disorganized meiotic spindles.

CONCLUSION(S)

We conclude that rhesus monkey oocytes are extremely sensitive to chilling injury. Their successful cryopreservation may require rapid cooling to outpace this injury.

Effect of meiotic stages and maturation protocols on bovine oocyte's resistance to cryopreservation

We investigated the effect of meiotic stages and two maturation protocols on bovine oocyte's resistance to cryopreservation. Oocytes at germinal vesicle breakdown (GVBD) and metaphase II (MII) stage as well as oocytes matured for 22 h in media supplemented with FSH or LH were vitrified by the open pulled straw method. After warming, oocytes underwent additional 16 h (GVBD group) or 2 h (MII group) maturation. Then they were subjected to in vitro fertilization and culture. Some oocytes that matured in the medium supplemented with LH were subjected to parthenogenetic activation after vitrification to determine their developmental potential in absence of fertilization. Survival of oocytes after vitrifying/warming was determined after 22 h in fertilization medium. Cleavage and blastocyst formation rates were used to assess their developmental competence. In both experiments, a portion of unvitrified MII oocytes were subjected to in vitro fertilization and culture as control groups. In Experiment 1, similar cleavage rates were obtained for both GVBD and MII oocytes (53.56 versus 58.01%, P > 0.05). However, significantly higher proportion of cleaved embryos from vitrified MII oocytes developed into blastocysts than those from vitrified GVBD oocytes (1.06 versus 8.37%, respectively, P < 0.01). In Experiment 2, vitrified MII oocytes matured in medium supplemented with LH were superior to vitrified MII oocytes matured in FSH supplementation not only in cleavage rates (61.13 versus 50.33%), but in blastocyst formation rates (11.79 versus 5.19%, P < 0.01) as well. Cleavage and blastocyst formation rates of parthenogenetically activated oocytes were similar to those that were fertilized. Nevertheless, the vitrifying/ warming process significantly compromised the oocytes' developmental capacity since the vitrified oocytes showed significant reduction in both cleavage and blastocyst rates compared to those of not vitrified controls in both experiments (P < 0.01). We showed that oocytes at different maturation stages respond to cryopreservation differently and MII stage oocytes have better resistance to cryopreservation than GVBD stage oocytes. The maturation protocols also influence oocyte's ability to survive cryopreservation. Poor developmental potential after vitrification seem to have resulted from the cryodamage to the oocyte itself. These results suggested the importance of maturation on the developmental competence of cryopreserved oocytes.

Cryopreservation of gametes and embryos of non-domestic species

Many species of mammals are threatened or endangered. Methods of assisted reproduction that are being used with increasing frequency to produce offspring of domestic animals and humans are often viewed as offering innovative ways to reproduce non-domestic species as well. Uncounted millions of live young of domestic or laboratory species have been produced from gametes and embryos stored at -70 degrees C or below, sometimes for as long as 25 to 35 yrs. Such methods of cryopreservation are now being applied with increasing frequency and urgency to preserve gametes and embryos of non-domestic and threatened species to establish "genome resource banks" or "frozen zoos." But levels of success to produce live young from such cryopreserved gametes or embryos vary considerably from species to species, as well as from individual to individual. It is sometimes thought that differences among species in fundamental characteristics of their gametes may determine the efficacy of cryopreservation and the production of live young. However, it may not be that ineffective cryopreservation is responsible for low success rates. Rather, the limiting factor may be insufficient information and knowledge of the most basic reproductive biology of such non-domestic species. Even standard methods of cryopreservation may be completely adequate to act as a "temporary" expedient to preserve germplasm of non-domestic species to permit time to acquire a fuller understanding of the biology and behavior of non-domestic species.

Lipolysis and ultrastructural changes of intracellular lipid vesicles after cooling of bovine and porcine GV-oocytes

The aim of our investigation was to compare the ultrastructure of lipid droplets, and the effect of cooling on intracellular lipid vesicles of bovine and porcine GV oocytes. The lipid droplets in bovine GV oocytes have a homogeneous structure. The utilization of lipids takes place directly from these vesicles without formation of interim lipid compounds. In contrast, there are two kinds of lipid droplets in porcine GV oocytes: 'dark', homogeneous vesicles next to 'grey' vesicles with electron-lucent streaks. Vesicles of each specific group are connected to each other. After a 12-h culture, the formation of the cisternal smooth endoplasmic reticulum layer was always associated with 'grey' lipid vesicles. This is evidence that during oogenesis lipolysis takes place only in 'grey' vesicles. It is supposed that cytoplasmic lipolysis has two stages: 'dark' vesicles change into a 'grey' form followed by a utilization of these 'grey' lipids. Furthermore, both types of lipid droplets in porcine oocytes changed morphologically during cooling: they changed into a spherical form with lucent streaks. Lipid droplets in bovine GV oocytes revealed no visible morphological changes after cooling.

Effects of chilling to 0 degrees C on the morphology of meiotic spindles in human metaphase II oocytes

OBJECTIVE

To determine the effects of chilling to 0 degrees C on the meiotic spindle of human metaphase II oocytes, as observed by optical sectioning microscopy.

DESIGN

Laboratory study.

SETTING

Academic research laboratory in a medical school.

PATIENT(S)

Seventy-two women undergoing infertility treatment donated a total of 108 oocytes.

INTERVENTION(S)

Metaphase II oocytes were stripped of their cumulus cells, cooled directly to 0 degrees C, and held for periods of 1 to 10 minutes. They were then fixed at 37 degrees C, stained for immunofluorescence, and examined microscopically.

MAIN OUTCOME MEASURE(S)

Morphology of the meiotic spindle in chilled and control oocytes.

RESULT(S)

Microscopic evaluations of 46 chilled oocytes revealed various time-dependent changes in microtubules compared to 9 control oocytes. After 1 minute at 0 degrees C, spindle damage was negligible, but in oocytes cooled for 2 or 3 minutes, there was obvious shortening of the spindle and loss of polarity. Cooling to 0 degrees C for 4 to 9 minutes resulted in increasingly more drastic changes; by 10 minutes the spindles had totally disappeared. Despite depolymerization of microtubular tubulin at 0 degrees C, the chromosomes did not become dispersed, but remained anchored even in the absence of spindles.

CONCLUSION(S)

Even brief exposure of human oocytes to temperatures near 0 degrees C causes profound alterations of the meiotic spindle.

Oocyte cryopreservation and ovarian tissue banking

Oocyte cryopreservation, despite its impact on conservation of genetic resources, is not yet an established technology. Several problems need to be solved before this technology can be applied regularly. Chilling membrane susceptibility and formation of ice due to the large volume of the cell are the major problems observed. However, during the last years, several studies were done to obtain viable oocytes after cryopreservation. The addition of molecules known to stabilize membranes and the creation of freezing systems with rapid cooling throughout the transition phase have yielded a good percentage of viable immature and mature oocytes More recently, storage of female gametes was achieved by cryopreservation of cortical ovarian tissue. The possibility of restoring fertility by transplantation of frozen ovarian tissue or its long-term culture in vitro represents an important future means of preserving the fertility of patients and of storing the gametes of rare animals.

Effect on fertilization and development by re-culture after freezing and thawing of bovine oocytes matured in vitro

This study evaluated the effect of 6-h repeat culture before insemination of frozen-thawed, in vitro-matured oocytes on their fertilizability and developmental capacity. Immature oocytes were cultured for 18 h or 24 h and were frozen incrementally. Post-thaw oocytes were repeat cultured for 0 h (control) or 6 h before insemination. With fertilizability, the proportion of enlarged sperm head was significantly (P<0.05) higher in oocytes cultured for 24 h without repeat culture (24:0 h; 51.8%) than those cultured for 24 h with repeat culture (24:6 h; 26.1%) and nonfrozen oocytes (25.9%). However, the proportion of male pronucleus (MPN) in the group of 24:0 h (32.4%) was significantly (P<0.05) lower than that of nonfrozen oocytes (64.3%); the formation of the female pronucleus and MPN were also significantly (P<0.01) lower (17.2%) than that of nonfrozen oocytes (56.1%). Polyspermic oocytes cultured for 18 h with repeat culture for 6 h (18:6 h) were significantly (P<0.05) higher (47.5%) than for nonfrozen oocytes (25.6%). Development to 8-cell stage in the group of 18:6 h was significantly (P<0.05) lower (1.6%) than that of nonfrozen oocytes (18.5%). The cleavage rates in the groups of 24:0 h (16.3%) and 24:6 h (23.4%) were also significantly (P<0.05) lower than for nonfrozen oocytes (63.3%). Development to blastocysts was low (3.9%), but hatched blastocysts were observed in frozen-thawed oocytes cultured for 18:0 h. These results indicate the post-thaw 6-h repeat culture did not greatly improve the fertilizability and embryonic development of oocytes cultured for 18 h or 24 h before freezing. Frozen-thawed oocytes after 24 h in vitro maturation without repeat culture especially had impaired capacities for fertilizability and development.