A morphological and functional study of the effect of slow freezing followed by complete in-vitro maturation of primary mouse ovarian follicles

Follicle isolation methods reveal plasticity of granulosa cell steroidogenic capacity during mouse in vitro follicle growth

Follicles are the functional unit of the ovary and several methods have been developed to grow follicles ex vivo, which recapitulate key events of oogenesis and folliculogenesis. Enzymatic digestion protocols are often used to increase the yield of follicles from the ovary. However, the impact of these protocols on the outermost theca and granulosa cells, and thereby follicle function, is not well defined. To investigate the impact of enzymatic digestion on follicle function, we collected preantral follicles from CD1 mice either by enzymatic digestion (Enzy-FL) or mechanical isolation (Mech-FL) and compared follicle growth, steroidogenesis and cell differentiation within an encapsulated in vitro follicle growth system which maintains the 3D architecture of the oocyte and its surrounding somatic cells. Follicles were encapsulated in 0.5% alginate and cultured for 8 days. Compared with Enzy-FL, Mech-FL grew more rapidly and produced significantly higher levels of androstenedione, estradiol and progesterone. The expression of theca-interstitial cell marker genes, Cyp17a1, which encodes 17-hydroxylase/17, 20-lyase and catalyzes the hydroxylation of pregnenolone and progesterone to 17-hydroxypregnenolone and 17-hydroxyprogesterone, and the conversion of these products into dehydroepiandrosterone and androstenedione, and Star, which encodes a transport protein essential for cholesterol entry into mitochondria, were also higher in Mech-FL than in Enzy-FL. Mech-FL maintained an intact theca-interstitial layer on the outer edge of the follicle that phenocopied in vivo patterns as confirmed by alkaline phosphatase staining, whereas theca-interstitial cells were absent from Enzy-FL from the onset of culture. Therefore, preservation of the theca cell layer at the onset of culture better supports follicle growth and function. Interestingly, granulosa cells in the outermost layers of Enzy-FL expressed CYP17A1 by Day 4 of culture while maintaining inhibin α-subunit expression and a cuboidal nucleus. Thus, in the absence of theca-interstitial cells, granulosa cells have the potential to differentiate into androgen-producing cells. This work may have implications for human follicle culture, where enzymatic isolation is required owing to the density of the ovarian cortex.

Equine Chorionic Gonadotropin as an Effective FSH Replacement for In Vitro Ovine Follicle and Oocyte Development

The use of assisted reproductive technologies (ART) still requires strategies through which to maximize individual fertility chances. In vitro folliculogenesis (ivF) may represent a valid option to convey the large source of immature oocytes in ART. Several efforts have been made to set up ivF cultural protocols in medium-sized mammals, starting with the identification of the most suitable gonadotropic stimulus. In this study, Equine Chorionic Gonadotropin (eCG) is proposed as an alternative to Follicle Stimulating Hormone (FSH) based on its long superovulation use, trans-species validation, long half-life, and low costs. The use of 3D ivF on single-ovine preantral (PA) follicles allowed us to compare the hormonal effects and to validate their influence under two different cultural conditions. The use of eCG helped to stimulate the in vitro growth of ovine PA follicles by maximizing its influence under FBS-free medium. Higher performance of follicular growth, antrum formation, steroidogenic activity and gap junction marker expression were recorded. In addition, eCG, promoted a positive effect on the germinal compartment, leading to a higher incidence of meiotic competent oocytes. These findings should help to widen the use of eCG to ivF as a valid and largely available hormonal support enabling a synchronized in vitro follicle and oocyte development.

Reversing complete mechanical transzonal projections disruption during mouse in vitro follicle culture with unaltered oocyte competence†

In vitro oocyte growth is widely studied as an alternative fertility preservation approach. Several animal models are used to generate extensive information on this complex process regulated by the constant and dynamic interaction between the oocyte and its somatic compartment throughout follicle growth and maturation. A two-dimensional attachment mouse secondary follicle culture system was used to assess the oocyte's capacity to overcome disconnection from its somatic companions at different developmental stages for final competence acquisition. To test this, complete mechanical denudation of oocytes from preantral (PA) and early antral (EA) follicles was performed. Established endpoints were the oocyte's potential to reconnect with somatic cells and the impact of connectivity disruption on mature oocyte quality. This study proves that oocytes from PA and EA cultured mouse follicles can overcome complete denudation, restoring likely functional transzonal projections with no significant differences in meiotic and developmental competence compared with those from intact cultured follicles. These novel findings constitute good premises for developing successful strategies to rescue human oocyte competence in the context of in vitro culture approaches such as nonhuman chorionic gonadotropin triggered in vitro maturation.

The in vitro effect of chick embryo extract on mice pre-antral follicles

Chick embryo extract (CEE) contains a variety of growth factors which may improve in vitro follicle growth. Therefore, the effect of CEE on mouse pre-antral follicle culture was evaluated. Different percentages of CEE (0, 0.50%, 1.00%, 5.00% and 10.00%) were added to culture medium. Hence, the osmolarity of media was measured. Pre-antral follicles with diameter of 120-150 μm were isolated from 12-14 days old mouse ovary and cultured for 12 days. After culture, the maturation rate was assessed. Granulosa cells viability was evaluated using MTT test and estradiol levels were evaluated using related radio-immunoassay (RIA). Genes expression (BMP15 and ALK6) was also evaluated. The osmolarity of media and granulosa cells viability were the same in all groups. Estradiol level in group with 10.00% CEE was significantly decreased compared to the control group. After 12 days culture, the percentage of antral follicles development was significantly higher in the group with 5.00% CEE compared to control group. The percentage of metaphase II and germinal vesicle breakdown oocytes was significantly higher in group 5.00% CEE compared to control group. The expression of BMP15 gene in antral follicles in 5.00% CEE and control groups was significantly lower compared to pre-antral follicles. However, the expression of ALK6 gene in antral follicles in 5.00% CEE and control groups was not significantly different compared to pre-antral follicles. The increasing effect of CEE on follicle viability with keeping normal gene expression indicates that addition of proper percentage of CEE to culture media improves culture conditions, making it a possible choice to be used as a follicular growth enhancer in infertility clinics.

Comparison of the Oocyte Quality Derived from Two-Dimensional Follicle Culture Methods and Developmental Competence of In Vitro Grown and Matured Oocytes

In vitro follicle growth (IVFG) is an emerging fertility preservation technique, which can obtain fertilizable oocytes from an in vitro culture system in female. This study aimed to compare efficiency of the most widely used two-dimensional follicle culture methods [with or without oil layer (O+ or O- group)]. Preantral follicles were isolated from mice and randomly assigned. Follicles were cultured for 10 days and cumulus-oocyte complexes harvested 16-18 hours after hCG treatment. Follicle and oocyte growth, hormones in spent medium, meiotic spindle localization, expression of reactive oxygen species (ROS), mitochondrial activity, and gene expression were evaluated. In follicle growth, survival, pseudoantral cavity formation, ovulation, and oocyte maturation were also significantly higher in O+ group than O- group. Hormone production was significantly higher in follicles cultured in O+ than O-. There were no significant differences in mRNA expression related to development. On the other hand, the level of ROS was increased while the mitochondrial activity of in vitro grown matured oocyte was less than in vivo matured oocytes. In conclusion, follicle culture with O+ group appears to be superior to the culture in O- group in terms of follicle growth, development, oocyte growth, maturation, and microorganelles in oocyte.

Further insights into the impact of mouse follicle stage on graft outcome in an artificial ovary environment

STUDY QUESTION

Are mouse preantral follicles differently affected by isolation, encapsulation and/or grafting procedures according to stage?

SUMMARY ANSWER

Isolated secondary follicles showed superior ability to survive and grow after transplantation, which was not related to a particular effect of the isolation and/or grafting procedure, but rather to their own ability to induce neoangiogenesis.

WHAT IS KNOWN ALREADY

Isolated and encapsulated mouse preantral follicles can survive (6-27%) and grow (80-100%) in a fibrin matrix with a low concentration of fibrinogen and thrombin (F12.5/T1) after short-term transplantation.

STUDY DESIGN, SIZE, DURATION

An in vivo experimental model using 20 donor Naval Medical Research Institute (NMRI) mice (6-25 weeks of age) and 14 recipient severe combined immunodeficient (SCID) mice (11-39 weeks of age) was applied. Each NMRI mouse underwent mechanical disruption of both ovaries and isolation of primordial-primary and secondary follicles with ovarian stromal cells, in order to encapsulate them in an F12.5/T1 matrix. Twelve out of 40 fibrin clots were immediately fixed as controls (D0) (10 for histology and 2 for scanning electron microscopy [SEM]) and the others (n = 28) were grafted to the inner part of the peritoneum for 2 (16 fibrin clots) or 7 (12 fibrin clots) days (D2 and D7).

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study involved the participation of the Gynecology Research Unit (Universitè Catholique de Louvain) and the Physiological Sciences Department (University of Brasília). Specific techniques were used to analyze the follicle recovery rate (hematoxylin-eosin staining), vascularization (CD34) and follicle ultrastructure (transmission electron microscopy [TEM] and SEM).

MAIN RESULTS AND THE ROLE OF CHANCE

After follicle isolation and encapsulation, a statistically higher percentage of normal follicles was observed in the secondary group (62%) than in the primordial-primary group (47%). Follicle recovery rates were 34% and 62% for primordial-primary and secondary follicles on D2, respectively, and 12% and 42% on D7, confirming that secondary follicles survive better than primordial-primary follicles after grafting. Concerning vascularization, both follicle stages exhibited similar vascularization to that seen in control mouse ovary on D7, but a significantly higher number of vessels and greater vessel surface area were detected in the secondary follicle group. Despite structural differences in fiber density between fibrin clots and ovarian tissue observed by SEM and TEM, preantral follicles appeared to be well encapsulated in the matrix, also showing a normal ultrastructure after grafting.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

As demonstrated by our results during the isolation procedure, we encapsulated a significantly higher number of round structures in the primordial-primary group than in the secondary group, which could partially explain the lower recovery rate of early-stage follicles in our previous study. However, it is not excluded that the physical and mechanical properties of the fibrin matrix may also play a role in follicle survival and growth, so further investigations are needed.

WIDER IMPLICATIONS OF THE FINDINGS

This research represents one more key step in the creation of the artificial ovary.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS) to C.A. Amorim as a research associate at FRS-FNRS and (grant 5/4/150/5 awarded to M.M. Dolmans), Fonds Spéciaux de Recherche, Fondation St Luc, Foundation Against Cancer, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES-Brazil) (grant #013/14 CAPES/WBI awarded to C.M. Lucci, with F. Paulini receiving a post-doctoral fellowship), and Wallonie-Bruxelles International, and donations from the Ferrero family. None of the authors have any competing interests to declare in relation to the topic.

Supplementation of culture media with vitamin E improves mouse antral follicle maturation and embryo development from vitrified ovarian tissue

AIM

The aim of this study was to evaluate the effects of preventive vitamin E (α-tocopherol) on antral follicle development and embryogenesis of oocytes obtained after vitrification of mouse ovarian tissue.

METHODS

Female Balb/c mice were killed by cervical dislocation after the injection of pregnant mare's serum gonadotrophin (10 IU) and their ovaries were randomly divided into three groups: control or non-vitrified (n = 10), vitrification 1 (5, 10% ethylene glycol + 5, 10% dimethylsulfoxide) (n = 15), and vitrification 2 (10, 15% ethylene glycol + 10, 15% dimethylsulfoxide) (n = 15) with ascending concentration of cryoprotectants. After toxicity tests and vitrification-warming, mechanically isolated antral follicles were cultured in α-minimum essential medium, which was supplemented with or without α-tocopherol (100 μM). The follicular maturation rates and embryo development were collected and assessed. Also, the viability, morphology and ultrastructure of derived antral follicles from vitrified ovaries were analyzed.

RESULTS

The morphology and ultrastructure of follicles were well preserved in the vitrified groups and α-tocopherol supplementation of culture media significantly increased the proportion of oocytes that reached metaphase II blastocyst rates compared to non-α-tocopherol supplemented media (P < 0.01).

CONCLUSION

Vitamin E improves in vitro maturation rates and blastocyst rates of oocytes that are isolated from vitrified ovarian tissue.

Three dimensional in vitro culture of preantral follicles following slow-freezing and vitrification of mouse ovarian tissue

To evaluate the effects slow-freezing and vitrification on three dimensional in vitro culture of preantral follicles, ovaries of 12-14 days old female NMRI mice were isolated and randomly assigned to fresh control, slow-freezing and vitrification groups. Slow-freezing was performed using programmable freezer. Vitrification was carried out in a medium consisting of ethylene glycol (EG) and dimethyl sulphoxide (Me2SO) by needle immersion method. middle sized preantral follicles were mechanically isolated and cultured for 12 days in 0.7% sodium alginate gel. The follicles development and quantitative expression of oocyte specific genes (Bmp15, Gdf9, Fgf8) and the growth related genes (Igf1, Kit, Kit-l) were assessed after 1, 8 and 12 days of culture. Both cryopreserved groups showed reduction of follicular survival rates compared to the control group on days 8 and 12 of culture (P < 0.05). Antrum formation rates reduced in slow-freezing after 12 days of culture (P < 0.05). Evaluation of gene expression showed reduction of Bmp15, Gdf9, Fgf8, Kit and Kit-l during 12 days of culture (P < 0.05). Kit and Kit-l expression in slow-freezing group significantly reduced on day 8 of culture (p < 0.05). Igf1 expression was lower in slow-freezing group on 1st day of culture than vitrification and control groups (P < 0.05). Finally, intergroup comparison showed same expression pattern of genes after 12 days of culture. Thus, cryopreservation of mouse ovaries by both methods can preserve most developmental parameters and expression of maturation genes. However, vitrification is a better method for cryopreservation of mouse ovaries due to greater antrum formation and expression of growth related markers.

Vitrification of mouse preantral follicles versus slow freezing: Morphological and apoptosis evaluation

The aim of this study was evaluation of survivability, maturation rate and apoptotic gene expression of preantral follicles after vitrification and slow freezing technique. Normal mouse preantral follicles were randomly divided into three experimental groups. In the control group, follicles were cultured immediately; in the vitrification and slow freezing groups, follicles were cultured after vitrification-warming and slow freezing-thawing procedures. Follicular viability was assessed by using 0.4% trypan blue, and molecular evaluation of messenger RNA levels of apoptosis-related genes was performed by the semi-quantitative RT-PCR method after 3 h of culture. Oocyte maturation rates were also evaluated on day 14 of culture. Survival and maturation rate in the slow freezing group were significantly lower than those in control and vitrification groups (P ≤ 0.05). Although there was no difference in Survivin expression among the three experimental groups, Bcl-2 expression was significantly lower in the slow freezing group compared to the other groups (P ≤ 0.05). The expression of Bax, P53, Fas and Bax/Bcl-2 ratio in the slow freezing group was significantly higher than control and vitrification groups (P ≤ 0.05). Preantral follicle vitrification seems to be better than slow freezing as seen in the survival, maturation and expression rates of apoptotic gene variants.

Ovarian follicle culture: advances and challenges for human and nonhuman primates

The removal and cryostorage of ovarian cortical biopsies is now offered as a fertility preservation option for young women. The only available option to restore fertility using this tissue is by transplantation, which may not be possible for all patients. The full potential of this tissue to restore fertility could be achieved by the development of in vitro systems that support oocyte development from the most immature stages to maturation. The techniques of in vitro growth (IVG) combined with in vitro maturation (IVM) are being developed with human tissue, but comparing different systems has been difficult because of the scarcity of tissue so nonhuman primates are being used as model systems. There are many challenges to developing a complete culture system that would support human oocyte development, and this review outlines the approaches being taken by several groups using tissue from women and nonhuman primate models to support each of the stages of oocyte development.

Angiopoietin 1 reduces rat follicular atresia mediated by apoptosis through the PI3K/Akt pathway

The aim of this study was to determine the effect of the local inhibition of ANGPT1 on steroid production, proliferation and apoptosis of ovarian follicular cells and on the PI3K/AKT pathway. We also examined the effect of ANGPTs on follicular cell apoptosis and proliferation in early antral follicles (EAFs) in culture. Follicular cells expressing PCNA decreased after ANGPT1 Ab treatment. Moreover, ANGPT1 inhibition increased the levels of active caspase 3 and androsterone, but decreased estradiol, AKT phosphorylation and the area of smooth muscle cell actin. In cultured EAFs from prepubertal rats treated with diethylstilbestrol (DES), ANGPT1 increased PCNA and decreased apoptosis while ANGPT2 reversed these effects. These results show that ANGPT1 alters steroidogenesis, reduces ovarian apoptosis, and stimulates cell proliferation in antral follicles. ANGPT1 may exert these roles by regulating ovarian vascular stability and/or by a direct effect on follicular cells, possibly involving the PI3K/AKT pathway.

Mouse ovarian follicle cryopreservation using vitrification or slow programmed cooling: assessment of in vitro development, maturation, ultra-structure and meiotic spindle organization

AIM

To compare different outcomes of vitrification and slow freezing of isolated pre-antral follicles and to evaluate different cryo-devices for vitrification of isolated follicles.

METHODS

Pre-antral follicles were isolated from mouse ovaries and cryopreserved using vitrification and slow freezing. A preliminary experiment was carried out to select the optimal cryo-device for vitrification of isolated follicles. A total of 414 follicles were randomly distributed among four groups: control (CT) fresh (n=100), nylon mesh (n=96), electron microscopy grid (n=102), and micro-capillary tips (n=116). Subsequently, a total of 979 follicles were randomly assigned to three different groups: CT fresh (n=256), vitrification (n=399) and slow freezing (n=324). CT and cryopreserved/thawed follicles were cultured in vitro and examined daily for development. Final maturation was triggered with human chorionic gonadotrophin and rates of oocyte maturation were calculated. The ultra-structure of cryopreserved/thawed follicles was studied using electron microscopy. Meiotic spindle presence and organization in mature oocytes were examined using the Oosight imaging system.

RESULTS

  Micro-capillary tips resulted in poor immediate post-warming survival but no differences were observed in the subsequent in vitro development characteristics between different cryo-devices. Nylon mesh proved to be the easiest carrier, particularly when large numbers of follicles were to be vitrified. Compared to vitrification, slow freezing resulted in a significantly lower number of intact follicles at the end of the culture period (P<0.0001). However all other outcome measures were comparable between both techniques.

CONCLUSIONS

Isolated follicles were more vulnerable to cryodamage after slow freezing as compared to vitrification.

Ultrastructure of isolated mouse ovarian follicles cultured in vitro

BACKGROUND

In vitro maturation of ovarian follicles, in combination with cryopreservation, might be a valuable method for preserving and/or restoring fertility in mammals with impaired reproductive function. Several culture systems capable of sustaining mammalian follicle growth in vitro have been developed and many studies exist on factors influencing the development of in vitro grown oocytes. However, a very few reports concern the ultrastructural morphology of in vitro grown follicles.

METHODS

The present study was designed to evaluate, by transmission and scanning electron microscopy, the ultrastructural features of isolated mouse preantral follicles cultured in vitro for 6 days in a standard medium containing fetal calf serum (FCS). The culture was supplemented or not with FSH.

RESULTS

The follicles cultured in FCS alone, without FSH supplementation (FCS follicles), did not form the antral cavity. They displayed low differentiation (juxta-nuclear aggregates of organelles in the ooplasm, a variable amount of microvilli on the oolemma, numerous granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment). Eighty (80)% of FSH-treated follicles formed the antral cavity (FSH antral follicles). These follicles showed various ultrastructural markers of maturity (spreading of organelles in ooplasm, abundant microvilli on the oolemma, scarce granulosa cell-oolemma contacts, granulosa cell proliferation). Areas of detachment of the innermost granulosa cell layer from the oocyte were also found, along with a diffuse granulosa cell loosening compatible with the antral formation. Theca cells showed an immature morphology for the stage reached. Twenty (20)% of FSH-treated follicles did not develop the antral cavity (FSH non-antral follicles) and displayed morphological differentiation features intermediate between those shown by FCS and FSH antral follicles (spreading of organelles in the ooplasm, variable amount of microvilli, scattered granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment).

CONCLUSIONS

It is concluded that FSH supports the in vitro growth of follicles, but the presence of a diffuse structural granulosa cell-oocyte uncoupling and the absence of theca development unveil the incomplete efficiency of the system. The present study contributes to explain, from a morphological point of view, the effects of culture conditions on the development of mouse in vitro grown follicles and to highlight the necessity of maintaining efficient intercellular communications to obtain large numbers of fully-grown mature germ cells.

Direct survival role of vascular endothelial growth factor (VEGF) on rat ovarian follicular cells

The aim of the present work was to analyze the direct effect of VEGF in follicular cell proliferation, apoptosis and activation of the PI3K/AKT and ERK/MEK signaling pathways in early antral follicles or granulosa cells. Antral follicles or granulosa cells were isolated from prepubertal female Sprague Dawley rats treated with DES.VEGF directly stimulates follicular cell proliferation and it also decreases apoptosis by inhibiting caspase 3 activation. In addition, VEGF increases the proliferation and inhibits the apoptosis of isolated granulosa cells in culture. VEGF activates the PI3K/AKT pathway evidenced by an increase in AKT phosphorylation levels and induces the phosphorylation of ERK1/2 in cultured antral follicles. These results demonstrate for the first time that VEGF has a proliferative and cytoprotective role in early antral follicles and in granulosa cells isolated from DES treated prepubertal rats and suggest that PI3K/AKT and ERK/MEK signaling pathways are involved in these processes.

Noninvasive index of cryorecovery and growth potential for human follicles in vitro

Cryopreservation of oocytes and embryos is commonly used to preserve fertility. However, women undergoing cancer treatment may not have the time or may not be good candidates for these options. Ovarian cortical tissue cryopreservation and subsequent tissue transplant has been proven successful yet inefficient in preserving larger secondary follicles, and is not recommended as a fertility preservation option for women with certain cancers. We evaluated cryopreservation of individual follicles as an alternative option in rodents, nonhuman primates, and human primates. Under optimal conditions, cryopreserved mouse secondary follicles were able to reestablish granulosa cell-oocyte interactions, which are essential for subsequent follicle growth. Individual secondary follicles survived cryopreservation, were able to be cultured in a three-dimensional alginate hydrogel matrix to the antral stage, and the enclosed oocytes were competent for fertilization. Using a vital imaging technique (pol-scope) employed in many fertility centers, we were able to bioassay the thawed, cultured follicles for the presence of transzonal connections between the somatic and germ cells. Perturbations in these linkages were shown to be reversed when follicles were cryopreserved under optimal freezing conditions. We applied the optimized cryopreservation protocol to isolated rhesus monkey and human secondary follicles, and using the birefringent bioassay, we were able to show good correlation between early follicle growth and healthy somatic cell-oocyte connections. Our results suggest that ovarian follicles can be cryopreserved, thawed, and analyzed noninvasively, making follicle preservation an additional option for young cancer patients.

A simple and efficient method for preparation of isolated ovarian follicles for transmission electron microscopy

OBJECTIVE

A simple method for preparation of isolated ovarian follicles for transmission electron microscopy (TEM) using transwell inserts is described.

MATERIALS AND METHODS

Pre-antral follicles were enzymatically isolated from mouse ovaries and cultured overnight on transwell insert polyester membranes. The following day, isolated ovarian follicles were processed for TEM by moving the transwell insert through successive wells containing the fixation and embedding reagents. After polymerization of the resin, the polyester membrane with the follicles embedded in the resin was disengaged from the transwell unit. The resin was sectioned. Semi-thin sections were stained with toluidine blue while ultra-thin sections were stained by uranyl acetate and examined by light microscopy and TEM, respectively.

RESULTS

Isolated ovarian follicles were easily processed in groups for TEM. Follicles were well embedded and there appeared to be no loss of tissue during processing. The ultra-structure of processed isolated ovarian follicles was well preserved with little evidence of processing artifacts.

CONCLUSIONS

In situ processing and preparation of isolated ovarian follicles by first allowing attachment on transwell insert membranes was shown to be a simple, rapid and effective method for TEM.

Secondary follicle growth and oocyte maturation by culture in alginate hydrogel following cryopreservation of the ovary or individual follicles

An option for fertility preservation for women facing a cancer diagnosis involves the cryopreservation of ovarian tissue for later re-transplantation or in vitro culture, with in vitro culture preferred to avoid reintroduction of the cancer. Small, immature follicles survive the freeze-thaw process, and can be matured through in follicle maturation (IFM) that involves an initial growth of the follicle and subsequent maturation of the oocyte. The ovarian tissue can be cryopreserved in two forms: (i) cortical strips consisting of follicles and surrounding stroma (Cryo-Ov) or (ii) individually isolated follicles (Cryo-In). The aim of this study was to assess the follicle growth and oocyte maturation for follicles that were cryopreserved either as strips or individually using a slow-freezing cryopreservation method. The two follicle groups, together with non-cryopreserved control follicles, were grown in an alginate-based three-dimensional culture system for 12 days. The overall survival, size increase and antrum formation rates were comparable among the three groups. At day 12 of culture, Androstenedione levels were decreased in the Cryo-Ov group relative to the other two, and the ratio of progesterone to estradiol was increased in the two cryopreserved groups relative to the control. Both Gja1 (known as connexin 43) and Gja4 (known as connexin 37) mRNA expression were decreased at day 6 in the cryopreserved groups relative to controls, and by day 12, Gja1 was similar for all three groups. Moreover, Cryo-In resulted in lower GVBD rate indicating some impaired oocyte development. Overall, the present study demonstrated that mouse preantral follicles, either within ovarian tissues or individually isolated, could be successfully cryopreserved by the slow-freezing method, as evidenced by post-thaw follicle development and steroidgenesis, oocyte maturation and molecular markers for oocyte and/or granulosa cells connection.

Preservation of fertility in young cancer patients: contribution of transmission electron microscopy

During the last decade, new technologies in reproductive medicine have emerged to preserve the fertility of women whose gonadal function is threatened by premature menopause or gonadotoxic treatments. To offer an individualized approach to these patients, different experimental procedures are under investigation, including oocyte cryopreservation and cryopreservation and transplantation of ovarian tissue in the form of cortical fragments, whole ovary or isolated follicles. This review shows that transmission electron microscopy (TEM), combined with other in-vivo and in-vitro analysis techniques, is a valuable tool in the establishment of new experimental protocols to preserve female fertility. Ultrastructural studies allow in-depth evaluation of the oocyte's unique morpho-functional characteristics, which explain its low cryotolerance, and provide essential information on follicular, stromal and endothelial cell integrity, as well as cellular interactions crucial for normal folliculogenesis. In order to be able to offer appropriate and efficient options in every clinical situation, oocyte in-vitro maturation and ovarian tissue transplantation need to be optimized. Further development of new approaches, such as follicular isolation and whole ovary transplantation, should be encouraged. Fine ultrastructural details highlighted by TEM studies will be useful for the further optimization of these emerging technologies.

Cryopreservation and xenotransplantation of human ovarian tissue: an ultrastructural study

OBJECTIVE

To analyze the ultrastructure of human ovarian follicles after cryopreservation and short-term xenografting.

DESIGN

Prospective experimental study.

SETTING

Academic gynecology and anatomy research units.

PATIENT(S)

Ovarian cortical biopsy specimens were obtained from 13 patients.

INTERVENTION(S)

Each ovarian biopsy specimen was dissected into pieces of 1 mm(3) and divided into three groups: [1] fresh tissue, [2] frozen-thawed tissue, and [3] frozen-thawed tissue xenografted onto the peritoneum of nude mice for 3 weeks.

MAIN OUTCOME MEASURE(S)

Follicular ultrastructure was assessed by light and transmission electron microscopy in [1] fresh, [2] frozen, and [3] frozen-grafted tissue.

RESULT(S)

Thirty-five ovarian follicles were analyzed by light and transmission electron microscopy. Twenty-five primordial and primary ovarian follicles were found. Most of them exhibited ultrastructurally well preserved features (fresh [N = 8/10], frozen [N = 7/10], and frozen-grafted [N = 4/5] tissue). Ten secondary follicles were present in xenografts. By transmission electron microscopy, all the healthy-looking secondary follicles (70%) were shown to contain intact oocytes, with features typical of earlier developmental stages, surrounded by several layers of follicular cells.

CONCLUSION(S)

The present study demonstrates, for the first time, that cryopreservation and xenotransplantation do not appear to greatly affect human primordial/primary follicle ultrastructure. Interestingly, in frozen-thawed xenografts, secondary human ovarian follicles presented a well preserved ultrastructure, but asynchrony between oocyte and granulosa cell development was detected. The possible causes for this asynchrony are discussed.

Comparison of the developmental potential of 2-week-old preantral follicles derived from vitrified ovarian tissue slices, vitrified whole ovaries and vitrified/transplanted newborn mouse ovaries using the metal surface method

Background

Cryopreservation of preantral follicles or ovarian tissues would enable the storage of large numbers of primordial follicles or preantral follicles and preserves the structural integrity of somatic and reproductive cells. In the present study, we compared the developmental potential of cryopreserved two-week-old mouse preantral follicles, ovarian tissue slices, two-week-old mouse ovaries and newborn mouse ovaries using a metal plate with a high cooling rate for cooling the droplet of vitrification solution.

Methods

Groups of 2 to 4 samples (including of 14-day old preantral follicles, ovarian tissue slices, whole ovaries, and whole newborn ovaries) were exposed to 4% ethylene glycol (EG) in DPBS + 10% FBS for 15 min and then rinsed in a vitrification solution composed of 6 M ethylene glycol and 0.4 M trehalose in DPBS + 10% FBS. Equilibration in room temperature was performed for 20–30 seconds for preantral follicle and 5 min equilibration was performed in an ice bath for ovaries. The samples were dropped onto the surface of metal plate around -180°C in the volume of 2 μl and 6 μl. After thawing, the ovarian tissue was mechanically isolated for collecting the preantral follicles. The thawed newborn ovaries were transplanted under the renal capsule of recipient male mice for 14 days. Preantral follicles collected from each groups were cultured individually in 20-μl droplets of α-MEM culture medium in culture dish for 12 days. On the day 12 of culture, the cumulus-oocyte complexes (COCs) were collected for IVM and IVF. Fertilization and embryo cleavage were scored.

Results

After the vitrification of 14-day-old preantral follicles using 2 μl or 6 μl droplet onto surface of metal plate, the results indicated that no significant difference in survival rate, antral-like cavity formation, COCs collected, 2 cell embryo cleavage and blastocyst development was found in vitrification of the 2 μl and 6 μl droplet groups. As comparing 14-day old ovarian tissue (ovarian tissue slices and whole ovaries) and whole newborn ovaries vitrified in 6 μl droplet, lower success rates of antral-like cavity formation and COCs collection were found in the whole ovaries group.

Conclusion

Our results suggest that the metal plate surface vitrification method is an appropriate and convenient method for cryopreservation of mouse ovaries and preantral follicles. The droplet volume of vitrification solution in 2 μl and 6 μl can be an option.

Demande de préservation de la fertilité chez la femme en cas de maladie auto-immune: possibilités et pratiques en France

Cancer is not the only disease where the question of the female fertility preservation is asked. In autoimmune diseases, alkylating agents are also used and it is now established that 20 g as a cumulative dose of cyclophosphamide is associated with premature ovarian failure in 50% of 20-year-old patients. Several strategies are discussed and offered to these patients to prevent the ovarian failure: GnRH agonist treatment, in vitro fertilization and embryos cryopreservation, oocytes cryopreservation and ovarian cortex cryopreservation. These techniques might also be associated one with the other. A survey was conducted in France in order to assess the practices realised in these diseases. Four centres were asked for these diseases, concerning 17 patients (mean age: 26.2 +/- 1.8 SEM [15-43]) and systemic lupus erythematosus was the most frequent disease (7/17). Ovarian cortex cryopreservation was realised for 6 patients. Embryos or oocytes cryopreservation was realised for 2 patients including one where ovarian cortex cryopreservation was associated. In 10 cases, considering the treatment and the patient's wish no fertility preservation was realised. Female fertility preservation in autoimmune diseases is a difficult question and a national registry, such as the one conducted by the GRECOT, can help to answer this question.

Effects of storing pig ovaries at 4 or 20 degrees C for different periods of time on the morphology and viability of pre-antral follicles

The purpose of this study was to evaluate the effect of cooling ovarian tissue on pig pre-antral follicles. Ovaries were maintained in saline solution (0.9%) at 4 or 20 degrees C for 6, 12 or 18 h. After storage, pre-antral follicles were morphologically evaluated. While primordial follicles were not affected by the storage, the percentage of morphologically normal growing follicles was significantly reduced in ovarian tissue stored at 20 degrees C for 12 or 18 h. To test the viability of stored follicles, growing follicles isolated from ovaries stored at 4 degrees C for 18 h and at 20 degrees C for 6 h were cultured for 3 days. Follicles stored in either condition presented the same growth pattern in vitro as fresh follicles. We conclude that storage of pig ovaries at 4 degrees C for up to 18 h or at 20 degrees C for up to 6 h does not affect the morphology of growing follicles or their ability to grow in vitro.

Effect of vitrification method on survivability, follicular growth and ovulation of preantral follicles in mice

AIM

This study was designed to compare the survival rates, follicular growth rates, and ovulation rates of vitrified preantral follicles (PF) from ovaries with those isolated from a vitrified ovarian cortical strip.

METHODS

Mouse ovaries were divided into three groups: those not treated by vitrification of the PF (control), those treated by vitrification of the PF isolated from the ovaries (group I), and those treated by vitrification of ovarian tissue followed by PF isolation (group II). The group I samples were exposed to equilibration solution (EG-20) for 5.0 min plus vitrification solution (EFS-40) for 0.5 min, while the group II samples were exposed to EG-20 for 10.0 min plus EFS-40 for 2.0 min, before vitrification. They were subsequently placed on an electron microscope grid, and submerged immediately in liquid nitrogen. After thawing, the survival rate and the growth rate of the follicles were evaluated every 2 days.

RESULTS

In the in vitro condition, the follicles grew and developed into antral follicles in groups I and II. The survival rate of the group I samples was higher than that of the group II samples during the in vitro culture (P<0.05). The growth rates of the follicles in group I were higher than those in group II after day 6 (P<0.05). The ovulation rate of the samples in group I was higher than that of group II (P<0.05).

CONCLUSION

These results demonstrated that direct PF vitrification appeared to be better than vitrification of the PF isolated from ovarian tissue.

Cryopreservation of Sheep Primordial Follicles

The aim of this study was to evaluate the efficiency of 1 M dimethylsulphoxide (DMSO), ethylene glycol (EG), propylene glycol (PROH) and glycerol (GLY) to cryopreserve primordial follicles. The first evaluation was performed soon after cryopreservation and the second evaluation after 4 days of in vitro culture, using the cryoprotectants that allowed the higher results (higher follicular survival rate) after cryopreservation. The results after follicular isolation (control) and cryopreservation using 1 M DMSO, EG, PROH and GLY showed that the mean number (+/- SEM) of live follicles per millilitre was 3204 (100%) +/- 319.27, 2798 (87%) +/- 239.14, 2492 (78%) +/- 345.8, 448 (14%) +/- 46.3 and 208 (7%) +/- 75.26, respectively. Higher follicular survival was reported when DMSO and EG were used. Control follicles and follicles cryopreserved with these two cryoprotectants were cultured and the percentage of follicular survival was 55% (control), 42% (EG) and 34% (DMSO). Similar results were found between control and follicles cryopreserved with EG. In conclusion, 1 M EG is the most effective cryoprotectant to preserve primordial follicles isolated from ovaries of sheep.

Effects of isolation method and pre-treatment with ethylene glycol or raffinose before vitrification on in vitro viability of mouse preantral follicles

Effects of isolation and vitrification protocols on follicular survival after warming were examined. Mouse preantral follicles enzymatically or mechanically isolated from ovaries of 12-day-old mice were exposed either to 2 M ethylene glycol (EG) for 2 or 5 min, or to ascending concentrations (0.15 then 0.3 M) of raffinose for 2 or 5 min each (2-2 and 5-5 min). They were then exposed to a vitrification solution (VS) composed of 6 M EG and 0.3 M raffinose for 0.5, 1, or 2 min before vitrification. Mechanically isolated follicles showed higher survival than enzymatically isolated follicles, regardless of periods of exposure to EG or raffinose and subsequent exposure to VS. After 10 days of culture, follicular growth and maturational ability of oocytes derived from vitrified follicles exposed to 2 M EG for 5 min and to VS for 1 min were higher than those from follicles exposed to raffinose solutions for 2-2 min and to VS for 1 min. Histological evaluation revealed that exposure of preantral follicles to raffinose solutions caused cytoplasmic vacuolation in granulosa cells which could be due to cellular shrinkage during dehydration; whereas, exposure to 2 M EG induced morphological alterations in follicles only to a lesser extent.

Natural history of the mammalian oocyte

Combining cryopreservation of immature oocytes with in-vitro growth/maturation techniques is the ambition of many IVF clinics. Whilst these techniques have been demonstrated in rodents their application to humans and domestic species has been slow. There are many technical reasons for the lack of progress in these species, but the major problem is that we have very little knowledge of how the oocyte acquires developmental competence during its growth within the follicle. The life history of the mammalian oocyte involves a complex series of co-ordinated developmental processes that in the human take place over several months. This review will consider: (i) growth and development of the oocyte; (ii) the newly regenerated debate on the existence of germ-line stem cells in the mammalian ovary; and (iii) strategies for producing oocytes in vitro.

Permeability of ovine primordial follicles to different cryoprotectants

OBJECTIVE

To determine the behavior of isolated primordial follicles that were exposed to different concentrations of dimethyl sulfoxide (DMSO), ethylene glycol (EG), propylene glycol (PROH), and glycerol (GLY).

DESIGN

Isolated primordial follicles were exposed to the cryoprotectant (CPA) solution and photographed to calculate their volume at different periods of exposure.

SETTING

Laboratorio Renzo Giuliani, University of Florence, Italy.

ANIMAL(S)

Lambs, 30-40 days old.

INTERVENTION(S)

Isolation of primordial follicles and subsequent exposure to CPA.

MAIN OUTCOME MEASURE(S)

Follicular volume.

RESULT(S)

At 2 minutes of CPA exposure, all follicles appeared to be shrunken. At approximately 5 minutes, shrinkage ceased, and follicles started to swell, absorbing the CPA and water to maintain osmotic equilibrium. When DMSO was tested, follicular dehydration in all concentrations did not exceed 17%; with PROH and EG, it reached 33% and 27%, respectively. The highest degree of dehydration (48%) was seen with GLY. In almost all tested concentrations, follicular shrinkage occurred up to 5 minutes.

CONCLUSION(S)

Volume changes in isolated primordial follicles can fluctuate according to the CPA used and its concentration.

Effects of lowered temperatures and media on short-term preservation of zebu (Bos indicus) preantral ovarian follicles

The maintenance of follicle quality during the transportation of ovaries is essential for the successful cryopreservation and in vitro development of preantral follicles. The objective of this study was to evaluate the effect of cooling ovarian tissue on the conservation of zebu cow preantral follicles. Ovarian pieces were immersed in saline or coconut water (CW) solutions and maintained at 4 or 20 degrees C for 6, 12, or 18 h. Preantral follicles were evaluated by histology and transmission electron microscopy. Storage of ovarian pieces at 20 degrees C for 12 or 18 h significantly reduced the percentage of morphologically normal follicles compared to controls. In contrast, conservation at 4 degrees C for up to 18 h and at 20 degrees C for up to 6 h kept the percentage of normal follicles similar to controls. However, the type of solution that the ovaries were immersed in had little effect on the results. Decreased cellular metabolism probably accounted for better preservation of preantral follicles at 4 degrees C. In conclusion, zebu cow ovaries were successfully stored at 4 degrees C for up to 18 h with no morphological damage to preantral follicles. However, at 20 degrees C, ovaries could only be stored for 6 h.

In vitro growth of preantral follicles isolated from cryopreserved ovine ovarian tissue

In the present study, we compared the in vitro development of sheep preantral follicles obtained from unfrozen or frozen ovarian cortex. After thawing, follicles stored by a slow-freezing protocol with dimethyl sulfoxide (DMSO) or ethylene glycol (EG) were mechanically isolated and cultured for 10 days. After 1 day, approximately 50% and 34% of the DMSO and EG follicles, respectively, showed overt signs of degeneration, as confirmed by histological analysis. Follicles that survived thawing grew and formed antral-like cavities, without significant differences among experimental groups. However, the percentages of healthy oocyte-cumulus cell complexes (OCCs) retrieved from in vitro-grown follicles, as well as estradiol, were lower in DMSO than in EG or unfrozen follicles. Although cryopreservation did not cause appreciable differences in follicle morphological aspects, frozen OCCs showed lower metabolic cooperativity levels, as determined by [3H]uridine uptake. During culture, oocytes increased in diameter, but the percentage of germinal vesicle stage-arrested oocytes showing a rimmed chromatin configuration was significantly lower in the frozen groups. Our results indicate that cryopreserved sheep preantral follicles underwent growth in vitro but that freezing/thawing specifically affected gap junctional permeability and impaired the progression of regulative processes, such as the acquisition of a specific oocyte chromatin configuration. Moreover, because the cryoprotectant toxicity test excluded the occurrence of direct cellular damage, this method allowed us to discriminate the effects exerted by different cryoprotectants during the cryopreservation procedure on whole-follicular development.

Effects of chilling on structural aspects of early preantral mouse follicles

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

In vitroculture of mouse GV oocytes and preantral follicles isolated from ovarian tissues cryopreserved by vitrification

Cryopreservation of ovarian tissues containing many immature oocytes occurs in both gamete/embryo research and clinical medicine. Using vitrification, we studied factors related to meiosis after cryopreservation using the COCs (cumulus oocyte complexes) and preantral follicles obtained from cryopreserved ovarian tissues. COCs were isolated and cultured for 17 approximately 19 hr. Thereafter, Metaphase II stage (MII stage) oocytes and fertilized oocytes after IVF were observed at a rate of 76.5% and 60.0%, respectively. Preantral follicles (100 approximately 130 microm in diameter) were isolated and cultured in alpha MEM containing hFSH, ITS, and FBS. HCG and EGF were added to the media to stimulate ovulation on the 12th day of culture. The survival rates of the follicles obtained from the frozen/thawed ovaries were 66.4%. After 12 days of culture, the diameter of the follicles isolated from fresh (620.2 +/- 11.3 microm) and frozen/thawed ovaries (518.7 +/- 15.1 microm) differed as did the estradiol concentrations (3474.2 +/- 159 pg/ml vs. 1508.2 +/- 134 pg/ml). After in vitro ovulation, MII stage oocytes were observed in 84.5% of the fresh group and 60.5% of the frozen/thawed group while the fertilization rate was 74.2% and 53.5%, respectively. These studies demonstrate that cryopreservation of mouse ovarian tissues by vitrification did not affect the oocyte's ability to undergo meiosis. Thus, this technique may become a powerful tool for the preservation of the female gamete.

Cryopreservation of ovine primordial follicles using dimethyl sulfoxide

OBJECTIVE

To verify the viability of isolated primordial follicles after exposure to different concentrations of dimethyl sulfoxide (DMSO) and after cryopreservation.

DESIGN

Randomized control trial.

SETTING

Laboratorio Renzo Giuliani, University of Florence, Italy.

ANIMAL(S)

Thirty- to 40-day-old lambs.

MAIN OUTCOME MEASURE(S)

Isolated primordial follicles were stained with trypan blue to evaluate the effect of different DMSO concentrations before and after the cryopreservation. Histological structure and follicular mortality were evaluated.

RESULT(S)

After the isolation procedure (control), a mean (+/-SE) of 800 +/- 203.86 live primordial follicles/mL were obtained. The number of live follicles in the toxicity test using the DMSO at 0, 0.5, 1.0, 1.5, 2.0, and 2.5 M was 782 +/- 193.96, 754 +/- 172.03, 778 +/- 191.58, 736 +/- 191.92, 476 +/- 122.9, and 316 +/- 83.52, respectively. The number of live follicles at 2.5 M was lower than that in the control procedure. After cryopreservation, the numbers decreased to 0 +/- 0, 232 +/- 44.20, 636 +/- 161.82, 628 +/- 181.28, 208 +/- 11.57, and 184 +/- 47.07, respectively at 0, 0.5, 1.0, 1.5, 2.0, and 2.5 M. The number of live follicles at 0, 0.5, 2.0, and 2.5 M were lower than that in the control procedure.

CONCLUSION(S)

After cryopreservation, only DMSO concentrations of 1.0 and 1.5 M showed a number of live follicles similar to that of the control procedure.

Survival of oocytes recovered from vitrified sheep ovarian tissues

The objective of this work was to develop an effective vitrification technique for cryopreserving oocytes in sheep ovarian tissues. Ovaries were surgically recovered from 15 pubertal ewes and the ovarian cortex was cut into sections. Ovarian tissues were placed in equilibration medium consisting of 4% (v/v) ethylene glycol (EG) and 20% (v/v) FBS in TCM-199 on ice for 30 min and transferred to vitrification solution (35% EG, 5% polyvinylpyrrolidone, 0.4M trehalose and 20% FBS in TCM-199) for 5 min. Ovarian tissues were vitrified by dropping the tissue on the surface of a steel cube cooled by liquid nitrogen. Cumulus-enclosed oocyte complexes (COC) were also collected and vitrified following the procedure used for ovarian tissues. After 2-3 weeks of storage in liquid nitrogen, ovarian tissues and COC were thawed at 37 degrees C in 0.3M trehalose and COC in ovarian tissues were mechanically and enzymatically isolated. Vitrified COC and freshly collected COC were washed twice in maturation medium (TCM-199 supplemented with 0.255 mM pyruvate and 10% heat-treated estrus cow serum) and cultured in 50 microl drops of maturation medium under paraffin oil for 23-25h at 39 degrees C in a humidified atmosphere of 5% CO(2) in air. After culture, cumulus cells were removed by hyaluronidase treatment and vortexing and oocytes were fixed and stained. No significant differences were observed between vitrified oocytes, oocytes recovered from vitrified ovarian tissues and non-vitrified control oocytes in the percentage of oocytes with acceptable staining per total number of oocytes fixed or with visible chromatin per total number of oocytes with acceptable staining. However, fewer (P<0.05) oocytes obtained from vitrified ovarian tissues (70%) reached metaphase II compared to vitrified oocytes (88%) and non-vitrified control oocytes (90%). In contrast, when oocytes with at least 3-5 layers of cumulus cells were considered from each of the three groups, no differences (P>0.05) were observed due to treatment in the percentages of oocytes developing to metaphase II. These results demonstrate that sheep oocytes can be successfully cryopreserved by vitrification of ovarian tissues and exhibit in vitro maturation rates similar to that of vitrified and non-vitrified oocytes.

Effects of storage time and temperature on atresia of goat ovarian preantral follicles held in M199 with or without indole-3-acetic acid supplementation

Maintenance of follicular quality after removal and during transport of ovaries is necessary for studies on development of preantral follicles in vitro. The present work investigated the effectiveness of M199 and M199IAA for preservation of goat preantral follicles in ovarian tissue. At the slaughterhouse, the ovarian pair of each animal was divided into 19 fragments. One ovarian fragment was immediately fixed (control--Time 0). The other 18 fragments were randomly distributed in M199 or M1991AA at 4, 20 or 39 degrees C and stored for 4, 12 or 24 h. Histological analysis showed that storage of ovarian fragments in either solution at 20 or 39 degrees C significantly reduced the percentage of normal preantral follicles when compared with the control, in all cases except after preservation in M199IAA at 20 degrees C for 4 h. In contrast, preservation at 4 degrees C, in either solution, kept the percentage of normal preantral follicles at control values. Reduced cellular metabolism may explain why the best preservation of preantral follicles was at 4 degrees C. The addition of IAA to the TCM 199 was effective for goat preantral follicle preservation at 20 degrees C for 4 h.

In vitro growth of human primordial follicles from frozen-banked ovarian tissue

The rarity of human oocytes frequently limits the success of assisted reproductive technology and delays research progress. Development of technologies to grow mature oocytes from the more abundant small follicles, perhaps after long-term storage at low temperatures, is a theoretically attractive solution to both problems. The length of the follicular growth span from the primordial to Graafian stage and changes in the trophic requirements of the cells, cellular interactions, morphogenesis and the sheer increase in bulk as the antrum forms are major challenges for cell culture technology. Even so, much progress has been made with animal follicles, and has begun with human tissue. A multi-step procedure, which reflects these changes, is perhaps the most likely to succeed. At present, the best strategy appears to be to initiate follicle growth in situ and isolate the follicles or granulosa-oocyte complexes once they have progressed to preantral stages. The final step is to mature the oocytes within their cumulus cells. The prospects of succeeding at each stage, and producing a fertile gamete at the end, are likely to be greater by preserving cellular interactions and the phenotype of follicle cells as these provide the physiological environment in which oocytes develop.

Effect of cooling rate and dehydration regimen on the histological appearance of human ovarian cortex following cryopreservation in 1, 2-propanediol

Thin slices of human ovarian cortex were evaluated following cryopreservation in 1,2-propanediol (PROH)/sucrose under various conditions. Following rapid thawing, 1 microm sections were assessed by light microscopy and oocyte abnormalities were further examined by electron microscopy. Follicles (n = 503) were predominantly primordial (91%), with no follicles larger than the proliferating primary stage. Proportions of intact pre-granulosa cells and oocytes (expressed as percentages of the total numbers observed) were significantly reduced following cooling at three different rates with the highest levels of intactness (55 and 85% respectively) being achieved with slow cooling. The frequency of oocyte abnormalities [loss of organelles (mitochondria), organelle-free areas, and/or cytoplasmic vacuolation] was significantly increased at all cooling rates with slow cooling resulting in the highest proportion (56%) of normal oocytes. With slow cooling, increasing dehydration time increased the proportions of intact pre-granulosa cells and oocytes (maximum 74 and 91% respectively after 90 min dehydration). Under these conditions, the highest proportion of follicles with all pre-granulosa cells intact (44%) was observed, as was the highest proportion of 'normal' oocytes (85%). In this study, single step dehydration in PROH/sucrose for 90 min and slow cooling/rapid thawing results in the highest proportion of intact human primordial and primary follicles.

Follicle culture after ovarian cryostorage

OBJECTIVES

Cryostorage of ovarian cortical tissue, before devastating chemo- and/or radiotherapy for cancer, permits survival of primordial and early preantral follicles. This work aims for a system allowing the long-term maturation in vitro (IVM) of small immature oocytes up to fertilisable metaphase II oocytes.

METHODS

A culture system allowing follicle attachment permitted the growth and maturation of isolated follicles (follicle diameter between 100 and 130 microns) from 14-day-old (prepuberal) mice. Follicle and oocyte development were observed under the inverted microscope and conditioned medium was used for biochemical analysis. Effects of recombinant gonadotrophins and oxygen tensions were studied for their specific effects on follicle development.

RESULTS

A 12-day culture period yielded full-grown oocytes which were able to complete meiosis (metaphase II). Live young were obtained after IVF and intra-uterine transfer of in vitro matured oocytes. Growth and maturation were only successful when recombinant gonadotropins were added and when the incubator had a 20% oxygen tension. This system enabled the growth of early preantral follicles after cryopreservation: 80% of frozen and thawed follicles survived up to culture-day 12 and yielded a comparable blastocyst formation rate as in controls.

CONCLUSIONS

The mouse model suggests that IVM is a valuable option after oocyte storage. The development of a comparable system for long-term culture of human follicles will imply the acquisition of non-invasive techniques to appreciate oocyte's maturity and developmental capacity.

Early preantral mouse follicle in vitro maturation: oocyte growth, meiotic maturation and granulosa-cell proliferation

Mechanically isolated early preantral mouse follicles were cultured singly for 16 d and fully grown oocytes were obtained from these follicles. We then compared in vitro and in vivo follicle growth by trypsinising the follicles and counting their cell numbers in a Neubauer-counting chamber and recording the diameter and meiotic status of oocytes under an inverted microscope. As long as the granulosa cells were within the basal membrane, proliferation was slow. From Day 6, when granulosa cells had broken through the basal membrane, the proliferation rate progressed up to Day 10 and decreased thereafter to approximately 12,000 cells per culture droplet. Incorporation of BrdU revealed that proliferating cells were evenly distributed throughout the follicle until antrum formation. As granulosa cell differentiation progressed, proliferation of mural-granulosa cells ceased, while cells around the oocytes continued dividing. Oocyte diameter increased discontinuously in relation to follicle remodelling. During the first growth phase, diameters increased from 56.5 (+/- 4.4 microns) to 67 (+/- 4.1 microns) until the onset of antral-like cavity formation. The last growth phase started after Day 10, and by Day 14 oocyte diameters were not significantly different from those of 26-d-old in vivo control oocytes. The potential to resume meiosis after mechanical removal of granulosa cells was first reached on Day 8; thereafter, removal of the corona showed that all oocytes cultured with FSH remained arrested at the GV stage up to Day 16. After Day 8, approximately 70% of all oocytes underwent GVBD as a result of granulosa-cell removal, but only 23% of these reached MII after 24 h. The in vivo controls reached a comparable GVBD rate (66%) when the granulosa was removed, but most of the oocytes (82%) underwent first polar body extrusion 24 h later. These results suggest that although oocyte diameters after IVM are not different from those of the controls, culture conditions are not yet adequate to support complete meiotic maturation.