In vitro culture and in vitro maturation of mouse preantral follicles with recombinant gonadotropins

New insights into the role of LH in early ovarian follicular growth: a possible tool to optimize follicular recruitment

Evidence shows that LH participates in enhancing transition from the early stage to the antral stage of folliculogenesis. It has been demonstrated that functional LH receptors are expressed, albeit at a very low level and even in smaller follicles, during the phase that was traditionally considered to be gonadotrophin independent, suggesting a role for LH in accelerating the rate of progression of non-growing and primary follicles to the preantral/antral stage. Hypogonadotropic hypogonadism, together with other clinical conditions of pituitary suppression, has been associated with reduced functional ovarian reserve. The reduction in LH serum concentration is associated with a low concentration of anti-Müllerian hormone. This is the case in hypothalamic amenorrhoea, pregnancy, long-term GnRH-analogue therapy and hormonal contraception. The effect seems to be reversible, such that after pregnancy and after discontinuation of drugs, the functional ovarian reserve returns to the baseline level. Evidence suggests that women with similar primordial follicle reserves could present with different numbers of antral follicles, and that gonadotrophins may play a fundamental role in permitting a normal rate of progression of follicles through non-cyclic folliculogenesis. The precise role of gonadotrophins in early folliculogenesis, as well as their use to modify the functional ovarian reserve, must be investigated.

Post-thaw viability of mouse preantral follicles after cryopreservation with cryotube freezing and OPS vitrification procedures

In the field of reproductive science, there is an increased interest in the application of ovarian preantral follicles. Since the ovary contains a great amount of preantral follicles (PAF), the cryopreservation and in vitro culture of such follicles support the fertility preservation of domestic animals with high genetic value, endangered or zoo animals, and women before anticancer therapy. To date, no standard freezing or vitrification protocol is available in human or animals. The aim of the present study was to examine the viability of preantral follicles cryopreserved using freezing or vitrification protocols: cryotube freezing or OPS vitrification.

Does the ovarian surface epithelium differentiate into primordial follicle and primary follicle precursor structures?

Purpose: The aim of this study is to investigate the differentiation capacity of ovarian surface epithelial cells both in cell culture conditions and in ovarian tissue sections. Materials and Methods: The ovaries of two prepubertal (4 weeks old) female rats were divided into small pieces and explant cell culture was created. Ovarian surface epithelium proliferating together with ovarian stromal cells in mixed cell culture was isolated and reproduced. In addition, ovarian surface epithelium was examined in histological sections of ovarian tissue and images were taken under the microscope. Results: The morphological appearance of the ovarian surface epithelium was found to be cobblestone. In the count performed under phase contrast microscopy, it was observed that 2x106 and 3x106 cells were grown in the culture dishes, respectively. Primordial follicle-like structures were observed in some areas of the petri dishes. On the histological sections, primordial and primary follicle precursor structures were observed on the basement membrane. Conclusion: Showing oocyte markers (Gdf-9, C-Mos, Zpc, Stella) and germ cell markers (Dazl, Vasa, Blimp1, Fragilis) both in cell cultures and in histological sections can give us valuable information in terms of monitoring the differentiation capacity of these cells.

Feasibility of Secondary Follicle Isolation, Culture and Achievement of In-Vitro Oocyte Maturation from Superovulated Ovaries: An Experimental Proof-of-Concept Study Using Mice

Fertility preservation through ovarian stimulation, aiming at cryopreserving mature oocytes or embryos, is sometimes unsuccessful. This clinical situation deserves novel approaches to overcome infertility following cancer treatment in patients facing highly gonadotoxic treatment. In this controlled experimental study, we investigated the feasibility of in-vitro culturing secondary follicles isolated from superovulated ovaries of mice recently treated with gonadotropins. The follicle yields of superovulated ovaries were 45.9% less than in unstimulated controls. Follicles from superovulated ovaries showed faster growth pace during the initial 7 days of culture and secreted more 17β-estradiol by the end of culture vs controls. Parameters reflecting the outcome of follicular development and oocyte maturation competence in vitro were similar between superovulated and control groups, with a similar follicle size at the end of culture and around 70% survival. Nearly half of cultured follicles met the criteria for in-vitro maturation in both groups and approximately 60% of those achieved a mature MII oocyte, similarly in both groups. Over 60% of obtained MII oocytes displayed normal-looking spindle and chromosome configurations, without significant differences between the groups. Using a validated follicle culture system, we demonstrated the feasibility of secondary follicle isolation, in-vitro culture and oocyte maturation with normal spindle and chromosome configurations obtained from superovulated mice ovaries.

Supportive techniques to investigate in vitro culture and cryopreservation efficiencies of equine ovarian tissue: A review

During the reproductive lifespan of a female, only a limited quantity of oocytes are naturally ovulated; therefore, the mammalian ovary possesses a substantial population of preantral follicles available to be handled and explored in vitro. Hence, the manipulation of preantral follicles enclosed in ovarian tissue aims to recover a considerable population of oocytes of high-value animals for potential application in profitable assisted reproductive technologies (ARTs). For this purpose, the technique of preantral follicle in vitro culture (IVC) has been the most common research tool, achieving extraordinary results with offspring production in the mouse model. Although promising outcomes have been generated in livestock animals after IVC of preantral follicles, the quantity and quality of embryo production with those oocytes are still poor. In recent years, the mare has become an additional model for IVC studies due to remarkable similarities with women and livestock animals regarding in vivo and in vitro ovarian folliculogenesis. For a successful IVC system, several factors should be carefully considered to provide an optimum culture environment able to support the viability and growth of preantral follicles enclosed in ovarian tissue. The cryopreservation of the ovarian tissue is another important in vitro manipulation technique that has been used to preserve the reproductive potential in humans and, in the future, may be used in highly valuable domestic animals or endangered species. Several improvements in cryopreservation protocols are necessary to support the utilization of ovarian tissue of different species in follow-up ARTs (e.g., ovarian fragment transplantation). This review aims to provide an update on the most current advances regarding supportive in vitro techniques used in equids to evaluate and manipulate preantral follicles and ovarian tissue, as well as methodological approaches used during IVC and cryopreservation techniques.

EFFECT OF SOMATOTROPIN AND THYROXINE ON THE IN VITRO DEVELOPMENT OF BOVINE PREANTRAL FOLLICLES

Abstract The aim of the study was to evaluate the effect of recombinant bovine somatotropin (rbST) and thyroxine (T4) on survival and growth of bovine preantral ovarian follicles (PAOF) cultured in vitro. Ovarian fragments were collected in local abattoirs and immediately fixed for classical histology and transmission electron microscopy (non-cultured control). The other fragments were then cultured in situ for seven days in minimum essential medium alone (MEM+ - cultured control) or in the presence of 1,000 ng/mL rbST and 20 ng/mL T4, isolated or associated. After seven days, there was a reduction (P<0.05) in the percentage of normal follicles in MEM+ alone or with T4. In oocyte diameter, there was a reduction in MEM+ alone. There was no influence (P>0.01) of the medium used on the follicular diameter of the PAOF cultured for seven days. Ultrastructural analysis showed cell damage. In conclusion, the presence of rbST maintains the rate of morphologically normal follicles during the culture for seven days (observed by optical microscopy), but it does not exert beneficial effects on its ultrastructural integrity and oocyte and follicular growth.

Protein profile of mouse ovarian follicles grown in vitro

STUDY QUESTION

Could the follicle proteome be mapped by identifying specific proteins that are common or differ between three developmental stages from the secondary follicle (SF) to the antrum-like stage?

SUMMARY ANSWER

From a total of 1401 proteins identified in the follicles, 609 were common to the three developmental stages investigated and 444 were found uniquely at one of the stages.

WHAT IS KNOWN ALREADY

The importance of the follicle as a functional structure has been recognized; however, up-to-date the proteome of the whole follicle has not been described. A few studies using proteomics have previously reported on either isolated fully-grown oocytes before or after meiosis resumption or cumulus cells.

STUDY DESIGN, SIZE, DURATION

The experimental design included a validated mice model for isolation and individual culture of SFs. The system was chosen as it allows continuous evaluation of follicle growth and selection of follicles for analysis at pre-determined developmental stages: SF, complete Slavjanski membrane rupture (SMR) and antrum-like cavity (AF). The experiments were repeated 13 times independently to acquire the material that was analyzed by proteomics.

PARTICIPANTS/MATERIALS, SETTING, METHODS

SFs (n = 2166) were isolated from B6CBA/F1 female mice (n = 42), 12 days old, from 15 l. About half of the follicles isolated as SF were analyzed as such (n = 1143) and pooled to obtain 139 μg of extracted protein. Both SMR (n = 359) and AF (n = 124) were obtained after individual culture of 1023 follicles in a microdrop system under oil, selected for analysis and pooled, to obtain 339 μg and 170 μg of protein, respectively. The follicle proteome was analyzed combining isoelectric focusing (IEF) fractionation with 1D and 2D LC-MS/MS analysis to enhance protein identification. The three protein lists were submitted to the 'Compare gene list' tool in the PANTHER website to gain insights on the Gene Ontology Biological processes present and to Ingenuity Pathway Analysis to highlight protein networks. A label-free quantification was performed with 1D LC-MS/MS analyses to emphasize proteins with different expression profiles between the three follicular stages. Supplementary western blot analysis (using new biological replicates) was performed to confirm the expression variations of three proteins during follicle development in vitro.

MAIN RESULTS AND THE ROLE OF CHANCE

It was found that 609 out of 1401 identified proteins were common to the three follicle developmental stages investigated. Some proteins were identified uniquely at one stage: 71 of the 775 identified proteins in SF, 181 of 1092 in SMR and 192 of 1100 in AF. Additional qualitative and quantitative analysis highlighted 44 biological processes over-represented in our samples compared to the Mus musculus gene database. In particular, it was possible to identify proteins implicated in the cell cycle, calcium ion binding and glycolysis, with specific expressions and abundance, throughout in vitro follicle development.

LARGE SCALE DATA

Data are available via ProteomeXchange with identifier PXD006227.

LIMITATIONS, REASONS FOR CAUTION

The proteome analyses described in this study were performed after in vitro development. Despite fractionation of the samples before LC-MS/MS, proteomic approaches are not exhaustive, thus proteins that are not identified in a group are not necessarily absent from that group, although they are likely to be less abundant.

WIDER IMPLICATIONS OF THE FINDINGS

This study allowed a general view of proteins implicated in follicle development in vitro and it represents the most complete catalog of the whole follicle proteome available so far. Not only were well known proteins of the oocyte identified but also proteins that are probably expressed only in granulosa cells.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Portuguese Foundation for Science and Technology, FCT (PhD fellowship SFRH/BD/65299/2009 to A.A.), the Swedish Childhood Cancer Foundation (PR 2014-0144 to K.A.R-.W.) and Stockholm County Council to K.A.R-.W. The authors of the study have no conflict of interest to report.

Maternal-Effect Gene Expression in Cultured Preantral Follicles Derived from Vitrified-Warmed Mouse Ovary

Objective

This study was conducted to assess survival of follicles, their oocyte maturation and fertilization potential as well as expression of early embryo developmental genes in in vitro cultured pre-antral follicles derived from vitrified-warmed mouse ovary.

Materials and Methods

In this experimental study, ovaries of 12-day old Naval Medical Research Institute (NMRI) female mice were placed into non-vitrified and vitrifiedwarmed groups. Isolated preantral follicles from experimental groups were cultured in vitro for 12 days. On the 12^th day of culture, oocyte maturation was induced and then matured oocytes were in vitro fertilized. The rates of oocyte maturation and two-cell stage embryo formation were assessed. Relative expression of Mater and Zar1 was evaluated on days 1, 6, 10 and 12 of culture. Data analysis was performed by t test and two-way ANOVA (P<0.05).

Results

Our data showed no significant difference between the control and vitrification groups in the rate of follicular survival, oocyte maturation and two-cell stage embryo formation. The level of gene expression was higher on the 6^thand 10^thdays of culture for Mater and Zar1 in vitrified-warmed group compared with non-vitrified group, however, there was no significant difference between the two groups.

Conclusion

It seems that the applied vitrification method did not reveal any negative effect on maturation and developmental competence of oocytes surrounded in preantral follicles and therefore could preserve follicular reserves efficiently.

High insulin concentrations promote the in vitro growth and viability of canine preantral follicles

To determine whether the effects of different concentrations of insulin on the development of canine preantral follicles in vitro were associated or not with FSH, secondary follicles were isolated and cultured. In Experiment 1, follicles were cultured in the following media: modified minimum essential medium (CtrlMEM) alone; CtrlMEM plus 5 ng mL⁻¹ insulin (Ins5ng); CtrlMEM plus 10 ng mL⁻¹ insulin (Ins10ng); and CtrlMEM plus 10 μg mL⁻¹ insulin. In Experiment 2, follicles were cultured in the same media but in the presence of sequential FSH (i.e. CtrlFSH, Ins5ngF, Ins10ngF and 10μgF, respectively). Increasing concentrations of FSH (100, 500 and 1000 ng mL⁻¹) were added sequentially to the culture medium on Days 0, 6 and 12 of culture. Viability were assessed at the end of culture and follicular diameter and the antrum formation rate at four time points (Days 0, 6, 12 and 18). In Experiment 1, the high insulin concentration significantly increased follicular viability (P<0.05). In contrast, in Experiment 2, viability was not affected by the inclusion of insulin. In addition, viability was significantly better in follicles cultured in CtrlFSH (P<0.05). The diameter of follicles in the high-insulin group in Experiment 1 and high-insulin plus FSH group in Experiment 2 was superior to other groups tested. In experiment 2, the Ins10μg and Ins10μgF groups exhibited significantly higher antrum formation rates than the other groups. In conclusion, in the absence of FSH, high concentrations of insulin have beneficial effects on follicular viability. However, to promote the growth of canine preantral follicles in vitro, it is recommended that a combination of insulin and FSH be added to the medium.

Effects of urinary and recombinant gonadotropins on in vitro maturation outcomes of mouse preantral follicles

Gonadotropins including follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play a crucial role in human-assisted reproduction techniques. Despite wide use of recombinant gonadotropins in clinical practice, the efficacy of urinary gonadotropins and the dosage of LH component have not yet been elucidated. This study was designed to investigate the difference of follicle culture outcomes according to various compositions of gonadotropins during in vitro culture of mouse preantral follicles. Ovaries were obtained from the 14-day-old C57BL/6 mice, and preantral follicles were isolated and cultured in culture media supplemented with human menopausal gonadotropin (hMG) 200 mIU/mL (group 1), recombinant FSH and LH (rFSH + rLH) 200 mIU/mL each (group 2), rFSH 200 mIU/mL + rLH 100 mIU/mL (group 3), or rFSH 200 mIU/mL + rLH 20 mIU/mL (group 4). Follicle survival rate was significantly lower in group 4. Antral follicles in lower doses of LH (groups 3, 4) showed a statistically significant larger diameter and tended to have a higher antral formation rate. However, follicles in group 1 tended to have a higher oocyte maturation rate. Estradiol concentration from conditioned media from 2:1 FSH/LH (group 3) was significantly higher than those from 1:1 FSH/LH (group 2) or 10:1 FSH/LH (group 4). Half dose of rLH to rFSH facilitated upregulation of growth differentiation factor 9 (Gdf9) expression in granulosa cells when compared to 1:1 FSH/LH or 10:1 FSH/LH. Conclusively, recombinant gonadotropins provided a comparable condition to hMG, and half dose of rLH to rFSH seems to be more suitable for follicular development during in vitro culture.

Isolation of ovarian components essential for growth and development of mammalian oocytes in vitro

Mammalian ovaries contain a large number of oocytes, most of which degenerate either before or at various stages of growth. Dynamic and precise regulation in the ovary involves many factors, each with a unique role. Identifying the single most important factor is impossible; however, it may be possible to identify factors essential for oocyte growth. It is evident that oocytes can grow into competent ova in vitro; however, how faithfully the follicle should mimic the in vivo conditions remains unclear. In the culture system discussed in this review, bovine and mouse oocyte-granulosa cell complexes, at approximately the late mid-growth stage, spread on a substratum without the involvement of theca cells. The structural simplicity of this system is advantageous because it reduces the basic conditions essential for regulation of oocyte growth. Apart from biological factors, high concentrations of polyvinylpyrrolidone (molecular weight: 360000) improved oocyte growth. Among ovarian factors, androstenedione was used to compensate for the absence of theca cells, and it promoted both follicular growth and acquisition of oocyte meiotic competence. Most oocytes cultured in a group were viable after long-term culture, suggesting that unlike ovarian events, there was no exhaustive follicle selection. Collectively, oocytes and their associated granulosa cells can establish independent units capable of supporting oocyte growth in appropriately modified culture media.

In vitro growth of mouse preantral follicles: effect of animal age and stem cell factor/insulin-like growth factor supplementation

OBJECTIVE

To determine whether animal age impacts in vitro preantral follicle growth. Effects of hCG, stem cell factor (SCF), and/or insulin-like growth factor (IGF) supplementation in growth medium were also investigated.

METHODS

Intact preantral follicles were mechanically isolated from fresh ovaries of BDF1 mice and cultured in growth medium for 9 to 11 days. Surviving follicles with antrum formation were transferred to maturation medium for 14 to 18 hours. Follicle survival, antrum formation, and retrieval of metaphase II (MII) oocytes were compared among three age categories (4-5, 7-8, and 10-11 week-old). By using 7- to 8-week-old mice, preantral follicles were cultured in growth medium supplemented with hCG (0, 5, or 10 mIU/mL), SCF (50 ng/mL), IGF-1 (50 ng/mL), and SCF+IGF-1.

RESULTS

Seven- to eight-week-old mice showed a higher follicle survival and antrum formation and produced more MII oocytes compared to other groups. In the 7- to 8-week-old mice, supplementation of 5 mIU/mL hCG significantly enhanced the antrum formation but the percentage of MII oocytes was similar to that of the control. Supplementation of SCF+IGF-1 did not enhance follicle survival or antrum formation but the percentage of MII oocytes increased modestly (39.1%) than in the control (28.6%, statistically not significant).

CONCLUSION

Seven- to eight-week-old mice showed better outcomes in growth of preantral follicles in vitro than 4- to 5- or 10- to 11-week-old mice. Supplementation of hCG enhanced antrum formation and supplementation of SCF+IGF-1 yielded more mature oocytes; hence, these should be considered in the growth of preantral follicles in vitro.

Conditions affecting growth and developmental competence of mammalian oocytes in vitro

Mammalian ovaries contain a large number of oocytes at different stages of growth. To utilize potential female gametes, it is important to develop culture systems that permit oocytes to achieve full growth and competence in order to undergo maturation, fertilization and development. The desired culture systems should meet at least the following three conditions: (i) oocytes remain healthy and functional so that they can execute intrinsic programs that direct their growth and development; (ii) granulosa cells that are adjacent to oocytes proliferate efficiently to prevent oocytes from becoming denuded; and (iii) granulosa cells maintain (and develop) appropriate associations with oocytes during the culture period. For this reason, several systems have been developed, and they can be classified into four categories based on the structure and components of the follicle/oocyte-granulosa cell complex and the location of the oocyte in the physical organization of the complex. The resultant diverse morphologies are due to multiple factors, including the method for initial isolation of follicles, the culture substrate, and hormones and other factors added into the medium. It is important to find an optimal combination of such factors involved in the process to facilitate future research efforts.

Oocyte growth in vitro: potential model for studies of oocyte-granulosa cell interactions

Various factors such as gonadotrophins, growth factors, and steroid hormones play important roles in the regulation of oocyte/follicular growth in mammalian ovaries. In addition to these factors, there is a bidirectional interaction between oocytes and granulosa cells that is essential for achieving optimal oocyte developmental competence. Oocytes play a key role in this interaction by secreting paracrine factors that alter the activities of neighboring cumulus cells, such as the expression of a specific amino acid transporter, cholesterol biosynthesis, and levels of glycolysis in the cumulus cells. Among the known oocyte-derived factors, growth differentiation factor 9 (GDF9) is the dominant factor mediating the regulation by oocytes leading to cumulus expansion and granulosa cell proliferation. GDF9 frequently interacts with other oocyte-derived factors in a synergistic manner. It seems reasonable to speculate that oocytes growing in vitro require interactions similar to those in vivo. Some of the oocyte-mediated regulations have been confirmed in vitro, providing evidence of the usefulness of culture systems as a strong tool for such studies. This review discusses in vitro culture of growing oocytes in terms of oocyte-granulosa cell interactions.

Secretion profiles from in vitro cultured follicles, isolated from fresh prepubertal and adult mouse ovaries or frozen-thawed prepubertal mouse ovaries

In vitro folliculogenesis could be a new technology to produce mature oocytes from immature follicles that have been isolated from cryopreserved or fresh ovarian tissue. This technique could also be a tool for evaluation of oocyte quality and/or for determination of follicular parameters during follicular growth. Our objective was to characterize in mice the secretion profiles of follicles that had been isolated mechanically during in vitro follicular growth and in relation to the growth curve. Early preantral follicles from fresh prepubertal and adult mouse ovaries or frozen-thawed prepubertal mouse ovaries were cultured individually in microdrops under oil for 12 days. Each day, two perpendicular diameters of the follicles were measured. From day-3 to day-12 of culture, culture medium was collected and preserved for determination of inhibin B, anti-Müllerian hormone (AMH) and estradiol levels. At the end of the culture, after maturation, the status of the oocyte was evaluated. Follicular growth and their individual hormone production did not always correlate. Inhibin B was never secreted from follicles of less than 200 μm diameter, whether the follicles were examined when fresh or after freezing-thawing. Estradiol secretion was never observed in frozen-thawed follicles. AMH was mainly secreted between day-3 and day-9. Despite similar morphological aspects at the start of culture, follicles selected for in vitro folliculogenesis were found to be heterogeneous and differed in their ability to grow and to produce hormones, even if they had similar growth curves. Follicles from frozen-thawed ovaries developed slowly and produced fewer hormones than freshly collected follicles.

Moment of addition of LH to the culture medium improves in vitro survival and development of secondary goat pre-antral follicles

The present study investigated the effects of time of addition of luteinizing hormone (LH) to culture medium on the in vitro development of caprine pre-antral follicles. Pre-antral follicles (≥ 150 μm) were isolated from fragments of the goat ovarian cortex and individually cultured for 18 days in the absence (control) or presence of 100 ng/ml LH, added on days 0, 6 or 12 of culture. Follicular development was assessed based on antral cavity formation, increased follicular diameter as well as follicular and fully grown oocyte (>110 μm) viability. The results showed that after 18 days of culture, the percentage of surviving follicles in the control treatment was significantly lower when compared to other treatments (p < 0.05). There were no significant differences in antrum formation, follicular diameter and oocyte viability. The addition of LH at D6 of culture significantly increased the rates of oocytes ≥ 110 μm and the resumption of meiosis (p < 0.05). In contrast, when LH was added at the onset of culture, only germinal vesicle oocytes were obtained. In conclusion, the moment of addition of LH to the culture medium affects the performance of in vitro culture of caprine pre-antral follicles. The addition of LH to the medium from day 6 of culture onward improved the rates of follicular survival, as well as the ability of oocytes to resume meiosis. However, prolonged exposure to LH (addition at the onset of culture onward) showed detrimental effects for the meiotic resumption.

Growth of bovine oocyte-granulosa cell complexes cultured individually in microdrops of various sizes

In mammalian embryo culture, the embryo:medium volume ratio can substantially affect embryo developmental performance. In the present study, we tested the possibility of improving the growth of bovine oocytes by reducing the medium volume, from a typical volume used in mouse follicle culture to a minimum possible level. A total of 282 complexes, each containing a growing oocyte 87-100 mum in diameter, were individually placed in microdrops of 2, 5, 10 or 20 microl and cultured for 13 days in a modified TCM-199 supplemented with 4% polyvinylpyrrolidone (molecular weight: 360 kDa). Oocyte diameter was measured every other day to trace the growth of each oocyte. Half the medium was replaced every other day or every day, and comparison revealed that daily replacement was more favorable for culture of these microdrops. The highest survival rate, 95%, occurred in the 20-microl microdrops, where most oocytes continued to grow throughout the culture period. In comparison, in the 5- and 10-microl microdrops, more oocytes died, and growth slowed towards the end of culture. In the 2-microl microdrops, which had the highest death rate, growth virtually ceased after 9 days. The surviving oocytes were usually accompanied by a characteristic dome-like structure of the granulosa cell mass, except in the 2-microl microdrops. In conclusion, the 20-microl microdrops allowed oocyte growth at an acceptable level, and any further reduction of the volume only had a negative impact on oocytes.

Comparison of urinary and recombinant follicle-stimulating hormone in in vitro growth, maturation, and fertilization of mouse preantral follicles

OBJECTIVE

To compare the effects of urinary and recombinant follicle-stimulating hormone (FSH) on follicular development, oocyte maturation, and fertilization.

DESIGN

Prospective randomized animal study.

SETTING

University-based research laboratory.

ANIMAL(S)

Normal (C57BL/6xDBA2) F1 mice.

INTERVENTION(S)

Collection of preantral follicles by mechanical dissection, in vitro growth (IVG) with urinary or recombinant FSH (100 mIU/mL), in vitro maturation (IVM), and fertilization.

MAIN OUTCOME MEASURE(S)

During IVG, follicle diameter and antral formation were evaluated. The number of cells per follicle was evaluated at the end of IVG. The 17beta-estradiol measurements were performed from conditioned media. After IVM, mucification and oocyte maturation rates were estimated and mature oocytes were fertilized.

RESULT(S)

No differences were observed in the antral formation rate of either group. Antral follicles in the urinary FSH group, however, showed a higher diameter but a lower number of cells per follicle than those in the recombinant FSH group. The level of 17beta-estradiol was also higher in the recombinant FSH group. The rate of mature oocytes developing into metaphase I or II was statistically significantly higher in the recombinant FSH group than in the urinary FSH group.

CONCLUSION(S)

Recombinant FSH provided better conditions than urinary FSH for the growth and development of mouse preantral follicles that could produce mature oocytes with fertilization capacity.

Effects of gonadotrophins, growth hormone, and activin A on enzymatically isolated follicle growth, oocyte chromatin organization, and steroid secretion

So far, standard follicle culture systems can produce blastocyst from less than 40% of the in vitro matured oocytes compared to over 70% in the in vivo counterpart. Because the capacity for embryonic development is strictly associated with the terminal stage of oocyte growth, the nuclear maturity status of the in vitro grown oocyte was the subject of this study. Mouse early preantral follicles (100-130 microm) and early antral follicles (170-200 microm) isolated enzymatically were cultured for 12 and 4 days, respectively, in a collagen-free dish. The serum-based media were supplemented with either 100 mIU/ml FSH (FSH only); 100 mIU/ml FSH + 10 mIU/ml LH (FSH-LH); 100 mIU/ml FSH + 1 mIU/ml GH (FSH-GH) or 100 mIU/ml FSH + 100 ng/ml activin A (FSH-AA). Follicle survival was highest in follicle stimulating hormone (FSH)-AA group in both cultured preantral (91.8%) and antral follicles (82.7%). Survival rates in the other groups ranged between 48% (FSH only, preantral follicle culture) and 78.7% (FSH only, antral follicle culture). Estradiol and progesterone were undetectable in medium lacking gonadotrophins while AA supplementation in synergy with FSH caused increased estradiol secretion and a simultaneously lowered progesterone secretion. Chromatin configuration of oocytes from surviving follicles at the end of culture revealed that there were twice more developmentally incompetent non-surrounded nucleolus (NSN) oocytes (>65%) than the competent surrounded nucleolus (SN) oocytes (<34%). We conclude that the present standard follicle culture system does not produce optimum proportion of developmentally competent oocytes.

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.

Correlation of somatic cell steroid secretion and quality of generated oocytes after in-vitro stimulation of mouse follicles

PURPOSE

To test the possibility of follicular somatic cell steroidogenesis as a marker for quality of their embraced oocytes.

METHODS

Mechanically isolated mouse preantral follicles were cultured and matured in-vitro (IVC/IVM) for study.

RESULTS

During IVC/IVM, oogenesis occurred concomitantly with folliculogenesis in a coordinated manner and simultaneously with progressive increments of somatic cell steroidogenesis. Follicular E(2) production of matured oocytes were significantly higher than that of immature ones. The majority of MII oocytes (32/36) and all developed blastocysts(12/12) were associated with active E(2) production prior to ovulation. In this study, 18 MII oocytes met both requirements for active and optimal E(2) production. 13 of them were fertilized and 10 developed into blastocysts.

CONCLUSION

Active somatic cell steroidogenesis prior to ovulation and an optimal steroid milieu at ovulation are prerequisites for generation of competent oocytes after follicular maturation in-vitro.

In vitro follicular development of cryopreserved mouse ovarian tissue

In a previous report, we showed that follicles isolated from frozen/thawed mouse ovarian tissues reached the mature follicle stage on the 12th day of culture. However, the developmental ability was lower than that of fresh ovarian tissue. The purpose of this study was to define a culture system with some technical modification for preantral follicles isolated from frozen/thawed ovarian tissue and to confirm cell injury. Ovaries obtained from three-week-old female mice were cryopreserved by the rapid freezing method. Preantral follicles isolated from frozen/thawed ovarian tissues were cultured for 12-16 days. The follicles were then stimulated with human chorionic gonadotropin. In vitro fertilization was performed on the released cumulus-oocyte complexes (COCs). Preantral follicle viability was assessed by supravital staining using Hoechst 33258. Using this stain cell death was found in part of the granulosa cells of a follicle obtained from frozen/thawed ovarian tissue. On the 14th and 16th days of culture, the diameters of follicles isolated from frozen/thawed ovaries were larger than on the 12th day of culture. The released COCs were fertilized and developed to the blastocyst stage in 15.8% (12/76) of the oocytes taken from the fresh group, and in 0% (0/73), 2.9% (2/69) and 19.1% (22/115) of the oocytes taken from the frozen/thawed group that had been cultured for 12, 14 and 16 days respectively. The preantral follicles isolated from frozen/thawed mouse ovarian tissues developed slowly compared with the freshly prepared preantral follicles. During prolonged culture from 12 to 16 days, these follicles obtained the potential to fertilize and develop to the blastocyst stage.

Impact of various endocrine and paracrine factors on in vitro culture of preantral follicles in rodents

Folliculogenesis is a complex process regulated by various paracrine and autocrine factors. In vitro growth systems of primordial and preantral follicles have been developed for future use of immature oocytes, as sources of fertilizable oocytes and for studying follicular growth and oocyte maturation mechanisms. Rodents were often chosen for in vitro follicular culture research and a lot of factors implicated in folliculogenesis have been identified using this model. To date, the mouse is the only species in which the whole process of follicular growth, oocyte maturation, fertilization and embryo transfer into recipient females was successfully performed. However, the efficiency of in vitro culture systems must still be considerably improved. Within the follicle, numerous events affect cell proliferation and the acquisition of oocyte developmental competency in vitro, including interactions between the follicular cells and the oocyte, and the composition of the culture medium. Effects of the acting factors depend on the stage of follicle development, the culture system used and the species. This paper reviews the action of endocrine, paracrine factors and other components of culture medium on in vitro growth of preantral follicles in rodents.

Morphological and ultrastructural analysis of sheep primordial follicles preserved in 0.9% saline solution and TCM 199

The objective was to determine the morphological and ultrastructural features of sheep primordial follicles preserved in either 0.9% saline solution or TCM 199 at different temperatures. Soon after death, the ovarian pair of each ewe (n = 5) was divided into 25 fragments. One fragment was immediately fixed for morphological evaluation (control). The other 24 fragments were randomly distributed in tubes containing 2 ml of 0.9% saline solution or TCM 199 and maintained at 4, 20 or 39 degrees C for 2, 4, 12, or 24h. Based on histological assessment, storage of ovarian fragments in 0.9% saline solution at 20 degrees C for up to 24h and in both solutions at 39 degrees C for 4, 12 or 24h increased (P < 0.01) the percentage of degenerate primordial follicles compared with controls. In contrast, preservation at 4 degrees C in both solutions, kept the percentage of morphologically normal primordial follicles similar to control values. Although histological integrity of primordial follicles was maintained in fragments stored at 20 degrees C for up to 24h in TCM 199, these results were not confirmed by ultrastructural analysis. Based on transmission electron microscopy, only primordial follicles stored at 4 degrees C for up to 24h, at 20 degrees C for up to 12h and at 39 degrees C for up to 2h in both solutions were ultrastructurally normal. In conclusion, sheep primordial follicles were successfully preserved at 4 degrees C for up to 24h, at 20 degrees C for up to 12h and at 39 degrees C for 2h in 0.9% saline solution or TCM 199.

In vitro growth and maturation as well as fertilization of mouse preantral oocytes from vitrified ovaries

OBJECTIVE

To examine the capacity for fertilization and development of preantral oocytes in oocyte-granulosa cell complexes (OGC) originating from vitrified ovaries.

DESIGN

Experimental animal study.

SETTING

University-based research laboratory.

ANIMAL(S)

Normal (C57BL/6xDBA2) F1 mice in a laboratory environment.

INTERVENTION(S)

Vitrification of mouse ovaries using polyester sheets as a storage device; collection of OGC by enzymatic treatment; in vitro growth (IVG), in vitro maturation (IVM), and in vitro fertilization (IVF).

MAIN OUTCOME MEASURE(S)

We performed histologic analysis of vitrified and warmed ovaries, and measured the successful rate in IVG, IVM, and IVF of oocytes in the OGC collected from the ovaries.

RESULT(S)

The cortical region of ovaries maintained good morphologic structure after vitrification and warming. Upon IVG and IVM, 75.9% of oocytes in OGC matured to the metaphase II (MII) stage. The fertilization rate of these oocytes was 57.5% as compared with 69.5% for fresh ovaries.

CONCLUSION(S)

The vitrification method used was effective for storage of ovaries. The oocytes enclosed in preantral follicles from the ovaries preserved capacity for fertilization and development to preimplantation embryos.

Mouse ovarian tissue cryopreservation has only a minor effect on in vitro follicular maturation and gene expression

PURPOSE

To establish a protocol for ovarian tissue cryopreservation which can retain fertility potential after thawing and to evaluate the impact of cryopreservation on development and gene expression during folliculogenesis.

METHODS

A controlled randomized study in a clinical and academic research setting in a university medical center was conducted to study cryopreservation and in vitro maturation (IVM) of mouse ovarian follicles. Preantral follicles isolated from either fresh (Group A) or cryopreserved (Group B) murine ovarian tissues were used to test their fertility potential by in vitro culture-in vitro maturation (IVC-IVM). Expression of Graafian follicles derived from both groups were detected by DNA microarray techniques for comparison.

RESULTS

Although there were no significant differences in IVM outcomes and follicular gene expression between the two experimental groups, cryopreservation appears to induce the expression of heat shock proteins, DNA-damage-inducible protein 45 and death-related apoptosis genes (i.e., Fas and Fas-ligand).

CONCLUSION

Cryopreservation may trigger biological events not amenable to normal cell function and follicular development. However, neither follicular development nor gene expression was dramatically changed after cryopreservation. These data suggest that although our current cryopreservation techniques yield competent follicles and mature oocytes, subtle changes observed in gene expression imply that the present cryopreservation techniques need to be further refined.