In vitro models for oocyte development

Why Is It So Difficult To Have Competent Oocytes from In vitro Cultured Preantral Follicles?

The developmental competence of oocytes is acquired gradually during follicular development, mainly through oocyte accumulation of RNA molecules and proteins that will be used during fertilization and early embryonic development. Several attempts to develop in vitro culture systems to support preantral follicle development up to maturation are reported in the literature, but oocyte competence has not yet been achieved in human and domestic animals. The difficulties to have fertilizable oocytes are related to thousands of mRNAs and proteins that need to be synthesized, long-term duration of follicular development, size of preovulatory follicles, composition of in vitro culture medium, and the need of multi-step culture systems. The development of a culture system that maintains bidirectional communication between the oocyte and granulosa cells and that meets the metabolic demands of each stage of follicle growth is the key to sustain an extended culture period. This review discusses the physiological and molecular mechanisms that determine acquisition of oocyte competence in vitro, like oocyte transcriptional activity, follicle and oocyte sizes, and length and regulation of follicular development in murine, human, and domestic animal species. The state of art of in vitro follicular development and the challenges to have complete follicular development in vitro are also highlighted.

Effect of increased oxygen availability and astaxanthin supplementation on the growth, maturation and developmental competence of bovine oocytes derived from early antral follicles

In vitro growth (IVG) culture of bovine oocyte-cumulus-granulosa complexes (OCGCs) is generally carried out for 12 or 14 days using conventional gas impermeable culture devices. The culture duration may be longer compared to follicular development in vivo. During follicular development, follicles receive oxygen from micro vessels; however, oxygen supply is limited under the culture using conventional gas impermeable devices. The purpose of this study was to investigate the effect of increasing dissolved oxygen availability using a gas permeable (GP) culture device with or without antioxidant (astaxanthin, Ax) supplementation on 8-day IVG culture systems for bovine OCGCs derived from early antral follicles. We cultured OCGCs in GP, GP supplemented with Ax (GP + Ax), and a conventional gas impermeable device (control) for 8 or 12 days. OCGC viability were significantly higher when cultured for 8 days than 12 days (p < 0.001) in all culture condition, but significant difference was not observed between groups (p > 0.05). Antrum formation rates of OCGCs were higher after 12 days than 8 days of culture in all culture condition (p < 0.001) and were significantly higher in the control than GP groups regardless of Ax supplementation (p < 0.05). Oocyte diameters were similar among day-8 GP + Ax, day-8 control and day-12 control groups (p > 0.05). Nuclear maturation rates of oocytes grown in vitro for 8 days were significantly higher in the GP + Ax group than in the control and the GP groups (p < 0.05) and similar to oocytes grown for 12 days regardless of the culture conditions (p > 0.05). The generation of reactive oxygen species in OCGCs on day 8 of IVG culture was significantly lower in the GP + Ax group than those of the GP and control groups (p < 0.05). IVG oocytes after eight days of culture developed into blastocysts, and the cleavage and blastocyst rates were similar in all treatment groups. However, in vivo-grown oocytes had significantly higher (p < 0.05) cleavage and blastocyst rates than the IVG oocytes in all groups. The present study demonstrates that increased oxygen availability using a GP culture device with Ax supplementation promotes oocyte growth and maturation competence but inhibits proliferation of granulosa cells and antrum formation compared with a conventional gas impermeable culture device, and that OCGCs can attain developmental competence after 8 days of IVG culture.

Characteristic of factors influencing the proper course of folliculogenesis in mammals

Folliculogenesis is the process of ovarian follicle formation,, taking presence during foetal period. During the follicular development, oogoniums undergo meiosis and oocytes are formed. In the ovaries of new born sows, primary and secondary follicles are present and, 90 days after birth, tertiary follicles appear. During development in the ovarian follicles growth of granulosa cells and differentiation of the thecal cells can be observed. A cavity filled with follicular fluid appears. Granulosa cells are divided into: mural cells and corona radiata, which together with the oocyte form the cumulus oophorus. Corona radiata cells, mural layers and oolemma contact each other by a network of gap junctions. Secreted from the pituitary gland, FSH and LH gonadotropin hormones act on receptors located in granular and follicular cells. In the postnatal life tertiary follicles and Graafian follicles are formed. When the follicle reaches a diameter of 1 mm, further growth depends on the secretion of gonadotropins. Mature ovarian follicles produce: progestins, androgens and oestrogens. The growth, differentiation and steroidogenic activity of ovarian follicles, in addition to FSH and LH, is also affected by prolactin, oxytocin, steroid and protein hormones, numerous proteins from the cytokine and interleukin family, metabolic hormones like insulin, glucocorticoids, leptin, thyroid hormones and growth hormones. Despite numerous studies, many processes related to folliculogenesis have not been discovered Learning the mechanisms regulating reproductive processes would allow to easily distinguish pathological processes and discover more and more genes and mechanisms of their expression in cells that build ovarian follicles.

New approaches to increasing oocyte yield from ruminants

Artificial insemination, superovulation and embryo transfer have had beneficial impacts on animal production but a limiting factor to realizing the full potential of these techniques and of other reproductive technologies is the availability of fertile oocytes. To overcome this problem, methods for maturing oocytes in vitro (IVM) have been developed. The production of bovine embryos by IVM is in commercial use but the rate of success and quality of embryos is low. The lack of success may be due to the quality of oocytes that are being matured and it would be preferable to utilize the abundant source of immature oocytes from preantral and primordial follicles by developing systems for in vitro growth (IVG). Several culture systems that utilize early growing follicles as a source of oocytes have been developed for laboratory species and these have been successful in producing live young. IVG in association with IVM and cryopreservation have the potential to maximize the genetic potential of high genetic merit females and shorten generation intervals. This paper presents the current status of technology for the in vitro growth and development of immature oocytes, in vitro maturation and cryopreservation of germ cells in domestic ruminants.

Maintaining the reproductive potential of cancer patients during cancer treatment

Cancer therapies are known to alter the reproductive potential in cancer patients. Due to improved survival rates in cancer patients of reproductive age, considerations of the long-term effects of cancer therapy have become more significant. Oncofertility is a new discipline in medicine that deals with maintaining the reproductive potential of cancer patients while they are receiving gonadotoxic cancer treatment. The purpose of this review is to explore how cancer treatment impairs reproductive functioning and present the current options for preservation of fertility in women. All patients with reproductive potential should be made aware of the possible treatment-related infertility and be offered appropriate fertility preservation options before cancer treatment is instituted. The hope is that, in the future, mechanism(s) can be developed to preserve immature germ cells in the ovary, so that they can be used for fertilization in vivo or in vitro.

Effects of ascorbic acid on in vitro culture of bovine preantral follicles

The objective of this study was to evaluate the effects of adding ascorbic acid to the media for in vitro culture of cattle ovarian fragments and to determine their effects on growth activation and viability of early-stage follicles. The ovarian cortex was divided into small fragments; one fragment was immediately fixed (control) and the other fragments were cultured in minimum essential medium (MEM) supplemented or not with various doses of ascorbic acid. Ovarian tissue was processed for histology, transmission electron microscopy (TEM) and immunohistochemical demonstration of proliferating cell nuclear antigen (PCNA). Compared with control fragments, the percentage of primordial follicles was reduced (p < 0.05) and the percentage of growing follicles had increased (p < 0.05) in cultured cortical fragments, independent of the tested medium or incubation time. Furthermore, compared with control tissue, culture of ovarian cortex for 8 days reduced the percentages of healthy, viable follicles (p < 0.05), but not when cultures were supplemented with 25, 50 or 100 μg/ml of ascorbic acid. Ultrastructural and immunohistochemical analysis of 8 day cultured ovarian cortical fragments, however, showed the integrity and viability of follicles only when fragments were cultured in presence of 50 μg/ml of ascorbic acid. In conclusion, this study demonstrated that addition of ascorbic acid to MEM at a concentration of 50 μg/ml not only stimulates the activation of 8 day in vitro cultured cattle primordial follicles and subsequent growth of activated follicles, but also safeguards the viability of these early-stage follicles.

Evaluation of maturation competence of metaphase II oocytes in mice based on the distance between pericentriolar materials of meiotic spindle: distance of PCM during oocyte maturation

PURPOSE

To ascertain whether metaphase II (MII) spindle shape influences oocyte competence, we examined the meiotic spindle organization in in vivo ovulated (IVO) oocytes and in spontaneously matured or follicle stimulating hormone (FSH)-induced oocytes.

METHODS

FSH-induced oocytes matured in Waymouth's MB752/1 or human tubal fluid (HTF) media and oocytes matured spontaneously in the basal medium were obtained, and spindles were detected by immunofluorescence. To evaluate the fertilization-associated differences in spindle morphology, we performed in vitro fertilization and analysed integrin mRNA expression.

RESULTS

The distance between the pericentriolar materials (PCMs) in oocytes matured under all conditions was initially more, but it reduced gradually and increased again thereafter. Therefore, oocytes exhibiting a reduction in the distance between PCMs had the highest development rate to blastocyst in each condition.

CONCLUSION

These results indicate that the 'maturation competence' of MII oocytes can be evaluated on the basis of the distance between PCMs.

Follicular interactions affect the in vitro development of isolated goat preantral follicles

The aim of this study was to evaluate the influence of the number of follicles per drop (one or three) and antral follicles on in vitro development of isolated goat preantral follicles. Preantral follicles were isolated through microdissection and distributed individually (control) or in groups of three follicles (treatment) in microdroplets of α-MEM with or without 1000 ng/ml follicle stimulating hormone (FSH) for Experiments 1 and 2, respectively. Experiment 3 was divided into four treatments according to the presence of one or three preantral follicles, associated or not with antral follicles. After culture, oocytes were retrieved from morphologically normal follicles and submitted to in vitro maturation (IVM) and live/dead fluorescent labelling. Results of Experiment 1 (basic medium without FSH) showed that culture of preantral follicles in groups enhances viability, growth and antrum formation after 12 days. However, in the presence of FSH (Experiment 2), only the recovery rate of fully grown oocytes for IVM was significantly affected by grouping of follicles. In Experiment 3, in general, co-culture of preantral follicles with an early antral follicle had a detrimental effect on viability, antrum formation and production of oocytes for IVM. In conclusion, the performance of in vitro culture of goat preantral follicles is affected by the number of follicles per drop, the presence of an antral follicle and FSH.

Formation of an antral follicle-like structure of bovine cumulus-oocyte complexes embedded individually or in groups in collagen gels

Culture techniques of antral follicle-like structure (AFLS) derived from cumulus-oocyte complexes (COCs) might provide important insights into follicular development and oocyte maturation. This study was undertaken to investigate the effects of embedding bovine COCs individually (one COC) or in groups (4-5 COCs) in collagen gels on the formation of AFLS and the meiotic status of oocytes. The observations of AFLS formation were performed every second day for 14 days. The AFLS was formed at Day 2 or 4 after the start of culture (Day=0), irrespective of the culture methods. The mean diameters of AFLS during Days 4-14 using the individual culture method were significantly higher (p<0.05) than those using the group culture method. However, the AFLS formation rate in the individual culture method was significantly lower compared to that in the group culture method (26.1% vs 62.7%, p<0.01). Almost all oocytes had undergone the germinal vesicle breakdown stage, irrespective of the culture method or AFLS formation. In conclusion, comparison with the individual culture method revealed that the mean diameters of AFLS in the group culture method were smaller, but more COCs formed AFLS. The group culture method might be useful for evaluating the various hypotheses of follicular formation and interfollicular communication. However, improvement of the group culture system is necessary to prevent the meiotic resumption of oocytes, because the AFLS formation is dependent on the cumulus/granulosa cells surrounding oocytes.

Dynamic oxygen enhances oocyte maturation in long-term follicle culture

Traditionally, follicles have been grown in standard incubators with atmospheric oxygen concentration. However, preantral follicles exist in the avascular cortex of the ovary. This study examines the effectiveness of an oxygen delivery protocol that more closely mimics the in vivo environment of the ovary on oocyte viability, maturation, parthenogenetic activation, and fertilization from in vitro cultured rat preantral follicles. Of 54 oocytes cultured in the dynamic oxygen environment, 35 were viable while only 22 of 50 oocytes cultured within an ambient oxygen concentration remained viable (p < 0.05). Germinal vesicle breakdown was observed in 56% of oocytes from the dynamic oxygen group compared to 30% of oocytes from the ambient oxygen group (p < 0.05). Parthenogenetic activation was observed in a significant number of oocytes from the dynamic oxygen group, while none of the oocytes from the ambient oxygen group activated (p < 0.05). However, the proportions of oocytes from the dynamic oxygen group that remained viable underwent germinal vesicle breakdown, and activated were still significantly less than those from the in vivo control group (p < 0.05). Fertilization of the oocytes from the dynamic oxygen group was confirmed through a successful trial of intracytoplasmic sperm injection.

Advanced methods of isolation and identification of porcine primordial follicles

An effective isolation and identification method of primordial follicles would greatly benefit the animal production practice, transgenic animal production and endangered species conservation in the future. This study has not only advanced the isolation method but also developed an identification marker of primordial follicles. After enzymatic digestion, Percoll gradient centrifugation and mesh filtrations, the obtained follicular separations were then subjected to a cell sorter in order to collect primordial follicles. The study greatly improved the yield of primordial follicles (from about 1.85 x 10(5) to 7.79 x 10(5) per prepubertal ovary) by means of increasing cell layer number from 1 ml to 2.5 ml after Percoll gradient centrifugation. Based on traditional morphological criteria, the purity of recovered primordial follicles was averagely about 82.43+/-9.41% (n=5) because of their similar size and appearance with somatic cells. To further exactly appreciate the purity of sorted primordial follicles, a germ cell-specific protein, MSY2, was used to recognize the oocytes of primordial follicles. The results of repeat experiments showed that about 98.31+/-0.73% (n=4) of the primordial follicles cluster was MSY2-positive, which indicated the identification method of primordial follicles was more effective and high-yielded than the previous methods because of its higher purity.

Isolation, follicular density, and culture of preantral follicles of buffalo fetuses of different ages

The aim of the present study was to determine the most desirable ovarian tissue section thickness to isolate preantral follicles (Experiment I), determine follicular density (follicles/mm(2) of cortex) of ovaries of fetal buffalo of different ages (Experiment II), and cultivate preantral follicles of buffalo fetuses (Experiment III). In Experiment I, ovary sections with different thicknesses (25, 50, 75, and 100 microm) had 415.0+/-285.2, 457.5+/-341.9, 585.0+/-309.3, and 685.0+/-278.8 isolated preantral follicles, respectively. In Experiment II, the follicular density of 46 buffalo fetuses with ages between 3 and 8 months was estimated to be between 0 and 7220, with means of 0.0, 2070.7+/-2190.3, 2570.8+/-1796.6, 2298.1+/-2286.5, 1277.5+/-1074.9, and 643.6+/-543.9 throughout the age range studied. The follicular density of 5-month-old fetuses was greatest, coinciding with the largest number of follicles isolated at this age. In Experiment III, preantral follicles isolated from the ovaries of buffalo fetuses aged from 5 to 9 months old were cultivated individually for 7 days in four different media: basic medium (Minimal Essential Medium (MEM), 10% SFB, kanamycin, pyruvate, glutamine, hypoxanthine) with additional ITS and FSH 0.5mg/ml (treatment 1); basic medium with FSH and EGF 100 ng/ml (treatment 2); basic medium with additional ITS, FSH, and EGF (treatment 3); basic medium supplemented with ITS and EGF (treatment 4). Integrity and morphological features, viability, and increase in diameter of follicles cultured in vitro were evaluated individually with an inverted microscope and an ocular micrometer. The results showed that follicle structure and form were maintained during culture. Growth and survival rates of treatments 1, 2, and 3 over 7 day culture were 23.25+/-17.06, 33.75+/-26.19, and 43.75+/-31.73 microm, and 31.3+/-22.7, 22.06+/-8.13, and 28.92+/-21.32%, respectively. However, neither growth nor survival was observed in treatment 4. In conclusion, this study showed that preantral follicles of buffalo fetuses can be cultured in vitro, and that FSH is essential for follicle survival.

Survival and meiotic competence of bovine oocytes originating from early antral ovarian follicles

The aim of the present study was to examine the growth and survival in culture, and the subsequent meiotic competence, of bovine oocytes recovered from early antral ovarian follicles. Follicles isolated by microdissection of the ovarian slices were sorted into two size groups: (I) 0.2-0.5 mm diameter; and (II) 0.4-0.7 mm diameter. Group I follicles were cultured intact while in Group II, cumulus-oocyte complexes with pieces of parietal granulosa were dissected from the follicles and cultured. Follicles or cumulus-oocyte complexes with parietal granulose were embedded in collagen gel and cultured in TCM 199 supplemented with 3% BSA and 4 mM hypoxanthine for 14 days (Group I) or 7-10 days (Group II). After this, cumulus-oocyte complexes were recovered from the gel. Oocytes that had lost the majority of the cumulus were fixed immediately after recovery. Cumulus-oocyte complexes showing normal morphology were either fixed immediately or were subjected to IVM for an additional 24h, and then were fixed. At the end of the growth culture, 57.6% of the compact COCs in Group I follicles were preserved in the GV configuration, 16.7% had resumed meiosis, and 25.8% were degenerated or did not show detectable chromatin. After IVM, the proportion of oocytes resuming meiosis increased significantly (from 16.7% versus 42.7%; P < 0.05), and 9.1% of all oocytes had reached TI or MII. The isolated cumulus-oocyte complexes in Group II began creating follicle-like structures following 24 h of growth culture (7.1%). The proportion of these structures reached 50.8% on days 2-3, and then gradually decreased due to degeneration. On day 10 only 5.8% of cumulus-oocyte complexes were classified as intact. Of the cumulus intact oocytes recovered from the newly created follicle-like structures at 7-10 days, 54.7% were in the germinal vesicle stage, 31.0% underwent germinal vesicle breakdown, 14.3% were degenerated or the chromatin configuration was not detectable. After 24 h of IVM, 67.6% of oocytes had resumed meiosis, and 21.6% of all oocytes had reached TI and MII. These results show that isolated early follicles and cumulus-oocyte complexes from intact early antral follicles can grow in culture and can develop meiotic competence.

In vitro growth of oocytes from primordial follicles isolated from frozen-thawed lamb ovaries

A study was conducted to develop an in vitro culture system for growing sheep oocytes from isolated primordial follicles. Enzymatically isolated neonatal sheep primordial follicles were cultured in Waymouth MB752/1 medium containing BSA (3 mg/ml) + ITS (1%, v/v) over 28 days. In Experiment 1, primordial follicles (average diameter 40.2+/-0.60 microm) were cultured at densities of 20, 50 and 100 follicles per well. Less than 20% of the oocytes survived to day 28 but there was a significant (P < 0.05) increase in median oocyte diameter from day 2 to day 28 for oocytes cultured at the higher densities of 50 and 100 follicles. In Experiment 2, two methods to improve oocyte:granulosa cell associations were tested. Altering the fibronectin coating regime did not improve oocyte survival and growth. In contrast lectin-aggregated primordial follicles cultured on non-coated wells showed significantly (P < 0.05) improved oocyte survival to 50% and increased median oocyte diameter compared to non-aggregated follicles. In Experiment 3, the effect of KIT ligand (KL) at 0 ng/ml, 10 ng/ml and 100 ng/ml, on lectin-aggregated primordial follicles cultured on non-coated wells was tested. KL at 100 ng/ml significantly (P < 0.05) increased median oocyte diameter compared to non-treated controls but had no effect on oocyte survival. In addition, follicles cultured with 100 ng/ml KL expressed mRNA for AMH, a gene expressed only in granulosa cells of growing follicles. In conclusion, culture of lectin-aggregated primordial follicles supported the long-term survival and growth of oocytes from isolated sheep primordial follicles. Culture of lectin-aggregates with 100 ng/ml KL further increased oocyte growth and induced granulosa cell differentiation.

Meiotic spindle morphogenesis in in vivo and in vitro matured mouse oocytes: insights into the relationship between nuclear and cytoplasmic quality

BACKGROUND

This work addresses the hypothesis that events occurring within the follicle soon after the LH surge are essential for coordinating morphogenesis of the spindle and cytoplasm in mouse oocytes matured in vivo (IVO); we further tested whether in vitro maturation (IVM) fails to support these events.

METHODS

Oocytes collected at 1, 2, 3, 4 and 5 h post-hCG or after IVM were analyzed for chromatin, nuclear lamina, microtubules (MTs) and centrosomal proteins by conventional fluorescence and confocal microscopy. In addition, these parameters were monitored in oocytes maintained in 50 microM roscovitine, followed by IVM, or in oocytes retrieved at 1.5 and 5 h post-hCG in vivo and cultured up to 16 h.

RESULTS

A G2/M delay was observed in IVO oocytes based upon persistence of cytoplasmic MTs, nuclear lamina and centrosomes at the cortex; rapid meiotic progression in IVM oocytes was related to loss of these markers, indicating that a global activation of MPF occurred in culture. Also, maturating-promoting factor (MPF) inactivation resulted in cultured oocytes that exhibited IVO characteristics after drug removal. IVO-like characteristics were also exhibited by oocytes retrieved at 5 but not at 1.5 h after hCG treatment, even though these oocytes were subsequently cultured.

CONCLUSIONS

The results emphasize the importance of coupling MT remodeling and cell cycle components during oocyte maturation to achieve a balanced coordination of nuclear and cytoplasmic maturation that under physiological conditions occurs within the first 5 h of LH stimulation.

Cryopreservation and culture of human ovarian cortical tissue containing early follicles

Maturation of oocytes from primordial follicles after cryopreservation of ovarian tissue with subsequent in vitro fertilisation would be an important method of infertility treatment for young women who are to undergo premature ovarian failure due to chemotherapy or genetic causes. Cryopreservation of human ovarian tissue is already feasible. Human primordial follicles can be cultured regularly to secondary and occasionally to early antral stages, yet cultures have to be further optimised before meiotically competent oocytes can be achieved for final maturation in vitro. Maturation in vitro (IVM) of oocytes obtained by aspiration from small antral follicles is already a feasible technique resulting in pregnancies, with many healthy infants born.

In vitro growth and development of bovine oocyte-granulosa cell complexes on the flat substratum: effects of high polyvinylpyrrolidone concentration in culture medium

The aim of this study was to establish a culture system to support the growth of bovine oocytes as enclosed in granulosa cell complexes that extend on a flat substratum. Such systems have been established for mouse oocytes but are not applicable to larger animals because it is difficult to maintain an appropriate association between the oocyte and companion somatic cells. Growing bovine oocytes with a mean diameter of 95 microm were isolated from early antral follicles: the growing stage corresponds to that of oocytes in preantral follicles of 12-day-old mice. Oocyte-granulosa cell complexes were cultured for 14 days in modified TCM199 medium supplemented with 5% fetal bovine serum, 4 mM hypoxanthine, and 0.1 microg/ml estradiol. The novel modification made for this medium was a high concentration, 4% (w/v), of polyvinylpyrrolidone (PVP; molecular weight of 360000). The flat substratum used was either an insert membrane fit in the culture plate or the bottom surface of the wells of 96-well culture plates. PVP influenced the organization of complexes, resulting in a firm association between the oocyte and the innermost layer of surrounding cells. More oocytes enclosed by a complete cell layer were recovered from the medium supplemented with 4% PVP than from the control medium. Similarly, of the oocytes initially introduced into the growth culture, a significantly larger proportion developed to the blastocyst stage from medium containing 4% PVP than from medium without PVP. When PVP medium was used, the overall yield of blastocysts was similar between the system with the insert membranes (12%) and that with the 96-well culture plates (9%). A calf was produced from one of four embryos derived from oocytes grown in 96-well culture plates, matured, and fertilized in vitro and then transferred to a recipient cow.

Distinctions in meiotic spindle structure and assembly during in vitro and in vivo maturation of mouse oocytes

To better understand the differences in cytoskeletal organization between in vivo (IVO) and in vitro (IVM) matured oocytes, we analyzed remodeling of the centrosome-microtubule complex in IVO and IVM mouse oocytes. Fluorescence imaging revealed dramatic differences in meiotic spindle assembly and organization between these two populations. Metaphase spindles at both meiosis I (M-I) and meiosis II (M-II) in IVO oocytes were compact, displayed focused spindle poles with distinct gamma-tubulin foci, and were composed of acetylated microtubules. In contrast, IVM oocytes exhibited barrel-shaped spindles with fewer acetylated microtubules and gamma-tubulin diffusely distributed throughout the spindle proper. With respect to meiotic progression, IVO oocytes were more synchronous in the rate and extent of anaphase to telophase of M-I and first polar body emission than were IVM counterparts. Furthermore, IVO oocytes showed a twofold increase in cytoplasmic microtubule organizing centers (MTOCs), and constitutive MTOC proteins (gamma-tubulin and pericentrin) were excluded from the first polar body. Inclusion of MTOC constitutive proteins in the polar body and diminished number of cytoplasmic MTOCs was observed in IVM oocytes. These findings were corroborated in IVO oocytes obtained from naturally ovulated and spontaneously cycling mice and highlight a fundamental distinction in the spatial and temporal regulation of microtubule dynamics between IVO and IVM oocytes

Novel Approach for the Three-Dimensional Culture of Granulosa Cell–Oocyte Complexes

The in vitro culture of immature ovarian follicles is used to examine the factors that regulate follicle development and may ultimately provide options for reproductive infertility. The objective of this study was to develop a three-dimensional in vitro culture system for the growth and development of individual granulosa cell-oocyte complexes. An alginate hydrogel was used to encapsulate immature mouse granulosa cell-oocyte complexes (GOCs) that were subsequently maintained in a serum-free in vitro culture. An overall incorporation efficiency of 50% was achieved. The complexes were assessed by transmission electron microscopy for changes in ultrastructure during in vitro growth. The architecture of the follicular complex was maintained during the encapsulation and the subsequent culture. The granulosa cells proliferated, and the oocytes also grew in volume and obtained the structural characteristics of mature oocytes including cortical granule formation, a well-developed zona pellucida with microvilli, normal mitochondria, and lattice-like structures in the cytoplasm. Oocytes retrieved and matured were able to resume meiosis, a necessary step for proper development. Thus, this system represents a new in vitro methodology for growth of individual granulosa cell-oocyte complexes.

In vitro growth, maturation, fertilization, and embryonic development of oocytes from porcine preantral follicles

This study was conducted to identify an in vitro culture system that would support intact porcine follicle growth from preantral follicle to antral stages, oocyte maturation, fertilization, and embryonic development; and to evaluate factors that influence porcine preantral follicle growth in vitro. Preantral follicles isolated from prepubertal porcine ovaries were cultured for 4 days in the presence of different concentrations of porcine serum and FSH, and with different numbers of follicles per well. A series of experiments showed that porcine antral follicles can be grown at a high frequency in vitro from healthy preantral follicles with intact theca when cultured in North Carolina State University 23 medium supplemented with 1.5 ng/ml FSH, 7.5% serum, and when cultured with three follicles per well. After 4 days of culture, 68% healthy cumulus-enclosed oocytes from these follicles were obtained, and 51% of the oocytes completed meiotic maturation to the metaphase II stage. Fifty-three percent of the mature oocytes underwent fertilization, 43% of the fertilized oocytes cleaved, and 13% developed to the blastocyst stage. The results show 1) that porcine preantral follicles can grow efficiently to the antral stage using these culture conditions, and 2) that oocytes from in vitro-matured porcine preantral follicles can acquire meiotic competence and undergo fertilization and embryonic development.

In vitro development of oocytes from porcine and bovine primary follicles

A limiting factor to realising the full potential of many of the new reproductive techniques is the lack of availability of fertile oocytes. Methods for maturing oocytes in vitro (IVM) have been developed to address this problem but the success rate and quality of embryos produced by IVM is variable. The variation in success may be due to the poor quality of oocytes that are being selected for maturation, since these would be taken from developed antral follicles. To attempt to eliminate this variation and increase the numbers produced, it may be better to use the large source of oocytes from preantral and primordial follicles by developing systems for in vitro growth (IVG). In vitro systems that utilise early growing follicles as a source of oocytes have been developed for laboratory species and these have been successful in producing live young. If successful, IVG in association with IVM would supercede existing technology for assisted reproduction in both humans and animals by making it possible to develop the desired number of high quality oocytes from small amounts of ovarian tissue. However, developing IVG systems for species with follicles that develop over several months presents enormous technical challenges. We have developed systems that permit the growth of individual porcine and bovine preantral follicles for periods of up to 20 days. Porcine follicles grown in micro-wells show a higher rate of survival if grown in the presence of serum than follicles grown under serum free conditions. Oocytes recovered from in vitro grown porcine follicles are capable of reaching metaphase II after in vitro maturation. A similar system has been developed for bovine follicles and survival rate is high under serum free conditions but as yet no oocytes from in vitro grown oocytes have been capable of completing meiotic maturation.

Growth and antrum formation of bovine preantral follicles in long-term culture in vitro

Culture of preantral follicles has important biotechnological implications through its potential to produce large quantities of oocytes for embryo production and transfer. A long-term culture system for bovine preantral follicles is described. Bovine preantral follicles (166 +/- 2.15 micrometer), surrounded by theca cells, were isolated from ovarian cortical slices. Follicles were cultured under conditions known to maintain granulosa cell viability in vitro. The effects of epidermal growth factor (EGF), insulin-like growth factor (IGF)-I, FSH, and coculture with bovine granulosa cells on preantral follicle growth were analyzed. Follicle and oocyte diameter increased significantly (P < 0.05) with time in culture. FSH, IGF-I, and EGF stimulated (P < 0.05) follicle growth rate but had no effect on oocyte growth. Coculture with granulosa cells inhibited FSH/IGF-I-stimulated growth. Most follicles maintained their morphology throughout culture, with the presence of a thecal layer and basement membrane surrounding the granulosa cells. Antrum formation, confirmed by confocal microscopy, occurred between Days 10 and 28 of culture. The probability of follicles reaching antrum development was 0.19 for control follicles. The addition of growth factors or FSH increased (P < 0.05) the probability of antrum development to 0.55. Follicular growth appeared to be halted by slower growth of the basement membrane, as growing follicles occasionally burst the basement membrane, extruding their granulosa cells. In conclusion, a preantral follicle culture system in which follicle morphology can be maintained for up to 28 days has been developed. In this system, FSH, EGF, and IGF-I stimulated follicle growth and enhanced antrum formation. This culture system may provide a valuable approach for studying the regulation of early follicular development and for production of oocytes for nuclear/embryo transfer, but further work is required.

Ammonia concentration in bovine follicular fluid and its effect during in vitro maturation on subsequent embryo development

10 mm) to determine ammonia concentration. Ammonia concentration was greater (P<0.001) in the bFF from smaller follicles compared with bFF from larger follicles, and ammonia concentration decreased (P10 mm follicles, respectively. In Experiment 2, abattoir oocytes (n=2885) were matured in vitro in media containing ammonia at the concentrations of 0 microM (Control), 29 microM (A1), 88 microM (A2), 132 microM (A3), 176 microM (A4) and 356 microM (A5), followed by in vitro fertilization and culture. There was no difference (P0.05) in cleavage rates and morula or blastocyst development between treatments, indicating that in vitro exposure of bovine oocytes to ammonia does not adversely influence subsequent embryonic development.

Factors determining competence of in vitro produced cattle embryos

Concerns have developed in regard to problems associated with pregnancies and calves produced after use of cattle blastocysts made in the laboratory for embryo transfer. For both empirical studies and commercial purposes, there is a need for assurance that the product of these biotechnologies results in a normally functioning entity of its kind. Ability to use more genetic material from a donor female and in producing blastocysts needs to be improved to increase the efficiency of utilizing in vitro biotechnologies in animal production agriculture and for biomedical purposes. The role of gametes used as raw materials for laboratory production cattle embryos and adequacy of culture systems in supporting development of embryos are discussed in relation to competency of embryos produced in vitro.