Oocyte maturation in vitro

Fertility preservation in breast cancer patients

Breast cancer is the most commonly diagnosed cancer in women. As long-term survival rates have improved, there has been a concurrent increase in quality of life considerations, of which fertility preservation is of utmost importance. A number of fertility preservation options are available to women diagnosed with breast cancer, including administration of a GnRH agonist during chemotherapy in an attempt to minimize ovarian damage, oocyte or embryo cryopreservation prior to the administration of chemotherapy, in vitro maturation of oocytes or ovarian tissue cryopreservation. The safety of pregnancy after a diagnosis of breast cancer has been confirmed in numerous studies.

Differential gene expression between in vivo and in vitro maturation: a comparative study with bovine oocytes derived from the same donor pool

Objective:

In vitro maturation has been shown to influence gene expression in oocytes, but a common shortcoming in reports on the matter has been the use of different donors in each experimental group thus disregarding donor effects. This study aimed to investigate the abundance of mRNA in oocytes matured in vivo and in vitro obtained from the same group of donors.

Methods:

A bovine model was used to assess the relative abundance of specific transcripts in in vitro-matured (IN VITRO-OPU) and in vivo-matured (IN VIVO-OPU) oocytes collected from the same donors by transvaginal ovum pick-up (OPU). Transcript abundance in oocytes from the IN VIVO-OPU group and oocytes matured in vitro but retrieved from different cows slaughtered at a commercial abattoir (IN VITRO-Abattoir group) was also compared. Total RNA was extracted from denuded oocytes and cDNA was produced via reverse transcription using an oligo(dT) primer for relative quantification of eight target transcripts by real-time PCR.

Results:

Oocytes in the IN VITRO-OPU group had lower (p<0.05) abundance of peroxiredoxin 1 (Prdx1), heat shock protein 70.1 (Hsp70.1), growth and differentiation factor 9 (Gdf9), and maternal antigen that embryo requires (Mater) transcripts than the oocytes in the IN VIVO-OPU group, all obtained from the same pool of donor cows. Similar results were seen in the comparisons involving the IN VIVO-OPU and IN VITRO-Abattoir groups (p<0.05).

Conclusion:

In vitro maturation affected the abundance of polyadenylated transcripts in the oocyte cytoplasm when compared to in vivo maturation induced by exogenous hormones in oocytes collected from the same donor pool.

Effect and possible mechanisms of melatonin treatment on the quality and developmental potential of aged bovine oocytes

After reaching the metaphase II (MII) stage, unfertilised oocytes undergo a time-dependent process of quality deterioration referred to as oocyte aging. The associated morphological and cellular changes lead to decreased oocyte developmental potential. This study investigated the effect of exogenous melatonin supplementation on in vitro aged bovine oocytes and explored its underlying mechanisms. The levels of cytoplasmic reactive oxygen species and DNA damage response in bovine oocytes increased during in vitro aging. Meanwhile, maturation promoting factor activity significantly decreased and the proportion of morphologically abnormal oocytes significantly increased. Melatonin supplementation significantly decreased quality deterioration in aged bovine MII oocytes (P < 0.05). Additionally, it decreased the frequency of aberrant spindle organisation and cortical granule release during oocyte aging (P < 0.05). In the melatonin-supplemented group, mitochondrial membrane potential and ATP production were significantly increased compared with control. Furthermore, melatonin treatment significantly increased the speed of development of bovine oocytes to the blastocyst stage after in vitro fertilisation and significantly decreased the apoptotic rate in the blastocysts (P < 0.05). The expression of Bax and Casp3 in the blastocysts was significantly reduced after treatment with melatonin, whereas expression of Bcl2 significantly increased (P < 0.05). In conclusion, these findings suggest that supplementation of aged bovine oocytes with exogenous melatonin improves oocyte quality, thereby enhancing the developmental capacity of early embryos.

Characterisation of the cellular and molecular responses of ovine oocytes and their supporting somatic cells to pre-ovulatory levels of LH and FSH during in vitro maturation

The response of Graafian follicles to pre-ovulatory surge levels of FSH and LH in vivo triggers the terminal differentiation of granulosa cells and oocyte maturation. In polyovular species, the LH-driven signalling uses the epidermal growth factor (EGF)-like ligands AREG, EREG and BTC to promote oocyte maturation and cumulus expansion. This experimental series used a physiologically relevant ovine in vitro maturation (IVM) system to evaluate the impact of exposure to pre-ovulatory levels (100 ng/ml) of LH and FSH on ovine cumulus cell expression of EGF-like ligands in vitro. The serum-free sheep IVM system supported high levels (91.4%) of gonadotrophin-induced maturation of cumulus-enclosed oocytes and embryo development to the blastocyst stage (34.5%). Results were equivalent to a serum-based IVM system (85.1% IVM, 25.8% blastocyst rate; P>0.05) but were significantly different (P<0.05) to serum-free medium without gonadotrophins (69.5% IVM; 8.0% blastocyst rate). Ovine BTC was cloned and sequenced. Gonadotrophin-induced AREG, EREG, BTC and EGFR expressions were quantified in cumulus and mural granulosa cells during IVM. A rapid induction of AREG expression was apparent in both cell types within 30 min of gonadotrophin exposure in vitro. LHCGR (LHR) was detected in mural cells and FSHR in both cumulus and mural granulosa cells. The data confirm the involvement of AREG and EGFR during gonadotrophin-induced cumulus expansion, oocyte maturation and the acquisition of developmental competence by sheep oocytes matured in vitro.

Oocyte maturity in relation to woman's age in in vitro fertilization cycles stimulated by single regimen

PURPOSE

During stimulated in vitro fertilization (IVF) cycle, up to 30% of the recovered oocytes are immature ones which have poor fertilization capacity; however, the precise influencing factors are largely unknown. Here, we analyzed the association of oocyte immaturity with woman's age in IVF cycles stimulated by single regimen.

MATERIALS AND METHODS

A total of one-hundred ninety five IVF cycles stimulated by recombinant FSH and GnRH antagonist protocol between 2003 and 2009 were analyzed retrospectively. The mean age of women was 34.2 ± 4.0 (26-45 years). After triggering by exogenous hCG, an ultrasound-guided retrieval of oocytes was performed 35-36 hours later. All clinical data were stratified by woman's age; group I: ≤ 30 (n=36), II: 31-35 (n=83), III: 36-40 (n=57), and IV: ≥ 41 (n=19).

RESULTS

The total retrieved oocytes, as well as immature oocytes, were significantly lower in group IV, however, the mean % of immature oocytes was significantly higher in group IV than other age groups. Oocyte immaturity tended to decrease as increasing age in women aged 40 years or less.

CONCLUSION

In stimulated IVF cycle, much higher oocyte immaturity was noted in women aged 41 years or more.

Successful in vitro culture of pre-antral follicles derived from vitrified murine ovarian tissue: oocyte maturation, fertilization, and live births

Cryopreservation of ovarian tissue is an important option for preserving the fertility of cancer patients undergoing chemotherapy and radiotherapy. In this study, we examined the viability and function of oocytes derived in vitro from pre-antral follicles as an alternative method for restoring fertility. Pre-antral follicles (specified as secondary follicle with a diameter around 100-130 μm) were mechanically isolated from vitrified-warmed and fresh adult mouse ovarian tissues and cultured for 12 days followed by an ovulation induction protocol at the end of this period to initiate oocyte maturation. Oocytes were then released from these follicles, fertilized in vitro, and cultured to the blastocyst stage and vitrified. After storage in liquid nitrogen for 2 weeks, groups of vitrified blastocysts were warmed and transferred into pseudo-pregnant recipient females. Although most of the isolated mouse pre-antral follicles from fresh (79.4%) and vitrified (75.0%) ovarian tissues survived the 12-day in vitro culture period, significantly fewer mature oocytes developed from vitrified-warmed pre-antral follicles than from the fresh controls (62.2 vs 86.4%, P<0.05). No difference was observed in embryo cleavage rates between these two groups, but the proportion of embryos that developed into blastocysts in the vitrification group was only half that of the controls (24.2 vs 47.2%, P<0.05). Nevertheless, live births of healthy normal pups were achieved after transfer of vitrified blastocysts derived from both experimental groups. This study shows that successful production of healthy offspring using an in vitro follicle culture system is feasible, and suggests that this procedure could be used in cancer patients who wish to preserve their fertility using ovarian tissue cryopreservation.

Role for cumulus cell-produced EGF-like ligands during primate oocyte maturation in vitro

The developmental competence of in vitro-matured (IVM) rhesus macaque cumulus oocyte complexes (COCs) is deficient compared with in vivo-matured (IVM) oocytes. To improve oocyte quality and subsequent embryo development following IVM, culture conditions must be optimized. A series of experiments was undertaken to determine the role of epidermal growth factor (EGF) during IVM of rhesus macaque COCs. The addition of Tyrphostin AG-1478 (a selective inhibitor of the EGF receptor EGFR) to the IVM medium yielded fewer oocytes maturing to metaphase II of meiosis II (MII), decreased cumulus expansion, and a lower percentage of embryos that developed to the blastocyst stage compared with untreated IVM controls, indicating that EGFR activation is important for IVM maturation in the rhesus macaque. However, the addition of recombinant human EGF (r-hEGF) to the IVM medium did not enhance outcome. The expression of mRNAs encoding the EGF-like factors amphiregulin, epiregulin, and betacellulin in cumulus cells indicates that these factors produced by cumulus cells may be responsible for maximal EGFR activation during oocyte maturation, precluding any further effect of exogenous r-hEGF. Additionally, these results illustrate the potential futility of exogenous supplementation of IVM medium without prior knowledge of pathway activity.

The in vitro growth and maturation of follicles

The development of technologies to grow oocytes from the most abundant primordial follicles to maturity in vitro holds many attractions for clinical practice, animal production technology and research. The production of fertile oocytes and live offspring has been achieved in mice following the long-term culture of oocytes in primordial follicles from both fresh and cryopreserved ovarian tissue. In contrast, in non-rodent species advances in follicle culture are centred on the growth of isolated preantral follicles. As a functional unit, mammalian preantral follicles are well-suited to culture but primordial and primary follicles do not grow well after isolation from the ovarian stroma. The current challenges for follicle culture are numerous and include: optimisation of culture media and the tailoring of culture environments to match the physiological needs of the cell in vivo; the maintenance of cell-cell communication and signalling during culture; and the evaluation of the epigenetic status, genetic health and fertility of in vitro derived mature oocytes. In large animals and humans, the complete in vitro growth and maturation of oocytes is only likely to be achieved following the development of a multistage strategy that closely mimics the ovary in vivo. In this approach, primordial follicle growth will be initiated in situ by the culture of ovarian cortex. Isolated preantral follicles will then be grown to antral stages before steroidogenic function is induced in the somatic cells. Finally, cytoplasmic and nuclear maturation will be induced in the in vitro derived oocytes with the production of fertile metaphase II gametes.

Nuclear maturation and structural components of nonhuman primate cumulus-oocyte complexes during in vivo and in vitro maturation

OBJECTIVE

To compare cumulus cell structure and timing of oocyte maturation of in vitro-matured (IVM) and in vivo-matured (VVM) nonhuman primate oocytes.

DESIGN

In vivo maturation and in vitro maturation of oocytes.

SETTING

Animal cell culture laboratory.

ANIMAL(S)

Forty-eight female rhesus macaques.

INTERVENTION(S)

Fifteen animals were administered FSH, and aspirated oocytes were cultured in vitro for 0, 3, 6, 12, or 24 hours (IVM). Thirty-three animals were administered FSH and hCG, and oocytes were collected 3, 6, 12, or 28-30 hours after hCG (VVM).

MAIN OUTCOME MEASURE(S)

Nuclear maturation and microtubule scores of oocytes and actin and tubulin transzonal processes of cumulus cells. Embryo development was observed for VVM oocytes.

RESULT(S)

The rate of nuclear maturation was faster for IVM oocytes compared with VVM oocytes. Actin transzonal processes decreased 0-12 hours after hCG administration for VVM oocytes. Tubulin transzonal processes of IVM and VVM oocytes decreased from 0 to 24 hours and from 0 to 3 hours, respectively. Embryo development improved as VVM time increased.

CONCLUSION(S)

Nuclear maturation and remodeling of cumulus-oocyte complex structural components associated with in vitro maturation do not parallel those of oocyte maturation in vivo, indicating that in vitro culture conditions continue to be suboptimal.

The role of transcription in EGF- and FSH-mediated oocyte maturation in vitro

Understanding mechanisms responsible for meiotic resumption in mammalian oocytes is critical for the identification of strategies to enhance developmental competence of in vitro-matured oocytes. Improvement of in vitro oocyte maturation systems is dependent on a better understanding of mechanisms that regulate oocyte maturation both in vivo and in vitro as well as on the identification of methods to manipulate the meiotic progression of oocytes matured in vitro in a physiological manner. The purpose of this review is two-fold: first, to examine the mechanisms that underlie the acquisition of oocyte developmental competence and regulation of oocyte maturation in vivo and in vitro; second, to present data examining the role of transcription in mediating the ability of EGF and FSH to induce oocyte maturation in vitro. Results presented support the conclusions that (1) EGF-induced oocyte maturation does not require nascent gene transcription in both mice and domestic cats; (2) FSH requires gene transcription to induce oocyte maturation in both species; (3) EGF must be present in the maturation medium to optimize the effectiveness of FSH to promote oocyte maturation; (4) the mechanism used by FSH to induce oocyte maturation in vitro appears to predominate over that used by EGF when both EGF and FSH are present in maturation medium used for either murine or feline cumulus oocyte complexes.

In vivo maturation of oocytes by extending the interval between human chorionic gonadotropin administration and oocyte retrieval

OBJECTIVE

To find whether the percentage of mature oocytes can be increased in the following ICSI cycle, in a selected group of patients with >or=47% immature oocytes, with the prolongation of hCG-to-oocyte retrieval interval.

DESIGN

Randomized study.

SETTING

In vitro fertilization unit in a medical center in Israel.

PATIENT(S)

From January 2003 to June 2005, in 72 of 2,650 intracytoplasmic sperm injection cycles (2.8%), >or=47% of the total aspirated oocytes were immature (group A). In the following treatment cycle, with similar controlled ovarian hyperstimulation, hCG was planned to be injected in the same interval (group B) as well as 3-4 hours earlier (group C). In fact, the hCG-to-oocyte retrieval interval in group C was statistically significantly longer (38.6 +/- 1.2 hours) compared with that in group B (35.3 +/- 0.7 hours).

INTERVENTION(S)

The clinical characteristics of the patients, ovarian stimulation, hormonal profile, and the intracytoplasmic sperm injection outcome of the various groups were assessed.

MAIN OUTCOME MEASURE(S)

The number and maturity of the aspirated oocytes.

RESULT(S)

The mean number of ampules needed for stimulation, treatment duration, serum E(2), and P level on the hCG day were similar in the various groups. Escaped ovulation did not occur in any of the patients. A larger number of aspirated oocytes, a statistically significantly larger percentage of mature oocytes (72%), and a statistically significantly lower percentage of metaphase I (12%), germinal vesicle (18%), and degenerated oocytes (8%) were found in group C compared with group A (50%; 16%, 21%, and 13%, respectively). Similar morphological distribution of the aspirated oocytes was observed among groups B and C. Clinical implantation and pregnancy rates were higher in group C compared with group B.

CONCLUSION(S)

In a selected group of patients with >or=47% immature oocytes per retrieval, a larger cohort of mature oocytes can be recruited by extending the hCG- to-oocyte retrieval interval in a subsequent cycle. This improved outcome directly affects the quality of embryos available for transfer and thus increases pregnancy rate.

Assessment of the integrity of human oocytes retrieved from cryopreserved ovarian tissue after xenotransplantation

BACKGROUND

Previous studies showed that immature oocytes stored in ovarian tissue could develop to the mature stage after transplantation. However, the quality and competency of the oocytes developed in xenografted ovarian tissue have never been investigated. As a pilot study to investigate this uncharted issue, we evaluated microtubule organization and chromatin configuration of human oocytes harvested from xenografted frozen-thawed ovarian tissue.

METHODS

Frozen-thawed human ovarian tissue was transplanted into severe combined immunodeficient mice. All animals were stimulated with gonadotrophin from 20 weeks after transplantation. Grafts were recovered 36 h after hCG administration. The oocytes were retrieved from the antral follicles (>2 mm diameter), cultured in vitro, stained for microtubule and chromatin localization.

RESULTS

Five oocytes from 21 female mice and seven oocytes from nine male mice were retrieved. Immunocytochemical examinations of these oocytes after in vitro maturation revealed only two developed to the metaphase II stage. Most oocytes were between prophase and metaphase with abnormal microtubule organization and chromatin configuration.

CONCLUSIONS

Immature oocytes in stored human ovarian tissue can grow to maturity in host animals after xenotransplantation. Retrieval of oocytes from the xenograft can be carried out and is reproducible. However, many oocytes, grown in host animals and further matured in vitro, showed aberrant microtubule organization and chromatin patterns.

Obstetric outcome of patients with polycystic ovary syndrome treated by in vitro maturation and in vitro fertilization–embryo transfer

OBJECTIVE

To assess the obstetric outcome of pregnancies resulting from in vitro maturation (IVM) and IVF-ET of immature oocytes retrieved from women with polycystic ovary syndrome (PCOS).

DESIGN

Prospective observational study.

SETTING

University fertility clinic.

PATIENT(S)

One hundred thirty-nine women undergoing 203 IVM treatment cycles.

INTERVENTION(S)

Immature oocyte recovery from unstimulated ovaries. In vitro oocyte maturation and fertilization. Fresh ET and assessment of obstetric outcomes in the pregnant women.

MAIN OUTCOME MEASURE(S)

Pregnancy and obstetric outcome.

RESULT(S)

Forty-one pregnancies were obtained in 187 ETs, resulting in a pregnancy rate of 21.9%. Except for three patients lost to follow-up in these pregnancies, the abortion and live birth rates were 36.8% (14 of 38) and 63.2% (24 of 38), respectively. The mean (+/-SD) gestational age and birth weight at delivery for singletons were 38.4 +/- 2.0 weeks (range, 33-41.6 weeks) and 3,252 +/- 516 g (1,750-4,100 g), respectively. For twins these were 36.7 +/- 1.9 weeks (34.6-39 weeks) and 2,361 +/- 304 g (1,900-2,990 g), respectively. Pregnancy complications occurred in five patients (13.2%); these included preterm labor (n = 3) and placenta previa (n = 2). Two patients (5.3%) had a major congenital anomaly diagnosed by ultrasonography.

CONCLUSION(S)

The abortion rate, gestational age and birth weight at delivery, and obstetric complications of pregnancies conceived by IVM-ET in women with PCOS were comparable with those of other women with PCOS being treated by conventional IVF-ET. In vitro maturation followed by IVF-ET seems to be a useful treatment option for women with PCOS, thus avoiding the risk of ovarian hyperstimulation syndrome.

Ovarian Aging in Two Species of Long-Lived Rockfish, Sebastes aleutianus and S. alutus1

Little is known about the ovary during aging in long-lived fish with respect to follicular stages and de novo oogenesis. We examined two species of rockfish, Sebastes aleutianus (rougheye rockfish) and Sebastes alutus (Pacific ocean perch). Fish were sampled offshore of British Columbia, age was estimated by otolith annuli, and the ovaries were examined histologically. In S. aleutianus, age up to 80 yr did not markedly alter the frequency distribution of oocytes, follicles, or their total numbers. Similarly, in a larger sample of S. alutus, the abundance of oocytes and follicles showed little age trend up through 77 yr. However, fish older than 50 yr lacked the largest and smallest oocyte size classes (40-60, >80 microm) and the smallest follicle size class (200-350 microm), which results from the later seasonal developmental state of these older fish. These data provide evidence that oogenesis continues at advanced ages in these two species, in contrast with long-held assumptions about mammals. These species represent an iteroparous extreme in the spectrum of life history strategies and merit investigation to determine the mechanisms for such an extended reproductive life span.

Perimenopausal conception

Fertility, defined as the ability to achieve a pregnancy, declines gradually over the woman's lifespan. Although this decline seems to begin from the age of 30 years, it is more obvious between 35 and 40 and increases dramatically thereafter. The age of 41 is considered to be the point when fertility stops and sterility starts. The actual menopause occurs approximately 10 years after the substantial loss of conception potential. Thus, the biological rather than the chronological age of the woman can predict more accurately her fertility potential. This decline in female reproductive potential correlates with ovarian factors, although a slight contribution from the uterus itself and from the neuroendocrine axis cannot be excluded. The ovarian reserve decreases with advancing age, while a parallel decrease in the quality of the oocytes is present, as indicated by the increased incidence of oocyte aneuploidy. The endocrine function of the ovary also declines with age, the later becoming unable to sustain its normal function in the neuroendocrine axis. Additionally, the role of the various endometrial factors remains controversial. On the other hand, exposure to toxic factors and the increased prevalence of infertility-related diseases like endometriosis and PID, may also contribute. Spontaneous conception rates are minimal in perimenopausal women, mainly due to a qualitative and quantitative loss of female gametes. In the rare case of spontaneous conception achievement, complications are more likely. The application of classic ovulation induction and IVF may serve some selected cases, where the woman's ovarian biological age does not correspond to her chronological one. However, the implantation, clinical pregnancy, and live birth rates in women of advanced age undergoing IVF treatment, show very poor results. On the other hand, preimplantation genetic diagnosis is an accurate diagnostic tool for exclusion of genetically deficient embryos prior to embryo transfer. Oocyte donation seems to be the most reliable option of the perimenopausal woman, since the cumulative birth rates after four treatment cycles is approximately 80%. Cryopreservation of ovarian tissue may be an alternative in nulliparas women <40 years of age who want to have children in the future or women with the same desire who, unfortunately, have had pelvic radiotherapy, chemotherapy, oophorectomy, or premature menopause. This technique has given encouraging results in animals, but has not achieved pregnancies in humans. In the future, the use of drugs to block oocyte depletion as well as recent techniques, such as cytoplasmic or germinal vesicle transfer, will be more widely tested and may offer an option to the perimenopausal woman who wishes to conceive.