Follicle-Stimulating Hormone Affects Metaphase I Chromosome Alignment and Increases Aneuploidy in Mouse Oocytes Matured in Vitro1

Oocyte environment: follicular fluid and cumulus cells are critical for oocyte health

Bidirectional somatic cell-oocyte signaling is essential to create a changing intrafollicular microenvironment that controls primordial follicle growth into a cohort of growing follicles, from which one antral follicle is selected to ovulate a healthy oocyte. Such intercellular communications allow the oocyte to determine its own fate by influencing the intrafollicular microenvironment, which in turn provides the necessary cellular functions for oocyte developmental competence, which is defined as the ability of the oocyte to complete meiosis and undergo fertilization, embryogenesis, and term development. These coordinated somatic cell-oocyte interactions attempt to balance cellular metabolism with energy requirements during folliculogenesis, including changing energy utilization during meiotic resumption. If these cellular mechanisms are perturbed by metabolic disease and/or maternal aging, molecular damage of the oocyte can alter macromolecules, induce mitochondrial mutations, and reduce adenosine triphosphate production, all of which can harm the oocyte. Recent technologies are now exploring transcriptional, translational, and post-translational events within the human follicle with the goal of identifying biomarkers that reliably predict oocyte quality in the clinical setting.

Is the mouse follicle culture a good model for the goat with respect to the development of preantral follicles in vitro?

The present study evaluated the efficiency of using 2 culture media developed for mice and for goats in the in vitro preantral follicle culture of each species. Murine and caprine secondary follicles were cultured in vitro with human recombinant follicle-stimulating hormone (murine medium) or with bovine recombinant follicle-stimulating hormone in association with growth hormone (caprine medium). The results showed that murine follicles cultured in caprine medium had lower (P < 0.05) rates of follicular survival and growth, whereas for caprine follicles, these variables were not affected by the type of medium used (P > 0.05). After in vitro maturation, a higher (P < 0.05) number of oocytes that resumed meiosis were observed in the murine medium for both species. In contrast, only in the caprine species estradiol production was significantly superior when the caprine medium was used. Higher progesterone production was observed in the presence of the murine medium only for murine follicles (P < 0.05). In conclusion, murine and caprine preantral follicles cultured under the same in vitro culture medium conditions respond differently; caprine oocytes grown in vitro in the presence of the murine medium show the greatest developmental competence among the tested combinations. Therefore, under the present experimental conditions, the mouse follicle culture has proved be a good model for the development of new culture media for caprine preantral follicles.

The phenotype of an IVF child is associated with peri-conception measures of follicular characteristics and embryo quality

STUDY QUESTION

Are childhood measures of phenotype associated with peri-conception parental, IVF treatment and/or embryonic characteristics of IVF children?

SUMMARY ANSWER

Birthweight, childhood body mass index (BMI) and height of pre-pubertal IVF children were strongly associated with peri-conception factors, including follicular and embryonic characteristics.

WHAT IS KNOWN ALREADY

A growing number of studies have identified a range of phenotypic differences between IVF and naturally conceived pre-pubertal children; for example, birthweights are lower following a fresh compared with a thawed embryo transfer.

STUDY DESIGN, SIZE, DURATION

This retrospective cohort study included IVF children (n = 96) born at term (>37 weeks) after a singleton pregnancy from the transfer of either fresh or thawed embryos in New Zealand. Between March 2004 and November 2008, these children were subjected to clinical assessment before puberty.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Clinical assessment provided anthropometric measures of children aged 3.5-11 years old. Peri-conception factors (n = 36) derived retrospectively from parental, treatment, laboratory and embryonic variables (n = 69) were analysed using multiple stepwise regression with respect to standard deviation scores (SDSs) of the birthweight, mid-parental corrected BMI and height of the IVF children. Data from children conceived from fresh (n = 60) or thawed (n = 36) embryos, that met inclusion criteria and had high-quality data with >90% completeness, were analysed.

MAIN RESULTS AND THE ROLE OF CHANCE

Embryo treatment at transfer was identified as a predictor of birthweight with thawed embryos resulting in heavier birthweights than fresh embryos [P = 0.02, 95% confidence interval (CI) fresh minus thawed: -1.047 to -0.006]. Birthweight SDS was positively associated with mid-parental corrected BMI SDS (P = 0.003, slope 0.339 ± 0.100). Four factors were related (P < 0.05) to mid-parental corrected height SDS. In particular, child height was inversely associated with the diameter of lead follicles at oocyte retrieval (P < 0.0001, slope -0.144 ± 0.040) and with the quality score of embryos at transfer (P = 0.0008, slope -0.425 ± 0.157), and directly associated with the number of follicles retrieved (P = 0.05, slope 1.011 ± 0.497). Child height was also positively associated with the transfer of a fresh as opposed to thawed embryo (P < 0.001, 95% CI 0.275-0.750).

LIMITATIONS, REASONS FOR CAUTION

More than one embryo was transferred in most cycles so mean development and quality data were used. The large number of variables measured was on a relatively small sample size. Large cohorts from multiple clinics using a variety of treatment protocols and embryology methods are needed to confirm the associations identified and ultimately to test these factors as possible predictors of phenotype.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to directly associate peri-conception measures of IVF treatment with a pre-pubertal child's phenotype. Demonstration that peri-conception measures relate to a pre-pubertal child's phenotype extends the range of factors that may influence growth and development. These findings, if corroborated by larger studies, would provide invaluable information for practitioners, who may want to consider the impact of ovarian stimulation protocols as well as the quality of the embryo transferred on a child's growth and development, in addition to their impact on pregnancy rate.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from the National Research Centre of Growth and Development New Zealand (grant 3682065) and the Australasian Paediatric Endocrine Group (APEG; grant 3621994), as well as a fellowship from Fertility Associates New Zealand awarded to M.P.G. In terms of competing interest, J.C.P is a shareholder of Fertility Associates. M.P.G. currently holds the position of Merck Serono Lecturer in Reproductive Biology. W.S.C. and P.L.H. have also received grants and non-financial support from Novo Nordisk, as well as personal fees from Pfizer that are unrelated to the current study. The other authors have no conflict of interest to declare.

Chromosomal aberrations in in-vitro matured oocytes influence implantation and ongoing pregnancy rates in a mouse model undergoing intracytoplasmic sperm injection

Implantation failure and early pregnancy loss have been reported to be closely related to the quality of mammalian oocytes; however, the pregnant outcome of embryos from in-vitro matured (IVM) oocytes remains unknown. In this study we examined spindle assembly and chromosome segregation during differentiation, and the duration of IVM of mouse oocytes. The resulting implantation and pregnancy outcomes were analyzed to clarify the relationship between the spindle and chromosomes of IVM oocytes and implantation and early pregnancy. Cumulus-enclosed germinal vesicle oocytes were collected and randomly cultured in IVM medium with different IVM durations. One part of IVM oocytes were analyzed the spindle and chromosome morphology by immunofluorescence method, and the other part of them were fertilized by intracytoplasmic sperm injection. The resulting embryos were transferred into pseudo-pregnant female mice, and the post-implantation and full term development was observed. The chromosome aberrations and incorrect spindle assembly seems not affect the early development and blastocyst cell number derived from IVM oocytes, however the development potential of the resulting embryos after implantation were significant decreased with the ratio increasing of chromosome aberrations and incorrect spindle assembly. Accordingly, the full-term development was also decreased. In conclusion, the present study showed the spindle assembly of in vitro-matured oocytes was one of the most important factors that affected the implantation and ongoing pregnancy rates of IVM oocytes, and the improvement by an appropriate duration of maturation in vitro will enhance the post-implantation development potential of the resulting embryos, and decrease implantation failure and early pregnancy loss.

Comparison of results of cycles treated with modified mild protocol and short protocol for ovarian stimulation

The ovarian stimulation has been applied in order to increase the number of oocytes to compensate for the poor results of in vitro fertilization, allowing the selection of one or more embryos to be transferred. Our aim is to compare the results obtained in IVF/ICSI cycles using the short protocol for controlled ovarian stimulation to the results from the modified mild protocol used in our department. A total of 240 cycles were conducted from January 2010 to December 2011. When comparing both protocols, it could be observed that there was a significant difference in the quantity of gonadotropins doses in the mild protocol and in the short protocol. No significant difference was observed regarding pregnancy rates per cycle, 22% and 26.2%, in short and mild protocols, respectively. The protocols of controlled ovarian stimulation are often associated with high risk of complications such as ovarian hyperstimulation syndrome, excessive emotional stress, high rates of treatment dropouts, and abdominal discomfort. With the data obtained in this study, one can conclude that there are less risks and complications for the patient when using the mild stimulation protocol. It was also observed that in this group there was a slightly higher rate.

Germline mosaicism does not explain the maternal age effect on trisomy

A variety of hypotheses have been proposed to explain the association between trisomy and increasing maternal age in humans, virtually all of which assume that the underlying mechanisms involve meiotic errors. However, recently Hultén and colleagues [Hulten et al., 2010b] proposed a provocative model-the Oocyte Mosaicism Selection Model (OMSM)-that links age-dependent trisomy 21 to pre-meiotic errors in the ovary. Specifically, they propose that nondisjunctional events occur in a proportion of germ cells as they mitotically proliferate, resulting in mosaicism for trisomy 21. Assuming that the presence of an additional chromosome 21 delays meiotic progression, these cells would be ovulated later in reproductive life, resulting in an age-dependent increase in aneuploid eggs. Because this model has important clinical implications, we initiated studies to test it. We first analyzed oocytes from two trisomy 21 fetuses, combining immunostaining with FISH to determine the likelihood of detecting the additional chromosome 21 at different stages of meiosis. The detection of trisomy was enhanced during the earliest stage of prophase (leptotene), before homologs synapsed. Accordingly, in subsequent studies we examined the chromosome content of leptotene oocytes in seven second trimester female fetuses, analyzing three chromosomes commonly associated with human trisomies (i.e., 13, 16, and 21). In contrast to the prediction of the OMSM, we found no evidence of trisomy mosaicism for any chromosome. We conclude that errors in pre-meiotic germ cells are not a major contributor to human aneuploidy and do not provide an explanation for the age-related increase in trisomic conceptions.

Amino acid turnover by human oocytes is influenced by gamete developmental competence, patient characteristics and gonadotrophin treatment

STUDY QUESTION

Can amino acid profiling differentiate between human oocytes with differing competence to mature to metaphase II (MII) in vitro?

SUMMARY ANSWER

Oocytes which remained arrested at the germinal vesicle (GV) stage after 24 h of in vitro maturation (IVM) displayed differences in the depletion/appearance of amino acids compared with oocytes which progressed to MII and patient age, infertile diagnosis and ovarian stimulation regime significantly affected oocyte amino acid turnover during IVM.

WHAT IS KNOWN ALREADY

Amino acid profiling has been proposed as a technique which can distinguish between human pronucleate zygotes and cleavage stage embryos with the potential to develop to the blastocyst stage and implant to produce a pregnancy and those that arrest. Most recently, the amino acid turnover by individual bovine oocytes has been shown to be predictive of oocyte developmental competence as indicated by the gamete's capacity to undergo fertilization and early cleavage divisions in vitro.

STUDY DESIGN, SIZE, DURATION

The study was conducted between March 2005 and March 2010. A total of 216 oocytes which were at the GV or metaphase I (MI) stages at the time of ICSI were donated by 67 patients.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

The research was conducted in university research laboratories affiliated to a hospital-based infertility clinic. Oocytes were cultured for 24 h and the depletion/appearance of amino acids was measured during the final 6 h of IVM. Amino acid turnover was analysed in relation to oocyte meiotic progression, patient age, disease aetiology and controlled ovarian stimulation regime.

MAIN RESULTS AND THE ROLE OF CHANCE

The depletion/appearance of key amino acids was linked to the maturation potential of human oocytes in vitro. Oocytes which arrested at the GV stage (n = 9) depleted significantly more valine and isoleucine than those which progressed to MI (n = 32) or MII (n = 107) (P < 0.05). Glutamate, glutamine, arginine and valine depletion or appearance differed in MII versus degenerating oocytes (n = 20) (P < 0.05). Glutamine, arginine, methionine, phenylalanine, total depletion and total turnover all differed in oocytes from patients aged < 35 years versus patients ≥35 years (P < 0.05). MII oocytes obtained following ovarian stimulation with recombinant FSH depleted more isoleucine (P < 0.05) and more alanine and lysine (P < 0.05) appeared than oocytes from hMG-stimulated cycles. MII oocytes from patients with a polycystic ovary (PCO) morphology (n = 33) depleted more serine (P < 0.05) than oocytes from women with normal ovaries (n = 61).

LIMITATIONS, REASONS FOR CAUTION

Immature oocytes collected at the time of ICSI were used as the model for human oocyte maturation. These oocytes have therefore failed to respond to the ovulatory hCG trigger in vivo (they are meiotically incompetent), and have limited capacity to support embryo development in vitro. The lack of cumulus cells and stress of the conditions in vitro may have influenced turnover of amino acids, and owing to the small sample sizes further studies are required to confirm these findings.

WIDER IMPLICATIONS OF THE FINDINGS

The findings provide support for the hypothesis that oocyte metabolism reflects oocyte quality. Longitudinal studies are required to link these functional metabolic indices of human oocyte quality with embryo developmental competence. Oocyte amino acid profiling may be a useful tool to quantify the impact of new assisted reproduction technologies (ART) on oocyte quality.

STUDY FUNDING/COMPETING INTERESTS

This project was funded by the UK Biology and Biotechnology Research Council (BB/C007395/1) and the Medical Research Council (G 0800250). K.E.H was in receipt of a British Fertility Society/Merck Serono studentship. H.J.L. is a shareholder in Novocellus Ltd, a company which seeks to devise a non-invasive biochemical test of embryo health.

Is there a detrimental effect of higher gonadotrophin dose on clinical pregnancy rate in normo-responders undergoing ART with long protocol?

BACKGROUND

In recent years, it has become evident that ovarian stimulation, although a central component of in vitro fertilization (IVF), may itself has detrimental effects on oogenesis, embryo quality, endometrial receptivity, and perhaps also perinatal outcomes.

OBJECTIVE

To evaluate the effect of higher gonadotrophin dose on clinical pregnancy rate in normo-responder ICSI cycles with long protocol.

METHODS

A retrospective study was planned in the Department of Reproductive Endocrinology of Zekai Tahir Burak Women's Health Education and Research Hospital. 362 normo-responders undergoing ICSI cycles with long protocol were included in the study. Group 1 (n = 260): Total gonadotrophin dose <2198 IU and Group 2 (n = 102): Total gonadotrophin dose >2198 IU. Laboratory IVF outcome, clinical pregnancy rate were evaluated.

RESULT(S)

There was no statistically significant difference between peak estradiol levels, endometrial thickness, fertilization rates among the Group 1 versus Group 2 (p > 0.05). But there was a statistically significant difference in age, baseline FSH, oocyte number, 2PN, and clinical pregnancy among the Group 1 versus Group 2. Clinical pregnancy rate were significantly higher in Group 1 compared with Group 2 (p < 0.001). Lower gonadotrophin dose, 2PN was an independent positive predictor of clinical pregnancy (OR 2.65 for gonadotrophin dose, OR 1.1 for 2PN) CONCLUSION(S): Higher total gonadotrophin dose adversely affect clinical pregnancy in normo-responder patients undergoing ICSI cycles with long protocol.

Patient selection criteria for blastocyst transfers in extended embryo culture programs

PURPOSE

To identify the correlation between different cycles, patient factors and blastocyst characteristics.

METHODS

The study included 420 patients undergoing ICSI cycles and 2781 graded blastocysts, which took into account the blastocyst quality. The correlations between the blastocyst parameters and the patient and cycle characteristics were assessed.

RESULTS

The blastocyst development was negatively correlated with the maternal age, BMI and dose of FSH. The ICM was negatively correlated with the FSH dose, whereas the TE quality was influenced by the FSH dose, the maternal age and the number of retrieved oocytes. The embryo morphology on days two and three may predict the blastocyst developmental competence.

CONCLUSIONS

Older patients and patients with high BMI should not be included in extended embryo culture programmes. The extended culture may not favour embryos with poor morphology on days two and three of development. Additionally, a lower ovarian stimulation and decreased oocyte yields may lead to the development of high-quality blastocysts.

Moderate ovarian stimulation does not increase the incidence of human embryo chromosomal abnormalities in in vitro fertilization cycles

CONTEXT

A high chromosomal abnormalities rate has been observed in human embryos derived from in vitro fertilization (IVF) treatments. The real incidence in natural cycles has been poorly studied, so whether this frequency may be induced by external factors, such as use of gonadotropins for ovarian stimulation, remains unknown.

DESIGN

We conducted a prospective cohort study in a University-affiliated private infertility clinic with a comparison between unstimulated and stimulated ovarian cycles in the same women. Preimplantation genetic screening by fluorescence in situ hybridization was performed in all viable d 3 embryos.

OBJECTIVE

The primary objective was to compare the incidence of embryo chromosomal abnormalities in an unstimulated cycle and in an ulterior moderate ovarian stimulated cycle. Secondary outcome measures were embryo quality, blastocyst rate of biopsied embryos, number of normal blastocysts per donor, type of chromosomal abnormalities, and clinical outcome.

RESULTS

One hundred eighty-five oocyte donors were initially recruited for the unstimulated cycle, and preimplantation genetic screening could be performed in 51 of them, showing 35.3% of embryo chromosomal abnormalities. Forty-six of them later completed a stimulated cycle. The sperm donor sample was the same for both cycles. The proportion of embryos displaying abnormalities in the unstimulated cycle was 34.8% (16 of 46), whereas it was 40.6% (123 of 303) in the stimulated cycle with risk difference=5.8 [95% confidence interval (CI)=-20.6-9.0], and relative risk=1.17 (95% CI=0.77-1.77) (P=0.45). When an intrasubject comparison was made, the abnormalities rate was 34.8% (95% CI=20.5-49.1) in the unstimulated cycle and 38.2% (95% CI=30.5-45.8) in the stimulated cycle [risk difference=3.4 (95% CI=-17.9-11.2); P=0.64]. No differences were observed for embryo quality and type of chromosomal abnormalities.

CONCLUSIONS

Moderate ovarian stimulation in young normo-ovulatory women does not significantly increase the embryo aneuploidies rate in in vitro fertilization-derived human embryos as compared with an unstimulated cycle. Whether these results can be extrapolated to infertile patients is still unknown.

Follicular fluid protein content (FSH, LH, PG4, E2 and AMH) and polar body aneuploidy

PURPOSE

Our objective was to identify a marker for oocyte aneuploidy in follicular fluid (FF) in women with an increased risk of oocyte aneuploidy after controlled ovarian hyperstimulation.

MATERIALS AND METHODS

Three groups of oocytes were constituted for polar body screening by FISH (chromosomes 13, 16, 18, 21 and 22): Group 1, advanced maternal age (n = 156); Group 2, implantation failure (i.e. no pregnancy after the transfer of more than 10 embryos; n = 101) and Group 3, implantation failure and advanced maternal age (n = 56). FSH and other proteins were assayed in the corresponding FF samples.

RESULTS

Of the 313 oocytes assessed, 35.78 % were abnormal. We found a significant difference between the follicular FSH levels in normal oocytes and abnormal oocytes (4.85 ± 1.75 IU/L vs. 5.41 ± 2.47 IU/L, respectively; p = 0.021). We found that the greater the number of chromosomal abnormalities per oocyte (between 0 and 3), the higher the follicular FSH level.

CONCLUSION

High FF FSH levels were associated with oocyte aneuploidy in women having undergone controlled ovarian hyperstimulation.

Molecular origin of female meiotic aneuploidies

Chromosome aneuploidy is a major cause of pregnancy loss, abnormal pregnancy and live births following both natural conception and in vitro fertilisation (IVF) and increases exponentially with maternal age in the decade preceding the menopause. Molecular genetic analysis has shown that these are predominantly maternal in origin and trisomies most frequently occur through errors in the first meiotic division. Analysis of chromosome copy number in the three products of female meiosis, the first and second polar bodies and the corresponding zygote by microarray comparative genomic hybridisation (array CGH), in women of advanced maternal age undergoing IVF, has recently revealed a pattern of frequent multiple meiotic errors, caused by premature predivision of sister chromatids in meiosis I and a high incidence of errors in meiosis II. This pattern is similar to those observed in various mouse models which implicate the gradual depletion of cohesins, which are essential for cohesion of sister chromatids, as the primary cause of age related aneuploidy in female meiosis. However, defects in other aspects of meiosis including the formation and stabilisation of chiasmata and the spindle assembly checkpoint (SAC) may also contribute. The challenge remains to explain the molecular basis of 'physiological' rather than 'chronological' female ageing and the contribution of multifactorial causes from the fetal to adult ovary. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Contributing factors for the incidence of aneuploidy in older patients undergoing intracytoplasmic sperm injection cycles

PURPOSE

To evaluate different factors that might affect the incidence of embryo aneuploidy in intracytoplasmic sperm injection cycles (ICSI).

METHODS

One hundred and ninety ICSI cycles in conjunction with preimplantation genetic screening (PGS) were included. The influence of the following variables on the aneuploidy incidence was evaluated: (i) maternal and (ii) paternal ages, (iii) dose of FSH administered, (iv) dose of FSH per number of retrieved matured oocytes (FSH/MII), (v) serum 17β-oestradiol levels on the ovulation trigger day, (vi) aspirated follicles and (vii) retrieved oocytes.

RESULTS

A total of 440 embryos were successfully biopsied, of which 240 were considered euploid and 200 were considered aneuploid. The paternal age (Slope: 0.2, p = 0.372), total dose of FSH (Slope: 0.2, p = 0.218), FSH/MII (Slope: 0.1, p = 0.296) and 17β-oestradiol levels (Slope: 0.2, p = 0.378) were not correlated with the presence of aneuploidy. However, the maternal age (Slope: 1.7, p < 0.01), aspirated follicles (Slope: 1.9, p < 0.01) and retrieved oocytes (Slope: 2.6, p < 0.01) were negatively correlated with the incidence of aneuploidy.

CONCLUSIONS

Even in older patients, lower oocyte yields may represent a more appropriate response to ovarian stimulation, allowing the most competent follicles and oocytes to develop and thereby reducing the occurrence of embryo aneuploidy.

Dose-dependent effects of gonadotropin on oocyte developmental competence and apoptosis

The aim of the present study was to evaluate the effect of gonadotropins (Gn) on oocyte maturation, developmental competence and apoptosis in an animal model. Bovine cumulus-oocyte complexes (COCs) were matured for 24 h in media supplemented with varying concentrations of Bravelle (B), B + Menopur (B+M) or B + Repronex (B + R) (Ferring Pharmaceuticals, Parsiappany, NJ, USA). Then, nuclear maturation, embryo development, and apoptosis in cumulus cells and oocytes were evaluated. Low to moderate Gn concentrations (75-75 00 mIUmL(-1)) effectively improved nuclear maturation and in vitro development. Higher concentrations of Gn (75 000 mIUmL(-1)) did not have any added beneficial effects and nuclear maturation and blastocyst rates in the presence of these concentrations were comparable to control (P>0.05). Most COCs showed slight apoptosis when exposed to 75, 750 and 75 00 mIUmL(-1) Gn; however, when the concentration was increased to 75 000 mIUmL(-1), the proportion of moderately apoptotic COCs increased. In conclusion, extremely high concentrations of Gn have detrimental effects on oocyte nuclear maturation and embryo development and increase apoptosis in cumulus cells, suggesting the importance of judicious use of Gn in assisted reproductive technologies (ART).

Effect of aging on superovulation efficiency, aneuploidy rates, and sister chromatid cohesion in mice aged up to 15 months

Human eggs are highly aneuploid, with female age being the only known risk factor. Here this aging phenomenon was further studied in Swiss CD1 mice aged between 1 and 15 mo. The mean number of eggs ± SEM recovered from mice following superovulation peaked at 22.5 ± 3.8 eggs/oviduct in 3-mo-old females, decreasing markedly between 6 and 9 mo old, and was only 2.1 ± 0.2 eggs/oviduct by 15 mo. Measurement of aneuploidy in these eggs revealed a low rate, ∼3-4%, in mice aged 1 and 3 mo, rising to 12.5% by 9 mo old and to 37.5% at 12 mo. Fifteen-month-old mice had the highest rate of aneuploidy, peaking at 60%. The in situ chromosome counting technique used here allowed us to measure with accuracy the distance between the kinetochores in the sister chromatids of the eggs analyzed for aneuploidy. We observed that this distance increased in eggs from older females, from 0.38 ± 0.01 μm at 1 mo old to 0.82 ± 0.03 μm by 15 mo. Furthermore, in 3- to 12-mo-old females, aneuploid eggs had significantly larger interkinetochore distances than euploid eggs from the same age, and measurements were similar to eggs from the oldest mice. However, the association between aneuploidy and interkinetochore distance was not observed at the oldest, 15-mo age, despite such measurements being maximal. We conclude that in aging CD1 mice, a reduction in the ovulated egg number precedes a rise in aneuploidy and, furthermore, except at very advanced ages, increased interkinetochore distance is associated with aneuploidy.

Chromosomal, metabolic, environmental, and hormonal origins of aneuploidy in mammalian oocytes

Aneuploidy is a leading cause of early embryo loss, miscarriage and birth defects in humans. It is predominantly brought about by the mis-segregation of homologous chromosomes (bivalents) in the first meiotic division (MI) of the oocyte, with advanced maternal age being a risk factor. Although its etiology is likely to be multifactorial the predominating factors remain amenable for study in models such as mice. Homologous chromosome separation in MI is achieved by the mono-orientation of functionally paired sister kinetochores but despite this unique division the Spindle Assembly Checkpoint (SAC), which prevents sister chromatid mis-segregation in mitosis, is functional in mouse oocytes. However, it remains to be fully established what types of error the SAC respond to, for example the presence of univalents, and how sensitive it is to attachment or tension defects in bivalent alignment. Such errors may increase with advanced maternal age as chromosomes lose their cohesive ties and the oocyte has less capacity to service the metabolic needs associated with meiotic division. Environmental insults and hormonal changes could also affect the fidelity of this process. Here we review how all these factors converge on the meiotic spindle during MI to cause mis-segregation errors.

Why is chromosome segregation error in oocytes increased with maternal aging?

It is well documented that female fertility is decreased with advanced maternal age due to chromosome abnormality in oocytes. Increased chromosome missegregation is mainly caused by centromeric cohesion reduction. Other factors such as weakened homologous recombination, improper spindle organization, spindle assembly checkpoint (SAC) malfunction, chromatin epigenetic changes, and extra-oocyte factors may also cause chromosome errors.

Multiple meiotic errors caused by predivision of chromatids in women of advanced maternal age undergoing in vitro fertilisation

Chromosome aneuploidy is a major cause of pregnancy loss, abnormal pregnancy and live births following both natural conception and in vitro fertilisation (IVF) and increases exponentially with maternal age in the decade preceding the menopause. Molecular genetic analysis following natural conception and spontaneous miscarriage demonstrates that trisomies arise mainly in female meiosis and particularly in the first meiotic division. Here, we studied copy number gains and losses for all chromosomes in the two by-products of female meiosis, the first and second polar bodies, and the corresponding zygotes in women of advanced maternal age undergoing IVF, using microarray comparative genomic hybridisation (array CGH). Analysis of the segregation patterns underlying the copy number changes reveals that premature predivision of chromatids rather than non-disjunction of whole chromosomes causes almost all errors in the first meiotic division and unlike natural conception, over half of aneuploidies result from errors in the second meiotic division. Furthermore, most abnormal zygotes had multiple aneuploidies. These differences in the aetiology of aneuploidy in IVF compared with natural conception may indicate a role for ovarian stimulation in perturbing meiosis in ageing oocytes.

Chromatin structure and ATRX function in mouse oocytes

Differentiation of chromatin structure and function during oogenesis is essential to confer the mammalian oocyte with meiotic and developmental potential. Errors in chromosome segregation during female meiosis and subsequent transmission of an abnormal chromosome complement (aneuploidy) to the early conceptus are one of the leading causes of pregnancy loss in women. The chromatin remodeling protein ATRX (α-thalassemia mental retardation X-linked) has recently emerged as a critical factor involved in heterochromatin formation at mammalian centromeres during meiosis. In mammalian oocytes, ATRX binds to centromeric heterochromatin domains where it is required for accurate chromosome segregation. Loss of ATRX function induces abnormal meiotic chromosome morphology, reduces histone H3 phosphorylation, and promotes a high incidence of aneuploidy associated with severely reduced fertility. The presence of centromeric breaks during the transition to the first mitosis in the early embryo indicates that the role of ATRX in chromosome segregation is mediated through an epigenetic mechanism involving the maintenance of chromatin modifications associated with pericentric heterochromatin (PCH) formation and chromosome condensation. This is consistent with the existence of a potential molecular link between centromeric and PCH in the epigenetic control of centromere function and maintenance of chromosome stability in mammalian oocytes. Dissecting the molecular mechanisms of ATRX function during meiosis will have important clinical implications towards uncovering the epigenetic factors contributing to the onset of aneuploidy in the human oocyte.

Evidence that carbonyl stress by methylglyoxal exposure induces DNA damage and spindle aberrations, affects mitochondrial integrity in mammalian oocytes and contributes to oocyte ageing

BACKGROUND

Highly reactive carbonyl compounds formed during glycolysis, such as methylglyoxal (MG), can lead to the formation of 'advanced glycation end products' (AGE) and carbonyl stress. Toxic AGEs are suspected to accumulate and play a role in reducing quality and developmental potential of mammalian oocytes of aged females and in PCOS and diabetic patients. Whether and how MG and AGE affect young and aged oocytes at the cellular level is unknown.

METHODS

The study consists of three parts. In Part A expression of MG-detoxifying enzymes glyoxalases 1 and 2 was analysed by RT-PCR at different stages of maturation in denuded oocytes (DO), cumulus-enclosed oocytes (CEO) and metaphase (M)II oocytes of the CD-1 mouse to obtain information on stage-specific susceptibility to carbonyl stress. DO and CEO from young and aged females and from stimulated cycles were exposed to MG during maturation in vitro to assess also age-related changes in sensitivity to carbonyl stress induced by MG. Induction of apoptosis by MG on in vitro maturing DO was assessed by terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling test. In Part B of the study, DO from large antral follicles of ovaries of adult, young MF-1 mice in late diestrous were exposed to MG to assess direct influences of MG and AGEs formed during continuous exposure to MG on rate and kinetics of maturation to MII, on DNA integrity (by γ-H2AX staining) in the germinal vesicle (GV) stage, and on spindle formation and chromosome alignment (by tubulin and pericentrin immunofluorescence and polarization microscopy), and chromosome segregation (by C-banding) during in vitro maturation. Since MG and AGEs can affect functionality of mitochondria in Part C, mitochondrial distribution and membrane potential was studied using JC-1 probe. Expression of a redox-sensitive mito-Grx1-roGFP2 protein in mitochondria of maturing oocytes by confocal laser scanning microscopy was employed to determine the inner mitochondrial glutathion (GSH)/glutathion disulfide (GSSG)-dependent redox potential.

RESULTS

Part A revealed that mRNA for glyoxalases decreases during meiotic maturation. Importantly, cumulus from aged mice in CEO obtained from stimulated cycles does not protect oocytes efficiently from MG-induced meiotic arrest during in vitro maturation. Part B showed that the MG-induced meiotic delay or arrest is associated with significant rises in spindle aberrations, chromosome congression failure and aberrant telophase I in oocytes. MG exposure of meiotically arrested GV-stage oocytes significantly increases the numbers of γ-H2AX spots in the nucleus suggesting increased DNA damage, while MG exposure during maturation affects chromatin condensation and induces chromosome lagging at anaphase I. Moreover, Part C revealed that carbonyl stress by chronic exposure to MG is associated with delays in changes in mitochondrial distribution and altered inner-mitochondrial GSH/GSSG redox potential, which might be particularly relevant for cytoskeletal dynamics as well as processes after fertilization. Sensitivity to a meiotic block by MG appears dependent on the genetic background.

CONCLUSIONS

The sensitivity to carbonyl stress by MG appears to increase with maternal age. Since MG-exposure induces DNA damage, meiotic delay, spindle aberrations, anaphase I lagging and epimutation, aged oocytes are particularly at risk for such disturbances in the absence of efficient protection by cumulus. Furthermore, disturbances in mitochondrial distribution and redox regulation may be especially critical for fertilization and developmental competence of oocytes exposed to MG and carbonyl stress before or during maturation, for instance, in aged females, or in PCOS or diabetic patients, in agreement with recent suggestions of correlations between poor follicular and embryonic development, lower pregnancy rate and presence of toxic AGEs in serum, irrespective of age.

Telomere length is associated with types of chromosome 21 nondisjunction: a new insight into the maternal age effect on Down syndrome birth

Advanced maternal age is a well-documented risk factor of chromosome 21 nondisjunction in humans, but understanding of this association at the genetic level is still limited. In particular, the state of maternal genetic age is unclear. In the present study, we estimated maternal genetic age by measuring telomere length of peripheral blood lymphocytes among age-matched mothers of children with Down syndrome (cases: N = 75) and mothers of euploid children (controls: N = 75) in an age range of 18-42 years. All blood samples were taken within 1 week of the birth of the child in both cases and controls. The telomere length estimation was performed by restriction digestion--Southern blot hybridization method. We stratified the cases on the basis of centromeric STR genotyping into maternal meiosis I (N = 48) and maternal meiosis II (N = 27) nondisjunction groups and used linear regression to compare telomere length as a function of age in the euploid, meiosis I and meiosis II groups. Our results show that all three groups have similar telomere length on average for younger mothers. As age increases, all groups show telomere loss, but that loss is largest in the meiosis II mother group and smallest in the euploid mother group with the meiosis I mother group in the middle. The regression lines for all three were statistically significantly different from each other (p < 0.001). Our results do not support the theory that younger women who have babies with Down syndrome do so because are 'genetically older' than their chronological age, but we provide the first evidence that older mothers who have babies with Down syndrome are 'genetically older' than controls, who have euploid babies at the same age. We also show for the first time that telomere length attrition may be associated in some way with meiosis I and meiosis II nondisjunction of chromosome 21 and subsequent Down syndrome births at advanced maternal age.

Trisomic pregnancy and elevated FSH: implications for the oocyte pool hypothesis

BACKGROUND

Some studies, but not all, support the hypothesis that trisomy frequency is related to the size of the oocyte pool, with the risk increased for women with fewer oocytes (older ovarian age). We tested this hypothesis by comparing hormonal indicators of ovarian age among women who had trisomic pregnancy losses with indicators among women with non-trisomic losses or chromosomally normal births. The three primary indicators of advanced ovarian age were low level of anti-Müllerian hormone (AMH), high level of follicle-stimulating hormone (FSH) and low level of inhibin B.

METHODS

The analysis drew on data from two hospital-based case-control studies. Data were analyzed separately and the evidence from the two sites was combined. We compared 159 women with trisomic pregnancy losses to three comparison groups: 60 women with other chromosomally abnormal losses, 79 women with chromosomally normal losses and 344 women with live births (LBs) age-matched to women with losses. We analyzed the hormone measures as continuous and as categorical variables. All analyses adjust for age in single years, day of blood draw, interval in storage and site.

RESULTS

AMH and inhibin B did not differ between women with trisomic losses and any of the three comparison groups. Mean ln(FSH) was 0.137 units (95% confidence interval (CI): 0.055, 0.219) higher for trisomy cases compared with LB controls; it was also higher, though not significantly so, for trisomy cases compared with women with other chromosomally abnormal losses or chromosomally normal losses. The adjusted odds ratio in relation to high FSH (≥ 10 mIU/ml) was significantly increased for trisomy cases versus LB controls (adjusted odds ratio (OR): 3.8, 95% CI: 1.6, 8.9).

CONCLUSIONS

The association of trisomy with elevated FSH is compatible with the oocyte pool hypothesis, whereas the absence of an association with AMH is not. Alternative interpretations are considered, including the possibility that elevated FSH may disrupt meiotic processes or allow recruitment of abnormal follicles.

Effect of incubation with different concentrations and durations of FSH for in-vitro maturation of murine oocytes

The purpose of the study was to evaluate whether a lower concentration of FSH or 2-h incubation with FSH would improve the outcome of in-vitro maturation of oocytes. The immature oocytes were obtained from FVB mice, and were allocated to four groups and incubated in the maturation media for 24 h. The maturation media were supplemented with 10 mIU/ml FSH for 24 h (group 1), 10 mIU/ml FSH for 2 h (group 2), 75 mIU/ml FSH for 24 h (group 3) or 75 mIU/ml FSH for 2 h (group 4). In each group, half of the in-vitro-matured oocytes were fertilized and cultured to blastocysts and the remaining matured oocytes were analysed for growth differentiation factor (GDF)-9 and bone morphogenetic protein (BMP)-15 mRNA to assess the oocyte quality. The maturation rates and oocyte BMP-15 mRNA concentrations were similar among the four groups. The GDF-9 mRNA concentrations were similar in group 2 and group 4. The fertilization and blastocyst rates were higher in groups 2 and 4 than in groups 1 and 3. It is concluded that 2-h incubation with FSH is better than 24-h incubation in terms of the fertilization rate and blastocyst development.

Increased incidence of mosaicism detected by FISH in murine blastocyst cultured in vitro

The majority of in-vitro-derived human preimplantation embryos are chromosomally abnormal but whether the same pattern exists in vivo is unknown. This would be impossible to demonstrate in humans. Hence we chose murine embryos to study this difference owing to their ease of manipulation and compared the incidence of mosaicism between in-vivo- and in-vitro-cultured embryos. Two groups of embryos were analysed. Group A (in vitro) were obtained 48h following superovulation and cultured in vitro until the blastocyst stage. Fluorescent in-situ hybridization (FISH) was performed at different stages that included the cleavage, morula and blastocyst stage. Group B (in vivo) were obtained on day 2 or day 5 and FISH was performed immediately without culture. There was an increase in chromosomal mosaicism seen from the cleavage stage up to the blastocyst stage in the in-vitro culture group. Overall chromosomal abnormality from day 3 to day 5 was found to be 30% (28/94) in group A. The incidence of chromosomal abnormalities in blastocysts from group B was significantly lower than group A blastocysts (8% (3/40) and 31% (20/64) respectively; P<0.05). These data show that in-vitro cultured embryos had a significantly higher incidence of mosaicisim in comparison with the in-vivo group. Cultured human embryos show high levels of chromosomal abnormalities but whether this is a pattern seen in all embryos or is the result of culture is unknown. To study this pattern we used mouse embryos and carried out chromosome analysis by fluorescent in-situ hybridization. We compared embryos that were cultured (in vitro) with those that were not (in vivo, i.e. grown exclusively in the mouse). We found that cultured embryos showed significantly higher chromosomal abnormalities as compared with in vivo embryos. This suggests that certain culture conditions are responsible for the high level of chromosomal abnormalities seen in these embryos, which should be investigated further.

Aurora kinase-A regulates microtubule organizing center (MTOC) localization, chromosome dynamics, and histone-H3 phosphorylation in mouse oocytes

Aurora kinases (AURKs) are conserved serine/threonine kinases, crucial in regulating cell cycle events. Mammalian oocytes express all three Aurk isoforms throughout meiosis, with AurkA being the predominant isoform. Inhibition of all AURK isoforms by pharmacological means disrupts oocyte meiosis. Therefore, AurkA short interfering RNA (siRNA) was performed to silence AurkA gene expression in mouse oocytes and to further assess the function of AurkA during meiosis by analyzing subsequent loss-of-function oocyte phenotypes. Results indicated that AurkA siRNA applied in our experiments specifically knocked down both AurkA gene and protein expression without influencing transcript levels of AurkB/AurkC and other endogenous protein expression, such as GAPDH and ERK-2. AURKA was not essential for resumption of meiosis, but it potentiated oocyte meiotic progression. Knockdown of AurkA led to a significant reduction in the number of oocytes proceeding to metaphase II (MII). AurkA siRNA resulted in abnormal spindle assembly, improper localization of microtubule organizing centers (MTOCs) and misalignment of chromosomes in metaphase I (MI) oocytes. Co-immunoprecipitations demonstrated that AURKA was physically associated with phospho-Histone H3 ser10 in meiotic oocytes. AurkA siRNA dramatically reduced Histone H3 ser10 phosphorylation, but not ser28, and resulted in a significant increase of abnormal chromosome segregation in MII oocytes. In conclusion, as a predominant isoform among Aurks in oocytes, AurkA plays critical roles in mouse oocyte meiosis by regulating spindle and chromosome dynamics.

Ovarian stimulation and the risk of aneuploid conceptions

OBJECTIVE

To examine the rate of aneuploidy in missed abortions in patients who conceived after FSH ovarian stimulation compared with women who conceived in a natural cycle.

DESIGN

Retrospective cohort.

SETTING

Academic reproductive endocrinology and infertility center.

PATIENT(S)

Women with karyotyping of products of conception (POC) from a missed abortion from January 1999 through August 2007. The rate of aneuploidy was compared between patients with a history of infertility who conceived naturally and patients with a history of infertility who conceived with FSH treatment.

INTERVENTION(S)

Ovarian stimulation with FSH, intrauterine insemination, and in vitro fertilization; genetic testing of POC after dilation and curettage.

MAIN OUTCOME MEASURE(S)

Embryonic karyotype.

RESULT(S)

A total of 229 pregnancies met inclusion criteria, and of these, 64% had an abnormal karyotype. The rate of aneuploidy was 63% in the study group and 70% in the control group. This difference was not statistically significant.

CONCLUSION(S)

The incidence of embryonic aneuploidy was not higher in pregnancies conceived with FSH stimulation compared with spontaneous conceptions in infertility patients. This suggests that exogenous FSH exposure does not increase the risk of aneuploidy.

In vitro developmental potential of macaque oocytes, derived from unstimulated ovaries, following maturation in the presence of glutathione ethyl ester

BACKGROUND

The inadequacies of oocyte in vitro maturation (IVM) systems for both non-human primates and humans are evidenced by reduced fertilization and poor embryonic development, and may be partly explained by significantly lower glutathione (GSH) contents compared with in vivo matured (IVO) oocytes. As this influence has not been fully explored, this study investigated the effect of the GSH donor, glutathione ethyl ester (GSH-OEt), on the IVM and development of macaque oocytes as a model of human oocyte IVM.

METHODS

Macaque oocytes derived from unstimulated ovaries were cultured in mCMRL-1066 alone or supplemented with 3 or 5 mM GSH-OEt. In vitro matured oocytes were subjected to the GSH assay, fixed for the assessment of spindle morphology or prepared ICSI. Embryo development of zygotes cultured in mHECM-9 was assessed up to Day 9 post-ICSI. RESULTS Supplementation of the maturation medium with GSH-OEt significantly increased oocyte maturation and normal fertilization rates compared with control oocytes, but only 5 mM GSH-OEt significantly increased the oocyte and cumulus cell GSH content. Confocal microscopy revealed significant differences in the spindle morphology between IVO and control in vitro matured metaphase II oocytes. Oocytes matured with 5 mM GSH-OEt exhibited spindle area and spindle pole width similar to that seen in the IVO oocyte. While no significant differences were observed in blastocyst rates, addition of 3 mM GSH-OEt during IVM significantly increased the proportion of embryos developing to the 5-8 cell stage while 5 mM GSH-OEt significantly increased the proportion of morula-stage embryos compared with controls.

CONCLUSIONS

Supplementation of the IVM medium with GSH-OEt promotes better maturation and normal fertilization of macaque oocytes compared with non-supplemented medium. However, further improvement of the primate oocyte IVM culture system is required to support better blastocyst development of oocytes derived from unstimulated ovaries.

Metabolism and karyotype analysis of oocytes from patients with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is associated with metabolic disturbances which include impaired insulin signalling and glucose metabolism in ovarian follicles. The oocyte is metabolically dependent upon its follicle environment during development, but it is unclear whether PCOS or polycystic ovarian (PCO) morphology alone affect oocyte metabolism and energy-demanding processes such as meiosis.

METHODS

Immature human oocytes were donated by PCOS (n = 14), PCO (n = 14) and control (n = 46) patients attending the assisted conception programme at Leeds Teaching Hospitals NHS Trust. Oocytes were cultured individually and carbohydrate metabolism was assessed during overnight in vitro maturation (IVM). Meiotic status was assessed and oocyte intracellular nicotinamide adenine dinucleotide phosphate (NAD(P)H) content and mitochondria activity were measured prior to karyotype analysis by multifluor in situ hybridization.

RESULTS

Patient aetiology had no significant effect on oocyte maturation potential or incidence of numerical chromosome abnormalities (44%), although PCOS and PCO oocytes were more likely to suffer predivision. Group G chromosomes were most likely to be involved in non-disjunction and predivision. PCOS was associated with increased glucose consumption (2.06 +/- 0.43 and 0.54 +/- 0.12 pmol/h for PCOS and control oocytes, respectively) and increased pyruvate consumption (18.4 +/- 1.2 and 13.9 +/- 0.9 pmol/h for PCOS and control oocytes, respectively) during IVM. Prior prescription of metformin significantly attenuated pyruvate consumption by maturing oocytes (8.5 +/- 1.8 pmol/h) from PCOS patients. Oocytes from PCO patients had intermediate metabolism profiles. Higher pyruvate turnover was associated with abnormal oocyte karyotypes (13.4 +/- 1.9 and 19.9 +/- 2.1 pmol/h for normal versus abnormal oocytes, respectively). Similarly, oocyte NAD(P)H content was 1.35-fold higher in abnormal oocytes.

CONCLUSIONS

The chromosomal constitution of in vitro matured oocytes from PCOS is similar to that of controls, but aspects of oocyte metabolism are perturbed by PCOS. Elevated pyruvate consumption was associated with abnormal oocyte karyotype.

High follicle-stimulating hormone increases aneuploidy in human oocytes matured in vitro

OBJECTIVE

To study the effect of FSH on the aneuploidy risk of human oocytes matured in vitro.

DESIGN

Prospective study.

SETTING

Hospital-based IVF center.

PATIENT(S)

Patients with male factor infertility undergoing intracytoplasmic sperm injection (ICSI) cycles.

INTERVENTION(S)

Immature oocytes were put into five groups according to the FSH concentration (0, 5.5, 22, 100, and 2,000 ng/mL) in in vitro maturation (IVM) medium. Spindles were observed under a polarized microscope before polar body biopsy. Fixed polar bodies and corresponding oocytes were examined on chromosomes 13, 16, 18, 21, and 22 by fluorescence in situ hybridization. Oocytes matured in 5.5 and 2,000 ng/mL FSH were immunostained for tubulin and chromatin.

MAIN OUTCOME MEASURE(S)

Aneuploidy rate, spindle visualization rate, and spindle morphology.

RESULT(S)

The frequency rates of aneuploidy were 26.7%, 23.3%, 36.75%, 46.67%, and 63.3% in the five FSH groups, respectively. There was a significantly higher aneuploidy rate in oocytes matured in the 2,000 ng/mL FSH group. The spindle visualization rates assessed under PolScope were not significantly different between aneuploid and normal oocytes. There was no difference in spindle morphology between the 2,000 and 5.5 ng/mL FSH groups.

CONCLUSION(S)

High-concentration FSH in IVM medium significantly increased the first meiotic division error, resulting in more aneuploid oocytes during IVM.

The impact of ovarian stimulation for IVF on the developing embryo

The use of assisted reproductive technologies (ART) has been increasing over the past three decades, and, in developed countries, ART account for 1-3% of annual births. In an attempt to compensate for inefficiencies in IVF procedures, patients undergo ovarian stimulation using high doses of exogenous gonadotrophins to allow retrieval of multiple oocytes in a single cycle. Although ovarian stimulation has an important role in ART, it may also have detrimental effects on oogenesis, embryo quality, endometrial receptivity and perinatal outcomes. In this review, we consider the evidence for these effects and address possible underlying mechanisms. We conclude that such mechanisms are still poorly understood, and further knowledge is needed in order to increase the safety of ovarian stimulation and to reduce potential effects on embryo development and implantation, which will ultimately be translated into increased pregnancy rates and healthy offspring.

Dynamics of protein phosphorylation during meiotic maturation

PURPOSE

To ask whether distinct kinase signaling pathways mediate cytoplasmic or nuclear maturation of mouse oocytes and if in vitro maturation influences the distribution and timing of these phosphorylation events.

METHODS

Mouse cumulus oocyte complexes (COCs) were matured under conditions known to influence oocyte quality (basal or supplemented media) and assayed with epitope specific antibodies that would distinguish between Cdk1 or tyrosine kinase targets at 0, 2, 4, 8, and 16 hrs. Semi-quantitative image analysis was used to assess the topographical patterns of protein phosphorylation during in vitro maturation. In vitro fertilization and embryo culture were used to examine the effects of culture conditions on developmental potential.

RESULTS

Protein tyrosine phosphorylation increased during meiotic progression from methaphase-I to metaphase-II. Levels were significantly higher in the oocyte cortex. Levels of cortical staining are enhanced in oocytes matured in supplemented media that displayed higher developmental competence. In contrast, bulk substrates for Cdk1 kinase localize to the meiotic spindle while cytoplasmic levels of kinase activity increase throughout meiotic progression; culture media had no measurable effect. Ablation of the tyrosine kinase Fyn significantly reduced cortical levels of tyrosine phosphorylation.

CONCLUSIONS

The findings indicate that distinct signaling pathways mediate nuclear and cytoplasmic maturation during in vitro maturation in a fashion consistent with a role for tyrosine kinases in cortical maturation and oocyte quality.

Mild ovarian stimulation for IVF

BACKGROUND

Mild ovarian stimulation for in vitro fertilization (IVF) aims to achieve cost-effective, patient-friendly regimens which optimize the balance between outcomes and risks of treatment.

METHODS

Pubmed and Medline were searched up to end of January 2008 for papers on ovarian stimulation protocols for IVF. Additionally, references to related studies were selected wherever possible.

RESULTS

Studies show that mild interference with the decrease in follicle-stimulating hormone levels in the mid-follicular phase was sufficient to override the selection of a single dominant follicle. Gonadotrophin-releasing hormone antagonists compared with agonists reduce length and dosage of gonadotrophin treatment without a significant reduction in the probability of live birth (OR 0.86, 95% CI 0.72-1.02). Mild ovarian stimulation may be achieved with limited gonadotrophins or with alternatives such as anti-estrogens or aromatase inhibitors. Another option is luteinizing hormone or human chorionic gonadotrophin administration during the late follicular phase. Studies regarding these approaches are discussed individually; small sample size of single studies along with heterogeneity in patient inclusion criteria as well as outcomes analysed does not allow a meta-analysis to be performed. Additionally, the implications of mild ovarian stimulation for embryo quality, endometrial receptivity, cost and the psychological impact of IVF treatment are discussed.

CONCLUSIONS

Evidence in favour of mild ovarian stimulation for IVF is accumulating in recent literature. However, further, sufficiently powered prospective studies applying novel mild treatment regimens are required and structured reporting of the incidence and severity of complications, the number of treatment days, medication used, cost, patient discomfort and number of patient drop-outs in studies on IVF is encouraged.

The clinical significance of the retrieval of a low number of oocytes following mild ovarian stimulation for IVF: a meta-analysis

BACKGROUND

Milder ovarian stimulation protocols for in vitro fertilization (IVF) are being developed to minimize adverse effects. Mild stimulation regimens result in a decreased number of oocytes at retrieval. After conventional ovarian stimulation for IVF, a low number of oocytes are believed to represent poor ovarian reserve resulting in reduced success rates. Recent studies suggest that a similar response following mild stimulation is associated with better outcomes.

METHODS

This review investigates whether the retrieval of a low number of oocytes following mild ovarian stimulation is associated with impaired implantation rates. Three randomized controlled trials comparing the efficacy of the mild ovarian stimulation regimen (involving midfollicular phase initiation of FSH and GnRH co-treatment) for IVF with a conventional long GnRH agonist co-treatment stimulation protocol could be identified by means of a systematic literature search.

RESULTS

These studies comprised a total of 592 first treatment cycles. Individual patient data analysis showed that the mild stimulation protocol results in a significant reduction of retrieved oocytes compared with conventional ovarian stimulation (median 6 versus 9, respectively, P < 0.001). Optimal embryo implantation rates were observed with 5 oocytes retrieved following mild stimulation (31%) versus 10 oocytes following conventional stimulation (29%) (P = 0.045).

CONCLUSIONS

The optimal number of retrieved oocytes depends on the ovarian stimulation regimen. After mild ovarian stimulation, a modest number of oocytes is associated with optimal implantation rates and does not reflect a poor ovarian response. Therefore, the fear of reducing the number of oocytes retrieved following mild ovarian stimulation appears to be unjustified.

Evolution of "determinants" in sex-determination: a novel hypothesis for the origin of environmental contingencies in avian sex-bias

Sex-determination is commonly categorized as either "genetic" or "environmental"-a classification that obscures the origin of this dichotomy and the evolution of sex-determining factors. The current focus on static outcomes of sex-determination provides little insight into the dynamic developmental processes by which some mechanisms acquire the role of sex determinants. Systems that combine "genetic" pathways of sex-determination (i.e., sex chromosomes) with "environmental" pathways (e.g., epigenetically induced segregation distortion) provide an opportunity to examine the evolutionary relationships between the two classes of processes and, ultimately, illuminate the evolution of sex-determining systems. Taxa with sex chromosomes typically undergo an evolutionary reduction in size of one of the sex chromosomes due to suppressed recombination, resulting in pronounced dimorphism of the sex chromosomes, and setting the stage for emergence of epigenetic compensatory mechanisms regulating meiotic segregation of heteromorphic sex chromosomes. Here we propose that these dispersed and redundant regulatory mechanisms enable environmental contingency in genetic sex-determination in birds and account for frequently documented context-dependence in avian sex-determination. We examine the evolution of directionality in such sex-determination as a result of exposure of epigenetic regulators of meiosis to natural selection and identify a central role of hormones in integrating female reproductive homeostasis, resource allocation to oocytes, and offspring sex. This approach clarifies the evolutionary relationship between sex-specific molecular genetic mechanisms of sex-determination and non-sex-specific epigenetic regulators of meiosis and demonstrates that both can determine sex. Our perspective shows how non-sex-specific mechanisms can acquire sex-determining function and, by establishing the explicit link between physiological integration of oogenesis and sex-determination, opens new avenues to the studies of adaptive sex-bias and sex-specific resource allocation in species with genetic sex-determination.

Review. Meiotic drive and sex determination: molecular and cytological mechanisms of sex ratio adjustment in birds

Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species.

Cytogenetic analysis of in vivo and in vitro matured oocytes derived from naturally cycling and stimulated mice

The objective of the study was to analyze the potential role of follicle stimulating hormone (FSH) in cytogenetic changes of in vivo and in vitro matured mouse oocytes and to determine whether the lower developmental potential of immature oocytes is due to a higher incidence of abnormalities in meiotic spindle organization and chromosome alignment as well as aneuploidy. In vivo matured oocytes were collected from naturally ovulated and superovulated (5.0 I U of recombinant follicle-stimulating hormone [rec-FSH] + recombinant human chorionic gonadotropin [rec-HCG]) mice. Immature oocytes were retrieved from naturally cycling mice and from mice primed with rec-FSH for 48 h. The immature oocytes were cultured 18 h for in vitro maturation (IVM). In vivo and in vitro matured oocytes were assessed for the meiotic spindle organization and chromosome alignment as well as aneuploidy. There was no significant difference of meiotic spindle organization, chromosomal alignment and aneuploidy between in vivo and in vitro matured oocytes derived from naturally cycling and stimulated mice. Therefore, the lower developmental potential of immature oocytes does not appear to be directly related to the incidence of abnormal meiotic spindle organization and chromosome alignment or to aneuploidy.

Less is more: increased gonadotropin use for ovarian stimulation adversely influences clinical pregnancy and live birth after in vitro fertilization

OBJECTIVE

To determine if attempts to maximize oocyte yield during ovarian stimulation translates into improved outcome of in vitro fertilization (IVF) cycles.

DESIGN

Retrospective study.

SETTING

Academic tertiary care IVF center.

PATIENT(S)

806 de-identified nondonor IVF cycles.

INTERVENTION(S)

Evaluation of fresh nondonor IVF cycles (n = 806) for the period January 1, 1999, to December 30, 2001.

MAIN OUTCOME MEASURE(S)

Cycle cancellation, clinical pregnancy, spontaneous miscarriage, and live birth after IVF.

RESULT(S)

Advancing age, independent of ovarian reserve status (reflected by early follicular phase FSH and estradiol) augured a worse prognosis for all outcomes. Higher gonadotropin use lowered cycle cancellations but was associated with a statistically significantly reduced likelihood of clinical pregnancy and live birth and a trend toward a higher likelihood for spontaneous miscarriage after IVF.

CONCLUSION(S)

Our data add to the accruing literature suggesting adverse influences of excess gonadotropin use on IVF outcomes. Although an aggressive approach to controlled ovarian hyperstimulation results in a statistically significant reduction in cycle cancellations, the excessive use of gonadotropins detrimentally influences live birth after IVF.