A reliable technique of nuclear transplantation for immature mammalian oocytes

Rescue of oocytes recovered from postmortem mouse ovaries

It is well known that the survivability of gametes of postmortem carcass was decreased as time passes after death. In this study, it was examined whether cytoplasmic replacement rescues the survivability of germinal vesicle stage (GV) oocytes of postmortem carcass in the mouse. Reactive oxygen species (ROS) levels and mitochondria numbers in GV oocytes of the dead mice stored at 4 degrees were significantly impaired after 44 h postmortem compared to the control (0 h). However, when kayoplasts of GV oocytes of postmortem carcass was transferred to recipient ooplasts (GV transfer), proportion of in vitro maturation (IVM), normal spindle morphology, in vitro and in vivo developmental ability after in vitro fertilization (IVF) of reconstituted oocytes was improved. Moreover, secondary follicle oocytes of postmortem carcass were developed, matured and fertilized in vitro and developed to go to term, when GV transfer was conducted at the GV phase. Thus, transfer of GV karyoplast recovered from postmortem carcass, which viability was decreased, into fresh GV recipient ooplasm, rescues survivability of reconstituted oocytes. It suggested the effective use of oocytes of dead animals in the mouse and this achievement must apply to other rare animal species, especially animals under control by human.

Improvement of early developmental competence of postovulatory-aged oocytes using metaphase II spindle injection in mice

Purpose

Assisted reproductive technology (ART) is a widely applied fertility treatment. However, the developmental competence of aged oocytes from women of a late reproductive age is seriously reduced and the aged oocytes often fail in fertilization even when ART is used. To resolve this problem, we examined usefulness of a new method “the metaphase II spindle transfer (MESI)” as ART using mouse oocytes.

Methods

This work was composed of two experiments. First, 24 hours after collection, embryos from oocytes (1‐day‐old oocytes, called postovulatory‐aged oocytes), were observed, after intracytoplasmic sperm injection (ICSI), and it was found that they were not able to reach the blastocyst stage. Next, the metaphase II chromosome‐spindle complexes from 1‐day‐old oocytes were injected into cytoplasts from oocytes just collected, using piezo pulses to generate reconstructed oocytes. This procedure was named metaphase II spindle injection (MESI).

Results

After ICSI, embryos from the reconstructed oocytes (32/105), which contained the genes of 1‐day‐old oocytes, were able to develop into the blastocyst stage. The fragmentation rate after ICSI was 28.6%. Thus, the developmental competence of 1‐day‐old oocytes was improved by MESI.

Conclusions

The MESI method has the potential to improve the success rate of infertility treatments for women of a late reproductive age.

Can cytoplasmic donation rescue aged oocytes?

BACKGROUND

The pregnancy and delivery rates following assisted reproductive technology (ART) start to decrease and that the miscarriage rate increases rapidly from 35 years old. The miscarriage rate exceeds 50% at 43 years old. The number of aneuploid fetuses in miscarriages increases according to female age, reaching more than 90% when women are over 40 years old.

METHODS

Different cytoplasmic donation technologies used to rescue aged oocytes with high percentage of aneuploidy were analyzed, and their efficacy compared.

MAIN FINDINGS RESULTS

Germinal vesicle transfer (GVT) might be superior to spindle chromosome transfer (ST) theoretically from the point of higher capability of rescuing the disjunction at meiosis I which cannot be helped by ST. However, actually, in vitro maturation (IVM) of oocyte after GVT has not yet been totally completed. ST among other nuclear donations showed the higher possibility to rescue them, due to the fact it does not require in vitro maturation and it has an ethical advantage over pronuclear transfer (PNT) which requires the destruction of an embryo.

CONCLUSION

Spindle chromosome transfer has the potential to rescue aged oocytes to some extent, but we have to continue the basic study further to establish the clinical application of cytoplasmic donation to rescue aged oocytes.

Novel reproductive technologies to prevent mitochondrial disease

BACKGROUND

The use of nuclear transfer (NT) has been proposed as a novel reproductive treatment to overcome the transmission of maternally-inherited mitochondrial DNA (mtDNA) mutations. Pathogenic mutations in mtDNA can cause a wide-spectrum of life-limiting disorders, collectively known as mtDNA disease, for which there are currently few effective treatments and no known cures. The many unique features of mtDNA make genetic counselling challenging for women harbouring pathogenic mtDNA mutations but reproductive options that involve medical intervention are available that will minimize the risk of mtDNA disease in their offspring. This includes PGD, which is currently offered as a clinical treatment but will not be suitable for all. The potential for NT to reduce transmission of mtDNA mutations has been demonstrated in both animal and human models, and has recently been clinically applied not only to prevent mtDNA disease but also for some infertility cases. In this review, we will interrogate the different NT techniques, including a discussion on the available safety and efficacy data of these technologies for mtDNA disease prevention. In addition, we appraise the evidence for the translational use of NT technologies in infertility.

OBJECTIVE AND RATIONALE

We propose to review the current scientific evidence regarding the clinical use of NT to prevent mitochondrial disease.

SEARCH METHODS

The scientific literature was investigated by searching PubMed database until Jan 2017. Relevant documents from Human Fertilisation and Embryology Authority as well as reports from both the scientific and popular media were also implemented. The above searches were based on the following key words: 'mitochondria', 'mitochondrial DNA'; 'mitochondrial DNA disease', 'fertility'; 'preimplantation genetic diagnosis', 'nuclear transfer', 'mitochondrial replacement' and 'mitochondrial donation'.

OUTCOMES

While NT techniques have been shown to effectively reduce the transmission of heteroplasmic mtDNA variants in animal models, and increasing evidence supports their use to prevent the transmission of human mtDNA disease, the need for robust, long-term evaluation is still warranted. Moreover, prenatal screening would still be strongly advocated in combination with the use of these IVF-based technologies. Scientific evidence to support the use of NT and other novel reproductive techniques for infertility is currently lacking.

WIDER IMPLICATIONS

It is mandatory that any new ART treatments are first adequately assessed in both animal and human models before the cautious implementation of these new therapeutic approaches is clinically undertaken. There is growing evidence to suggest that the translation of these innovative technologies into clinical practice should be cautiously adopted only in highly selected patients. Indeed, given the limited safety and efficacy data, close monitoring of any offspring remains paramount.

Cytoplasmic Determination of Meiotic Spindle Size Revealed by a Unique Inter-Species Germinal Vesicle Transfer Model

Spindle sizes are different in diverse species and cell types. In frogs, the meiotic spindle size is positively correlated with the egg cell volume. Across species, relatively small mouse oocytes (70–80 μm) have a relatively large spindle while larger pig oocytes (about 120 μm) have a considerably smaller spindle. In this study we investigated whether species-specific oocyte spindle size was determined by cytoplasmic or nuclear factors. By exchanging the germinal vesicle between mouse and pig oocytes, we obtained two kinds of reconstructed oocytes: one with mouse ooplasm and pig GV (mCy-pGV oocyte), and the other with pig ooplasm and mouse GV (pCy-mGV oocyte). We show that the MII spindle size of the mCy-pGV oocyte is similar to that of the mouse meiotic spindle and significantly larger than that of the pig meiotic spindle. The timing of oocyte maturation also followed that of the species from which the oocyte cytoplasm arose, although some impact of the origin of the GV was observed. These data suggest that spindle size and the timing of meiotic progression are governed by cytoplasmic components rather than cytoplasmic volume and GV materials.

Assessment of nuclear transfer techniques to prevent the transmission of heritable mitochondrial disorders without compromising embryonic development competence in mice

To evaluate and compare mitochondrial DNA (mtDNA) carry-over and embryonic development potential between different nuclear transfer techniques we performed germinal vesicle nuclear transfer (GV NT), metaphase-II spindle-chromosome-complex (MII-SCC) transfer and pronuclear transfer (PNT) in mice. No detectable mtDNA carry-over was seen in most of the reconstructed oocytes and embryos. No significant differences were seen in mtDNA carry-over rate between GV NT (n=20), MII-SCC transfer (0.29 ± 0.63; n=21) and PNT (0.29 ± 0.75; n=25). Blastocyst formation was not compromised after either PNT (88%; n=18) or MII-SCC transfer (86%; n=27). Further analysis of blastomeres from cleaving embryos (n=8) demonstrated undetectable mtDNA carry-over in all but one blastomere. We show that NT in the germ line is potent to prevent transmission of heritable mtDNA disorders with the applicability for patients attempting reproduction.

The root of reduced fertility in aged women and possible therapentic options: current status and future perspects

It is well known that maternal ageing not only causes increased spontaneous abortion and reduced fertility, but it is also a high genetic disease risk. Although assisted reproductive technologies (ARTs) have been widely used to treat infertility, the overall success is still low. The main reasons for age-related changes include reduced follicle number, compromised oocyte quality especially aneuploidy, altered reproductive endocrinology, and increased reproductive tract defect. Various approaches for improving or treating infertility in aged women including controlled ovarian hyperstimulation with intrauterine insemination (IUI), IVF/ICSI-ET, ovarian reserve testing, preimplantation genetic diagnosis and screening (PGD/PGS), oocyte selection and donation, oocyte and ovary tissue cryopreservation before ageing, miscarriage prevention, and caloric restriction are summarized in this review. Future potential reproductive techniques for infertile older women including oocyte and zygote micromanipulations, derivation of oocytes from germ stem cells, ES cells, and iPS cells, as well as through bone marrow transplantation are discussed.

Oocytes isolated from dairy cows with reduced ovarian reserve have a high frequency of aneuploidy and alterations in the localization of progesterone receptor membrane component 1 and aurora kinase B

Oocytes isolated from cows of reproductive age with reduced antral follicle counts (AFC) have a diminished capacity of embryonic development, which may be related to alterations in the mechanism that directs the proper segregation of chromosomes. Because we demonstrated that progesterone receptor membrane component 1 (PGRMC1) is involved in chromosome congression and metaphase II (MII) plate formation, the present study was designed to determine 1) if the decrease in oocyte developmental competence observed in dairy cows with a reduced AFC is due to a higher incidence of aneuploidy and 2) whether alterations in PGRMC1 contributes to the incidence of aneuploidy. Oocytes from ovaries with reduced AFC and age-matched controls were matured in vitro and the occurrence of aneuploidy determined as well as the mRNA level and localization of PGRMC1. Although oocytes from ovaries with reduced AFC were capable of undergoing meiosis in vitro, these oocytes showed a 3-fold increase in aneuploidy compared to oocytes isolated from control ovaries (P < 0.05). Although Pgrmc1 mRNA levels were not altered, PGRMC1 and aurora kinase B (AURKB) failed to localize to precise focal points on MII chromosomes of oocytes from ovaries with reduced AFC. Furthermore, when oocytes of control ovaries were cultured with an inhibitor of AURKB activity, their MII plate was disrupted and PGRMC1 was not properly localized to the chromosomes. These results suggest that alterations in PGRMC1 and/or AURKB localization account in part for the increased aneuploidy and low development competence of oocytes from ovaries with reduced AFC.

Effect of age, GV transfer and modified nucleocytoplasmic ratio on PKCα in mouse oocytes and early embryos

Protein kinase C (PKC) is a family of Ser/Thr protein kinases that can be activated by Ca2+, phospholipid and diacylglycerol. There is evidence that PKC plays key roles in the meiotic maturation and activation of mammalian oocytes. The present study aimed to monitor the effect of age, germinal vesicle (GV) transfer and modified nucleoplasmic ratio on the subcellular distribution profile of PKCα, an important isozyme of PKC, in mouse oocytes undergoing meiotic maturation and following egg activation. Germinal vesicle oocytes were collected from 6–8-week-old and 12-month-old mice. Germinal vesicle-reconstructed oocytes and GV oocytes with one-half or one-third of the original oocyte volume were created using micromanipulation and electrofusion. The subcellular localization of PKCα was detected by immunocytochemistry and laser confocal microscopy. Our study showed that PKCα had a similar location pattern in oocytes and early embryos from young and old mice. PKCα was localized evenly in ooplasm, with weak staining in GV at the GV stage, and present in the entire meiosis II (MII) spindle at the MII stage. In pronuclear and 2-cell embryos, PKCα was concentrated in the nucleus except for the nucleolus. After the GV oocytes were reconstructed, the resultant MII oocytes and embryos showed a similar distribution of PKCα between reconstructed and unreconstructed controls. After one-half or two-thirds of the cytoplasm was removed from the GV oocytes, PKCα still had a similar location pattern in MII oocytes and early embryos from the GV oocytes with modified nucleoplasmic ratio. Our study showed that age, GV transfer and modified nucleocytoplasmic ratio does not affect distribution of PKCα during mouse oocyte maturation, activation, and early embryonic mitosis.

Chromosome transfer in mature oocytes

In this article, we describe detailed protocols for the isolation and transfer of spindle-chromosomal complexes between mature, metaphase II-arrested oocytes. In brief, the spindle-chromosomal complex is visualized using a polarized microscope and extracted into a membrane-enclosed karyoplast. Chromosomes are then reintroduced into an enucleated recipient egg (cytoplast), derived from another female, by karyoplast-cytoplast membrane fusion. Newly reconstructed oocytes consist of nuclear genetic material from one female and cytoplasmic components, including mitochondria and mitochondrial DNA (mtDNA), from another female. This approach yields developmentally competent oocytes suitable for fertilization and producing embryonic stem cells or healthy offspring. The protocol was initially developed for monkey oocytes but can also be used in other species, including mouse and human oocytes. Potential clinical applications include mitochondrial gene replacement therapy to prevent transmission of mtDNA mutations and treatment of infertility caused by cytoplasmic defects in oocytes. Chromosome transfer between the cohorts of oocytes isolated from two females can be completed within 2 h.

Surgery-assisted reproductive technology hybrid therapy: a reproductive procedure for an infertile woman of late reproductive age with multiple myomas

AIM

To produce a successful pregnancy in a 38-year-old infertile patient with relapsed myoma using a technique we refer to as 'surgery-assisted reproductive technology (ART) hybrid therapy' because it combines ART for cryopreservation of in vitro fertilized eggs with reproductive surgery.

METHODS

A 38-year-old nulliparous woman who had undergone abdominal myomectomy and in whom magnetic resonance imaging showed multiple myomas was treated at our University-affiliated hospital and outpatient clinic. Blastocysts were cryopreserved during the preoperative period. Laparoscopic myomectomy was performed after preoperative treatment with a GnRH agonist. Ten months after the operation, the youngest cryopreserved blastocyst was transferred into the uterus and implanted successfully.

RESULTS

Treatment resulted in successful implantation and pregnancy. In January 2008, the course of pregnancy had been uneventful and the patient gave birth to a male infant weighing 2998 grams by cesarean section at 37 weeks of gestation.

CONCLUSION

We have treated eight patients using hybrid therapy with encouraging results, and we describe these cases herein briefly.

Meiotic maturation failure induced by DICER1 deficiency is derived from primary oocyte ooplasm

RNA interference (RNAi) has diverse functions across cellular processes, including a role in the development of the mammalian oocyte. Mouse primary oocytes deficient in the key RNAi enzyme DICER1 exhibit pronounced defects in chromosome congression and spindle formation during meiotic maturation. The cause of this meiotic maturation failure is unknown. In this study, observations of chromosomes and spindle microtubules during prometaphase in DICER1-deficient oocytes indicate that chromosome congression and spindle formation are overtly normal. Spindle breakdown and chromosome displacement occur after the metaphase plate has formed, during the metaphase to anaphase transition. We hypothesised that this defect could be attributed to either RNAi-mediated regulation of nuclear factors, such as the regulation of centromere chromatin assembly, or the regulation of mRNA expression within the cytoplasm. By transplanting germinal vesicles between DICER1-deficient and wild-type primary oocytes, we show that, unexpectedly, the meiotic failure is not caused by a deficiency derived from the germinal vesicle component. Instead, we reveal that the ooplasm of primary oocytes contains DICER1-dependent factors that are crucial for chromosome segregation and meiotic maturation.

Effects of ooplasm manipulation on DNA methylation and growth of progeny in mice

New techniques to boost male and female fertility are being pioneered at a rapid pace in fertility clinics to increase the efficiency of assisted reproduction methods in couples in which natural conception has not been achieved. This study investigates the possible epigenetic effects of ooplasm manipulation methods on postnatal growth and development using a mouse genetic model, with particular emphasis on the possible effects of intergenotype manipulations. We performed interstrain and control intrastrain maternal pronuclear transfers, metaphase-II spindle transfers, and ooplasm transfer between C57BL/6 and DBA/2 mice, and found no major, long-term growth defects or epigenetic abnormalities, in either males or females, associated with intergenotype transfers. Ooplasm transfer itself was associated with reduced viability, and additional subtle effects of ooplasm strain of origin were observed. Both inter- and intrastrain ooplasm transfer were associated with subtle, transient effects on growth early in life. We also performed inter- and intrastrain germinal vesicle transfers (GVTs). Interstrain GVT females, but not males, had significantly lower body weights at birth and thereafter compared with the intrastrain GVT and non-GVT controls. No GVT-associated changes were observed in DNA methylation of the Mup1, Rasgrf1, H19, Snrpn, or Peg3 genes, nor any difference in expression of the imprinted Rasgrf1, Igf2r, or Mest genes. These results indicate that some ooplasm manipulation procedures may exert subtle effects on growth early in life, while intergenotype GVT can result in significant growth deficiencies after birth.

Developmental competence of gametes reconstructed by germinal vesicle transplantation from fresh and cryopreserved bovine oocytes

OBJECTIVE

To evaluate the use of fresh or frozen bovine oocytes as an animal model for reconstructing artificial gametes by germinal vesicle transplantation (GVT), to study nucleocytoplasmic interaction and define clinical procedures for ooplasm donation in humans.

DESIGN

Prospective experimental study.

SETTING

University-based experimental laboratory.

ANIMAL(S)

Bovine oocytes from slaughterhouse ovaries.

INTERVENTION(S)

A total of 446 gametes were reconstructed from fresh immature oocytes; nuclear and cytoplasmic competencies were analyzed through the assessment of meiotic progression and cytoskeleton reorganization; embryonic developmental capability was evaluated after parthenogenetic activation of metaphase II (MII) reconstructed oocytes. Furthermore, the distribution of mitochondria in karyoplast and cytoplast in grafted oocytes was studied. Finally, meiotic and developmental competencies were determined in 199 gametes reconstructed from vitrified immature oocytes.

MAIN OUTCOME MEASURE(S)

Maturational and developmental rate of reconstructed oocytes, cytoskeleton organization, and mitochondrial distribution.

RESULT(S)

Gametes reconstructed from either fresh or cryopreserved immature oocytes showed similar meiotic competence (41.6% vs. 37.7%, respectively). All reconstituted oocytes that reached MII displayed a normal distribution of cytoskeletal elements. Embryonic developmental capability was higher in oocytes derived from fresh than from cryopreserved gametes (30.8% vs. 8.1%, respectively). Finally, oocyte centrifugation was effective in obtaining karyoplasts with <5% of mitochondria.

CONCLUSION(S)

Cows can provide a suitable organism model to develop GVT technique in both research and clinical settings as well as in fertility preservation programs.

Cryopreservation of immature bovine oocytes to reconstruct artificial gametes by germinal vesicle transplantation

Joining immature gamete cryopreservation and germinal vesicle transplantation (GVT) technique could greatly improve assisted reproductive technologies in animal breeding and human medicine. The present work was aimed to assess the most suitable cryopreservation protocol between slow freezing and vitrification for immature denuded bovine oocytes, able to preserve both nuclear and cytoplasmic competence after thawing. In addition, the outcome of germinal vesicle transfer procedure and gamete reconstruction was tested on the most effective cryopreservation system. Oocytes, isolated from slaughterhouse ovaries, were stored after cumulus cells removal either by slow freezing or by vitrification in open pulled straws. After thawing, oocytes were matured for 24 h in co-culture with an equal number of just isolated intact cumulus enclosed oocytes, and fixed in order to evaluate the stage of meiotic progression and cytoskeleton organization. Our results showed that after warming, vitrified oocytes reached metaphase II (MII) in a percentage significantly higher than oocytes cryopreserved by slow freezing (76.2% and 36.5% respectively, p < 0.05). Moreover, vitrification process preserved the organization of cytoskeleton elements in a higher proportion of oocytes than slow freezing procedure. Therefore vitrification has been identified as the elective method for denuded immature oocytes banking and it has been applied in the second part of the study. Our results showed that 38.3% of oocytes reconstructed from vitrified gametes reached the MII of meiotic division, with efficiency not different from oocytes reconstructed with fresh gametes. We conclude that vitrification represents a suitable method of GV stage denuded oocyte banking since both nuclear and cytoplasmic components derived from cryopreserved immature oocytes can be utilized for GVT.

Transmission of Y chromosomes from XY female mice was made possible by the replacement of cytoplasm during oocyte maturation

The B6.Y(TIR) sex-reversed female mouse is anatomically normal at young ages but fails to produce offspring. We have previously shown that its oocytes go through the meiotic cell cycle up to the second metaphase; however, the meiotic spindle is not properly organized, the second meiotic division goes awry after activation or fertilization, and none of the oocytes initiate embryonic development. In the present study, we transferred the nuclei of GV-stage oocytes from XY females into the enucleated GV-stage oocytes from (B6.DBA)F1.XX females. The resultant reconstructed oocytes properly assembled second meiotic spindles after in vitro maturation and produced healthy offspring after in vitro fertilization. Some male pups inherited maternal Y chromosomes. We conclude that the cytoplasm of the XY oocyte is insufficient to support spindle formation at the second metaphase whereas its replacement with the cytoplasmic material from an XX oocyte allows normal development.

What can we learn from gene expression profiling of mouse oocytes?

Mammalian ooplasm supports the preimplantation development and reprograms the introduced nucleus transferred from a somatic cell to confer pluripotency in a cloning experiment. However, the underlying molecular mechanisms of oocyte competence remain unknown. Recent advances in microarray technologies have allowed gene expression profiling of such tiny specimens as oocytes and preimplantation embryos, generating a flood of information about gene expressions. So, what can we learn from it? Here, we review the initiative global gene expression studies of mouse and/or human oocytes, focusing on the lists of maternal transcripts and their expression patterns during oogenesis and preimplantation development. Especially, the genes expressed exclusively in oocytes should contribute to the uniqueness of oocyte competence, driving mammalian development systems of oocytes and preimplantation embryos. Furthermore, we discuss future directions for oocyte gene expression profiling, including discovering biomarkers of oocyte quality and exploiting the microarray data for ‘making oocytes’.

Spindle assembly in the absence of chromosomes in mouse oocytes

This study was carried out to investigate the contributions of chromosomes to spindle assembly in mouse oocytes. We generated two groups of cytoplasts (holo- and hemi-cytoplasts) by enucleation of germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) oocytes using micromanipulation technology. Afterin vitroculture for 18 h, spindles with different shapes (bi-, mono-, or multipolar) formed in most of these cytoplasts except in hemi-GV cytoplasts. Two or more spindles were observed in most of holo-GV, holo-MI, and holo-MII cytoplasts (76.1, 77.0, and 83.7% respectively). However, the proportions of hemi-MI and hemi-MII cytoplasts with multiple sets of spindles decreased to 17.6 and 20.7% respectively. A single bipolar spindle was observed in each sham-operated oocyte generated by removing different volumes of cytoplasm from the oocytes and keeping nuclei intact. Localization of γ-tubulin showed that microtubule organizing centers (MTOCs) were dispersed at each pole of the multiple sets of spindles formed in holo-cytoplasts. However, most of the MTOCs aggregated at the two poles of the bipolar spindle in sham-operated oocytes. Our results demonstrate that chromosomes are not essential for initiating spindle assembly but for directing distinct MTOCs to aggregate to form a bipolar spindle. Some factors of undetermined nature may pre-exist in an inactive form in GV-stage ooplasm, serving as initiators of spindle assembly upon their activation. Moreover, GV materials released into the cytoplasm may facilitate spindle assembly in normal meiotic maturation.

Cryopreservation and in vitro maturation of germinal vesicle stage oocytes of animals for application in assisted reproductive technology

Cryopreservation, in vitro maturation, fertilization and culture can be applied to various processes across a wide range of species, that is, for the breeding and reproduction of farm animals, preservation of genetic variants in laboratory animals, and the conservation of wild species. In particular, the storage of oocytes by cryopreservation and IVM following cryopreservation, might become effective alternative assisted reproduction treatments for infertile patients. For example, in a clinical context, these techniques might be important for patients who are at risk of losing their ovarian function because of extirpative therapy, chemotherapy or radiation. Thus, it is important for assisted reproductive technology to improve IVM and cryopreservation techniques. In the present review, we introduce our recent studies on vitrification and IVM of germinal vesicle stage oocytes in animals.

Time course of meiotic progression after transferring primary spermatocyte into ooplasm at different stages

This study attempted to investigate the time course of meiotic progression after transferring primary spermatocyte (PS) into ooplasm at different maturing stages. In present experiments, PSs were introduced into maturing ooplasts or oocytes by electrofusion. Higher fusion rate was obtained by phytohemagglutinin (PHA) agglutination than by perivitelline space (PVS) insertion. When the ooplasms prepared at 0, 2, 5, and 8.5 hr of in vitro maturation (IVM) were used as recipients and PSs were used as donors, the reconstructed cells extruded the first polar body (PB1) approximately 8.5, 7, 5.5, and 3 hr after electrofusion, respectively. Especially, when ooplasm cultured for 8.5 hr in vitro after GV removal was fused with PS, the PB1 was emitted 7-11 hr after electrofusion. Additionally, the PB1 extrusions of GV and pro-MI oocytes fertilized with PSs were 2.5 hr earlier than control oocytes. The results suggest that (1) PSs undergo the first meiosis in different time courses when introduced into ooplasm at different maturing stages; (2) GV material plays an important role in determining the timing of PB1 extrusion; and (3) first meiotic division of GV and pro-MI oocytes can be accelerated by introducing PS.

Butyrolactone I reversibly alters nuclear configuration, periooplasmic microtubules and development of porcine oocytes

In the present study, we investigated the effects of specific cdc2 kinase inhibitor, butyrolactone I (BL I) on the prevention of germinal vesicle breakdown, changes of microtubular structures, and development of porcine oocytes after removal of the drug. In Experiment 1, cumulus-oocyte complexes (COCs) were cultured (44 h) in NCSU-23 medium containing different concentrations of BL I. The percentages of oocytes remaining at GV stage were 0, 0, 32, 80, and 84% (P<0.05), and the maturation rates were 86, 63, 30, 0, and 0% (P<0.05) for oocytes treated with 0, 10, 20, 40, and 80 microM of BL I, respectively. When oocytes were released from BL I incubation (Experiment 2) and cultured for an additional 44 h, 79, 84, and 83% of oocytes resumed meiosis, but only 52, 38 and 17% of oocytes reached normal metaphase II (MII) stage in the groups treated with 20, 40 and 80 microM BL I, respectively. In Experiments 3-5, reversibility and development of oocytes and embryos were evaluated after removal of the inhibitor. A reduced duration of BL I incubation (22 h) at 20 microM increased the percentage of oocytes remaining at the GV stage compared to the control group (85% versus 9%, P<0.05). Blastocyst rates were lower in treatment groups than in the control (44 h) group (0-14% versus 24%; P<0.05). However, all developing blastocysts possessed similar cell numbers, regardless of the drug-treated or non-treated controls. Taken together, treatment with 20-80 microM of BL I effectively prevented the resumption of meiosis and polymerization of periooplasmic microtubules. Furthermore, reversibility of the oocytes after reduced duration of BL I treatment was satisfactory.

Nuclear transfer methods to study aging

Maternal age affects oocyte quality and early embryo development. Aberrant meiosis of oocytes and compromised early embryo development from older females could originate from defects in the nucleus, the cytoplasm, or both. Nuclear transfer has been used for decades as a tool to study nuclear-cytoplasmic interactions in early embryos, and has uncovered genomic imprinting, nuclear reprogramming, and produced animal clones. Here, we describe the technique for investigating nuclear-cyoplasmic interactions in oocytes and zygotes in female reproductive aging. Nuclear transfer can be performed efficiently and effects of the technique itself on meiosis and early embryo development are minimal as long as care is taken to minimize insult to oocytes or embryos. This protocol first focuses on use of nuclear transfer to study nucleus versus cytoplasmic origin in agingassociated meiosis defects in oocytes at the germinal vesicle (GV) stage. Then, nuclear transfer is used at the zygote stage to study nuclear and cytoplasmic abnormality and apoptosis in early development.

Cytogenetic analysis and developmental assessment of mouse embryos derived from in vitro fertilization of oocytes reconstructed by meiosis-II chromosome transplantation

An electrofusion methodology for transferring meiosis-II chromosomes (M-II-t) has not been completely established. The present study compared the use of two temperatures (fusion at 37 C for Group A and 25 C for Group B) during an electrofusion procedure for mouse oocyte M-II-t and investigated the cytogenetic normality and developmental competence of embryos derived from in vitro fertilization using oocytes reconstructed by M-II-t. The M-II-t oocytes were fertilized in vitro and cultured to the blastocyst stage; the resultant embryos were analyzed cytogenetically. Subsequently, chromosomal normality of the resultant embryos at the prometaphase stage of first cleavage division and the integrity of the meiosis-II spindles of the reconstructed oocytes were analyzed. The success rate of electrofusion in Group B was 92.1%, which was significantly different from that in Group A (49.2%) (P<0.05). The fertilization rates (A, 80.7%; B, 77.2%) and development rates (A, 70.9%; B, 65.5%) in the M-II-t groups were significantly lower than those in the control group (95.0 and 92.2%, respectively) (P<0.05). The incidence of chromosomal abnormalities in the Group A embryos (20.5%) at the blastocyst stage was significantly higher than that in the control group embryos (8.5%) (P<0.05), but the incidence of chromosomal abnormalities in Group B (12.5%) was not significantly different compared with the other groups. A temperature of 25 C during the electrofusion procedure for M-II-t resulted in a good fusion rate, good development rate, and efficient production of chromosomally normal blastocysts. Furthermore, the incidence of chromosomal abnormalities in the first cleavage embryos at the prometaphase stage in Group B (9.6%) did not differ significantly from that in the control group (6.6%). The spindle morphology of the M-II-t oocytes in Group B was normal.

The kinase inhibitor indirubin-3′-oxime prevents germinal vesicle breakdown and reduces parthenogenetic development of pig oocytes

Oocytes undergo spontaneous germinal vesicle breakdown (GVBD) after being released from the follicular environment; this potentially prevents manipulation of the oocyte at the germinal vesicle (GV) stage. The objectives of this study were to investigate the effects of indirubin, a potent cdc2 kinase inhibitor, on GVBD and microtubular structure of porcine oocytes. Cumulus-oocyte-complexes (COCs) were collected from abattoir-derived ovaries and were randomly allocated to different concentrations of indirubin treatments (0, 10, 25, 50, and 100 microM in Experiment 1 and 0, 50, 75, and 100 microM in Experiment 2) during 44 h of IVM. The influences on the GVBD, microtubules, and maturation rates were evaluated using epifluorescence microscopy. The percentages of oocytes remaining at the GV stage were 0, 16, 26, 69, and 85% for oocytes treated with 0, 10, 25, 50, and 100 microM of indirubin, respectively, which differed among treatment groups (P<0.05). However, there were no significant differences between the oocytes treated with 75 and 100 microM (79 and 81%). The cytoplasmic microtubules were fragmented in oocytes maintained at the GV stage and the chromatin became condensed or aggregated. When COCs were incubated with indirubin (50-75 microM) for 22 h and then transferred to maturation medium for 44 h (Experiments 3-5), the percentages of oocytes reaching the metaphase II stage were generally higher than when the COCs were cultured in the presence of the drug for 44 h (62-65% versus 44-46%). However, the parthenogenetic development of the oocytes in Experiment 6 was reduced significantly in drug-treated oocytes. In summary, treatment with 50-75 microM of indirubin effectively prevented GVBD in porcine oocytes, but the developmental competence of the oocytes was compromised.

Construction and fertilization of reconstituted human oocytes

Construction of artificial gametes may be made possible by transferring somatic cells into enucleated oocytes and inducing chromosomal halving of their nuclei. This study examines the possibility of constructing viable human gametes, and their potential for participation in normal fertilization. Spare germinal vesicle-stage oocytes were donated by consenting patients undergoing intracytoplasmic sperm injection (ICSI). Approximately 62% of in-vitro matured oocytes survived enucleation and subsequent cumulus cell injection. Following micromanipulation and subsequent activation, about 40% of the reconstituted oocytes yielded two pronuclear-like entities. This was not accompanied by extrusion of a polar body, but resulted in the formation of two 'putative haploid' pronuclei. Therefore selective removal of a female pronucleus marker was required to restore a balanced ploidy. Male pronuclei were identified by association with sperm mitochondria. Additional pronuclei were then removed, allowing further cleavage. Zygotes derived were 'putatively haploid' in approximately 38% of cases with a limited number of chromosomes assessed. However, on karyotypic analysis, blastomeres isolated from cleaving embryos showed a chaotic distribution of chromosomes. Oocytes could induce 'putative haploidization' of transplanted somatic cell nuclei independently of donor cell gender. Fertilization of artificial oocytes was followed by embryonic cleavage despite blastocyst development and chromosomal content possibly being compromised.

Mammalian oocyte therapies

In assisted human reproduction, the cytoplasm of oocytes recovered from follicles is often abnormal. Its lower quality, especially in older patients, may be responsible for certain chromosomal abnormalities or developmental arrest. Thus, the deficiency of some vital molecules, which are necessary for oocyte maturation, can be the cause of infertility in women. Moreover, mutated mitochondrial DNA (mtDNA) that is located in the oocyte cytoplasm might be transmitted to offspring. With the advance of new micromanipulation techniques like the oocyte nucleus replacement or cytoplasmic transfer, some of these abnormalities could be theoretically eliminated. In this review, we briefly discuss some of these approaches and their potential use in assisted human reproduction.

Production of live offspring from mouse germinal vesicle–stage oocytes vitrified by a modified stepwise method, SWEID

OBJECTIVE

To evaluate viability and subsequent developmental ability in mouse germinal vesicle (GV) oocytes ultrarapidly vitrified with serial stepwise exposure.

DESIGN

Experimental animal study.

SETTING

University-based research laboratory.

ANIMAL(S)

Three- to 4-week-old female (C57BL/6J x CBA) F1 mice in a laboratory environment.

INTERVENTION(S)

Vitrified and thawed GV oocytes were subjected to in vitro maturation, fertilization, and culture, some of which were transferred to recipients.

MAIN OUTCOME MEASURE(S)

Postthaw survival, maturation, cleavage, development to blastocysts, and live births.

RESULT(S)

In the single-step preequilibrium, the rates of postthaw survival, maturation to metaphase II, and development to blastocysts were 97.5%, 95.8%, and 23.7%, respectively. In the serial 10-step preequilibrium developed in this study, which is named SWEID, the corresponding rates were 98.6%, 92.6%, and 42.9%, respectively, showing a statistically significantly higher rate of development to blastocysts in the SWEID group than in the single-step group. Transfer of two-cell-stage embryos derived from the GV oocytes vitrified by SWEID resulted in the production of live offspring.

CONCLUSION(S)

This is the first report that shows live birth after cryopreservation of mouse GV oocytes using an ultrarapid vitrification. Our method, SWEID, may have advantage in allowing storage of female gametes toward advances in infertility treatment and reproductive biology.

Nucleocytoplasmic ratio of fully grown germinal vesicle oocytes is essential for mouse meiotic chromosome segregation and alignment, spindle shape and early embryonic development

BACKGROUND

This study examined the effect of nucleocytoplasmic ratio of fully grown germinal vesicle (GV) oocytes on meiotic chromosome segregation and alignment, spindle shape, Ca(2+) oscillations and capacity of early embryonic development in mouse.

METHODS

GV oocytes with reduced volume (equal to 1/5 to 4/5 of an intact oocyte) were made by micromanipulation to remove different amounts of cytoplasm, and then matured and fertilized in vitro.

RESULTS

When >1/2 of GV oocyte cytoplasm was removed, the time-course of GV breakdown (GVBD) was delayed and oocyte maturation rate decreased significantly. Abnormal chromosome segregation rate increased if >1/2 of the cytoplasm was removed from the oocyte. Length and structure of meiotic spindle and chromosome alignment were also impaired by the reduction of cytoplasmic volume. Once matured in vitro, the oocytes could undergo Sr(2+)-induced Ca(2+) oscillations and form pronuclei in a manner independent of nucleocytoplasmic ratio, but their ability to develop to 2-cell embryos was affected if >1/2 of their cytoplasm was removed from the GV oocytes.

CONCLUSIONS

These results suggest that nucleocytoplasmic ratio is essential for normal meiotic chromosome segregation, spindle formation and chromosome alignment over the metaphase spindle, and development to 2-cell stage, for which 1/2 of the volume of the GV oocyte appears to be a threshold.

Mitochondrial DNA mutations in human disease

The human mitochondrial genome is extremely small compared with the nuclear genome, and mitochondrial genetics presents unique clinical and experimental challenges. Despite the diminutive size of the mitochondrial genome, mitochondrial DNA (mtDNA) mutations are an important cause of inherited disease. Recent years have witnessed considerable progress in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer. However, many challenges remain, including the prevention and treatment of these diseases. This review explores the advances that have been made and the areas in which future progress is likely.

Developmental incompetency of denuded mouse oocytes undergoing maturation in vitro is ooplasmic in nature and is associated with aberrant Oct-4 expression

BACKGROUND

Germinal vesicle (GV) oocytes constitute a potential resource but their developmental competence is questionable especially when surrounding cumulus cells are removed. The intercellular factors/mechanisms underlying such poor embryonic competence may originate at a nuclear and/or ooplasmic level.

METHODS

Immature or mature oocytes were obtained from three mouse strains following pregnant mare serum gonadotropin (PMSG) or PMSG+ human chorionic gonadotropin (hCG) treatment. Immature oocytes were denuded of cumulus cells prior to in vitro maturation. Pronuclear (PN) transfer was used to examine nuclear-ooplasmic interplay on resultant embryonic development and Oct-4 immuno-staining patterns.

RESULTS

Embryos arising from ooplasts of in vivo matured oocytes displayed significant increases in blastocyst formation rates and total blastomere numbers when compared to those created from ooplasts of denuded oocytes. Oct-4 staining was more pronounced and restricted to the inner cell mass (ICM) in blastocysts arising from the ooplasm of in vivo matured zygotes than in those created from denuded oocytes.

CONCLUSIONS

Developmental defect(s) appear to develop primarily in the ooplasm of oocytes that are denuded of their cumulus cells prior to in vitro maturation. Such oocytes result in embryos with poor developmental competence. These defects result in anomalies in cell number and Oct-4 expression during the morula-blastocyst developmental transition.

Transfer of germinal vesicle to ooplasm of young mice could not rescue ageing-associated chromosome misalignment in meiosis of oocytes from aged mice

BACKGROUND

[corrected] Transferring a germinal vesicle (GV) from an aged woman's oocyte into ooplasm from a younger woman has been proposed as a possible way to overcome the problem of age-related decline in female fertility. Here we assessed this possibility by determining whether ooplasts derived from young mice could rescue ageing-associated chromosome misalignment in meiosis of oocytes from aged mice.

METHODS

Three groups of reconstructed oocytes, young GV-young cytoplast (group YY), aged GV-young cytoplast (group AY), and young GV-aged cytoplast (group YA), were created by micromanipulation and electrofusion.

RESULTS

Nuclear transplantation was successful in 89.8-94.4% of GV-ooplast complexes, and maturation rate of the reconstructed oocytes was 93.5-97.9%. Confocal microscopy analysis showed a significantly higher rate (49.2%) of chromosome misalignment in ageing mice than in young mice (16.9%), and 57.1% of oocytes in group AY exhibited chromosome misalignment, while the abnormality rate in groups YY and YA was 16.3 and 16.7% respectively. Calcium imaging showed that the three groups of reconstructed oocytes exhibited a similar pattern of calcium oscillations upon stimulation with bovine sperm extracts. Fertilization rate and developmental capacity to 2-cell embryos were also similar among the three groups of oocytes.

CONCLUSIONS

Our findings suggest that: (i) the ooplasm from young mice could not rescue ageing-associated chromosome misalignment in meiosis of GV from aged mice; and (ii) behaviour of chromosome alignment over metaphase spindle is predominantly determined by GV material.

Effect of Treating Induced Mitochondrial Damage on Embryonic Development and Epigenesis

Germinal vesicle transplantation (GVT) has been proposed as a possible treatment to correct age-related oocyte aneuploidy caused by dysfunctional ooplasm. How healthy ooplasm regulates normal meiosis and subsequent development has yet to be elucidated, but impaired mitochondrial metabolism may be attributable to incomplete segregation of the oocyte chromosomes. In the present study, after ooplasmic mitochondrial damage by photoirradiating chloromethyl-X-rosamine, examination of the oocyte nuclei's ability to survive after transfer into healthy ooplasts was performed. To assess their fertilizability and potential for development, GVT oocytes were fertilized by intracytoplasmic sperm injection (ICSI) and transferred to foster mice. Condition of the offspring at birth was assessed, and epigenetic analysis was performed. Photosensitization consistently inhibited oocyte maturation. However, after GVT of photosensitized nuclei into healthy ooplasts, 67.2% were reconstituted, and 76.2% of these matured normally, with an overall rate of 51.2%, much higher than that (6.0%) in the mitochondrially injured oocytes. After ICSI, 65.8% (52/79) of GVT oocytes were fertilized normally, and 21.1% (11/52) eventually reached the blastocyst stage. The transfer of 132 two-cell GVT embryos into the oviducts of pseudopregnant females resulted in 17 apparently healthy live offspring. For some key developmental genes, a high level of expression was identified in the GVT and "rescue"-derived fetal adnexa. Thus, one can induce in oocyte mitochondria a photosensitization-based type of damage, which consistently inhibits GV breakdown, meiotic spindle formation, chromosomal segregation, and polar body extrusion. Germinal vesicle transplanted and rescued oocytes were able to undergo maturation, fertilization, and embryonic cleavage and, ultimately, to develop to term. This approach may provide a model with which to study the age-related ooplasmic dysfunction seen in human oocytes.

Age-associated alteration of gene expression patterns in mouse oocytes

Decreasing oocyte competence with maternal aging is a major factor in human infertility. To investigate the age-dependent molecular changes in a mouse model, we compared the expression profiles of metaphase II oocytes collected from 5- to 6-week-old mice with those collected from 42- to 45-week-old mice using the NIA 22K 60-mer oligo microarray. Among approximately 11,000 genes whose transcripts were detected in oocytes, about 5% (530) showed statistically significant expression changes, excluding the possibility of global decline in transcript abundance. Consistent with the generally accepted view of aging, the differentially expressed genes included ones involved in mitochondrial function and oxidative stress. However, the expression of other genes involved in chromatin structure, DNA methylation, genome stability and RNA helicases was also altered, suggesting the existence of additional mechanisms for aging. Among the transcripts decreased with aging, we identified and characterized a group of new oocyte-specific genes, members of the human NACHT, leucine-rich repeat and PYD-containing (NALP) gene family. These results have implications for aging research as well as for clinical ooplasmic donation to rejuvenate aging oocytes.

Genetic and epigenetic modifications associated with human ooplasm donation and mitochondrial heteroplasmy – considerations for interpreting studies of heritability and reproductive outcome

The mitochondrial heteroplasmy present in offspring from IVF and human ooplasm donation is troublesome and merits further exploration in a debate that is already complex and controversial. Improving the understanding of mitochondrial genomics in this context is important because mitochondriopathies can impact crucial cellular processes in renal, cardiovascular, central nervous, and endocrine systems. Relevant epigenetic consequences of mitochondrial heteroplasmy include associated abnormalities in mitochondrial translation products. Furthermore, as transmission and inheritance patterns of mtDNA are species-specific, it remains to be proven if findings derived from animal studies are applicable to human offspring. As an alternative to gamete research and proteomics based on animal experimentation, continued molecular characterization of the de novo human mitochondriopathies is posed to offer further insights regarding mitochondrial heteroplasmy. In this context, because knowledge of human mitochondrial genetics remains limited and the risks associated with ooplasm donation cannot be quantified, we do not favor its use for our patients at present. However, the small number of infants already conceived from this experimental approach warrant careful longitudinal evaluation. In particular, observational study of the few children born after ooplasm donation could provide opportunities to assess human mtDNA transmission and inheritance. Such findings could help identify features distinguishing natural mtDNA heteroplasmy from heteroplasmy observed after ooplasm donation. Future investigations should also quantify the degree any such heteroplasmy can exist innocuously. Disclosure of mtDNA mutations potentially affecting children conceived from IVF and ooplasm donation must be included during patient education at centers contemplating such treatment.

Distribution of mitochondria in reconstructed mouse oocytes

It has been suggested that nucleus replacement (transfer) may be used as an efficient oocyte therapy in order to prevent transmission of mutated mitochondrial DNA from mother to offspring in humans. The essential and not yet answered question is how mitochondria surrounding the karyoplast will be distributed in the newly reconstructed oocytes. In our model experiments, we have evaluated the distribution of mitochondria in reconstructed immature mouse oocytes when germinal vesicle karyoplasts, with labeled mitochondria, were fused to unlabeled cytoplasts. The penetration of mitochondria from karyoplasts into cytoplasts can be detected almost immediately after the beginning of fusion. In immature reconstructed oocytes, mitochondria are first located in the oocyte center but they are homogenously distributed within the whole cytoplasm before the completion of maturation. Fusion of oocytes at different stages of maturation suggests that the speed of mitochondria distribution is cell cycle dependent.

Implications of cloning technique for reproductive medicine

The birth of Dolly following the transfer of mammary gland nuclei into enucleated eggs established cloning as a feasible technique in mammals, but the moral implications and high incidence of developmental abnormalities associated with cloning have induced the majority of countries to legislate against its use with human gametes. Because of such negative connotations, restrictive political reactions could jeopardize the therapeutic and scientific promise that certain types of cloning may present. For example, in addition to its proposed use as a way of generating stem cells, the basic technique of nuclear transplantation has proven useful in other ways, including its application to immature eggs as a new approach to the prevention of the aneuploidy common in older women, and for some recent advances in preimplantation genetic diagnosis. Thus, while attempts at reproductive cloning in man would seem premature and even dangerous at present, this field will require rational rather than emotional reactions as a basis for legislation if the therapeutic promise of stem cell research and the experimental potential of nuclear transplantation techniques are to be fully realized.

Asynchronous cytoplast and karyoplast transplantation reveals that the cytoplasm determines the developmental fate of the nucleus in mouse oocytes

The relationship between nucleus and cytoplasm can be well revealed by nuclear transplantation. Here, we have investigated the behavior changes of the reconstructed oocytes after transferring the karyoplasts from mouse GV, MI, and MII oocytes into the cytoplasts at the different developmental stages. When the GV cytoplast was used as recipient and MI or MII karyoplast was used as donor (MI-GV pair and MII-GV pair), the reconstructed pairs extruded a polar body after electrofusion and culture. Both the cytoplasm and the polar body had a metaphase spindle in the MI-GV pair, while only a clutch of condensed chromatin was observed in the cytoplasm and polar body of the MII-GV pair. When the MI cytoplast was used as recipient and GV or MII karyoplast was used as donor (GV-MI pair and MII-MI pair), the reconstructed pairs also extruded a polar body. Each had one spindle and a group of metaphase chromosomes in the cytoplasm and polar body, respectively. When the MII cytoplast was used as recipient and GV or MI karyoplast was used as donor (GV-MII pair and MI-MII pair), the reconstructed pairs were activated, became parthenogenetic embryos and even developed to hatching blastocysts after electrofusion. The result from immunoblotting showed that MAP kinase activity was high in the MI and MII cytoplasts, while not detected in GV cytoplast. The results demonstrate that the cytoplasmic environment determines the behavior of asynchronous donors.

Oocyte-induced haploidization

This paper describes the technical approach to treatment of age-related oocyte aneuploidy. Although one solution can be oocyte/embryo selection, another is represented by the nuclear transplantation procedure. The efficiency of nuclear transplantation into immature oocytes is described as a way of generating embryos, and the possibility that viable female gametes can be constructed by transfer of diploid somatic cell nuclei into enucleated oocytes. Germinal vesicle (GV)-stage mouse oocytes were collected from unstimulated ovaries and somatic nuclei were obtained from mouse cumulus cells obtained after ovarian stimulation. Spare human GV-stage oocytes were donated from consenting patients undergoing intracytoplasmic sperm injection (ICSI) treatment, and human somatic cells were stromal cells coming from uterine biopsies performed on consenting patients undergoing endometrial cell co-culture. GV ooplasts, prepared by enucleation, were transplanted with either GV or somatic nuclei by micromanipulation. Grafted oocytes were electrofused and cultured to allow maturation, following which they were selected at random for insemination or cytogenetic analysis. GV transplantation was accomplished with an overall efficiency of approximately 80 and 70% in the mouse and the human respectively. The maturation rate of 96% (mouse) and 62% (human) following reconstitution was comparable to that of control oocytes, as was the incidence of aneuploidy among the reconstituted oocytes. The reconstituted human oocytes were successfully fertilized by ICSI at a rate of 52%. After the transfer of mouse cumulus or human endometrial cell nuclei into enucleated immature oocytes, a polar body was extruded in >40%. In a limited number of observations where the nucleus of an aged oocyte was transferred into a younger ooplasm, the chromosomes segregated normally at the time of polar body extrusion. The technique of nuclear transplantation itself did not increase the incidence of chromosomal anomalies in the mouse or human, since their oocytes reconstituted with homologous donor GV resumed meiosis to metaphase II and maintained a normal ploidy. In addition, immature mouse ooplasts induced haploidization of transplanted somatic cell nuclei. Although further evaluation of their genetic status is needed, the procedure may offer a realistic way of producing normal oocytes in cases of aged-related infertility. While the procedure is technically similar to cloning, it would generate a unique individual as a result of the contribution of both parental genomes.

Ooplasmic influence on nuclear function during the metaphase II-interphase transition in mouse oocytes

Nuclear and pronuclear transfer procedures were used to assess the functional competence of the nucleus and cytoplasm of mouse germinal vesicle-stage oocytes denuded of granulosa cells and matured in vitro or in vivo before artificial activation using a sequential treatment of A23187 + cycloheximide. Following activation, in vitro-matured oocytes were "fertilized" by inserting a male pronucleus (PN), cultured to the 2-cell stage, and then transferred to the oviducts of foster mothers. No live births were noted, whereas a 17% live birth rate was observed when in vivo-matured oocytes were used. The developmental competency of other zygotes was similarly assessed following the exchange of haploid PN of matured and activated eggs with the female PN of fertilized zygotes. When PN of oocytes subjected to maturation and activation in vitro were transferred, only 1 of 79 reconstructed zygotes developed to term. In contrast, the live birth rate was 21% (11 of 53) for zygotes reconstructed with PN from in vivo-matured oocytes. Moreover, a live birth rate of 23% (8 of 35) was observed for reconstructed zygotes with female PN from "hybrid" oocytes created by transferring the metaphase II nuclei of in vitro-matured oocytes into enucleated, in vivo-matured oocytes before activation. Such results suggest that the nucleus of an in vitro-matured oocyte can support embryonic development, but only when it is activated in the proper ooplasmic milieu. The cellular factors creating this ooplasmic milieu appear to develop normally in vivo during follicle maturation to metaphase II, but they fail to do so when the oocytes are denuded of granulosa cells and cultured in vitro before the final stages of maturation. In parallel studies, male and female PN of in vivo-fertilized zygotes were inserted into oocytes that were activated and enucleated following either in vitro or in vivo maturation. Live birth rates were comparable at 19% (5 of 27) and 18% (9 of 49), respectively, suggesting that, regardless of the environment of the final stages of oocyte maturation, the resultant ooplasm is competent to support all aspects of embryonic development once activation and PN formation has been completed. Such findings only point further toward the importance of the condition of the ooplasmic milieu at the time of chemical activation. Whether a similar situation exists when eggs are activated following sperm penetration remains to be determined.

Maturation of the reconstructed oocytes by germinal vesicle transfer in rabbits and mice

The present study was designed to evaluate the feasibility of germinal vesicle (GV) transfer in rabbits and mice. The GV oocytes were collected from ovaries and cultured in 20 microg/mL 3-isobutyl-1-methylxanthin (IBMX) in TCM199 medium, which caused oocytes to shrink, enlarging the perivitelline space to facilitate the GV removal and transfer. Pairs of GV-cytoplast complexes were fused with electric pulses, and the fused, reconstructed oocytes were cultured in TCM199 for 24 h. Results are as follows: 1) The exposure time of rabbit GV oocytes to IBMX medium affected the success of GV removal. For oocytes cultured for 2 and 3 h in IBMX medium, removed rates were 56% and 44, respectively, significantly higher (P < 0.05) than removal rates of GV oocytes cultured for 1 and 4 h (27% and 27%, respectively); 2) There was no significant difference (P > 0.1) in fusion and maturation rates of rabbit reconstructed oocytes collected at 72 and 84 h after initiation of FSH injection to donors; 3) eCG in the maturation media improved development of rabbit-to-rabbit GV transferred oocytes but had no positive effect on mouse-to-rabbit GV transferred oocytes; 4) When mouse GV-karyoplasts were injected into enucleated rabbit oocytes, fusion rates of GV-karyoplasts measuring 40- to 50-microm and 80- to 90-microm in diameters obtained were 84% and 93%, respectively. The rates were significantly higher (P < 0.05) than fusion rates after transferring GV-karyoplasts measuring 30- to 35-microm in diameter (63%). The maturation rate (89%) of reconstructed oocytes composed of 80- to 90-microm mouse GV-karyoplasts and rabbit GV-enucleated cytoplasts was higher than that seen for oocytes composed of 40- to 50-microm (77%, P<0.05) or 30- to 35-microm (59%, P<0.01) mouse karyoplasts. Thirty-five of the 63 (56%) mature mouse-to-rabbit reconstructed oocytes had the normal complement of 20 chromosomes.

Human germline gene therapy reconsidered

This paper reevaluates the notion of human germline gene therapy (HGLGT) in light of developments in biomedicine, biotechnology, and ethical and policy analysis. The essay makes the following key points. First, because the distinction among "therapy," "prevention," and "enhancement" is not clear in human genetics, "gene therapy" is an inadequate descriptor of the process and goals of germline genetic alterations. The alternate use of the phrase "human germline genome modification" (HGLGM) could avoid a misleading label. Second, procedures that could be construed as genetic "enhancement" may not be as morally problematic as some have supposed, once one understands that the boundaries between therapy, prevention, and enhancement are not obvious in genetic medicine. Third, HGLGM might be the medically and morally most appropriate way of avoiding the birth of a child with a genetic disease in only a small range of cases. Fourth, there are still many ethical and scientific problems relating to the safety and efficacy of HGLGM.

Preliminary findings in germinal vesicle transplantation of immature human oocytes

Transplanting a germinal vesicle (GV) from an aged woman's oocyte into a younger ooplasm has been proposed as a possible way to reduce the incidence of oocyte aneuploidy which is considered to be responsible for age-related infertility. In this study, we have assessed the efficiency of each step involved in nuclear transplantation-specifically cell survival, nuclear-cytoplasmic reconstitution, and the capacity of the reconstituted oocytes for in-vitro maturation. In addition, we have evaluated the fertilizability and karyotypic status of the manipulated oocytes by intracytoplasmic sperm injection (ICSI) and fluorescent in-situ hybridization technique respectively. Nuclear transplantation was accomplished with an overall efficiency of 73%. Due to the limited availability of materials, most nuclear transplantation procedures were performed between sibling oocytes. The maturation rate of 62% following reconstitution was comparable with that of control oocytes, as was the incidence of aneuploidy among the reconstituted oocytes. The ICSI results of the reconstituted oocytes yielded a survival rate of 77%, a fertilization rate of 52%, and a satisfactory early embryonic cleavage. Furthermore, in a limited number of observations where the nucleus of an aged oocyte was transferred into a younger ooplasm, there was an appropriate chromosomal segregation. These findings demonstrate that human oocytes reconstituted with GV nuclei are able to undergo maturation, fertilization, and early embryo cleavage, and maintain a normal ploidy. Although in-vitro maturation seems to be a limiting step, this technique would allow us to investigate further the nuclear-ooplasmic relationship during meiotic maturation.