Transplantation of photoreceptors into the degenerative retina: Current state and future perspectives

The mammalian retina displays no intrinsic regenerative capacities, therefore retinal degenerative diseases such as age-related macular degeneration (AMD) or retinitis pigmentosa (RP) result in a permanent loss of the light-sensing photoreceptor cells. The degeneration of photoreceptors leads to vision impairment and, in later stages, complete blindness. Several therapeutic strategies have been developed to slow down or prevent further retinal degeneration, however a definitive cure i.e. replacement of the lost photoreceptors, has not yet been established. Cell-based treatment approaches, by means of photoreceptor transplantation, have been studied in pre-clinical animal models over the last three decades. The introduction of pluripotent stem cell-derived retinal organoids represents, in principle, an unlimited source for the generation of transplantable human photoreceptors. However, safety, immunological and reproducibility-related issues regarding the use of such cells still need to be solved. Moreover, the recent finding of cytoplasmic material transfer between donor and host photoreceptors demands reinterpretation of several former transplantation studies. At the same time, material transfer between healthy donor and dysfunctional patient photoreceptors also offers a potential alternative strategy for therapeutic intervention. In this review we discuss the history and current state of photoreceptor transplantation, the techniques used to assess rescue of visual function, the prerequisites for effective transplantation as well as the main roadblocks, including safety and immune response to the graft, that need to be overcome for successful clinical translation of photoreceptor transplantation approaches.

Ooplasmic transfer in human oocytes: efficacy and concerns in assisted reproduction

BACKGROUND

Ooplasmic transfer (OT) technique or cytoplasmic transfer is an emerging technique with relative success, having a significant status in assisted reproduction. This technique had effectively paved the way to about 30 healthy births worldwide. Though OT has long been invented, proper evaluation of the efficacy and risks associated with this critical technique has not been explored properly until today. This review thereby put emphasis upon the applications, efficacy and adverse effects of OT techniques in human.

MAIN BODY

Available reports published between January 1982 and August 2017 has been reviewed and the impact of OT on assisted reproduction was evaluated. The results consisted of an update on the efficacy and concerns of OT, the debate on mitochondrial heteroplasmy, apoptosis, and risk of genetic and epigenetic alteration.

SHORT CONCLUSION

The application of OT technique in humans demands more clarity and further development of this technique may successfully prove its utility as an effective treatment for oocyte incompetence.

Assisted reproductive technologies: advances in medical practice or human subject research?

Although human subject research is regulated by federal agencies, the differences between research and innovative clinical practice are often blurred. Research and innovative practices share the similar goals of obtaining additional knowledge and improving medical treatment. Research, however, is more specifically defined as "a systematic investigation, including research development, testing and evaluation, designed to develop or contribute to generalizable knowledge." Aprocedure consistent with this definition is subject to distinct federal regulations and other ethical procedural safeguards. When unregulated innovative practices, not neatly fitting within this definition of research, are first implemented, safeguards do not necessarily exist because use of these procedures is primarily guided by individual physician judgment. Recognizing that the application of innovative advancements in ART may very well benefit numerous prospective infertile patients and may initially appear to be safe and effective, these new and novel procedures may be associated with yet unknown long-term risks and safety concerns unless more formal scientific study is conducted to support efficacy and safety.

Role of the mitochondrial genome in assisted reproductive technologies and embryonic stem cell-based therapeutic cloning

Mitochondria play a pivotal role in cellular metabolism and are important determinants of embryonic development. Mitochondrial function and biogenesis rely on an intricate coordination of regulation and expression of nuclear and mitochondrial genes. For example, several nucleus-derived transcription factors, such as mitochondrial transcription factor A, are required for mitochondrial DNA replication. Mitochondrial inheritance is strictly maternal while paternally-derived mitochondria are selectively eliminated during early embryonic cell divisions. However, there are reports from animals as well as human patients that paternal mitochondria can occasionally escape elimination, which in some cases has led to severe pathologies. The resulting existence of different mitochondrial genomes within the same cell has been termed mitochondrial heteroplasmy. The increasing use of invasive techniques in assisted reproduction in humans has raised concerns that one of the outcomes of such techniques is an increase in the incidence of mitochondrial heteroplasmy. Indeed, there is evidence that heteroplasmy is a direct consequence of ooplasm transfer, a technique that was used to 'rescue' oocytes from older women by injecting ooplasm from young oocytes. Mitochondria from donor and recipient were found in varying proportions in resulting children. Heteroplasmy is also a byproduct of nuclear transfer, as has been shown in studies on cloned sheep, cattle and monkeys. As therapeutic cloning will depend on nuclear transfer into oocytes and the subsequent generation of embryonic stem cells from resulting blastocysts, the prospect of mitochondrial heteroplasmy and its potential problems necessitate further studies in this area.

Activation of maturation promoting factor in Bufo arenarum oocytes: injection of mature cytoplasm and germinal vesicle contents

Although progesterone is the established maturation inducer in amphibians, Bufo arenarum oocytes obtained during the reproductive period (spring-summer) resume meiosis with no need of an exogenous hormonal stimulus if deprived of their enveloping follicle cells, a phenomenon called spontaneous maturation. In this species it is possible to obtain oocytes competent and incompetent to undergo spontaneous maturation according to the seasonal period in which animals are captured. Reinitiation of meiosis is regulated by maturation promoting factor (MPF), a complex of the cyclin-dependent kinase p34cdc2 and cyclin B. Although the function and molecule of MPF are common among species, the formation and activation mechanisms of MPF differ according to species. This study was undertaken to evaluate the presence of pre-MPF in Bufo arenarum oocytes incompetent to mature spontaneously and the effect of the injection of mature cytoplasm or germinal vesicle contents on the resumption of meiosis. The results of our treatment of Bufo arenarum immature oocytes incompetent to mature spontaneously with sodium metavanadate (NaVO3) and dexamethasone (DEX) indicates that these oocytes have a pre-MPF, which activates and induces germinal vesicle breakdown (GVBD) by dephosphorylation on Thr-14/Tyr-15 by cdc25 phosphatase and without cyclin B synthesis. The injection of cytoplasm containing active MPF is sufficient to activate an amplification loop that requires the activation of cdc25 and protein kinase C, the decrease in cAMP levels, and is independent of protein synthesis. However, the injection of germinal vesicle content also induces GVBD in the immature receptor oocyte, a process dependent on protein synthesis but not on cdc25 phosphatase or PKC activity.

Impact of Assisted Reproductive Technologies: A Mitochondrial Perspective of Cytoplasmic Transplantation

Many of the assisted reproductive techniques associated with maternal aging, disease states, or implantation failure aim to correct poor developmental capacity. These techniques are highly invasive and require the exchange of nuclear or cytoplasmic material from a donor oocyte to compensate for deficiencies inherent in the affected individual. These techniques are based on the assumption that the cytoplasm of the donor oocyte can effectively substitute the necessary component(s) to enable development to proceed. Several studies have attempted to inject cytoplasm from "normal" (young) donors, into aged eggs, again assuming that beneficial components of the cytoplasm are transferred to restore developmental capacity. These invasive assisted reproduction technology (ART) procedures aim to eliminate chromosomal abnormalities, improve the quality of oocytes deficient in some important cytoplasmic factors necessary for maturation and/or subsequent development, and eliminate maternally inherited diseases (particularly mitochondrial myopathies). However, in order to develop such ART, understanding the processes involving mitochondrial DNA replication and transcription is imperative, as asynchrony between mitochondrial and nuclear genomes may cause problems in mitochondrial function, localization, and biogenesis.

Ooplasmic transfer: problems and prospects

Cytoplasmic transfer between human oocytes, which represents a complete cytoplasmic exchange, has been performed recently as a means to improve the outcome of assisted reproduction and becomes a hotspot of researches. Many studies have indicated that mitochondria in the oocytoplasm obviously affect fertilization of the oocytes and early embryo development. However, ooplasmic transfer can lead to mitochondrial DNA heteroplasmy and the prospect of mitochondrial heteroplasmy and its potential problems necessitate further studies. The authors reviews the ooplasmic transfer, the relation between ooplasm and fertilization and embryo development, and the mitochondrial heteroplasmy. The authors also propose a new theory of "reverse cloning technique".

Role of the mitochondrial genome in preimplantation development and assisted reproductive technologies

Our fascination for mitochondria relates to their origin as symbiotic, semi-independent organisms on which we, as eukaryotic beings, rely nearly exclusively to produce energy for every cell function. Therefore, it is not surprising that these organelles play an essential role in many events during early development and in artificial reproductive technologies (ARTs) applied to humans and domestic animals. However, much needs to be learned about the interactions between the nucleus and the mitochondrial genome (mtDNA), particularly with respect to the control of transcription, replication and segregation during preimplantation. Nuclear-encoded factors that control transcription and replication are expressed during preimplantation development in mice and are followed by mtDNA transcription, but these result in no change in mtDNA copy number. However, in cattle, mtDNA copy number increases during blastocyst expansion and hatching. Nuclear genes influence the mtDNA segregation patterns in heteroplasmic animals. Because many ARTs markedly modify the mtDNA content in embryos, it is essential that their application is preceded by careful experimental scrutiny, using suitable animal models.

Injection of somatic cell cytoplasm into oocytes before intracytoplasmic sperm injection impairs full-term development and increases placental weight in mice

This study investigated the effects on fertilized embryo development of somatic cytoplasm after its injection into intact mouse oocytes. Mature oocytes collected from female B6D2F1 mice were injected with cumulus cell cytoplasm of different volumes and from different mouse strains (B6D2F1, ICR, and C57BL/6), or with embryonic cytoplasm. After culture for 1 h, B6D2F1 sperm were injected into those oocytes by intracytoplasmic sperm injection (ICSI). The oocytes were examined for pre- and postimplantation developmental competence. Increases in the volume of the somatic cytoplasm from onefold to fourfold resulted in an impairment of blastocyst development and full-term development (28% and 7%, respectively, vs. 96% and 63%, respectively, in the control group; P < 0.01). An increase in the volume of somatic cytoplasm reduced the expression of POU5F1 (more commonly known as OCT4) in expanded blastocysts. The frequency of embryos that developed to the blastocyst stage did not differ when B6D2F1 or ICR somatic cytoplasm was injected, but injection of C57BL/6 somatic cytoplasm induced a two-cell block in embryo development. Injection of the cytoplasm from fertilized embryos did not reduce the frequency of embryos attaining full-term development. Interestingly, somatic cytoplasm significantly increased the placental weight of ICSI embryos, even the injection of onefold cytoplasm (0.20 +/- 0.02 [n = 32] vs. 0.12 +/- 0.02 in the control group [n = 87]; P < 0.01). These findings indicate that the injection of somatic cytoplasm into oocytes before ICSI causes a decrease in preimplantation development, clearly impairs full-term development, and causes placental overgrowth in fertilized embryos. To our knowledge, placental overgrowth phenotypes are only caused by interspecies hybridization and cloning, and in genetically modified mice. Here, we report for the first time that somatic cytoplasm causes abnormal placentas in fertilized embryos. This study suggests that somatic cell cytoplasmic material is one cause of the low rate of full-term development in cloned mammals.

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.

[Progress in ooplasmic transfer]

Many studies indicated mitochondria in oocytoplasm affects obviously the fertilization of the oocytes and early embryo development. The decrease of ATP content and mitochondrial DNA(mtDNA) content, and mtDNA defects can make the fertilization of oocytes and embryo development decreased, which is the key one of reason that the reproductive ability is low in aged women and aged animal. Ooplasmic transfer increases the fertilizability of the aged oocytes and the early embryonic viability, it has led to the birth of health babies, and become a hotspot in the realm of human assisted reproduction biotechnology and animal clone. However, Ooplasmic transfer can lead to mtDNA become heteroplastic, which is the mtDNA of donor and recipient coexist in offspring. At present, how the heterogeneous ooplasm influences the embryogenesis and development is not entirely clear. This paper reviews the ooplasmic transfer in summary, the relation between ooplasm and fertilization and embryo development, the hereditary behavior of heterogeneous mitochondria DNA and it's examination after ooplasmic transfer.

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.

Cytoplasmic and molecular reconstruction of Xenopus embryos:synergy of dorsalizing and endo-mesodermalizing determinants drives early axial patterning

Ablation of vegetal cytoplasm from newly fertilized Xenopus eggs results in the development of permanent blastula-type embryos (PBEs). PBEs cleave normally and develop into a very simple tissue consisting only of atypical epidermis. We tried to restore complete embryonic development in PBEs by cytoplasmic transplantation or by mRNA injection. We show a two-step reconstruction of the body plan. In the first step, PBEs injected with either marginal cytoplasm or synthetic VegT RNA restored gastrulation and mesoderm formation, but not axial patterning. Injection of Xwnt8 mRNA (acting upstream of β-catenin and thus substitutes for the dorsal determinant)did not restore axial development in PBEs. Simultaneous injections of Xwnt8 and VegT into PBEs resulted in dorsal axis development, showing the synergy of these molecules in axial development. These results suggest that the mixing of two cytoplasmic determinants, i.e. the dorsal determinant in the vegetal pole and the endo-mesodermal determinant in the whole vegetal half, triggers the early axial developmental process in Xenopus embryos.

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.

Production of cloned pigs by whole-cell intracytoplasmic microinjection

Cloning by somatic cell nuclear transfer has been successfully achieved by both fusing of a donor cell with and injecting an isolated donor cell nucleus into an enucleated oocyte. However, each of the above methods involves extended manipulation of either the oocytes (fusion) or the donor cells (nucleus isolation). Additionally, cloning efficiency can be reduced by low fusion rate of the cell fusion method, and specialized micromanipulation equipment and exacting nucleus isolation techniques are required for the nucleus injection method. Here we report a whole-cell injection technique for nuclear transfer in pigs and the production of cloned piglets with comparable, if not higher, efficiency than the other two nuclear transfer procedures. First, we tested the feasibility of this technique with three types of frequently used donor cells (cumulus, mural granulosa, and fibroblasts) and obtained the optimal nuclear reprogramming conditions for these cells. We further improved our protocol by avoiding ultraviolet exposure during enucleation and achieved a 37% blastocyst rate. We then conducted whole-cell injection using skin fibroblasts from the ear of a sow transgenic for two genes, the porcine lactoferrin and the human factor IX, and produced four live-born cloned transgenic piglets from three recipients. The present study demonstrated the applicability of producing normal, cloned piglets by the simple and less labor-intensive whole-cell intracytoplasmic injection.

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.

Parental exposure to low-dose X-rays in Drosophila melanogaster induces early emergence in offspring, which can be modulated by transplantation of polar cytoplasm

In recent years there has been growing concern over the biological effects of low-dose X-rays, but few studies have addressed this issue. Our laboratory had observed flies (Drosophila melanogaster) irradiated with low-dose X-rays tend to emerge earlier than normal flies. This observation led us to quantitatively examine the effects of low-dose X-irradiation on development in the fly. Following exposure of prepupal (day 5) flies to 0.5 Gy X-rays, the time to emergence was slightly shorter than in the sham controls. This tendency was increased when the X-ray exposure came during the pupal stage (day 7). In these flies, the time to eclosion decreased significantly, by an average of 30 h sooner than sham controls. A further experiment examined whether such radiation effects could be observed in the unexposed F1 generation of exposed individuals. Greater radiation effects on early F1 emergence were seen when the time between exposure and mating was 3 days, indicating an effect on early spermatid development. Early F1 emergence was also observed after exposure of female flies to X-rays during late previtellogeny. Furthermore, rapid emergence could be induced in the F1 embryos of unexposed parents by transferring the polar cytoplasm (precursor cells of the germ cell line) from F1 embryos of exposed flies. These results show that radiation-induced effects can be transmitted to the next generation through the germ cell line.

[Cloning techniques for mitochondrial diseases and prenatal diagnosis]

Disorders caused by mutation in the mitochondrial DNA are uncommon. Due to the special pattern of inheritance and of the variability of penetrance the options to affected couples to have healthy children are few. So far traditional prenatal diagnosis is of limited benefit. The problems may be overcome by oocyte donation. However, if the couple wants their own biological offspring, no good method is available today. We discuss ooplasmic and nuclear transfer as possible future options for these couples to have healthy biological children.

Micromanipulation of the human oocyte

Intracytoplasmic sperm injection (ICSI) provides an excellent outcome in a consistent manner, and is therefore used worldwide as a routine procedure. Since its introduction, few modifications have been made to its methodology. Recently, a combination of ICSI with micro-hole drilling by laser (LA-ICSI) of the zona pellucida appeared to decrease oocyte degeneration rates and to improve embryo quality and implantation. Cytoplasmic transfer is a more recently introduced procedure where the objective is to improve the quality of patients' oocytes by transferring cytoplasm from a good quality donor oocyte, in cases where it is assumed that cytoplasm is compromised. Nuclear transfer, involving exchange of nuclei between donor and receptor oocytes, is still an experimental procedure, the objective being similar to cytoplasmic transfer in improving oocyte/embryo quality. A nuclear transfer procedure involving somatic cells for reproductive purposes should not be used in humans, for ethical and technical considerations. On the other hand, nuclear transfer for therapeutic purposes to obtain stem cells may be considered in respect of its unique potential in medicine. Finally, the most recently emerged new concept under investigation is the haploidization of somatic cells for the purpose of creating artificial gametes.

Mesodermal and axial determinants contribute to mesoderm regionalization in Bufo arenarum embryos

The existence of mesodermal determinants in the equator of Bufo arenarum embryos has been previously demonstrated. In this work, their role in dorso-ventral regionalization of mesoderm was studied by transferring the determinants to animal blastomeres. The transfer was performed by cleavage reorientation and cytoplasmic microinjection. Forced inclination during early cleavage caused deviation of the third cleavage plane and annexation of equatorial cytoplasm into animal quartets. Animal blastomeres from embryos oriented with the dorsal side up, incorporated ventro-equatorial cytoplasm and formed blood cells, mesenchyme, and coelomic epithelium. In contrast, animal blastomeres from embryos oriented with the ventral side up, acquired dorso-equatorial cytoplasm and developed notochord, somites, mesenchyme, coelomic epithelium and nervous tissue. In order to investigate if this dorso-ventral differentiation pattern responds to an interaction of mesodermal and axial factors, isolated 8-cell-stage animal quartets were microinjected with subcortical cytoplasm from: (a) the ventro-equatorial region of synchronous embryos; (b) the vegetal pole of uncleaved eggs; (c) a combination of both cytoplasms. As expected, the implanted ventro-equatorial cytoplasm promoted ventral mesoderm differentiation. Conversely, the joint transfer of ventro-equatorial cytoplasm and vegetal pole cytoplasm behaved as the dorso-equatorial cytoplasm, promoting dorso-lateral mesoderm and neural formation. Thus, mesoderm regionalization in B. arenarum embryos seems to be caused by a concurrent action of both mesodermal and axial determinants.

Technical approaches to correction of oocyte aneuploidy

BACKGROUND

This study describes the technical approaches used in treatment of age-related oocyte aneuploidy, the efficiency of each step of nuclear transplantation into mouse and human oocytes, and the ability of germinal vesicle (GV) transplantation to restore artificially induced ooplasmic damage. Finally, it examines the possibility of constructing viable female gametes by transferring diploid somatic cell nuclei into enucleated oocytes.

METHODS

GV stage mouse oocytes were collected from unstimulated ovaries, and human GV oocytes were donated from consenting patients undergoing ICSI. Stromal (somatic) cells were isolated from uterine biopsies of consenting patients. Mouse cumulus cells were obtained after ovarian stimulation. GV ooplasts prepared by removing nuclei were transplanted either with GV nuclei or with somatic cells by micromanipulation. Grafted oocytes were electrofused and cultured to allow maturation, following which they were inseminated or analysed cytogenetically. Ooplasmic dysfunction was induced by photosensitization with a mitochondria-specific fluorescent dye.

RESULTS

GV transplantation had an overall efficiency of 87 and 73% in the mouse and humans respectively. Maturation rates of 95 (mouse) and 64% (human) following reconstitution were comparable with those in control oocytes, as was the incidence of aneuploidy for five chromosome-specific probes after aneuploidy among the reconstituted oocytes. Photosensitization of oocytes significantly reduced the maturation rate to 4.2%, whereas 61.9% of oocytes matured after transfer of photosensitized GV karyoplasts into healthy ooplasts, with 52% of these mature oocytes being successfully fertilized by ICSI. Enucleated immature oocytes receiving mouse cumulus or human endometrial cell nuclei extruded a polar body in >40% of cases. Five out of seven successfully transferred aged human nuclei exhibited the expected number of signals with five chromosome-specific probes suggesting an appropriate chromosome separation in young ooplasm.

CONCLUSIONS

Nuclear transplantation itself does not appear to interfere with chromosome segregation and can possibly rescue oocytes with damaged mitochondria. Finally, immature mouse ooplasm supported separation of somatic chromosomes to expected numbers, implying that haploidization may be occurring. The roles of genetic imprinting and fidelity of chromosome segregation are unknown.

Ooplasmic transfer: animal models assist human studies

Ooplasmic transplantation is based on the premise that ooplasmic components are compromised in some individuals. In theory, the transfer of small amounts of healthy ooplasm can correct such deficits, allowing for improved development and implantation. The technique is based on a well-established background of experimental embryology demonstrating that cytoplasmic manipulation in oocytes and early embryos can be entirely compatible with normal development. Cytoplasm has been manipulated via karyoplast and cytoplast transfer and by cytoplasmic injection. Term development has been obtained following such manipulations in a variety of mammalian species. While some manipulative scenarios have exhibited compromised development, others have exhibited improved development. Developmental problems involving specific epigenetic and mitochondrial incompatibilities have been observed in a very limited subset of animal studies. These studies are based on genetic and physical models that have little relation to the actual substance of ooplasmic transplantation in the human. In fact, the majority of animal studies suggest that ooplasmic transplantation is well-founded and unlikely to result in negative developmental consequences. Furthermore, there are considerable physical, physiological and developmental differences between human and rodent eggs and embryos. These differences suggest that potentially negative issues raised by rodent results may not be relevant in the human.

The role of maternal mitochondria during oogenesis, fertilization and embryogenesis

This review examines the place of mitochondria in the life cycle through oogenesis, ovulation and early embryogenesis. Mitochondria are semi-autonomous organelles responsible for the bulk of oxidative energy production in the body. They play central roles in ageing, in apoptosis and in many non-Mendelian-inherited bioenergetic and neurological diseases. Originating as free alpha-proteobacteria that entered into a symbiotic relationship with the ancestral eukaryotic organisms, they now have a highly restricted genome of ~16 kb, encoding for 37 genes of the oxidative phosphorylation pathway. Mitochondria are inherited through the mother and special mechanisms have evolved to eliminate the contribution of the spermatozoon in early embryonic development. Most mitochondrial genes have become translocated to the nucleus, and nuclear and mitochondrial genes have co-evolved. This, coupled with a high mutation rate in the remaining mitochondrial DNA, has resulted in a high degree of concordance between them. Disharmony between nuclear and mitochondrial genes is thus likely to complicate cloning technology and the experimental reconstruction of chimeric embryos by cytoplasmic or nuclear transfer.

Donor oocyte cytoplasmic transfer did not enhance implantation of embryos of women with poor ovarian reserve

PURPOSE

To determine whether donor oocyte cytoplasm transferred into the oocytes of women < or = 40 years or with diminished ovarian reserve would enhance embryo quality, implantation, or pregnancy rates.

METHODS

Study subjects included women > or = 40 years (15) or with abnormal FSH levels (3). Healthy volunteers (18) produced oocytes for cryopreservation. Donor oocytes were thawed and cytoplasm from surviving oocytes was injected with a single sperm into the cytoplasm of recipient oocytes. Outcome measures included embryo quality scores, implantation, and pregnancy rates.

RESULTS

Eighteen donors produced 213 oocytes for cryopreservation and 39/171 (22.8%) survived thawing. Eighteen recipients initiated 25 IVF cycles with embryo transfer in 20 cycles after cytoplasmic transfer (CT). Four cycles resulted in three biochemical losses and one aneuploid clinical loss. Embryo quality did not improve with CT compared to pre-CT IVF cycles in six recipients.

CONCLUSIONS

CT with cryopreserved donor oocyte cytoplasm did not enhance success in women with advanced reproductive age or low ovarian reserve.

Effects of follicular size of cytoplast donor on the efficiency of cloning in cattle

In cattle, oocytes obtained from follicles smaller than 3 mm in diameter can undergo maturation in vitro, progressing to MII and undergoing fertilization, but are developmentally incompetent. Cytoplasts were prepared from in vitro matured oocytes aspirated from small (1-3 mm) or large (6-12 mm) follicles and fused to serum starved mural granulosa cells. Following activation, reconstructed embryos were cultured for 7 days and classified G1 to G4, before being processed for nuclei counting or transferred to synchronized recipients. Oocytes from small follicles had lower rates of polar body extrusion (59.6 vs. 69%; 731/1230 vs. 608/857) and fusion (71.4 vs. 78.8%; 360/497 vs. 364/465; P < 0.06). There were no differences in total rate of blastocysts development (60 vs. 59.8%; small vs. large), or any grade classification. A significant interaction was detected between follicle size and embryo grade with G3 embryos from small follicles having a greater cell number. Developmental competence of G1 and G2 embryos did not differ at day 27 (48 vs. 46%; 16/33 vs. 17/37; small vs. large). Although there were no differences in fetal size between the two groups, differences in allantois length (53 vs. 86 mm; small vs. large; P < 0.002) and allantois width (9.5 vs. 13 mm; small vs. large; P < 0.06) were seen. No differences in survival to term (2/13 in each group) were observed. These results indicate that cytoplasts from follicles of 1-3 and 6-12 mm in diameter are equally developmentally competent when used in a nuclear transfer procedure.

Interaction theory of mammalian mitochondria

We generated mice with deletion mutant mtDNA by its introduction from somatic cells into mouse zygotes. Expressions of disease phenotypes are limited to tissues expressing mitochondrial dysfunction. Considering that all these mice share the same nuclear background, these observations suggest that accumulation of the mutant mtDNA and resultant expressions of mitochondrial dysfunction are responsible for expression of disease phenotypes. On the other hand, mitochondrial dysfunction and expression of clinical abnormalities were not observed until the mutant mtDNA accumulated predominantly. This protection is due to the presence of extensive and continuous interaction between exogenous mitochondria from cybrids and recipient mitochondria from embryos. Thus, we would like to propose a new hypothesis on mitochondrial biogenesis, interaction theory of mitochondria: mammalian mitochondria exchange genetic contents, and thus lost the individuality and function as a single dynamic cellular unit.

Pregnancy after cytoplasmic transfer in a couple suffering from idiopathic infertility: case report

Couples suffering from idiopathic infertility are among the most difficult to treat in IVF cycles due to the unknown cause of failure to reproduce. This can lead to years of unsuccessful attempts to conceive and often the abandonment of treatment. In some couples, the only observable problem is the development of poor quality embryos. In this case report, we describe the successful use of cytoplasmic donation in a couple where the high level of embryo fragmentation and poor embryo development was thought to be the unique cause of failure to conceive after intracytoplasmic sperm injection (ICSI). We noted a strong reduction in embryo fragmentation and a consequent increase in embryo quality after the treatment. Transfer of four of the embryos receiving donor cytoplasm led to a pregnancy with two gestational sacs and the birth of healthy twins.

Nuclear plasticity and timing mechanisms of the initiation of alkaline phosphatase expression in cytoplasm-transferred blastomeres of ascidians

Egg cytoplasm containing endoderm determinants was transferred to presumptive-muscle or presumptive-epidermis blastomeres isolated from cleavage-stage embryos of the ascidian Halocynthia roretzi. We investigated three aspects of the expression of endoderm-specific alkaline phosphatase (ALP) activity. First, we examined whether ectopic ALP expression, an indication of ectopic endoderm formation, was promoted in cytoplasm-transferred blastomeres isolated at late-cleavage stage. The results showed that the cell fate was converted by the introduced cytoplasm, even in recipient blastomeres in which the cell fate was already restricted to muscle or epidermis, and in those where expression of the muscle- or epidermis-specific genes was already initiated. Next, we examined the formation of endoderm and other tissue in embryos by double staining for ALP and muscle- or epidermis-specific marker. Regions positive for ALP and positive for muscle or epidermis marker were mutually exclusive. These results suggested that muscle- or epidermis-specific genes that were already expressed in the recipient blastomeres were down-regulated in ectopically forming endoderm cells. This is evidence for nuclear plasticity during ascidian embryogenesis. In the last series of experiments, we investigated the timing of the appearance of ALP activity in cytoplasm-transferred embryos. In the partial embryos that were derived from various combination of recipient blastomeres and donor cytoplasm obtained from various staged eggs and embryos, the timing seemed to coincide with the time that starts when cell fusion for cytoplasmic transfer was done. Therefore, the clock that determines the timing of the initiation of ALP expression is likely to start at the moment of cell fusion. Several possible hypotheses for the timing mechanism are discussed.

Mouse-rabbit germinal vesicle transfer reveals that factors regulating oocyte meiotic progression are not species-specific in mammals

A series of experiments were designed to evaluate the meiotic competence of mouse oocyte germinal vesicle (GV) in rabbit ooplasm. In experiment 1, an isolated mouse GV was transferred into rabbit GV-stage cytoplast by electrofusion. It was shown that 71.8% and 63.3% of the reconstructed oocytes completed the first meiosis as indicated by the first polar body (PB1) emission when cultured in M199 and M199 + PMSG, respectively. Chromosomal analysis showed that 75% of matured oocytes contained the normal 20 mouse chromosomes. When mouse spermatozoa were microinjected into the cytoplasm of oocytes matured in M199 + PMSG and M199, as many as 59.4% and 48% finished the second meiosis as revealed by the second polar body (PB2) emission and a few fertilized eggs developed to the eight-cell stage. In experiment 2, a mouse GV was transferred into rabbit MII-stage cytoplast. Only 13.0-14.3% of the reconstructed oocytes underwent germinal vesicle breakdown (GVBD) and none proceeded past the MI stage. When two mouse GVs were transferred into an enucleated rabbit oocyte, only 8.7% went through GVBD. In experiment 3, a whole zona-free mouse GV oocyte was fused with a rabbit MII cytoplast. The GVBD rates were increased to 51.2% and 49.4% when cultured in M199 + PMSG and M199, respectively, but none reached the MII stage. In experiment 4, a mouse GV was transferred into a partial cytoplasm-removed rabbit MII oocyte in which the second meiotic apparatus was still present. GVBD occurred in nearly all the reconstructed oocytes when one or two GVs were transferred and two or three metaphase plates were observed in ooplasm after culturing in M199 + PMSG for 8 hr. These data suggest that cytoplasmic factors regulating the progression of the first and the second meioses are not species-specific in mammalian oocytes and that these factors are located in the meiotic apparatus and/or its surrounding cytoplasm at MII stage.

Evaluation of the meiotic spindle apparatus in metaphase II human oocytes following cytoplasmic donation

PURPOSE

To determine if the removal of cytoplasm from metaphase II human donor oocytes damages the meiotic spindle apparatus.

MATERIALS AND METHODS

Cryopreservation of metaphase II human oocytes was performed using a fast-freeze, fast-thaw protocol. Upon thaw, oocytes were incubated for 3-4 h and then used for cytoplasmic donation (test oocytes). Oocytes thawed but not used for donation served as controls. Test and control oocytes were fixed using a microtubule-stabilizing buffer. Tubulin was localized using antitubulin monoclonal antibody. Chromosomes were identified by counterstaining with DAPI.

RESULTS

Forty-four oocytes had cytoplasm removed (test group) while 12 were not used for the procedure (controls). Twenty-three oocytes survived the donation procedure. Rates of normal spindle structure for the control and test groups were 21/23 (91.3%) and 12/12 (100%), respectively.

CONCLUSION

The removal of cytoplasm from a metaphase II human donor oocyte does not appear to significantly increase the damage to chromosome alignment or to the spindle structure.

Reproduction in the Noughties: will the scientists have all the fun?

The past 20-30 years have seen major advances in our understanding of human reproduction and in our ability to manipulate it, as well as major social changes in human reproductive and sexual attitudes. Many of these advances and changes developed out of the first successful in vitro fertilisation (IVF) of the human oocyte. It is also the case that 30 years ago few foresaw what was to come, and many were at best doubtful and often were very critical of the scientific work which led to human IVF and to many of the subsequent developments. This lack of foresight provides us with a lesson about the dangers that we face in looking forward and attempting to predict the future. This review will try to convey, not comprehensively but through examples, the flavour of current activities in Assisted Reproduction clinics and research laboratories around the world and what is being talked about for the future in respect of emergent patient demands and anticipated clinical needs. This clinically driven approach will form the basis for consideration of some underlying scientific aspects of reproductive research, some of the ethicolegal issues that may arise, and the implications of this anticipated future for our current approaches to medical education. The future will be considered not simply in terms of the New Reproduction itself but also in its interaction with the opportunities and challenges presented by the New Genetics. It is perhaps in the interaction between these two fields of endeavour that some of the most difficult challenges ahead lie.

Mitochondria in human offspring derived from ooplasmic transplantation

Ooplasmic transfer from fertile donor oocytes into potentially compromised recipient patient oocytes has led to the birth of nearly 30 babies worldwide. Cytoplasmic transplantation has caused apprehension, since the mixing of human ooplasm from two different maternal sources may generate mitochondrial (mt) heteroplasmy (both recipient and donor mtDNA) in offspring. This investigation traced the mitochondrial donor population both during the ooplasmic transfer technique and in the bloods of two 1 year old children using mtDNA fingerprinting. Donor ooplasm stained for active mitochondria was transferred into recipient ooplasm and the mitochondria were visualized by confocal microscopy after the microinjection procedure and fertilization. Heteroplasmy was found in the blood from each of the children. This report is the first case of human germline genetic modification resulting in normal healthy children.

Viable rabbits derived from reconstructed oocytes by germinal vesicle transfer after intracytoplasmic sperm injection (ICSI)

Abnormal oocyte spindle due to the improper function of ooplasm is associated with female infertility of advanced maternal age. A possible way to overcome this problem is to transfer an oocyte germinal vesicle (GV) which contains genetic materials of a patient with a history of poor embryo development to the cytoplast from a donor oocyte. Here we demonstrate that GV transfer is feasible using a rabbit model. When the GVs were transferred to auto- or hetero-cytoplasts of GV stage oocytes, around 80% of the reconstructed oocytes could mature in vitro and 7.1-9.4% of the oocytes developed to blastocyst stage after intracytoplasmic sperm injection (ICSI). Transfer of 93 fertilized eggs reconstructed via GV transfer into six recipients resulted in two live offspring. Results of this experiment indicate that GV transfer can potentially become a new approach in treatment of infertility because of advanced maternal age.

Mitochondrial DNA heteroplasmy after human ooplasmic transplantation

OBJECTIVE

To determine the patterns of mitochondrial inheritance in embryos, fetuses, and infants after ooplasmic transplantation using the technique of mitochondrial DNA (mtDNA) fingerprinting.

DESIGN

Prospective clinical study.

SETTING

The IVF program at Saint Barnabas Medical Center, a nonprofit community hospital.

PATIENT(S)

In a total of 23 cases with recurrent implantation failure after IVF ooplasmic transplantation was performed. Thirteen embryos from two patients and amniotic cells from four patients were investigated for heteroplasmy. Placenta and fetal cord blood cells from four newborn babies/infants were also investigated.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

mtDNA fingerprinting, polymerase chain reaction, and DNA sequencing analysis.

RESULT(S)

In addition to the recipient maternal mitochondrial DNA, a small proportion of donor mitochondrial DNA was detected in samples with the following frequencies: embryos (n = 6/13), amniocytes (n = 1/4), placenta (n = 2/4), and fetal cord blood (n = 2/4). Fingerprinting showed that nuclear DNA was not inherited from the donor in placenta or fetal cord blood of the babies.

CONCLUSION(S)

Ooplasmic transfer can result in sustained mtDNA heteroplasmy representing both donor and recipient. This was shown by mtDNA fingerprinting of embryos, amniocytes, fetal placenta, and cord blood. These results show that the donor-derived mitochondrial population persists after ooplasmic transfer and may be replicated during fetal development.

Spontaneous and artificial changes in human ooplasmic mitochondria

Our research has focused on promoting the development of compromised embryos by transferring presumably normal ooplasm, including mitochondria, to oocytes during intracytoplasmic insemination. Because of the enigma of mitochondrial heteroplasmy, the mixing of populations of oocyte cytoplasm has provoked considerable debate. We are currently investigating oocyte mitochondrial (mt) DNA mutations and the effects of ooplasmic transplantation on mitochondrial inheritance and mitochondrial functionality. Ageing human oocytes could accumulate mtDNA deletions, which might lead to detrimental development. Elimination of abnormal, rearranged mtDNA, such that the offspring inherit only normal mitochondria, is postulated to occur by a mtDNA 'bottleneck'. Among compromised human oocytes (n = 74) and early embryos (n = 137), investigations have shown the occurrence of deltamtDNA4977, the so-called common deletion, to be 33% among oocytes and 8% among embryos. Using a nested polymerase chain reaction (PCR) strategy of long followed by short PCR, another 23 novel mtDNA rearrangements were found: various rearrangements were present in 51% of the oocytes (n = 295) and 32% of early embryos (n = 197). The difference in the percentage of mtDNA rearrangements between oocytes and embryos was significant (P < 0.0001) and implies that there could be a process of selection as fertilized oocytes become embryos. There was no significant relationship between the percentage of human oocytes or embryos that contained mtDNA rearrangements and age. The first series of ooplasmic transfers have been performed in women with repeated implantation failure associated with slow and morphologically abnormal development of their embryos. In a total of 23 attempts in 21 women, eight healthy babies have been born and other pregnancies are ongoing. By examining the donor and recipient blood samples it is possible to distinguish differences in their mtDNA fingerprint. A small proportion of donor mitochondrial DNA was detected in samples with the following frequencies: embryos (six out of 13), amniocytes (one out of four), placenta (two out of four), and fetal cord blood (two out of four). Ooplasmic transfer can thus result in sustained mtDNA heteroplasmy representing both the donor and recipient.

Birth after the injection of sperm and the cytoplasm of tripronucleate zygotes into metaphase II oocytes in patients with repeated implantation failure after assisted fertilization procedures

OBJECTIVE

To assess the technique of injecting a single sperm and cytoplasm obtained from tripronucleate zygotes into metaphase II oocytes for the treatment of patients with repeated implantation failure after intracytoplasmic sperm injection or IVF.

DESIGN

Clinical study.

SETTING

Private infertility clinic.

PATIENT(S)

Patients with repeated implantation failure after intracytoplasmic sperm injection or IVF.

INTERVENTION(S)

The metaphase II oocytes of recipients were injected with their husbands' spermatozoa and cytoplasm aspirated from the tripronucleate zygotes of donors.

MAIN OUTCOME MEASURE(S)

Fertilization after cytoplasm and sperm injection, embryo development, and successful pregnancy.

RESULT(S)

In total, 62 metaphase II oocytes from nine recipients were injected. Of the 62 injected oocytes, 3 (5%) degenerated and 43 (69%) had two pronuclei 18 hours after injection. Thirty-nine oocytes with two pronuclei cleaved to the two-cell to six-cell stage after another 24 hours of culture. All cleaved embryos were transferred into the uteruses of recipients. Four clinical pregnancies occurred in four recipients. No abnormal chromosomes were observed after amniocentesis and karyotyping in all pregnancies. Five healthy infants were born.

CONCLUSION(S)

Injection of the cytoplasm of tripronucleate zygotes may enhance the clinical pregnancy rate in patients with repeated implantation failure after intracytoplasmic sperm injection or IVF.

Ooplasmic transfer in mature human oocytes

Ooplasmic transplantation aimed at restoring normal growth in developmentally compromised oocytes and embryos was evaluated in seven couples (eight cycles) with multiple implantation failures. Two approaches were investigated to transfer ooplasm from donor eggs at metaphase II (MII) stage into patient MII eggs: (i) electrofusion of a ooplasmic donor fragment into each patient egg (three cycles), and (ii) direct injection of a small amount of ooplasm from a donor egg into each patient egg (five cycles). Some donor eggs were used multiple times. Donor eggs were divided into two groups, one being used for ooplasmic extraction and the other one for egg donation. Cleaved embryos resulting from the latter were cryopreserved, where numbers and satisfactory development permitted. A second control group consisted of embryos derived from patient eggs after intracytoplasmic sperm injection without ooplasmic transfer. This was performed when sufficient number of eggs were available (n = 5). Donor eggs (n = 40) were evaluated cytogenetically after micromanipulation in order to confirm the presence of chromosomes. One egg was anuclear and the recipient embryos were not transferred. Normal fertilization was significantly higher after injection of ooplasm (63%) in comparison with fusion (23%). Pronuclear anomalies appeared enhanced after fusion with ooplasts. Embryo morphology was not improved in the three cycles with electrofusion and patients did not become pregnant. An improvement in embryo morphology was noted in two patients after injection of ooplasm and both became pregnant, but one miscarried. A third pregnancy was established in the repeat patient, without obvious embryo improvement. One baby was born and the third pregnancy is ongoing with a normal karyotype. Two other patients with male factor infertility had poor embryos after ooplasmic injection, but the donor embryo controls were also poor. The patients did not become pregnant and had no donor embryos frozen. Ooplasmic transfer at the MII stage may be promising in patients with compromised embryos; however, evaluation of ooplasmic anomalies and optimization of techniques will require further investigation prior to widescale application.