Fertilizable oocytes reconstructed from patient's somatic cell nuclei and donor ooplasts

Ovarian aging: energy metabolism of oocytes

In women who are getting older, the quantity and quality of their follicles or oocytes and decline. This is characterized by decreased ovarian reserve function (DOR), fewer remaining oocytes, and lower quality oocytes. As more women choose to delay childbirth, the decline in fertility associated with age has become a significant concern for modern women. The decline in oocyte quality is a key indicator of ovarian aging. Many studies suggest that age-related changes in oocyte energy metabolism may impact oocyte quality. Changes in oocyte energy metabolism affect adenosine 5'-triphosphate (ATP) production, but how related products and proteins influence oocyte quality remains largely unknown. This review focuses on oocyte metabolism in age-related ovarian aging and its potential impact on oocyte quality, as well as therapeutic strategies that may partially influence oocyte metabolism. This research aims to enhance our understanding of age-related changes in oocyte energy metabolism, and the identification of biomarkers and treatment methods.

Proteomic Analysis and Reprogramming Potential of the Porcine Intra-Ooplasmic Nanovesicles

Oocytes contain reprogramming machinery that can transform somatic cells into totipotent cells. In this study, we aimed to isolate and characterize nanovesicles from mature porcine oocytes and described them for the first time as "intra-ooplasmic vesicles (IOVs)". Isolated IOVs had an average diameter of 186.3 ± 10.8 nm. Proteomic analysis revealed 467 peptide reads, with the top 20 proteins related to reprogramming, antioxidative defense, cytoskeleton, heat shock proteins, and metabolism. Protein-protein interaction and gene ontology analysis indicated that these proteins were involved in various biological pathways, including protein folding, metabolism, and cellular responses to stress. Supplementing cultured fibroblasts with IOVs resulted in the expression of the pluripotency marker OCT4 and the early trophoblastic marker CDX2 and increased expression of the corresponding mRNAs together with increasing KLF4 and SALL4 expression. IOV treatment of fibroblasts for 14 consecutive days resulted in changes in cell morphology, with increased expression of ZEB2 and YBX3 as markers for epithelial-to-mesenchymal transition (EMT). These results provide a rationale for further characterization of IOVs, investigation of potential reprogramming capabilities for EMT, and the generation of induced pluripotent or oligopotent stem cells.

Mitochondria in Human Fertility and Infertility

In human spermatozoa and oocytes (and their surrounding granulosa cells), mitochondria carry out important functions relating to human fertility and infertility. Sperm mitochondria are not transmitted to the future embryo, but are closely related to the generation of energy needed for sperm movement, capacitation, and acrosome reactions, as well as for sperm-oocyte fusion. On the other hand, oocyte mitochondria produce energy required for oocyte meiotic division and their abnormalities can thus cause oocyte and embryo aneuploidy. In addition, they play a role in oocyte calcium metabolism and in essential epigenetic events during the oocyte-to-embryo transition. They are transmitted to the future embryos and may thus cause hereditary diseases in the offspring. Due to the long life span of the female germ cells, the accumulation of mitochondrial DNA abnormalities often causes ovarian aging. Mitochondrial substitution therapy is the only way of dealing with these issues nowadays. New therapies based on mitochondrial DNA editing are under investigation.

Artificial Oocyte: Development and Potential Application

Millions of people around the world suffer from infertility, with the number of infertile couples and individuals increasing every year. Assisted reproductive technologies (ART) have been widely developed in recent years; however, some patients are unable to benefit from these technologies due to their lack of functional germ cells. Therefore, the development of alternative methods seems necessary. One of these methods is to create artificial oocytes. Oocytes can be generated in vitro from the ovary, fetal gonad, germline stem cells (GSCs), ovarian stem cells, or pluripotent stem cells (PSCs). This approach has raised new hopes in both basic research and medical applications. In this article, we looked at the principle of oocyte development, the landmark studies that enhanced our understanding of the cellular and molecular mechanisms that govern oogenesis in vivo, as well as the mechanisms underlying in vitro generation of functional oocytes from different sources of mouse and human stem cells. In addition, we introduced next-generation ART using somatic cells with artificial oocytes. Finally, we provided an overview of the reproductive application of in vitro oogenesis and its use in human fertility.

Haploidy in somatic cells is induced by mature oocytes in mice

Haploidy is naturally observed in gametes; however, attempts of experimentally inducing haploidy in somatic cells have not been successful. Here, we demonstrate that the replacement of meiotic spindles in mature metaphases II (MII) arrested oocytes with nuclei of somatic cells in the G0/G1 stage of cell cycle results in the formation of de novo spindles consisting of somatic homologous chromosomes comprising of single chromatids. Fertilization of such oocytes with sperm triggers the extrusion of one set of homologous chromosomes into the pseudo-polar body (PPB), resulting in a zygote with haploid somatic and sperm pronuclei (PN). Upon culture, 18% of somatic-sperm zygotes reach the blastocyst stage, and 16% of them possess heterozygous diploid genomes consisting of somatic haploid and sperm homologs across all chromosomes. We also generate embryonic stem cells and live offspring from somatic-sperm embryos. Our finding may offer an alternative strategy for generating oocytes carrying somatic genomes.

Stem Cell Paracrine Signaling for Treatment of Premature Ovarian Insufficiency

Premature ovarian insufficiency is a common disorder affecting young women and represents the worst-case ovarian scenario due to the substantial impact on the reproductive lifespan of these patients. Due to the complexity of this condition, which is not fully understood, non-effective treatments have yet been established for these patients. Different experimental approaches are being explored and strategies based on stem cells deserve special attention. The regenerative and immunomodulatory properties of stem cells have been successfully tested in different tissues, including ovary. Numerous works point out to the efficacy of stem cells in POI treatment, and a wide range of clinical trials have been developed in order to prove safety and effectiveness of stem cells therapy-in diminished ovarian reserve and POI women. The main purpose of this review is to describe the state of the art of the treatment of POI involving stem cells, especially those that use mobilization of stem cells or paracrine signaling.

Stem cells and reproduction

Reproductive biotechnology has developed rapidly and is now able to overcome many birth difficulties due to infertility or the transmission of genetic diseases. Here we introduce the next generation of assisted reproductive technologies (ART), such as mitochondrial replacement technique (MRT) or genetic correction in eggs with micromanipulation. Further, we suggest that the transmission of genetic information from somatic cells to subsequent generations without gametes should be useful for people who suffer from infertility or genetic diseases. Pluripotent stem cells (PSCs) can be converted into germ cells such as sperm or oocytes in the laboratory. Notably, germ cells derived from nuclear transfer embryonic stem cells (NT-ESCs) or induced pluripotent stem cells (iPSCs) inherit the full parental genome. The most important issue in this technique is the generation of a haploid chromosome from diploid somatic cells. We hereby examine current science and limitations underpinning these important developments and provide recommendations for moving forward.

Advances in improving fertility in women through stem cell-based clinical platforms

INTRODUCTION

Due to their regenerative ability, stem cells are looked at as a promising tool for improving infertility treatments in women. As the main limiting factor in female fertility is represented by the decrease of ovarian reserve, the main goals of stem cell-based clinical platforms would be to obtain in vitro or in vivo neo-oogenesis. Refractory endometrial factor infertility also represents an obstacle for female reproduction for which stem cells might provide novel treatment strategies. Areas covered: A systematic search of the literature was performed on MEDLINE/PubMed database to identify relevant articles using stem-cell based clinical or research platforms in the field of female infertility. Expert opinion: In vitro oogenesis has not so far developed beyond the stage of oocyte-like cells whose normal progression to mature oocytes and ability to be fertilized was not proved. Extensive epigenetic programming of gamete precursors and the complex interactions between somatic and germ cells required for human oogenesis likely represent the main obstacles in stem-cell-based neo-oogenesis. Also resuming oogenesis in vivo in adulthood still appears a distant hypothesis, as there is still a lack of consensus about the existence and functionality of adult ovarian stem cells.

Blastocysts derivation from somatic cell fusion with premature oocytes (prematuration somatic cell fusion)

This study was undertaken to investigate the development of immature oocytes after their fusion with male somatic cells expressing red fluorescence protein (RFP). RFP-expressing cells were fused with immature oocytes, matured in vitro and then parthenogenetically activated. Somatic nuclei showed spindle formation, 1st polar body extrusion after in vitro maturation and protruded the 2nd polar body after parthenogenetic activation. RFP was expressed in the resultant embryos; two-cell stage and blastocysts. Chromosomal analysis showed aneuploidy in 81.82% of the resulting blastocysts while 18.18% of the resulting blastocysts were diploid. Among eight RFP-expressing blastocysts, Xist mRNAs was detected in six while Sry mRNA was detected in only one blastocyst. We propose "prematuration somatic cell fusion" as an approach to generate embryos using somatic cells instead of spermatozoa. The current approach, if improved, would assist production of embryos for couples where the male partner is sterile, however, genetic and chromosomal analysis of the resultant embryos are required before transfer to the mothers.

Interventions in the prolongation of reproductive life in women

Women may seek to prolong their reproductive span for a variety of reasons. For many this implies reproduction at a late age, possibly driven by lifestyle decisions, but for others affected by a natural or a cancer treatment-induced premature ovarian failure it may simply mean seeking to achieve the normal reproductive span. The range of interventions now available to address the issue of prolonging reproductive life has never been greater, although several of the approaches discussed remain in the realm of future application through being dependent on ongoing scientific developments.

In vitro development of non-enucleated rat oocytes following microinjection of a cumulus nucleus and chemical activation

The present study examined in vitro development and the cytological status of non-enucleated rat oocytes after microinjection of cumulus nuclei and chemical activation. Oocyte–cumulus complexes were collected from gonadotropin-treated prepubertal female Wistar rats 14 h after human chorionic gonadotropin (hCG) injection. Cumulus nuclei were injected into ovulated oocytes and then stimulated in the presence of 5 mM SrCl2 for 20 min at various time points (0–3.5 h) after injection. Some of the reconstituted eggs were cultured to observe the pronuclear formation, cleavage, and blastocyst formation. The incidences of eggs forming at least one pronucleus or containing two pronuclei were not significantly different among the periods (82.4–83.5% and 43.4–51.9%, respectively). Nor did the incidences of eggs cleaving (86.7–97.7%) and developing to the blastocyst stage (0–3.5%) differ depending on when, after injection, stimulation began. When some of the reconstituted eggs were observed for cytological morphology 1–1.5 h after injection, 71.7% of the eggs caused premature chromatin condensation, but only 46.2% of them formed two spindles around each of maternal and somatic chromatins. However, the morphology of the somatic spindles differed from that of the spindles, which formed around the oocyte chromatins. Only 7.5% of the eggs contained the normal chromosomal number. In many reconstituted oocytes, before activation, an abnormal spindle formation was observed in the somatic chromatins. In conclusion, these results show that non-enucleated rat oocytes injected with cumulus nuclei can form pronuclei and cleave following chemical activation, whereas blastocyst formation is very limited, probably caused by abnormalities in the spindle formation and distribution of somatic chromatids.

Artificial gametes

In vitro fertilization (IVF) has been an efficient medical treatment for infertility in the past decades. However, conventional IVF approaches may be insufficient when gametes are lacking or non-viable thus precluding a significant number of patients from treatment. Ultimately, creation of artificial gametes may provide an universal solution for all indications. Somatic cell nuclear transfer (SCNT) has provided successful cloning in different animal species indicating that a derived technology may be applicable in infertility treatment procedures. Attempts to produce functional male or female gamete through nuclear transfer have been described through the process called haploidization. Initial successes have been observed, however, significant alterations at spindle construction and chromosomal segregation were also described. Stem cell technology may provide an alternative route to obtain fully functional gametes. Both sperm cells and oocytes were obtained using specific culture conditions for embryo originated stem cell. These two mainstream approaches are presented in the current review. Both of these techniques are involving sophisticated methods and consequently both of them demonstrate technical and ethical challenges. Related questions on (mitotic/meiotic) cell division, genetic/epigenetic alterations and cell renewal are needed to be addressed before clinical application.

Genetics, epigenetics and gene silencing in differentiating mammalian embryos

A highly complex pattern of differentiation involving maternal and embryonic factors characterizes the early development of mammalian embryos. These complex genetic and proteonomic patterns of early growth also involve various forms of gene silencing and tissue reprogramming. Understanding the nature of fundamental developmental events is hence essential to appreciate the significance of natural and induced forms of remodelling, damaged forms of gene expression and gene silencing during the initial stages of growth. Natural forms of remodelling include subtle genetic events involved in, for example, the changing nature of imprinting from before fertilization or the inactivation of one X chromosome in female blastocysts. Induced forms include the consequences of nuclear transfer and embryo cloning or the immediate effects of placing embryos in culture media. Animal and human studies are described in this paper, relating reprogramming to detailed embryological and clinical knowledge gained through the use of IVF, preimplantation genetic diagnosis and the establishment in vitro of stem cells. Attention concentrates on the consequences of variations in all growth stages from the formation of oocytes, through fertilization, the differentiation of blastocysts and early haemopoietic stages in mammalian species. Unique features of gene expression or gene modification are described for each developmental stage.

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.

Derivation of a human blastocyst after heterologous nuclear transfer to donated oocytes

This paper describes the derivation of a blastocyst following heterologous nuclear transfer (NT) into a human oocyte. It also demonstrates that a major obstacle to continuing research in human NT is the availability of suitable human oocytes. In this study, 36 oocytes were donated by 11 women undergoing four different treatments and their developmental potential was evaluated after NT. The time from oocyte collection to NT seems to be crucial, and only oocytes that were enucleated within 1 h proved successful. After enucleation of oocytes, fusion with undifferentiated human embryonic stem cells and in-vitro culture, early cleavage and blastocyst development of fused complexes was observed. The DNA fingerprinting comparison of the donor cells and derived blastocyst revealed successful heterologous NT, since both oocytes and donor cells were recovered from different patients. It has therefore been demonstrated that NT can be achieved in humans, using heterologous donor nuclei and surplus and donated oocytes. However, if the promise of this new science is to achieve its potential in the foreseeable future, it will be necessary to identify new sources of oocytes that can be used immediately after retrieval.

Current advances in artificial gametes

The birth of Louise Brown, the first IVF baby, in 1978 marked a breakthrough in infertility treatment. In recent decades, several important new techniques have been introduced. One limiting factor has been the requirement to use reproductive cells (gametes) for fertilization and for embryonic development. Somatic cell nuclear transfer (cloning) has been successful in mammals, opening a potential new approach for the treatment of human infertility. In addition, nuclear transfer to achieve embryo development starting from somatic cells instead of gametes, and the creation of artificial oocytes/spermatozoa has been attempted. The present paper reviews the various alternative approaches to haploidization of somatic cells. It has been observed that chromosome segregation (of the donor somatic nucleus) may take place; however, this process is largely random, thus leading to major cytogenetic abnormalities. An alternative approach is related to stem cell technology, to be further explored in the future. Culture conditions may be adjusted so that the totipotent embryonic stem cells will differentiate to specific gametes, sperm cells or egg cells. Injecting spermatozoa produced in this manner into recipient oocytes has led to pronuclear formation and early cleavage stages in some embryos. Finally, the birth of parthenogenetic mice indicates that some of these epigenetic problems can be overcome, and that some of the embryos may survive to birth.

Cytogenetic analysis of human somatic cell haploidization

Despite recent interest in the derivation of female and male gametes through somatic cell nuclear transfer, there is still insufficient data on chromosomal analysis of these gametes resulting from haploidization, especially involving a human nuclear donor and recipient oocytes. The objective of this study was to investigate the fidelity of chromosomal separation during haploidization of human cumulus cells by in-vitro matured human enucleated MII oocytes. A total of 129 oocytes were tested 4-7, 8-14, or 15-21 h after nuclear transfer (NT) followed by electro-stimulation, resulting in 71.3% activation efficiency on average. Haploidization was documented by the formation of two separate groups of chromosomes, originating from either polar body/pronucleus (PB/PN), or only 2PN, which were tested by 5-colour FISH, or DNA analysis for copy number of chromosomes 13, 16, 18, 21, 22 and X. Two PN were formed more frequently than PB/PN, irrespective of incubation time. In agreement with recent reports on mouse oocytes, as many as 90.2% of the resulting haploid sets tested showed abnormal chromosome segregation, suggesting unsuitability of the resulting artificial gametes for practical application at the present time.

Epigenetic reprogramming in early embryonic development: effects of in-vitro production and somatic nuclear transfer

A considerable proportion of offspring, in particular in ruminants and mice, born from nuclear transfer (NT)-derived and in-vitro-produced (IVP) embryos is affected by multiple abnormalities of which a high birthweight and an extended gestation length are the predominant features; a phenomenon that has been called 'large offspring syndrome' (LOS). The underlying mechanisms are largely unknown at present, but alterations of epigenetic modifications of embryonic and fetal gene expression patterns, primarily caused by alterations in DNA methylation are thought to be involved in this syndrome. In mammals, DNA methylation is essential for the regulation of transcription during development and differentiation. This review summarizes results from studies in which mRNA expression patterns from IVP and NT-derived embryos were compared with those of their in-vivo counterparts. Numerous aberrations have been found ranging from suppression of expression to de-novo overexpression or more frequently to a significant up- or down-regulation of a specific gene. These observations emphasize the need for further epigenetic studies during preimplantation embryo development to gain insight into the molecular regulation correlated with an undisturbed embryonic and fetal development. Understanding molecular mechanisms will aid improvements in biotechnologies applied to early embryos in all species, including humans.

Nuclear and Microtubule Dynamics of G2/M Somatic Nuclei During Haploidization in Germinal Vesicle-Stage Mouse Oocytes

During the haploidization process, it is expected that diploid chromosomes of somatic cells will be reduced to haploid for the generation of artificial gametes. In the present study, we aimed to use enucleated mouse oocytes at the germinal vesicle-stage (G2/M) as recipients for somatic cells that are also synchronized to the G2/M stage for haploidization. The reconstructed oocytes were then induced to undergo meiosis in vitro and observed for their nuclear morphology and microtubule network formation at various expected stages of the meiotic division. Following in vitro maturation, more than half (62/119, 52.1%) of the reconstructed oocytes completed the first round of meiosis-like division, as evidenced by the extrusion of pseudopolar bodies (PBs). However, accelerated PB extrusion, approximately 3-4 h earlier than that by control oocytes occurred. Furthermore, abnormally large pseudo-PBs, as large as four times the normal PB sizes, were observed. During the process of in vitro maturation at both the expected stages of metaphase I (MI) and metaphase II (MII), condensed chromosomes were observed in 38.7% and 55.2% of oocytes, respectively. However, two other types of nuclear configurations were also observed: 1) uneven distribution of chromatin and 2) an interphase-like nucleus, indicating deficiencies in chromosome condensation. Following oocyte activation, more than half (21/33, 63.6%) of the reconstructed oocytes with pseudo-PBs formed separated pseudopronuclei (PN), suggesting formation of functional spindles. The formation of bipolar spindle-like microtubule network at both the expected MI and MII stages during in vitro maturation was confirmed by immunohistochemistry. In summary, this study demonstrated that a high proportion of G2/M somatic nuclei appear to undergo meiosis-like division, in two successive steps, forming a pseudo-PB and two separate pseudo-PN upon in vitro maturation and activation treatment. Moreover, the enucleated geminal vesicle cytoplast retained its capacity for meiotic division following the introduction of a somatic G2/M nucleus.

Reprogramming of epigenetic inheritance by somatic cell nuclear transfer

Somatic cloning by nuclear transfer returns a differentiated cell to a totipotent stage, a process termed nuclear reprogramming. During this de-differentiation process, genes inactivated during tissue differentiation are re-activated in a temporal and spatial special manner. It is believed that tissue differentiation occurs through epigenetic mechanisms, genetic inheritance that does not involve changes in DNA sequences. Developmental abnormalities and a high mortality rate in cloned offspring have frequently been observed and probably result from incomplete nuclear reprogramming. In this review, the reprogramming of two epigenetic mechanisms, imprinting and X chromosome inactivation, as well as recent attempts to modify pre-existing epigenetic marks in donor cells to improve nuclear transfer efficacy, are discussed.

Averting abnormal inheritance: potential of gene therapy and preimplantation diagnosis

Serious inherited disease in children can be averted by preimplantation genetic diagnosis (PGD) and potentially by gene therapy in addition to prenatal diagnosis. PGD is now well established and provides a secure, if expensive and complex form of care. Gene therapy has been practised only in animals, although its success in alleviating various conditions in adults and newborns, together with the scientific drive of the genome project, make it a highly likely approach over coming years. Pros and cons of both approaches are contrasted and compared. Newer reproductive techniques such as somatic cell hybridization promise to add new dimensions to gene therapy, and could be combined with PGD. This paper discusses the finer details of these options, their safety and the ethical issues they have raised.

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.

Microfilament disruption is required for enucleation and nuclear transfer in germinal vesicle but not metaphase II human oocytes

OBJECTIVE

To evaluate the usefulness of microfilament disruption before enucleation and nuclear transfer in human oocytes at different stages of maturation.

DESIGN

Prospective experimental study.

SETTING

Private clinics.

PATIENT(S)

Infertile couples undergoing assisted reproduction attempts.

INTERVENTION(S)

Oocyte enucleation and nuclear transfer, activation of reconstructed oocytes.

MAIN OUTCOME MEASURE(S)

Oocyte survival, nuclear transfer efficacy, activation outcomes.

RESULT(S)

Survival rate and nuclear transfer efficacy of germinal vesicle oocytes exposed to the microfilament disrupting agent cytochalasin B before enucleation were 88% and 80%, respectively. These figures dropped, respectively, to 8% and 2% when cytochalasin treatment was omitted. By contrast, cytochalasin-treated and -untreated metaphase II oocytes showed similar survival rate (87% vs. 90%) and nuclear transfer efficacy (78% vs. 87%). This also applied to metaphase II oocytes matured in vitro from the germinal vesicle stage. Cytochalasin treatment did not affect activation rate of reconstructed oocytes, but it increased the occurrence of oocytes with multiple female pronuclei.

CONCLUSION(S)

Microfilament disruption before enucleation is required for germinal vesicle oocytes but not for metaphase II oocytes.

Definitions of human fertilization and preimplantation growth revisited

Assisted reproductive techniques and the science of embryology have advanced rapidly over the last decades. The fact that social and moral objectives vary from country to country has resulted in differences not only in legislation, but also in the definition of embryological terms. Among the latest additions to the field has been nuclear transfer technology, which has led to concerns about the possibilities of human cloning. These facts call for a review of gametogenesis and early embryogenesis. The aim of the present paper is to initiate a discussion on terminology with a view to reaching a consensus. As a starting point definitions are proposed for the most important terms.

Fertilization of mouse oocytes using somatic cells as male germ cells

Female and male mouse somatic cells were injected into mouse F(1) oocytes. The cells used included cumulus cells (female) and muscle derived fibroblasts (male). The ability of the cells to fertilize oocytes and support embryonic development was examined. Following activation of the injected oocytes, two second polar bodies were extruded and two pronuclei were formed, one derived from the oocyte chromosomes and the other from the somatic cell chromosomes in a similar way to that observed following fertilization with secondary spermatocytes. Both second polar bodies contained DNA. The fertilization rates by cumulus cells were 10-29%. This was dependent on the artificial activation protocol and on the age of the oocytes. Older oocytes recovered 16-17 h after human chorionic gonadotrophin (HCG) injection were more likely to produce two second polar bodies and two pronuclei than young oocytes which were retrieved at 13-14 h after HCG injection (P < 0.01). The fertilization rates with fibroblasts were 29% using the most effective activation regime and aged oocytes. Most (80-90%) of the 'zygotes' produced by somatic cells cleaved to two cells in culture and ~50% reached the morula stage. However, the developmental competence of the embryos to reach blastocysts was limited. The present study demonstrates that mouse somatic cells undergo haploidization when injected into metaphase II oocytes, fertilize oocytes as diploid male germ cells and support preimplantation development to a degree.

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.

Somatic cell haploidization: an update

Oocyte donation is the only method of treating female sterility caused by complete absence of oocytes, with the loss of genetic motherhood. Genetic fatherhood of males with complete absence of spermatozoa can only be restored by assisted reproduction treatment if sperm precursor cells belonging to the male germline can still be recovered from the testis. Otherwise, sperm donation is the only available solution. Somatic nucleus haploidization after injection into previously enucleated donor oocytes (diploid-to-haploid reduction) might enable the reconstruction of new oocytes carrying the complete nuclear genome of female patients lacking their own oocytes. Such newly formed oocytes could subsequently be fertilized by spermatozoa from the patient's husband. In cases of male infertility with complete absence of the germline, the patient's somatic cell nuclei could be injected into the oocytes without previous enucleation, and somatic nucleus haploidization would occur in the presence of the original female nucleus (triploid-to-diploid reduction), hopefully leading to the formation of a diploid embryo. Both interventions differ substantially from cloning because embryos are formed by syngamy with the male and female genomes originating from the two genetic parents, as in natural fertilization. Ultrastructural remodelling of mouse somatic cell nucleoli can be achieved in enucleated metaphase II mouse oocytes. Haploidization has also been attempted with Sertoli cells and with fibroblasts, both of which are also available in male patients. Experiments are currently under way to assess the regularity of chromatid segregation during somatic nucleus haploidization.

Current features of preimplantation genetic diagnosis

More than 4000 preimplantation genetic diagnosis (PGD) cycles have been performed, suggesting that PGD may no longer be considered a research activity. The important present feature of PGD is its expansion to a variety of conditions, which have never been considered as an indication for prenatal diagnosis, including the late-onset disorders with genetic predisposition and preimplantation non-disease testing, with the further improvement of the accuracy of PGD for single gene disorders. PGD has also become a useful tool for the improvement of the effectiveness of IVF, through avoiding the transfer of chromosomally abnormal embryos, representing more than half of the embryos routinely transferred in IVF patients of advanced maternal age and other poor prognosis patients. PGD is of particular hope for the carriers of balanced chromosomal translocations, as it allows accurate pre-selection of a few balanced or normal embryos resulting from the extremely poor meiotic outcome, especially in reciprocal translocations. With the current progress in polymerase chain reaction- (PCR-) based detection of chromosomal abnormalities in oocytes and embryos, PGD may soon be performed for both chromosomal and single gene disorders using the same biopsied polar body or blastomere, frequently required with the currently expanded PGD application. The available clinical outcome data of more than 3000 PGD embryo transfers further suggest an acceptable pregnancy rate and safety of the procedure, as demonstrated by the follow-up information available for more than 500 children born from these PGD transfers.

Fundamentals of human embryonic growth in vitro and the selection of high-quality embryos for transfer

Knowledge of the nature of embryo growth, and the handling and scoring of quality in human embryos are significant aspects for embryologists in IVF clinics. This review describes the formation, growth and maturation of human oocytes, many aspects of fertilization in vitro, embryonic transcription during preimplantation stages, and the formation of polarities, timing controls, role of mitochondria and functions of endocrine and paracrine systems. Modern concepts are fully discussed, together with their significance in the practice of IVF. This knowledge is essential for the correct clinical care of human embryos growing in vitro, especially in view of their uncharacteristic tendency to vary widely in implantation potential. Underlying causes of such variation have not been identified. Stringent tests must be enforced to ensure human embryos develop under optimal conditions, and are scored for quality using the most advanced techniques. Optimal methods of culture are described, including methods such as co-culture introduced to improve embryo quality but less important today. Detailed attention is given to quality as assessed from embryonic characteristics determined by timers, polarities, disturbed embryo growth and anomalous cell cycles. Methods for classification are described. Approaches to single embryo transfers are described, including the use of sequential media to produce high-quality blastocysts. These approaches, and others involved in surgical methods to remove fragments, transfer ooplasm or utilize newer approaches such as preimplantation diagnosis of chromosomal complements in embryos are covered. New outlooks in this field are summarized.

Predictive value of testicular histology in secretory azoospermic subgroups and clinical outcome after microinjection of fresh and frozen-thawed sperm and spermatids

BACKGROUND

A retrospective study was carried out on 159 treatment cycles in 148 secretory azoospermic patients to determine whether histopathological secretory azoospermic subgroups were predictive for gamete retrieval, and to evaluate outcome of microinjection using fresh or frozen-thawed testicular sperm and spermatids.

METHODS

Sperm and spermatids were recovered by open testicular biopsy and microinjected into oocytes. Fertilization and pregnancy rates were assessed.

RESULTS

In hypoplasia, 97.7% of the 44 patients had late spermatids/sperm recovered. In maturation-arrest (MA; 47 patients), 31.9% had complete MA, and 68.1% incomplete MA due to a focus of early (36.2%) or late (31.9%) spermiogenesis. Gamete retrieval was achieved in 53.3, 41.2 and 93.3% of the cases respectively. In Sertoli cell-only syndrome (SCOS; 57 patients), 61.4% were complete SCOS, whereas incomplete SCOS cases showed one focus of MA (5.3%), or of early (29.8%) and late (3.5%) spermiogenesis. Only 29.8% of the patients had a successful gamete retrieval, 2.9% in complete and 77.3% in incomplete SCOS cases. In total, there were 87 ICSI, 39 elongated spermatid injection (ELSI) and 33 round spermatid injection (ROSI) treatment cycles, with mean values of fertilization rate of 71.4, 53.6 and 17%, and clinical pregnancy rates of 31.7, 26.3 and 0% respectively.

CONCLUSIONS

Histopathological subgroups were positively correlated with successful gamete retrieval. No major outcome differences were observed between testicular sperm and elongated spermatids, either fresh or frozen-thawed. However, injection of intact round-spermatids showed very low rates of fertilization and no pregnancies.

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.