Minireview: Parthenogenesis in mammals

Queering the genome: ethical challenges of epigenome editing in same-sex reproduction

In this article, I explore the ethical dimensions of same-sex reproduction achieved through epigenome editing-an innovative and transformative technique. For the first time, I analyse the potential normativity of this disruptive approach for reproductive purposes, focusing on its implications for lesbian couples seeking genetically related offspring. Epigenome editing offers a compelling solution to the complex ethical challenges posed by traditional gene editing, as it sidesteps genome modifications and potential long-term genetic consequences. The focus of this article is to systematically analyse the bioethical issues related to the use of epigenome editing for same-sex reproduction. I critically assess the ethical acceptability of epigenome editing with reproductive purposes from multiple angles, considering harm perspectives, the comparison of ethical issues related to gene and epigenome editing, and feminist theories. This analysis reveals that epigenome editing emerges as an ethically acceptable means for lesbian couples to have genetically related children. Moreover, the experiments of a reproductive use of epigenome editing discussed in this article transcend bioethics, shedding light on the broader societal implications of same-sex reproduction. It challenges established notions of biological reproduction and prompts a reevaluation of how we define the human embryo, while poses some issues in the context of gender self-identification and family structures. In a world that increasingly values inclusivity and diversity, this article aims to reveal a progressive pathway for reproductive medicine and bioethics, as well as underscores the need for further philosophical research in this emerging and fertile domain.

Induction of Somatic Embryogenesis in Plants: Different Players and Focus on WUSCHEL and WUS-RELATED HOMEOBOX (WOX) Transcription Factors

In plants, other cells can express totipotency in addition to the zygote, thus resulting in embryo differentiation; this appears evident in apomictic and epiphyllous plants. According to Haberlandt's theory, all plant cells can regenerate a complete plant if the nucleus and the membrane system are intact. In fact, under in vitro conditions, ectopic embryos and adventitious shoots can develop from many organs of the mature plant body. We are beginning to understand how determination processes are regulated and how cell specialization occurs. However, we still need to unravel the mechanisms whereby a cell interprets its position, decides its fate, and communicates it to others. The induction of somatic embryogenesis might be based on a plant growth regulator signal (auxin) to determine an appropriate cellular environment and other factors, including stress and ectopic expression of embryo or meristem identity transcription factors (TFs). Still, we are far from having a complete view of the regulatory genes, their target genes, and their action hierarchy. As in animals, epigenetic reprogramming also plays an essential role in re-establishing the competence of differentiated cells to undergo somatic embryogenesis. Herein, we describe the functions of WUSCHEL-RELATED HOMEOBOX (WOX) transcription factors in regulating the differentiation-dedifferentiation cell process and in the developmental phase of in vitro regenerated adventitious structures.

Mesenchymal Stem Cell-Conditioned Medium Modulates Apoptotic and Stress-Related Gene Expression, Ameliorates Maturation and Allows for the Development of Immature Human Oocytes after Artificial Activation

The aim of the present study was to determine whether mesenchymal stem cell-conditioned medium (MSC-CM) modulates apoptotic and stress-related gene expression, and ameliorates maturation and developmental potential of immature human oocytes after artificial activation. A total of 247 surplus immature germinal vesicle (GV) oocytes obtained from infertile women were allocated into two in vitro maturation (IVM) groups: 1: GV oocytes (n = 116) matured in vitro (fIVM), and 2: GV oocytes (n = 131) that were vitrified, then in vitro matured (vIVM). Also, two maturation media were used: Alpha-minimum essential medium (α-MEM) and human umbilical cord-derived MSCs (hUCM). After 36 h of incubation, the IVM oocytes were examined for nuclear maturation. In IVM-matured oocytes, cytoplasmic maturation was evaluated after artificial activation through Ionomycin. Moreover, the quantitative expressions of B-cell CLL/lymphoma 2 (BCL2), BCL2-associated X protein (BAX), superoxide dismutase (SOD), and Heat shock proteins (HSP70) in matured oocytes were assessed by quantitative Real-time polymerase chain reaction (qRT-PCR) and compared with fresh and vitrified in vivo matured oocytes, which were used as fIVM and vIVM controls, respectively. The highest maturation rate was found in hUCM in fIVM, and the lowest maturation rate was found using α-MEM in vIVM (85.18% and 71.42%, respectively). The cleavage rate in fIVM was higher than that in vIVM (83.4% vs. 72.0%). In addition, the cleavage rate in α-MEM was lower than that in the hUCM (66.0% vs. 89.4%). Furthermore, the difference between parthenote embryo arrested in 4-8 cells (p < 0.04) and the quality of embryo arrested in 8-cell (p < 0.007) were significant. The developmental stages of parthenote embryos in hUCM versus α-MEM were as follows: 2-4 cell (89.45% vs. 66.00%, respectively), 4-8 cell (44.31% vs. 29.11%, respectively), morula (12.27% vs. 2.63%, respectively), and blastocysts (2.5% vs. 0%, respectively). The messenger RNA (mRNA) expression levels of BCL2, BAX and SOD were significantly different (p < 0.05) between the matured IVM oocytes. Overall, hUCM showed potential efficacy in terms of ameliorating oocyte maturation and in promoting the development and mRNA expression of BAX, BCL2, and SOD.

Androgenesis: where males hijack eggs to clone themselves

Androgenesis is a form of quasi-sexual reproduction in which a male is the sole source of the nuclear genetic material in the embryo. Two types of androgenesis occur in nature. Under the first type, females produce eggs without a nucleus and the embryo develops from the male gamete following fertilization. Evolution of this type of androgenesis is poorly understood as the parent responsible for androgenesis (the mother) gains no benefit from it. Ultimate factors driving the evolution of the second type of androgenesis are better understood. In this case, a zygote is formed between a male and a female gamete, but the female genome is eliminated. When rare, androgenesis with genome elimination is favoured because an androgenesis-determining allele has twice the reproductive success of an allele that determines sexual reproduction. Paradoxically, except in hermaphrodites, a successful androgenetic strain can drive such a male-biased sex ratio that the population goes extinct. This likely explains why androgenesis with genome elimination appears to be rarer than androgenesis via non-nucleate eggs, although both forms are either very rare or remain largely undetected in nature. Nonetheless, some highly invasive species including ants and freshwater clams are androgenetic, for reasons that are largely unexplained.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.

Non-invasive assessment of porcine oocyte quality by supravital staining of cumulus-oocyte complexes with lissamine green B

We evaluated the usefulness of lissamine green B (LB) staining of cumulus-oocyte complexes (COC) as a non-invasive method of predicting maturational and developmental competence of slaughterhouse-derived porcine oocytes cultured in vitro. Cumulus cells of freshly aspirated COCs were evaluated either morphologically on the basis of thickness of cumulus cell layers, or stained with LB, which penetrates only non-viable cells. The extent of cumulus cell staining was taken as an inverse indicator of membrane integrity. The two methods of COC grading were then examined as predictors of nuclear maturation and development after parthenogenetic activation. In both cases LB staining proved a more reliable indicator than morphological assessment (P < 0.05). The relationship between LB staining and cumulus cell apoptosis was also examined. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for DNA fragmentation revealed that oocytes within COCs graded as low quality by either LB staining or visual morphology showed significantly greater DNA fragmentation (P < 0.05) than higher grades, and that LB and visual grading were of similar predictive value. Expression of the stress response gene TP53 showed significantly higher expression in COCs graded as low quality by LB staining. However expression of the apoptosis-associated genes BAK and CASP3 was not significantly different between high or low grade COCs, suggesting that mRNA expression of BAK and CASP3 is not a reliable method of detecting apoptosis in porcine COCs. Evaluation of cumulus cell membrane integrity by lissamine green B staining thus provides a useful new tool to gain information about the maturational and developmental competence of porcine oocytes.

Mitochondria, the Cell Cycle, and the Origin of Sex via a Syncytial Eukaryote Common Ancestor

Theories for the origin of sex traditionally start with an asexual mitosing cell and add recombination, thereby deriving meiosis from mitosis. Though sex was clearly present in the eukaryote common ancestor, the order of events linking the origin of sex and the origin of mitosis is unknown. Here, we present an evolutionary inference for the origin of sex starting with a bacterial ancestor of mitochondria in the cytosol of its archaeal host. We posit that symbiotic association led to the origin of mitochondria and gene transfer to host's genome, generating a nucleus and a dedicated translational compartment, the eukaryotic cytosol, in which-by virtue of mitochondria-metabolic energy was not limiting. Spontaneous protein aggregation (monomer polymerization) and Adenosine Tri-phosphate (ATP)-dependent macromolecular movement in the cytosol thereby became selectable, giving rise to continuous microtubule-dependent chromosome separation (reduction division). We propose that eukaryotic chromosome division arose in a filamentous, syncytial, multinucleated ancestor, in which nuclei with insufficient chromosome numbers could complement each other through mRNA in the cytosol and generate new chromosome combinations through karyogamy. A syncytial (or coenocytic, a synonym) eukaryote ancestor, or Coeca, would account for the observation that the process of eukaryotic chromosome separation is more conserved than the process of eukaryotic cell division. The first progeny of such a syncytial ancestor were likely equivalent to meiospores, released into the environment by the host's vesicle secretion machinery. The natural ability of archaea (the host) to fuse and recombine brought forth reciprocal recombination among fusing (syngamy and karyogamy) progeny-sex-in an ancestrally meiotic cell cycle, from which the simpler haploid and diploid mitotic cell cycles arose. The origin of eukaryotes was the origin of vertical lineage inheritance, and sex was required to keep vertically evolving lineages viable by rescuing the incipient eukaryotic lineage from Muller's ratchet. The origin of mitochondria was, in this view, the decisive incident that precipitated symbiosis-specific cell biological problems, the solutions to which were the salient features that distinguish eukaryotes from prokaryotes: A nuclear membrane, energetically affordable ATP-dependent protein-protein interactions in the cytosol, and a cell cycle involving reduction division and reciprocal recombination (sex).

Parent-of-origin effects on genome-wide DNA methylation in the Cape honey bee (Apis mellifera capensis) may be confounded by allele-specific methylation

BACKGROUND

Intersexual genomic conflict sometimes leads to unequal expression of paternal and maternal alleles in offspring, resulting in parent-of-origin effects. In honey bees reciprocal crosses can show strong parent-of-origin effects, supporting theoretical predictions that genomic imprinting occurs in this species. Mechanisms behind imprinting in honey bees are unclear but differential DNA methylation in eggs and sperm suggests that DNA methylation could be involved. Nonetheless, because DNA methylation is multifunctional, it is difficult to separate imprinting from other roles of methylation. Here we use a novel approach to investigate parent-of-origin DNA methylation in honey bees. In the subspecies Apis mellifera capensis, reproduction of females occurs either sexually by fertilization of eggs with sperm, or via thelytokous parthenogenesis, producing female embryos derived from two maternal genomes.

RESULTS

We compared genome-wide methylation patterns of sexually-produced, diploid embryos laid by a queen, with parthenogenetically-produced diploid embryos laid by her daughters. Thelytokous embryos inheriting two maternal genomes had fewer hypermethylated genes compared to fertilized embryos, supporting the prediction that fertilized embryos have increased methylation due to inheritance of a paternal genome. However, bisulfite PCR and sequencing of a differentially methylated gene, Stan (GB18207) showed strong allele-specific methylation that was maintained in both fertilized and thelytokous embryos. For this gene, methylation was associated with haplotype, not parent of origin.

CONCLUSIONS

The results of our study are consistent with predictions from the kin theory of genomic imprinting. However, our demonstration of allele-specific methylation based on sequence shows that genome-wide differential methylation studies can potentially confound imprinting and allele-specific methylation. It further suggests that methylation patterns are heritable or that specific sequence motifs are targets for methylation in some genes.

Three-day-old human unfertilized oocytes after in vitro fertilization/intracytoplasmic sperm injection can be activated by calcium ionophore a23187 or strontium chloride and develop to blastocysts

Our objective was to observe the effectiveness of the calcium ionophore A23187 or strontium chloride on the activation and subsequent embryonic development of 3-day-old human unfertilized oocytes after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). A total of 279 3-day-old unfertilized oocytes after IVF or ICSI were randomized to be activated by the calcium ionophore A23187 (n=138) or strontium chloride (n=141). The activated oocytes were cultured in vitro for 3-5 days. Activation rate, pronucleus formation, cleavage rate, and developmental potential of parthenotes during culture were evaluated. A total of 170 unfertilized oocytes were activated; 65 developed to cleavage stage, 19 developed to greater than the eight-cell stage, and five blastocysts were obtained. The activation rate of the calcium ionophore A23187 group was higher than that of the strontium chloride group (75.4% and 46.8%, respectively; p<0.05); there was significant difference between two groups (p<0.05). Among the 44 cleaved oocytes in the calcium ionophore A23187 group, eight developed to the two- to four-cell stage, 17 developed to the five- to eight-cell stage, 15 developed to greater than the eight-cell stage, and four blastocysts were obtained. Among the 21 cleaved oocytes in the strontium chloride group, six developed to the two- to four- cell stage, 10 developed to the five- to eight-cell stage, four developed to greater than the eight-cell stage, and one blastocyst was obtained. Three-day-old unfertilized human oocytes after IVF or ICSI could be activated by the calcium ionophore A23187 or strontium chloride, and a small part of parthenogenetic embryos developed into blastocysts. The treatment with the calcium ionophore A23187 was better than that of strontium chloride in respect to the activation rate of 3-day-old unfertilized human oocytes after IVF or ICSI.

The chromosomal constitution of embryos arising from monopronuclear oocytes in programmes of assisted reproduction

The assessment of oocytes showing only one pronucleus during assisted reproduction is associated with uncertainty. A compilation of data on the genetic constitution of different developmental stages shows that affected oocytes are able to develop into haploid, diploid, and mosaic embryos with more or less complex chromosomal compositions. In the majority of cases (~80%), haploidy appears to be caused by gynogenesis, whereas parthenogenesis or androgenesis is less common. Most of the diploid embryos result from a fertilization event involving asynchronous formation of the two pronuclei or pronuclear fusion at a very early stage. Uniparental diploidy may sometimes occur if one pronucleus fails to develop and the other pronucleus already contains a diploid genome or alternatively a haploid genome undergoes endoreduplication. In general, the chance of obtaining a biparental diploid embryo appears higher after conventional in vitro fertilization than after intracytoplasmic sperm injection. If a transfer of embryos obtained from monopronuclear oocytes is envisaged, it should be tried to culture them up to the blastocyst since most haploid embryos are not able to reach this stage. Comprehensive counselling of patients on potential risks is advisable before transfer and a preimplantation genetic diagnosis could be offered if available.

Research with parthenogenetic stem cells will help decide whether a safer clinical use is possible

The derivation and use of parthenogenetic stem cells (pESCs) are envisaged as a reliable alternative to conventional embryonic stem cells. Similar to embryonic stem cells in their proliferation, expression of pluripotency markers and capacity to multilineage differentiation, pESCs are at a lower risk of immune rejection within stem cell-based therapeutics. Moreover, pESCs represent an important model system to study the effect of paternally imprinted genes on cell differentiation. However, currently available information about the genetic and epigenetic behaviour of pESCs is limited. Thus, a detailed look at the biology of parthenogenetic (PG) embryos and PG-derived cell lines would allow gaining insight into the full potential of pESC in biotechnology. In this commentary article we review some features related to the biology of PG embryos and pESCs. In addition, novel traits on bovine pESCs (bpESCs) are discussed.

Effects of chemical combinations on the parthenogenetic activation of mouse oocytes

The aim of this study was to identify an optimal method for the parthenogenetic activation of mouse oocytes. Ethanol (EH), strontium chloride (SrCl₂) and ionomycin calcium salt were each combined with cytochalasin B to induce the parthenogenetic activation of CD-1^® mouse oocytes. Among the EH combination groups, the blastocyst formation and hatching rates of the group that was activated with EH and CB for 5 min were significantly higher compared with those of the groups that were activated for 7 and 10 min (P<0.05). Among the SrCl₂ combination groups, the blastocyst formation and hatching rates of the group that was activated with SrCl₂ and CB for 30 min were significantly higher compared with those of the groups that were activated for 1 and 2 h (P<0.05). Among the ionomycin calcium salt combination groups, the blastocyst formation and hatching rates of the group that was activated with ionomycin and CB for 3 min were higher compared with those of the groups that were activated for 5 and 7 min (P<0.05). Compared with the other two combinations, the experimental indicators of the EH combination groups were notably superior (P<0.05). For combined activation, simultaneous activation with two substances was significantly more effective than successive activation (P<0.05). For combined activation with EH and cytochalasin B in mouse oocytes, 5 min of parthenogenetic activation had significant advantages with regard to cleavage, blastocyst formation and blastocyst hatching rates. In addition, the activation rate of combined activation was higher than that of single activators. For combined activation, the simultaneous application of two activators has a superior effect.

Parthenogenesis in mammals: pros and cons in pluripotent cell derivation

Embryonic stem cells (ESCs) represent a useful tool for cell therapy studies, however the use of embryos for their derivation give rise to ethical, religious and legal problems when applied to the human. During the last years parthenogenesis has been proposed as an alternative source to obtain ESCs. Based on the fact that parthenotes avoid many concerns surrounding the “ad hoc” in vitro production and following destruction of viable human embryos. Unfortunately many aspects related to parthenogenetic cell biology are not fully understood and still need to be elucidated. In this review we describe advantages and limits of these cells. We discuss their typical ESC morphology and high telomerase activity, which disappears after differentiation. We examine the pluripotency signature that they share with bi-parental ESCs. We review their high differentiation plasticity that allow for the derivation of several mature cell type populations when we expose these cells to adequate conditions. On the other hand, in-depth analysis demonstrated chromosome mal-segregation and altered mechanisms controlling centriole arrangement and mitotic spindle formation in these cells. We hypothesize their monoparental origin as one of the possible cause of these anomalies and suggest a great caution if a therapeutic use is considered.

Cellular and genetic analysis of oocytes and embryos in a human case of spontaneous oocyte activation

Unusual and consistent defects in infertility patients merit attention as these may indicate an underlying genetic abnormality, in turn necessitating tailored management strategies. We describe a case of repeated early pregnancy loss from in vivo conceptions, followed by cancelled embryo transfers after one IVF and one ICSI/PGD cycle. Following the unexpected presence of cleaved embryos at the fertilization check in the first IVF attempt, oocytes and embryos were subsequently analyzed in an ICSI/PGD case. Part of the oocyte cohort was fixed at retrieval for a cellular evaluation of microtubules, microfilaments and chromatin. The remaining oocytes were injected with sperm, and resultant embryos were biopsied for genetic analysis by fluorescence in situ hybridization (FISH), single-nucleotide polymorphism (SNP) microarray for 23 chromosome pairs, as well as with PCR for sex chromosomes. The presence of interphase microtubule networks and pronuclear structures indicated that oocytes were spontaneously activated by the time of retrieval. FISH revealed aneuploidy in all seven blastomeres analyzed, with all but two lacking Y chromosomes. Microarray SNP analysis showed an exclusively maternal origin of all blastomeres analyzed, which was further confirmed by PCR. From our multi-faceted analyses, we conclude that spontaneous activation, or parthenogenesis, was probably the pathology underlying our patient's recurrent inability to maintain a normal pregnancy. Such analyses may prove beneficial not only in diagnosing case-specific aberrations for other patients with similar or related failures, but also for furthering our general understanding of oocyte activation.

Parthenogenic blastocysts derived from cumulus-free in vitro matured human oocytes

Background

Approximately 20% of oocytes are classified as immature and discarded following intracytoplasmic sperm injection (ICSI) procedures. These oocytes are obtained from gonadotropin-stimulated patients, and are routinely removed from the cumulus cells which normally would mature the oocytes. Given the ready access to these human oocytes, they represent a potential resource for both clinical and basic science application. However culture conditions for the maturation of cumulus-free oocytes have not been optimized. We aimed to improve maturation conditions for cumulus-free oocytes via culture with ovarian paracrine/autocrine factors identified by single cell analysis.

Methodology/Principal Finding

Immature human oocytes were matured in vitro via supplementation with ovarian paracrine/autocrine factors that were selected based on expression of ligands in the cumulus cells and their corresponding receptors in oocytes. Matured oocytes were artificially activated to assess developmental competence. Gene expression profiles of parthenotes were compared to IVF/ICSI embryos at morula and blastocyst stages. Following incubation in medium supplemented with ovarian factors (BDNF, IGF-I, estradiol, GDNF, FGF2 and leptin), a greater percentage of oocytes demonstrated nuclear maturation and subsequently, underwent parthenogenesis relative to control. Similarly, cytoplasmic maturation was also improved as indicated by development to blastocyst stage. Parthenogenic blastocysts exhibited mRNA expression profiles similar to those of blastocysts obtained after IVF/ICSI with the exception for MKLP2 and PEG1.

Conclusions/Significance

Human cumulus-free oocytes from hormone-stimulated cycles are capable of developing to blastocysts when cultured with ovarian factor supplementation. Our improved IVM culture conditions may be used for obtaining mature oocytes for clinical purposes and/or for derivation of embryonic stem cells following parthenogenesis or nuclear transfer.

Patient-specific pluripotent stem cells: promises and challenges

Tissue transplantation is a well-established tool for the treatment of degenerative and malignant disorders, yet its use in clinical practice is hampered by the need for human-leukocyte-antigen-compatible donors and a shortage of suitable graft tissue. The discovery of human embryonic stem cells a decade ago raised hopes that a universal resource for the cell-based treatment of various conditions would soon become available. Embryonic stem cells derived by somatic-cell nuclear transfer or parthenogenesis can provide human-leukocyte-antigen-matched cells, which may be transplanted without the need for immunosuppressive treatment. However, technical hurdles and ethical concerns about use of oocytes and involvement of embryos have limited the clinical use of these cells. An alternative approach involves adult somatic cells being reprogrammed to enter a pluripotent state. Such manipulation of these readily available cells has enabled derivation of patient-specific, pluripotent stem-cell lines, without progression through the blastocyst stage. This Review critically analyzes the currently available methods for the generation of pluripotent stem cells, and discusses prospects for their clinical use.

Parthenogenesis as an approach to pluripotency: advantages and limitations involved

Embryonic stem cells (ESCs) are invaluable cells derived from the inner cell mass of the mammalian blastocyst. They have nearly indefinite self-renewal, retain their developmental potential after prolonged periods in culture and display great plasticity that allow them to differentiate into all cell types of the body. They provide exciting opportunities to develop unique models for developmental research and hold great potential for cell and tissue replacement therapy. However, these unique cells cannot be obtained without destroying an embryo and, despite the potential therapeutic usefulness, their derivation in the human raises substantial ethical as well as legal and political concerns because it unavoidably involves the destruction of viable embryos. In the recent years a number of scientific proposals that do not require the generation and subsequent destruction of human embryos have been put forward in an attempt to fill the gap between ethical questions and potential scientific and medical benefits. In this review we briefly summarize data obtained from the literature related to these different alternative approaches and focus in more details on our experience in the derivation of parthenothes, as a possible alternative source for pluripotent cells, discussing the advantages as well as the limits of these cell lines.

Differentiation potential of histocompatible parthenogenetic embryonic stem cells

Embryonic stem cells (ESCs) hold unique promise for the development of cell replacement therapies, but derivation of therapeutic products from ESCs is hampered by immunological barriers. Creation of HLA-typed ESC banks, or derivation of customized ESC lines by somatic cell nuclear transfer, have been envisioned for engineering histocompatible ESC-derived products. Proof of principle experiments in the mouse have demonstrated that autologous ESCs can be obtained via nuclear transfer and differentiated into transplantable tissues, yet nuclear transfer remains a technology with low efficiency. Parthenogenesis provides an additional means for deriving ESC lines. In parthenogenesis, artificial oocyte activation initiates development without sperm contribution and no viable offspring are produced in the absence of paternal gene expression. Development proceeds readily to the blastocyst stage, from which parthenogenetic ESC (pESC) lines can be derived with high efficiency. We have recently shown that when pESC lines are derived from hybrid mice, early recombination events produce heterozygosity at the major histocompatibility complex (MHC) loci in some of these lines, enabling the generation of histocompatible differentiated cells that can engraft immunocompetent MHC-matched mouse recipients. Here, we explore the differentiation potential of murine pESCs derived in our laboratory.

In vitro development of human oocytes after parthenogenetic activation or intracytoplasmic sperm injection

OBJECTIVE

To compare directly in vitro developmental competence between parthenogenetically activated and intracytoplasmic sperm injection (ICSI)-fertilized oocytes.

DESIGN

For each patient, three metaphase II oocytes were randomized to the ICSI procedure, while n-3 were allocated to parthenogenetic activation.

SETTING

University hospital infertility unit.

PATIENTS

Thirty-eight patients, aged 35.2 +/- 3.3 years (mean +/- SD) selected for ICSI.

INTERVENTIONS

After 1 hour from denudation, oocytes were either fertilized by ICSI (n = 114) or chemically activated (n = 104). Fertilized and activated oocytes were cultured for up to 3 and 5 days, respectively.

MAIN OUTCOME MEASURES

Development rate, cell number, and morphological grade during culture.

RESULTS

The two groups showed no significant differences between rates of fertilization and parthenogenetic activation, development, and blastomere number on days 2 and 3 of culture. However, parthenotes showed a lower morphological grade, and a significantly lower proportion went on cleaving to day 3, when only activated rather than total numbers of oocytes were considered. On day 5 after activation, nine oocytes (8.6%) reached the blastocyst stage, representing 12.9% of parthenotes.

CONCLUSIONS

Since most parameters examined in this study were similar between activated and fertilized oocytes, parthenogenetic activation may be a useful tool for the preclinical evaluation of experimental procedures.

Sperm N-acetylglucosaminidase is involved in primary binding to the zona pellucida

The glycosidase-recognizing N-acetylglucosamine terminal residue, N-acetylglucosaminidase (NAG), has been repetitively implicated in fertilization. Nevertheless, its role in the multiple steps comprising this process is a matter of debate because it has been involved in zona pellucida (ZP) binding and penetration and polyspermy block. In this study, the involvement of NAG during sperm interaction with the ZP was analysed. Soluble ZP was able to inhibit sperm NAG activity, suggesting that it can be recognized as a ligand by this enzyme. Sperm-ZP binding assays were carried out under conditions where acrosome reaction (AR) could not take place (salt-stored oocytes and a modified medium where Ca(2+) was replaced by Sr(2+)). Different NAG-specific reagents-an inhibitor (2-acetamido-2-deoxy-D-glucono-1,5-lactone), a substrate (p-nitrophenyl-N-acetylglucosaminide) and an anti-NAG antibody-were able to impair sperm binding to the ZP when present during these assays. The lactone was also able to inhibit oocyte penetration during IVF assays, although not when present after primary binding had taken place. This result was not related to the interference of lactone with AR or zona penetrability. Exogenous NAG also inhibited sperm-oocyte interaction when present during binding and IVF assays or used for oocyte pre-incubation. These results suggest the participation of NAG in sperm primary binding to the ZP.

Embryonic Stem Cells from Parthenotes

While human embryonic stem cells (hESCs) hold tremendous therapeutic potential, they also create societal and ethical dilemmas. Adult and placental stem cells represent two alternatives to the hESC, but may have technical limitations. An additional alternative is the stem cell derived from parthenogenesis. Parthenogenesis is a reproductive mechanism that is common in lower organisms and produces a live birth from an oocyte activated in the absence of sperm. However, parthenogenetic embryos will develop to the blastocyst stage and so can serve as a source of embryonic stem cells. Parthenogenetic ESCs (pESCs) have been shown to have the properties of self-renewal and the capacity to generate cell derivatives from the three germ layers, confirmed by contributions to chimeric animals and/or teratoma formation when injected into SCID mice. Therefore, this mechanism for generating stem cells has the ethical advantage of not involving the destruction of viable embryos. Moreover, the cells do not involve the union of male and female and so genetic material will be derived exclusively from the female oocyte donor (with the attendant potential immunological advantages). This chapter describes the biology underlying parthenogenesis, as well as provides detailed technical considerations for the production of pESCs.

Hybrid embryos produced by transferring panda or cat somatic nuclei into rabbit MII oocytes can develop to blastocyst in vitro

The developmental potential of hybrid embryos produced by transferring panda or cat fibroblasts into nucleated rabbit oocytes was assessed. Both the panda-rabbit and the cat-rabbit hybrid embryos were able to form blastocysts in vitro. However, the rates of attaining the two-cell, four-cell, eight-cell, morula, or blastocyst stages for panda-rabbit hybrids were significantly greater than those of cat-rabbit hybrids (P<0.05). Transferring the rabbit fibroblasts into nucleated rabbit oocytes, 31.0% of the blastocyst rate was obtained, which was significantly higher than that of both the panda-rabbit and the cat-rabbit hybrid embryos (P<0.05). Whether or not the second polar body (PB2) was extruded from the one-cell hybrid embryos (both panda-rabbit and cat-rabbit hybrids) significantly affected their developmental capacity. Embryos without an extruded PB2 showed a higher capacity to develop into blastocysts (panda-rabbit: 19.2%; cat-rabbit: 4.3%), while embryos with extruded PB2 could only develop to the morula stage. The hybrid embryos formed pronucleus-like structures (PN) in 2-4 hr after activation, and the number of PN in one-cell embryos varied from one to five. Tracking of the nucleus in the egg after fusion revealed that the somatic nucleus could approach and aggregate with the oocyte nucleus spontaneously. Chromosome analysis of the panda-rabbit blastocysts showed that the karyotype of the hybrid embryos (2n=86) consisted of chromosomes from both the panda (2n=42) and the rabbit (2n=44). The results demonstrate that (1) it is possible to produce genetic hybrid embryos by interspecies nuclear transfer; (2) the developmental potential of the hybrid embryos is highly correlated to the donor nucleus species; and (3) the hybrid genome is able to support the complete preimplantation embryonic development of the hybrids.

Developmental kinetics of bovine nuclear transfer and parthenogenetic embryos

Early developmental kinetics of nuclear transfer (NT) embryos reconstituted with blastomeres and parthenogenones produced by ionophore activation followed by either dimethylaminopurine (DMAP) or cycloheximide (CHX) treatment was studied. In vitro produced (IVP) embryos served as controls. Embryos were cultured to the hatched blastocyst stage, and images were recorded every 0.5 h throughout the culture period. The longest cell cycle shifted from 4th to 5th cycle (26 +/- 4 and 44 +/- 5 h) in NT-embryos compared to IVP-embryos (41 +/- 2 and 20 +/- 3 h) and showed greater asynchrony between blastomeres than any other embryo category. Compared to DMAP, CHX prolonged the 1(st) (23 +/- 1 vs. 33 +/- 1 h) and shortened the 3(rd) cell cycle (17 +/- 2 vs. 13 +/- 1 h). Moreover, though cytoskeleton activity was initialised, a larger proportion of CHX embryos was unable to accomplish first cleavage. The parthegenones differed from IVP embryos with respect to the lengths of the 1st, 3rd, and 4th cell cycles and time of hatching. The findings are discussed in relation to known ultrastructural, chromosomal and genomic aberrations found in NT embryos and parthenogenones. We hypothesize that the shift of the longest cell cycle in NT embryos is associated with a shift in the time of major genomic transition.

Administration of increasing amounts of gonadotrophin compromises preimplantation development of parthenogenetic mouse embryos

The aim of the present study was to examine the effect of ovarian stimulation with increasing amounts of pregnant mare's serum gonadotrophin (PMSG) on preimplantation development of diploid parthenogenetic embryos in vitro. Administration of 5, 10 and 20 IU PMSG significantly increased the number of oocytes obtained per mouse in a dose-dependent manner. The amount of PMSG administered did not alter the proportion of degenerate oocytes. However, there was a significant decrease in the proportion of 8-cell/compacted embryos after 53 h of culture with the administration of increasing amounts of PMSG. Proportion of embryos reaching at the blastocyst stage after 79 h of culture was reduced significantly in both the 10 and 20 IU PMSG groups. Reduced blastocyst development after 96 h of culture, however, was significant only in the 20 IU PMSG group. Total blastocyst, trophectoderm and inner cell mass numbers were also reduced significantly with the administration of 20 IU PMSG. It is concluded on the basis of these observations that preimplantation development of diploid parthenogenetic oocytes, which depends virtually entirely on maternal molecules accumulated during oogenesis along with gene products derived from the maternal genome, is compromised with the administration of increasing amounts of PMSG.