Rhesus monkeys produced by nuclear transfer

Physiological basis for xenotransplantation from genetically modified pigs to humans

The collective efforts of scientists over multiple decades have led to advancements in molecular and cellular biology-based technologies including genetic engineering and animal cloning that are now being harnessed to enhance the suitability of pig organs for xenotransplantation into humans. Using organs sourced from pigs with multiple gene deletions and human transgene insertions, investigators have overcome formidable immunological and physiological barriers in pig-to-nonhuman primate (NHP) xenotransplantation and achieved prolonged pig xenograft survival. These studies informed the design of Revivicor's (Revivicor Inc, Blacksburg, VA) genetically engineered pigs with 10 genetic modifications (10 GE) (including the inactivation of 4 endogenous porcine genes and insertion of 6 human transgenes), whose hearts and kidneys have now been studied in preclinical human xenotransplantation models with brain-dead recipients. Additionally, the first two clinical cases of pig-to-human heart xenotransplantation were recently performed with hearts from this 10 GE pig at the University of Maryland. Although this review focuses on xenotransplantation of hearts and kidneys, multiple organs, tissues, and cell types from genetically engineered pigs will provide much-needed therapeutic interventions in the future.

Advancing primatology through ethical and scientific perspectives on rhesus monkey (Macaca mulatta) cloning

A critical turning point was reached in research with the recent success in cloning rhesus monkeys (Macaca mulatta), a major advancement in primatology. This breakthrough marks the beginning of a new age in biomedical research, ushered by improved somatic cell nuclear transfer techniques and creative trophoblast replacement strategies. The successful cloning of rhesus monkeys presents the possibility of producing genetically homogeneous models that are highly advantageous for studying complex biological processes, testing drugs, and researching diseases. However, this achievement raises important ethical questions, particularly regarding animal welfare and the broader ramifications of primate cloning. Approaching the future of primate research with balance is critical, as the scientific world stands on the brink of these revolutionary breakthroughs. This paper aims to summarise the consequences, ethical challenges and possible paths forward in primatology arising from rhesus monkey cloning.

Reprogramming mechanism dissection and trophoblast replacement application in monkey somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) successfully clones cynomolgus monkeys, but the efficiency remains low due to a limited understanding of the reprogramming mechanism. Notably, no rhesus monkey has been cloned through SCNT so far. Our study conducts a comparative analysis of multi-omics datasets, comparing embryos resulting from intracytoplasmic sperm injection (ICSI) with those from SCNT. Our findings reveal a widespread decrease in DNA methylation and the loss of imprinting in maternally imprinted genes within SCNT monkey blastocysts. This loss of imprinting persists in SCNT embryos cultured in-vitro until E17 and in full-term SCNT placentas. Additionally, histological examination of SCNT placentas shows noticeable hyperplasia and calcification. To address these defects, we develop a trophoblast replacement method, ultimately leading to the successful cloning of a healthy male rhesus monkey. These discoveries provide valuable insights into the reprogramming mechanism of monkey SCNT and introduce a promising strategy for primate cloning.

Cloning in action: can embryo splitting, induced pluripotency and somatic cell nuclear transfer contribute to endangered species conservation?

The term 'cloning' refers to the production of genetically identical individuals but has meant different things throughout the history of science: a natural means of reproduction in bacteria, a routine procedure in horticulture, and an ever-evolving gamut of molecular technologies in vertebrates. Mammalian cloning can be achieved through embryo splitting, somatic cell nuclear transfer, and most recently, by the use of induced pluripotent stem cells. Several emerging biotechnologies also facilitate the propagation of genomes from one generation to the next whilst bypassing the conventional reproductive processes. In this review, we examine the state of the art of available cloning technologies and their progress in species other than humans and rodent models, in order to provide a critical overview of their readiness and relevance for application in endangered animal conservation.

The role of mtDNA in oocyte quality and embryo development

The mitochondrial genome resides in the mitochondria present in nearly all cell types. The porcine (Sus scrofa) mitochondrial genome is circa 16.7 kb in size and exists in the multimeric format in cells. Individual cell types have different numbers of mitochondrial DNA (mtDNA) copy number based on their requirements for ATP produced by oxidative phosphorylation. The oocyte has the largest number of mtDNA of any cell type. During oogenesis, the oocyte sets mtDNA copy number in order that sufficient copies are available to support subsequent developmental events. It also initiates a program of epigenetic patterning that regulates, for example, DNA methylation levels of the nuclear genome. Once fertilized, the nuclear and mitochondrial genomes establish synchrony to ensure that the embryo and fetus can complete each developmental milestone. However, altering the oocyte's mtDNA copy number by mitochondrial supplementation can affect the programming and gene expression profiles of the developing embryo and, in oocytes deficient of mtDNA, it appears to have a positive impact on the embryo development rates and gene expression profiles. Furthermore, mtDNA haplotypes, which define common maternal origins, appear to affect developmental outcomes and certain reproductive traits. Nevertheless, the manipulation of the mitochondrial content of an oocyte might have a developmental advantage.

Introduction to stem cells

Stem cells have self-renewal capability and can proliferate and differentiate into a variety of functionally active cells that can serve in various tissues and organs. This review discusses the history, definition, and classification of stem cells. Human pluripotent stem cells (hPSCs) mainly include embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs). Embryonic stem cells are derived from the inner cell mass of the embryo. Induced pluripotent stem cells are derived from reprogramming somatic cells. Pluripotent stem cells have the ability to differentiate into cells derived from all three germ layers (endoderm, mesoderm, and ectoderm). Adult stem cells can be multipotent or unipotent and can produce tissue-specific terminally differentiated cells. Stem cells can be used in cell therapy to replace and regenerate damaged tissues or organs.

Generation of Transgenic Sperm Expressing GFP by Lentivirus Transduction of Spermatogonial Stem Cells In Vivo in Cynomolgus Monkeys

Nonhuman primates (NHPs) have been considered as the best models for biomedical research due to their high similarities in genomic, metabolomic, physiological and pathological features to humans. However, generation of genetically modified NHPs through traditional methods, such as microinjection into the pronuclei of one-cell embryos, is prohibitive due to the targeting efficiency and the number of NHPs needed as oocyte/zygote donors. Using spermatogonial stem cells (SSCs) as the target of gene editing, producing gene-edited sperm for fertilization, is proven to be an effective way to establish gene editing animal disease models. In this experiment, we used ultrasound to guide the echo dense injection needle into the rete testis space, allowing the EGFP lentivirus to be slowly injected at positive pressure from the rete testis into seminiferous tubules. We found Thy1 can be used as a surface marker of cynomolgus monkey SSCs, confirming that SSCs carry the GFP gene. Finally, we successfully obtained transgenic sperm, with a similar freezing and recovery rate to that of WT animals.

Interspecific Nuclear Transfer Blastocysts Reconstructed from Arabian Oryx Somatic Cells and Domestic Cow Ooplasm

Cloning, commonly referred to as somatic cell nuclear transfer (SCNT), is the technique of enucleating an oocyte and injecting a somatic cell into it. This study was carried out with interspecific SCNT technology to clone the Arabian Oryx utilizing the oryx's fibroblast cells and transfer it to the enucleated oocytes of a domestic cow. The recipient oocytes were extracted from the cows that had been butchered. Oryx somatic nuclei were introduced into cow oocytes to produce embryonic cells. The study was conducted on three groups, Oryx interspecific somatic cell nuclear transfer into enucleated oocytes of domestic cows, cow SCNT "the same bovine family species", used as a control group, and in vitro fertilized (IVF) cows to verify all media used in this work. The rates of different embryo developmental stages varied slightly (from 1- cell to morula stage). Additionally, the oryx interspecies Somatic cell nuclear transfer blastocyst developmental rate (9.23%) was comparable to that of cow SCNT (8.33%). While the blastula stage rate of the (IVF) cow embryos exhibited a higher cleavage rate (42%) in the embryo development stage. The results of this study enhanced domestic cow oocytes' ability to support interspecific SCNT cloned oryx, and generate a viable embryo that can advance to the blastula stage.

The role of passage numbers of donor cells in the development of Arabian Oryx – Cow interspecific somatic cell nuclear transfer embryos

The cloning between different animals known as interspecific somatic cell nuclear transfer (iSCNT) was carried out for endangered species. The iSCNT has been characterized by a poor success rate due to several factors that influence the formation of the SCNT in various cytoplasms. The cell cycle of the transferred somatic cell, the passage number of the cultured somatic cell, the mitochondria oocytes, and their capabilities are among these factors. This study investigates the role of the passage number of the Arabian Oryx somatic cell culture when transplanted to an enucleated domestic cow oocyte and embryo development in vitro. The fibroblast somatic cell of the Arabian Oryx was cultured for several passage lanes (3–13). The optimal passage cell number was found to be 10–13 Oryx cell lines that progressed to various cell stages up to the blastula stage. There was some variation between the different passage numbers of the oryx cell line. The 3–9 cell line did not show a good developmental stage. These could be attributed to several factors that control the iSCNT as stated by several investigators. More investigation is needed to clarify the role of factors that affect the success rate for the iSCNT.

Oocyte maturation abnormalities - A systematic review of the evidence and mechanisms in a rare but difficult to manage fertility pheneomina

A small proportion of infertile women experience repeated oocyte maturation abnormalities (OMAS). OMAS include degenerated and dysmorphic oocytes, empty follicle syndrome, oocyte maturation arrest (OMA), resistant ovary syndrome and maturation defects due to primary ovarian insufficiency. Genetic factors play an important role in OMAS but still need specifications. This review documents the spectrum of OMAS and to evaluate the multiple subtypes classified as OMAS. In this review, readers will be able to understand the oocyte maturation mechanism, gene expression and their regulation that lead to different subtypes of OMAs, and it will discuss the animal and human studies related to OMAS and lastly the treatment options for OMAs. Literature searches using PubMed, MEDLINE, Embase, National Institute for Health and Care Excellence were performed to identify articles written in English focusing on Oocyte Maturation Abnormalities by looking for the following relevant keywords. A search was made with the specified keywords and included books and documents, clinical trials, animal studies, human studies, meta-analysis, randomized controlled trials, reviews, systematic reviews and options written in english. The search detected 3,953 sources published from 1961 to 2021. After title and abstract screening for study type, duplicates and relevancy, 2,914 studies were excluded. The remaining 1,039 records were assessed for eligibility by full-text reading and 886 records were then excluded. Two hundred and twenty seven full-text articles and 0 book chapters from the database were selected for inclusion. Overall, 227 articles, one unpublished and one abstract paper were included in this final review. In this review study, OMAS were classified and extensively evaluatedand possible treatment options under the light of current information, present literature and ongoing studies. Either genetic studies or in vitro maturation studies that will be handled in the future will lead more informations to be reached and may make it possible to obtain pregnancies.

Assisted Reproductive Techniques and Genetic Manipulation in the Common Marmoset

Genetic modification of nonhuman primate (NHP) zygotes is a useful method for the development of NHP models of human diseases. This review summarizes the recent advances in the development of assisted reproductive and genetic manipulation techniques in NHP, providing the basis for the generation of genetically modified NHP disease models. In this study, we review assisted reproductive techniques, including ovarian stimulation, in vitro maturation of oocytes, in vitro fertilization, embryo culture, embryo transfer, and intracytoplasmic sperm injection protocols in marmosets. Furthermore, we review genetic manipulation techniques, including transgenic strategies, target gene knock-out and knock-in using gene editing protocols, and newly developed gene-editing approaches that may potentially impact the production of genetically manipulated NHP models. We further discuss the progress of assisted reproductive and genetic manipulation techniques in NHP; future prospects on genetically modified NHP models for biomedical research are also highlighted.

Effect of Additional Cytoplasm of Cloned Embryo on In Vitro Developmental Competence and Reprogramming Efficiency in Mice

Somatic cell nuclear transfer (SCNT) is an important technique for biological science research. Cytoplasm injection cloning technology (CICT) was developed to improve the reprogramming efficiency as well as to overcome the limitations of SCNT. CICT uses an additional cytoplasm fused with an enucleated oocyte to restore the cytoplasmic volume of the cloned embryo, and this method could improve the reprogramming efficiency of the cloned embryo. In this study, we show that CICT can be adapted to mouse species to overcome the inefficiency of the SCNT method. In this study, results indicate that the two-cell embryo and blastocyst rates of cloned embryos with the use of the CICT method were significantly higher (p < 0.05) than that of the SCNT method (96.6% ± 1.1% vs. 86.7% ± 6.0%, 29.5% ± 2.6% vs. 22.1% ± 3.0%, respectively). Furthermore, the apoptotic cell number per blastocyst was significantly lower in the CICT group than that in the SCNT group (1.7 ± 0.2 vs. 2.9 ± 0.3, p < 0.05). Moreover, the acH3K9/K14 expression level in the CICT group was greater than that of the SCNT group (p < 0.05), and the relative acH3K56 level in the CICT group was significantly (p < 0.05) higher than that in the SCNT group. These results indicate that CICT helps improve the in vitro developmental competence and quality of cloned embryos.

Partial Reprogramming As An Emerging Strategy for Safe Induced Cell Generation and Rejuvenation

BACKGROUND

Conventional cell reprogramming involves converting a somatic cell line into induced pluripotent stem cells (iPSC), which subsequently can be re-differentiated to specific somatic cell types. Alternatively, partial cell reprogramming converts somatic cells into other somatic cell types by transient expression of pluripotency genes thus generating intermediates that retain their original cell identity, but are responsive to appropriate cocktails of specific differentiation factors. Additionally, biological rejuvenation by partial cell reprogramming is an emerging avenue of research.

OBJECTIVE

Here, we will briefly review the emerging information pointing to partial reprogramming as a suitable strategy to achieve cell reprogramming and rejuvenation, bypassing cell dedifferentiation.

METHODS

In this context, regulatable pluripotency gene expression systems are the most widely used at present to implement partial cell reprogramming. For instance, we have constructed a regulatable bidirectional adenovector expressing Green Fluorescent Protein and oct4, sox2, klf4 and c-myc genes (known as the Yamanaka genes or OSKM).

RESULTS

Partial cell reprogramming has been used to reprogram fibroblasts to cardiomyocytes, neural progenitors and neural stem cells. Rejuvenation by cyclic partial reprogramming has been achieved both in vivo and in cell culture using transgenic mice and cells expressing the OSKM genes, respectively, controlled by a regulatable promoter.

CONCLUSION

Partial reprogramming emerges as a powerful tool for the genesis of iPSC-free induced somatic cells of therapeutic value and for the implementation of in vitro and in vivo rejuvenation keeping cell type identity unchanged.

In Vitro Culture of Rhesus Macaque (Macaca mulatta) Embryos

Production of nonhuman primate (NHP) embryos in vitro begins with recovery of gametes. Females undergo a controlled ovary stimulation to produce multiple preovulatory follicles from which oocytes may be recovered. Mature ova are subjected to in vitro fertilization (IVF) and presumptive zygotes are cultured to the intended stage of development. Essential to this practice is the culture medium unique to each step in the process. Here we describe medium preparation, oocyte recovery, in vitro fertilization, and in vitro culture (IVC) of embryos in the rhesus macaque model.

Microinjection and Micromanipulation: A Historical Perspective

Microinjection/micromanipulation is more than 100 years old. It is a technique that is instrumental in biomedical research and healthcare. Its longevity lies in its preciseness in mechanical retrieval, or delivery of biological materials, which in some cases is simply necessary or more effective than other retrieval/delivery means. Microinjection is favored for its straightforwardness in transferring contents from micromolecules to macromolecules and from organelles to cells. Microinjection/micromanipulation has been practiced over the century like an art form. Variations in handlings and instruments can be tolerated to a surprising degree with satisfactory outcomes. Throughout the century, microinjection developed as an indispensable tool along with the evolution of biomedical fields: from transgenics to gene targeting, from animal cloning to human infertility treatment, from nuclease-guided genetic engineering to RNA-guided genome editing (Fig. 1). The birth of the CRISPRology rejuvenated microinjection. For microinjection/micromanipulation, the second century has already begun with the early arrival of computerized instrumentation and lately of the high-throughput nanomanipulators potentially operable by artificial intelligence. As we yin-yang both systemic and precision approaches in research and medicine, microinjection will no doubt continue to find its unique place in the future.

Generation of genetically engineered non-human primate models of brain function and neurological disorders

Research with non-human primates (NHP) has been essential and effective in increasing our ability to find cures for a large number of diseases that cause human suffering and death. Extending the availability and use of genetic engineering techniques to NHP will allow the creation and study of NHP models of human disease, as well as broaden our understanding of neural circuits in the primate brain. With the recent development of efficient genetic engineering techniques that can be used for NHP, there's increased hope that NHP will significantly accelerate our understanding of the etiology of human neurological and neuropsychiatric disorders. In this article, we review the present state of genetic engineering tools used in NHP, from the early efforts to induce exogeneous gene expression in macaques and marmosets, to the latest results in producing germline transmission of different transgenes and the establishment of knockout lines of specific genes. We conclude with future perspectives on the further development and employment of these tools to generate genetically engineered NHP.

Cloning of Macaque Monkeys by Somatic Cell Nuclear Transfer

Generation of genetically uniform non-human primates may help to establish animal models for primate biology and biomedical research. In this study, we have successfully cloned cynomolgus monkeys (Macaca fascicularis) by somatic cell nuclear transfer (SCNT). We found that injection of H3K9me3 demethylase Kdm4d mRNA and treatment with histone deacetylase inhibitor trichostatin A at one-cell stage following SCNT greatly improved blastocyst development and pregnancy rate of transplanted SCNT embryos in surrogate monkeys. For SCNT using fetal monkey fibroblasts, 6 pregnancies were confirmed in 21 surrogates and yielded 2 healthy babies. For SCNT using adult monkey cumulus cells, 22 pregnancies were confirmed in 42 surrogates and yielded 2 babies that were short-lived. In both cases, genetic analyses confirmed that the nuclear DNA and mitochondria DNA of the monkey offspring originated from the nucleus donor cell and the oocyte donor monkey, respectively. Thus, cloning macaque monkeys by SCNT is feasible using fetal fibroblasts.

The origin and evolution of the term "clone"

In biology, the term "clone" is most widely used to designate genetically identical cells or organisms that are asexually descended from a common progenitor. The concept of clonality in hematology-oncology has received much attention in recent years, as the advent of next-generation sequencing platforms has provided new tools for detection of clonal populations in patients, and experiments on primary cells have provided fascinating new insights into the clonal architecture of human malignancies. The term "clone" is used more loosely by the general public to mean any close or identical copy. Cloning of humans has been a staple of science fiction films and dystopian novels since Aldous Huxley's Brave New World was published in 1932. Here I trace the origin and evolution of the word clone, from its first use as an agricultural and botanical term in 1903, to its widespread adoption in biology, adaptation by artists, and contemporary use in hematology-oncology.

Brains, genes, and primates

One of the great strengths of the mouse model is the wide array of genetic tools that have been developed. Striking examples include methods for directed modification of the genome, and for regulated expression or inactivation of genes. Within neuroscience, it is now routine to express reporter genes, neuronal activity indicators, and opsins in specific neuronal types in the mouse. However, there are considerable anatomical, physiological, cognitive, and behavioral differences between the mouse and the human that, in some areas of inquiry, limit the degree to which insights derived from the mouse can be applied to understanding human neurobiology. Several recent advances have now brought into reach the goal of applying these tools to understanding the primate brain. Here we describe these advances, consider their potential to advance our understanding of the human brain and brain disorders, discuss bioethical considerations, and describe what will be needed to move forward.

Induced pluripotent stem cell technology in regenerative medicine and biology

The potential of human embryonic stem cells (ESCs) for regenerative medicine is unquestionable, but practical and ethical considerations have hampered clinical application and research. In an attempt to overcome these issues, the conversion of somatic cells into pluripotent stem cells similar to ESCs, commonly termed nuclear reprogramming, has been a top objective of contemporary biology. More than 40 years ago, King, Briggs, and Gurdon pioneered somatic cell nuclear reprogramming in frogs, and in 1981 Evans successfully isolated mouse ESCs. In 1997 Wilmut and collaborators produced the first cloned mammal using nuclear transfer, and then Thomson obtained human ESCs from in vitro fertilized blastocysts in 1998. Over the last 2 decades we have also seen remarkable findings regarding how ESC behavior is controlled, the importance of which should not be underestimated. This knowledge allowed the laboratory of Shinya Yamanaka to overcome brilliantly conceptual and technical barriers in 2006 and generate induced pluripotent stem cells (iPSCs) from mouse fibroblasts by overexpressing defined combinations of ESC-enriched transcription factors. Here, we discuss some important implications of human iPSCs for biology and medicine and also point to possible future directions.

Assisted reproductive technology in nonhuman primates

Nonhuman primates (NHP) are the closest animal species to humans and have been widely used for studying human reproductive physiology. Assisted reproductive technology (ART) in Old World NHPs provides great opportunity for studying fertilization, embryo development, embryonic stem cell (ESC) derivation for regenerative medicine, somatic cell nuclear transfer (cloning), and transgenic NHP models of inherited genetic disorders. Here we present two ART protocols developed for rhesus monkey (Macaca mulatta) and baboon (Papio cynocephalus).

Cloning of non-human primates: the road "less traveled by"

Early studies on cloning of non-human primates by nuclear transfer utilized embryonic blastomeres from preimplantation embryos which resulted in the reproducible birth of live offspring. Soon after, the focus shifted to employing somatic cells as a source of donor nuclei (somatic cell nuclear transfer, SCNT). However, initial efforts were plagued with inefficient nuclear reprogramming and poor embryonic development when standard SCNT methods were utilized. Implementation of several key SCNT modifications was critical to overcome these problems. In particular, a non-invasive method of visualizing the metaphase chromosomes during enucleation was developed to preserve the reprogramming capacity of monkey oocytes. These modifications dramatically improved the efficiency of SCNT, yielding high blastocyst development in vitro. To date, SCNT has been successfully used to derive pluripotent embryonic stem cells (ESCs) from adult monkey skin fibroblasts. These remarkable advances have the potential for development of human autologous ESCs and cures for many human diseases. Reproductive cloning of nonhuman primates by SCNT has not been achieved yet. We have been able to establish several pregnancies with SCNT embryos which, so far, did not progress to term. In this review, we summarize the approaches, obstacles and accomplishments of SCNT in a non-human primate model.

Dynamic distribution of NuMA and microtubules in human fetal fibroblasts, developing oocytes and somatic cell nuclear transferred embryos

BACKGROUND

The nuclear mitotic apparatus (NuMA) plays a central role in the assembly and maintenance of spindle poles. Somatic cell nuclear transfer (SCNT) studies on non-human primates have shown that meiotic spindle removal during enucleation causes depletion of NuMA and the minus-end-directed motor protein (HSET) from the ooplasm, and this in turn leads to failure of embryo development. To determine whether NuMA from somatic cells could compensate for NuMA loss during enucleation, the distribution of NuMA and microtubule organization were investigated in human fibroblasts, developing oocytes and SCNT embryos.

METHODS

Human fetal fibroblasts, oocytes at various maturation stages and human embryos reconstructed by different SCNT methods were analyzed for NuMA and α-tubulin using immunofluorescent confocal microscopy.

RESULTS

NuMA was detected in interphase nuclei of fibroblasts and oocytes. During mitosis and meiosis, NuMA relocated to the domain surrounding the two spindle poles. During the enucleation process, NuMA was removed along with the meiotic spindle. At 2 h after injection into a donor cell, transitory bipolar spindles were organized and NuMA was detected in the reformed poles. NuMA could be detected spreading uniformly across the nucleoplasm of one pseudo-pronucleus in SCNT embryos but was excluded from the nucleolus. Regardless of the method used for SCNT (enucleation-injection or injection-pronuclei enucleation), NuMA aggregated and relocated to the reformed spindle poles at metaphase of the first mitotic event. At interphase, NuMA relocated throughout the nucleus in developmentally arrested SCNT embryos.

CONCLUSIONS

Our results show that donor cell nuclei contain NuMA, which might contribute to the maintenance of spindle morphology in SCNT embryos. Normal spindle and NuMA expression were found in human SCNT embryos at different developmental stages.

Bovine somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) is a technique by which the nucleus of a differentiated cell is introduced into an oocyte from which its genetic material has been removed by a process called enucleation. In mammals, the reconstructed embryo is artificially induced to initiate embryonic development (activation). The oocyte turns the somatic cell nucleus into an embryonic nucleus. This process is called nuclear reprogramming and involves an important change of cell fate, by which the somatic cell nucleus becomes capable of generating all the cell types required for the formation of a new individual, including extraembryonic tissues. Therefore, after transfer of a cloned embryo to a surrogate mother, an offspring genetically identical to the animal from which the somatic cells where isolated, is born. Cloning by nuclear transfer has potential applications in agriculture and biomedicine, but is limited by low efficiency. Cattle were the second mammalian species to be cloned after Dolly the sheep, and it is probably the most widely used species for SCNT experiments. This is, in part due to the high availability of bovine oocytes and the relatively higher efficiency levels usually obtained in cattle. Given the wide utilization of this species for cloning, several alternatives to this basic protocol can be found in the literature. Here we describe a basic protocol for bovine SCNT currently being used in our laboratory, which is amenable for the use of the nuclear transplantation technique for research or commercial purposes.

Epigenetic modifications of embryonic stem cells: current trends and relevance in developing regenerative medicine

Epigenetics is a growing field not only in the area of cancer research but recently in stem cells including human embryonic stem cell (hESC) research. The hallmark of profiling epigenetic changes in stem cells lies in maintaining pluripotency or multipotency and in attaining lineage specifications that are relevant for regenerative medicine. Epigenetic modifications including DNA methylation, histone acetylation and methylation, play important roles in regulating gene expressions. Other epigenetic modifications include X chromosome silencing, genomic stability and imprinting and mammalian development. This review attempts to elucidate the mechanism(s) behind epigenetic modifications and review techniques scientists use for identifying each modification. We also discuss some of the trends of epigenetic modifications in the fields of directed differentiation of embryonic stem cells and de-differentiation of somatic cells.

Pluripotency and nuclear reprogramming

Embryonic stem cells are promising donor cell sources for cell transplantation therapy, which may in the future be used to treat various diseases and injuries. However, as is the case for organ transplantation, immune rejection after transplantation is a potential problem with this type of therapy. Moreover, the use of human embryos presents serious ethical difficulties. These issues may be overcome if pluripotent stem cells are generated from patients' somatic cells. Here, we review the molecular mechanisms underlying pluripotency and the currently known methods of inducing pluripotency in somatic cells.

Nuclear reprogramming: what has been done and potential avenues for improvements

A major challenge for reproductive biologists is the development of novel strategies to improve cloning efficiency. Even in species for which cloning is relatively successful, like cattle, the efficiency is still unacceptably low. In this review article we critically analyse all approaches that have been suggested by different laboratories in the field so far. As will be discussed below, so far none of these gives rise to a dramatic increase in cloning efficiency. Possibly, a multi-step approach including a pre-treatment of donor cells to modify their chromatin, along with improved culture system for cloned embryos would be the most promising.

Impairments in embryonic genome activation in rhesus monkey somatic cell nuclear transfer embryos

Somatic cell nuclear transfer (SCNT) is a remarkable process in which a somatic cell nucleus is acted upon by the ooplasm via mechanisms that today remain unknown. Here we show the developmental competence (% blastocyst) of embryos derived from SCNT (21%) was markedly (p < 0.05) impaired compared with those derived from in vitro fertilization (IVF) (42.1%) in rhesus monkey. Also, SCNT embryos were abnormal in their time course of embryonic development. SCNT produced embryos reached the eight-cell stage faster than did IVF produced embryos. We compare the transcription patterns of five nucleolar-related proteins-nucleolin, nucleophosmin, fibrillarin, PAF53, and UBF-in single IVF and SCNT blastocysts by RT-PCR. The SCNT embryos showed abnormal gene transcription. Immunolocalization of fibrillarin was undetectable in 8-cell and 16-cell SCNT embryos, indicating embryonic genomic activation was delayed in monkey embryos produced by SCNT compared to their IVF-derived counterparts. Some of SCNT embryos appeared to relative higher developmental potential and fibrillarin expression by prolonged exposure of incoming nuclei to a cytoplasm. Thus, our data show that SCNT embryos are characterized by abnormal cleavage and the timely onset of embryonic genome transcription, deficits that may explain their reduced pre- and postimplantation developmental capacity.

Lazarus's gate: challenges and potential of epigenetic reprogramming of somatic cells

The past year has seen tremendous advances in epigenetic reprogramming of somatic cells. Direct genesis of pluripotent stem cells, in contrast to earlier somatic cell nuclear transfer (SCNT) techniques, removes significant ethical and regulatory concerns regarding the utilization of human oocytes and zygotes, and represents a significant step toward the development of nonxenogeneic production methods. While significant technical hurdles remain, this and related technologies are enabling new approaches toward clinical treatments, basic research and diagnostics, and drug evaluation.

The non-human primate oocyte and embryo as a model for women, or is it vice versa?

The role of the non-human primate (NHP) oocyte and embryo in translational research is considered here including both in vitro activities directly involving oocytes or embryos as well as animal studies that impact reproductive function. Reasons to consider NHPs as animal research models along with their limitations are summarized. A case is made that in limited instances, such as in the development and application of the assisted reproductive technologies or in the study of embryonic stem cells, the human oocyte and embryo have acted as models for the monkey. The development of strategies for the preservation of fertility is used as an example of ongoing research in the non-human primate that cannot be conducted in women for ethical reasons. In animal studies, monitoring reproductive potential, responses to embryonic stem cell transplantation, along with translational research in the field of contraceptive development for women are considered as subjects that benefit from the availability of a NHP model.

Reprogramming following somatic cell nuclear transfer in primates is dependent upon nuclear remodeling

BACKGROUND

Somatic cell nuclear transfer (SCNT) requires cytoplast-mediated reprogramming of the donor nucleus. Cytoplast factors such as maturation promoting factor are implicated based on their involvement in nuclear envelope breakdown (NEBD) and premature chromosome condensation (PCC). Given prior difficulties in SCNT in primates using conventional protocols, we hypothesized that the ability of cytoplasts to induce nuclear remodeling was instrumental in efficient reprogramming.

METHODS

NEBD and PCC in monkey (Macaca mulatta) SCNT embryos were monitored by lamin A/C immunolabeling.

RESULTS

Initially, a persistent lamin A/C signal from donor cell nuclei after fusion with cytoplasts was observed indicative of incomplete NEBD following SCNT and predictive of developmental arrest. We then identified fluorochrome-assisted enucleation and donor cell electrofusion as likely candidates for inducing premature cytoplast activation and a consequent lack of nuclear remodeling. Modified protocols designed to prevent premature cytoplast activation during SCNT showed robust NEBD and PCC. Coincidently, over 20% of SCNT embryos reconstructed with fetal fibroblasts progressed to blastocysts. Similar results were obtained with other somatic cells. Reconstructed blastocysts displayed patterns of Oct-4 expression similar to fertilized embryos reflecting successful reprogramming.

CONCLUSIONS

Our results represent a significant breakthrough in elucidating the role of nuclear remodeling events in reprogramming following SCNT.

Mouse zygotes as recipients in embryo cloning

Zygotes have not been recognized as nuclear recipients since enucleated zygotes receiving nuclei from beyond two-cell stage embryos are not able to form blastocysts. In the present study, a new technique of zygote enucleation is presented, which consists in selectively removing the nuclear membrane with genetic material of pronuclei, but leaving other pronuclear components in the cytoplasm. With selective enucleation it is possible - after transfer of eight-cell stage nuclei - to obtain 70.5 and 7.8% of preimplantation and full-term development respectively. Origin of cloned mice from introduced nuclei was confirmed by the coat colour and glucose phosphate isomerase (GPI) isozyme of the donor. We suggest that some pronuclear factors - taken away from the zygotes in the karyoplasts upon classical enucleation - are needed to reprogram the introduced nuclei.

Contrasting effects of in vitro fertilization and nuclear transfer on the expression of mtDNA replication factors

Mitochondrial DNA (mtDNA) is normally only inherited through the oocyte. However, nuclear transfer (NT), the fusion of a donor cell with an enucleated oocyte, can transmit both donor cell and recipient oocyte mtDNA. mtDNA replication is under the control of nuclear-encoded replication factors, such as polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). These are first expressed during late preimplantation embryo development. To account for the persistence of donor cell mtDNA, even when introduced at residual levels (mtDNA(R)), we hypothesized that POLG and TFAM would be upregulated in intra- and interspecific (ovine-ovine) and intergeneric (caprine-ovine) NT embryos when compared to in vitro fertilized (IVF) embryos. For the intra- and interspecific crosses, PolGA (catalytic subunit), PolGB (accessory subunit), and TFAM mRNA were expressed at the 2-cell stage in both nondepleted (mtDNA(+)) and mtDNA(R) embryos with protein being expressed up to the 16-cell stage for POLGA and TFAM. However, at the 16-cell stage, there was significantly more PolGA expression in the mtDNA(R) embryos compared to their mtDNA(+) counterparts. Expression for all three genes first matched IVF embryos at the blastocyst stage. In the intergeneric model, POLG was upregulated during preimplantation development. Although these embryos did not persist further than the 16+-cell stage, significantly more mtDNA(R) embryos reached this stage. However, the vast majority of these embryos were homoplasmic for recipient oocyte mtDNA. The upreglation in mtDNA replication factors was most likely due to the donor cells still expressing these factors prior to NT.

Stem cell plasticity: the debate begins to clarify

The stem cell story begins with the recognition of the regenerative powers of the head of the Lernean Hydra and the human liver (Prometheus) by the ancient Greeks. In modern times, the adult human stem cell has been epitomized by the hematopoietic stem cell in the bone marrow. More recently, bone marrow derived cells were reported to contribute to nonhematopoietic organs, suggesting a level of plasticity not previously expected. However, other reports failed to repeat some of these results, resulting in a heated debate on the plasticity of adult stem cells that has crossed over into the public domain and become a matter of political impact on the use of embryonic vs adult stem cells for organ regeneration or gene therapy. This review discusses the current status of the "plasticity" debate and presents existing data on detection methodology, underlying mechanisms, physiological implications, and clinical significance.

Cloned blastocysts produced by nuclear transfer from somatic cells in cynomolgus monkeys (Macaca fascicularis)

In nonhuman primates (NHPs), there have so far been few reports about nuclear transfer (NT), especially using adult somatic cells. The objective of this study was to determine the developmental competence of NT embryos derived from various somatic cells embryonic stem (ES), amniotic epithelial, cumulus, or fetal fibroblast cells] and the nuclear transfer method, such as electro fusion or piezo microinjection, activation with chemical reagent [ionomycine/6-dimethylaminopurine (DMAP), calcium ionophore A23187/DMAP, or cycloheximide (CHX)] and reprogramming time (1, 2, or 4 h; in this study, the duration from injection or fusion to activation was defined as the reprogramming time). Our results showed that a 1-h reprogramming and activation with ionomycin/DMAP are suitable for NT in monkeys. Developing cleaved embryos up to the six-cell stage was similar among all experiments. However, beyond the eight-cell stage, developmental rates were higher in NT embryos reconstructed with fetal fibroblast cells and amniotic epithelial cells, and we were able to produce NT blastocysts from these cells. Interestingly, electro fusion is sufficient for amniotic epithelial cells and piezo microinjection is better suited for fetal fibroblast cells to produce NT blastocysts, thus suggesting that the best method for somatic cell NT may be different between cell types.

Centrosome inheritance after fertilization and nuclear transfer in mammals

Centrosomes, the main microrubule organizing centers in a cell, are nonmembrane-bound semi-conservative organelles consisting of numerous centrosome proteins that typically surround a pair of perpendicularly oriented cylindrical centrioles. Centrosome matrix is therefore oftentimes referred to as pericentriolar material (PCM). Through their microtubule organizing functions centrosomes are also crucial for transport and distribution of cell organelles such as mitochondria and macromolecular complexes. Centrosomes undergo cell cycle-specific reorganizations and dynamics. Many of the centrosome-associated proteins are transient and cell cycle-specific while others, such as y-tubulin, are permanently associated with centrosome structure. During gametogenesis, the spermatozoon retains its proximal centriole while losing most of the PCM, whereas the oocyte degenerates centrioles while retaining centrosomal proteins. In most mammals including humans, the spermatozoon contributes the proximal centriole during fertilization. Biparental centrosome contributions to the zygote are typical for most species with some exceptions such as the mouse in which centrosomes are maternally inherited and centrioles are assembled de novo during the blastocyst stage. After nuclear transfer in reconstructed embryos, the donor cell centrosome complex is responsible for carrying out functions that are typically fulfilled by the sperm centrosome complex during normal fertilization, including spindle organization, cell cycle progression and development. In rodents, donor cell centrioles are degraded after nuclear transfer, and centrosomal proteins from both donor cell and recipient oocytes contribute to mitotic spindle assembly. However, questions remain about the faithful reprogramming of centrosomes in cloned mammals and its consequences for embryo development. The molecular dynamics of donor cell centrosomes in nuclear transfer eggs need further analysis. The fate and functions of centrosome components in nuclear transfer embryos are being investigated by using molecular imaging of centrosome proteins labeled with specific markers including, but not limited to, green fluorescent protein (GFP).

Artificial insemination in black-handed spider monkey (Ateles geoffroyi)

Artificial insemination (AI) was performed in spider monkeys; these primates are vulnerable to extinction and usually do not reproduce spontaneously in captivity. Uterine cycles were followed by daily assessment of vaginal cytology, and corroborated a posteriori by concentrations of 17-beta estradiol and progesterone, measured by radioimmunoassay (RIA), in fecal samples collected once daily. Five females between 13 to 27 years old were inseminated intravaginally (with fresh semen) twice each during the periovulatory phase (Days 9-12 of the menstrual cycle; Day 0, first day of menstrual bleeding), from September to the first 3 weeks of November (most fertile months). Transcervical AI was not useful in this primate because the liquid portion of the semen completely solidified instead of liquefying as in other primates. Pregnancies were apparently achieved in 5 of 14 attempts. One female became pregnant after the first round of inseminations, delivered a healthy infant, was inseminated and got pregnant again (subsequently aborted). One female aborted, apparently due to an intramural uterine leiomyoma. Another two females stopped menstruating for a few months, then restarted menstruating (these females may have been pregnant and aborted). In conclusion, in spider monkeys: (1) captivity-induced stress did not inhibit reproduction; (2) fecal steroid hormones were useful to assess cyclicity; (3) the semen coagulum, which apparently is a tightly packed and large reservoir of spermatozoa, must not be discarded but used in AI; (4) old female spider monkeys did not have cessation of reproductive function.

Epigenetic Marks in Cloned Rhesus Monkey Embryos: Comparison with Counterparts Produced In Vitro1

Until now, no primate animals have been successfully cloned to birth with somatic cell nuclear transfer (SCNT) procedures, and little is known about the molecular events that occurred in the reconstructed embryos during preimplantation development. In many SCNT cases, epigenetic reprogramming of the donor nuclei after transfer into enucleated oocytes was hypothesized to be crucial to the reestablishment of embryonic totipotency. In the present study, we focused on two major epigenetic marks, DNA methylation and histone H3 lysine 9 (H3K9) acetylation, which we examined by indirect immunofluorescence and confocal laser scanning microscopy. During preimplantation development, 67% of two-cell- and 50% of eight-cell-cloned embryos showed higher DNA methylation levels than their in vitro fertilization (IVF) counterparts, which undergo gradual demethylation until the early morula stage. Moreover, whereas an asymmetric distribution of DNA methylation was established in an IVF blastocysts with a lower methylation level in the inner cell mass (ICM) than in the trophectoderm, in most cloned blastocysts, ICM cells maintained a high degree of methylation. Finally, two donor cell lines (S11 and S1-04) that showed a higher level of H3K9 acetylation supported more blastocyst formation after nuclear transfer than the other cell line (S1-03), with a relatively low level of acetylation staining. In conclusion, we propose that abnormal DNA methylation patterns contribute to the poor quality of cloned preimplantation embryos and may be one of the obstacles to successful cloning in primates.

Nuclear Transfer: Preservation of a Nuclear Genome at the Expense of Its Associated mtDNA Genome(s)

Nuclear transfer technology has uses across theoretical and applied applications, but advances are restricted by continued poor success rates and health problems associated with live offspring. Development of reconstructed embryos is dependent upon numerous interlinking factors relating both to the donor cell and the recipient oocyte. For example, abnormalities in gene expression following somatic cell nuclear transfer (SCNT) have been linked with an inability of the oocyte cytoplasm to sufficiently epigenetically reprogram the nucleus. Furthermore, influences on the propagation of mitochondria and mitochondrial DNA (mtDNA) could be of great importance in determining the early developmental potential of NT embryos and contributing to their genetic identity. mtDNA encodes some of the subunits of the electron transfer chain, responsible for cellular ATP production. The remaining subunits and those factors required for mtDNA replication, transcription and translation are encoded by the nucleus, necessitating precise intergenomic communication. Additionally, regulation of mtDNA copy number, via the processes of mtDNA transcription and replication, is essential for normal preimplantation embryo development and differentiation. Unimaternal transmission following natural fertilization usually results in the presence of a single identical population of mtDNA, homoplasmy. Heteroplasmy can result if mixed populations of mtDNA genomes co-exist. Many abnormalities observed in NT embryos, fetuses, and offspring may be caused by deficiencies in OXPHOS, perhaps resulting in part from heteroplasmic mtDNA populations. Additionally, incompatibilities between the somatic nucleus and the cytoplast may be exacerbated by increased genetic divergence between the two genomes. It is important to ensure that the nucleus is capable of sufficiently regulating mtDNA, requiring a level of compatibility between the two genomes, which may be a function of evolutionary distance. We suggest that abnormal expression of factors such as TFAM and POLG in NT embryos will prematurely drive mtDNA replication, hence impacting on early development.