Somatic Cell Nuclear Transfer Using Freeze-Dried Protaminized Donor Nuclei

Somatic cell nuclear transfer (SCNT) is the only nuclear reprogramming method that allows rewinding an adult nucleus into a totipotent state. As such, it offers excellent opportunities for the multiplication of elite genotypes or endangered animals, whose number have shrunk to below the threshold of safe existence. Disappointingly, SCNT efficiency is still low. Hence, it would be wise to store somatic cells from threatened animals in biobanks. We were the first to show that freeze-dried cells allow generating blastocysts upon SCNT. Only a few papers have been published on the topic since then, and viable offspring have not been produced. On the other hand, lyophilization of mammalian spermatozoa has made considerable progress, partially due to the physical stability that protamines provide to the genome. In our previous work, we have demonstrated that a somatic cell could be made more amenable to the oocyte reprogramming by the exogenous expression of human Protamine 1. Given that the protamine also provides natural protection against dehydration stress, we have combined the cell protaminization and lyophilization protocols. This chapter comprehensively describes the protocol for somatic cell protaminization, lyophilization, and its application in SCNT. We are confident that our protocol will be relevant for establishing somatic cells stocks amenable to reprogramming at low cost.

Production of mouse offspring from zygotes fertilized with freeze-dried spermatids

Mouse cloning by nuclear transfer using freeze-drying (FD) somatic cells is now possible, but the success rate is significantly lower than that of FD spermatozoa. Because spermatozoa, unlike somatic cells, are haploid cells with hardened nuclei due to protamine, the factors responsible for their tolerance to FD treatment remain unclear. In this study, we attempt to produce offspring from FD spermatid, a haploid sperm progenitor cell whose nuclei, like somatic cells, have not yet been replaced by protamine. We developed a method for collecting FD spermatids from testicular suspension. Despite the significantly lower success rate than that of FD spermatozoa, healthy offspring were obtained when FD spermatids were injected into oocytes. Offspring were also obtained from FD spermatids derived from immature male mice that had not yet produced spermatozoa. These results suggest that nuclear protaminization, rather than haploid nuclei, is one of the key processes responsible for tolerance to FD treatment.

Healthy cloned offspring derived from freeze-dried somatic cells

Maintaining biodiversity is an essential task, but storing germ cells as genetic resources using liquid nitrogen is difficult, expensive, and easily disrupted during disasters. Our aim is to generate cloned mice from freeze-dried somatic cell nuclei, preserved at -30 °C for up to 9 months after freeze drying treatment. All somatic cells died after freeze drying, and nucleic DNA damage significantly increased. However, after nuclear transfer, we produced cloned blastocysts from freeze-dried somatic cells, and established nuclear transfer embryonic stem cell lines. Using these cells as nuclear donors for re-cloning, we obtained healthy cloned female and male mice with a success rate of 0.2-5.4%. Here, we show that freeze-dried somatic cells can produce healthy, fertile clones, suggesting that this technique may be important for the establishment of alternative, cheaper, and safer liquid nitrogen-free bio-banking solutions.

Technical, Biological and Molecular Aspects of Somatic Cell Nuclear Transfer – A Review

Since the announcement of the birth of the first cloned mammal in 1997, Dolly the sheep, 24 animal species including laboratory, farm, and wild animals have been cloned. The technique for somatic cloning involves transfer of the donor nucleus of a somatic cell into an enucleated oocyte at the metaphase II (MII) stage for the generation of a new individual, genetically identical to the somatic cell donor. There is increasing interest in animal cloning for different purposes such as rescue of endangered animals, replication of superior farm animals, production of genetically engineered animals, creation of biomedical models, and basic research. However, the efficiency of cloning remains relatively low. High abortion, embryonic, and fetal mortality rates are frequently observed. Moreover, aberrant developmental patterns during or after birth are reported. Researchers attribute these abnormal phenotypes mainly to incomplete nuclear remodeling, resulting in incomplete reprogramming. Nevertheless, multiple factors influence the success of each step of the somatic cloning process. Various strategies have been used to improve the efficiency of nuclear transfer and most of the phenotypically normal born clones can survive, grow, and reproduce. This paper will present some technical, biological, and molecular aspects of somatic cloning, along with remarkable achievements and current improvements.

Evaluating the long-term effect of space radiation on the reproductive normality of mammalian sperm preserved on the International Space Station

Space radiation may cause DNA damage to cells and concern for the inheritance of mutations in offspring after deep space exploration. However, there is no way to study the long-term effects of space radiation using biological materials. Here, we developed a method to evaluate the biological effect of space radiation and examined the reproductive potential of mouse freeze-dried spermatozoa stored on the International Space Station (ISS) for the longest period in biological research. The space radiation did not affect sperm DNA or fertility after preservation on ISS, and many genetically normal offspring were obtained without reducing the success rate compared to the ground-preserved control. The results of ground x-ray experiments showed that sperm can be stored for more than 200 years in space. These results suggest that the effect of deep space radiation on mammalian reproduction can be evaluated using spermatozoa, even without being monitored by astronauts in Gateway.

Current Approaches of Preservation of Cells During (freeze-) Drying

The widespread application of therapeutic cells requires a successful stabilization of cells for the duration of transport and storage. Cryopreservation is currently considered the gold standard for the storage of active cells; however, (freeze-) drying cells could enable higher shelf life stability at ambient temperatures and facilitate easier transport and storage. During (freeze-) drying, freezing, (primary and secondary) drying and also the reconstitution step pose the risk of potential cell damage. To prevent these damaging processes, a wide range of protecting excipients has emerged, which can be classified, according to their chemical affiliation, into sugars, macromolecules, polyols, antioxidants and chelating agents. As many excipients cannot easily permeate the cell membrane, researchers have established various techniques to introduce especially trehalose intracellularly, prior to drying. This review aims to summarize the main damaging mechanisms during (freeze-) drying and to introduce the most common excipients with further details on their stabilizing properties and process approaches for the intracellular loading of excipients. Additionally, we would like to briefly explain recently discovered advantages of drying microorganisms, sperm, platelets, red blood cells, and eukaryotic cells, paying particular attention to the drying technique and residual moisture content.

Dry storage of mammalian spermatozoa and cells: state-of-the-art and possible future directions

This review provides a snapshot of the current state-of-the-art of drying cells and spermatozoa. The major successes and pitfalls of the most relevant literature are described separately for spermatozoa and cells. Overall, the data published so far indicate that we are closer to success in spermatozoa, whereas the situation is far more complex with cells. Critical for success is the presence of xeroprotectants inside the spermatozoa and, even more so, inside cells to protect subcellular compartments, primarily DNA. We highlight workable strategies to endow gametes and cells with the right combination of xeroprotectants, mostly sugars, and late embryogenesis abundant (LEA) or similar 'intrinsically disordered' proteins to help them withstand reversible desiccation. We focus on the biological aspects of water stress, and in particular cellular and DNA damage, but also touch on other still unexplored issues, such as the choice of both dehydration and rehydration methods or approaches, because, in our view, they play a primary role in reducing desiccation damage. We conclude by highlighting the need to exhaustively explore desiccation strategies other than lyophilisation, such as air drying, spin drying or spray drying, ideally with new prototypes, other than the food and pharmaceutical drying strategies currently used, tailored for the unique needs of cells and spermatozoa.

Dog cloning from post-mortem tissue frozen without cryoprotectant

Successful reproductive cloning depends on obtaining intact donor nuclei from viable cells, ideally isolated by tissue biopsy of a living donor. However, owners and veterinarians often freeze deceased animals, which eventually causes damage to cellular micro-organelles due to the formation of intracellular water crystals. In the present study, we have reported the production of viable cloned puppies using donor nuclei of cells obtained from frozen carcasses. Five cases of deceased and frozen canine specimens were presented to be cloned. Skin fibroblast cell lines were successfully established for four specimens. Significant longer time was needed for the cell growth from frozen tissues (4 days) to reach 80% confluency compared to fresh tissue and frozen tissues frozen for 1- or 2-days. Similarly, SA-βgal positive cells (death cells) were significantly higher in frozen cells for 2- or 4- days compared to samples from fresh or frozen (1 day) sources. The cloning efficiency (CE) and the pregnancy rates (PR) of frozen cells were lower than those obtained from fresh or living donors (CE 2.4 ± 1.8% vs. 0.6 ± 0.3%, PR 21.7 ± 16.1% vs. 7.7 ± 5.3% for fresh vs. frozen, respectively). Here we demonstrate is the possibility to produce healthy offspring from cell lines obtained from frozen tissue collected post-mortem.

Effect of chelating and antioxidant agents on morphology and DNA methylation in freeze-drying rabbit (Oryctolagus cuniculus) spermatozoa

Freeze-drying (FD) has been exhaustively tried in several mammalian species as an alternative technique to sperm cryopreservation, but few studies have been done in rabbits (Oryctolagus cuniculus). The main objective of this study was to compare the protective effect of various antioxidants added to EDTA medium on structural and functional components of FD rabbit spermatozoa and on their status of global DNA methylation. FD media used were composed of basic FD medium (10 mM Tris-HCl buffer and 50 mM NaCl) supplemented with either 50 mM EDTA alone (EDTA) or added with 105 µM of rosmarinic acid (RA, EDTA-RA) or 10 µM of melatonin (MLT, EDTA-MLT). The effect of each medium on the preservation of FD spermatozoon structure was evaluated with light and scanning electron microscopy (SEM). Global DNA methylation was quantified in all FD sperm samples as well as in fresh spermatozoa. Morphologically, fracture points were evidenced in the neck, mid and principal piece of the spermatozoon tail. No differences in spermatozoon fracture points were evidenced among FD treatments: intact spermatozoa were the largest (p < .01) category, whereas the most frequent (p < .01) injury was the neck fracture, resulting in tailless heads. At SEM, the head of spermatozoa showed a well-conserved shape and intact membrane in all treatments. DNA methylation status was the same in all FD treatments. In conclusion, supplementation of EDTA, EDTA-RA and EDTA-MLT during FD preserved rabbit sperm morphological integrity and methylation status as well. Therefore, the difficulty of getting viable offspring using FD semen is likely unrelated to the impact of the lyophilization process on DNA methylation and morphology of lyophilized spermatozoa.

Assessing the tolerance to room temperature and viability of freeze-dried mice spermatozoa over long-term storage at room temperature under vacuum

Freeze-drying has been frequently used to preserve food and microorganisms at room temperature (RT) for extended periods of time; however, its application to mammalian species is difficult. Here, we developed a method to prolong the stability of freeze-dried (FD) mice spermatozoa at RT for more than one year without using any cryoprotectant agents. Our data showed that maintaining a vacuum in ampoules is critical to ensuring the viability of FD spermatozoa, as the stability of spermatozoa DNA increased when imperfectly vacuumed ampoules were detected using a non-destructive test and eliminated. Finally a large number of healthy offspring were obtained from mice oocytes fertilized with FD spermatozoa stored at RT for more than one year. Although the birth rate from three-month stored spermatozoa was lower than that from one-day stored spermatozoa, no further reduction was observed even in one-year stored spermatozoa. Therefore, FD spermatozoa preserved in this study were highly tolerant to warm temperatures. This method of storage shows a great potential for the preservation of genetic resources of mammalian species, such as genetically-modified mouse strains, without the use of electric power.

Nuclear quiescence and histone hyper-acetylation jointly improve protamine-mediated nuclear remodeling in sheep fibroblasts

Recently we have demonstrated the possibility to replace histones with protamine, through the heterologous expression of human protamine 1 (hPrm1) gene in sheep fibroblasts. Here we have optimized protaminization of somatic nucleus by adjusting the best concentration and exposure time to trichostatin A (TSA) in serum-starved fibroblasts (nuclear quiescence), before expressing Prm1 gene. To stop cell proliferation, we starved cells in 0.5% FBS in MEM ("starved"-ST group), whereas in the Control group (CTR) the cells were cultured in 10% FBS in MEM. To find the most effective TSA concentration, we treated the cells with increasing concentrations of TSA in MEM + 10% FBS. Our results show that combination of cell culture conditions in 50 nM TSA, is more effective in terminating cell proliferation than ST and CTR groups (respectively 8%, 17.8% and 90.2% p<0.0001). Moreover, nuclear quiescence marker genes expression (Dicer1, Smarca 2, Ezh1 and Ddx39) confirmed that our culture conditions kept the cells in a nuclear quiescent state. Finally, ST and 50 nM TSA jointly increased the number of spermatid-like cell (39.4%) at higher rate compared to 25 nM TSA (20.4%, p<0.05) and 100 nM TSA (13.7%, p<0.05). To conclude, we have demonstrated that nuclear quiescence in ST cells and the open nuclear structure conferred by TSA resulted in an improved Prm1-mediated conversion of somatic nuclei into spermatid-like structures. This finding might improve nuclear reprogramming of somatic cells following nuclear transfer.

Freeze-drying of mammalian cells using trehalose: preservation of DNA integrity

The aim of this study was to investigate preservation of biomolecular structures, particularly DNA, in freeze-dried fibroblasts, after loading with trehalose via freezing-induced uptake. Cells were freeze-dried with trehalose alone or in a mixture of albumin and trehalose. Albumin was added to increase the glass transition temperature and storage stability. No viable cells were recovered after freeze-drying and rehydration. FTIR studies showed that membrane phase behavior of freeze-dried cells resembles that of fresh cells. However, one day after rehydration membrane phase separation was observed, irrespective of the presence or absence of trehalose during freeze-drying. Freeze-drying did not affect the overall protein secondary structure. Analysis of DNA damage via single cell gel electrophoresis (‘comet assay’) showed that DNA damage progressively increased with storage duration and temperature. DNA damage was prevented during storage at 4 °C. It is shown that trehalose reduces DNA damage during storage, whereas addition of albumin did not seem to have an additional protective effect on storage stability (i.e. DNA integrity) despite the fact that albumin increased the glass transition temperature. Taken together, DNA in freeze-dried somatic cells can be preserved using trehalose as protectant and storage at or below 4 °C.

Generation of cloned mice and nuclear transfer embryonic stem cell lines from urine-derived cells

Cloning animals by nuclear transfer provides the opportunity to preserve endangered mammalian species. However, there are risks associated with the collection of donor cells from the body such as accidental injury to or death of the animal. Here, we report the production of cloned mice from urine-derived cells collected noninvasively. Most of the urine-derived cells survived and were available as donors for nuclear transfer without any pretreatment. After nuclear transfer, 38–77% of the reconstructed embryos developed to the morula/blastocyst, in which the cell numbers in the inner cell mass and trophectoderm were similar to those of controls. Male and female cloned mice were delivered from cloned embryos transferred to recipient females, and these cloned animals grew to adulthood and delivered pups naturally when mated with each other. The results suggest that these cloned mice had normal fertility. In additional experiments, 26 nuclear transfer embryonic stem cell lines were established from 108 cloned blastocysts derived from four mouse strains including inbreds and F1 hybrids with relatively high success rates. Thus, cells derived from urine, which can be collected noninvasively, may be used in the rescue of endangered mammalian species by using nuclear transfer without causing injury to the animal.

Somatic cells, stem cells, and induced pluripotent stem cells: how do they now contribute to conservation?

More than a decade has now passed since the birth of the first endangered species produced from an adult somatic cell reprogrammed by somatic cell nuclear transfer. At that time, advances made in domestic and laboratory animal species provided the necessary foundation for attempting cutting-edge technologies on threatened and endangered species. In addition to nuclear transfer, spermatogonial stem cell transplantation and induction of pluripotent stem cells have also been explored. Although many basic scientific questions have been answered and more than 30 wild species have been investigated, very few successes have been reported. The majority of studies document numerous obstacles that still need to be overcome to produce viable gametes or embryos for healthy offspring production. This chapter provides an overview of somatic cell and stem cell technologies in different taxa (mammals, fishes, birds, reptiles and amphibians) and evaluates the potential and impact of these approaches for animal species conservation.

The value of frozen cartilage tissues without cryoprotection for genetic conservation

Animal tissues frozen without cryoprotection are thought to be inappropriate for use as a donor for somatic cell nuclear transfer (SCNT) studies. Cells in tissues that have been frozen without a cryoprotectant are commonly thought to be dead or to have lost genomic integrity. However, in this study we show that the frozen auricular cartilage tissues of anatolian buffalo contain a considerable number of viable healthy cells. The cells in auricular cartilage tissues are resistant to cryo-injury at -80°C. Primary cell cultures were established from defrosted ear tissues which were frozen without cryoprotectant. The growth and functional characteristics of primary cell cultures are characterized according to cell growth curve, cell cycle analysis, karyotype and GAG synthesis. The results indicate that frozen cartilage tissues could be valuable materials for the conservation of species and SCNT technology.

Sheep: the first large animal model in nuclear transfer research

The scope of this article is not to provide an exhaustive review of nuclear transfer research, because many authoritative reviews exist on the biological issues related to somatic and embryonic cell nuclear transfer. We shall instead provide an overview on the work done specifically on sheep and the value of this work on the greater nuclear transfer landscape.

Retention of structure and function of the cat germinal vesicle after air-drying and storage at suprazero temperature

The study explored a novel approach for preserving the maternal genome without the entire oocyte by air-drying the cat germinal vesicle (GV) in the presence of the disaccharide trehalose. Specifically, we examined GV structure and function after desiccation, storage at 4 °C (up to 32 wk), and rehydration including the ability to resume meiosis after injection into a fresh, conspecific cytoplast. In experiment 1, DNA integrity was similar to fresh controls after 1 and 4 wk storage in the presence of trehalose, but was more fragmented at later time points (especially after 32 wk). Nuclear envelope integrity was sustained in >90% of oocytes stored for 0, 4, or 16 wk regardless of protective treatment. In experiment 2, compacted, air-dried GVs were stored for 2 or 4 wk, rehydrated, and injected into fresh cytoplasts. After culture for 24 h in vitro, up to 73% of oocytes reconstructed with desiccated GVs preserved in trehalose resumed meiosis compared to 30% of those dried in the absence of the disaccharide. At each storage time point, trehalose presence during air-drying was advantageous for resumption of meiosis, with >20% of oocytes completing nuclear maturation to metaphase II. This demonstrates a potential for preserving the female genome using the GV alone and for multiple weeks after desiccation. Trehalose enhanced the process by retaining the ability of a dried and rehydrated GV to resume communication with the surrounding cytoplasm of the recipient oocyte to permit reaching metaphase II and likely sustain subsequent embryo development.

Recent advancements in cloning by somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) cloning is the sole reproductive engineering technology that endows the somatic cell genome with totipotency. Since the first report on the birth of a cloned sheep from adult somatic cells in 1997, many technical improvements in SCNT have been made by using different epigenetic approaches, including enhancement of the levels of histone acetylation in the chromatin of the reconstructed embryos. Although it will take a considerable time before we fully understand the nature of genomic programming and totipotency, we may expect that somatic cell cloning technology will soon become broadly applicable to practical purposes, including medicine, pharmaceutical manufacturing and agriculture. Here we review recent progress in somatic cell cloning, with a special emphasis on epigenetic studies using the laboratory mouse as a model.

Genomic stability of lyophilized sheep somatic cells before and after nuclear transfer

The unprecedented decline of biodiversity worldwide is urging scientists to collect and store biological material from seriously threatened animals, including large mammals. Lyophilization is being explored as a low-cost system for storage in bio-banks of cells that might be used to expand or restore endangered or extinct species through the procedure of Somatic Cell Nuclear Transfer (SCNT). Here we report that the genome is intact in about 60% of lyophylized sheep lymphocytes, whereas DNA damage occurs randomly in the remaining 40%. Remarkably, lyophilized nuclei injected into enucleated oocytes are repaired by a robust DNA repairing activity of the oocytes, and show normal developmental competence. Cloned embryos derived from lyophylized cells exhibited chromosome and cellular composition comparable to those of embryos derived from fresh donor cells. These findings support the feasibility of lyophylization as a storage procedure of mammalian cells to be used for SCNT.

Nuclear transfer in the mouse oocyte

The nuclear transfer (NT) technique in the mouse has enabled us to generate cloned mice and to establish NT embryonic stem (ntES) cells. Direct nuclear injection into mouse oocytes with a piezo impact drive unit can aid in the bypass of several steps of the original cell fusion procedure. It is important to note that only the NT approach can reveal dynamic and global modifications in the epigenome without using genetic modification as well as generating live animals from single cells. Thus, these techniques could also be applied to the preservation of genetic material from any mouse strain instead of preserving embryos or gametes. Moreover, with this technique, we can use not only living cells but also the nuclei of dead cells from frozen mouse carcasses for NT. This chapter describes our most recent protocols of NT into the mouse oocyte for cloning mice and for the establishment of ntES cells from cloned embryos.

Novel Approaches to the Cryopreservation of Human Spermatozoa: History and Development of the Spermatozoa Vitrification Technology

Cryobiology is very intensively applied in reproductive and veterinary medicine for preservation of gametes, embryos and reproductive tissues. Sub-zero temperatures combined with appropriate cryoprotective agents preserve the physiological and reproductive functions of the cells making long-term storage possible without loss of viability. With the use of cryoprotective agents it has become possible to develop cryopreservation techniques, such as the slow conventional freezing and vitrification that are in use in the present times. In slow controlled-rate conventional freezing extracellular ice crystals are formed whereas in vitrification no ice crystals are formed. Glass formation is compatible with the survival of the cell and the preservation of its intracellular structures provided the type(s) and concentrations of cryoprotectant used are not chemo- or osmotoxic. However, irrespective of the type of cooling method employed the cryosurvival of cells and tissues is influenced by the size and maturity of cells, amounts of intracellular water, quality and quantity of intracellular lipids, type of cells, their function and morphology. The intracellular milieu of cryopreserved cells and tissues remain less understood. The application of nanotechnology may help reveal and help advance our knowledge of the cryobiological principles involved in cryosurvival. At this moment the methods of cryopreservation that merit further investigation are vitrification and lyophilization. Vitrification is cheap if reagents are prepared in-house and the procedure can be performed rapidly. It has been successfully applied for gametes and embryos (of different stages of development), and reproductive cells/tissues, somatic cells and stem cells. However, vitrification is more demanding technically and requires operation and storage at sub-zero temperatures. On the other hand lyophilization deserves further investigation because it is a cheaper form of cryopreservation that may enable cryostorage at less demanding temperatures of 4°C and may even allow transport at ambient temperature. These possibilities are explored in this review.

Genome of non-living cells: trash or recycle?

Reproductive technologies have been often used as a tool in research not strictly connected with developmental biology. In this study, we retrace the experimental routes that have led to the adoption of two reproductive technologies, ICSI and somatic cell nuclear transfer (SCNT), as biological assays to probe the 'functionality' of the genome from dead cells. The structural peculiarities of the spermatozoa nucleus, namely its lower water content and its compact chromatin structure, have made it the preferred cell for these experiments. The studies, primarily focused on mice, have demonstrated an unexpected stability of the spermatozoa nuclei, which retained the capacity to form pronuclei once injected into the oocytes even after severe denaturing agents like acid treatment and high-temperature exposure. These findings inspired further research culminating in the production of mice after ICSI of lyophilized spermatozoa. The demonstrated non-equivalence between cell vitality and nuclear vitality in spermatozoa prompted analogous studies on somatic cells. Somatic cells were treated with the same physical stress applied to spermatozoa and were injected into enucleated sheep oocytes. Despite the presumptive fragile nuclear structure, nuclei from non-viable cells (heat treated) directed early and post-implantation embryonic development on nuclear transfer, resulting in normal offspring. Recently, lyophilized somatic cells used for nuclear transfer have developed into normal embryos. In summary, ICSI and SCNT have been useful tools to prove that alternative strategies for storing banks of non-viable cells are realistic. Finally, the potential application of freeze-dried spermatozoa and cells is also discussed.

Chromosomal integrity and DNA damage in freeze-dried spermatozoa

Freeze-drying technology may one day be used to preserve mammalian spermatozoa indefinitely without cryopreservation. Freeze-dried mouse spermatozoa stored below 4°C for up to 1 year have maintained the ability to fertilize oocytes and support normal development. The maximum storage period for spermatozoa increases at lower storage temperatures. Freeze-drying, per se, may reduce the integrity of chromosomes in freeze-dried mouse spermatozoa, but induction of chromosomal damage is suppressed if spermatozoa are incubated with divalent cation chelating agents prior to freeze-drying. Nevertheless, chromosomal damage does accumulate in spermatozoa stored at temperatures above 4°C. Currently, no established methods or strategies can prevent or reduce damage accumulation, and damage accumulation during storage is a serious obstacle to advances in freeze-drying technology. Chromosomal integrity of freeze-dried human spermatozoa have roughly background levels of chromosomal damage after storage at 4°C for 1 month, but whether these spermatozoa can produce healthy newborns is unknown. The safety of using freeze-dried human spermatozoa must be evaluated based on the risks of heritable chromosome and DNA damage that accumulates during storage.

Offspring from intracytoplasmic sperm injection of aged mouse oocytes treated with caffeine or MG132

Postovulatory mammalian oocytes age significantly in culture. B6D2F1 or ICR strain mouse oocytes were collected 16 h after hCG injection and then cultured for up to 40 h post hCG at 37 °C under 5% CO(2) in air. After intracytoplasmic sperm injection (ICSI), B6D2F1 and ICR oocytes lost full-term developmental potential by 30 h and 26 h after hCG administration, respectively. However, using supplementation with 10 mM caffeine or 1-5 μM of MG132, we could obtain live offspring from oocytes at 34 h (BDF1, 5%-21%) or 28 h (ICR, 5%-18%), whereas none were obtained from untreated aged oocytes. Caffeine maintained normal meiotic spindle morphology, whereas MG132 maintained maturation-promoting factor activity. These treatments did not affect the potential of fresh oocytes for fertilization and subsequent development. Thus, it should be safe to use these chemicals in routine in vitro fertilization and offspring could be generated by ICSI of aged fertilization failed oocytes.

Interspecies somatic cell nuclear transfer: a salvage tool seeking first aid

Much emphasis is currently given to the use of Interspecific Somatic Cell Nuclear Transfer (ISCNT) as a potential salvage tool for endangered animals. In this short review we present a survey on all data published so far on ISCNT, including abstract communication in international meetings. From the analysis of these data it appears that the results obtained are very preliminary and often confusing on the real stage of the embryonic development obtained. Moreover, the acronym ISCNT is improperly used because in many reports the nuclei and oocyte donor are not within the same species, but belong to different order and sometimes taxa, therefore, we classified all the ISCNT reports by allocating cell and oocyte donors to their respective order/species/class. The efficiency of cloning is low in all species owing to incomplete nuclear reprogramming of differentiated cells under the current procedures. ISCNT, however, poses additional hurdles which are rarely addressed in previously published work, and on which we focus in this review: mt/genomic DNA compatibility; embryonic genome activation of the donor nucleus by the recipient oocyte; availability of suitable foster mothers for ISCNT embryos. All these issues are discussed here, and possible solutions for the successful application of somatic cell nuclear transfer to endangered animals are also put forth.

Inhibition of class IIb histone deacetylase significantly improves cloning efficiency in mice

Since the first mouse clone was produced by somatic cell nuclear transfer, the success rate of cloning in mice has been extremely low. Some histone deacetylase inhibitors, such as trichostatin A and scriptaid, have improved the full-term development of mouse clones significantly, but the mechanisms allowing for this are unclear. Here, we found that two other specific inhibitors, suberoylanilide hydroxamic acid and oxamflatin, could also reduce the rate of apoptosis in blastocysts, improve the full-term development of cloned mice, and increase establishment of nuclear transfer-generated embryonic stem cell lines significantly without leading to obvious abnormalities. However, another inhibitor, valproic acid, could not improve cloning efficiency. Suberoylanilide hydroxamic acid, oxamflatin, trichostatin A, and scriptaid are inhibitors for classes I and IIa/b histone deacetylase, whereas valproic acid is an inhibitor for classes I and IIa, suggesting that inhibiting class IIb histone deacetylase is an important step for reprogramming mouse cloning efficiency.

Functional full-term placentas formed from parthenogenetic embryos using serial nuclear transfer

Mammalian parthenogenetic embryos invariably die in mid-gestation from imprinted gene defects and placental hypoplasia. Based on chimera experiments, trophoblastic proliferation is supposed to be inhibited in the absence of a male genome. Here, we show that parthenogenetic mouse embryonic cell nuclei can be reprogrammed by serial rounds of nuclear transfer without using any genetic modification. The durations of survival in uteri of cloned foetuses derived from green fluorescent protein (GFP)-labelled parthenogenetic cell nuclei were extended with repeated nuclear transfers. After five repeats, live cloned foetuses were obtained up to day 14.5 of gestation; however, they did not survive longer even when we repeated nuclear transfer up to nine times. All foetuses showed intestinal herniation and possessed well-expanded large placentas. When embryonic stem (ES) cells derived from fertilised embryos were aggregated with the cloned embryos, full-term offspring with large placentas were obtained from the chimeric embryos. Those placentas were derived from parthenogenetic cell nuclei, judging from GFP expression. The patterns of imprinted gene expression and methylation status were similar to their parthenogenetic origin, except for Peg10, which showed the same level as in the normal placenta. These results suggest that there is a limitation for foetal development in the ability to reprogramme imprinted genes by repeated rounds of nuclear transfer. However, the placentas of parthenogenetic embryos can escape epigenetic regulation when developed using nuclear transfer techniques and can support foetal development to full gestation.

Effect of trichostatin A on chromatin remodeling, histone modifications, DNA replication, and transcriptional activity in cloned mouse embryos

Our group and others have found that the treatment of embryos with trichostatin A (TSA) after cloning by somatic cell nuclear transfer (SCNT) results in a significant improvement in efficiency. We believe that TSA treatment improves nuclear remodeling via histone modifications, which are important in the epigenetic regulation of gene silencing and expression. Some studies found that treatment of SCNT-generated embryos with TSA improved lysine acetylation of core histones in a manner similar to that seen in normally fertilized embryos. However, how histone methylation is modified in TSA-treated cloned embryos is not completely understood. In the present study, we found that TSA treatment caused an increase in chromosome decondensation and nuclear volume in SCNT-generated embryos similar to that in embryos produced by intracytoplasmic sperm injection. Histone acetylation increased in parallel with chromosome decondensation. This was associated with a more effective formation of DNA replication complexes in treated embryos. We also found a differential effect of TSA on the methylation of histone H3 at positions K4 and K9 in SCNT-generated embryos that could contribute to genomic reprogramming of the somatic cell nuclei. In addition, using 5-bromouridine 5'-triphosphate-labeled RNA, we showed that TSA enhanced the levels of newly synthesized RNA in 2-cell embryos. Interestingly, the amount of SCNT-generated embryos showing asymmetric expression of nascent RNA was reduced significantly in the TSA-treated group compared with the nontreated group at the 2-cell stage. We conclude that the incomplete and inaccurate genomic reprogramming of SCNT-generated embryos was improved by TSA treatment. This could enhance the reprogramming of somatic nuclei in terms of chromatin remodeling, histone modifications, DNA replication, and transcriptional activity.

How to improve the success rate of mouse cloning technology

It has now been 13 years since the first cloned mammal Dolly the sheep was generated from somatic cells using nuclear transfer (SCNT). Since then, this technique has been considered an important tool not only for animal reproduction but also for regenerative medicine. However, the success rate is still very low and the mechanisms involved in genomic reprogramming are not yet clear. Moreover, the NT technique requires donated fresh oocyte, which raises ethical problems for production of human cloned embryo. For this reason, the use of induced pluripotent stem cells for genomic reprogramming and for regenerative medicine is currently a hot topic in this field. However, we believe that the NT approach remains the only valid way for the study of reproduction and basic biology. For example, only the NT approach can reveal dynamic and global modifications in the epigenome without using genetic modification, and it can generate offspring from a single cell or even a frozen dead body. Thanks to much hard work by many groups, cloning success rates are increasing slightly year by year, and NT cloning is now becoming a more applicable method. This review describes how to improve the efficiency of cloning, the establishment of clone-derived embryonic stem cells and further applications.

Preservation of sperm within the mouse cauda epididymidis in salt or sugars at room temperature

The development of preservation techniques for male gametes at room temperature might allow us to store them in a simple and cost-effective manner. In this study, we studied the use of pure salt or sugar to preserve the whole cauda epididymidis, because it is known that food can be preserved in this way at room temperature for long periods. Mouse epididymides were placed directly in powdered salt (NaCl) or sugars (glucose or raffinose) for 1 day to 1 year at room temperature. Spermatozoa were recovered from the preserved organs after being rehydrated with medium and then isolated sperm heads were microinjected into fresh oocytes. Importantly, the oocyte activation capacity of spermatozoa was maintained after epididymal storage in NaCl for 1 year, whereas most untreated spermatozoa failed to activate oocytes within 1 month of storage. Pronuclear morphology, the rate of extrusion of a second polar body and the methylation status of histone H3 lysine 9 (H3K9me3) in those zygotes were similar to those of zygotes fertilized with fresh spermatozoa. However, the developmental ability of the zygotes decreased within 1 day of sperm storage. This effect led to nuclear fragmentation at the 2-cell embryo stage, irrespective of the storage method used. Thus, although the preserved sperm failed to allow embryo development, their oocyte activation factors were maintained by salt storage of the epididymis for up to 1 year at room temperature.

Sex-reversed somatic cell cloning in the mouse

Somatic cell nuclear transfer has many potential applications in the fields of basic and applied sciences. However, it has a disadvantage that can never be overcome technically-the inflexibility of the sex of the offspring. Here, we report an accidental birth of a female mouse following nuclear transfer using an immature Sertoli cell. We produced a batch of 27 clones in a nuclear transfer experiment using Sertoli cells collected from neonatal male mice. Among them, one pup was female. This "male-derived female" clone grew into a normal adult and produced offspring by natural mating with a littermate. Chromosomal analysis revealed that the female clone had a 39,X karyotype, indicating that the Y chromosome had been deleted in the donor cell or at some early step during nuclear transfer. This finding suggests the possibility of resuming sexual reproduction after a single male is cloned, which should be especially useful for reviving extinct or endangered species.

Cloning of ES cells and mice by nuclear transfer

We have been able to develop a stable nuclear transfer (NT) method in the mouse, in which donor nuclei are directly injected into the oocyte using a piezo-actuated micromanipulator. Although the piezo unit is a complex tool, once mastered it is of great help not only in NT experiments, but also in almost all other forms of micromanipulation. Using this technique, embryonic stem (ntES) cell lines established from somatic cell nuclei can be generated relatively easily from a variety of mouse genotypes and cell types. Such ntES cells can be used not only for experimental models of human therapeutic cloning but also as a means of preserving mouse genomes instead of preserving germ cells. Here, we describe our most recent protocols for mouse cloning.

Production of healthy cloned mice from bodies frozen at -20 degrees C for 16 years

Cloning animals by nuclear transfer provides an opportunity to preserve endangered mammalian species. However, it has been suggested that the "resurrection" of frozen extinct species (such as the woolly mammoth) is impracticable, as no live cells are available, and the genomic material that remains is inevitably degraded. Here we report production of cloned mice from bodies kept frozen at -20 degrees C for up to 16 years without any cryoprotection. As all of the cells were ruptured after thawing, we used a modified cloning method and examined nuclei from several organs for use in nuclear transfer attempts. Using brain nuclei as nuclear donors, we established embryonic stem cell lines from the cloned embryos. Healthy cloned mice were then produced from these nuclear transferred embryonic stem cells by serial nuclear transfer. Thus, nuclear transfer techniques could be used to "resurrect" animals or maintain valuable genomic stocks from tissues frozen for prolonged periods without any cryopreservation.