Increasing efficiency in production of cloned piglets

Treatment of Donor Cells with Oxidative Phosphorylation Inhibitor CPI Enhances Porcine Cloned Embryo Development

Somatic cell nuclear transfer (SCNT) technology holds great promise for livestock industry, life science and human biomedicine. However, the development and application of this technology is limited by the low developmental potential of SCNT embryos. The developmental competence of cloned embryos is influenced by the energy metabolic status of donor cells. The purpose of this study was to investigate the effects of CPI, an oxidative phosphorylation inhibitor, on the energy metabolism pathways of pig fibroblasts and the development of subsequent SCNT embryos. The results showed that treatment of porcine fibroblasts with CPI changed the cellular energy metabolic pathways from oxidative phosphorylation to glycolysis and enhanced the developmental ability of subsequent SCNT embryos. The present study establishes a simple, new way to improve pig cloning efficiency, helping to promote the development and application of pig SCNT technology.

Production of Cloned Pigs by Handmade Cloning

Somatic cell nuclear transfer (SCNT) in pigs is a promising technology in biomedical research by association with transgenesis for xenotransplantation and disease modeling technologies. Handmade cloning (HMC) is a simplified SCNT method that does not require micromanipulators and facilitates the generation of cloned embryos in large quantities. As a result of HMC fine-tuning for porcine-specific requirements of both oocytes and embryos, HMC has become uniquely efficient (>40% blastocyst rate, 80-90% pregnancy rates, 6-7 healthy offspring per farrowing, and with negligible losses and malformations). Therefore, this chapter describes our HMC protocol to obtain cloned pigs.

An Alternative Way to Improve Mammalian Embryo Development In Vitro: Culture of Zona Pellucida-Free Embryos

An increasing number of data proves that the presence of the zona pellucida is not essential to mammalian embryo production, including maturation, fertilization, and embryo culture. In fact, the structure of the zona pellucida of in vitro-produced embryos differs significantly from its in vivo counterpart, influencing metabolism and requiring disproportionate efforts to crack open at the time of hatching. This review aims to focus attention on this field and stimulate research in zona-free embryo culture. In domestic animals, extensive application of purpose-designed culture systems for zona-free embryos proved the feasibility of this approach. It may open new possibilities and increase efficiency in both transgenic research and human-assisted reproduction.

Influence of oocyte selection, activation with a zinc chelator and inhibition of histone deacetylases on cloned porcine embryo and chemically activated oocytes development

The aim of this study was to evaluate the effects of alternative protocols to improve oocyte selection, embryo activation and genomic reprogramming on in vitro development of porcine embryos cloned by somatic cell nuclear transfer (SCNT). In Experiment 1, in vitro-matured oocytes were selected by exposure to a hyperosmotic sucrose solution prior to micromanipulation. In Experiment 2, an alternative chemical activation protocol using a zinc chelator as an adjuvant (ionomycin + N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) + N-6-dimethylaminopurine (6-DMAP)) was compared with a standard protocol (ionomycin + 6-DMAP) for the activation of porcine oocytes or SCNT embryos. In Experiment 3, presumptive cloned zygotes were incubated after chemical activation in a histone deacetylase inhibitor (Scriptaid) for 15 h, with the evaluation of embryo yield and total cell number in day 7 blastocysts. In Experiment 1, cleavage rates tended to be higher in sucrose-treated oocytes than controls (123/199, 61.8% vs. 119/222, 53.6%, respectively); however, blastocyst rates were similar between groups. In Experiment 2, cleavage rates were higher in zygotes treated with TPEN than controls but no difference in blastocyst rates between groups occurred. For Experiment 3, the exposure to Scriptaid did not improve embryo development after cloning. Nevertheless, the total number of cells was higher in cloned zygotes treated with Scriptaid than SCNT controls. In conclusion, oocyte selection by sucrose as well as treatments with zinc chelator and an inhibitor of histone deacetylases did not significantly improve blastocyst yield in cloned and parthenotes. However, the histone deacetylases inhibitor produced a significant improvement in the blastocyst quality.

Improved preimplantation development of porcine somatic cell nuclear transfer embryos by caffeine treatment

This study examined the effects of a caffeine treatment to improve nuclear reprogramming in porcine cloned embryos. Embryonic development and the expression of genes related to pluripotency (POU5F1, SOX2, NANOG, and CDX2) were compared after caffeine supplementation during manipulation at different concentrations (0, 1.25, 2.5, and 5.0 mM) and after varying the delayed activation time (control, 1, 2, and 4 h) after fusion. Caffeine added to media during manipulation produced a higher rate of development to blastocysts in the 1.25 mM group than in the other concentration groups (22.8% vs. 16.1%, 16.2%, and 19.2%; p < 0.05). When caffeine was added during the 4 h delayed activation, the 1.25 mM caffeine concentration produced a significantly higher rate of development than those in the other 4 h-activation-delayed caffeine concentration groups (22.4% vs. 9.4%, 14.0%, and 11.1%; p < 0.05). On the other hand, no significant improvement over that in the control group was observed when caffeine was supplemented during both the manipulation period and delayed activation period (16.0% vs. 15.2%), respectively. The levels of POU5F1, SOX2, and NANOG expression in blastocysts were significantly higher in the delayed activation caffeine group (4 h, 1.25 mM) than in the control group (1 h, 0 mM; p < 0.05). In conclusion, a caffeine treatment at 1.25 mM during delayed activation for 4 h can improve the preimplantation development of porcine somatic cell nuclear transfer embryos by activating nuclear reprogramming.

Cloning: A Sleeping Beauty Awaiting the Kiss?

The first 20 years of somatic cell nuclear transfer can hardly be described as a success story. Controversially, many factors leading to the fiasco are not intrinsic features of the technique itself. Misunderstandings and baseless accusations alongside with unsupported fears and administrative barriers hampered cloners to overcome the initial challenging period with obvious difficulties that are common features of a radically new approach. In spite of some promising results of mostly sporadic and small-scale experiments, the future of cloning is still uncertain. On the other hand, a reincarnation, just like the idea of electric cars, may result in many benefits in various areas of science and economy. One can only hope that-in contrast to electric cars-the ongoing paralyzed phase will not last for 100 years, and breakthroughs achieved in some promising areas will provide enough evidence to intensify research and large-scale application of cloning in the next decade.

High Pregnancy and Calving Rates with a Limited Number of Transferred Handmade Cloned Bovine Embryos

A major obstacle of widespread commercial application of bovine somatic cell nuclear transfer is the low overall efficiency, that is, healthy calf-late pregnancy per transferred embryo rate. In this study, we report a series of experiments with a limited number of embryos created with handmade cloning (HMC) and transferred without or after open pulled straw vitrification. Embryo reconstruction was performed by using in vitro matured oocytes and adult ear skin fibroblasts. In two experiments, a total of 53 D7 blastocysts were developed from 188 reconstructed embryos. Fresh transfer of seven blastocysts into six recipients has resulted in three early pregnancies, two of them developed over 90 days and eventually resulted in healthy calves (33% offspring/transfer rate). In another two experiments, a total of 11 D7 blastocysts were obtained from 36 reconstructed embryos. Out of these, eight have reexpanded 18 hours after vitrification and warming. Transfer of these blastocysts into eight recipients has resulted in four early pregnancies and two live births; 25% offspring/transfer rate. These results indicate that low overall efficiency may not be an intrinsic feature of cattle cloning, and selection of the right procedures may help to overcome the actual limitations.

Production of Genetically Engineered Porcine Embryos by Handmade Cloning

Genetic engineering is essential to realize the full potentials of pigs both as livestock and as animal models of human disease. With the development of new genetic engineering technologies, such as the clustered regularly interspaced short palindromic repeats-associated endonuclease 9 (CRISPR/Cas9) system, the porcine genome can be engineered with high efficiency. In this chapter, we describe a protocol in employing the CRISPR/Cas9 system to genetically engineer the porcine genome in fibroblast cells, the procedures to establish single-cell-derived porcine fibroblast cell colonies carrying the desired genetic modifications, and the handmade cloning (HMC) technique to generate cloned embryos ready for embryo transfer.

Developmental Competence and Epigenetic Profile of Porcine Embryos Produced by Two Different Cloning Methods

The "Dolly" based cloning (classical nuclear transfer, [CNT]) and the handmade cloning (HMC) are methods that are nowadays routinely used for somatic cloning of large domestic species. Both cloning protocols share several similarities, but differ with regard to the required in vitro culture, which in turn results in different time intervals until embryo transfer. It is not yet known whether the differences between cloned embryos from the two protocols are due to the cloning methods themselves or the in vitro culture, as some studies have shown detrimental effects of in vitro culture on conventionally produced embryos. The goal of this study was to unravel putative differences between two cloning methods, with regard to developmental competence, expression profile of a panel of developmentally important genes and epigenetic profile of porcine cloned embryos produced by either CNT or HMC, either with (D5 or D6) or without (D0) in vitro culture. Embryos cloned by these two methods had a similar morphological appearance on D0, but displayed different cleavage rates and different quality of blastocysts, with HMC embryos showing higher blastocyst rates (HMC vs. CNT: 35% vs. 10%, p < 0.05) and cell numbers per blastocyst (HMC vs. CNT: 31 vs. 23 on D5 and 42 vs. 18 on D6, p < 0.05) compared to CNT embryos. With regard to histone acetylation and gene expression, CNT and HMC derived cloned embryos were similar on D0, but differed on D6. In conclusion, both cloning methods and the in vitro culture may affect porcine embryo development and epigenetic profile. The two cloning methods essentially produce embryos of similar quality on D0 and after 5 days in vitro culture, but thereafter both histone acetylation and gene expression differ between the two types of cloned embryos.

Genetically engineered pigs as models for human disease

Genetically modified animals are vital for gaining a proper understanding of disease mechanisms. Mice have long been the mainstay of basic research into a wide variety of diseases but are not always the most suitable means of translating basic knowledge into clinical application. The shortcomings of rodent preclinical studies are widely recognised, and regulatory agencies around the world now require preclinical trial data from nonrodent species. Pigs are well suited to biomedical research, sharing many similarities with humans, including body size, anatomical features, physiology and pathophysiology, and they already play an important role in translational studies. This role is set to increase as advanced genetic techniques simplify the generation of pigs with precisely tailored modifications designed to replicate lesions responsible for human disease. This article provides an overview of the most promising and clinically relevant genetically modified porcine models of human disease for translational biomedical research, including cardiovascular diseases, cancers, diabetes mellitus, Alzheimer's disease, cystic fibrosis and Duchenne muscular dystrophy. We briefly summarise the technologies involved and consider the future impact of recent technical advances.

Summary: An overview of porcine models of human disease, including cardiovascular diseases, cancers, diabetes mellitus, Alzheimer's disease, cystic fibrosis and Duchenne muscular dystrophy. We summarise the technologies involved and potential future impact of recent technical advances.

Evaluation of porcine stem cell competence for somatic cell nuclear transfer and production of cloned animals

Porcine somatic cell nuclear transfer (SCNT) has been used extensively to create genetically modified pigs, but the efficiency of the methodology is still low. It has been hypothesized that pluripotent or multipotent stem cells might result in increased SCNT efficacy as these cells are closer than somatic cells to the epigenetic state found in the blastomeres and therefore need less reprogramming. Our group has worked with porcine SCNT during the last 20 years and here we describe our experience with SCNT of 3 different stem cell lines. The porcine stem cells used were: Induced pluripotent stem cells (iPSCs) created by lentiviral doxycycline-dependent reprogramming and cultered with a GSK3β- and MEK-inhibitor (2i) and leukemia inhibitor factor (LIF) (2i LIF DOX-iPSCs), iPSCs created by a plasmid-based reprogramming and cultured with 2i and fibroblast growth factor (FGF) (2i FGF Pl-iPSCs) and embryonic germ cells (EGCs), which have earlier been characterized as being multipotent. The SCNT efficiencies of these stem cell lines were compared with that of the two fibroblast cell lines from which the iPSC lines were derived. The blastocyst rates for the 2i LIF DOX-iPSCs were 14.7%, for the 2i FGF Pl-iPSC 10.1%, and for the EGCs 34.5% compared with the fibroblast lines yielding 36.7% and 25.2%. The fibroblast- and EGC-derived embryos were used for embryo transfer and produced live offspring at similar low rates of efficiency (3.2 and 4.0%, respectively) and with several instances of malformations. In conclusion, potentially pluripotent porcine stem cells resulted in lower rates of embryonic development upon SCNT than multipotent stem cells and differentiated somatic cells.

Successful cloning of an adult breeding boar from the novel Chinese Guike No. 1 swine specialized strain

Somatic cloning, also known as somatic cell nuclear transfer (SCNT), is a promising technology which has been expected to rapidly extend the population of elaborately selected breeding boars with superior production performance. Chinese Guike No. 1 pig breed is a novel swine specialized strain incorporated with the pedigree background of Duroc and Chinese Luchuan pig breeds, thus inherits an excellent production performance. The present study was conducted to establish somatic cloning procedures of adult breeding boars from the Chinese Guike No. 1 specialized strain. Ear skin fibroblasts were first isolated from a three-year-old Chinese Guike No. 1 breeding boar, and following that, used as donor cell to produce nuclear transfer embryos. Such cloned embryos showed full in vitro development and with the blastocyst formation rate of 18.4 % (37/201, three independent replicates). Finally, after transferring of 1187 nuclear transfer derived embryos to four surrogate recipients, six live piglets with normal health and development were produced. The overall cloning efficiency was 0.5 % and the clonal provenance of such SCNT derived piglets was confirmed by DNA microsatellite analysis. All of the cloned piglets were clinically healthy and had a normal weight at 1 month of age. Collectively, the first successful cloning of an adult Chinese Guike No. 1 breeding boar may lay the foundation for future improving the pig production industry.

Effect of histone acetylation modification with MGCD0103, a histone deacetylase inhibitor, on nuclear reprogramming and the developmental competence of porcine somatic cell nuclear transfer embryos

Cloning remains as an important technique to enhance the reconstitution and distribution of animal population with high-genetic merit. One of the major detrimental factors of this technique is the abnormal epigenetic modifications. MGCD0103 is known as a histone deacetylase inhibitor. In this study, we investigated the effect of MGCD0103 on the in vitro blastocyst formation rate in porcine somatic cell nuclear transferred (SCNT) embryos and expression in acetylation of the histone H3 lysine 9 and histone H4 lysine 12. We compared the in vitro embryonic development of SCNT embryos treated with different concentrations of MGCD0103 for 24 hours. Our results reported that treating with 0.2-μM MGCD0103 for 24 hours effectively improved the development of SCNT embryos, in comparison to the control group (blastocyst formation rate, 25.5 vs. 10.7%, P < 0.05). Then we tested the in vitro development of SCNT embryos treated with 0.2-μM MGCD0103 for various intervals after activation. Treatment for 6 hours significantly improved the development of pig SCNT embryos, compared with the control group (blastocyst formation rate, 21.2 vs. 10.5%, P < 0.05). Furthermore, MGCD0103 supplementation significantly (P < 0.05) increases the average fluorescence intensity of AcH3K9 and AcH4K12 in embryos at the pseudo-pronuclear stage. To examine the in vivo development, MGCD0103-treated SCNT embryos were transferred into two surrogate sows, one of whom became pregnant and three fetuses developed. These results suggest that MGCD0103 can enhance the nuclear reprogramming and improve in vitro developmental potential of porcine SCNT embryos.

Efficient production of biallelic GGTA1 knockout pigs by cytoplasmic microinjection of CRISPR/Cas9 into zygotes

BACKGROUND

Xenotransplantation is considered to be a promising solution to the growing demand for suitable donor organs for transplantation. Despite tremendous progress in the generation of pigs with multiple genetic modifications thought to be necessary to overcoming the severe rejection responses after pig-to-non-human primate xenotransplantation, the production of knockout pigs by somatic cell nuclear transfer (SCNT) is still an inefficient process. Producing genetically modified pigs by intracytoplasmic microinjection of porcine zygotes is an alluring alternative. The porcine GGTA1 gene encodes for the α1,3-galactosyltransferase that synthesizes the Gal epitopes on porcine cells which constitute the major antigen in a xenotransplantation setting. GGTA1-KO pigs have successfully been produced by transfecting somatic cells with zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), or CRISPR/Cas targeting GGTA1, followed by SCNT.

METHODS

Here, we microinjected a CRISPR/Cas9 vector coding for a single-guide RNA (sgRNA) targeting exon 8 of the GGTA1 gene into the cytoplasm of 97 in vivo-derived porcine zygotes and transferred 86 of the microinjected embryos into three hormonally synchronized recipients. Fetuses and piglets were analyzed by flow cytometry for remaining Gal epitopes. DNA was sequenced to detect mutations at the GGTA1 locus.

RESULTS

Two of the recipients remained pregnant as determined by ultrasound scanning on day 25 of gestation. One pregnancy was terminated on day 26, and six healthy fetuses were recovered. The second pregnancy was allowed to go to term and resulted in the birth of six healthy piglets. Flow cytometry analysis revealed the absence of Gal epitopes in four of six fetuses (66%), indicating a biallelic KO of GGTA1. Additionally, three of the six live-born piglets (50%) did not express Gal epitopes on their cell surface. Two fetuses and two piglets showed a mosaicism with a mixed population of Gal-free and Gal-expressing cells. Only a single piglet did not have any genomic modifications. Genomic sequencing revealed indel formation at the GGTA1 locus ranging from +17 bp to -20 bp.

CONCLUSIONS

These results demonstrate the efficacy of CRISPR/Cas to generate genetic modifications in pigs by simplified technology, such as intracytoplasmic microinjection into zygotes, which would significantly facilitate the production of genetically modified pigs suitable for xenotransplantation. Importantly, this simplified injection protocol avoids the penetration of the vulnerable pronuclear membrane, and is thus compatible with higher survival rates of microinjected embryos, which in turn facilitates production of genetically modified piglets.

Ovulation Statuses of Surrogate Gilts Are Associated with the Efficiency of Excellent Pig Cloning

Somatic cell nuclear transfer (SCNT) is an assisted reproductive technique that can produce multiple copies of excellent livestock. However, low cloning efficiency limits the application of SCNT. In this study, we systematically investigated the major influencing factors related to the overall cloning efficiency in pigs. Here, 13620 cloned embryos derived from excellent pigs were transferred into 79 surrogate gilts, and 119 live cloned piglets were eventually generated. During cloning, group of cloned embryos derived from excellent Landrace or Large white pigs presented no significant differences of cleavage and blastocyst rates, blastocyst cell numbers, surrogate pregnancy and delivery rates, average numbers of piglets born and alive and cloning efficiencies, and group of 101-150, 151-200 or 201-250 cloned embryos transferred per surrogate also displayed a similar developmental efficiency. When estrus stage of surrogate gilts was compared, group of embryo transfer on Day 2 of estrus showed significantly higher pregnancy rate, delivery rate, average number of piglets born, average alive piglet number or cloning efficiency than group on Day 1, Day 3, Day 4 or Day 5, respectively (P<0.05). And, in comparison with the preovulation and postovulation groups, group of surrogate gilts during periovulation displayed a significantly higher overall cloning efficiency (P<0.05). Further investigation of surrogate estrus stage and ovulation status displayed that ovulation status was the real factor underlying estrus stage to determine the overall cloning efficiency. And more, follicle puncture for preovulation, not transfer position shallowed for preovulation or deepened for postovulation, significantly improved the average number of piglets alive and cloning efficiency (P<0.05). In conclusion, our results demonstrated that ovulation status of surrogate gilts was the fundamental factor determining the overall cloning efficiency of excellent pigs, and follicle puncture, not transfer position change, improved cloning efficiency. This work would have important implications in preserving and breeding excellent livestock and improving the overall cloning efficiency.

Artificial cloning of domestic animals

Domestic animals can be cloned using techniques such as embryo splitting and nuclear transfer to produce genetically identical individuals. Although embryo splitting is limited to the production of only a few identical individuals, nuclear transfer of donor nuclei into recipient oocytes, whose own nuclear DNA has been removed, can result in large numbers of identical individuals. Moreover, clones can be produced using donor cells from sterile animals, such as steers and geldings, and, unlike their genetic source, these clones are fertile. In reality, due to low efficiencies and the high costs of cloning domestic species, only a limited number of identical individuals are generally produced, and these clones are primarily used as breed stock. In addition to providing a means of rescuing and propagating valuable genetics, somatic cell nuclear transfer (SCNT) research has contributed knowledge that has led to the direct reprogramming of cells (e.g., to induce pluripotent stem cells) and a better understanding of epigenetic regulation during embryonic development. In this review, I provide a broad overview of the historical development of cloning in domestic animals, of its application to the propagation of livestock and transgenic animal production, and of its scientific promise for advancing basic research.

Postmortem findings in cloned and transgenic piglets dead before weaning

Important factors contributing to the well-known high mortality of piglets produced by SCNT are gross malformations of vital organs. The aim of the present retrospective study was to describe malformations found in cloned piglets, transgenic or not, dying or culled before weaning on Day 28. Large White (LW) embryos were transferred to 78 LW recipients, while 72 recipients received Göttingen embryos (67 transgenic and five not transgenic) and 56 received Yucatan embryos (43 transgenic and 13 not transgenic). Overall pregnancy rate was 76%, and there were more abortions in recipients with minipig embryos than in those with LW embryos (26% and 24% vs. 6%). Piglets (n = 815) were born from 128 sows with 6.5 ± 0.4 full-born piglets per litter. The overall rate of stillborn piglets was 21% of all born with the number of stillborn piglets ranging from one to nine in a litter. The mortality of the surviving piglets during the first month was 48%. Thus, altogether 58% of the full-born piglets died before weaning. In 87 of the 128 litters (68%), one to 12 of the piglets showed major or minor malformations. Malformations were found in 232 piglets (29.5% of all born). A single malformation was registered in 152 piglets, but several piglets showed two (n = 58) or more (n = 23) malformations (7.4% and 2.8% of all born, respectively). A significantly higher malformation rate was found in transgenic Göttingen and Yucatan piglets (32% and 46% of all born, respectively) than in nontransgenic LW (17%). There was a gender difference in the transgenic minipigs because male piglets had a higher rate of malformations (49.1%) than females (29.7%). The most common defects in the cloned piglets were in the digestive (12.2%), circulatory (9.4%), reproductive (11.3%), and musculoskeletal (9.1%) systems. Malformations of the musculoskeletal system were most frequent in Göttingen (16.3% vs. approximately 5.5% in the two other breeds), whereas abnormal cardiopulmonary systems were most frequent in Yucatan piglets (26.9% vs. 2.1% in LW and 5.3% in Göttingen). In conclusion, these results show that pig cloning results in a considerable loss of piglets and that many of these can be related to various malformations that all are also seen in noncloned piglets. Because approximately half of the cloned piglets still survive, even with eventual unknown minor malformations, use of pigs as models for human diseases is still realistic. However, continued efforts are needed to further reduce the level of malformations.