Transgene Expression of Green Fluorescent Protein and Germ Line Transmission in Cloned Pigs Derived from In Vitro Transfected Adult Fibroblasts

Unexpected impairment of INa underpins reentrant arrhythmias in a knock-in swine model of Timothy syndrome

Timothy syndrome 1 (TS1) is a multi-organ form of long QT syndrome associated with life-threatening cardiac arrhythmias, the organ-level dynamics of which remain unclear. In this study, we developed and characterized a novel porcine model of TS1 carrying the causative p.Gly406Arg mutation in CACNA1C, known to impair CaV1.2 channel inactivation. Our model fully recapitulated the human disease with prolonged QT interval and arrhythmic mortality. Electroanatomical mapping revealed the presence of a functional substrate vulnerable to reentry, stemming from an unforeseen constitutional slowing of cardiac activation. This signature substrate of TS1 was reliably identified using the reentry vulnerability index, which, we further demonstrate, can be used as a benchmark for assessing treatment efficacy, as shown by testing of multiple clinical and preclinical anti-arrhythmic compounds. Notably, in vitro experiments showed that TS1 cardiomyocytes display Ca2+ overload and decreased peak INa current, providing a rationale for the arrhythmogenic slowing of impulse propagation in vivo.

Production of transgenic first filial puppies expressing mutated human amyloid precursor protein gene

Propagation of transgenic animals by germline transmission using assisted reproductive technologies such as in vitro fertilization (IVF) is the most efficient way to produce transgenic colonies for biomedical research. The objective of this study was to generate transgenic puppies from a founder dog expressing the mutated human amyloid precursor protein (mhAPP) gene. Experiment I assessed the characteristics of the semen prepared by freshly diluted, swim-up, and Percoll gradient methods using a computer-assisted semen analyzer (CASA). Motile and progressively motile sperm counts were higher in the Percoll gradient samples (p < 0.05) than in the swim-up and freshly diluted samples. In Experiment II, a total of 59, 70, and 65 presumptive zygotes produced by fresh, Percoll gradient, and swim-up methods, respectively, were transferred to surrogates (5 for each group); the Percoll gradient (27.27%) and swim-up samples (14.29%) showed the highest blastocyst formation rates, while fresh diluted semen did not produce any blastocyst. Experiment III examined the full-term developmental ability of embryos. Among the 5 surrogates in the Percoll gradient group, one (20.0%) became pregnant; it had 4 (6.15%) sacs and delivered 4 (6.15%; 2 males and 2 females) live puppies. Among the 4 puppies, 2 (50.0%) were found to transmit the transgene on their nail and toe under GFP fluorescence. Furthermore, the integration and expression of the mhAPP transgene were examined in the umbilical cords of all the IVF-derived puppies, and the presence of the transgene was only observed in the GFP-positive puppies. Thus, semen prepared by the Percoll method could generate transgenic puppies by male germline transmission using the IVF technique. Our result will help propagate transgenic dogs efficiently, which will foster human biomedical research.

Efficient delivery of a large-size Cas9-EGFP vector in porcine fetal fibroblasts using a Lonza 4D-Nucleofector system

BACKGROUND

Porcine fetal fibroblasts (PFFs) are important donor cells for generating genetically modified pigs, but the transfection efficiencies of PFFs are often unsatisfactory especially when large-size vectors are to be delivered. In this study, we aimed to optimize the transfection conditions for delivery of a large-size vector in PFFs using Lonza 4D-Nucleofector™ vessels and strips.

METHODS

We firstly delivered a 13 kb Cas9-EGFP and a 3.5 kb pMAX-GFP vector into PFFs via 7 programs recommended by the Lonza basic protocol. We then tested 6 customized dual-electroporation programs for delivering the 13 kb plasmid into PFFs. In addition, we screened potential alternative electroporation buffers to the Nucleofector™ P3 solution. Finally, three CRISPR/Cas9-sgRNAs targeting Rosa26, H11, and Cep112 loci were delivered into PFFs with different single and dual-electroporation programs.

RESULTS

Notably lower transfection efficiencies were observed when delivering the 13 kb vector than delivering the 3.5 kb vector in PFFs via the single-electroporation programs. The customized dual-electroporation program FF-113 + CA-137 exhibited higher transfection efficiencies than any of the single-electroporation programs using vessels (98.1%) or strips (89.1%) with acceptable survival rates for the 13 kb vector. Entranster-E buffer generated similar transfection efficiencies and 24-hour survival rates to those from the P3 solution, thus can be used as an alternative electroporation buffer. In the genome-editing experiments, the FF-113 + CA-137 and CA-137 + CA-137 programs showed significantly superior (P < 0.01) efficiencies to ones from the single-electroporation programs in vessels and strips. Entranster-E buffer produced higher indel efficiencies than the P3 buffer.

CONCLUSIONS

We markedly increased the delivery efficiencies for a large vector via customized dual-electroporation programs using Lonza 4D-Nucleofector™ system, and Entranster-E buffer can be used as an alternative electroporation buffer to Nucleofector™ P3 buffer.

Characterization of Green Fluorescent Protein in Heart Valves of a Transgenic Swine Model for Partial Heart Transplant Research

A transgenic strain of pigs was created to express green fluorescent protein (GFP) ubiquitously using a pCAGG promoter. Here, we characterize GFP expression in the semilunar valves and great arteries of GFP-transgenic (GFP-Tg) pigs. Immunofluorescence was performed to visualize and quantify GFP expression and colocalization with nuclear staining. GFP expression was confirmed in both the semilunar valves and great arteries of GFP-Tg pigs compared to wild-type tissues (aorta, p = 0.0002; pulmonary artery, p = 0.0005; aortic valve; and pulmonic valve, p < 0.0001). The quantification of GFP expression in cardiac tissue allows this strain of GFP-Tg pigs to be used for future research in partial heart transplantation.

Extranuclear Inheritance of Mitochondrial Genome and Epigenetic Reprogrammability of Chromosomal Telomeres in Somatic Cell Cloning of Mammals

The effectiveness of somatic cell nuclear transfer (SCNT) in mammals seems to be still characterized by the disappointingly low rates of cloned embryos, fetuses, and progeny generated. These rates are measured in relation to the numbers of nuclear-transferred oocytes and can vary depending on the technique applied to the reconstruction of enucleated oocytes. The SCNT efficiency is also largely affected by the capability of donor nuclei to be epigenetically reprogrammed in a cytoplasm of reconstructed oocytes. The epigenetic reprogrammability of donor nuclei in SCNT-derived embryos appears to be biased, to a great extent, by the extranuclear (cytoplasmic) inheritance of mitochondrial DNA (mtDNA) fractions originating from donor cells. A high frequency of mtDNA heteroplasmy occurrence can lead to disturbances in the intergenomic crosstalk between mitochondrial and nuclear compartments during the early embryogenesis of SCNT-derived embryos. These disturbances can give rise to incorrect and incomplete epigenetic reprogramming of donor nuclei in mammalian cloned embryos. The dwindling reprogrammability of donor nuclei in the blastomeres of SCNT-derived embryos can also be impacted by impaired epigenetic rearrangements within terminal ends of donor cell-descended chromosomes (i.e., telomeres). Therefore, dysfunctions in epigenetic reprogramming of donor nuclei can contribute to the enhanced attrition of telomeres. This accelerates the processes of epigenomic aging and replicative senescence in the cells forming various tissues and organs of cloned fetuses and progeny. For all the above-mentioned reasons, the current paper aims to overview the state of the art in not only molecular mechanisms underlying intergenomic communication between nuclear and mtDNA molecules in cloned embryos but also intrinsic determinants affecting unfaithful epigenetic reprogrammability of telomeres. The latter is related to their abrasion within somatic cell-inherited chromosomes.

Generation of Transgenic Cloned Buffalo Embryos Harboring the EGFP Gene in the Y Chromosome Using CRISPR/Cas9-Mediated Targeted Integration

Sex control technology is of great significance in the production of domestic animals, especially for rapidly breeding water buffalo (bubalus bubalis), which served as a research model in the present study. We have confirmed that a fluorescence protein integrated into the Y chromosome is fit for sexing pre-implantation embryos in the mouse. Firstly, we optimized the efficiency of targeted integration of exogenous gene encoding enhanced green fluorescent protein (eGFP) and mCherry in Neuro-2a cells, mouse embryonic stem cells, mouse embryonic cells (NIH3T3), buffalo fetal fibroblast (BFF) cells. The results showed that a homology arm length of 800 bp on both sides of the target is more efficient that 300 bp or 300 bp/800 bp. Homology-directed repair (HDR)-mediated knock-in in BFF cells was also significantly improved when cells were supplemented with pifithrin-μ, which is a small molecule that inhibits the binding of p53 to mitochondria. Three pulses at 250 V resulted in the most efficient electroporation in BFF cells and 1.5 μg/mL puromycin was found to be the optimal concentration for screening. Moreover, Y-Chr-eGFP transgenic BFF cells and cloned buffalo embryos were successfully generated using CRISPR/Cas9-mediated gene editing combined with the somatic cell nuclear transfer (SCNT) technique. At passage numbers 6–8, the growth rate and cell proliferation rate were significantly lower in Y-Chr-eGFP transgenic than in non-transgenic BFF cells; the expression levels of the methylation-related genes DNMT1 and DNMT3a were similar; however, the expression levels of the acetylation-related genes HDAC1, HDAC2, and HDAC3 were significantly higher (p < 0.05) in Y-Chr-eGFP transgenic BFF cells compared with non-transgenic cells. Y-Chr-eGFP transgenic BFFs were used as donors for SCNT, the results showed that eGFP reporter is suitable for the visualization of the sex of embryos. The blastocyst rates of cloned buffalo embryos were similar; however, the cleavage rates of transgenic cloned embryos were significantly lower compared with control. In summary, we optimized the protocol for generating transgenic BFF cells and successfully generated Y-Chr-eGFP transgenic embryos using these cells as donors.

Xenotransplantation: Progress Along Paths Uncertain from Models to Application

For more than a century, transplantation of tissues and organs from animals into man, xenotransplantation, has been viewed as a potential way to treat disease. Ironically, interest in xenotransplantation was fueled especially by successful application of allotransplantation, that is, transplantation of human tissue and organs, as a treatment for a variety of diseases, especially organ failure because scarcity of human tissues limited allotransplantation to a fraction of those who could benefit. In principle, use of animals such as pigs as a source of transplants would allow transplantation to exert a vastly greater impact than allotransplantation on medicine and public health. However, biological barriers to xenotransplantation, including immunity of the recipient, incompatibility of biological systems, and transmission of novel infectious agents, are believed to exceed the barriers to allotransplantation and presently to hinder clinical applications. One way potentially to address the barriers to xenotransplantation is by genetic engineering animal sources. The last 2 decades have brought progressive advances in approaches that can be applied to genetic modification of large animals. Application of these approaches to genetic engineering of pigs has contributed to dramatic improvement in the outcome of experimental xenografts in nonhuman primates and have encouraged the development of a new type of xenograft, a reverse xenograft, in which human stem cells are introduced into pigs under conditions that support differentiation and expansion into functional tissues and potentially organs. These advances make it appropriate to consider the potential limitation of genetic engineering and of current models for advancing the clinical applications of xenotransplantation and reverse xenotransplantation.

Generation of transgenic-cloned Huanjiang Xiang pigs systemically expressing enhanced green fluorescent protein

Huanjiang Xiang pig is a unique native minipig breed originating in Guangxi, China, and has great utility value in agriculture and biomedicine. Reproductive biotechnologies such as somatic cell nuclear transfer (SCNT) and SCNT-mediated genetic modification show great potential value in genetic preservation and utilization of Huanjiang Xiang pigs. Our previous work has successfully produced cloned and transgenic-cloned embryos using somatic cells from a Huanjiang Xiang pig. In this study, we firstly report the generation of transgenic-cloned Huanjiang Xiang pigs carrying an enhanced green fluorescent protein (eGFP) gene. A total of 504 SCNT-derived embryos were transferred to two surrogate recipients, one of which became pregnant and gave birth to three live piglets. Exogenous eGFP transgene had integrated in all of the three Huanjiang Xiang piglets identified by genotyping. Furthermore, expression of eGFP was also detected from in vitro cultured skin fibroblast cells and various organs or tissues from positive transgenic-cloned Huanjiang Xiang pigs. The present work provides a practical method to preserve this unique genetic resource and also lays a foundation for genetic modification of Huanjiang Xiang pigs with improved values in agriculture and biomedicine.

SURF1 knockout cloned pigs: Early onset of a severe lethal phenotype

Leigh syndrome (LS) associated with cytochrome c oxidase (COX) deficiency is an early onset, fatal mitochondrial encephalopathy, leading to multiple neurological failure and eventually death, usually in the first decade of life. Mutations in SURF1, a nuclear gene encoding a mitochondrial protein involved in COX assembly, are among the most common causes of LS. LSSURF1 patients display severe, isolated COX deficiency in all tissues, including cultured fibroblasts and skeletal muscle. Recombinant, constitutive SURF1-/- mice show diffuse COX deficiency, but fail to recapitulate the severity of the human clinical phenotype. Pigs are an attractive alternative model for human diseases, because of their size, as well as metabolic, physiological and genetic similarity to humans. Here, we determined the complete sequence of the swine SURF1 gene, disrupted it in pig primary fibroblast cell lines using both TALENs and CRISPR/Cas9 genome editing systems, before finally generating SURF1-/- and SURF1-/+ pigs by Somatic Cell Nuclear Transfer (SCNT). SURF1-/- pigs were characterized by failure to thrive, muscle weakness and highly reduced life span with elevated perinatal mortality, compared to heterozygous SURF1-/+ and wild type littermates. Surprisingly, no obvious COX deficiency was detected in SURF1-/- tissues, although histochemical analysis revealed the presence of COX deficiency in jejunum villi and total mRNA sequencing (RNAseq) showed that several COX subunit-encoding genes were significantly down-regulated in SURF1-/- skeletal muscles. In addition, neuropathological findings, indicated a delay in central nervous system development of newborn SURF1-/- piglets. Our results suggest a broader role of sSURF1 in mitochondrial bioenergetics.

Generation of a Stable Transgenic Swine Model Expressing a Porcine Histone 2B-eGFP Fusion Protein for Cell Tracking and Chromosome Dynamics Studies

Transgenic pigs have become an attractive research model in the field of translational research, regenerative medicine, and stem cell therapy due to their anatomic, genetic and physiological similarities with humans. The development of fluorescent proteins as molecular tags has allowed investigators to track cell migration and engraftment levels after transplantation. Here we describe the development of two transgenic pig models via SCNT expressing a fusion protein composed of eGFP and porcine Histone 2B (pH2B). This fusion protein is targeted to the nucleosomes resulting a nuclear/chromatin eGFP signal. The first model (I) was generated via random insertion of pH2B-eGFP driven by the CAG promoter (chicken beta actin promoter and rabbit Globin poly A; pCAG-pH2B-eGFP) and protected by human interferon-β matrix attachment regions (MARs). Despite the consistent, high, and ubiquitous expression of the fusion protein pH2B-eGFP in all tissues analyzed, two independently generated Model I transgenic lines developed neurodegenerative symptoms including Wallerian degeneration between 3-5 months of age, requiring euthanasia. A second transgenic model (II) was developed via CRISPR-Cas9 mediated homology-directed repair (HDR) of IRES-pH2B-eGFP into the endogenous β-actin (ACTB) locus. Model II transgenic animals showed ubiquitous expression of pH2B-eGFP on all tissues analyzed. Unlike the pCAG-pH2B-eGFP/MAR line, all Model II animals were healthy and multiple pregnancies have been established with progeny showing the expected Mendelian ratio for the transmission of the pH2B-eGFP. Expression of pH2B-eGFP was used to examine the timing of the maternal to zygotic transition after IVF, and to examine chromosome segregation of SCNT embryos. To our knowledge this is the first viable transgenic pig model with chromatin-associated eGFP allowing both cell tracking and the study of chromatin dynamics in a large animal model.

Mitochondrial Haplotypes Influence Metabolic Traits in Porcine Transmitochondrial Cybrids

In farm animals, mitochondrial DNA mutations exist widely across breeds and individuals. In order to identify differences among mtDNA haplotypes, two porcine transmitochondrial cybrids were generated by fusion of a Lantang pig cell line devoid of mitochondrial DNA with enucleated cytoplasm from either a Large White pig or a Xiang pig harboring potentially divergent mitochondrial haplotypes. These cybrid cells were subjected to mitochondrial genome sequencing, copy number detecting and analysis of biochemical traits including succinate dehydrogenase (SDH) activity, ATP content and susceptibility to reactive oxygen species (ROS). The Lantang and Xiang mitochondrial genomes were highly homologous with only 18 polymorphic sites, and differed radically from the Large White with 201 and 198 mutations respectively. The Large White and Xiang cybrids exhibited similar mtDNA copy numbers and different values among biochemical traits, generated greater ROS production (P < 0.05) and less SDH activity (P < 0.05) and a lesser ATP content (P < 0.05). The results show that functional differences exist between cybrid cells which differ in mitochondrial genomic background. In conclusion, transmitochondrial cybrids provide the first direct evidence on pig biochemical traits linking different mitochondrial genome haplotypes.

In vitro development of porcine transgenic nuclear-transferred embryos derived from newborn Guangxi Bama mini-pig kidney fibroblasts

Porcine transgenic cloning has potential applications for improving production traits and for biomedical research purposes. To produce a transgenic clone, kidney fibroblasts from a newborn Guangxi Bama mini-pig were isolated, cultured, and then transfected with red and green fluorescent protein genes using lipofectamine for nuclear transfer. The results of the present study show that the kidney fibroblasts exhibited excellent proliferative capacity and clone-like morphology, and were adequate for generation of somatic cell nuclear transfer (SCNT)-derived embryos, which was confirmed by their cleavage activity and blastocyst formation rate of 70.3% and 7.9%, respectively. Cells transfected with red fluorescent protein genes could be passed more than 35 times. Transgenic embryos cloned with fluorescent or blind enucleation methods were not significantly different with respect to cleavage rates (92.5% vs. 86.8%, p > 0.05) and blastocyst-morula rates (26.9% vs. 34.0%, p > 0.05), but were significantly different with respect to blastocyst rates (3.0% vs. 13.2%, p < 0.05). Cleavage (75.3%, 78.5% vs. 78.0%, p > 0.05), blastocyst (14.1%, 16.1% vs. 23.1%, p > 0.05) and morula/blastocyst rates (43.5%, 47.0% vs. 57.6%, p > 0.05) were not significantly different between the groups of transgenic cloned embryos, cloned embryos, and parthenogenetic embryos. This indicates that long-time screening by G418 caused no significant damage to kidney fibroblasts. Thus, kidney fibroblasts represent a promising new source for transgenic SCNT, and this work lays the foundation for the production of genetically transformed cloned Guangxi Bama mini-pigs.

Incompatibility of nucleus and mitochondria causes xenomitochondrial cybrid unviable across human, mouse, and pig cells

The nucleus and mitochondria are on correlative dependence; they interact in the process of protein transportation and energy metabolism. The compatibility of nucleus and mitochondria is essential for interspecies somatic cell nuclear transfer (iSCNT) and xenomitochondrial cybrid. In order to test the compatibility of nucleus and mitochondria among human, mouse, and pig cells, we compared the performances of cybrids that fused inter- and intra-species. The ρ0 cells from human and pig cell lines were created as nucleus donors which were transfected with GFP-neo for cell selective system in advance, and mitochondria donor cells were labeled by Mitochondria-RFP. Human and mouse platelets were also used as a mitochondrial donor. Results indicated that all interspecies cybrids declined to die in 2-4 d after the cell fusion in the selection medium, while intraspecies cybrid cells survived and formed stable clones. As a conclusion, the incompatibility between nucleus and mitochondria is the critical factor for the formation of interspecies cybrids.

Modeling amyotrophic lateral sclerosis in hSOD1 transgenic swine

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that occurs in two clinically indistinguishable forms: sporadic (SALS) and familial (FALS), the latter linked to several gene mutations, mostly inheritable in a dominant manner. Nearly 20% of FALS forms are linked to mutations in the Cu/Zn superoxide dismutase (SOD1) gene. Research on ALS relies on transgenic models and particularly on mice carrying a glycine-to-alanine conversion at the 93rd codon (G93A) of the hSOD1 gene. Although G93A transgenic mice have been widely employed in clinical trials and basic research, doubts have been recently raised from numerous reliable sources about their suitability to faithfully reproduce human disease. Besides, the scientific community has already foreseen swine as an attractive and alternative model to nonhuman primates for modeling human diseases due to closer anatomical, physiological and biochemical features of swine rather than rodents to humans. On this basis, we have produced the first swine ALS model by in vitro transfection of cultured somatic cells combined with somatic cell nuclear transfer (SCNT). To achieve this goal we developed a SOD1(G93A) (superoxide dismutase 1 mutated in Gly93-Ala) vector, capable of promoting a high and stable transgene expression in primary porcine adult male fibroblasts (PAF). After transfection, clonal selection and transgene expression level assessment, selected SOD1(G93A) PAF colonies were used as nuclei donors in SCNT procedures. SOD1(G93A) embryos were transferred in recipient sows, and pregnancies developed to term. A total of 5 piglets survived artificial hand raising and weaning and developed normally, reaching adulthood. Preliminary analysis revealed transgene integration and hSOD1(G93A) expression in swine tissues and 360° phenotypical characterization is ongoing. We believe that our SOD1(G93A) swine would provide an essential bridge between the fundamental work done in rodent models and the reality of treating ALS.

Pluripotent cells in farm animals: state of the art and future perspectives

Pluripotent cells, such as embryonic stem (ES) cells, embryonic germ cells and embryonic carcinoma cells are a unique type of cell because they remain undifferentiated indefinitely in in vitro culture, show self-renewal and possess the ability to differentiate into derivatives of the three germ layers. These capabilities make them a unique in vitro model for studying development, differentiation and for targeted modification of the genome. True pluripotent ESCs have only been described in the laboratory mouse and rat. However, rodent physiology and anatomy differ substantially from that of humans, detracting from the value of the rodent model for studies of human diseases and the development of cellular therapies in regenerative medicine. Recently, progress in the isolation of pluripotent cells in farm animals has been made and new technologies for reprogramming of somatic cells into a pluripotent state have been developed. Prior to clinical application of therapeutic cells differentiated from pluripotent stem cells in human patients, their survival and the absence of tumourigenic potential must be assessed in suitable preclinical large animal models. The establishment of pluripotent cell lines in farm animals may provide new opportunities for the production of transgenic animals, would facilitate development and validation of large animal models for evaluating ESC-based therapies and would thus contribute to the improvement of human and animal health. This review summarises the recent progress in the derivation of pluripotent and reprogrammed cells from farm animals. We refer to our recent review on this area, to which this article is complementary.

Differentiation potential and GFP labeling of sheep bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are an important cell population in the bone marrow microenvironment. MSCs have the capacity to differentiate in vitro into several mesenchymal tissues including bone, cartilage, fat, tendon, muscle, and marrow stroma. This study was designed to isolate, expand, and characterize the differentiation ability of sheep bone marrow-derived MSCs and to demonstrate the possibility to permanently express a reporter gene. Bone marrow was collected from the iliac crest and mononuclear cells were separated by density gradient centrifugation. Sheep MSCs cell lines were stable characterized as CD44+ and CD34- and then transfected with a green fluorescent protein (GFP) reporter gene. The GFP expression was maintained in about half (46.6%) of cloned blastocysts produced by nuclear transfer of GFP+ sheep MSCs, suggesting the possibility to establish multipotent embryonic cells' lines carrying the fluorescent tag for comparative studies on the differentiation capacity of adult stem cells (MSCs) versus embryonic stem cells. We found that sheep MSCs under appropriate culture conditions could be induced to differentiate into adipocytes, chondrocytes, and osteoblast lineages. Our results confirm the plasticity of sheep MSCs and establish the foundation for the development of a pre-clinical sheep model to test the efficiency and safety of cell replacement therapy.

Somatic cell nuclear transfer and transgenesis in large animals: current and future insights

Somatic cell nuclear transfer (SCNT) was first developed in livestock for the purpose of accelerating the widespread use of superior genotypes. Although many problems still exist now after fifteen years of research owing to the limited understanding of genome reprogramming, SCNT has provided a powerful tool to make copies of selected individuals in different species, to study genome pluripotency and differentiation, opening new avenues of research in regenerative medicine and representing the main route for making transgenic livestock. Besides well-established methods to deliver transgenes, recent development in enzymatic engineering to edit the genome provides more precise and reproducible tools to target-specific genomic loci especially for producing knockout animals. The interest in generating transgenic livestock lies in the agricultural and biomedical areas and it is, in most cases, at the stage of research and development, with few exceptions that are making the way into practical applications.

Roscovitine is a novel agent that can be used for the activation of porcine oocytes reconstructed with adult cutaneous or fetal fibroblast cell nuclei

The present study was undertaken to investigate the preimplantation developmental competence of cloned pig embryos that were derived from fibroblast cell nuclei by different methods for the activation of reconstructed oocytes. In subgroups IA and IB, nuclear-transferred (NT) oocytes derived from either adult cutaneous or fetal fibroblast cells that had been classified as nonapoptotic by intra vitam analysis for programmed cell death using the YO-PRO-1 DNA fluorochrome underwent sequential physical (i.e., electrical) and chemical activation (SE-CA). This novel method of SE-CA, which was developed and optimized in our laboratory, involves treatment of reconstituted oocytes with direct current pulses and subsequent exposure to 7.5 μM calcium ionomycin, followed by incubation with 30 μM R-roscovitine (R-RSCV), 0.7 mM 6-dimethylaminopurine and 3.5 μg/mL cycloheximide. In subgroups IIA and IIB, NT oocytes were subjected to the standard method of simultaneous fusion and activation mediated by direct current pulses. The proportion of cloned embryos in subgroup IA that reached the morula and blastocyst stages was 145/248 (58.5%) and 78/248 (31.5%), respectively. The proportions of cloned embryos in subgroup IB that reached the morula and blastocyst stages were 186/264 (70.5%) and 112/264 (42.4%), respectively. In turn, subgroup IIA yielded proportions at the morula and blastocyst stages of 110/234 (47.0%) and 49/234 (20.9%), respectively. Subgroup IIB yielded proportions at the morula and blastocyst stages of 144/243 (59.3%) and 74/243 (30.5%), respectively. In summary, the SE-CA of NT oocytes reconstructed from either type of nonapoptotic/nonnecrotic (i.e., YO-PRO-1-negative) fibroblast cell resulted in porcine cloned embryos with considerably better in vitro developmental outcomes than those of cloned embryos generated using the simultaneous fusion and activation approach. To our knowledge, this is the first report of the successful stimulation of porcine NT oocytes using electric pulses followed by an additional activation with a higher dose (1.5 times) of calcium ionomycin and subsequent exposure to a combination of 30 μM R-RSCV and lower concentrations (by 3 times) of 6-dimethylaminopurine and cycloheximide. Moreover, we report here the first use of R-RSCV, a novel meiosis-promoting factor-related p34(cdc2) kinase inhibitor, in the oocyte activation protocol for the somatic cell cloning of pigs.

Rapid non-invasive genotyping of reporter transgenic mammals

Here we describe a non-invasive method for rapid and highly reproducible genotyping of transgenic mammals with ubiquitous expression of fluorophore reporters. Hair samples from transgenic mice and pigs with systemic expression of the fluorophore reporter Venus were analyzed with a fluorescence microscope in few minutes. The hair samples can be preserved for long-term storage at ambient temperature conditions. This non-invasive method is useful for genotyping of transgenic large animals and contributes to animal welfare by reducing stress and discomfort of the animals during sample collection.

Characterization, GFP gene Nucleofection, and allotransplantation in injured tendons of ovine amniotic fluid-derived stem cells

Amniotic fluid has drawn increasing attention in the recent past as a cost-effective and accessible source of fetal stem cells. Amniotic fluid-derived mesenchymal stem cells (AFMSCs) that display high proliferation rate, large spectrum of differentiation potential, and immunosuppressive features are considered optimal candidates for allogeneic repair of mesenchymal damaged tissues. In this study, ovine AFMSCs (oAFMSCs) isolated from 3-month-old sheep fetuses were characterized for their proliferation rate, specific surface antigen and pluripotency marker expression, genomic stability, and mesenchymal lineage differentiation during their in vitro expansion (12 passages) and after nucleofection. The high proliferation rate of oAFMSCs gradually decreased during the first six subculture passages while the expression of surface molecules (CD29, CD58, CD166) and of pluripotency-associated markers (OCT4, TERT, NANOG, SOX2), the in vitro osteogenic differentiation potential, and a normal karyotype were maintained. Afterwards, oAFMSCs were nucleofected with a selectable plasmid coding for green fluorescent protein (GFP) using two different programs, U23 and C17, previously optimized for human mesenchymal stem cells. Transfection efficiencies were ∼63% and ∼37%, while cell recoveries were ∼10% and ∼22%, respectively. Nucleofected oAFMSCs expressing the GFP transgene conserved their pluripotency marker profile and retained a normal karyotype and the osteogenic differentiation ability. Seven single clones with a GFP expression ranging from 80% to 97% were then isolated and expanded over 1 month, thus providing stably transfected cells with long-term therapeutic potential. The in vivo behavior of GFP-labeled oAFMSCs was tested on a previously validated preclinical model of experimentally induced Achille's tendon defect. The allotransplanted oAFMSCs were able to survive within the host tissue for 1 month enhancing the early phase of tendon healing as indicated by morphological and biomechanical results. Altogether these data suggest that genetically modified oAFMSCs might represent a valuable tool for in vivo preclinical studies in a highly valid translational model.

GFP-transgenic animals for in vivo imaging: rats, rabbits, and pigs

Specifically, gene-encoded biological probes serve as stable and high-performance tools to visualize cellular fate in living animals. The rat, as with the mouse, has offered important animal models for biology and medical research, and has provided a wealth of physiological and pharmacological data. The larger-body animals, in comparison to the mouse have allowed the application of various physiological and surgical manipulations that may prove to have biological significance. We have further extended the techniques of genetic engineering to rats, rabbits, and pigs, and have created corresponding GFP-transgenic animals. The GFP-positive organs of these animals provide valuable sensors in preclinical settings for cell therapy and transplantation studies. In this chapter, we highlight expression profiles in these animal resources and describe examples of preclinical applications.

Welfare assessment in transgenic pigs expressing green fluorescent protein (GFP)

Since large animal transgenesis has been successfully attempted for the first time about 25 years ago, the technology has been applied in various lines of transgenic pigs. Nevertheless one of the concerns with the technology--animal welfare--has not been approached through systematic assessment and statements regarding the welfare of transgenic pigs have been based on anecdotal observations during early stages of transgenic programs. The main aim of the present study was therefore to perform an extensive welfare assessment comparing heterozygous transgenic animals expressing GFP with wildtype animals along various stages of post natal development. The protocol used covered reproductory performance and behaviour in GFP and wildtype sows and general health and development, social behaviour, exploratory behaviour and emotionality in GFP and wildtype littermates from birth until an age of roughly 4 months. The absence of significant differences between GFP and wildtype animals in the parameters observed suggests that the transgenic animals in question are unlikely to suffer from deleterious effects of transgene expression on their welfare and thus support existing anecdotal observations of pigs expressing GFP as healthy. Although the results are not surprising in the light of previous experience, they give a more solid fundament to the evaluation of GFP expression as being relatively non-invasive in pigs. The present study may furthermore serve as starting point for researchers aiming at a systematic characterization of welfare relevant effects in the line of transgenic pigs they are working with.

Determination of the optimal concentration of several selective drugs useful for generating multi-transgenic porcine embryonic fibroblasts

Porcine embryonic fibroblasts (PEFs) are widely used as donor cells for somatic cell nuclear transfer (SCNT) in pigs. Transfection of PEFs with exogenous DNA is essential for producing genetically modified (GM; transgenic or knockout) pigs via SCNT. In this case, selectable markers are strictly required selecting and enriching stably transfected cells. The most frequently used selective drug for this purpose is a neomycin analogue (G418/geneticin); neo has been widely used as a selectable marker gene in the genomic manipulation of pigs. However, little is known about optimal concentrations of other selection drugs. This often hampers functional analysis of the porcine genome and development of individual GM pigs. This study explores the optimal concentrations of selective drugs, other than neomycin, that can be used for the selection of transfected PEFs. Porcine embryonic fibroblasts were incubated in media containing different concentrations of drugs for up to 10 days, to determine the optimal drug concentrations fatal for PEFs. The following concentrations were found to be optimal selective concentrations for use with PEFs: G418/geneticin, 400 μg/ml; blasticidin S, 8 μg/ml; hygromycin B, 40 μg/ml; puromycin, 2 μg/ml; and zeocin, 800 μg/ml. Repeated transfections with plasmids carrying selectable markers resulted in the generation of multidrug-resistant swine transfectants. Furthermore, these markers were found to be independent. The present information will be useful for the production of SCNT-mediated GM piglets that express multiple transgenes.

Production of offspring from cloned transgenic RFP female dogs and stable generational transmission of the RFP gene

The purpose of this study was to analyze the reproductive ability of transgenic female dogs born bysomatic cell nuclear transfer and to determine inheritance of the red fluorescent protein (RFP) transgene. The four founder transgenic bitches (F0) reached puberty at 340.8 ± 39.6 days after birth and were bred with wild-type male dogs by natural mating or by artificial insemination. The bitches all became pregnant and successfully delivered 13 puppies (F1), of which two females were bred with wild-type dogs to deliver 7 offspring (F2), including 1 stillbirth. Among the 19 live offspring, 10 puppies showed emission of RFP under UV light and the presence of the RFP transgene was confirmed by genomic PCR and Southern blot analyses. In conclusion, transgenic RFP female dogs exhibited normal reproductive ability and expression of the transgene was demonstrated in F1 and F2 generations.

The enhanced performance of bone allografts using osteogenic-differentiated adipose-derived mesenchymal stem cells

Adipose tissue was only recently considered as a potential source of mesenchymal stem cells (MSCs) for bone tissue engineering. To improve the osteogenicity of acellular bone allografts, adipose MSCs (AMSCs) and bone marrow MSCs (BM-MSCs) at nondifferentiated and osteogenic-differentiated stages were investigated in vitro and in vivo. In vitro experiments demonstrated a superiority of AMSCs for proliferation (6.1±2.3 days vs. 9.0±1.9 days between each passage for BM-MSCs, respectively, P<0.001). A significantly higher T-cell depletion (revealed by mixed lymphocyte reaction, [MLR]) was found for AMSCs (vs. BM-MSCs) at both non- and differentiated stages. Although nondifferentiated AMSCs secreted a higher amount of vascular endothelial growth factor [VEGF] in vitro (between 24 and 72 h of incubation at 0.1-21% O(2)) than BM-MSCs (P<0.001), the osteogenic differentiation induced a significantly higher VEGF release by BM-MSCs at each condition (P<0.001). After implantation in the paraspinal muscles of nude rats, a significantly higher angiogenesis (histomorphometry for vessel development (P<0.005) and VEGF expression (P<0.001)) and osteogenesis (as revealed by osteocalcin expression (P<0.001) and micro-CT imagery for newly formed bone tissue (P<0.05)) were found for osteogenic-differentiated AMSCs in comparison to BM-MSCs after 30 days of implantation. Osteogenic-differentiated AMSCs are the best candidate to improve the angio-/osteogenicity of decellularized bone allografts.

Versatile co-expression of graft-protective proteins using 2A-linked cassettes

BACKGROUND

Expression of multiple graft-protective proteins targeted to different locations (i.e., intracellular, cell surface, and secreted) has become an increasingly important goal in xenotransplantation. The 2A "ribosome skip" signal is used as a linker to enable transgene co-expression, but some studies have shown that post-translational modification and trafficking of 2A-linked proteins may be adversely affected depending on their position relative to 2A. We tested whether several relevant proteins, subject to a range of processing and localization mechanisms, could be efficiently co-expressed using the 2A system.

METHODS

Six expression cassettes were constructed, each containing up to four 2A-linked open reading frames, encoding combinations of human CD55, thrombomodulin (TBM), CD39, CTLA4-Ig and hygromycin resistance. Each linker incorporated a furin cleavage site to remove the carboxy-terminal extension that remains on upstream proteins after 2A processing. The cassettes were used to produce vectors for transfection, adenoviral transduction and transgenesis. Expression was detected by flow cytometry and/or Western blotting.

RESULTS

All proteins were expressed in the appropriate location following transient transfection of COS-7 cells, irrespective of the number of linked genes. The percentage of stable transfectants expressing a linked gene was increased 10-fold (from 4-5% to 58-67%) by incorporating the hygromycin resistance gene into the cassette. Stable transfection of transgenic GalT KO pig fibroblasts with a hygromycin- TBM-CD39 construct resulted in surface expression of both TBM and CD39 by the majority of hygromycin-resistant cells. Expression was maintained after flow cytometric sorting and expansion. Adenoviral transduction of NIT-1 mouse insulinoma cells with a TBM-CD39 construct resulted in strong expression of both genes on the cell surface. Mice transgenic for 3-gene (CD55- TBM-CD39) or 4-gene (CD55- TBM-CTLA4Ig-CD39) constructs expressed all genes except CD55.

CONCLUSIONS

These results confirm the versatility of the 2A system, and demonstrate that careful construct design can minimize potential problems with post-translational modification and trafficking. In addition, incorporation of a selection marker into the 2A-linked chain can dramatically increase the proportion of stable transfectants expressing proteins of interest. This provides a powerful method for the rapid modification of existing genetically modified pigs.

Effect of roscovitine-treated donor cells on development of porcine cloned embryos

Synchronization of the donor cell cycle is an important factor for successful animal cloning by nuclear transfer. To improve the efficiency of porcine cloning, in the present report, we evaluated effects of contact inhibition, serum starvation and roscovitine treatment of donor cells on in vitro and in vivo developmental potency of cloned porcine embryos. Fibroblasts derived from a porcine foetus at day 30 of gestation were isolated and cultured to 70% confluency. Then, cells were either cultured to 100% confluency for contact inhibition, or cultured in 0.5% serum for 72 h for serum starvation or with 15 μM roscovitine for 24 h. Cells were most effectively synchronized at G0/G1 in the serum starvation group (87.5%) compared with the contact inhibition and roscovitine treatment groups (76.3% and 79.9% respectively p < 0.05). However, after somatic cell nuclear transfer followed by in vitro culture, the serum starvation group showed a significantly lower blastocyst formation rate (5.6%) compared with the contact inhibition and roscovitine treatment groups (11.6% and 20.0% respectively). Differential expression of apoptosis-related genes and the level of apoptosis in each treatment group explain the variation in developmental competence among the groups. Significantly higher level of apoptosis was observed in the serum starvation group. On the other hand, the roscovitine treatment group shows the lowest level of apoptosis and the best in vitro development among the groups. Cloned embryos derived from roscovitine-treated donor cells were transferred to surrogate pigs. Three healthy live piglets were produced. In conclusion, we suggest that roscovitine treatment of donor cells improves development of cloned porcine embryos and can raise the efficiency of cloned piglet production.

Perspectives on transgenic livestock in agriculture and biomedicine: an update

It has been 30 years since the first transgenic mouse was generated and 26 years since the first example of transferring the technology to livestock was published. While there was tremendous optimism in those initial years, with most convinced that genetically modified animals would play a significant role in agricultural production, that has not come to be. So at first sight one could conclude that this technology has, to a large extent, failed. On the contrary, it is believed that it has succeeded beyond our original expectations, and we are now at what is perhaps the most exciting time in the development and implementation of these technologies. The original goals, however, have drastically changed and it is now biomedical applications that are playing a central role in pushing both technical and scientific developments. The combination of advances in somatic cell nuclear transfer, the development of induced pluripotent stem cells and the completion of the sequencing of most livestock genomes ensures a bright and exciting future for this field, not only in livestock but also in companion animal species.

Production of transgenic canine embryos using interspecies somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) has emerged as an important tool for producing transgenic animals and deriving transgenic embryonic stem cells. The process of SCNT involves fusion of in vitro matured oocytes with somatic cells to make embryos that are transgenic when the nuclear donor somatic cells carry ‘foreign’ DNA and are clones when all the donor cells are genetically identical. However, in canines, it is difficult to obtain enough mature oocytes for successful SCNT due to the very low efficiency of in vitro oocyte maturation in this species that hinders canine transgenic cloning. One solution is to use oocytes from a different species or even a different genus, such as bovine oocytes, that can be matured easily in vitro. Accordingly, the aim of this study was: (1) to establish a canine fetal fibroblast line transfected with the green fluorescent protein (GFP) gene; and (2) to investigate in vitro embryonic development of canine cloned embryos derived from transgenic and non-transgenic cell lines using bovine in vitro matured oocytes. Canine fetal fibroblasts were transfected with constructs containing the GFP and puromycin resistance genes using FuGENE 6®. Viability levels of these cells were determined by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Interspecies SCNT (iSCNT) embryos from normal or transfected cells were produced and cultured in vitro. The MTT measurement of GFP-transfected fetal fibroblasts (mean OD = 0.25) was not significantly different from non-transfected fetal fibroblasts (mean OD = 0.35). There was no difference between transgenic iSCNT versus non-transgenic iSCNT embryos in terms of fusion rates (73.1% and 75.7%, respectively), cleavage rates (69.7% vs. 73.8%) and development to the 8–16-cell stage (40.1% vs. 42.7%). Embryos derived from the transfected cells completely expressed GFP at the 2-cell, 4-cell, and 8–16-cell stages without mosaicism. In summary, our results demonstrated that, following successful isolation of canine transgenic cells, iSCNT embryos developed to early pre-implantation stages in vitro, showing stable GFP expression. These canine–bovine iSCNT embryos can be used for further in vitro analysis of canine transgenic cells and will contribute to the production of various transgenic dogs for use as specific human disease models.

Confirmation of germ-line transmission in the red fluorescence protein (RFP) transgenic cloned male cat

The production of transgenic animals is highly desirable for biotechnology and basic research. We investigated the reproductive ability of a red fluorescence protein (RFP) transgenic cloned male cat (RFP TG cat) by natural mating with a domestic female cat. The RFP expression levels were examined in early embryogenesis, tissues from 45-day-old two fetuses, and four RFP TG cat offspring. The RFP gene was detected in tissue samples from one dead kitten, including several organs and the skin. Also, under a fluorescent light source, we were able to directly detect the RFP expression of in in vitro-produced blastocysts derived with sperm from the RFP TG cat. These results indicate that the RFP TG cat exhibits normal reproductive fertility, stable germ-line transmission of the RFP transgene, and characteristic RFP expression in its offspring. We isolated feline neural progenitor cells from a 45-day-old fetus derived from the natural mating of the RFP TG cat with a domestic female cat. Isolated brain and retinal progenitor cells were successfully passaged at least four times post isolation (day 23), and showed a high RFP expression level. This method of producing genetically modified cloned cats will be important for generating biomedical models of human diseases.

Manipulating the cell differentiation through lentiviral vectors

The manipulation of cell differentiation is important to create new sources for the treatment of degenerative diseases or solve cell depletion after aggressive therapy against cancer. In this chapter, the use of a tissue-specific promoter lentiviral vector to obtain a myocardial pure lineage from murine embryonic stem cells (mES) is described in detail. Since the cardiac isoform of troponin I gene product is not expressed in skeletal or other muscle types, short mouse cardiac troponin proximal promoter is used to drive reporter genes. Cells are infected simultaneously with two lentiviral vectors, the first expressing EGFP to monitor the transduction efficiency, and the other expressing a puromycin resistance gene to select the specific cells of interest. This technical approach describes a method to obtain a pure cardiomyocyte population and can be applied to other lineages of interest.

Optimization of square-wave electroporation for transfection of porcine fetal fibroblasts

Development of a transgenic porcine biomedical research model requires effective delivery of DNA into the donor cell followed by selection of genetically modified somatic cell lines to be used for nuclear transfer. The objective of the current study was 2-fold: (1) to compare the effectiveness of a single 1 ms pulse of different voltages (V; 100, 150, 200, 250, 300, 350) and multiple 1 ms pulses (1, 2, 3, 4 or 5) at 300 V for delivery and expression of super-coiled GFP vector in surviving cells of three fetal fibroblast cell lines, and (2) to determine the ability of these electroporation parameters to produce stably transfected fibroblast colonies following G418 selection. Cell line (P < 0.001) and voltage (P < 0.001) affected DNA delivery into the cell as assessed by GFP expression while survival at 24 h was affected by voltage (P < 0.001) and not by cell line (P = 0.797). Using a single pulse while increasing voltage resulted in the percentage of GFP expressing cells increasing from 3.2 +/- 0.8% to 43.0 +/- 3.4% while survival decreased from 90.5 +/- 8.0% to 44.8 +/- 2.0%. The number of pulses at 300 V significantly affected survival (P < 0.001) and GFP expression (P < 0.001). Survival steadily decreased following 1-5 pulses from 63.2 +/- 6.3% to 3.0 +/- 0.3% with GFP expression of surviving cells increasing from 35.6 +/- 2.67% to 71.4 +/- 6.1%. Electroporation of a selectable marker at a 1:1 copy number ratio to a co-electroporated transgene resulted in 83% of G418 resistant colonies also being PCR positive for the secondary transgene. These electroporation conditions, specifically, three 1 ms pulses of 300 V to 200 muL of 1 x 10(6) cells/mL in the presence of 12.5 mug DNA/mL effectively introduced DNA into somatic cells. The utilization of these conditions produced numerous transgenic fibroblast colonies following G418 selection that when used for somatic cell nuclear transfer resulted in the production of live offspring.

Application of genetically modified and cloned pigs in translational research

Pigs are increasingly being recognized as good large-animal models for translational research, linking basic science to clinical applications in order to establish novel therapeutics. This article reviews the current status and future prospects of genetically modified and cloned pigs in translational studies. It also highlights pigs specially designed as disease models, for xenotransplantation or to carry cell marker genes. Finally, use of porcine somatic stem and progenitor cells in preclinical studies of cell transplantation therapy is also discussed.

Genetic manipulation in pigs

PURPOSE OF REVIEW

Recent developments in the field of genetic engineering have made it possible to add, delete or exchange genes from one species to another. This technology has special relevance to the field of xenotransplantation, in which the elimination of a species-specific disparity could make the difference between success and failure of an organ transplant. This review focuses on developments in both the techniques and applications of genetically modified animals.

RECENT FINDINGS

Advances have been made using existing techniques for genetic modifications of swine and in the development of new, emerging technologies, including enzymatic engineering and the use of small interfering RNA. Applications of the modified animals have provided evidence that genetically modified swine have the potential to overcome both physiologic and immunologic barriers that have previously impeded this field. The use of alpha-1,3-galactosyltransferase gene-knockout animals as donors have shown marked improvements in xenograft survivals.

SUMMARY

Techniques for genetic engineering of swine have been directed toward avoiding naturally existing cellular and antibody responses to species-specific antigens. Organs from genetically engineered animals have enjoyed markedly improved survivals in nonhuman primates, especially in protocols directed toward the induction of tolerance, presumably by avoiding immunization to new antigens.

Production of a reporter transgenic pig for monitoring Cre recombinase activity

The pig is thought to be the most suitable non-human source of organs for xenotransplantation and is widely used as a model of human disease. Using pigs as disease models requires the design of conditional Cre recombinase-loxP gene modifications, which, in turn, requires a Cre-expressing pig with defined patterns of expression controlled by the use of a tissue-specific promoter. In order to monitor Cre recombinant expression in vivo, it is important to create a reporter strain. We have generated reporter a pig that is based on a single vector that drives the ubiquitous expression of the enhanced green fluorescent protein (EGFP). The EGFP gene is expressed only after Cre-mediated excision of loxP-flanked stop sequences. These reporter transgenic pigs will be of great value for monitoring Cre recombinase activity in vivo.