A novel method for the production of transgenic cloned pigs: electroporation-mediated gene transfer to non-cultured cells and subsequent selection with puromycin

Electroporation-based CRISPR gene editing in adult buffalo fibroblast cells

Electroporation is a widely used method for delivering CRISPR components into cells; however, it presents challenges when applied to difficult-to-transfect cells like adult buffalo fibroblasts. In this study, the ITGB2 gene (encoding the CD18 protein), plays vital for cellular adhesion and immune responses, was selected for editing experiments. To optimize electroporation conditions, we investigated parameters such as electric field strength, pulse duration, plasmid DNA amount, cuvette type, and cell type. The best transfection rates were obtained in a 4 mm gap cuvette with a single 20-millisecond pulse of 300 V using a 10 μg of all-in-one CRISPR plasmid for 106 cells in 100 μL of electroporation buffer. Increasing DNA quantity enhanced transfection rates but compromised cell viability. The 4 mm cuvette gap had high transfection rates than the 2 mm gap, and newborn cells exhibited higher transfection rates than adult cells. We achieved transfection rates of 10-12% with a cell viability of 25-30% for adult fibroblast cells. Subsequently, successfully edited the ITGB2 gene with a 30% editing efficiency, confirmed through various analysis methods, including T7E1 assay, TIDE and ICE analysis, and TA cloning. In conclusion, electroporation conditions reported here can edit buffalo gene(s) for various biotechnological research applications.

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.

Optimized Approaches for the Induction of Putative Canine Induced Pluripotent Stem Cells from Old Fibroblasts Using Synthetic RNAs

Simple Summary

A non-integrating and self-replicating Venezuelan equine encephalitis RNA replicon system can potentially make a great contribution to the generation of clinically applicable canine induced pluripotent stem cells. Our study shows a new method to utilize the synthetic RNA-based approach for canine somatic cell reprogramming regarding transfection and reprogramming efficiency.

Abstract

Canine induced pluripotent stem cells (ciPSCs) can provide great potential for regenerative veterinary medicine. Several reports have described the generation of canine somatic cell-derived iPSCs; however, none have described the canine somatic cell reprogramming using a non-integrating and self-replicating RNA transfection method. The purpose of this study was to investigate the optimal strategy using this approach and characterize the transition stage of ciPSCs. In this study, fibroblasts obtained from a 13-year-old dog were reprogrammed using a non-integrating Venezuelan equine encephalitis (VEE) RNA virus replicon, which has four reprogramming factors (collectively referred to as T7-VEE-OKS-iG and comprised of hOct4, hKlf4, hSox2, and hGlis1) and co-transfected with the T7-VEE-OKS-iG RNA and B18R mRNA for 4 h. One day after the final transfection, the cells were selected with puromycin (0.5 µg/mL) until day 10. After about 25 days, putative ciPSC colonies were identified showing TRA-1-60 expression and alkaline phosphatase activity. To determine the optimal culture conditions, the basic fibroblast growth factor in the culture medium was replaced with a modified medium supplemented with murine leukemia inhibitory factor (mLIF) and two kinase inhibitors (2i), PD0325901(MEK1/2 inhibitor) and CHIR99021 (GSK3β inhibitor). The derived colonies showed resemblance to naïve iPSCs in their morphology (dome-shaped) and are dependent on mLIF and 2i condition to maintain an undifferentiated phenotype. The expression of endogenous pluripotency markers such as Oct4, Nanog, and Rex1 transcripts were confirmed, suggesting that induced ciPSCs were in the late intermediate stage of reprogramming. In conclusion, the non-integrating and self-replicating VEE RNA replicon system can potentially make a great contribution to the generation of clinically applicable ciPSCs, and the findings of this study suggest a new method to utilize the VEE RNA approach for canine somatic cell reprogramming.

Efficient generation of GHR knockout Bama minipig fibroblast cells using CRISPR/Cas9-mediated gene editing

Dwarfism, also known as growth hormone deficiency (GHD), is a disease caused by genetic mutations that result in either a lack of growth hormone or insufficient secretion of growth hormone, resulting in a person's inability to grow normally. In the past, many studies focusing on GHD have made use of models of other diseases such as metabolic or infectious diseases. A viable GHD specific model system has not been used previously, thus limiting the interpretation of GHD results. The Bama minipig is unique to Guangxi province and has strong adaptability and disease resistance, and an incredibly short stature, which is especially important for the study of GHD. In addition, studies of GHR knockout Bama minipigs and GHR knockout Bama minipig fibroblast cells generated using CRISPR/Cas9 have not been previously reported. Therefore, the Bama minipig was selected as an animal model and as a tool for the study of GHD in this work. In this study, a Cas9 plasmid with sgRNA targeting the first exon of the GHR gene was transfected into Bama minipig kidney fibroblast cells to generate 22 GHR knockout Bama minipig kidney fibroblast cell lines (12 male monoclonal cells and 10 female monoclonal cells). After culture and identification, 11 of the 12 male clone cell lines showed double allele mutations, and the rate of positive alteration of GHR was 91.67%. Diallelic mutation of the target sequence occurred in 10 female clonal cell lines, with an effective positive mutation rate of 100%. Our experimental results not only showed that CRISPR/Cas9 could efficiently be used for gene editing in Bama minipig cells but also identified a highly efficient target site for the generation of a GHR knockout in other porcine models. Thus, the generation of GHR knockout male and female Bama fibroblast cells could lay a foundation for the birth of a future dwarfism model pig. We anticipate that the "mini" Bama minipig will be of improved use for biomedical and agricultural scientific research and for furthering our understanding of the genetic underpinnings of GHD.

Efficient Generation of Transgenic Buffalos (Bubalus bubalis) by Nuclear Transfer of Fetal Fibroblasts Expressing Enhanced Green Fluorescent Protein

The possibility of producing transgenic cloned buffalos by nuclear transfer of fetal fibroblasts expressing enhanced green fluorescent protein (EGFP) was explored in this study. When buffalo fetal fibroblasts (BFFs) isolated from a male buffalo fetus were transfected with pEGFP-N1 (EGFP is driven by CMV and Neo is driven by SV-40) by means of electroporation, Lipofectamine-LTX and X-tremeGENE, the transfection efficiency of electroporation (35.5%) was higher than Lipofectamine-LTX (11.7%) and X-tremeGENE (25.4%, P < 0.05). When BFFs were transfected by means of electroporation, more embryos from BFFs transfected with pEGFP-IRES-Neo (EGFP and Neo are driven by promoter of human elongation factor) cleaved and developed to blastocysts (21.6%) compared to BFFs transfected with pEGFP-N1 (16.4%, P < 0.05). A total of 72 blastocysts were transferred into 36 recipients and six recipients became pregnant. In the end of gestation, the pregnant recipients delivered six healthy calves and one stillborn calf. These calves were confirmed to be derived from the transgenic cells by Southern blot and microsatellite analysis. These results indicate that electroporation is more efficient than lipofection in transfecting exogenous DNA into BFFs and transgenic buffalos can be produced effectively by nuclear transfer of BFFs transfected with pEGFP-IRES-Neo.

Generation of Transgenic Porcine Fibroblast Cell Lines Using Nanomagnetic Gene Delivery Vectors

The transgenic process allows for obtaining genetically modified animals for divers biomedical applications. A number of transgenic animals for xenotransplantation have been generated with the somatic cell nuclear transfer (SCNT) method. Thereby, efficient nucleic acid delivery to donor cells such as fibroblasts is of particular importance. The objective of this study was to establish stable transgene expressing porcine fetal fibroblast cell lines using magnetic nanoparticle-based gene delivery vectors under a gradient magnetic field. Magnetic transfection complexes prepared by self-assembly of suitable magnetic nanoparticles, plasmid DNA, and an enhancer under an inhomogeneous magnetic field enabled the rapid and efficient delivery of a gene construct (pCD59-GFPBsd) into porcine fetal fibroblasts. The applied vector dose was magnetically sedimented on the cell surface within 30 min as visualized by fluorescence microscopy. The PCR and RT-PCR analysis confirmed not only the presence but also the expression of transgene in all magnetofected transgenic fibroblast cell lines which survived antibiotic selection. The cells were characterized by high survival rates and proliferative activities as well as correct chromosome number. The developed nanomagnetic gene delivery formulation proved to be an effective tool for the production of genetically engineered fibroblasts and may be used in future in SCNT techniques for breeding new transgenic animals for the purpose of xenotransplantation.

Emerging Technologies to Create Inducible and Genetically Defined Porcine Cancer Models

There is an emerging need for new animal models that address unmet translational cancer research requirements. Transgenic porcine models provide an exceptional opportunity due to their genetic, anatomic, and physiological similarities with humans. Due to recent advances in the sequencing of domestic animal genomes and the development of new organism cloning technologies, it is now very feasible to utilize pigs as a malleable species, with similar anatomic and physiological features with humans, in which to develop cancer models. In this review, we discuss genetic modification technologies successfully used to produce porcine biomedical models, in particular the Cre-loxP System as well as major advances and perspectives the CRISPR/Cas9 System. Recent advancements in porcine tumor modeling and genome editing will bring porcine models to the forefront of translational cancer research.

Production of transgenic cloned pigs expressing the far-red fluorescent protein monomeric Plum

Monomeric Plum (Plum), a far-red fluorescent protein with photostability and photopermeability, is potentially suitable for in vivo imaging and detection of fluorescence in body tissues. The aim of this study was to generate transgenic cloned pigs exhibiting systemic expression of Plum using somatic cell nuclear transfer (SCNT) technology. Nuclear donor cells for SCNT were obtained by introducing a Plum-expression vector driven by a combination of the cytomegalovirus early enhancer and chicken beta-actin promoter into porcine fetal fibroblasts (PFFs). The cleavage and blastocyst formation rates of reconstructed SCNT embryos were 81.0% (34/42) and 78.6% (33/42), respectively. At 36-37 days of gestation, three fetuses systemically expressing Plum were obtained from one recipient to which 103 SCNT embryos were transferred (3/103, 2.9%). For generation of offspring expressing Plum, rejuvenated PFFs were established from one cloned fetus and used as nuclear donor cells. Four cloned offspring and one stillborn cloned offspring were produced from one recipient to which 117 SCNT embryos were transferred (5/117, 4.3%). All offspring exhibited high levels of Plum fluorescence in blood cells, such as lymphocytes, monocytes and granulocytes. In addition, the skin, heart, kidney, pancreas, liver and spleen also exhibited Plum expression. These observations demonstrated that transfer of the Plum gene did not interfere with the development of porcine SCNT embryos and resulted in the successful generation of transgenic cloned pigs that systemically expressed Plum. This is the first report of the generation and characterization of transgenic cloned pigs expressing the far-red fluorescent protein Plum.

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.

A transgenic zebrafish model for monitoring glucocorticoid receptor activity

Gene regulation resulting from glucocorticoid receptor and glucocorticoid response element interactions is a hallmark feature of stress response signaling. Imbalanced glucocorticoid production and glucocorticoid receptor activity have been linked to socioeconomically crippling neuropsychiatric disorders, and accordingly there is a need to develop in vivo models to help understand disease progression and management. Therefore, we developed the transgenic SR4G zebrafish reporter line with six glucocorticoid response elements used to promote expression of a short half-life green fluorescent protein following glucocorticoid receptor activation. Herein, we document the ability of this reporter line to respond to both chronic and acute exogenous glucocorticoid treatment. The green fluorescent protein expression in response to transgene activation was high in a variety of tissues including the brain, and provided single-cell resolution in the effected regions. The specificity of these responses is demonstrated using the partial agonist mifepristone and mutation of the glucocorticoid receptor. Importantly, the reporter line also modeled the temporal dynamics of endogenous stress response signaling, including the increased production of the glucocorticoid cortisol following hyperosmotic stress and the fluctuations of basal cortisol concentrations with the circadian rhythm. Taken together, these results characterize our newly developed reporter line for elucidating environmental or genetic modifiers of stress response signaling, which may provide insights to the neuronal mechanisms underlying neuropsychiatric disorders such as major depressive disorder.

Completion of the swine genome will simplify the production of swine as a large animal biomedical model

Background

Anatomic and physiological similarities to the human make swine an excellent large animal model for human health and disease.

Methods

Cloning from a modified somatic cell, which can be determined in cells prior to making the animal, is the only method available for the production of targeted modifications in swine.

Results

Since some strains of swine are similar in size to humans, technologies that have been developed for swine can be readily adapted to humans and vice versa. Here the importance of swine as a biomedical model, current technologies to produce genetically enhanced swine, current biomedical models, and how the completion of the swine genome will promote swine as a biomedical model are discussed.

Conclusions

The completion of the swine genome will enhance the continued use and development of swine as models of human health, syndromes and conditions.

Il2rg gene-targeted severe combined immunodeficiency pigs

A porcine model of severe combined immunodeficiency (SCID) promises to facilitate human cancer studies, the humanization of tissue for xenotransplantation, and the evaluation of stem cells for clinical therapy, but SCID pigs have not been described. We report here the generation and preliminary evaluation of a porcine SCID model. Fibroblasts containing a targeted disruption of the X-linked interleukin-2 receptor gamma chain gene, Il2rg, were used as donors to generate cloned pigs by serial nuclear transfer. Germline transmission of the Il2rg deletion produced healthy Il2rg(+/-) females, while Il2rg(-/Y) males were athymic and exhibited markedly impaired immunoglobulin and T and NK cell production, robustly recapitulating human SCID. Following allogeneic bone marrow transplantation, donor cells stably integrated in Il2rg(-/Y) heterozygotes and reconstituted the Il2rg(-/Y) lymphoid lineage. The SCID pigs described here represent a step toward the comprehensive evaluation of preclinical cellular regenerative strategies.

α1,3-galactosyltransferase deficiency in germ-free miniature pigs increases N-glycolylneuraminic acids as the xenoantigenic determinant in pig-human xenotransplantation

In this study, we examined whether Hanganutziu-Deicher (H-D) antigens are important as an immunogenic non-α1,3-galactose (Gal) epitope in pigs with a disrupted α1,3-galactosyltransferase gene. The targeting efficiency of the AO blood genotype was achieved (2.2%) in pig fibroblast cells. A total of 1800 somatic cell nuclear transfer (SCNT) embryos were transferred to 10 recipients. One recipient developed to term and naturally delivered two piglets. The α1,3-galactosyltransferase activity in lung, liver, spleen, and testis of heterozygote α1,3-galactosyltransferase gene knockout (GalT-KO) pigs was significantly decreased, whereas brain and heart showed very low decreasing levels of α1,3-galactosyltransferase activity when compared to those of control. Enzyme-linked lectinosorbent assay showed that the heterozygote GalT-KO pig had more sialylα2,6- and sialylα2,3-linked glycan than the control. Furthermore, the heart, liver, and kidney of the heterozygote GalT-KO pig had a higher N-glycolylneuraminic acid (Neu5Gc) content than the control, whereas the lung of the heterozygote GalT-KO pig had Neu5Gc content similar to the control. Collectively, the data strongly indicated that Neu5Gc is a more critical xenoantigen to overcoming the next acute immune rejection in pig to human xenotransplantation.

Development of transgenic cloned pig models of skin inflammation by DNA transposon-directed ectopic expression of human β1 and α2 integrin

Integrins constitute a superfamily of transmembrane signaling receptors that play pivotal roles in cutaneous homeostasis by modulating cell growth and differentiation as well as inflammatory responses in the skin. Subrabasal expression of integrins α2 and/or β1 entails hyperproliferation and aberrant differentiation of keratinocytes and leads to dermal and epidermal influx of activated T-cells. The anatomical and physiological similarities between porcine and human skin make the pig a suitable model for human skin diseases. In efforts to generate a porcine model of cutaneous inflammation, we employed the Sleeping Beauty DNA transposon system for production of transgenic cloned Göttingen minipigs expressing human β1 or α2 integrin under the control of a promoter specific for subrabasal keratinocytes. Using pools of transgenic donor fibroblasts, cloning by somatic cell nuclear transfer was utilized to produce reconstructed embryos that were subsequently transferred to surrogate sows. The resulting pigs were all transgenic and harbored from one to six transgene integrants. Molecular analyses on skin biopsies and cultured keratinocytes showed ectopic expression of the human integrins and localization within the keratinocyte plasma membrane. Markers of perturbed skin homeostasis, including activation of the MAPK pathway, increased expression of the pro-inflammatory cytokine IL-1α, and enhanced expression of the transcription factor c-Fos, were identified in keratinocytes from β1 and α2 integrin-transgenic minipigs, suggesting the induction of a chronic inflammatory phenotype in the skin. Notably, cellular dysregulation obtained by overexpression of either β1 or α2 integrin occurred through different cellular signaling pathways. Our findings mark the creation of the first cloned pig models with molecular markers of skin inflammation. Despite the absence of an overt psoriatic phenotype, these animals may possess increased susceptibility to severe skin damage-induced inflammation and should be of great potential in studies aiming at the development and refinement of topical therapies for cutaneous inflammation including psoriasis.

[TSA improve transgenic porcine cloned embryo development and transgene expression]

Uncompleted epigenetic reprogramming is attributed to the low efficiency of producing transgenic cloned animals. Histone modification associated with epigenetics can directly influence the embryo development and transgene expression. Trichostatin A (TSA), as an inhibitor of histone deacetylase, can change the status of histone acetylation, improve somatic cell reprogramming, and enhance cloning efficiency. TSA prevents the chromatin structure from being condensed, so that transcription factor could binds to DNA sequence easily and enhance transgene expression. Our study established the optimal TSA treatment on porcine donor cells and cloned embryos, 250 nmol/L, 24 h and 40 nmol/L, 24 h, respectively. Furthermore, we found that both the cloned embryo and the donor cell treated by TSA resulted in the highest development efficiency. Meanwhile, TSA can improve transgene expression in donor cell and cloned embryo. In summary, TSA can significantly improve porcine reconstructed embryo development and transgene expression.

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.

Neurogenic differentiation of EGFP gene transfected amniotic fluid-derived stem cells from pigs at intermediate and late gestational ages

The aims of this study were (i) to determine whether amniotic fluid-derived stem cells (amniotic fluid-derived stem; AFS cells) could be isolated from pigs at intermediate and late gestational ages, and (ii) to determine if these AFS cells could be differentiated in vitro into neural lineages following transfection with a reporter gene, enhanced green fluorescence protein (EGFP). Amniotic fluid-derived stem cells were isolated from embryonic day 60 and day 110 porcine amniotic fluid respectively, and transfected with EGFP gene using lipofection. The transfected AFS cells were induced to differentiate into cells of neuronal lineages. Markers associated with undifferentiated AFS cells and their neural derivatives were tested by polymerase chain reaction. The results demonstrated that porcine AFS cells could be isolated at intermediate and late gestational ages and that transfected AFS expressed EGFP and could be induced to differentiate in vitro. Undifferentiated AFS cells expressed POU5F1, THY1 and SOX2, while following differentiation cells expressed markers for astrocytes (GFAP), oligodendrocytes (GALC) and neurons (NF, ENOS and MAP2).

Pig transgenesis by Sleeping Beauty DNA transposition

Modelling of human disease in genetically engineered pigs provides unique possibilities in biomedical research and in studies of disease intervention. Establishment of methodologies that allow efficient gene insertion by non-viral gene carriers is an important step towards development of new disease models. In this report, we present transgenic pigs created by Sleeping Beauty DNA transposition in primary porcine fibroblasts in combination with somatic cell nuclear transfer by handmade cloning. Göttingen minipigs expressing green fluorescent protein are produced by transgenesis with DNA transposon vectors carrying the transgene driven by the human ubiquitin C promoter. These animals carry multiple copies (from 8 to 13) of the transgene and show systemic transgene expression. Transgene-expressing pigs carry both transposase-catalyzed insertions and at least one copy of randomly inserted plasmid DNA. Our findings illustrate critical issues related to DNA transposon-directed transgenesis, including coincidental plasmid insertion and relatively low Sleeping Beauty transposition activity in porcine fibroblasts, but also provide a platform for future development of porcine disease models using the Sleeping Beauty gene insertion technology.

Osteogenic and neurogenic differentiation of EGFP gene transfected neural stem cells derived from the brain of porcine fetuses at intermediate and late gestational age

The aims of this study were (i) to determine whether NSCs (neural stem cells) could be isolated from the brain of porcine fetuses at intermediate and late gestational age and (ii) to determine if these stem cells could be differentiated in vitro into osteogenic and neurogenic lineages following transfection with a reporter gene, EGFP (enhanced green fluorescence protein). The NSCs were isolated from the brains of porcine fetuses at intermediate and late gestational age and transfected with EGFP gene using lipofection. The transfected NSCs cells were induced to differentiate into cells of osteogenic and neurogenic lineages. Markers associated with NSCs and their osteogenic and neurogenic derivatives were tested by PCR. The results demonstrated that NSCs could be isolated from the brain of porcine fetus at intermediate and late gestational age and that transfected NSCs expressed EGFP and could be induced to differentiate in vitro. NSCs expressed CD-90, Hes1, Oct4, Sox2 and Nestin, while following differentiation cells expressed markers for osteogenic (osteocalcin and osteonectin) and neurogenic cells such as astrocyte [GFAP (glial fibrillary acidic protein)], oligodendrocyte [GALC (galactosylceramide)] and neuron [NF (neurofilament), ENO2 (enolase 2) and MAP (microtubule-associated protein)].

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.

Development of cloned embryos from porcine neural stem cells and amniotic fluid-derived stem cells transfected with enhanced green fluorescence protein gene

We assessed the developmental ability of embryos cloned from porcine neural stem (NS) cells, amniotic fluid-derived stem (AFS) cells, fetal fibroblast cells, adult fibroblast, and mammary gland epithelial cells. The five cell lines were transfected with enhanced green fluorescence protein gene respectively using lipofection. NS and AFS cells were induced to differentiate in vitro. Stem cells and their differentiated cells were harvested for analysis of the markers using RT-PCR. The five cell lines were used for nuclear transfer. The two-cell stage-cloned embryos derived from each cell line were transferred into the oviducts of surrogate mothers. The results showed that both NS and AFS cells expressed POU5F1, THY1 and SOX2, and they were both induced to differentiate into astrocyte (GFAP+), oligodendrocyte (GalC+), neuron (NF+, ENO2+, and MAP2+), adipocyte (LPL+ and PPARG-D+), osteoblast (osteonectin+ and osteocalcin+), myocyte (MYF6+ and MYOD+), and endothelium (PECAM1+, CD34+, CDH5+, and NOS3+) respectively. Seven cloned fetuses (28 days and 32 days) derived from stem cells were obtained. The in vitro developmental ability (morula-blastocyst rate was 28.26-30.07%) and in vivo developmental ability (pregnancy rate were 1.67-2.17%) of the embryos cloned from stem cells were higher (P<0.05) than that of the embryos cloned from somatic cells (morula-blastocyst rate was 16.27-19.28% and pregnancy rate was 0.00%), which suggests that the undifferentiated state of the donor cells increases cloning efficiency.

Transgene expression of enhanced green fluorescent protein in cloned rabbits generated from in vitro-transfected adult fibroblasts

Live rabbits have previously been generated through nuclear transfer using adult cells as nuclear donors. We demonstrated in this study that transfected adult rabbit fibroblasts are also capable of supporting full-term development. The fibroblasts were transfected with a pEGFP-C1 plasmid using lipofectamine() 2000, and the transgenic cells were derived from conditioned medium. The transgenic fibroblasts were cultured until confluent and then serum-starved prior to be used as nuclear donors. After nuclear transfer and activation, 22% (12/55) of the transgenic cloned embryos developed to the blastocyst stage. A total of 114 embryos at the 4- to 8-cell stage were transferred to the oviducts of 8 pseudo-pregnant mothers; 5 of these animals became pregnant, and 3 of the 5 mother rabbits carried the pregnancy to term. Caesarean section was performed on the 3 pregnant mothers, yielding 4 kits, one of which has survived for more than 9 months. Green fluorescence could be detected in the toenails of the living cloned rabbit and the offspring from the living cloned rabbit under ultraviolet light. DNA analyses confirmed that all 4 cloned rabbits were genetically identical to the transgenic donor cells, and that they all carried the EGFP gene. The present study demonstrated that transgenic rabbits can be generated through nuclear transfer. These results may facilitate future developments in the genetic engineering of rabbits.

Transgenic-cloned pigs systemically expressing red fluorescent protein, Kusabira-Orange

Genetically engineered pigs with cell markers such as fluorescent proteins are highly useful in lines of research that include the tracking of transplanted cells or tissues. In this study, we produced transgenic-cloned pigs carrying a gene for the newly developed red fluorescent protein, humanized Kusabira-Orange (huKO), which was cloned from the coral stone Fungia concinna. The nuclear transfer embryos, reconstructed with fetal fibroblast cells that had been transduced with huKO cDNA using retroviral vector D Delta Nsap, developed efficiently in vitro into blastocysts (28.0%, 37/132). Nearly all (94.6%, 35/37) of the cloned blastocysts derived from the transduced cells exhibited clear huKO gene expression. A total of 429 nuclear transfer embryos were transferred to four recipients, all of which became pregnant and gave birth to 18 transgenic-cloned offspring in total. All of the pigs highly expressed huKO fluorescence in all of the 23 organs and tissues analyzed, including the brain, eyes, intestinal and reproductive organs, skeletal muscle, bone, skin, and hoof. Furthermore, such expression was also confirmed by histological analyses of various tissues such as pancreatic islets, renal corpuscles, neuronal and glial cells, the retina, chondrocytes, and hematopoietic cells. These data demonstrate that transgenic-cloned pigs exhibiting systemic red fluorescence expression can be efficiently produced by nuclear transfer of somatic cells retrovirally transduced with huKO gene.

Identification of genes downregulated during differentiation of porcine mesenteric adipocytes

Adipose tissue development is a process that comprises not only hypertrophy, but also hyperplasia, of adipocytes. Although the proliferation of undifferentiated preadipocytes plays an important part in hyperplasia, this process is less well understood than the post-proliferation differentiation process. Despite the potential importance of porcine visceral adipose tissue to both meat production and biomedical research, there has been little study of this tissue and, in particular, its development and differentiation. To detect the genes involved in the maintenance of porcine visceral preadipocytes in an undifferentiated state or in the inhibition of adipocyte differentiation, we performed suppression subtractive hybridization using mesenteric preadipocytes in which fragments of the genes that are downregulated at 2 d of differentiation were enriched. We selected 672 clones and subjected them to differential screening and semiquantitative reverse transcription (RT)-PCR. As a result, we identified 34 downregulated genes. Among these, the detailed expression patterns of 6 genes were examined using real-time RT-PCR in both preadipocytes during in vitro differentiation and cell fractions directly isolated from pig mesenteric adipose tissue. The expressions of connective tissue growth factor, AXL receptor tyrosine kinase, stromal membrane-associated protein 1-like, and retinoic acid-induced 14 were significantly downregulated during adipocyte differentiation in vitro (P < 0.05), and the expressions of Rho/Rac guanine nucleotide exchange factor 2 and secreted frizzled-related protein 4 also tended to be decreased, although not significantly. Furthermore, all 6 genes showed significantly greater expression in stromal vascular cells, which contain preadipocytes, than in mature adipocytes (P < 0.05), raising the possibility that these genes are involved in adipocyte differentiation in vivo as well as in vitro.

High in vitro development after somatic cell nuclear transfer and trichostatin A treatment of reconstructed porcine embryos

Abnormal epigenetic modification is supposed to be one of factors accounting for inefficient reprogramming of the donor cell nuclei in ooplasm after somatic cell nuclear transfer (SCNT). Trichostatin A (TSA) is an inhibitor of histone deacetylase, potentially enhancing cloning efficiency. The aim of our present study was to establish the optimal TSA treatment in order to improve the development of handmade cloned (HMC) porcine embryos and examine the effect of TSA on their development. The blastocyst percentage of HMC embryos treated with 37.5 nM TSA for 22-24 h after activation increased up to 80% (control group-54%; P<0.05). TSA mediated increase in histone acetylation was proved by immunofluorescence analysis of acH3K9 and acH4K16. 2-cell stage embryos derived from TSA treatment displayed significant increase in histone acetylation compared to control embryos, whereas no significant differences were observed at blastocyst stage. During time-lapse monitoring, no difference was observed in the kinetics of 2-cell stage embryos. Compact morula (CM) stage was reached 15 h later in TSA treated embryos compared to the control. Blastocysts (Day 5 and 6) from HMC embryos treated with TSA were transferred to 2 recipients resulting in one pregnancy and birth of one live and five dead piglets. Our data demonstrate that TSA treatment after HMC in pigs may affect reprogramming of the somatic genome resulting in higher in vitro embryo development, and enable full-term in vivo development.

Development of porcine transgenic nuclear-transferred embryos derived from fibroblast cells transfected by the novel technique of nucleofection or standard lipofection

The aim of our study was to determine the in vitro developmental potential of porcine nuclear-transferred (NT) embryos that had been reconstructed with Tg(pWAPhGH-GFPBsd) transgene-expressing fibroblast cells. The gene construct was introduced into fibroblast cells by the novel method of nucleofection or standard lipofection. NT oocytes derived from foetal and adult dermal fibroblast cells were stimulated by either simultaneous fusion and electrical activation (Groups IA and IB) or sequential electrical and chemical activation (Groups IIA and IIB). The percentages of cloned embryos that reached the morula and blastocyst stages were 152/254 (59.8%) and 77/254 (30.3%) or 139/276 (50.4%) and 45/276 (16.3%) in Groups IA or IB, respectively. The rates of NT embryos that developed to the morula and blastocyst stages were 103/179 (57.5%) and 41/179 (22.9%) or 84/193 (43.5%) and 27/193 (14.0%) in Groups IIA and IIB, respectively. In conclusion, the in vitro developmental competences of porcine transgenic NT embryos that had been reconstructed with the Tg(pWAPhGH-GFPBsd) gene-transfected fibroblast cells were relatively high. Further, the nucleofection efficiency of all the porcine fibroblast cell lines as estimated by intra-vitam fluorescent evaluation based on the index of reporter eGFP transgene expression was nearly 100%. However, PCR analysis for transgene screening confirmed the absence of Tg(pWAPhGH-GFPBsd) fusion gene in some of the nucleofected cell lines. To our knowledge, the novel method of nucleofection is the first to transfect nuclear donor cells in the production of transgenic cloned embryos.

Efficient transfection of primarily cultured porcine embryonic fibroblasts using the Amaxa Nucleofection system

Porcine embryonic fibroblasts (PEF) are important as donor cells for nuclear transfer for generation of genetically modified pigs. In this study, we determined an optimal protocol for transfection of PEF with the Amaxa Nucleofection system, which directly transfers DNA into the nucleus of cells, and compared its efficiency with conventional lipofection and electroporation. Cell survival and transfection efficiency were assessed using dye-exclusion assay and a green fluorescent protein (GFP) reporter construct, respectively. Our optimized nucleofection parameters yielded survival rates above 60%. Under these conditions, FACS analysis demonstrated that 79% of surviving cells exhibited transgene expression 48 h after nucleofection when program U23 was used. This efficiency was higher than that of transfection of PEFs with electroporation (ca. 3-53%) or lipofection (ca. 3-8%). Transfected cells could be expanded as stably transgene-expressing clones over a month. When porcine nuclear transfer (NT) was performed using stable transformant expressing GFP as a donor cell, 5-6% of reconstituted embryos developed to blastocysts, from which 30-50% of embryos exhibited NT-embryo-derived green fluorescence. Under the conditions evaluated, nucleofection exhibited higher efficiency than conventional electroporation and lipofection, and may be a useful alternative for generation of genetically engineered pigs through nuclear transfer.

Production of transgenic and non-transgenic clones in miniature pigs by somatic cell nuclear transfer

Miniature pigs have been recognized as valuable experimental animals in various fields such as medical and pharmaceutical research. However, the amount of information on somatic cell cloning in miniature pigs, as well as genetically modified miniature pigs, is much less than that available for common domestic pigs. The objective of the present study was to establish an efficient technique of cloning miniature pigs by somatic cell nuclear transfer. A high pregnancy rate was achieved following transfer of parthenogenetic (3/3) and cloned (5/6) embryos using female miniature pigs in the early pregnancy period as recipients after estrus synchronization with prostaglandin F2 alpha analog and gonadotrophins. The production efficiency of the cloned miniature pigs using male and female fetal fibroblasts as nucleus donors was 0.9% (2/215 and 3/331, respectively). Cloned miniature pigs were also produced efficiently (7.8%, 5/64) by transferring reconstructed embryos into the uteri of common domestic pigs. When donor cells transfected with the green fluorescent protein (GFP) gene were used in nuclear transfer, the production efficiency of the reconstructed embryos and rate of blastocyst development were comparable to those obtained by non-transfected cells. When transfected cell-derived reconstructed embryos were transferred to three common domestic pig recipients, all became pregnant, and a total of ten transgenic cloned miniature pigs were obtained (piglet production efficiency: 2.7%, 10/365). Hence, we were able to establish a practical system for producing cloned and transgenic-cloned miniature pigs with a syngeneic background.

Pigs taking wing with transposons and recombinases

Swine production has been an important part of our lives since the late Mesolithic or early Neolithic periods, and ranks number one in world meat production. Pig production also contributes to high-value-added medical markets in the form of pharmaceuticals, heart valves, and surgical materials. Genetic engineering, including the addition of exogenous genetic material or manipulation of the endogenous genome, holds great promise for changing pig phenotypes for agricultural and medical applications. Although the first transgenic pigs were described in 1985, poor survival of manipulated embryos; inefficiencies in the integration, transmission, and expression of transgenes; and expensive husbandry costs have impeded the widespread application of pig genetic engineering. Sequencing of the pig genome and advances in reproductive technologies have rejuvenated efforts to apply transgenesis to swine. Pigs provide a compelling new resource for the directed production of pharmaceutical proteins and the provision of cells, vascular grafts, and organs for xenotransplantation. Additionally, given remarkable similarities in the physiology and size of people and pigs, swine will increasingly provide large animal models of human disease where rodent models are insufficient. We review the challenges facing pig transgenesis and discuss the utility of transposases and recombinases for enhancing the success and sophistication of pig genetic engineering. 'The paradise of my fancy is one where pigs have wings.' (GK Chesterton).

Somatic cell nuclear transfer in pigs: recent achievements and future possibilities

During the past 6 years, considerable advancement has been achieved in experimental embryology of pigs. This process was mainly generated by the rapidly increasing need for transgenic pigs for biomedical research purposes, both for future xenotransplantation to replace damaged human organs or tissues, and for creating authentic animal models for human diseases to study aetiology, pathogenesis and possible therapy. Theoretically, among various possibilities, an established somatic cell nuclear transfer system with genetically engineered donor cells seems to be an efficient and reliable approach to achieve this goal. However, as the result of unfortunate coincidence of known and unknown factors, porcine embryology had been a handicapped branch of reproductive research in domestic animals and a very intensive and focused research was required to eliminate or minimise this handicap. This review summarises recent achievements both in the background technologies (maturation, activation, embryo culture) and the actual performance of the nuclear replacement. Recent simplified methods for in vivo development after embryo transfer are also discussed. Finally, several fields of potential application for human medical purposes are discussed. The authors conclude that although in this early phase of research no direct evidence can be provided about the practical use of transgenic pigs produced by somatic cell nuclear transfer as organ donors or disease models, the future chances even in medium term are good, and at least proportional with the efforts and sums that are invested into this research area worldwide.

Relation between human decay-accelerating factor (hDAF) expression in pig cells and inhibition of human serum anti-pig cytotoxicity: value of highly expressed hDAF for xenotransplantation

BACKGROUND

Although the successful production of alpha1,3-galactosyltransferase-knockout (GT-KO) pigs has increased expectations of clinical xenotransplantation, additional modifications of genetically engineered pigs are still being explored, because even GT-KO pigs are incapable of inhibiting the host's immunological response completely. One of the potential candidates is a complement-regulatory protein, such as human decay-accelerating factor (hDAF). However, there are few reports on how high the expression level of hDAF in pig cells would be required for suppression of complement activation. The purpose of this study was to examine the relationship between the level of hDAF expression and its inhibitory effect on human serum cytotoxicity.

METHODS

An expression (pCAGGS) vector containing the hDAF gene was transfected into pig fibroblasts using an electroporation system (Gene Pulser II). Forty-eight to fifty-two hours after transfection, the cells were stained with FITC-labeled anti-hDAF antibody and then applied to the cell sorter. hDAF-transfected cells with various expression levels were collected by gating on fluorescence intensity. The level of hDAF expression was determined relative to that in human control endothelial cells. Collected cells expressing x1, x5, x10, x15 and x30 hDAF were incubated into 96-well plates for 16 h, and the cells were subjected to 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT) assay.

RESULTS

hDAF expression levels in transfected cells at the time of MTT assay (16 h after sorting) were comparable to those immediately after sorting. hDAF expression in pig cells five times higher than in human endothelial cells was effective in inhibiting complement-dependent cytotoxicity of most human sera. However, 15- to 30-fold expression of hDAF was required for effective inhibition of human sera with the highest cytotoxic capacity.

CONCLUSIONS

A much higher level of hDAF expression in pig cells than previously considered necessary might be required to provide additional benefit in inhibiting antibody-mediated rejection. Genetically engineered pigs that express very high levels of hDAF would be beneficial for xenotransplantation.

In vitro developmental competence of pig nuclear transferred embryos: effects of GFP transfection, refrigeration, cell cycle synchronization and shapes of donor cells

The present study was designed to evaluate the feasibility of producing pig transgenic blastocysts expressing enhanced green fluorescent protein (GFP) and to examine the effects of shape and preparation methods of donor cells on in vitro developmental ability of pig nuclear transferred embryos (NTEs). In experiment 1, the effect of GFP transfection on development of pig NTEs was evaluated. The cleavage and blastocyst rates showed no significant difference between NTEs derived from transfected and non-transfected donors. In experiment 2, the effect of different nuclear donor preparation methods on in vitro development of NTEs was examined. The cleavage rate showed no statistically significant differences among three preparation methods. The blastocyst rates of donor cells treated once at −4 °C and those of freshly digested cells were similar to each other (26.3% vs 17.9%). The lowest blastocyst rates (5.88%) were observed when cells cryopreserved at −196 °C were used as donors. In experiment 3, the effect of different cell cycle synchronization methods on the in vitro development potential of pig NTEs was evaluated. The cleavage rate of NTEs derived from cycling cells was much better than that of NTEs derived from serum-starved cells (64.4% vs 50.5%, p < 0.05), but no significant difference was observed between the the blastocyst rates of the two groups. In experiment 4, the effect of different shapes of cultured fibroblast cells on the in vitro development of pig NTEs was examined. The fusion rate for couplets derived from rough cells was poorer than that observed in couplets derived from round smooth cells (47.8% vs 76.8%, p < 0.05). However, there were no significant differences observed in the cleavage rate and blastocyst rate. In conclusion, the present study indicated that (i) refrigerated pig GFP-transfected cells could be used as donors in nuclear transfer and these NTEs could be effectively developed to blastocyst stage; (ii) serum starvation of GFP-transfected cells is not required for preimplantation development of pig NTEs; and (iii) a rough surface of GFP-transfected donor cells affects fusion rate negatively but has no influence on the cleavage rate or blastocyst rate of pig NTEs.

Preparation of enzymatically active human Myc-tagged-NCre recombinase exhibiting immunoreactivity with anti-Myc antibody

The Cre-loxP system has been recognized as a tool for conditional gene targeting in mice. However, most anti-Cre antibodies fail to react with Cre expressed in vivo. In an attempt to directly detect Cre by antibodies in vivo, we constructed the tagged-NCre (NCreMH) gene by connecting the human Myc and His tag sequences to the 3' end of the NCre gene carrying a nuclear localizing signal (NLS) sequence. The production of NCre protein and the recombinase activity were detected after co-transfection with pCMV-NCreMH and pCETZ-17 carrying the loxP-flanked lacZ gene into NIH3T3 cells. This activity was also confirmed in vivo after gene transfer of pCMV-NCreMH and pCRTEIL-6 carrying loxP-flanked HcRed1 and EGFP cDNAs, into oviductal epithelium by electroporation. Immunohistochemical staining using anti-Myc antibody demonstrated that the area positive for enhanced green fluorescent protein (EGFP) fluorescence was immunostained with the antibody. These findings indicate that NCreMH is useful as an alternative to NCre for gene targeting.