Potential of primary kidney cells for somatic cell nuclear transfer mediated transgenesis in pig

Multiplexed genome engineering for porcine fetal fibroblasts with gRNA-tRNA arrays based on CRISPR/Cas9

Multiplex gene modifications are highly required for various fields of porcine research. In many species, the CRISPR/Cas9 system has been widely applied for genomic editing and provides a potential tool for introducing multiplex genome mutations simultaneously. Here, we present a CRISPR-Cas9 gRNA-tRNA array (GTR-CRISPR) for multiplexed engineering of porcine fetal fibroblasts (PFFs). We successfully produced multiple sgRNAs using only one Pol III promoter by taking advantage of the endogenous tRNA processing mechanism in porcine cells. Using an all-in-one construct carrying GTR and Cas9, we disrupted the IGFBP3, MSTN, MC4R, and SOCS2 genes in multiple codon regions in one PFF cell simultaneously. This technique allows the simultaneous disruption of four genes with 5.5% efficiency. As a result, this approach may effectively target multiple genes at the same time, making it a powerful tool for establishing multiple genes mutant cells in pigs.

- Invited Review - Reproductive technologies needed for the generation of precise gene-edited pigs in the pathways from laboratory to farm

Gene editing (GE) offers a new breeding technique (NBT) of sustainable value to animal agriculture. There are 3 GE working sites covering 5 feasible pathways to generate GE pigs along with the crucial intervals of GE/genotyping, microinjection/electroporation, induced pluripotent stem cells, somatic cell nuclear transfer, cryopreservation, and nonsurgical embryo transfer. The extension of NBT in the new era of pig breeding depends on the synergistic effect of GE and reproductive biotechnologies; the outcome relies not only on scientific due diligence and operational excellence but also on the feasibility of application on farms to improve sustainability.

A humanized minipig model for the toxicological testing of therapeutic recombinant antibodies

The safety of most human recombinant proteins can be evaluated in transgenic mice tolerant to specific human proteins. However, owing to insufficient genetic diversity and to fundamental differences in immune mechanisms, small-animal models of human diseases are often unsuitable for immunogenicity testing and for predicting adverse outcomes in human patients. Most human therapeutic antibodies trigger xenogeneic responses in wild-type animals and thus rapid clearance of the drugs, which makes in vivo toxicological testing of human antibodies challenging. Here we report the generation of Göttingen minipigs carrying a mini-repertoire of human genes for the immunoglobulin heavy chains γ1 and γ4 and the immunoglobulin light chain κ. In line with observations in human patients, the genetically modified minipigs tolerated the clinically non-immunogenic IgG1κ-isotype monoclonal antibodies daratumumab and bevacizumab, and elicited antibodies against the checkpoint inhibitor atezolizumab and the engineered interleukin cergutuzumab amunaleukin. The humanized minipigs can facilitate the safety and efficacy testing of therapeutic antibodies.

Production of Pigs From Porcine Embryos Generated in vitro

Generating porcine embryos in vitro is a critical process for creating genetically modified pigs as agricultural and biomedical models; however, these embryo technologies have been scarcely applied by the swine industry. Currently, the primary issue with in vitro-produced porcine embryos is low pregnancy rate after transfer and small litter size, which may be exasperated by micromanipulation procedures. Thus, in this review, we discuss improvements that have been made to the in vitro porcine embryo production system to increase the number of live piglets per pregnancy as well as abnormalities in the embryos and piglets that may arise from in vitro culture and manipulation techniques. Furthermore, we examine areas related to embryo production and transfer where improvements are warranted that will have direct applications for increasing pregnancy rate after transfer and the number of live born piglets per litter.

Early disruption of photoreceptor cell architecture and loss of vision in a humanized pig model of usher syndromes

Usher syndrome (USH) is the most common form of monogenic deaf-blindness. Loss of vision is untreatable and there are no suitable animal models for testing therapeutic strategies of the ocular constituent of USH, so far. By introducing a human mutation into the harmonin-encoding USH1C gene in pigs, we generated the first translational animal model for USH type 1 with characteristic hearing defect, vestibular dysfunction, and visual impairment. Changes in photoreceptor architecture, quantitative motion analysis, and electroretinography were characteristics of the reduced retinal virtue in USH1C pigs. Fibroblasts from USH1C pigs or USH1C patients showed significantly elongated primary cilia, confirming USH as a true and general ciliopathy. Primary cells also proved their capacity for assessing the therapeutic potential of CRISPR/Cas-mediated gene repair or gene therapy in vitro. AAV-based delivery of harmonin into the eye of USH1C pigs indicated therapeutic efficacy in vivo.

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

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

Transgenic pigs expressing near infrared fluorescent protein-A novel tool for noninvasive imaging of islet xenotransplants

BACKGROUND

Islet xenotransplantation is a promising concept for beta-cell replacement therapy. Reporter genes for noninvasive monitoring of islet engraftment, graft mass changes, long-term survival, and graft failure support the optimization of transplantation strategies. Near-infrared fluorescent protein (iRFP) is ideal for fluorescence imaging (FI) in tissue, but also for multispectral optoacoustic tomography (MSOT) with an even higher imaging depth. Therefore, we generated reporter pigs ubiquitously expressing iRFP.

METHODS

CAG-iRPF720 transgenic reporter pigs were generated by somatic cell nuclear transfer from FACS-selected stable transfected donor cells. Neonatal pig islets (NPIs) were transplanted into streptozotocin-diabetic immunodeficient NOD-scid IL2Rg^null (NSG) mice. FI and MSOT were performed to visualize different numbers of NPIs and to evaluate associations between signal intensity and glycemia. MSOT was also tested in a large animal model.

RESULTS

CAG-iRFP transgenic NPIs were functionally equivalent with wild-type NPIs. Four weeks after transplantation under the kidney capsule, FI revealed a twofold higher signal for 4000-NPI compared to 1000-NPI grafts. Ten weeks after transplantation, the fluorescence intensity of the 4000-NPI graft was inversely correlated with glycemia. After intramuscular transplantation into diabetic NSG mice, MSOT revealed clear dose-dependent signals for grafts of 750, 1500, and 3000 NPIs. Dose-dependent MSOT signals were also revealed in a pig model, with stronger signals after subcutaneous (depth ∼6 mm) than after submuscular (depth ∼15 mm) placement of the NPIs.

CONCLUSIONS

Islets from CAG-iRFP transgenic pigs are fully functional and accessible to long-term monitoring by state-of-the-art imaging modalities. The novel reporter pigs will support the development and preclinical testing of novel matrices and engraftment strategies for porcine xeno-islets.

Selective cytotoxicity mechanisms and biodistribution of diamond nanoparticles on the skin cancer in C57 mouse

The cytotoxicity of diamond nanoparticles (DNs) to various cell lines has been on focus by numerous scientists. The cellular toxicity system of DNs has not been fully understood or explained in skin cancer, at this point. This research was carried out to discover and reveal the potential impacts of DNs on the secluded brain, heart, liver, kidney, and skin in addition to evaluation of their cytotoxicity mechanism under test conditions. Their biological activities, for example cell viability, the level of reactive oxygen species (ROS), lipid peroxidation, cytochrome c release and Apoptosis/Necrosis were evaluated. Additionally, the bio-distribution of these nanomaterials in tissues was examined in the C57 mouse. Relying on the findings of the investigation, DNs were found to increase the ROS level, Malondialdehyde (MDA) content, release of cytochrome c, and cell death in skin significantly compared to other groups. In the C57 mouse, DNs were observed to have accumulated in skin tissue more intensively than they did in other organs. The present study presents for the proof that DNs can completely induce cell death signaling in skin cancer without bringing about a high cytotoxicity in other tissues. Results suggest that DNs can be valuable in recognition of skin cancer.

A scalable, clinically severe pig model for Duchenne muscular dystrophy

Large animal models for Duchenne muscular dystrophy (DMD) are crucial for evaluation of diagnostic procedures and treatment strategies. Pigs cloned from male cells lacking DMD exon 52 (DMDΔ52) resemble molecular, clinical and pathological hallmarks of DMD, but die before sexual maturity and cannot be propagated by breeding. Therefore, we generated female DMD+/- carriers. A single founder animal had 11 litters with 29 DMDY/-, 34 DMD+/- as well as 36 male and 29 female wild-type offspring. Breeding with F1 and F2 DMD+/- carriers resulted in additional 114 DMDY/- piglets. With intensive neonatal management, the majority survived for 3-4 months, providing statistically relevant cohorts for experimental studies. Pathological investigations and proteome studies of skeletal muscles and myocardium confirmed the resemblance of human disease mechanisms. Importantly, DMDY/- pigs reveal progressive myocardial fibrosis and increased expression of connexin-43, associated with significantly reduced left ventricular ejection fraction already at age 3 months. Furthermore, behavioral tests provided evidence for impaired cognitive ability. Our breeding cohort of DMDΔ52 pigs and standardized tissue repositories provide important resources for studying DMD disease mechanisms and for testing novel treatment strategies.

The Missing Link: Cre Pigs for Cancer Research

The Cre/loxP system is a powerful tool for the generation of animal models with precise spatial and temporal gene expression. It has proven indispensable in the generation of cancer models with tissue specific expression of oncogenes or the inactivation of tumor suppressor genes. Consequently, Cre-transgenic mice have become an essential prerequisite in basic cancer research. While it is unlikely that pigs will ever replace mice in basic research they are already providing powerful complementary resources for translational studies. But, although conditionally targeted onco-pigs have been generated, no Cre-driver lines exist for any of the major human cancers. To model human pancreatic cancer in pigs, Cre-driver lines were generated by CRISPR/Cas9-mediated insertion of codon-improved Cre (iCre) into the porcine PTF1A gene, thus guaranteeing tissue and cell type specific function which was proven using dual fluorescent reporter pigs. The method used can easily be adapted for the generation of other porcine Cre-driver lines, providing a missing tool for modeling human cancers in large animals.

Improved efficiencies in the generation of multigene-modified pigs by recloning and using sows as the recipient

This study was performed to improve production efficiency at the level of recipient pig and donor nuclei of transgenic cloned pigs used for xenotransplantation. To generate transgenic pigs, human endothelial protein C receptor (hEPCR) and human thrombomodulin (hTM) genes were introduced using the F2A expression vector into GalT-/-/hCD55+ porcine neonatal ear fibroblasts used as donor cells and cloned embryos were transferred to the sows and gilts. Cloned fetal kidney cells were also used as donor cells for recloning to increase production efficiency. Pregnancy and parturition rates after embryo transfer and preimplantation developmental competence were compared between cloned embryos derived from adult and fetal cells. Significantly higher parturition rates were shown in the group of sows (50.0 vs. 4.1%), natural oestrus (20.8 vs. 0%), and ovulated ovary (16.7 vs. 5.6%) compared with gilt, induced and non-ovulated, respectively (P < 0.05). When using gilts as recipients, final parturitions occurred in only the fetal cell groups and significantly higher blastocyst rates (15.1% vs. 21.3%) were seen (P < 0.05). Additionally, gene expression levels related to pluripotency were significantly higher in the fetal cell group (P < 0.05). In conclusion, sows can be recommended as recipients due to their higher efficiency in the generation of transgenic cloned pigs and cloned fetal cells also can be recommended as donor cells through correct nuclear reprogramming.

Direct conversion of porcine primary fibroblasts into hepatocyte-like cells

The pig is an important model organism for biomedical research, mainly due to its extensive genetic, physiological and anatomical similarities with humans. Until date, direct conversion of somatic cells into hepatocyte-like cells (iHeps) has only been achieved in rodents and human cells. Here, we employed lentiviral vectors to screen a panel of 12 hepatic transcription factors (TF) for their potential to convert porcine fibroblasts into hepatocyte-like cells. We demonstrate for the first time, hepatic conversion of porcine somatic cells by over-expression of CEBPα, FOXA1 and HNF4α2 (3TF-piHeps). Reprogrammed 3TF-piHeps display a hepatocyte-like morphology and show functional characteristics of hepatic cells, including albumin secretion, Dil-AcLDL uptake, storage of lipids and glycogen and activity of cytochrome P450 enzymes CYP1A2 and CYP2C33 (CYP2C9 in humans). Moreover, we show that markers of mature hepatocytes are highly expressed in 3TF-piHeps, while fibroblastic markers are reduced. We envision piHeps as useful cell sources for future studies on drug metabolism and toxicity as well as in vitro models for investigation of pig-to-human infectious diseases.

Pig Cloning Using Somatic Cell Nuclear Transfer

Porcine cloning technology can be used to produce progenies genetically identical to the donor cells from high-quality breeding pigs. In addition, genetically modified pigs have been produced by somatic cell nuclear transfer using genetically modified porcine fetal fibroblasts. The method of preparing genetically modified pigs is critical for establishing pig models for human diseases, and for generating donor animals for future xenotransplantation. This chapter describes detailed procedures for generating cloned pigs using fetal fibroblasts as nuclear donors.

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.

Cas9-expressing chickens and pigs as resources for genome editing in livestock

Genetically modified animals continue to provide important insights into the molecular basis of health and disease. Research has focused mostly on genetically modified mice, although other species like pigs resemble the human physiology more closely. In addition, cross-species comparisons with phylogenetically distant species such as chickens provide powerful insights into fundamental biological and biomedical processes. One of the most versatile genetic methods applicable across species is CRISPR-Cas9. Here, we report the generation of transgenic chickens and pigs that constitutively express Cas9 in all organs. These animals are healthy and fertile. Functionality of Cas9 was confirmed in both species for a number of different target genes, for a variety of cell types and in vivo by targeted gene disruption in lymphocytes and the developing brain, and by precise excision of a 12.7-kb DNA fragment in the heart. The Cas9 transgenic animals will provide a powerful resource for in vivo genome editing for both agricultural and translational biomedical research, and will facilitate reverse genetics as well as cross-species comparisons.

CRISPR/Cas9-mediated MSTN disruption accelerates the growth of Chinese Bama pigs

CRISPR/Cas9-mediated genome editing technology is a simple and highly efficient and specific genome modification approach with wide applications in the animal industry. CRISPR/Cas9-mediated genome editing combined with somatic cell nuclear transfer rapidly constructs gene-edited somatic cell-cloned pigs for the genetic improvement of traits or simulation of human diseases. Chinese Bama pigs are an excellent indigenous minipig breed from Bama County of China. Research on genome editing of Chinese Bama pigs is of great significance in protecting its genetic resource, improving genetic traits and in creating disease models. This study aimed to address the disadvantages of slow growth and low percentage of lean meat in Chinese Bama pigs and to knock out the myostatin gene (MSTN) by genome editing to promote growth and increase lean meat production. We first used CRISPR/Cas9-mediated genome editing to conduct biallelic knockout of the MSTN, followed by somatic cell nuclear transfer to successfully generate MSTN biallelic knockout Chinese Bama pigs, which was confirmed to have significantly faster growth rate and showed myofibre hyperplasia when they reached sexual maturity. This study lays the foundation for the rapid improvement of production traits of Chinese Bama pigs and the generation of gene-edited disease models in this breed.

Chaetocin Improves Pig Cloning Efficiency by Enhancing Epigenetic Reprogramming and Autophagic Activity

Efficient epigenetic reprogramming is crucial for the in vitro development of mammalian somatic cell nuclear transfer (SCNT) embryos. The aberrant levels of histone H3 lysine 9 trimethylation (H3K9me3) is an epigenetic barrier. In this study, we evaluated the effects of chaetocin, an H3K9me3-specific methyltransferase inhibitor, on the epigenetic reprogramming and developmental competence of porcine SCNT embryos. The SCNT embryos showed abnormal levels of H3K9me3 at the pronuclear, two-cell, and four-cell stages compared to in vitro fertilized embryos. Moreover, the expression levels of H3K9me3-specific methyltransferases (suv39h1 and suv39h2) and DNA methyltransferases (DNMT1, DNMT3a, and DNMT3b) were higher in SCNT embryos. Treatment with 0.5 nM chaetocin for 24 h after activation significantly increased the developmental competence of SCNT embryos in terms of the cleavage rate, blastocyst formation rate, hatching rate, cell number, expression of pluripotency-related genes, and cell survival rate. In particular, chaetocin enhanced epigenetic reprogramming by reducing the H3K9me3 and 5-methylcytosine levels and restoring the abnormal expression of H3K9me3-specific methyltransferases and DNA methyltransferases. Chaetocin induced autophagic activity, leading to a significant reduction in maternal mRNA levels in embryos at the pronuclear and two-cell stages. These findings revealed that chaetocin enhanced the developmental competence of porcine SCNT embryos by regulating epigenetic reprogramming and autophagic activity and so could be used to enhance the production of transgenic pigs for biomedical research.

A Single Amino Acid Substitution in the Matrix Protein (M51R) of Vesicular Stomatitis New Jersey Virus Impairs Replication in Cultured Porcine Macrophages and Results in Significant Attenuation in Pigs

In this study, we explore the virulence of vesicular stomatitis New Jersey virus (VSNJV) in pigs and its potential relationship with the virus’s ability to modulate innate responses. For this purpose, we developed a mutant of the highly virulent strain NJ0612NME6, containing a single amino acid substitution in the matrix protein (M51R). The M51R mutant of NJ0612NME6 was unable to suppress the transcription of genes associated with the innate immune response both in primary fetal porcine kidney cells and porcine primary macrophage cultures. Impaired viral growth was observed only in porcine macrophage cultures, indicating that the M51 residue is required for efficient replication of VSNJV in these cells. Furthermore, when inoculated in pigs by intradermal scarification of the snout, M51R infection was characterized by decreased clinical signs including reduced fever and development of less and smaller secondary vesicular lesions. Pigs infected with M51R had decreased levels of viral shedding and absence of RNAemia compared to the parental virus. The ability of the mutant virus to infect pigs by direct contact remained intact, indicating that the M51R mutation resulted in a partially attenuated phenotype capable of causing primary lesions and transmitting to sentinel pigs. Collectively, our results show a positive correlation between the ability of VSNJV to counteract the innate immune response in swine macrophage cultures and the level of virulence in pigs, a natural host of this virus. More studies are encouraged to evaluate the interaction of VSNJV with macrophages and other components of the immune response in pigs.

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.

Somatic gene editing ameliorates skeletal and cardiac muscle failure in pig and human models of Duchenne muscular dystrophy

Frameshift mutations in the DMD gene, encoding dystrophin, cause Duchenne muscular dystrophy (DMD), leading to terminal muscle and heart failure in patients. Somatic gene editing by sequence-specific nucleases offers new options for restoring the DMD reading frame, resulting in expression of a shortened but largely functional dystrophin protein. Here, we validated this approach in a pig model of DMD lacking exon 52 of DMD (DMDΔ52), as well as in a corresponding patient-derived induced pluripotent stem cell model. In DMDΔ52 pigs1, intramuscular injection of adeno-associated viral vectors of serotype 9 carrying an intein-split Cas9 (ref. 2) and a pair of guide RNAs targeting sequences flanking exon 51 (AAV9-Cas9-gE51) induced expression of a shortened dystrophin (DMDΔ51-52) and improved skeletal muscle function. Moreover, systemic application of AAV9-Cas9-gE51 led to widespread dystrophin expression in muscle, including diaphragm and heart, prolonging survival and reducing arrhythmogenic vulnerability. Similarly, in induced pluripotent stem cell-derived myoblasts and cardiomyocytes of a patient lacking DMDΔ52, AAV6-Cas9-g51-mediated excision of exon 51 restored dystrophin expression and amelioreate skeletal myotube formation as well as abnormal cardiomyocyte Ca2+ handling and arrhythmogenic susceptibility. The ability of Cas9-mediated exon excision to improve DMD pathology in these translational models paves the way for new treatment approaches in patients with this devastating disease.

Early weaning completely eliminates porcine cytomegalovirus from a newly established pig donor facility for xenotransplantation

For clinical xenotransplantation, transplants must be free of porcine cytomegalovirus (PCMV). Piglets become infected primarily in the perinatal period by the mother sow. While individual donor animals can be protected from infection by isolation husbandry, success is not guaranteed and this strategy poses the risk of undetected infections and raises animal welfare questions. Here, we present the establishment of a completely PCMV-negative pig herd for breeding donor animals for xenotransplantation. Eleven pregnant DanAvl Basic hybrid sows were purchased from a designated pathogen-free (DPF), PCMV-positive colony and transferred to a new pig facility at the Centre for Innovative Medical Models (CiMM) 4 weeks prior to farrowing. At the age of 24 hours, piglets were early-weaned and transferred to a commercially available Rescue Deck system dedicated to motherless rearing of piglets. Sows were removed from the facility. The PCMV status of F1-generation animals was determined at regular intervals over a period of 14 months by a sensitive real-time PCR-based detection method testing blood, nasal swabs and cultured peripheral blood mononuclear cells (PBMCs). F1 sows were used as recipients of genetically modified embryos to generate a xenotransplant donor herd. Offspring were tested for PCMV accordingly. All offspring have remained PCMV negative over the whole observation period of 14 months. A completely PCMV-negative pig herd for xenotransplantation has thus been successfully established.

Gene Editing in Primary Cells of Cattle and Pig

Gene Editing by CRISPR/Cas has revolutionized many aspects of biotechnology within a short period of time. This is also true for the genetic manipulation of livestock species, but their specific challenges such as the lack of stem cells, the limited proliferative capacity of primary cells, and the genetic diversity of the pig and cattle populations need consideration when CRISPR/Cas is applied. Here we present guidelines for CRISPRing primary cells in pig and cattle, with a specific focus on testing gRNA in vitro, on generating single cell clones, and on identifying modifications in single cell clones.

OCT4/POU5F1 is required for NANOG expression in bovine blastocysts

Mammalian preimplantation development involves two lineage specifications: first, the CDX2-expressing trophectoderm (TE) and a pluripotent inner cell mass (ICM) are separated during blastocyst formation. Second, the pluripotent epiblast (EPI; expressing NANOG) and the differentiated primitive endoderm (PrE; expressing GATA6) diverge within the ICM. Studies in mice revealed that OCT4/POU5F1 is at the center of a pluripotency regulatory network. To study the role of OCT4 in bovine preimplantation development, we generated OCT4 knockout (KO) fibroblasts by CRISPR-Cas9 and produced embryos by somatic cell nuclear transfer (SCNT). SCNT embryos from nontransfected fibroblasts and embryos produced by in vitro fertilization served as controls. In OCT4 KO morulae (day 5), ∼70% of the nuclei were OCT4 positive, indicating that maternal OCT4 mRNA partially maintains OCT4 protein expression during early development. In contrast, OCT4 KO blastocysts (day 7) lacked OCT4 protein entirely. CDX2 was detected only in TE cells; OCT4 is thus not required to suppress CDX2 in the ICM. Control blastocysts showed a typical salt-and-pepper distribution of NANOG- and GATA6-positive cells in the ICM. In contrast, NANOG was absent or very faint in the ICM of OCT4 KO blastocysts, and no cells expressing exclusively NANOG were observed. This mimics findings in OCT4-deficient human blastocysts but is in sharp contrast to Oct4-null mouse blastocysts, where NANOG persists and PrE development fails. Our study supports bovine embryogenesis as a model for early human development and exemplifies a general strategy for studying the roles of specific genes in embryos of domestic species.

Bone marrow mesenchymal stem cells as nuclear donors improve viability and health of cloned horses

Introduction

Cell plasticity is crucial in cloning to allow an efficient nuclear reprogramming and healthy offspring. Hence, cells with high plasticity, such as multipotent mesenchymal stem cells (MSCs), may be a promising alternative for horse cloning. In this study, we evaluated the use of bone marrow-MSCs (BM-MSCs) as nuclear donors in horse cloning, and we compared the in vitro and in vivo embryo development with respect to fibroblasts.

Materials and methods

Zona-free nuclear transfer was performed using BM-MSCs (MSC group, n=3432) or adult fibroblasts (AF group, n=4527). Embryos produced by artificial insemination (AI) recovered by uterine flushing and transferred to recipient mares were used as controls (AI group).

Results

Blastocyst development was higher in the MSC group than in the AF group (18.1% vs 10.9%, respectively; p<0.05). However, pregnancy rates and delivery rates were similar in both cloning groups, although they were lower than in the AI group (pregnancy rates: 17.7% [41/232] for MSC, 12.5% [37/297] for AF and 80.7% [71/88] for AI; delivery rates: 56.8% [21/37], 41.5% [17/41] and 90.1% [64/71], respectively). Remarkably, the gestation length of the AF group was significantly longer than the control (361.7±10.9 vs 333.9±8.7 days), in contrast to the MSC group (340.6±8.89 days). Of the total deliveries, 95.2% (20/21) of the MSC-foals were viable, compared to 52.9% (9/17) of the AF-foals (p<0.05). In addition, the AF-foals had more physiological abnormalities at birth than the MSC-foals; 90.5% (19/21) of the MSC-delivered foals were completely normal and healthy, compared to 35.3% (6/17) in the AF group. The abnormalities included flexural or angular limb deformities, umbilical cord enlargement, placental alterations and signs of syndrome of neonatal maladjustment, which were treated in most cases.

Conclusion

In summary, we obtained 29 viable cloned foals and found that MSCs are suitable donor cells in horse cloning. Even more, these cells could be more efficiently reprogrammed compared to fibroblasts.

Production of Pigs by Hand-Made Cloning Using Mesenchymal Stem Cells and Fibroblasts

Mesenchymal stem cells (MSCs) exhibited self-renewal and less differentiation, making the MSCs promising candidates for adult somatic cell nuclear transfer (SCNT). In this article, we tried to produce genome identical pigs through hand-made cloning (HMC), with MSCs and adult skin fibroblasts as donor cells. MSCs were derived from either adipose tissue or peripheral blood (aMSCs and bMSCs, respectively). MSCs usually showed the expression pattern of CD29, CD73, CD90, and CD105 together with lack of expression of the hematopoietic markers CD34and CD45. Flow cytometry results demonstrated high expression of CD29 and CD90 in both MSC lines, while CD73, CD34, and CD45 expression were not detected. In contrary, in reverse transcription-polymerase chain reaction (RT-PCR) analysis, CD73 and CD34 were detected indicating that human antibodies CD73 and CD34 were not suitable to identify porcine cell surface markers and porcine MSC cellular surface markers of CD34 might be different from other species. MSCs also had potential to differentiate successfully into chondrocytes, osteoblasts, and adipocytes. After HMC, embryos reconstructed with aMSCs had higher blastocyst rate on day 5 and 6 than those reconstructed with bMSCs and fibroblasts (29.6% ± 1.3% and 41.1% ± 1.4% for aMSCs vs. 23.9% ± 1.2% and 35.5% ± 1.6% for bMSCs and 22.1% ± 0.9% and 33.3% ± 1.1% for fibroblasts, respectively). Live birth rate per transferred blastocyst achieved with bMSCs (1.59%) was the highest among the three groups. This article was the first report to compare the efficiency among bMSCs, aMSCs, and fibroblasts for boar cloning, which offered a realistic perspective to use the HMC technology for commercial breeding.

Photorhabdus luminescens lectin A (PllA): A new probe for detecting α-galactoside-terminating glycoconjugates

Lectins play important roles in infections by pathogenic bacteria, for example, in host colonization, persistence, and biofilm formation. The Gram-negative entomopathogenic bacterium Photorhabdus luminescens symbiotically lives in insect-infecting Heterorhabditis nematodes and kills the insect host upon invasion by the nematode. The P. luminescens genome harbors the gene plu2096, coding for a novel lectin that we named PllA. We analyzed the binding properties of purified PllA with a glycan array and a binding assay in solution. Both assays revealed a strict specificity of PllA for α-galactoside-terminating glycoconjugates. The crystal structures of apo PllA and complexes with three different ligands revealed the molecular basis for the strict specificity of this lectin. Furthermore, we found that a 90° twist in subunit orientation leads to a peculiar quaternary structure compared with that of its ortholog LecA from Pseudomonas aeruginosa We also investigated the utility of PllA as a probe for detecting α-galactosides. The α-Gal epitope is present on wild-type pig cells and is the main reason for hyperacute organ rejection in pig to primate xenotransplantation. We noted that PllA specifically recognizes this epitope on the glycan array and demonstrated that PllA can be used as a fluorescent probe to detect this epitope on primary porcine cells in vitro In summary, our biochemical and structural analyses of the P. luminescens lectin PllA have disclosed the structural basis for PllA's high specificity for α-galactoside-containing ligands, and we show that PllA can be used to visualize the α-Gal epitope on porcine tissues.

Direct introduction of gene constructs into the pronucleus-like structure of cloned embryos: a new strategy for the generation of genetically modified pigs

Due to a rising demand of porcine models with complex genetic modifications for biomedical research, the approaches for their generation need to be adapted. In this study we describe the direct introduction of a gene construct into the pronucleus (PN)-like structure of cloned embryos as a novel strategy for the generation of genetically modified pigs, termed "nuclear injection". To evaluate the reliability of this new strategy, the developmental ability of embryos in vitro and in vivo as well as the integration and expression efficiency of a transgene carrying green fluorescence protein (GFP) were examined. Eighty percent of the cloned pig embryos (633/787) exhibited a PN-like structure, which met the prerequisite to technically perform the new method. GFP fluorescence was observed in about half of the total blastocysts (21/40, 52.5%), which was comparable to classical zygote PN injection (28/41, 68.3%). In total, 478 cloned embryos injected with the GFP construct were transferred into 4 recipients and from one recipient 4 fetuses (day 68) were collected. In one of the fetuses which showed normal development, the integration of the transgene was confirmed by PCR in different tissues and organs from all three primary germ layers and placenta. The integration pattern of the transgene was mosaic (48 out of 84 single-cell colonies established from a kidney were positive for GFP DNA by PCR). Direct GFP fluorescence was observed macro- and microscopically in the fetus. Our novel strategy could be useful particularly for the generation of pigs with complex genetic modifications.

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

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

In vitro production of cloned and transgenically cloned embryos from Guangxi Huanjiang Xiang pig

Guangxi Huanjiang Xiang pig is a unique miniature pig strain that is originally from Huanjiang Maonan Autonomous County of Guangxi province, China, and shows great potential in agricultural and biomedical research. Although cloning and genetic modification of this pig would enhance its application value, cloning of this strain has not yet been reported. We sought to establish appropriate cloning procedures and produce transgenic embryos in Huanjiang Xiang pigs through the following methods. We isolated fibroblasts from tails of Huanjiang Xiang pig and genetically modified them using Xfect transfection. Fibroblasts, either in non-transgenic or transgenic forms, were used as donor cells for reconstructed embryos by somatic cell nuclear transfer (SCNT), and in vitro development was monitored after the reconstruction. We found no difference in blastocyst formation rate between non-transgenic and transgenic embryos (10.8% vs. 10.3%; P ≥ 0.05). In addition, we tested whether Scriptaid, a widely used histone deacetylase inhibitor, could enhance the in vitro development of Huanjiang Xiang pig cloned embryos. Treatment with 500 nM Scriptaid for 16 h post-activation significantly increased the blastocyst formation rate (26.1% vs. 10.8% for non-transgenic nuclear transfer groups with vs. without the Scriptaid treatment and 28.5% vs. 10.3% for transgenic nuclear transfer groups with vs. without the Scriptaid treatment; P < 0.05). This study provided a basis for further generation of cloned and transgenically cloned Huanjiang Xiang pigs used in agricultural and biomedical research.

Efficient modification of the myostatin gene in porcine somatic cells and generation of knockout piglets

Myostatin (MSTN) is a negative regulator of myogenesis, and disruption of its function causes increased muscle mass in various species. Here, we report the generation of MSTN-knockout (KO) pigs using genome editing technology combined with somatic-cell nuclear transfer (SCNT). Transcription activator-like effector nuclease (TALEN) with non-repeat-variable di-residue variations, called Platinum TALEN, was highly efficient in modifying genes in porcine somatic cells, which were then used for SCNT to create MSTN KO piglets. These piglets exhibited a double-muscled phenotype, possessing a higher body weight and longissimus muscle mass measuring 170% that of wild-type piglets, with double the number of muscle fibers. These results demonstrate that loss of MSTN increases muscle mass in pigs, which may help increase pork production for consumption in the future.

Establishment, Differentiation, Electroporation and Nuclear Transfer of Porcine Mesenchymal Stem Cells

The limited success of somatic cell nuclear transfer (SCNT) is largely attributed to defects in epigenetic reprogramming of the donor genome. Donor cell types with distinct potential competence may offer different epigenetic flexibility for subsequent genome reprogramming in SCNT. Stem cells possibly enable their genomes to be more readily reprogrammed than differentiated cells. To improve the efficiency of cloning, porcine mesenchymal stem cells (pMSCs) were isolated and well identified by 6-channel flow cytometry and differentiation assays and were used as donors in SCNT. Compared with porcine embryonic fibroblasts (pEFs), our results showed that pMSCs markedly enhanced cloned embryo development in terms of cleavage and blastocyst formation (p < 0.05). To enhance the epigenetic flexibility of pMSCs, classical reprogramming factors (RFs) were transfected by electroporation, and we achieved optimization with ectopic expression of RFs in pMSCs. Our results suggest that the epigenetic status of donor cells has an improvement on genome reprogramming, and multipotent pMSCs favoured subsequent embryonic development.

Nuclear transfer and transgenesis in the pig

Somatic cell nuclear transfer (SCNT) using genetically modified donor cells facilitates the generation of tailored pig models for biomedical research and for xenotransplantation. Up to now, SCNT is the main way to generate gene-targeted pigs, since germ line-competent pluripotent stem cells are not available for this species. In this chapter, we introduce our routine workflow for the production of genetically engineered pigs, especially focused on the genetic modification of somatic donor cells, SCNT using in vitro matured oocytes, and laparoscopic embryo transfer.

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.

Regulatory sequences of the porcine THBD gene facilitate endothelial-specific expression of bioactive human thrombomodulin in single- and multitransgenic pigs

BACKGROUND

Among other mismatches between human and pig, incompatibilities in the blood coagulation systems hamper the xenotransplantation of vascularized organs. The provision of the porcine endothelium with human thrombomodulin (hTM) is hypothesized to overcome the impaired activation of protein C by a heterodimer consisting of human thrombin and porcine TM.

METHODS

We evaluated regulatory regions of the THBD gene, optimized vectors for transgene expression, and generated hTM expressing pigs by somatic cell nuclear transfer. Genetically modified pigs were characterized at the molecular, cellular, histological, and physiological levels.

RESULTS

A 7.6-kb fragment containing the entire upstream region of the porcine THBD gene was found to drive a high expression in a porcine endothelial cell line and was therefore used to control hTM expression in transgenic pigs. The abundance of hTM was restricted to the endothelium, according to the predicted pattern, and the transgene expression of hTM was stably inherited to the offspring. When endothelial cells from pigs carrying the hTM transgene--either alone or in combination with an aGalTKO and a transgene encoding the human CD46-were tested in a coagulation assay with human whole blood, the clotting time was increased three- to four-fold (P<0.001) compared to wild-type and aGalTKO/CD46 transgenic endothelial cells. This, for the first time, demonstrated the anticoagulant properties of hTM on porcine endothelial cells in a human whole blood assay.

CONCLUSIONS

The biological efficacy of hTM suggests that the (multi-)transgenic donor pigs described here have the potential to overcome coagulation incompatibilities in pig-to-primate xenotransplantation.

Dystrophin-deficient pigs provide new insights into the hierarchy of physiological derangements of dystrophic muscle

Duchenne muscular dystrophy (DMD) is caused by mutations in the X-linked dystrophin (DMD) gene. The absence of dystrophin protein leads to progressive muscle weakness and wasting, disability and death. To establish a tailored large animal model of DMD, we deleted DMD exon 52 in male pig cells by gene targeting and generated offspring by nuclear transfer. DMD pigs exhibit absence of dystrophin in skeletal muscles, increased serum creatine kinase levels, progressive dystrophic changes of skeletal muscles, impaired mobility, muscle weakness and a maximum life span of 3 months due to respiratory impairment. Unlike human DMD patients, some DMD pigs die shortly after birth. To address the accelerated development of muscular dystrophy in DMD pigs when compared with human patients, we performed a genome-wide transcriptome study of biceps femoris muscle specimens from 2-day-old and 3-month-old DMD and age-matched wild-type pigs. The transcriptome changes in 3-month-old DMD pigs were in good concordance with gene expression profiles in human DMD, reflecting the processes of degeneration, regeneration, inflammation, fibrosis and impaired metabolic activity. In contrast, the transcriptome profile of 2-day-old DMD pigs showed similarities with transcriptome changes induced by acute exercise muscle injury. Our studies provide new insights into early changes associated with dystrophin deficiency in a clinically severe animal model of DMD.

Factors influencing the efficiency of generating genetically engineered pigs by nuclear transfer: multi-factorial analysis of a large data set

BACKGROUND

Somatic cell nuclear transfer (SCNT) using genetically engineered donor cells is currently the most widely used strategy to generate tailored pig models for biomedical research. Although this approach facilitates a similar spectrum of genetic modifications as in rodent models, the outcome in terms of live cloned piglets is quite variable. In this study, we aimed at a comprehensive analysis of environmental and experimental factors that are substantially influencing the efficiency of generating genetically engineered pigs. Based on a considerably large data set from 274 SCNT experiments (in total 18,649 reconstructed embryos transferred into 193 recipients), performed over a period of three years, we assessed the relative contribution of season, type of genetic modification, donor cell source, number of cloning rounds, and pre-selection of cloned embryos for early development to the cloning efficiency.

RESULTS

109 (56%) recipients became pregnant and 85 (78%) of them gave birth to offspring. Out of 318 cloned piglets, 243 (76%) were alive, but only 97 (40%) were clinically healthy and showed normal development. The proportion of stillborn piglets was 24% (75/318), and another 31% (100/318) of the cloned piglets died soon after birth. The overall cloning efficiency, defined as the number of offspring born per SCNT embryos transferred, including only recipients that delivered, was 3.95%. SCNT experiments performed during winter using fetal fibroblasts or kidney cells after additive gene transfer resulted in the highest number of live and healthy offspring, while two or more rounds of cloning and nuclear transfer experiments performed during summer decreased the number of healthy offspring.

CONCLUSION

Although the effects of individual factors may be different between various laboratories, our results and analysis strategy will help to identify and optimize the factors, which are most critical to cloning success in programs aiming at the generation of genetically engineered pig models.