Production and characterization of soluble human TNFRI-Fc and human HO-1(HMOX1) transgenic pigs by using the F2A peptide

Mechanisms and strategies to promote cardiac xenotransplantation

End stage heart failure is a terminal disease, and the only curative therapy is orthotopic heart transplantation. Due to limited organ availability, alternative strategies have received intense interest for treatment of patients with advanced heart failure. Recent studies using gene-edited porcine organs suggest that cardiac xenotransplantation may provide a future source of organs. In this review, we highlight the historical milestones for cardiac xenotransplantation and the gene editing strategies designed to overcome immunological barriers, which have culminated in a recent cardiac pig-to-human xenotransplant. We also discuss recent results of studies on the engineering of human-porcine chimeric organs that may provide an alternative and complementary strategy to overcome some of the major immunological barriers to producing a new source of transplantable organs.

A desirable transgenic strategy using GGTA1 endogenous promoter-mediated knock-in for xenotransplantation model

Pig-to-human organ transplantation is a feasible solution to resolve the shortage of organ donors for patients that wait for transplantation. To overcome immunological rejection, which is the main hurdle in pig-to-human xenotransplantation, various engineered transgenic pigs have been developed. Ablation of xeno-reactive antigens, especially the 1,3-Gal epitope (GalT), which causes hyperacute rejection, and insertion of complement regulatory protein genes, such as hCD46, hCD55, and hCD59, and genes to regulate the coagulation pathway or immune cell-mediated rejection may be required for an ideal xenotransplantation model. However, the technique for stable and efficient expression of multi-transgenes has not yet been settled to develop a suitable xenotransplantation model. To develop a stable and efficient transgenic system, we knocked-in internal ribosome entry sites (IRES)-mediated transgenes into the α 1,3-galactosyltransferase (GGTA1) locus so that expression of these transgenes would be controlled by the GGTA1 endogenous promoter. We constructed an IRES-based polycistronic hCD55/hCD39 knock-in vector to target exon4 of the GGTA1 gene. The hCD55/hCD39 knock-in vector and CRISPR/Cas9 to target exon4 of the GGTA1 gene were co-transfected into white yucatan miniature pig fibroblasts. After transfection, hCD39 expressed cells were sorted by FACS. Targeted colonies were verified using targeting PCR and FACS analysis, and used as donors for somatic cell nuclear transfer. Expression of GalT, hCD55, and hCD39 was analyzed by FACS and western blotting. Human complement-mediated cytotoxicity and human antibody binding assays were conducted on peripheral blood mononuclear cells (PBMCs) and red blood cells (RBCs), and deposition of C3 by incubation with human complement serum and platelet aggregation were analyzed in GGTA1 knock-out (GTKO)/CD55/CD39 pig cells. We obtained six targeted colonies with high efficiency of targeting (42.8% of efficiency). Selected colony and transgenic pigs showed abundant expression of targeted genes (hCD55 and hCD39). Knocked-in transgenes were expressed in various cell types under the control of the GGTA1 endogenous promoter in GTKO/CD55/CD39 pig and IRES was sufficient to express downstream expression of the transgene. Human IgG and IgM binding decreased in GTKO/CD55/CD39 pig and GTKO compared to wild-type pig PBMCs and RBCs. The human complement-mediated cytotoxicity of RBCs and PBMCs decreased in GTKO/CD55/CD39 pig compared to cells from GTKO pig. C3 was also deposited less in GTKO/CD55/CD39 pig cells than wild-type pig cells. The platelet aggregation was delayed by hCD39 expression in GTKO/CD55/CD39 pig. In the current study, knock-in into the GGTA1 locus and GGTA1 endogenous promoter-mediated expression of transgenes are an appropriable strategy for effective and stable expression of multi-transgenes. The IRES-based polycistronic transgene vector system also caused sufficient expression of both hCD55 and hCD39. Furthermore, co-transfection of CRISPR/Cas9 and the knock-in vector not only increased the knock-in efficiency but also induced null for GalT by CRISPR/Cas9-mediated double-stranded break of the target site. As shown in human complement-mediated lysis and human antibody binding to GTKO/CD55/CD39 transgenic pig cells, expression of hCD55 and hCD39 with ablation of GalT prevents an effective immunological reaction in vitro. As a consequence, our technique to produce multi-transgenic pigs could improve the development of a suitable xenotransplantation model, and the GTKO/CD55/CD39 pig developed could prolong the survival of pig-to-primate xenotransplant recipients.

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.

Porcine genome engineering for xenotransplantation

The extreme shortage of human donor organs for treatment of patients with end-stage organ failures is well known. Xenotransplantation, which might provide unlimited organ supply, is a most promising strategy to solve this problem. Domestic pigs are regarded as ideal organ-source animals owing to similarity in anatomy, physiology and organ size to humans as well as high reproductive capacity and low maintenance cost. However, several barriers, which include immune rejection, inflammation and coagulative dysfunctions, as well as the cross-species transmission risk of porcine endogenous retrovirus, blocked the pig-to-human xenotransplantation. With the rapid development of genome engineering technologies and the potent immunosuppressive medications in recent years, these barriers could be eliminated through genetic modification of pig genome together with the administration of effective immunosuppressants. A number of candidate genes involved in the regulation of immune response, inflammation and coagulation have been explored to optimize porcine xenograft survival in non-human primate recipients. PERV inactivation in pigs has also been accomplished to firmly address the safety issue in pig-to-human xenotransplantation. Many encouraging preclinical milestones have been achieved with some organs surviving for years. Therefore, the clinical trials of some promising organs, such as islet, kidney and heart, are aimed to be launched in the near future.

Efficient generation of GGTA1-deficient pigs by electroporation of the CRISPR/Cas9 system into in vitro-fertilized zygotes

BACKGROUND

Xenoantigens are a major source of concern with regard to the success of interspecific xenografts. GGTA1 encodes α1,3-galactosyltransferase, which is essential for the biosynthesis of galactosyl-alpha 1,3-galactose, the major xenoantigen causing hyperacute rejection. GGTA1-modified pigs, therefore, are promising donors for pig-to-human xenotransplantation. In this study, we developed a method for the introduction of the CRISPR/Cas9 system into in vitro-fertilized porcine zygotes via electroporation to generate GGTA1-modified pigs.

RESULTS

We designed five guide RNAs (gRNAs) targeting distinct sites in GGTA1. After the introduction of the Cas9 protein with each gRNA via electroporation, the gene editing efficiency in blastocysts developed from zygotes was evaluated. The gRNA with the highest gene editing efficiency was used to generate GGTA1-edited pigs. Six piglets were delivered from two recipient gilts after the transfer of electroporated zygotes with the Cas9/gRNA complex. Deep sequencing analysis revealed that five out of six piglets carried a biallelic mutation in the targeted region of GGTA1, with no off-target events. Furthermore, staining with isolectin B4 confirmed deficient GGTA1 function in GGTA1 biallelic mutant piglets.

CONCLUSIONS

We established GGTA1-modified pigs with high efficiency by introducing a CRISPR/Cas9 system into zygotes via electroporation. Multiple gene modifications, including knock-ins of human genes, in porcine zygotes via electroporation may further improve the application of the technique in pig-to-human xenotransplantation.

Transcriptional Regulation of HMOX1 Gene in Hezuo Tibetan Pigs: Roles of WT1, Sp1, and C/EBPα

Heme oxygenase 1 (HMOX1) is a stress-inducing enzyme with multiple cardiovascular protective functions, especially in hypoxia stress. However, transcriptional regulation of swine HMOX1 gene remains unclear. In the present study, we first detected tissue expression profiles of HMOX1 gene in adult Hezuo Tibetan pig and analyzed the gene structure. We found that the expression level of HMOX1 gene was highest in the spleen of the Hezuo Tibetan pig, followed by liver, lung, and kidney. A series of 5’ deletion promoter plasmids in pGL3-basic vector were used to identify the core promoter region and confirmed that the minimum core promoter region of swine HMOX1 gene was located at −387 bp to −158 bp region. Then we used bioinformatics analysis to predict transcription factors in this region. Combined with site-directed mutagenesis and RNA interference assays, it was demonstrated that the three transcription factors WT1, Sp1 and C/EBPα were important transcription regulators of HMOX1 gene. In summary, our study may lay the groundwork for further functional study of HMOX1 gene.

Will Genetic Engineering Carry Xenotransplantation of Pig Islets to the Clinic?

PURPOSE OF REVIEW

Porcine islets represent a potentially attractive beta-cell source for xenotransplantation into patients with type 1 diabetes, who are not eligible to islet allo-transplantation due to a lack of suitable human donor organs. Recent progress in genetic engineering/gene editing of donor pigs provides new opportunities to overcome rejection of xeno-islets, to improve their engraftment and insulin secretion capacity, and to reduce the risk for transmission of porcine endogenous retroviruses. This review summarizes the current issues and progress in islet xenotransplantation with special emphasis on genetically modified/gene edited donor pigs.

RECENT FINDINGS

Attempts to overcome acute rejection of xeno-islets, especially after intraportal transplantation into the liver, include the genetic elimination of specific carbohydrate antigens such as αGal, Neu5Gc, and Sd(a) for which humans and-in part-non-human primates have natural antibodies that bind to these targets leading to activation of complement and coagulation. A complementary approach is the expression of one or more human complement regulatory proteins (hCD46, hCD55, hCD59). Transgenic attempts to overcome cellular rejection of islet xenotransplants include the expression of proteins that inhibit co-stimulation of T cells. Expression of glucagon-like peptide-1 and M3 muscarinic receptors has been shown to increase the insulin secretion of virally transduced porcine islets in vitro and it will be interesting to see the effects of these modifications in transgenic pigs and islet products derived from them. Genome-wide inactivation of porcine endogenous retrovirus (PERV) integrants by mutating their pol genes using CRISPR/Cas9 is a recent approach to reduce the risk for PERV transmission by xeno-islets. Genetic engineering/gene editing of xeno-islet donor pigs facilitated major progress towards clinical islet xenotransplantation. The required set of genetic modifications will depend on the source of islets (fetal/neonatal vs. adult), the mode of delivery (encapsulated vs. free), and the transplantation site.

Establishment and identification of cell lines from type O blood Korean native pigs and their efficiency in supporting embryonic development via somatic cell nuclear transfer

Due to their similarities with humans in anatomy, physiology, and genetics miniature pigs are becoming an attractive model for biomedical research. We aim to establish and evaluate blood type O cells derived from Korean native pig (KNP), a typical miniature pig breed in Korea. Ten cell lines derived from 8 KNP piglets and one adult female KNP (kidney and ear tissues) were established. To confirm the presence of blood type O, genomic DNA, fucosyltransferase (FUT) expression, and immunofluorescence staining were examined. Additionally, fluorescence-activated cell sorting and somatic cell nuclear transfer were performed to investigate the normality of the cell lines and to evaluate their effectiveness in embryo development. We found no significant bands corresponding to specific blood group A, and no increase in FUT expression in cell lines derived from piglets No. 1, No. 4, No. 5, No. 8, and the adult female KNP; moreover, they showed normal levels of expression of α 1,3-galactosyltransferase and cytidine monophosphate-N-acetylneuraminic acid hydroxylase. There was no significant difference in embryo development between skin and kidney fibroblasts derived from the blood type O KNPs. In conclusion, we successfully established blood type O KNP cell lines, which may serve as a useful model in xenotransplantation research.

Assembling multiple xenoprotective transgenes in pigs

This review gives a brief overview of the genetic modifications necessary for grafted porcine tissues and organs to overcome rejection in human recipients. It then focuses on the problem of generating and breeding herds of donor pigs carrying modified endogenous genes and multiple xenoprotective transgenes. A xenodonor pig optimised for human clinical use could well require the addition of ten or more xenoprotective transgenes. It is impractical to produce the required combination of transgene by cross-breeding animals bearing individual transgenes at unlinked genetic loci, because independent segregation means that huge numbers of pigs would be required to produce relatively few donor animals. A better approach is to colocate groups of transgenes at a single genomic locus. We outline current methods to assemble transgene arrays and consider their pros and cons. These include polycistronic expression systems, in vitro recombination of large DNA fragments in PAC and BAC vectors, transposon vectors, classical gene targeting by homologous recombination at permissive loci such as ROSA26, targeted transgene placement aided by gene editing systems such as CRISPR/Cas9, and transgene placement by site-specific recombination such as Min-tagging using the Bxb1recombinase.

Strong xenoprotective function by single-copy transgenes placed sequentially at a permissive locus

BACKGROUND

Multiple xenoprotective transgenes are best grouped at a single locus to avoid segregation during breeding and simplify production of donor animals.

METHODS

We used transgene stacking to place a human CD55 transgene adjacent to a human heme oxygenase 1 construct at the porcine ROSA26 locus. A transgenic pig was analyzed by PCR, RT-PCR, droplet digital PCR, immunohistochemistry, immunofluorescence, and flow cytometry. Resistance to complement-mediated cell lysis and caspase 3/7 activation were determined in vitro.

RESULTS

The ROSA26 locus was retargeted efficiently, and animals were generated by nuclear transfer. RNA and protein analyses revealed abundant expression in all organs analyzed, including pancreatic beta cells. Transgenic porcine kidney fibroblasts were almost completely protected against complement-mediated lysis and showed reduced caspase 3/7 activation.

CONCLUSION

Step-by-step placement enables highly expressed single-copy xenoprotective transgenes to be grouped at porcine ROSA26.

Genetic characteristics of polycistronic system‑mediated randomly‑inserted multi‑transgenes in miniature pigs and mice

Multi-transgenic technology is superior to single transgenic technology in biological and medical research. Multi-transgene insertion mediated by a polycistronic system is more effective for the integration of polygenes. The multi-transgene insertion patterns and manners of inheritance are not completely understood. Copy number quantification is one available approach for addressing this issue. The present study determined copy numbers in two multi-transgenic mice (K3 and L3) and two multi-transgenic miniature pigs (Z2 and Z3) using absolute quantitative polymerase chain reaction analysis. For the F0 generation, a given transgene was able to exhibit different copy number integration capacities in different individuals. For the F1 generation, the most notable characteristic was that the copy number proportions were different among pedigrees (P<0.05). The results of the present study demonstrated that transgenes within the same vector exhibited the same integration trend between the F0 and F1 generations. In conclusion, intraspecific consistency and intergenerational copy numbers were compared and the integration capacity of each specific transgene differed in multi-transgenic animals. In particular, the copy number of one transgene may not be used to represent other transgenes in polycistronic vector-mediated multi-transgenic organisms. Consequently, in multi-transgenic experimental animal disease model research or breeding, copy numbers provide an important reference. Therefore, each transgene in multi-transgenic animals must be separately screened to prevent large copy number differences, and inconsistent expression between transgenes and miscellaneous data, in subsequent research.

Generation of CMAHKO/GTKO/shTNFRI-Fc/HO-1 quadruple gene modified pigs

As an alternative source of organs for transplantation into humans, attention has been directed to pigs due to their similarities in biological features and organ size. However, severe immune rejection has prevented successful xenotransplantation using pig organs and tissues. To overcome immune rejection, recently developed genetic engineering systems such as TALEN coupled with somatic cell nuclear transfer (SCNT) to make embryos could be used to produce pigs compatible with xenotransplantation. We used the TALEN system to target the non-Gal antigen cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) gene in pigs that is naturally deleted in humans. Gal-deleted cells expressing both soluble human tumor necrosis factor receptor I IgG₁-Fc (shTNFRI-Fc) and human hemagglutinin -tagged-human heme oxygenase-1 (hHO-1) were transfected with a TALEN target for CMAH. Cells lacking CMAH were negatively selected using N-glyconeuraminic acid (Neu5Gc)/magnetic beads and the level of Neu5Gc expression of isolated cells were analyzed by FACS and DNA sequencing. Cloned embryos using 3 different genetically modified cell clones were respectively transferred into 3 recipients, with 55.6% (5/9) becoming pregnant and three cloned pigs were produced. Successful genetic disruption of the CMAH gene was confirmed by sequencing, showing lack of expression of CMAH in tail-derived fibroblasts of the cloned piglets. Besides decreased expression of Neu5Gc in piglets produced by SCNT, antibody-mediated complement-dependent cytotoxicity assays and natural antibody binding for examining immuno-reactivity of the quadruple gene modified pigs derived from endothelial cells and fibroblasts were reduced significantly compared to those of wild type animals. We conclude that by combining the TALEN system and transgenic cells, targeting of multiple genes could be useful for generating organs for xenotransplantation. We produced miniature pigs with quadruple modified genes CMAHKO/GTKO/shTNFRI-Fc/hHO-1 that will be suitable for xenotransplantation by overcoming hyperacute, acute and anti-inflammatory rejection.

Postneonatal Mortality and Liver Changes in Cloned Pigs Associated with Human Tumor Necrosis Factor Receptor I-Fc and Human Heme Oxygenase-1 Overexpression

Soluble human tumor necrosis factor (shTNFRI-Fc) and human heme oxygenase 1 (hHO-1) are key regulators for protection against oxidative and inflammatory injury for xenotransplantation. Somatic cells with more than 10 copy numbers of shTNFRI-Fc and hHO-1 were employed in somatic cell nuclear transfer to generate cloned pigs, thereby resulting in seven cloned piglets. However, produced piglets were all dead within 24 hours after birth. Obviously, postnatal death with liver apoptosis was reported in the higher copy number of shTNFRI-Fc and hHO-1 piglets. In liver, the transcript levels of ferritin heavy chain, light chain, transferrin, and inducible nitric oxide synthase were significantly highly expressed compared to those of lower copy number of shTNFRI-Fc and hHO-1 piglets (P < 0.05). Also, H₂O₂ contents were increased, and superoxide dismutase was significantly lower in the higher copy number of shTNFRI-Fc and hHO-1 piglets (P < 0.05). These results indicate that TNFRI-Fc and hHO-1 overexpression may apparently induce free iron in the liver and exert oxidative stress by enhancing reactive oxygen species production and block normal postneonatal liver metabolism.

Supplementation with spermine during in vitro maturation of porcine oocytes improves early embryonic development after parthenogenetic activation and somatic cell nuclear transfer

Spermine plays an important role in protection from reactive oxygen species (ROS) in bacteria, yeast, and mammalian cells, but there are few studies on the effects of spermine on porcine oocyte maturation and subsequent embryo development. The aim of this study was to determine the effects of spermine on in vitro maturation (IVM) of porcine oocytes and their developmental competence after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT). We evaluated nuclear maturation, intracellular glutathione (GSH), and ROS levels in oocytes, and their subsequent embryonic development, as well as gene expression in mature oocytes, cumulus cells, and PA blastocysts. After treatment with various concentrations of spermine in IVM culture medium, there was no significant difference in nuclear maturation rate. However, spermine treatment groups (10- 500 µM) showed significantly increased intracellular GSH levels and decreased ROS levels compared to the control ( < 0.05). Furthermore, 10 µM spermine supported significantly higher blastocyst formation rates after PA than the control group ( < 0.05). According to the optimal condition from the PA results, we investigated the effects of 10 µM spermine on SCNT, and it also significantly improved blastocyst formation rates compared with the control group ( < 0.05). In evaluating the effects of 10 µM spermine on gene expression, there was significantly lower expression of a proapoptotic gene () and higher expression of an antiapoptotic gene () in cumulus cells ( < 0.05). was increased in spermine-treated oocytes. Levels of transcription for and were significantly increased in PA blastocysts. In conclusion, 10 µM spermine supplementation during IVM improved the development of porcine PA and SCNT embryos by increasing intracellular GSH, scavenging ROS levels, and regulating gene expression.

The Introduction of Human Heme Oxygenase-1 and Soluble Tumor Necrosis Factor-α Receptor Type I With Human IgG1 Fc in Porcine Islets Prolongs Islet Xenograft Survival in Humanized Mice

Apoptosis during engraftment and inflammation induce poor islet xenograft survival. We aimed to determine whether overexpression of human heme oxygenase-1 (HO-1) or soluble tumor necrosis factor-α receptor type I with human IgG1 Fc (sTNF-αR-Fc) in porcine islets could improve islet xenograft survival. Adult porcine islets were transduced with adenovirus containing human HO-1, sTNF-αR-Fc, sTNF-αR-Fc/HO-1 or green fluorescent protein (control). Humanized mice were generated by injecting human cord blood-derived CD34(+) stem cells into NOD-scid-IL-2Rγ(null) mice. Both HO-1 and sTNF-αR-Fc reduced islet apoptosis under in vitro hypoxia or cytokine stimuli and suppressed RANTES induction without compromising insulin secretion. Introduction of either gene into islets prolonged islet xenograft survival in pig-to-humanized mice transplantation. The sTNF-αR-Fc/HO-1 group showed the best glucose tolerance. Target genes were successfully expressed in islet xenografts. Perigraft infiltration of macrophages and T cells was suppressed with decreased expression of RANTES, tumor necrosis factor-α and IL-6 in treatment groups; however, frequency of pig-specific interferon-γ-producing T cells was not decreased, and humoral response was not significant in any group. Early apoptosis of islet cells was suppressed in the treatment groups. In conclusion, overexpression of HO-1 or sTNF-αR-Fc in porcine islets improved islet xenograft survival by suppressing both apoptosis and inflammation. HO-1 or sTNF-αR-Fc transgenic pigs have potential for islet xenotransplantation.

Multi‑transgenic minipig models exhibiting potential for hepatic insulin resistance and pancreatic apoptosis

There are currently no multi‑transgenic minipig models of diabetes for the regulation of multiple genes involved in its pathogenesis. The foot and mouth disease virus 2A (F2A)‑mediated polycistronic system possesses several advantages, and the present study developed a novel multi‑transgenic minipig model associated with diabetes using this system. The tissue‑specific polycistronic system used in the present study consisted of two expression cassettes, separated by an insulator: (i) 11‑β‑hydroxysteroid dehydrogenase 1 (11β‑HSD1), driven by the porcine liver‑specific apolipoprotein E promoter; (ii) human islet amyloid polypeptide (hIAPP) and C/EBP homologous protein (CHOP), linked to the furin digested site and F‑2A, driven by the porcine pancreas‑specific insulin promoter. In the present study, porcine fetal fibroblasts were transfected with this vector. Following somatic cell nuclear transfer using 10 cell clones and the transplantation of 1,459 embryos in total, three Landrace x Yorkshire surrogates became pregnant and delivered three Wuzhishan piglets. Genomic polymerase chain reaction (PCR) demonstrated that the piglets were multi‑transgenic. Reverse transcription‑quantitative PCR confirmed that 11β‑HSD1 transcription was upregulated in the targeted liver. Similarly, hIAPP and CHOP were expressed at high levels, compared with the control (P<0.05 and P<0.01) in the pancreas, consistent with the western blotting and immunohistochemistry results. The primary results also showed that overexpression of 11β‑HSD1 in the liver increased the liver fat lipid parameters; and the levels of hIAPP and CHOP in the pancreatic islet cells, leading to delayed β‑cell development and apoptosis. This novel tissue‑specific polycistronic system offers a promising starting point for efficiently mimicking multigenic metabolic disease.

Oct4 overexpression facilitates proliferation of porcine fibroblasts and development of cloned embryos

Octamer-binding transcription factor 4 (Oct4) is a critical molecule for the self-renewal and pluripotency of embryonic stem cells. Recent reports have shown that Oct4 also controls cell-cycle progression and enhances the proliferation of various types of cells. As the high proliferation of donor fibroblasts is critical to the production of transgenic pigs, using the somatic cell nuclear transfer technique, we analysed the effect of Oct4 overexpression on the proliferation of porcine fibroblasts and embryos. Porcine endogenous Oct4 cDNA was cloned, sequenced and inserted into an expression vector. The vector was transfected into porcine fibroblasts, and a stable Oct4-overexpressed cell line was established by antibiotic selection. Oct4 expression was validated by the immunostaining of Oct4. Cell morphology was changed to sharp, and both proliferation and migration abilities were enhanced in Oct4-overexpressed cells. Real-time RT-PCR results showed that p16, Bcl2 and Myc were upregulated in Oct4-overexpressed cells. Somatic cell nuclear transfer was performed using Oct4-overexpressed cells, and the development of Oct4 embryos was compared with that of wild-type cloned embryos. The cleavage and blastocyst formation rates were improved in the Oct4 embryos. Interestingly, blastocyst formation of the Oct4 embryos was observed as early as day 5 in culture, while blastocysts were observed from day 6 in wild-type cloned embryos. In conclusion, the overexpression of Oct4 enhanced the proliferation of both porcine fibroblasts and embryos.