Yangqing Lu

Brief Report: Chimeric Pigs Produced from Induced Pluripotent Stem Cells Demonstrate Germline Transmission and No Evidence of Tumor Formation in Young Pigs

The recent development of porcine induced pluripotent stem cells (piPSCs) capable of generating chimeric animals, a feat not previously accomplished with embryonic stem cells or iPSCs in a species outside of rodents, has opened the doors for in‐depth study of iPSC tumorigenicity, autologous transplantation, and other key aspects to safely move iPSC therapies to the clinic. The study of iPSC tumorigenicity is critical as previous research in the mouse showed that iPSC‐derived chimeras possessed large numbers of tumors, rising significant concerns about the safety of iPSC therapies. Additionally, piPSCs capable of generating germline chimeras could revolutionize the transgenic animal field by enabling complex genetic manipulations (e.g., knockout or knockin of genes) to produce biomedically important large animal models or improve livestock production. In this study, we demonstrate for the first time in a nonrodent species germline transmission of iPSCs with the live birth of a transgenic piglet that possessed genome integration of the human POU5F1 and NANOG genes. In addition, gross and histological examination of necropsied porcine chimeras at 2, 7, and 9 months showed that these animals lacked tumor formation and demonstrated normal development. Tissue samples positive for human POU5F1 DNA showed no C‐MYC gene expression, further implicating C‐MYC as a cause of tumorigenicity. The development of germline‐competent porcine iPSCs that do not produce tumors in young chimeric animals presents an attractive and powerful translational model to study the efficacy and safety of stem cell therapies and perhaps to efficiently produce complex transgenic animals. STEM CELLS 2011;29:1640–1643

Avian-Induced Pluripotent Stem Cells Derived Using Human Reprogramming Factors

Avian species are important model animals for developmental biology and disease research. However, unlike in mice, where clonal lines of pluripotent stem cells have enabled researchers to study mammalian gene function, clonal and highly proliferative pluripotent avian cell lines have been an elusive goal. Here we demonstrate the generation of avian induced pluripotent stem cells (iPSCs), the first nonmammalian iPSCs, which were clonally isolated and propagated, important attributes not attained in embryo-sourced avian cells. This was accomplished using human pluripotency genes rather than avian genes, indicating that the process in which mammalian and nonmammalian cells are reprogrammed is a conserved process. Quail iPSCs (qiPSCs) were capable of forming all 3 germ layers in vitro and were directly differentiated in culture into astrocytes, oligodendrocytes, and neurons. Ultimately, qiPSCs were capable of generating live chimeric birds and incorporated into tissues from all 3 germ layers, extraembryonic tissues, and potentially the germline. These chimera competent qiPSCs and in vitro differentiated cells offer insight into the conserved nature of reprogramming and genetic tools that were only previously available in mammals.

Rapid Heterotrophic Ossification with Cryopreserved Poly(ethylene glycol-) Microencapsulated BMP2-Expressing MSCs

Autologous bone grafting is the most effective treatment for long-bone nonunions, but it poses considerable risks to donors, necessitating the development of alternative therapeutics. Poly(ethylene glycol) (PEG) microencapsulation and BMP2 transgene delivery are being developed together to induce rapid bone formation. However, methods to make these treatments available for clinical applications are presently lacking. In this study we used mesenchymal stem cells (MSCs) due to their ease of harvest, replication potential, and immunomodulatory capabilities. MSCs were from sheep and pig due to their appeal as large animal models for bone nonunion. We demonstrated that cryopreservation of these microencapsulated MSCs did not affect their cell viability, adenoviral BMP2 production, or ability to initiate bone formation. Additionally, microspheres showed no appreciable damage from cryopreservation when examined with light and electron microscopy. These results validate the use of cryopreservation in preserving the viability and functionality of PEG-encapsulated BMP2-transduced MSCs.

Induced pluripotency in chicken embryonic fibroblast results in a germ cell fate.

Germ cells (GCs) are critically important as the vehicle that passes genetic information from one generation to the next. Correct development of these cells is essential and perturbation in their development often leads to reproductive failure and disease. Despite the importance of GCs, little is known about the mechanisms underlying the acquisition and maintenance of the GC character. Using a reprogramming strategy, we demonstrate that overexpression of ectopic transcription factors in embryonic fibroblasts can lead to the generation of chicken induced primordial germ cells (ciPGCs). These ciPGCs express pluripotent markers POU5F1, SSEA1, and the GC defining proteins, CVH and DAZL, closely resembling in vivo sourced PGCs instead of embryonic stem cells. Moreover, CXCR4 expressing ciPGCs were capable of migrating to the embryonic gonad after injection into the vasculature of stage 15 embryos, indicating the acquisition of a GC fate in these cells. Direct availability of ciPGCs in vitro would facilitate the study of GC development as well as provide a potential strategy for the conservation of important genetics of agricultural and endangered birds using somatic cells.

α-1,3-Galactosyltransferase Knockout Pig Induced Pluripotent Stem Cells: A Cell Source for the Production of Xenotransplant Pigs

The shortage of human organs and tissues for transplant has led to significant interest in xenotransplantation of pig tissues for human patients. However, transplantation of pig organs results in an acute immune rejection, leading to death of the organ within minutes. The α-1,3-galactosyltransferase (GALT) gene has been knocked out in pigs to reduce rejection, yet additional genes need to be modified to ultimately make pig tissue immunocompatible with humans. The development of pig induced pluripotent stem cells (piPSCs) from GALT knockout (GALT-KO) tissue would provide an excellent cell source for complex genetic manipulations (e.g., gene targeting) that often require highly robust and proliferative cells. In this report, we generated GALT-KO piPSCs by the overexpression of POU5F1, SOX2, NANOG, LIN28, KLF-4, and C-MYC reprogramming genes. piPSCs showed classical stem cell morphology and characteristics, expressing integrated reprogramming genes in addition to the pluripotent markers AP, SSEA1, and SSEA4. GALT-KO piPSCs were highly proliferative and possessed doubling times and telomerase activity similar to human embryonic stem cells. These results demonstrated successful reprogramming of GALT-KO fibroblasts into GALT-KO piPSCs. GALT-KO piPSCs are potentially an excellent immortal cell source for the generation of pigs with complex genetic modifications for xenotransplantation, somatic cell nuclear transfer, or chimera formation.

Nonviral Minicircle Generation of Induced Pluripotent Stem Cells Compatible with Production of Chimeric Chickens

Chickens are vitally important in numerous countries as a primary food source and a major component of economic development. Efforts have been made to produce transgenic birds through pluripotent stem cell [primordial germ cells and embryonic stem cells (ESCs)] approaches to create animals with improved traits, such as meat and egg production or even disease resistance. However, these cell types have significant limitations because they are hard to culture long term while maintaining developmental plasticity. Induced pluripotent stem cells (iPSCs) are a novel class of stem cells that have proven to be robust, leading to the successful development of transgenic mice, rats, quail, and pigs and may potentially overcome the limitations of previous pluripotent stem cell systems in chickens. In this study we generated chicken (c) iPSCs from fibroblast cells for the first time using a nonviral minicircle reprogramming approach. ciPSCs demonstrated stem cell morphology and expressed key stem cell markers, including alkaline phosphatase, POU5F1, SOX2, NANOG, and SSEA-1. These cells were capable of rapid growth and expressed high levels of telomerase. Late-passage ciPSCs transplanted into stage X embryos were successfully incorporated into tissues of all three germ layers, and the gonads demonstrated significant cellular plasticity. These cells provide an exciting new tool to create transgenic chickens with broad implications for agricultural and transgenic animal fields at large.

Livestock induced pluripotent stem cells.

Chimeric animals generated from livestock-induced pluripotent stem cells (iPSCs) have opened the door of opportunity to genetically manipulate species for the production of biomedical models, improving traits of agricultural importance and potentially providing a system to test novel iPSC therapies. The potential of pluripotent stem cells in livestock has long been recognized, with many attempts being chronicled to isolate, culture and characterize pluripotent cells from embryos. However, in most cases, livestock stem cells derived from embryonic sources have failed to reach a pluripotent state marked by the inability to form chimeric animals. The in-depth understanding of core pluripotency factors and the realization of how these factors can be harnessed to reprogram adult cells into an induced pluripotent state has changed the paradigm of livestock stem cells. In this review, we will examine the advancements in iPSC technology in mammalian and avian livestock species.

Derivation of chicken induced pluripotent stem cells tolerant to Newcastle disease virus-induced lysis through multiple rounds of infection.

BackgroundNewcastle disease (ND), caused by Newcastle disease virus (NDV), is a devastating disease of poultry and wild birds. ND is prevented by rigorous biocontainment and vaccination. One potential approach to prevent spread of the virus is production of birds that show innate resistance to NDV-caused disease. Induced pluripotent stem cell (iPSC) technology allows adult cells to be reprogrammed into an embryonic stem cell-like state capable of contributing to live offspring and passing on unique traits in a number of species. Recently, iPSC approaches have been successfully applied to avian cells. If chicken induced pluripotent stem cells (ciPSCs) are genetically or epigenetically modified to resist NDV infection, it may be possible to generate ND resistant poultry. There is limited information on the potential of ciPSCs to be infected by NDV, or the capacity of these cells to become resistant to infection. The aim of the present work was to assess the characteristics of the interaction between NDV and ciPSCs, and to develop a selection method that would increase tolerance of these cells to NDV-induced cellular damage.ResultsResults showed that ciPSCs were permissive to infection with NDV, and susceptible to virus-mediated cell death. Since ciPSCs that survived infection demonstrated the ability to recover quickly, we devised a system to select surviving cells through multiple infection rounds with NDV. ciPSCs that sustained 9 consecutive infections had a statistically significant increase in survival (up to 36 times) compared to never-infected ciPSCs upon NDV infection (tolerant cells). Increased survival was not caused by a loss of permissiveness to NDV replication. RNA sequencing followed by enrichment pathway analysis showed that numerous metabolic pathways where differentially regulated between tolerant and never-infected ciPSCs.ConclusionsResults demonstrate that ciPSCs are permissive to NDV infection and become increasingly tolerant to NDV under selective pressure, indicating that this system could be applied to study mechanisms of cellular tolerance to NDV.

Generation of Avian Induced Pluripotent Stem Cells.

Avian species are among the most diverse vertebrates on our planet and significantly contribute to the balance of the ecology. They are also important food source and serve as a central animal model to decipher developmental biology and disease principles. Derivation of induced pluripotent stem cells (iPSCs) from avian species would enable conservation of genetic diversity as well as offer a valuable cell source that facilitates the use of avian models in many areas of basic and applied research. In this chapter, we describe methods used to successfully reprogram quail fibroblasts into iPSCs by using human transcription factors and the techniques critical to the characterization of their pluripotency.

Culture of Pig Induced Pluripotent Stem Cells without Direct Feeder Contact in Serum Free Media

Background: Reprogramming pig somatic cells into induced pluripotent stem cells (iPSCs) have promising applications in basic biology, disease model development and xenotransplantation. In the mouse, embryonic stem cell (ESC) technology has revolutionized the field enabling gene targeting, complex screening strategies and the creation of animals that show unique characteristics of interest. Recent breakthroughs utilizing induced pluripotent stem cell technology in the pig have made it possible to produce pig pluripotent stem cells that resemble germline chimeric competent mouse ESCs. However, an optimal culture system for piPSC expansion has yet to be developed. Most reports have maintained piPSCs in undefined systems that use xenoproducts and feeder layers, which are potential sources of contamination. Methods: In this study, new lines of pig iPSCs (piPSC) were generated from pig fibroblast cells by overexpressing six reprogramming genes: POU5F1, SOX2, NANOG, LIN28, KLF4 and C-MYC. These new lines were tested for their ability to be maintained on a Matrigel substrate in the established mouse 2i+LIF system, the human mTeSR1 system and variations of a feeder conditioned media system. Analysis and identification of piPSCs were performed using immunocytochemistry, flow cytometry and by examining embryoid body formation and differentiation. Results: The newly generated piPSCs showed morphological features, immunoreactivity and reactivation of endogenous pluripotency networks consistent with iPSCs. Similar to cells cultured on feeders, piPSCs maintained under all 7 feeder-free conditions expressed POU5F1 and NANOG, SSEA-1, SSEA-4 and TRA1-81. However, flow cytometry demonstrated that piPSCs cultured in feeder conditioned media with KnockOut Serum Replacement and basic fibroblast growth factor (FGF2) showed significantly higher levels of SSEA1 and SSEA4 expression than cells cultured in a 2i+LIF or mTeSR1 system. Conclusion: These findings demonstrate that piPSCs can be maintained in defined systems without serum and direct feeder contact, increasing their potential use in both agricultural and biomedical fields.