Non-viral reprogramming of fibroblasts into induced pluripotent stem cells by Sleeping Beauty and piggyBac transposons

Applications of genome editing tools in stem cells towards regenerative medicine: An update

Precise and site specific genome editing through application of emerging and modern gene engineering techniques, namely zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) have swiftly progressed the application and use of the stem cell technology in the sphere of in-vitro disease modelling and regenerative medicine. Genome editing tools facilitate the manipulating of any gene in various types of cells with target specific nucleases. These tools aid in elucidating the genetics and etiology behind different diseases and have immense promise as novel therapeutics for correcting the genetic mutations, make alterations and cure diseases permanently that are not responding and resistant to traditional therapies. These genome engineering tools have evolved in the field of biomedical research and have also shown to have a significant improvement in clinical trials. However, their widespread use in research revealed potential safety issues, which need to be addressed before implementing such techniques in clinical purposes. Significant and valiant attempts are being made in order to surpass those hurdles. The current review outlines the advancements of several genome engineering tools and describes suitable strategies for their application towards regenerative medicine.

Expression of reprogramming factors in mesenchymal stem cells isolated from equine umbilical cord Wharton’s jelly and amniotic fluid

Stem cells represent the most promising population for regenerative cell therapy and have gained much attention during the recent past. Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into trilineages. Like haematopoietic cells, mesenchymal cells have been shown to proliferate and form fibroblast-like colonies in vitro. Despite major progress in our general knowledge related to the application of adult stem cells, finding alternative sources for bone marrow MSCs has remained a challenge. A wide diversity of isolation procedures for mesenchymal stromal cells from various tissues of the placenta, umbilical cord and Wharton's jelly have been described for humans and other species. In this study, we isolated established umbilical cord Wharton’s jelly as a primary source for isolation of mesenchymal stem cells since it is a rich source of stem cells and no ethical concerns are involved. Equine umbilical cord Wharton’s jelly segments were collected during foaling time and digested enzymatically and cultured in-vitro in culture medium. In addition to the study of their morphology and colony forming units, the expression of reprogramming factors by the isolated MSCs were also studied. The isolated MSCs were observed to be plastic adherent, clonogenic and their morphology were polygonal, star shaped and fibroblast like. They revealed a strong expression of pluripotent stemness markers OCT-4, SOX-2, Nanog and KLF-4. From the current study, it can be concluded that Wharton's jelly is a rich source of stem cells with stemness properties expressing the reprogramming factors and mesenchymal like morphology and could be used as an alternate for the bone marrow derived mesenchymal stem cells for cell based regenerative therapies.

Contemporary Transposon Tools: A Review and Guide through Mechanisms and Applications of Sleeping Beauty, piggyBac and Tol2 for Genome Engineering

Transposons are mobile genetic elements evolved to execute highly efficient integration of their genes into the genomes of their host cells. These natural DNA transfer vehicles have been harnessed as experimental tools for stably introducing a wide variety of foreign DNA sequences, including selectable marker genes, reporters, shRNA expression cassettes, mutagenic gene trap cassettes, and therapeutic gene constructs into the genomes of target cells in a regulated and highly efficient manner. Given that transposon components are typically supplied as naked nucleic acids (DNA and RNA) or recombinant protein, their use is simple, safe, and economically competitive. Thus, transposons enable several avenues for genome manipulations in vertebrates, including transgenesis for the generation of transgenic cells in tissue culture comprising the generation of pluripotent stem cells, the production of germline-transgenic animals for basic and applied research, forward genetic screens for functional gene annotation in model species and therapy of genetic disorders in humans. This review describes the molecular mechanisms involved in transposition reactions of the three most widely used transposon systems currently available (Sleeping Beauty, piggyBac, and Tol2), and discusses the various parameters and considerations pertinent to their experimental use, highlighting the state-of-the-art in transposon technology in diverse genetic applications.

Lentiviral mediated gene delivery as an effective therapeutic approach for Parkinson disease

Continual strategies to devise a complete therapeutic cure for neurodegenerative conditions has been a challenge, majorly due to the presence of blood brain barrier. Lack of targeted delivery in order to minimize loss of dopamine (DA) neurones has been a major challenge to overcome anomalies in Parkinson Disease (PD). PD is a neuromotor degenerative disorder deteriorating motor coordination in affected individuals. Recent research has highlighted the use of lentiviral vectors (LVs) for selective delivery of neuroprotective substance for complete halt of disease progression in PD. LVs have the ability to infect both dividing and non-dividing cells along with non-encoding capability of viral protein that might elicit an immune response. This review will mainly focus on understanding the basic mechanism of action of LVs and its therapeutic aid in PD.

Generation of Murine Induced Pluripotent Stem Cells through Transposon-Mediated Reprogramming

The seminal discovery of induced pluripotent stem (iPS) cells through ectopic expression of a cocktail of gene factors (OCT4, SOX2, KLF4, and c-MYC) by the group of Yamanaka was a major breakthrough, gained widespread acclaim and garnered much attention in the field of stem cell science. The iPS cells possess most of the characteristics and advantages of embryonic stem (ES) cells without the association of ethical stigma for their derivation. In addition, these cells can give rise to any cell type of the body and thus have tremendous potential for many downstream applications in research and regenerative medicine. The original method requires viral transduction of several reprogramming factors, which may be associated with an increased risk of oncogenicity and insertional mutagenesis. Nonviral methods for generation of iPS cells through somatic cell reprogramming are powerful tools for establishing in vitro disease models, development of new protocols for treatment of different diseases, and creating transgenic mice models. Here, we present a detailed protocol for the generation of transposon-mediated iPS cells from mouse embryonic fibroblasts (MEFs) and give a short overview of the characterization of the generated iPS cell lines.

A versatile bulk electrotransfection protocol for murine embryonic fibroblasts and iPS cells

Although electroporation has been widely accepted as the main gene transfer tool, there is still considerable scope to improve the electroporation efficiency of exogenous DNAs into primary cells. Here, we developed a square-wave pulsing protocol using OptiMEM-GlutaMAX for highly efficient transfection of murine embryonic fibroblasts (MEF) and induced pluripotency stem (iPS) cells using reporter genes as well as gRNA/Cas9-encoding plasmids. An electrotransfection efficiency of > 95% was achieved for both MEF and iPS cells using reporter-encoding plasmids. The protocol was efficient for plasmid sizes ranging from 6.2 to 13.5 kb. Inducing the error prone non-homologous end joining repair by gRNA/Cas9 plasmid transfection, a high rate of targeted gene knockouts of up to 98% was produced in transgenic cells carrying a single-copy of Venus reporter. Targeted deletions in the Venus transgene were efficiently (up to 67% deletion rate) performed by co-electroporation of two gRNA-encoding plasmids. We introduced a plasmid electrotransfection protocol which is straight-forward, cost-effective, and efficient for CRISPRing murine primary cells. This protocol is promising to make targeted genetic engineering using the CRISPR/Cas9 plasmid system.

Potential of transposon-mediated cellular reprogramming towards cell-based therapies

Induced pluripotent stem (iPS) cells present a seminal discovery in cell biology and promise to support innovative treatments of so far incurable diseases. To translate iPS technology into clinical trials, the safety and stability of these reprogrammed cells needs to be shown. In recent years, different non-viral transposon systems have been developed for the induction of cellular pluripotency, and for the directed differentiation into desired cell types. In this review, we summarize the current state of the art of different transposon systems in iPS-based cell therapies.

Reprogramming and transdifferentiation - two key processes for regenerative medicine

Regenerative medicine based on transplants obtained from donors or foetal and new-born mesenchymal stem cells, encounter important obstacles such as limited availability of organs, ethical issues and immune rejection. The growing demand for therapeutic methods for patients being treated after serious accidents, severe organ dysfunction and an increasing number of cancer surgeries, exceeds the possibilities of the therapies that are currently available. Reprogramming and transdifferentiation provide powerful bioengineering tools. Both procedures are based on the somatic differentiated cells, which are easily and unlimitedly available, like for example: fibroblasts. During the reprogramming procedure mature cells are converted into pluripotent cells - which are capable to differentiate into almost any kind of desired cells. Transdifferentiation directly converts differentiated cells of one type into another differentiated cells type. Both procedures allow to obtained patient's dedicated cells for therapeutic purpose in regenerative medicine. In combination with biomaterials, it is possible to obtain even whole anatomical structures. Those patient's dedicated structures may serve for them upon serious accidents with massive tissue damage but also upon cancer surgeries as a replacement of damaged organ. Detailed information about reprogramming and transdifferentiation procedures as well as the current state of the art are presented in our review.

In Vitro and In Vivo Interspecies Chimera Assay Using Early Pig Embryos

Chimeric pigs harboring organs derived from human stem cells are promising for patient-specific regenerative therapies. Induced pluripotent stem cells (iPSCs) can contribute to all cell types of the fetus, including germline after injection into embryos. However, ethical concerns prohibit testing human iPSCs in chimera assays. Here, we evaluated porcine embryos as hosts for an interspecies chimera assay using iPSCs from either cynomolgus monkeys (cyiPSCs) or mouse (miPSCs). To establish an in vitro culture system compatible for cyiPSCs and porcine embryos, we determined blastocyst development in eight different stem cell media. The highest developmental rates of blastocysts were achieved in Knockout Dulbecco's modified Eagle's medium with 20% knockout serum replacement. We found that cyiPSCs injected into porcine embryos survived in vitro and were mostly located in the trophectoderm (TE). Instead, when miPSCs were injected into porcine embryos, the cells rapidly proliferated. The behavior of chimeras developed in vitro was recapitulated in vivo; cyiPSCs were observed in the TE, but not in the porcine epiblast. However, when miPSCs were injected into in vivo derived porcine embryos, mouse cells were found in both, the epiblast and TE. These results demonstrate that porcine embryos could be useful for evaluating the interspecies chimera-forming ability of iPSCs from different species.

A single amino acid switch converts the Sleeping Beauty transposase into an efficient unidirectional excisionase with utility in stem cell reprogramming

The Sleeping Beauty (SB) transposon is an advanced tool for genetic engineering and a useful model to investigate cut-and-paste DNA transposition in vertebrate cells. Here, we identify novel SB transposase mutants that display efficient and canonical excision but practically unmeasurable genomic re-integration. Based on phylogenetic analyses, we establish compensating amino acid replacements that fully rescue the integration defect of these mutants, suggesting epistasis between these amino acid residues. We further show that the transposons excised by the exc⁺/int⁻ transposase mutants form extrachromosomal circles that cannot undergo a further round of transposition, thereby representing dead-end products of the excision reaction. Finally, we demonstrate the utility of the exc⁺/int⁻ transposase in cassette removal for the generation of reprogramming factor-free induced pluripotent stem cells. Lack of genomic integration and formation of transposon circles following excision is reminiscent of signal sequence removal during V(D)J recombination, and implies that cut-and-paste DNA transposition can be converted to a unidirectional process by a single amino acid change.

Transposon mediated reprogramming of buffalo fetal fibroblasts to induced pluripotent stem cells in feeder free culture conditions

Commonly, induced pluripotent stem (iPS) cells are generated by viral transduction of four core reprogramming genes, but recent evidences suggest that slightly different combination of transcription factors improve the efficiency and quality of generated iPS cells. However, vectors like retro- and lentiviral may cause insertional mutagenesis due to its integrating ability. Hence, alternate methods with safety concerns are needed to be investigated. Therefore, the present study was undertaken to reprogram buffalo fibroblasts using non-viral piggyBac (PB) transposon mediated transfer of six transcription factors. To generate buffalo iPS cells, fibroblasts were isolated from buffalo fetus at passage 2. The cells were co-electroporated with a PB transposon having CAGGS promoter driven cassette of Oct4, Sox2, Klf4, cMyc, Nanog, and Lin28 transcription factors separated by self-cleaving 2A peptide and a helper plasmid pCMV-PB transposase. After 12-14 days post electroporation, fibroblast cells morphology was observed to change to round structures which formed loose aggregates of cells on day 18. Putative iPS cell colonies were propagated in feeder free system and characterized through expression of pluripotency markers such as alkaline phosphatase, SSEA-1, SSEA-4, SSEA-5, TRA-1-81, Oct4, Nanog and Sox2 and endogenous genes supported the stemness property of the generated cells. These cells differentiated in vitro to form embryoid bodies and were found to express three germ layers markers. In conclusion, generation of buffalo iPS cells using transposon system provides insights into viral-free iPS technology which will facilitate genetic modification of the buffalo genome and help in the production of transgenic animals using genetically modified iPS cells.

An insight into non-integrative gene delivery approaches to generate transgene-free induced pluripotent stem cells

Over a decade ago, a landmark study that reported derivation of induced Pluripotent Stem Cells (iPSCs) by reprogramming fibroblasts has transformed stem cell research attracting the interest of the scientific community worldwide. These cells circumvent the ethical and immunological concerns associated with embryonic stem cells, and the limited self-renewal ability and restricted differentiation potential linked to adult stem cells. iPSCs hold great potential for understanding basic human biology, in vitro disease modeling, high-throughput drug testing and discovery, and personalized regenerative medicine. The conventional reprogramming methods involving retro- and lenti-viral vectors to deliver reprogramming factors in somatic cells to generate iPSCs nullify the clinical applicability of these cells. Although these gene delivery systems are efficient and robust, they carry an enormous risk of permanent genetic modifications and are potentially tumorigenic. To evade these safety concerns and derive iPSCs for human therapy, tremendous technological advancements have resulted in the development of non-integrating viral- and non-viral approaches. These gene delivery techniques curtail or eliminate the risk of any genomic alteration and enhance the prospects of iPSCs from bench-to-bedside. The present review provides a comprehensive overview of non-integrating viral (adenoviral vectors, adeno-associated viral vectors, and Sendai virus vectors) and DNA-based, non-viral (plasmid transfection, minicircle vectors, transposon vectors, episomal vectors, and liposomal magnetofection) approaches that have the potential to generate transgene-free iPSCs. The understanding of these techniques could pave the way for the use of iPSCs for various biomedical applications.

Expression and purification of a rapidly degraded protein, TMEM8B-a, in mammalian cell line

TMEM8B-a protein is the longer, predominant isoform of the TMEM8B gene product, which is a tumor metastasis suppressor in nasopharyngeal carcinoma (NPC) and lung cancer. TMEM8B-a is rapidly degraded via the proteasome pathway mediated by ezrin in many NPC and lung cancer cell lines, but TMEM8B-a is not ubiquitinated. In this study, we report the recombinant production of full-length modified TMEM8B-a in mammalian cells. We used the PiggyBac transposon system to efficiently generate normal and lung cancer cell lines with stable TMEM8B-a protein expression. 293FT cells were the best host cell line to express TMEM8B-a protein. Then, we treated the stable 293FT cell lines with various small-molecule inhibitors and demonstrated that treatment with MG-132 and bortezomib, which target the proteasome and disrupt its function, could prevent TMEM8B-a degradation and induce protein expression in 293FT cells. Finally, we utilized the combination of Twin-Strep-tag and Strep-Tactin XT resin to successfully purify the TMEM8B-a protein. The final yield was estimated to be approximately 10-20 μg of the purified TMEM8B-a per 3.0 × 10⁸ 293FT cells.

Preclinical and clinical advances in transposon-based gene therapy

Transposons derived from Sleeping Beauty (SB), piggyBac (PB), or Tol2 typically require cotransfection of transposon DNA with a transposase either as an expression plasmid or mRNA. Consequently, this results in genomic integration of the potentially therapeutic gene into chromosomes of the desired target cells, and thus conferring stable expression. Non-viral transfection methods are typically preferred to deliver the transposon components into the target cells. However, these methods do not match the efficacy typically attained with viral vectors and are sometimes associated with cellular toxicity evoked by the DNA itself. In recent years, the overall transposition efficacy has gradually increased by codon optimization of the transposase, generation of hyperactive transposases, and/or introduction of specific mutations in the transposon terminal repeats. Their versatility enabled the stable genetic engineering in many different primary cell types, including stem/progenitor cells and differentiated cell types. This prompted numerous preclinical proof-of-concept studies in disease models that demonstrated the potential of DNA transposons for ex vivo and in vivo gene therapy. One of the merits of transposon systems relates to their ability to deliver relatively large therapeutic transgenes that cannot readily be accommodated in viral vectors such as full-length dystrophin cDNA. These emerging insights paved the way toward the first transposon-based phase I/II clinical trials to treat hematologic cancer and other diseases. Though encouraging results were obtained, controlled pivotal clinical trials are needed to corroborate the efficacy and safety of transposon-based therapies.

Interaction of iPSC-derived neural stem cells on poly(L-lactic acid) nanofibrous scaffolds for possible use in neural tissue engineering

Tissue engineering is a rapidly growing technological area for the regeneration and reconstruction of damage to the central nervous system. By combining seed cells with appropriate biomaterial scaffolds, tissue engineering has the ability to improve nerve regeneration and functional recovery. In the present study, mouse induced pluripotent stem cells (iPSCs) were generated from mouse embryonic fibroblasts (MEFs) with the non-integrating episomal vectors pCEP4-EO2S-ET2K and pCEP4-miR-302-367 cluster, and differentiated into neural stem cells (NSCs) as transplanting cells. Electrospinning was then used to fabricate randomly oriented poly(L-lactic acid) (PLLA) nanofibers and aligned PLLA nanofibers and assessed their cytocompatibility and neurite guidance effect with iPSC-derived NSCs (iNSCs). The results demonstrated that non-integrated iPSCs were effectively generated and differentiated into iNSCs. PLLA nanofiber scaffolds were able to promote the adhesion, growth, survival and proliferation of the iNSCs. Furthermore, compared with randomly oriented PLLA nanofibers, the aligned PLLA nanofibers greatly directed neurite outgrowth from the iNSCs and significantly promoted neurite growth along the nanofibrous alignment. Overall, these findings indicate the feasibility of using PLLA nanofiber scaffolds in combination with iNSCs in vitro and support their potential for use in nerve tissue engineering.

Murine pluripotent stem cells with a homozygous knockout of Foxg1 show reduced differentiation towards cortical progenitors in vitro

Foxg1 is a transcription factor critical for the development of the mammalian telencephalon. Foxg1 controls the proliferation of dorsal telencephalon progenitors and the specification of the ventral telencephalon. Homozygous knockout of Foxg1 in mice leads to severe microcephaly, attributed to premature differentiation of telencephalic progenitors, mainly of cortical progenitors. Here, we analyzed the influence of a Foxg1 knockout on differentiation of murine pluripotent stem cells (mPSCs) in an in vitro model of neuronal development. Murine PSCs were prone to neuronal differentiation in embryoid body like culture with minimal medium conditions, based on the intrinsic default of PSCs to develop into cortical progenitors. Differences between Foxg1 wildtype (Foxg1^WT) and knockout (Foxg1^KO) mPSCs were analyzed. Several mPSC lines with homozygous mutations in Foxg1 were produced using the CRISPR/Cas9 system leading to loss of functional domains. Analysis of mRNA expression using quantitative Real-Time (q) PCR revealed that Foxg1^KO mPSCs expressed significantly less mRNA of Foxg1, Emx1, and VGlut1 compared to Foxg1^WT controls, indicating reduced differentiation towards dorsal telencephalic progenitors. However, the size of the derived EB-like structures did not differ between Foxg1^WT and Foxg1^KO mPSCs. These results show that loss of dorsal telencephalic progenitors can be detected using a simple and rapid differentiation protocol. This study is a first hint that this differentiation method can be used to analyze even extreme phenotypes that are lethal in vivo.

Germline Competent Pluripotent Mouse Stem Cells Generated by Plasmid Vectors

We developed nonintegrated methods to reprogram mouse embryonic fibroblast (MEF) cells into induced pluripotent stem cells (iPSCs) using pig pOct4, pSox2, and pc-Myc as well as human hKLF4, hAID, and hTDG that were carried by plasmid vectors. The 4F method employed pOct4, pSox2, pc-Myc, and hKLF4 to derive iPSC clones with naive embryonic stem cell (ESC)-like morphology. These 4F clones expressed endogenous mouse Nanog protein and could generate chimeras. In addition to the four conventional reprogramming factors used in the 4F method, hAID and hTDG were utilized in a 6F method to increase the conversion efficiency of reprogramming by approximately five-fold. One of the 6F plasmid derived iPSC (piPSC) clones was shown to be germline transmission competent.

Differentiation of Induced Pluripotent Stem Cells to Lentoid Bodies Expressing a Lens Cell-Specific Fluorescent Reporter

Curative approaches for eye cataracts and other eye abnormalities, such as myopia and hyperopia currently suffer from a lack of appropriate models. Here, we present a new approach for in vitro growth of lentoid bodies from induced pluripotent stem (iPS) cells as a tool for ophthalmological research. We generated a transgenic mouse line with lens-specific expression of a fluorescent reporter driven by the alphaA crystallin promoter. Fetal fibroblasts were isolated from transgenic fetuses, reprogrammed to iPS cells, and differentiated to lentoid bodies exploiting the specific fluorescence of the lens cell-specific reporter. The employment of cell type-specific reporters for establishing and optimizing differentiation in vitro seems to be an efficient and generally applicable approach for developing differentiation protocols for desired cell populations.

Pluripotent stem cells and livestock genetic engineering

The unlimited proliferative ability and capacity to contribute to germline chimeras make pluripotent embryonic stem cells (ESCs) perfect candidates for complex genetic engineering. The utility of ESCs is best exemplified by the numerous genetic models that have been developed in mice, for which such cells are readily available. However, the traditional systems for mouse genetic engineering may not be practical for livestock species, as it requires several generations of mating and selection in order to establish homozygous founders. Nevertheless, the self-renewal and pluripotent characteristics of ESCs could provide advantages for livestock genetic engineering such as ease of genetic manipulation and improved efficiency of cloning by nuclear transplantation. These advantages have resulted in many attempts to isolate livestock ESCs, yet it has been generally concluded that the culture conditions tested so far are not supportive of livestock ESCs self-renewal and proliferation. In contrast, there are numerous reports of derivation of livestock induced pluripotent stem cells (iPSCs), with demonstrated capacity for long term proliferation and in vivo pluripotency, as indicated by teratoma formation assay. However, to what extent these iPSCs represent fully reprogrammed PSCs remains controversial, as most livestock iPSCs depend on continuous expression of reprogramming factors. Moreover, germline chimerism has not been robustly demonstrated, with only one successful report with very low efficiency. Therefore, even 34 years after derivation of mouse ESCs and their extensive use in the generation of genetic models, the livestock genetic engineering field can stand to gain enormously from continued investigations into the derivation and application of ESCs and iPSCs.

Induced Pluripotent Stem Cells With Six Reprogramming Factors From Prairie Vole, Which Is an Animal Model for Social Behaviors

Prairie voles show strong pair bonding with their mating partners, and they demonstrate parental behavior toward their infants, indicating that the prairie vole is a unique animal model for analysis of molecular mechanisms of social behavior. Until a recent study, the signaling pathway of oxytocin was thought to be critical for the social behavior of prairie voles, but neuron-specific functional research may be necessary to identify the molecular mechanisms of social behavior. Prairie vole pluripotent stem cells of high quality are essential to elucidate the molecular mechanisms of social behaviors. Generation of high-quality induced pluripotent stem cells (iPSCs) would help to establish a genetically modified prairie vole, including knockout and knock-in models, based on the pluripotency of iPSCs. Thus, we attempted to establish high-quality prairie vole-derived iPSCs (pv-iPSCs) in this study. We constructed a polycistronic reprogramming vector, which included six reprograming factors (Oct3/4, Sox2, Klf4, c-myc, Lin28, and Nanog). Furthermore, we evaluated the effect of six reprogramming factors, which included Oct3/4 with the transactivation domain (TAD) of MyoD. Implantation of the pv-iPSCs into immunodeficient mice caused a teratoma with three germ layers. Furthermore, the established pv-iPSCs tested positive for stem cell markers, including alkaline phosphatase activity (ALP), stage-specific embryonic antigen (SSEA)-1, and dependence on leukemia inhibitory factor (LIF). Our data indicate that our newly established pv-iPSCs may be a useful tool for genetic analysis of social behavior.

The Importance of Ubiquitination and Deubiquitination in Cellular Reprogramming

Ubiquitination of core stem cell transcription factors can directly affect stem cell maintenance and differentiation. Ubiquitination and deubiquitination must occur in a timely and well-coordinated manner to regulate the protein turnover of several stemness related proteins, resulting in optimal embryonic stem cell maintenance and differentiation. There are two switches: an E3 ubiquitin ligase enzyme that tags ubiquitin molecules to the target proteins for proteolysis and a second enzyme, the deubiquitinating enzyme (DUBs), that performs the opposite action, thereby preventing proteolysis. In order to maintain stemness and to allow for efficient differentiation, both ubiquitination and deubiquitination molecular switches must operate properly in a balanced manner. In this review, we have summarized the importance of the ubiquitination of core stem cell transcription factors, such as Oct3/4, c-Myc, Sox2, Klf4, Nanog, and LIN28, during cellular reprogramming. Furthermore, we emphasize the role of DUBs in regulating core stem cell transcriptional factors and their function in stem cell maintenance and differentiation. We also discuss the possibility of using DUBs, along with core transcription factors, to efficiently generate induced pluripotent stem cells. Our review provides a relatively new understanding regarding the importance of ubiquitination/deubiquitination of stem cell transcription factors for efficient cellular reprogramming.

Cytoplasmic injection of murine zygotes with Sleeping Beauty transposon plasmids and minicircles results in the efficient generation of germline transgenic mice

Transgenesis in the mouse is an essential tool for the understanding of gene function and genome organization. Here, we describe a simplified microinjection protocol for efficient germline transgenesis and sustained transgene expression in the mouse model employing binary Sleeping Beauty transposon constructs of different topology. The protocol is based on co-injection of supercoiled plasmids or minicircles, encoding the Sleeping Beauty transposase and a transposon construct, into the cytoplasm of murine zygotes. Importantly, this simplified injection avoids the mechanical penetration of the vulnerable pronuclear membrane, resulting in higher survival rates of treated embryos and a more rapid pace of injections. Upon translation of the transposase, transposase-catalyzed transposition into the genome results in stable transgenic animals carrying monomeric transgenes. In summary, cytoplasmic injection of binary transposon constructs is a feasible, plasmid-based, and simplified microinjection method to generate genetically modified mice. The modular design of the components allows the multiplexing of different transposons, and the generation of multi-transposon transgenic mice in a single step.

Human adipose stem cell and ASC-derived cardiac progenitor cellular therapy improves outcomes in a murine model of myocardial infarction

BACKGROUND

Adipose tissue is an abundant and potent source of adult stem cells for transplant therapy. In this study, we present our findings on the potential application of adipose-derived stem cells (ASCs) as well as induced cardiac-like progenitors (iCPs) derived from ASCs for the treatment of myocardial infarction.

METHODS AND RESULTS

Human bone marrow (BM)-derived stem cells, ASCs, and iCPs generated from ASCs using three defined cardiac lineage transcription factors were assessed in an immune-compromised mouse myocardial infarction model. Analysis of iCP prior to transplant confirmed changes in gene and protein expression consistent with a cardiac phenotype. Endpoint analysis was performed 1 month posttransplant. Significantly increased endpoint fractional shortening, as well as reduction in the infarct area at risk, was observed in recipients of iCPs as compared to the other recipient cohorts. Both recipients of iCPs and ASCs presented higher myocardial capillary densities than either recipients of BM-derived stem cells or the control cohort. Furthermore, mice receiving iCPs had a significantly higher cardiac retention of transplanted cells than all other groups.

CONCLUSION

Overall, iCPs generated from ASCs outperform BM-derived stem cells and ASCs in facilitating recovery from induced myocardial infarction in mice.

Derivation and characterization of bovine induced pluripotent stem cells by transposon-mediated reprogramming

Induced pluripotent stem cells (iPSCs) are a seminal breakthrough in stem cell research and are promising tools for advanced regenerative therapies in humans and reproductive biotechnology in farm animals. iPSCs are particularly valuable in species in which authentic embryonic stem cell (ESC) lines are yet not available. Here, we describe a nonviral method for the derivation of bovine iPSCs employing Sleeping Beauty (SB) and piggyBac (PB) transposon systems encoding different combinations of reprogramming factors, each separated by self-cleaving peptide sequences and driven by the chimeric CAGGS promoter. One bovine iPSC line (biPS-1) generated by a PB vector containing six reprogramming genes was analyzed in detail, including morphology, alkaline phosphatase expression, and typical hallmarks of pluripotency, such as expression of pluripotency markers and formation of mature teratomas in immunodeficient mice. Moreover, the biPS-1 line allowed a second round of SB transposon-mediated gene transfer. These results are promising for derivation of germ line-competent bovine iPSCs and will facilitate genetic modification of the bovine genome.

Induced pluripotent stem cells: Mechanisms, achievements and perspectives in farm animals

Pluripotent stem cells are unspecialized cells with unlimited self-renewal, and they can be triggered to differentiate into desired specialized cell types. These features provide the basis for an unlimited cell source for innovative cell therapies. Pluripotent cells also allow to study developmental pathways, and to employ them or their differentiated cell derivatives in pharmaceutical testing and biotechnological applications. Via blastocyst complementation, pluripotent cells are a favoured tool for the generation of genetically modified mice. The recently established technology to generate an induced pluripotency status by ectopic co-expression of the transcription factors Oct4, Sox2, Klf4 and c-Myc allows to extending these applications to farm animal species, for which the derivation of genuine embryonic stem cells was not successful so far. Most induced pluripotent stem (iPS) cells are generated by retroviral or lentiviral transduction of reprogramming factors. Multiple viral integrations into the genome may cause insertional mutagenesis and may increase the risk of tumour formation. Non-integration methods have been reported to overcome the safety concerns associated with retro and lentiviral-derived iPS cells, such as transient expression of the reprogramming factors using episomal plasmids, and direct delivery of reprogramming mRNAs or proteins. In this review, we focus on the mechanisms of cellular reprogramming and current methods used to induce pluripotency. We also highlight problems associated with the generation of iPS cells. An increased understanding of the fundamental mechanisms underlying pluripotency and refining the methodology of iPS cell generation will have a profound impact on future development and application in regenerative medicine and reproductive biotechnology of farm animals.

Cellular reprogramming for understanding and treating human disease

In the last two decades we have witnessed a paradigm shift in our understanding of cells so radical that it has rewritten the rules of biology. The study of cellular reprogramming has gone from little more than a hypothesis, to applied bioengineering, with the creation of a variety of important cell types. By way of metaphor, we can compare the discovery of reprogramming with the archeological discovery of the Rosetta stone. This stone slab made possible the initial decipherment of Egyptian hieroglyphics because it allowed us to see this language in a way that was previously impossible. We propose that cellular reprogramming will have an equally profound impact on understanding and curing human disease, because it allows us to perceive and study molecular biological processes such as differentiation, epigenetics, and chromatin in ways that were likewise previously impossible. Stem cells could be called “cellular Rosetta stones” because they allow also us to perceive the connections between development, disease, cancer, aging, and regeneration in novel ways. Here we present a comprehensive historical review of stem cells and cellular reprogramming, and illustrate the developing synergy between many previously unconnected fields. We show how stem cells can be used to create in vitro models of human disease and provide examples of how reprogramming is being used to study and treat such diverse diseases as cancer, aging, and accelerated aging syndromes, infectious diseases such as AIDS, and epigenetic diseases such as polycystic ovary syndrome. While the technology of reprogramming is being developed and refined there have also been significant ongoing developments in other complementary technologies such as gene editing, progenitor cell production, and tissue engineering. These technologies are the foundations of what is becoming a fully-functional field of regenerative medicine and are converging to a point that will allow us to treat almost any disease.