Exogenous enzymes upgrade transgenesis and genetic engineering of farm animals

Production of MSTN Gene-Edited Embryos of Buffalo Using the CRISPR/Cas9 System and SCNT

The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system and somatic cell nuclear transfer (SCNT) have been used to produce genome-edited farm animal species for improved production and health traits; however, these tools are rarely used in the buffalo and can play a pivotal role in milk and meat production in tropical and subtropical countries. In this study, we aimed to produce myostatin (MSTN) gene-edited embryos of the Murrah buffalo using the CRISPR/Cas9 system and SCNT. For this, fibroblast cells were electroporated with sgRNAs carrying all-in-one CRISPR/Cas9 plasmids targeting the first exon of the MSTN gene. Following puromycin selection, single-cell clonal populations were established and screened using the TA cloning and Sanger sequencing methods. Of eight single-cell clonal populations, one with a monoallelic and another with a biallelic heterozygous gene editing event were identified. These two gene-edited clonal cell populations were successfully used to produce blastocyst-stage embryos using the handmade cloning method. This work establishes the technical foundation for generation of genome-edited cloned embryos in the buffalo.

Quantitative analysis of CRISPR/Cas9-mediated provirus deletion in blue egg layer chicken PGCs by digital PCR

Primordial germ cells (PGCs), the precursors of sperm and oocytes, pass on the genetic material to the next generation. The previously established culture system of chicken PGCs holds many possibilities for functional genomics studies and the rapid introduction of desired traits. Here, we established a CRISPR/Cas9-mediated genome editing protocol for the genetic modification of PGCs derived from chickens with blue eggshell color. The sequence targeted in the present report is a provirus (EAV-HP) insertion in the 5'-flanking region of the SLCO1B3 gene on chromosome 1 in Araucana chickens, which is supposedly responsible for the blue eggshell color. We designed pairs of guide RNAs (gRNAs) targeting the entire 4.2 kb provirus region. Following transfection of PGCs with the gRNA, genomic DNA was isolated and analyzed by mismatch cleavage assay (T7EI). For absolute quantification of the targeting efficiencies in homozygous blue-allele bearing PGCs a digital PCR was established, which revealed deletion efficiencies of 29% when the wildtype Cas9 was used, and 69% when a high-fidelity Cas9 variant was employed. Subsequent single cell dilutions of edited PGCs yielded 14 cell clones with homozygous deletion of the provirus. A digital PCR assay proved the complete absence of this provirus in cell clones. Thus, we demonstrated the high efficiency of the CRISPR/Cas9 system in introducing a large provirus deletion in chicken PGCs. Our presented workflow is a cost-effective and rapid solution for screening the editing success in transfected PGCs.

The domesticated buffalo - An emerging model for experimental and therapeutic use of extraembryonic tissues

Large animals play important roles as model animals for biomedical sciences and translational research. The water buffalo (Bubalus bubalis) is an economically important, multipurpose livestock species. Important assisted reproduction techniques, such as in vitro fertilization, cryo-conservation of sperm and embryos, embryo transfer, somatic cell nuclear transfer, genetic engineering, and genome editing have been successfully applied to buffaloes. Recently, detailed whole genome data and transcriptome maps have been generated. In addition, rapid progress has been made in stem cell biology of the buffalo. Apart from embryonic stem cells, bubaline extra-embryonic stem cells have gained particular interest. The multipotency of non-embryonic stem cells has been revealed, and their utility in basic and applied research is currently investigated. In particular, success achieved in bubaline extra-embryonic stem cells may have important roles in experimental biology and therapeutic regenerative medicine. Progress in other farm animals in assisted reproduction techniques, stem cell biology and genetic engineering, which could be of importance for buffalo, will also be briefly summarized.

Systematic optimization of square-wave electroporation conditions for bovine primary fibroblasts

BACKGROUND

Gene transfer by electroporation is an established method for the non-viral mediated transfection of mammalian cells. Primary cells pose a particular challenge for electroporation-mediated gene transfer, since they are more vulnerable than immortalized cells, and have a limited proliferative capacity. Improving the gene transfer by using square wave electroporation in difficult to transfect cells, like bovine fetal fibroblasts, is a prerequisite for transgenic and further downstream experiments.

RESULTS

Here, bovine fetal fibroblasts were used for square-wave electroporation experiments in which the following parameters were systematically tested: electroporation buffer, electroporation temperature, pulse voltage, pulse duration, pulse number, cuvette type and plasmid DNA amount. For the experiments a commercially available square-wave generator was applied. Post electroporation, the bovine fetal fibroblasts were observed after 24 h for viability and reporter expression. The best results were obtained with a single 10 millisecond square-wave pulse of 400 V using 10 μg supercoiled plasmid DNA and 0.3 × 10⁶ cells in 100 μl of Opti-MEM medium in 4 mm cuvettes. Importantly, the electroporation at room temperature was considerably better than with pre-cooled conditions.

CONCLUSIONS

The optimized electroporation conditions will be relevant for gene transfer experiments in bovine fetal fibroblasts to obtain genetically engineered donor cells for somatic cell nuclear transfer and for reprogramming experiments in this species.

Development of genome engineering technologies in cattle: from random to specific

The production of transgenic farm animals (e.g., cattle) via genome engineering for the gain or loss of gene functions is an important undertaking. In the initial stages of genome engineering, DNA micro-injection into one-cell stage embryos (zygotes) followed by embryo transfer into a recipient was performed because of the ease of the procedure. However, as this approach resulted in severe mosaicism and has a low efficiency, it is not typically employed in the cattle as priority, unlike in mice. To overcome the above issue with micro-injection in cattle, somatic cell nuclear transfer (SCNT) was introduced and successfully used to produce cloned livestock. The application of SCNT for the production of transgenic livestock represents a significant advancement, but its development speed is relatively slow because of abnormal reprogramming and low gene targeting efficiency. Recent genome editing technologies (e.g., ZFN, TALEN, and CRISPR-Cas9) have been rapidly adapted for applications in cattle and great results have been achieved in several fields such as disease models and bioreactors. In the future, genome engineering technologies will accelerate our understanding of genetic traits in bovine and will be readily adapted for bio-medical applications in cattle.

Advances in genome editing for improved animal breeding: A review

Since centuries, the traits for production and disease resistance are being targeted while improving the genetic merit of domestic animals, using conventional breeding programs such as inbreeding, outbreeding, or introduction of marker-assisted selection. The arrival of new scientific concepts, such as cloning and genome engineering, has added a new and promising research dimension to the existing animal breeding programs. Development of genome editing technologies such as transcription activator-like effector nuclease, zinc finger nuclease, and clustered regularly interspaced short palindromic repeats systems begun a fresh era of genome editing, through which any change in the genome, including specific DNA sequence or indels, can be made with unprecedented precision and specificity. Furthermore, it offers an opportunity of intensification in the frequency of desirable alleles in an animal population through gene-edited individuals more rapidly than conventional breeding. The specific research is evolving swiftly with a focus on improvement of economically important animal species or their traits all of which form an important subject of this review. It also discusses the hurdles to commercialization of these techniques despite several patent applications owing to the ambiguous legal status of genome-editing methods on account of their disputed classification. Nonetheless, barring ethical concerns gene-editing entailing economically important genes offers a tremendous potential for breeding animals with desirable traits.

Non-conventional expression systems for the production of vaccine proteins and immunotherapeutic molecules

The increasing demand for recombinant vaccine antigens or immunotherapeutic molecules calls into question the universality of current protein expression systems. Vaccine production can require relatively low amounts of expressed materials, but represents an extremely diverse category consisting of different target antigens with marked structural differences. In contrast, monoclonal antibodies, by definition share key molecular characteristics and require a production system capable of very large outputs, which drives the quest for highly efficient and cost-effective systems. In discussing expression systems, the primary assumption is that a universal production platform for vaccines and immunotherapeutics will unlikely exist. This review provides an overview of the evolution of traditional expression systems, including mammalian cells, yeast and E.coli, but also alternative systems such as other bacteria than E. coli, transgenic animals, insect cells, plants and microalgae, Tetrahymena thermophila, Leishmania tarentolae, filamentous fungi, cell free systems, and the incorporation of non-natural amino acids.

Clinical potential of human-induced pluripotent stem cells : Perspectives of induced pluripotent stem cells

The recent establishment of induced pluripotent stem (iPS) cells promises the development of autologous cell therapies for degenerative diseases, without the ethical concerns associated with human embryonic stem (ES) cells. Initially, iPS cells were generated by retroviral transduction of somatic cells with core reprogramming genes. To avoid potential genotoxic effects associated with retroviral transfection, more recently, alternative non-viral gene transfer approaches were developed. Before a potential clinical application of iPS cell-derived therapies can be planned, it must be ensured that the reprogramming to pluripotency is not associated with genome mutagenesis or epigenetic aberrations. This may include direct effects of the reprogramming method or "off-target" effects associated with the reprogramming or the culture conditions. Thus, a rigorous safety testing of iPS or iPS-derived cells is imperative, including long-term studies in model animals. This will include not only rodents but also larger mammalian model species to allow for assessing long-term stability of the transplanted cells, functional integration into the host tissue, and freedom from undifferentiated iPS cells. Determination of the necessary cell dose is also critical; it is assumed that a minimum of 1 billion transplantable cells is required to achieve a therapeutic effect. This will request medium to long-term in vitro cultivation and dozens of cell divisions, bearing the risk of accumulating replication errors. Here, we review the clinical potential of human iPS cells and evaluate which are the most suitable approaches to overcome or minimize risks associated with the application of iPS cell-derived cell therapies.

Sleeping Beauty transposition: from biology to applications

Sleeping Beauty (SB) is the first synthetic DNA transposon that was shown to be active in a wide variety of species. Here, we review studies from the last two decades addressing both basic biology and applications of this transposon. We discuss how host-transposon interaction modulates transposition at different steps of the transposition reaction. We also discuss how the transposon was translated for gene delivery and gene discovery purposes. We critically review the system in clinical, pre-clinical and non-clinical settings as a non-viral gene delivery tool in comparison with viral technologies. We also discuss emerging SB-based hybrid vectors aimed at combining the attractive safety features of the transposon with effective viral delivery. The success of the SB-based technology can be fundamentally attributed to being able to insert fairly randomly into genomic regions that allow stable long-term expression of the delivered transgene cassette. SB has emerged as an efficient and economical toolkit for safe and efficient gene delivery for medical applications.

The growth and reproduction performance of TALEN-mediated β-lactoglobulin-knockout bucks

With the technological development of several engineered endonucleases (EENs), such as zinc-finger nucleases, transcription activator-like effector nucleases (TALENs) and CRISPR/Cas9, gene targeting by homologous recombination has been efficiently improved to generate site-specifically genetically modified livestock. However, few studies have been done to investigate the health and fertility of these animals. The purpose of the present study is to investigate if gene targeting events and a recloning procedure would affect the production traits of EEN-mediated gene targeted bucks. TALEN-mediated β-lactoglobulin (BLG) gene mono-allelic knockout (BLG (+/-)) goats and bi-allelic knockout (BLG (-/-)) buck produced by using sequential gene targeting combined with recloning in fibroblasts from BLG (+/-) buck were used to evaluate their health and fertility. Birth weight and postnatal growth of BLG (+/-) bucks were similar to the wild-type goats. None of the parameters for both fresh and frozen-thawed semen quality were significantly different in BLG (+/-) or BLG (-/-) bucks compared to their corresponding comparators. In vitro fertilization (IVF) test revealed that the proportion of IVF oocytes developing to the blastocyst stage was identical among BLG (+/-), BLG (-/-) and wild-type bucks. Conception rates of artificial insemination were respectively 42.3, 38.0 and 42.6 % for frozen-thawed semen from the BLG (+/-), BLG (-/-) and wild-type bucks. In addition, germline transmission of the targeted BLG modification was in accordance with Mendelian rules. These results demonstrated that the analyzed growth and reproductive traits were not impacted by targeting BLG gene and recloning, implicating the potential for dairy goat breeding of BLG (+/-) and BLG (-/-) bucks.

Lentiviral transgenesis in mice via a simple method of viral concentration

Transgenic animals are important in vivo models for biological research. However, low transgenic rates are commonly reported in the literature. Lentiviral transgenesis is a promising method that has greater efficiency with regard to generating transgenic animals, although the transgenic rate of this approach is highly dependent on different transgenes and concentrated lentiviruses. In this study, we modified a method to concentrate lentiviruses using a table centrifuge, commonly available in most laboratories, and carried out analysis of the transgenic efficiency in mice. Based on 26 individual constructs and 627 live pups, we found that the overall transgenic rate was more than 30%, which is higher than obtained with pronuclear microinjection. In addition, we did not find any significant differences in transgenic efficiency when the size of inserts was less than 5000 bp. These results not only show that our modified method can successfully generate transgenic mice but also suggest that this approach could be generally applied to different constructs when the size of inserts is less than 5000 bp. It is anticipated that the results of this study can help encourage the wider laboratory use of lentiviral transgenesis in mice.

One-step Multiplex Transgenesis via Sleeping Beauty Transposition in Cattle

Genetically modified cattle are important for developing new biomedical models and for an improved understanding of the pathophysiology of zoonotic diseases. However, genome editing and genetic engineering based on somatic cell nuclear transfer suffer from a low overall efficiency. Here, we established a highly efficient one-step multiplex gene transfer system into the bovine genome.

Establishment of cell-based transposon-mediated transgenesis in cattle

Transposon-mediated transgenesis is a well-established tool for genome modification in small animal models. However, translation of this active transgenic method to large animals warrants further investigations. Here, the piggyBac (PB) and sleeping beauty (SB) transposon systems were assessed for stable gene transfer into the cattle genome. Bovine fibroblasts were transfected either with a helper-independent PB system or a binary SB system. Both transposons were highly active in bovine cells increasing the efficiency of DNA integration up to 88 times over basal nonfacilitated integrations in a colony formation assay. SB transposase catalyzed multiplex transgene integrations in fibroblast cells transfected with the helper vector and two donor vectors carrying different transgenes (fluorophore and neomycin resistance). Stably transfected fibroblasts were used for SCNT and on in vitro embryo culture, morphologically normal blastocysts that expressed the fluorophore were obtained with both transposon systems. The data indicate that transposition is a feasible approach for genetic engineering in the cattle genome.

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.