Production of transgenic livestock: Promise fulfilled1

Growth and reproductive traits of F1-generation transgenic goats for human granulocyte-colony stimulating factor

To ensure that animal welfare requirements and phenotypic characteristics of the newly produced transgenic lines are not compromised, an evaluation of all individuals is necessary. This can be inferred by the analysis of the growth and reproduction parameters. The present study was designed to determine the impact of the insertion of human granulocyte-colony stimulating factor (hG-CSF) transgene on growth and reproductive characteristics in first-generation (F1) goats from two transgenic lines. Bodyweight (BW) development (BW at birth, mean BW gain before weaning, BW at weaning, mean BW gain after weaning, BW at puberty), as well as reproductive parameters (age at puberty, ejaculate volume, concentration, total sperm per ejaculate, massal motility, progressive individual motility, major and minor defects) were similar (P > 0.05) between transgenic (T) and non-transgenic (NT) goats. Significant (P < 0.05) differences in mean (±s.d.) white blood cell count were observed between T and NT in first day of life (174.6 ± 14.7 × 103 and 15.0 ± 4.0 × 103 cells/µL), and during (66.8 ± 21.1 × 103 and 17.0 ± 4.6 × 103 cells/µL) and after (36.6 ± 4.0 × 103 and 15.5 ± 2.2 × 103 cells/µL) suckling, even though hG-CSF has not been detected in blood serum in any analysis. Although other cell counts were occasionally higher in T animals, differential counts showed that this difference was mainly due to an increased number of neutrophils, which represents 84.6%, 67.2% and 56.8% of total white blood cell count respectively, in the three time periods. Kidney and liver biochemical analyses indicated that all goats were healthy. Thus, it is possible to assume that all animals are normal and had no deleterious effects on either growth or reproductive parameters by the presence of transgene or as a consequence of leukocyte profile alteration.

Gene editing in birds takes flight

The application of gene editing (GE) technology to create precise changes to the genome of bird species will provide new and exciting opportunities for the biomedical, agricultural and biotechnology industries, as well as providing new approaches for producing research models. Recent advances in modifying both the somatic and germ cell lineages in chicken indicate that this species, and conceivably soon other avian species, has joined a growing number of model organisms in the gene editing revolution.

Modification of the Genome of Domestic Animals

In the past few years, new technologies have arisen that enable higher efficiency of gene editing. With the increase ease of using gene editing technologies, it is important to consider the best method for transferring new genetic material to livestock animals. Microinjection is a technique that has proven to be effective in mice but is less efficient in large livestock animals. Over the years, a variety of methods have been used for cloning as well as gene transfer including; nuclear transfer, sperm mediated gene transfer (SMGT), and liposome-mediated DNA transfer. This review looks at the different success rate of these methods and how they have evolved to become more efficient. As well as gene editing technologies, including Zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the most recent clustered regulatory interspaced short palindromic repeats (CRISPRs). Through the advancements in gene-editing technologies, generating transgenic animals is now more accessible and affordable. The goals of producing transgenic animals are to 1) increase our understanding of biology and biomedical science; 2) increase our ability to produce more efficient animals; and 3) produce disease resistant animals. ZFNs, TALENs, and CRISPRs combined with gene transfer methods increase the possibility of achieving these goals.

Targeting Human α-Lactalbumin Gene Insertion into the Goat β-Lactoglobulin Locus by TALEN-Mediated Homologous Recombination

Special value of goat milk in human nutrition and well being is associated with medical problems of food allergies which are caused by milk proteins such as β-lactoglobulin (BLG). Here, we employed transcription activator-like effector nuclease (TALEN)-assisted homologous recombination in goat fibroblasts to introduce human α-lactalbumin (hLA) genes into goat BLG locus. TALEN-mediated targeting enabled isolation of colonies with mono- and bi-allelic transgene integration in up to 10.1% and 1.1%, respectively, after selection. Specifically, BLG mRNA levels were gradually decreasing in both mo- and bi-allelic goat mammary epithelial cells (GMECs) while hLA demonstrated expression in GMECs in vitro. Gene-targeted fibroblast cells were efficiently used in somatic cell nuclear transfer, resulting in production of hLA knock-in goats directing down-regulated BLG expression and abundant hLA secretion in animal milk. Our findings provide valuable background for animal milk optimization and expedited development for agriculture and biomedicine.

Disruption of exogenous eGFP gene using RNA-guided endonuclease in bovine transgenic somatic cells

Genome-editing technologies are considered to be an important tool for generating gene knockout cattle models. Here, we report highly efficient disruption of a chromosomally integrated eGFP gene in bovine somatic cells using RNA-guided endonucleases, a new class of programmable nucleases developed from a bacterial Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 system. In the present study, we obtained homogenously eGFP-expressing primary fibroblasts from cloned bovine transgenic embryonic tissues and employed them for further analysis. CRISPR/Cas9 plasmids specifically targeting the eGFP gene were transfected into the eGFP fibroblasts by electroporation. After 10 days of culture, more than 40% of the cells had lost eGFP expression in fluorescence activated cell sorting (FACS) analysis. Targeted sequences of the transfected cells were analyzed, and various small indel mutations (6-203 bp deletions) in the target sequence were found. The fibroblasts mutated with the CRISPR/Cas9 system were applied for somatic cell nuclear transfer, and the reconstructed embryos were successfully developed into the blastocyst stage. In conclusion, the CRISPR/Cas9 system was successfully utilized in bovine cells and cloned embryos. This will be a useful technique to develop livestock transgenesis for agricultural science.

Chromatin structure analysis enables detection of DNA insertions into the mammalian nuclear genome

Background

Genetically modified organisms (GMOs) have numerous biomedical, agricultural and environmental applications. Development of accurate methods for the detection of GMOs is a prerequisite for the identification and control of authorized and unauthorized release of these engineered organisms into the environment and into the food chain. Current detection methods are unable to detect uncharacterized GMOs, since either the DNA sequence of the transgene or the amino acid sequence of the protein must be known for DNA-based or immunological-based detection, respectively.

Methods

Here we describe the application of an epigenetics-based approach for the detection of mammalian GMOs via analysis of chromatin structural changes occurring in the host nucleus upon the insertion of foreign or endogenous DNA.

Results

Immunological methods combined with DNA next generation sequencing enabled direct interrogation of chromatin structure and identification of insertions of various size foreign (human or viral) DNA sequences, DNA sequences often used as genome modification tools (e.g. viral sequences, transposon elements), or endogenous DNA sequences into the nuclear genome of a model animal organism.

Conclusions

The results provide a proof-of-concept that epigenetic approaches can be used to detect the insertion of endogenous and exogenous sequences into the genome of higher organisms where the method of genetic modification, the sequence of inserted DNA, and the exact genomic insertion site(s) are unknown.

General significance

Measurement of chromatin dynamics as a sensor for detection of genomic manipulation and, more broadly, organism exposure to environmental or other factors affecting the epigenomic landscape are discussed.

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Insertion of DNA sequences into a host genome causes chromatin structure remodeling.

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ChIP-seq identifies molecular signatures of DNA insertion into the mammalian genome.

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Focus on epigenetic marks limits sequencing data amount required for GMO detection.

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Proof-of-concept for use of chromatin dynamics as a sensor of genomic manipulation.

Modification of Animal Products for Fat and Other Characteristics

This chapter includes information about modification of animal products using biotechnology and the importance of different modifications on the natural composition. The species considered for modified products include beef and dairy cattle, sheep, goats, poultry, and a wide variety of fishes. Moreover, the discussion includes the importance of animal food, nongenetically engineered animal modified food products, genetically engineered animal modified food items primarily for meat, milk, or egg and genetically engineered animal food along the transgenic approach for animal welfare. Modern biotechnology can improve productivity, consistency, and quality of alter animal food, fiber, and medical products. The transgenic technology is potentially valuable to alter characters of economic importance in a rapid and precise way. The food safety issue related to genetic engineering is also included in this chapter. The harm of such modified food and transgenic strategy should also be understood by the reader along with its advantages. In this context, transgenic approaches in animal biotechnology are under discussion that ranges from animal food production to their adverse effects.

Domestic animal models for biomedical research

Experimental animals in biomedical research provide insights into disease mechanisms and models for determining the efficacy and safety of new therapies and for discovery of corresponding biomarkers. Although mouse and rat models are most widely used, observations in these species cannot always be faithfully extrapolated to human patients. Thus, a number of domestic species are additionally used in specific disease areas. This review summarizes the most important applications of domestic animal models and emphasizes the new possibilities genetic tailoring of disease models, specifically in pigs, provides.

Assisted reproductive techniques for cattle breeding in developing countries: a critical appraisal of their value and limitations

Commercialization of animal biotechnologies, including those related to reproduction [also known as assisted reproductive techniques (ARTS)], is an increasing reality in developing countries, following the enormous flow of information around us and the increasing global commercial interests in areas where cattle production has its major assets. The present review discusses the achievements of various biotechnological tools for reproduction in cattle including semen handling for artificial insemination (AI), superovulation and embryo transfer (MOET), in vitro handling of oocytes and production of embryos, reproductive cloning and emerging technologies (sex selection, gene targeting and nuclear transfer for livestock transgenesis, genomics for marker-assisted selection, etc.). The application of these technologies for cattle breeding is critically discussed in relation to their impact in the improvement of the efficiency of dairy and beef production in developed and - particularly - in developing countries, which ultimately rule the possibilities of a competitive and sound production of food for human consumption. Despite the remarkable progress made and the punctual importance of some of the above-mentioned technologies, AI remains the most important assisted reproductive technology (ART) in developing countries. Any attempt to gain widespread of any other ART under the predominant economical conditions in developing countries ought to match the simplicity and the success of AI as a breeding tool.

Enhance beef cattle improvement by embryo biotechnologies

Embryo biotechnology has become one of the prominent high businesses worldwide. This technology has evolved through three major changes, that is, traditional embryo transfer (in vivo embryo production by donor superovulation), in vitro embryo production by ovum pick up with in vitro fertilization and notably current cloning technique by somatic cell nuclear transfer and transgenic animal production. Embryo biotechnology has widely been used in dairy and beef cattle industry and commercial bovine embryo transfer has become a large international business. Currently, many developed biotechnologies during the period from early oocyte stage to pre-implantation embryos can be used to create new animal breeds and accelerate genetic progression. Based on recent advances in embryo biotechnologies and authors current studies, this review will focus on a description of the application of this technology to beef cattle improvement and discuss how to use this technology to accelerate beef cattle breeding and production. The main topics of this presentation include the following: (i) how to increase calf production numbers from gametes including sperm and oocyte; (ii) multiple ovulation and embryo transfer breeding schemes; (iii) in vitro fertilization and intracytoplasm sperm injection in bovine; (iv) pronuclear development and transgenic animals; (v) sex selection from sperm and embryos; (vi) cloning and androgenesis; (vii) blastocyst development and embryonic stem cells; (viii) preservation of beef cattle genetic resources; and (ix) conclusions.

The effect of transgenesis on rabbit thyroid tissue structure

This study was aimed to compare structures of the thyroid tissue of transgenic rabbits expressing the human clotting factor VIII under the murine whey acidic protein promoter (mWAP-hFVIII rabbits) with the non-transgenic controls. Thyroid tissue samples were taken from transgenic and non-transgenic New Zealand White rabbits, examined by optical microscopy and analysed morphometrically. The analysis revealed no significant differences (P > 0.05) in the relative volume of basic thyroid structures. Furthermore, no significant differences (P > 0.05) were observed when measuring the epithelial height and nuclear diameter of the follicular cells. Altogether, this study demonstrates no negative effect of the mWAP-hFVIII transgenesis on the rabbit thyroid gland structure.

Bovine somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) is a technique by which the nucleus of a differentiated cell is introduced into an oocyte from which its genetic material has been removed by a process called enucleation. In mammals, the reconstructed embryo is artificially induced to initiate embryonic development (activation). The oocyte turns the somatic cell nucleus into an embryonic nucleus. This process is called nuclear reprogramming and involves an important change of cell fate, by which the somatic cell nucleus becomes capable of generating all the cell types required for the formation of a new individual, including extraembryonic tissues. Therefore, after transfer of a cloned embryo to a surrogate mother, an offspring genetically identical to the animal from which the somatic cells where isolated, is born. Cloning by nuclear transfer has potential applications in agriculture and biomedicine, but is limited by low efficiency. Cattle were the second mammalian species to be cloned after Dolly the sheep, and it is probably the most widely used species for SCNT experiments. This is, in part due to the high availability of bovine oocytes and the relatively higher efficiency levels usually obtained in cattle. Given the wide utilization of this species for cloning, several alternatives to this basic protocol can be found in the literature. Here we describe a basic protocol for bovine SCNT currently being used in our laboratory, which is amenable for the use of the nuclear transplantation technique for research or commercial purposes.

Animal transgenesis: an overview

Transgenic animals are extensively used to study in vivo gene function as well as to model human diseases. The technology for producing transgenic animals exists for a variety of vertebrate and invertebrate species. The mouse is the most utilized organism for research in neurodegenerative diseases. The most commonly used techniques for producing transgenic mice involves either the pronuclear injection of transgenes into fertilized oocytes or embryonic stem cell-mediated gene targeting. Embryonic stem cell technology has been most often used to produce null mutants (gene knockouts) but may also be used to introduce subtle genetic modifications down to the level of making single nucleotide changes in endogenous mouse genes. Methods are also available for inducing conditional gene knockouts as well as inducible control of transgene expression. Here, we review the main strategies for introducing genetic modifications into the mouse, as well as in other vertebrate and invertebrate species. We also review a number of recent methodologies for the production of transgenic animals including retrovirus-mediated gene transfer, RNAi-mediated gene knockdown and somatic cell mutagenesis combined with nuclear transfer, methods that may be more broadly applicable to species where both pronuclear injection and ES cell technology have proven less practical.

The role of native bovine α-lactalbumin in bovine mammary epithelial cell apoptosis and casein expression

Folding variants of α-lactalbumin (α-la) are known to induce cell death in a number of cell types, including mammary epithelial cells (MEC). The native conformation of α-la however has not been observed to exhibit this biological activity. Here we report that native bovine α-la reduced the viability of primary bovine mammary epithelial cells (BMEC) and induced caspase activity in mammospheres, which are alveolar-like structures formed by culturing primary BMEC on extracellular matrix in the presence of lactogenic hormones. These observations suggest a possible role for bovine α-la in involution and/or maintaining the luminal space in mammary alveoli during lactation. In addition, co-incubation of bovine α-la in an in-vitro mammosphere model resulted in decreased β-casein mRNA expression and increased αs1- and κ-casein mRNA expression. This differential effect on casein expression levels is unusual and raises the possibility of manipulating expression levels of individual caseins to alter dairy processing properties. Manipulation of α-la levels could be further investigated for its potential to enhance milk protein expression and/or improve lactational persistency by influencing the balance between proliferation and apoptosis of BMEC, which has a major influence on the milk-producing capacity of the mammary gland.

Impacts of animal science research on United States sheep production and predictions for the future

One hundred years ago, there were more than 48 million sheep in the United States. In 1910, they were valued at $4/head, with 43% of income coming from the sale of sheep, lambs, and meat and 57% coming from wool. Over the years, fluctuations in this ratio have challenged the breeder and researcher alike. By 2007, sheep numbers had declined to 6.2 million, with the average sheep shearing 3.4 kg of wool (representing <10% of income), 0.2 kg more than in 1909 but 0.5 kg less than fleeces in 1955. Sheep operations have declined by more than 170,000 in the past 40 yr. A cursory examination of this information might lead one to conclude that animal science research has made little impact on sheep production in the United States. On the contrary, lamb crops in the new millennium (range = 109 to 115%) are greater than those recorded in the 1920s (85 to 89%) and dressed lamb weights increased from 18 to 32 kg from 1940 to the present. In the past century, researchers conducted thousands of investigations, with progress reported in new, existing, and crossbreed evaluations, quantitative and molecular genetics, selection, nutrition, fiber, meat, hides, milk, growth, physiology, reproduction, endocrinology, management, behavior, the environment, disease, pharmacology, toxicology, and range, pasture, and forage utilization such that a vast amount of new information was accrued. Our understanding of sheep has benefited also from research conducted on other species, and vice versa. Many factors that have contributed to the decline in the sheep industry are not influenced easily by academic research (e.g., low per capita consumption of lamb meat, predation, reluctance to adopt new technologies, cost and availability of laborers with sheep-related skills, and fewer young people pursuing careers in agriculture). The size of the US sheep industry is expected to remain stable, with possible slow growth in the foreseeable future. To remain profitable, producers will take advantage of new (or previously unused) technologies, the desire of the public for things natural, domestic niche and international fiber markets, and the ability of the sheep to control noxious weeds and thrive in suboptimal ecosystems.

A brief overview of transgenic farm animals

Transgenesis offers new possibilities to rapidly modify the genome of living organisms. The application of transgenesis to farm animals faces many problems, more than those observed in the transgenesis of laboratory animals, as there are currently many different techniques available to obtain transgenic animals, which all have problems regarding low efficiency and high costs. When these techniques are applied to farm animals the problems concerning transgenesis are multiplied. Two main techniques, male pronuclear microinjection and sperm mediated gene transfer, utilised in farm animal transgenesis, are briefly presented. The improvement of these techniques and the employment of other biotechnologies such as cloning, could expand the uses of transgenic farm animals for human health.

Lactation performance of transgenic goats expressing recombinant human butyryl-cholinesterase in the milk

The production of recombinant proteins in the milk of transgenic animals has attracted significant interest in the last decade, as a valuable alternative for the production of recombinant proteins that cannot be or are inefficiently produced using conventional systems based on microorganisms or animal cells. Several recombinant proteins of pharmaceutical and biomedical interest have been successfully expressed in high quantities (g/l) in the milk of transgenic animals. However, this productivity may be associated with a compromised mammary physiology resulting, among other things, from the extraordinary demand placed on the mammary secretory cells. In this study we evaluated the lactation performance of a herd of 50 transgenic goats expressing recombinant human butyryl-cholinesterase (rBChE) in the milk. Our findings indicate that high expression levels of rBChE (range 1-5 g/l) are produced in these animals at the expense of an impaired lactation performance. The key features characterizing these transgenic performances were the decreased milk production, the reduced milk fat content which was associated with an apparent disruption in the lipid secretory mechanism at the mammary epithelium level, and a highly increased presence of leukocytes in milk which is not associated with mammary infection. Despite of having a compromised lactation performance, the amount of rBChE produced per transgenic goat represents several orders of magnitude more than the amount of rBChE present in the blood of hundreds of human donors, the only other available source of rBChE for pharmaceutical and biodefense applications. As a result, this development constitutes another successful example in the application of transgenic animal technology.

Animal transgenesis: state of the art and applications

There is a constant expectation for fast improvement of livestock production and human health care products. The advent of DNA recombinant technology and the possibility of gene transfer between organisms of distinct species, or even distinct phylogenic kingdoms, has opened a wide range of possibilities. Nowadays we can produce human insulin in bacteria or human coagulation factors in cattle milk. The recent advances in gene transfer, animal cloning, and assisted reproductive techniques have partly fulfilled the expectation in the field of livestock transgenesis. This paper reviews the recent advances and applications of transgenesis in livestock and their derivative products. At first, the state of art and the techniques that enhance the efficiency of livestock transgenesis are presented. The consequent reduction in the cost and time necessary to reach a final product has enabled the multiplication of transgenic prototypes around the world. We also analyze here some emerging applications of livestock transgenesis in the field of pharmacology, meat and dairy industry, xenotransplantation, and human disease modeling. Finally, some bioethical and commercial concerns raised by the transgenesis applications are discussed.

Production of endothelial nitric oxide synthase (eNOS) over-expressing piglets

Vascular function, vascular structure, and homeostasis are thought to be regulated in part by nitric oxide (NO) released by endothelial cell nitric oxide synthase (eNOS), and NO released by eNOS plays an important role in modulating metabolism of skeletal and cardiac muscle in health and disease. The pig is an optimal model for human diseases because of the large number of important similarities between the genomic, metabolic and cardiovascular systems of pigs and humans. To gain a better understanding of cardiovascular regulation by eNOS we produced pigs carrying an endogenous eNOS gene driven by a Tie-2 promoter and tagged with a V5 His tag. Nuclear transfer was conducted to create these animals and the effects of two different oocyte activation treatments and two different culture systems were examined. Donor cells were electrically fused to the recipient oocytes. Electrical fusion/activation (1 mM calcium in mannitol: Treatment 1) and electrical fusion (0.1 mM calcium in mannitol)/chemical activation (200 microM Thimerosal for 10 min followed by 8 mM DTT for 30 min: Treatment 2) were used. Embryos were surgically transferred to the oviducts of gilts that exhibited estrus on the day of fusion or the day of transfer. Two cloned transgenic piglets were born from Treatment 1 and low oxygen, and another two from Treatment 2 and normal oxygen. PCR, RT-PCR, Western blotting and immunohistochemistry confirmed that the pigs were transgenic, made message, made the fusion protein and that the fusion protein localized to the endothelial cells of placental vasculature from the conceptuses as did the endogenous eNOS. Thus both activation conditions and culture systems are compatible with development to term. These pigs will serve as the founders for a colony of miniature pigs that will help to elucidate the function of eNOS in regulating muscle metabolism and the cardiorespiratory system.

Gene expression profiling in porcine mammary gland during lactation and identification of breed- and developmental-stage-specific genes

A total of 28941 ESTs were sequenced from five 5'-directed non-normalized cDNA libraries, which were assembled into 2212 contigs and 5642 singlets using CAP3. These sequences were annotated and clustered into 6857 unique genes, 2072 of which having no functional annotations were considered as novel genes. These genes were further classified into Gene Ontology categories. By comparing the expression profiles, we identified some breed- and developmental-stage-specific gene groups. These genes may be relative to reproductive performance or play important roles in milk synthesis, secretion and mammary involution. The unknown EST sequences and expression profiles at different developmental stages and breeds are very important resources for further research.

Human lactoferrin transgenic rabbits produced efficiently using dimethylsulfoxide - sperm-mediated gene transfer

Transgenic animal mammary gland bioreactors are used to produce recombinant proteins. However, it is difficult to validate whether these transgenic domestic animals are able to express the recombinant protein efficiently in their mammary glands before the birth of transgenic offspring. In the present study, a simple and efficient method was established to evaluate the functionality of animal mammary gland tissue-expressed cassettes. The gene transfer vector pGBC2LF was constructed, and the expression of human lactoferrin (LF) gene was controlled by the goat β-casein gene 5′ flanking sequence. To obtain the most efficient transfection, the influence of DNA concentration, dimethylsulfoxide (DMSO) concentration, and the ratio of linear-to-circular DNA required for associating DNA with spermatozoa were evaluated. Transfection of exogenous DNA into rabbit spermatozoa was found to be efficient using 30 μg mL–1 DNA, DMSO at a final concentration of 3%, and a 3 : 1 ratio of linear-to-circular DNA, with 29 of 85 (34.1%) in vitro-fertilised embryos being transgenic. Using DMSO–sperm-mediated gene transfer (DMSO-SMGT), 89 rabbit offspring were produced, with 46 of these (57.1%) being transgenic. As mammary gland bioreactor models, 17 of 21 (81%) transgenic female rabbits could express human LF protein in their glands. During lactation of the transgenic rabbits, the highest level of human LF protein expressed was 153 ± 31 μg mL–1, and the mean expression level in all of the transgenic rabbits was 103 ± 20 μg mL–1 in the third week, declining gradually after this time. Our results demonstrate that transgenic rabbits produced by DMSO–SMGT were able to express human LF protein in the correct tissue.

Future and applications of cloning

The birth of viable offspring from somatic cell nuclear transfer (SCNT) in mammals caused a major re-examination of the understanding of the commitment of cells to specific tissue lineages during differentiation. The questions of whether cells undergo dedifferentiation or transdifferentiation during the development of offspring and how these changes are controlled is a source of ongoing debate that is yet to be resolved. Irrespective of the outcome of this debate, it is clear that cloning using SCNT has a place and purpose in the future of research and animal breeding. The future uses of SCNT could include the production of transgenic mice, the production of transgenic livestock and assisting with the re-establishment of endangered species. Human medicine also would benefit from future use of SCNT because it would allow the production of patient-specific embryonic stem cells.