Development of transgenic chickens expressing bacterial beta-galactosidase

The role of embryonic stem cells, transcription and growth factors in mammals: A review

Mammals represent a relevant species in worldwide cultures with significant commercial value. These animals are considered an attractive large animal model for biomedical and biotechnology research. The development of large animal experimental models may open alternative strategies for investigating stem cells (SCs) physiology and potential application in the veterinary field. The embryonic stem cells (ESCs) are known to possess natural pluripotency that confers the ability to differentiate into various tissues in vivo and in vitro. These notable characteristics can be useful for research and innovative applications, including biomedicine, agriculture and industry. Transcription factors play a crucial role in preserving stem cell self-renewal, whereas growth factors are involved in both growth and differentiation. However, to date, many questions concerning pluripotency, cellular differentiation regulator genes, and other molecules such as growth factors and their interactions in many mammalian species remain unresolved. The purpose of this review is to provide an overall review regarding the study of ESCs in mammals and briefly discuss the role of transcription and growth factors.

Research Note: Embryonic viability by weight difference between donor and surrogate eggs in a surrogate eggshell incubation system

A surrogate eggshell incubation system is a well-defined method to apply to avian genetic modification. In this study, we tried to investigate whether the egg weight differences between donor and surrogate eggs have an effect on donor viability. The groups were divided by egg weight differences between the donor and surrogate eggs into 4 in each system. The viability at d 4 was evaluated at the end of System II, the embryos alive were transferred into the second surrogate eggshells, and the viability at d 5, 6 was evaluated at early phase of System III. Then, the viability of System III was evaluated at different incubation period: d 6–12, d 13–18, d 19–21, and hatching rate was evaluated at d 22. Although the effect of egg weight differences between the donor and surrogate eggs was not observed, a specific group in System III showed higher survival and hatching rate than other group (P > 0.05).

Genetically engineered birds; pre-CRISPR and CRISPR era

Generating biopharmaceuticals in genetically engineered bioreactors continues to reign supreme. Hence, genetically engineered birds have attracted considerable attention from the biopharmaceutical industry. Fairly recent genome engineering methods have made genome manipulation an easy and affordable task. In this review, we first provide a broad overview of the approaches and main impediments ahead of generating efficient and reliable genetically engineered birds, and various factors that affect the fate of a transgene. This section provides an essential background for the rest of the review, in which we discuss and compare different genome manipulation methods in the pre-CRISPR and CRISPR era in the field of avian genome engineering.

Improving germline transmission efficiency in chimeric chickens using a multi-stage injection approach

Although different strategies have been developed to generate transgenic poultry, low efficiency of germline transgene transmission has remained a challenge in poultry transgenesis. Herein, we developed an efficient germline transgenesis method using a lentiviral vector system in chickens through multiple injections of transgenes into embryos at different stages of development. The embryo chorioallantoic membrane (CAM) vasculature was successfully used as a novel route of gene transfer into germline tissues. Compared to the other routes of viral vector administration, the embryo’s bloodstream at Hamburger-Hamilton (HH) stages 14–15 achieved the highest rate of germline transmission (GT), 7.7%. Single injection of viral vectors into the CAM vasculature resulted in a GT efficiency of 2.7%, which was significantly higher than the 0.4% obtained by injection into embryos at the blastoderm stage. Double injection of viral vectors into the bloodstream at HH stages 14–15 and through CAM was the most efficient method for producing germline chimeras, giving a GT rate of 13.6%. The authors suggest that the new method described in this study could be efficiently used to produce transgenic poultry in virus-mediated gene transfer systems.

Genome editing of avian species: implications for animal use and welfare

Avian species are used as model systems in research and have contributed to ground-breaking concepts in developmental biology, immunology, genetics, virology, cancer and cell biology. The chicken in particular is an important research model and an agricultural animal as a major contributor to animal protein resources for the global population. The development of genome editing methods, including CRISPR/Cas9, to mediate germline engineering of the avian genome will have important applications in biomedical, agricultural and biotechnological activities. Notably, these precise genome editing tools have the potential to enhance avian health and productivity by identifying and validating beneficial genetic variants in bird populations. Here, we present a concise description of the existing methods and current applications of the genome editing tools in bird species, focused on chickens, with attention on animal use and welfare issues for each of the techniques presented.

Recent Advances in the Application of CRISPR/Cas9 Gene Editing System in Poultry Species

CRISPR/Cas9 system genome editing is revolutionizing genetics research in a wide spectrum of animal models in the genetic era. Among these animals, is the poultry species. CRISPR technology is the newest and most advanced gene-editing tool that allows researchers to modify and alter gene functions for transcriptional regulation, gene targeting, epigenetic modification, gene therapy, and drug delivery in the animal genome. The applicability of the CRISPR/Cas9 system in gene editing and modification of genomes in the avian species is still emerging. Up to date, substantial progress in using CRISPR/Cas9 technology has been made in only two poultry species (chicken and quail), with chicken taking the lead. There have been major recent advances in the modification of the avian genome through their germ cell lineages. In the poultry industry, breeders and producers can utilize CRISPR-mediated approaches to enhance the many required genetic variations towards the poultry population that are absent in a given poultry flock. Thus, CRISPR allows the benefit of accessing genetic characteristics that cannot otherwise be used for poultry production. Therefore CRISPR/Cas9 becomes a very powerful and robust tool for editing genes that allow for the introduction or regulation of genetic information in poultry genomes. However, the CRISPR/Cas9 technology has several limitations that need to be addressed to enhance its use in the poultry industry. This review evaluates and provides a summary of recent advances in applying CRISPR/Cas9 gene editing technology in poultry research and explores its potential use in advancing poultry breeding and production with a major focus on chicken and quail. This could aid future advancements in the use of CRISPR technology to improve poultry production.

Avians as a Model System of Vascular Development

For more than 2000 years, the avian embryo has helped scientists understand questions of developmental and cell biology. As early as 350 BC Aristotle described embryonic development inside a chicken egg (Aristotle, Generation of animals. Loeb Classical Library (translated), vol. 8, 1943). In the seventeenth century, Marcello Malpighi, referred to as the father of embryology, first diagramed the microscopic morphogenesis of the chick embryo, including extensive characterization of the cardiovascular system (Pearce Eur Neurol 58(4):253-255, 2007; West, Am J Physiol Lung Cell Mol Physiol 304(6):L383-L390, 2016). The ease of accessibility to the embryo and similarity to mammalian development have made avians a powerful system among model organisms. Currently, a unique combination of classical and modern techniques is employed for investigation of the vascular system in the avian embryo. Here, we will introduce the essential techniques of embryonic manipulation for experimental study in vascular biology.

Avian Satellite Cell Plasticity

Simple Summary

Adult muscle regeneration and reconstruction is dependent on a population of adult stem cells, known as satellite cells. These cells were suggested to exhibit a certain degree of plasticity, being able to differentiate into lineages unassociated with muscle cells. In this study, we have used a range of visualization methods, as well as PCR, to identify a population of satellite cells obtained from samples of chicken muscles. Then, the cells, expressing a previously introduced detectable transgene, were introduced into chicken embryos and detected after three and eighteen days of their development. The traces of cell populations derived from the introduced satellite cells were detected in a range of embryonic tissues in both of the studied timeframes. The results of this study give further proof of the plasticity of muscle satellite cells, showing the potential locations of their migration during embryonic development.

Abstract

Adult myogenesis is dependent on a population of precursor cells, located between the sarcolemma and the basal lamina of the muscle fiber. These satellite cells, usually present in a quiescent state, become activated in response to mechanical muscle strain, differentiating and fusing to add new nuclei to enlarging muscles. As their myogenic lineage commitment is induced on demand, muscle satellite cells exhibit a certain amount of plasticity, possibly being able to be directed to differentiate into non-myogenic fates. In this study, myosatellite cells were isolated from chicken muscle samples, characterized in vitro and introduced into developing blastoderms. They were further investigated using fluorescence microscopy, immunohistochemistry and PCR, to determine their location in embryos after three and eighteen days. The results of the in vitro analysis confirmed that the cells obtained from the Pectoralis thoracicus are highly myogenic, based on the expression of Pax7, Myogenin, MyoD, Desmin and the myotube assay. Furthermore, the investigation of satellite cells within the embryo showed their migration to the regions of Pectoralis thoracicus, heart, liver, gizzard, proventriculus, intestine and brain. Overall, the results of the study proved the high myogenicity of chicken Pectoralis thoracicus cell isolates, as well as provided new information about their migration pathways following introduction into the blastocyst. The presence of the introduced LacZ or eGFP transgenes across the embryo, even 20 days after myosatellite cell injection, further supports the notion that satellite cells exhibit significant plasticity, potentially transdifferentiating into non-muscle lineages.

Designing A Transgenic Chicken: Applying New Approaches toward A Promising Bioreactor

Specific developmental characteristics of the chicken make it an attractive model for the generation of transgenic organisms. Chicken possess a strong potential for recombinant protein production and can be used as a powerful bioreactor to produce pharmaceutical and nutritional proteins. Several transgenic chickens have been generated during the last two decades via viral and non-viral transfection. Culturing chicken primordial germ cells (PGCs) and their ability for germline transmission ushered in a new stage in this regard. With the advent of CRISPR/Cas9 system, a new phase of studies for manipulating genomes has begun. It is feasible to integrate a desired gene in a predetermined position of the genome using CRISPR/Cas9 system. In this review, we discuss the new approaches and technologies that can be applied to generate a transgenic chicken with regards to recombinant protein productions.

Applications of Gene Editing in Chickens: A New Era Is on the Horizon

The chicken represents a valuable model for research in the area of immunology, infectious diseases as well as developmental biology. Although it was the first livestock species to have its genome sequenced, there was no reverse genetic technology available to help understanding specific gene functions. Recently, homologous recombination was used to knockout the chicken immunoglobulin genes. Subsequent studies using immunoglobulin knockout birds helped to understand different aspects related to B cell development and antibody production. Furthermore, the latest advances in the field of genome editing including the CRISPR/Cas9 system allowed the introduction of site specific gene modifications in various animal species. Thus, it may provide a powerful tool for the generation of genetically modified chickens carrying resistance for certain pathogens. This was previously demonstrated by targeting the Trp38 region which was shown to be effective in the control of avian leukosis virus in chicken DF-1 cells. Herein we review the current and future prospects of gene editing and how it possibly contributes to the development of resistant chickens against infectious diseases.

Tracing Gene Expression Through Detection of β-galactosidase Activity in Whole Mouse Embryos

The Escherichia coli LacZ gene, encoding β-galactosidase, is largely used as a reporter for gene expression and as a tracer in cell lineage studies. The classical histochemical reaction is based on the hydrolysis of the substrate X-gal in combination with ferric and ferrous ions, which produces an insoluble blue precipitate that is easy to visualize. Therefore, β-galactosidase activity serves as a marker for the expression pattern of the gene of interest as the development proceeds. Here we describe the standard protocol for the detection of β-galactosidase activity in early whole mouse embryos and the subsequent method for paraffin sectioning and counterstaining. Additionally, a procedure for clarifying whole embryos is provided to better visualize X-gal staining in deeper regions of the embryo. Consistent results are obtained by performing this procedure, although optimization of reaction conditions is needed to minimize background activity. Limitations in the assay should be also considered, particularly regarding the size of the embryo in whole mount staining. Our protocol provides a sensitive and a reliable method for β-galactosidase detection during the mouse development that can be further applied to the cryostat sections as well as whole organs. Thus, the dynamic gene expression patterns throughout development can be easily analyzed by using this protocol in whole embryos, but also detailed expression at the cellular level can be assessed after paraffin sectioning.

Advances in genetic engineering of the avian genome: "Realising the promise"

This review provides an historic perspective of the key steps from those reported at the 1st Transgenic Animal Research Conference in 1997 through to the very latest developments in avian transgenesis. Eighteen years later, on the occasion of the 10th conference in this series, we have seen breakthrough advances in the use of viral vectors and transposons to transform the germline via the direct manipulation of the chicken embryo, through to the establishment of PGC cultures allowing in vitro modification, expansion into populations to analyse the genetic modifications and then injection of these cells into embryos to create germline chimeras. We have now reached an unprecedented time in the history of chicken transgenic research where we have the technology to introduce precise, targeted modifications into the chicken genome, ranging from; new transgenes that provide improved phenotypes such as increased resilience to economically important diseases; the targeted disruption of immunoglobulin genes and replacement with human sequences to generate transgenic chickens that express "humanised" antibodies for biopharming; and the deletion of specific nucleotides to generate targeted gene knockout chickens for functional genomics. The impact of these advances is set to be realised through applications in chickens, and other bird species as models in scientific research, for novel biotechnology and to protect and improve agricultural productivity.

Expression of recombinant human lysozyme in egg whites of transgenic hens

Chicken egg lysozyme (cLY) is an enzyme with 129 amino acid (AA) residue enzyme. This enzyme is present not only in chicken egg white but also in mucosal secretions such as saliva and tears. The antibacterial properties of egg white can be attributed to the presence of lysozyme, which is used as an anti-cancer drug and for the treatment of human immunodeficiency virus (HIV) infection. In this study, we constructed a lentiviral vector containing a synthetic cLY signal peptide and a 447 bp synthetic human lysozyme (hLY) cDNA sequence driven by an oviduct-specific ovalbumin promoter, and microinjected into the subgerminal cavity of stage X chick embryos to generate transgenic chicken. The transgene inserted in the chicken chromosomes directs the synthesis and secretion of hLY which has three times higher specific activity than cLY. Three G₁ transgenic chickens were identified, the only female of which expressed recombinant human lysozyme (rhLY) at 57.66 ± 4.10 μg/ml in the egg white and the G₂ transgenic hens of the G₁ transgenic cock A011 expressed rhLY at 48.72 ± 1.54 μg/ml. This experiment demonstrated that transgenic hens with stable oviduct-specific expression of recombinant human lysozyme proteins can be created by microinjection of lentiviral vectors. The results of this research could be contribute to the technological development using transgenic hens as a cost-effective alternative to other mammalian systems, such as cow, sheep and goats, for the production of therapeutic proteins and other applications.

Avians as a model system of vascular development

For more than 2,000 years, philosophers and scientists have turned to the avian embryo with questions of how life begins (Aristotle and Peck Generations of Animals. Loeb Classics, vol. XIII. Harvard University Press, Cambridge, 1943; Needham, A history of embryology. Abelard-Schuman, New York, 1959). Then, as now, the unique accessibility of the embryo both in terms of acquisition of eggs from domesticated fowl and ease at which the embryo can be visualized by simply opening the shell has made avians an appealing and powerful model system for the study of development. Thus, as the field of embryology has evolved through observational, comparative, and experimental embryology into its current iteration as the cellular and molecular biology of development, avians have remained a useful and practical system of study.

Transgenic quail as a model for research in the avian nervous system: a comparative study of the auditory brainstem

Research performed on transgenic animals has led to numerous advances in biological research. However, using traditional retroviral methods to generate transgenic avian research models has proved problematic. As a result, experiments aimed at genetic manipulations on birds have remained difficult for this popular research tool. Recently, lentiviral methods have allowed the production of transgenic birds, including a transgenic Japanese quail (Coturnix coturnix japonica) line showing neuronal specificity and stable expression of enhanced green fluorescent protein (eGFP) across generations (termed here GFP quail). To test whether the GFP quail may serve as a viable alternative to the popular chicken model system, with the additional benefit of genetic manipulation, we compared the development, organization, structure, and function of a specific neuronal circuit in chicken (Gallus gallus domesticus) with that of the GFP quail. This study focuses on a well-defined avian brain region, the principal nuclei of the sound localization circuit in the auditory brainstem, nucleus magnocellularis (NM), and nucleus laminaris (NL). Our results demonstrate that structural and functional properties of NM and NL neurons in the GFP quail, as well as their dynamic properties in response to changes in the environment, are nearly identical to those in chickens. These similarities demonstrate that the GFP quail, as well as other transgenic quail lines, can serve as an attractive avian model system, with the advantage of being able to build on the wealth of information already available from the chicken.

Different gene transfer methods at the very early, early, late and whole embryonic stages in chicken

New technologies in gene transfer combined with experimental embryology make the chicken embryo an excellent model system for gene function studies. The techniques of in ovo electroporation, in vitro culture for ex ovo electroporation and retrovirus-mediated gene transfer have already been fully developed in chicken. Yet to our knowledge, there are no definite descriptions on the features and application scopes of these techniques. The survival rates of different in vitro culture methods were compared and the EGFP expression areas of different gene transfer techniques were explored. It was that the optimal timings of removing embryo for EC culture and Petri dish system was at E1.5 and E2.5, respectively; and optimal timing of injecting retrovirus is at E0. Results indicated that the EC culture, in ovo electroporation, the Petri dish system and retrovirus-mediated method are, respectively, suitable for the very early, early, late and whole embryonic stages in chicken. Comparison of different gene transfer methods and establishment of optimal timings are expected to provide a better choice of the efficient method for a particular experiment.

Avian biomodels for use as pharmaceutical bioreactors and for studying human diseases

Animal-based biotechnologies involve the use of domestic animals for the production of pharmaceuticals and various proteins in milk and eggs, as disease models, as tools for stem cell research and animal cloning, and as sources of organs for xenotransplantation into humans. Avian species offer several advantages over mammalian models, and they have been used historically to advance the fields of embryology, immunology, oncology, virology, and vaccine development. In addition, avian species can be used for studying the etiology of human ovarian cancer and other human diseases such as disorders based on the abnormal metabolism of lipids and as unique mechanisms for the biosynthesis and transport of cholesterol. This review integrates recent progress and insight into the molecular and physiologic mechanisms associated with transgenic birds and gives an overview of the use of avian models as pharmaceutical bioreactors and as tools for studying human diseases.

Production of recombinant human erythropoietin/Fc fusion protein by genetically manipulated chickens

We previously reported the production of human erythropoietin (hEpo) using genetically manipulated (GM) chickens. The recombinant hEpo was produced in the serum and egg white of the GM chickens, and the oligosaccharide chain structures of the serum-derived hEpo were more favorable than those of the egg white-derived hEpo. In the present study, a retroviral vector encoding an expression cassette for a fusion protein of hEpo and the Fc region of human immunoglobulin G (hEpo/Fc) was injected into developing chicken embryos, with the aim of recovering the serum-derived hEpo from egg yolk through the yolk accumulation mechanism of maternal antibodies. The GM chickens that hatched stably produced the hEpo/Fc fusion protein not only in their serum and egg white, but also in the egg yolk as expected. Lectin blot analyses revealed that significant amounts of the oligosaccharide chains of hEpo/Fc produced in the serum and eggs of GM chickens terminated with galactose, and that the oligosaccharide chains of the serum- and yolk-derived hEpo/Fc incorporated sialic acid residues. Moreover, biological activity assessment using Epo-dependent cells revealed that the yolk-derived hEpo/Fc exhibited a comparable performance to the serum- and CHO-derived hEpo/Fc. These results indicate that transport of Fc fusion proteins from the blood circulation to the yolk in chickens represents an effective strategy for the production of pharmaceutical glycoproteins using transgenic chicken bioreactors.

Postnatal refractive development in the Brown Norway rat: Limitations of standard refractive and ocular component dimension measurement techniques

PURPOSE

The genetic tractability of the rat and its larger eye size as compared to the mouse make it an attractive model for studies of ocular development and emmetropisation. This study aimed to provide normative data in the strain of rat being used for the rat genome sequencing project whilst also evaluating standard measurement techniques.

METHODS

Ocular refraction (retinoscopy, Hartinger coincidence optometry) and ocular component dimensions (keratometry, A-scan ultrasonography, calliper measures, eye weight) were measured at intervals from eye-opening to adulthood.

RESULTS

There was no convincing evidence of visually guided emmetropisation during normal development. Key measurement techniques such as high-resolution A-scan ultrasonography, which work effectively in several other animal species, were unusable or inaccurate in the rat.

CONCLUSIONS

This study found no evidence of emmetropisation during normal development in rat. As in mice, technical difficulties prevent accurate measurement of ocular refraction and vitreous chamber depth and may complicate tests of emmetropisation to imposed blur.

Generation of transgenic quail through germ cell-mediated germline transmission

Here, we describe the production of transgenic quail via a germline transmission system using postmigratory gonadal primordial germ cells (gPGCs). gPGCs retrieved from the embryonic gonads of 5-day-old birds were transduced with a lentiviral vector and subsequently transferred into recipient embryos. Testcross and genetic analyses revealed that among three germline chimeric G0 quail, one male produced transgenic offspring; of 310 hatchlings from the transgenic germline chimera, 24 were identified as donor-derived offspring, and 6 were transgenic (6/310, 1.9%). Conventional transgenesis using stage X blastodermal embryos was also conducted, but the efficiency of transgenesis was similar between the two systems (<1.6 vs. 1.9% for the conventional and gPGC-mediated systems, respectively). However, substantial advantages can be gained from gPGC-mediated method in that it enables an induced germline modification, whereas direct retroviral transfer to stage X embryos causes mosaic integration. The use of gonadal PGCs for transgenesis may lead to the production of bioreactors.

Development of Transgenic Chickens Expressing Human Parathormone Under the Control of a Ubiquitous Promoter by Using a Retrovirus Vector System

Transgenic chickens, ubiquitously expressing a human protein, could be a very useful model system for studying the role of human proteins in embryonic development as well as for efficiently producing pharmaceutical drugs as bioreactors. Human parathormone (hPTH) secreted from parathyroid glands plays a significant role in calcium homeostasis and is an important therapeutic agent for the treatment of osteoporosis in humans. Here, by using a robust replication-defective Moloney murine leukemia virus-based retrovirus vector encapsidated with vesicular stomatitis virus G glycoprotein, we generated transgenic chickens expressing hPTH under the control of a ubiquitous Rous sarcoma virus promoter. The recombinant retrovirus was injected into the subgerminal cavity of freshly laid eggs at the blastodermal stage. After 21 d of incubation, 42 chicks hatched from 473 retrovirus-injected eggs. All 42 living chicks were found to express the vector-encoded hPTH gene in diverse organs, as revealed by PCR and reverse transcription-PCR analysis by using primer pairs specific for hPTH. Four days after hatching, 6 chicks died and 14 chicks showed phenotypic deformities. At 18 wk of age, only 3 G(0) chickens survived. They also released the hPTH hormone in their blood and transmitted the hPTH gene to G(1) embryos. However, although the embryos were alive at d 18 of incubation, none hatched. An electrochemiluminescence immunoassay further showed that the hPTH expression level was markedly elevated in mammalian cells infected by the retrovirus vector. Thus, we demonstrated that transgenic chickens, expressing a human protein under the control of a ubiquitous promoter, not only could be an efficient bioreactor for the production of pharmaceutical drugs, but also could be useful for studies on the role of human proteins in embryonic development. To our knowledge, this is the first report on the production of a human protein (hPTH) in transgenic chickens under the control of a ubiquitous promoter by using a replication-defective Moloney murine leukemia virus-based retrovirus vector system.

The chicken genome: some good news and some bad news

The sequencing of the chicken genome has generated a wealth of good news for poultry science. It allows the chicken to be a major player in 21st century biology by providing an entrée into an arsenal of new technologies that can be used to explore virtually any chicken phenotype of interest. The initial technological onslaught has been described in this symposium. The wealth of data available now or soon to be available cannot be explained by simplistic models and will force us to treat the inherent complexity of the chicken in ways that are more realistic but at the same time more difficult to comprehend. Initial single nucleotide polymorphism analyses suggest that broilers retain a remarkable amount of the genetic diversity of predomesticated Jungle Fowl, whereas commercial layer genomes display less diversity and broader linkage disequilibrium. Thus, intensive commercial selection has not fixed a genome rich in wide selective sweeps, at least within the broiler population. Rather, a complex assortment of combinations of ancient allelic diversity survives. Low levels of linkage disequilibrium will make association analysis in broilers more difficult. The wider disequilibrium observed in layers should facilitate the mapping of quantitative trait loci, and at the same time make it more difficult to identify the causative nucleotide change(s). In addition, many quantitative traits may be specific to the genetic background in which they arose and not readily transferable to, or detectable in, other line backgrounds. Despite the obstacles it presents, the genetic complexity of the chicken may also be viewed as good news because it insures that long-term genetic progress will continue via breeding using quantitative genetics, and it surely will keep poultry scientists busy for decades to come. It is now time to move from an emphasis on obtaining "THE" chicken genome sequence to obtaining multiple sequences, especially of foundation stocks, and a broader understanding of the full genetic and phenotypic diversity of the domesticated chicken.

Production of scFv-Fc fusion protein using genetically manipulated quails

The use of transgenic avian species as a transgenic bioreactor for the production of recombinant proteins has been proposed. In recent years, although various procedures for generating transgenic chickens have been reported, the expression of a useful protein at a commercially feasible level has rarely been attained. In this study, we injected a concentrated retroviral vector into quail embryos to generate genetically manipulated quails that produce recombinant proteins. We found that transgene expression in the whole body at a high level was observed for viral injection into the heart of the developing embryos after a 48-h incubation. For the practical production of a useful protein, a retroviral vector encoding an anti-prion scFv-Fc gene under the control of the beta-actin promoter was injected into quail embryos. The quails that hatched stably produced scFv-Fc at a high level in their serum and egg white. The production of scFv-Fc was maintained throughout the breeding period. scFv-Fc purified from the egg white retained the antigen-binding activity. This system exhibited the potential of transgenic quails for the commercial production of recombinant proteins.

Production of Chick Germline Chimeras from Fluorescence-Activated Cell-Sorted Gonocytes

Modification of the chicken germline has been difficult, because it has been challenging to fractionate sufficient numbers of primordial germ cells for manipulation and implantation into developing embryos. A technique to enrich cell suspensions for primordial germ cells, using fluorescence-activated cell sorting (FACS), has recently been developed. The objective of the current study was to demonstrate that the FACS-enriched early embryonic gonocytes could fully participate in development of the germline. Therefore, cells were disassociated from stage 27 gonads, incubated with mouse anti-stage-specific embryonic antigen-1, which was detected with goat-antimouse IgM-fluorescein isothiocyanate, and the fluorescently labeled cells were sorted from the unlabeled cells using FACS. The isolated gonocyte population was injected into the blastoderm of unincubated stage X embryos, the germinal crescent of 3-d embryos, and into the circulation of stage 17 embryos that were pretreated with busulfan. Barred Plymouth Rock gonocytes were implanted exclusively into recipient White Leghorn embryos, and White Leghorn gonocytes were implanted exclusively into Barred Plymouth Rock recipient embryos. Embryos were cultured until hatch, and male putative chimeras were reared to sexual maturity. Germline chimerism was evaluated by observing feather color of the progeny. All injection methods resulted in germline chimeras demonstrating that FACS-sorted gonocytes can fully participate in development. Moreover, it was demonstrated that gonocytes isolated from stage 27 embryonic gonads can be introduced into embryos at an earlier stage of development, and the introduced gonocytes can fully participate in germline development.

Chromosomal localization of a proinsulin transgene in Japanese quail by laser pressure catapulting

Transgenic avian bioreactors produce therapeutic recombinant proteins in egg white. To date, however, methods for transgenic modification of the avian genome or determining transgenic status of individual birds are scarce. The dual, but interrelated, goals of this research were to: (1) develop a method of detecting stable DNA insertion into Japanese quail; and (2) provide a method for gene location on avian chromosomes. We created Teflon-coated coverslip slides to facilitate laser pressure catapulting of avian chromosomes for DNA amplification and nucleotide sequencing. Transgenic G2 Japanese quail, containing germline incorporation of proinsulin, were identified by isolation of chromosomes using laser microdissection and laser pressure catapulting. Subsequent amplification of each chromosome identified 2-5 chromosomes with the proinsulin transgene inserted. Nucleotide sequencing of each chromosomal insertion was identical to the proinsulin portion of the original vector. By applying laser pressure catapulting and PCR of individual chromosomes, we were able to determine that the transgene correctly inserted into avian chromosomes and that the majority of the insertions occurred within microchromosomes. Because many potential therapeutic transgenes have similar or nearly identical nucleotide sequence to the host's native gene, laser microdissection and subsequent analysis may be required for detailed documentation of transgene expression before proceeding with transgenic protein production.

Endless versatility in the biotechnological applications of Kluyveromyces LAC genes

Most microorganisms adapted to life in milk owe their ability to thrive in this habitat to the evolution of mechanisms for the use of the most abundant sugar present on it, lactose, as a carbon source. Because of their lactose-assimilating ability, Kluyveromyces yeasts have long been used in industrial processes involved in the elimination of this sugar. The identification of the genes conferring Kluyveromyces with a system for permeabilization and intracellular hydrolysis of lactose (LAC genes), along with the current possibilities for their transfer into alternative organisms through genetic engineering, has significantly broadened the industrial profitability of lactic yeasts. This review provides an updated overview of the general properties of Kluyveromyces LAC genes, and the multiple techniques involving their biotechnological utilization. Emphasis is also made on the potential that some of the latest technologies, such as the generation of transgenics, will have for a further benefit in the use of these and related genes.

Blood-Borne Stem Cells Differentiate into Vascular and Cardiac Lineages During Normal Development

Recent investigations have indicated that hematopoietic stem cells (HSCs) have the potential to differentiate into multiple non-blood cell lineages and contribute to the cellular regeneration of various tissues and multiple organs. Most studies to date on HSC potential have examined the adult, focusing on their potential to repair tissue under pathological conditions (e.g., ischemic injury, organ failure). Comparatively little is known about the physiological role of HSCs in normal tissue homeostasis in the adult, and even less of their contribution to organogenesis during prenatal development. This study reports the contribution of blood-borne cells to various organ systems of the developing embryo using a quail-chick parabiosis model. Under these conditions, the developing circulatory systems fuse between ED6-ED8, resulting in free exchange of circulating cells. Cells of quail origin, identified by quail-specific antibodies at ED15, were found in numerous organs of the parabiotic chick embryo. Circulating cells contributed to developing vasculature, where they differentiated into endothelial, smooth muscle, and adventitial tissues. In the heart, differentiation of circulating cells into cardiomyocytes was demonstrated using double immunolabeling for QCPN and sarcomeric actin or myosin. These results were confirmed by intramyocardial injection of quail bone marrow cells that were found to express markers of myocytes, coronary smooth muscle, and epicardium. Experiments using lacZ-transgenic chick embryos for a second positive cellular marker showed that fusion between chick and quail cells was a rare event. These results suggest that during development, multipotent cells are present in the embryonic circulation and home into different organs where they undergo tissue-specific differentiation. Moreover, the demonstration that blood-borne cells contribute to the development of various organs lends credence to claims that hematopoietic stem cells have utility for treating diseased or damaged tissues in the adult.

Expression of foreign genes in chicks by hydrodynamics-based naked plasmid transfer in vivo

The study of gene function in vivo is considered one of the top achievements of modern biology, inasmuch as it provides tools to study gene function in the context of the whole animal. In chickens, techniques of DNA-mediated gene transfer are less advanced than in other animal or livestock models, and remain a significant challenge. The study presented here is the first to show that a hydrodynamics-based gene-transfer technique, originally developed for naked DNA transfer in mice, can be applied to chickens. Rapid injection of naked plasmids containing expression cassettes into the jugular vein of 6- to 10-day-old chicks resulted in specific expression of the transgenes. A CMV promoter-driven luciferase reporter gene was expressed at significant levels in the liver during the first 3 days post-injection with lower levels also detected in the kidney. Significantly, all injected birds showed detectable levels of luciferase expression. Similarly, injection of a plasmid containing the secreted human coagulation factor IX (hFIX) gene under the control of human alpha-1-anti-trypsin promoter resulted in detectable levels of the hFIX in the plasma during the first 2 days post-injection. The method described herein has the potential for a quick and simple route for gain and loss-of function experiments in chicken liver and kidney, as well as for studying systemic effects of secreted proteins and hormones.

Identification of the lacZ insertion site and beta-galactosidase expression in transgenic chickens

The quail:chick chimera system is a classical research model in developmental biology. An improvement over the quail:chick chimera system would be a line of transgenic chickens expressing a reporter gene. Transgenic chickens carrying lacZ and expressing bacterial beta-galactosidase have been generated, but complete characterization of the insertion event and characterization of beta-galactosidase expression have not previously been available. The genomic sequences flanking the retroviral insertion site have now been identified by using inverse polymerase chain reaction (PCR), homozygous individuals have been identified by using PCR-based genotyping, and beta-galactosidase expression has been evaluated by using Western analysis and histochemistry. Based upon the current draft of the chicken genome, the viral insertion carrying the lacZ gene has been located on chromosome 11 within the predicted gene for neurotactin/fractalkine (CX3CL1); neurotactin mRNA expression appears to be missing from the brain of homozygous individuals. When Generation 2 (G2) lacZ-positive individuals were inter-mated, they generated 361 G3 progeny; 82 were homozyous for lacZ (22.7%), 97 were wild-type non-transgenic (26.9%), and 182 (50.4%) were hemizygous for lacZ. Western analysis revealed the highest expression in the muscle and liver. With the identification of homozygous birds, the line of chickens is now designated NCSU-Blue1.

Generation of tissue-specific transgenic birds with lentiviral vectors

Birds are of great interest for a variety of research purposes, and effective methods for manipulating the avian genome would greatly accelerate progress in fields that rely on birds as model systems for biological research, such as developmental biology and behavioral neurobiology. Here, we describe a simple and effective method for producing transgenic birds. We used lentiviral vectors to produce transgenic quails that express GFP driven by the human synapsin gene I promoter. Expression of GFP was specific to neurons and consistent across multiple generations. Expression was sufficient to allow visualization of individual axons and dendrites of neurons in vivo by intrinsic GFP fluorescence. Tissue-specific transgene expression at high levels provides a powerful tool for biological research and opens new avenues for genetic manipulation in birds.

Culture of chicken embryos in surrogate eggshells

The chick embryo is a classical model to study embryonic development. However, most researchers have not studied the effect of embryonic manipulation on chick hatchability. The objective of this study was to determine the effect of egg orientation and type of sealing film on the hatchability of cultured embryos. Windows were made in the small end of recipient surrogate chicken eggshells, and donor embryos were placed into the recipient eggshell for the first 3 d of incubation. Survival over the first 3 d was maximized (P < 0.05) when windowed eggs sealed with Saran Wrap were positioned with the window-end down compared with window-end up. Three-day-old cultured embryos were transferred into recipient turkey eggshells, sealed with cling film, and cultured until hatch. Water weight loss of the surrogate eggshell cultures regardless of cling film type was not significantly different from control intact eggs. The embryos cultured in turkey eggshells and sealed with Handi Wrap exhibited higher hatchability (75% +/- 10.2%) than cultures sealed with Saran Wrap (45.2% +/- 13.8%). Hatchability of control intact eggs (86.4% +/- 5.3%) was not significantly (P > 0.05) different from the hatchability of eggs sealed with Handi Wrap, which suggested that Handi Wrap was an excellent sealant for chick embryos cultured after 3 d of incubation.

High-level expression of single-chain Fv-Fc fusion protein in serum and egg white of genetically manipulated chickens by using a retroviral vector

We report here the generation of transgenic chickens using a retroviral vector for the production of recombinant proteins. It was found that the transgene expression was suppressed when a Moloney murine leukemia virus-based retroviral vector was injected into chicken embryos at the blastodermal stage. When a concentrated viral solution was injected into the heart of developing embryos after 50 to 60 h of incubation, transgene expression was observed throughout the embryo, including the gonads. For practical production, a retroviral vector encoding an expression cassette of antiprion single-chain Fv fused with the Fc region of human immunoglobulin G1 (scFv-Fc) was injected into chicken embryos. The birds that hatched stably produced scFv-Fc in their serum and eggs at high levels (approximately 5.6 mg/ml). We obtained transgenic progeny from a transgenic chicken generated with this procedure. The transgene was stably integrated into the chromosomes of transgenic progeny. The transgenic progeny also expressed scFv-Fc in the serum and eggs.

Excision of foreign gene product with cathepsin D in chicken hepatoma cell line

To easily and rapidly recover exogenous gene products from chicken egg yolk, we constructed pVTG-catD (VTG, vitellogenin; catD, cathepsin D), a vector cassette carrying two catD-recognition signal peptides (catD-RSPs) in addition to the cloning site. An enhanced green fluorescence protein (EGFP)-encoding DNA fragment was ligated into the pVTG-catD. When the resultant construct pVTG-EGFP-catD containing histidine- and myc-tags was transfected into the chicken hepatoma cell line LMH, EGFP-expression at 24h post-cultivation was confirmed by fluorescence microscopy. Because a signal peptide (NTVLAEF) encoded in pVTG-EGFP-catD is recognized by catD, the VTG-EGFP fusion protein digested with catD was detectable by Western blotting. Digested exogenous gene product was recovered with nickel resin. These results indicate that catD-recognition sites bearing pVTG-catD and His-tags are functional in chicken LMH cells. Therefore, the system described here may be of use in making excision exogenous gene products in the chicken and in creating homozygous knock-in chickens.

Retrovirus-mediated gene transfer and expression of EGFP in chicken

Here, we successfully demonstrate expression of the EGFP (enhanced green fluorescence protein) gene in chickens using replication-defective MLV (murine leukemia virus)-based retrovirus vectors encapsidated with VSV-G (vesicular stomatitis virus G glycoprotein). The recombinant retrovirus was injected beneath the blastoderm of non-incubated chicken embryos (stage X). After 12 days incubation, all of the eight living embryos assayed were found to express this vector-encoded EGFP gene, which was under the control of the RSV (Rous Sarcoma Virus) promoter, in diverse organ tissues, including head, beak, neck, wing, hock, tail, toes, heart, amnion, and yolk sac. Surprisingly, despite the presumed cytotoxicity of EGFP, some embryos hatched and survived and these had prominent green fluorescent spots, both in internal organs and externally.

Transgenic chickens as bioreactors for protein-based drugs

The potential of using transgenic animals for the synthesis of therapeutic proteins was suggested over twenty years ago. Considerable progress has been made in developing methods for the production of transgenic animals and specifically in the expression of therapeutic proteins in the mammary glands of cows, sheep and goats. Development of transgenic hens for protein production in eggs has lagged behind these systems. The positive features associated with the use of the chicken in terms of cost, speed of development of a production flock and potentially appropriate glycosylation of target proteins have led to significant advances in transgenic chicken models in the past few years.

Telomerase activity and differential expression of telomerase genes and c-myc in chicken cells in vitro

This study examined telomerase activity and gene expression profiles for three genes in Gallus gallus domesticus: telomerase reverse transcriptase (chTERT), telomerase RNA (chTR), and c-myc. Expression of these genes was studied in chicken embryonic stem (chES) cells, chicken embryo fibroblasts (CEFs), and DT40 cells using quantitative real-time polymerase chain reaction. Our results establish that, relative to transcription levels in telomerase-negative CEFs, chTERT and chTR are up-regulated in telomerase-positive chES cells. Transcription levels of chTERT, chTR, and c-myc are dramatically up-regulated in telomerase-positive DT40 cells, relative to CEFs and chES cells. These results are consistent with a model in which telomerase activity is up-regulated in proliferating embryonic stem cells requiring stable telomeres to endure multiple rounds of cell division; down-regulated in differentiated, lifespan-limited cells; and dramatically up-regulated in immortalized, transformed cells for which uncontrolled proliferation is correlated with c-myc dysregulation and telomerase activity.

Status of transgenic chicken models for developmental biology

The chick embryo is a classic model that has been used to gain insight into developmental processes and cell fate within the embryo for over a century. For the most part, investigators have implanted quail cells into a chicken embryo. A more powerful tool for developmental biology research than the quail:chick chimera system would be to have lines of transgenic chickens expressing reporter genes that are readily available to the research community. However, avian transgenic technology has been fraught with technical difficulties, and transgenic chickens expressing reporter genes have only recently been developed. The goal of this review is to report the technologies that have been used to generate transgenic chickens and to discuss the challenges in generating avian transgenics for developmental biology research.

Avian pluripotent stem cells

Pluripotent embryonic stem cells are undifferentiated cells capable of proliferation and self-renewal and have the capacity to differentiate into all somatic cell types and the germ line. They provide an in vitro model of early embryonic differentiation and are a useful means for targeted manipulation of the genome. Pluripotent stem cells in the chick have been derived from stage X blastoderms and 5.5 day gonadal primordial germ cells (PGCs). Blastoderm-derived embryonic stem cells (ESCs) have the capacity for in vitro differentiation into embryoid bodies and derivatives of the three primary germ layers. When grafted onto the chorioallantoic membrane, the ESCs formed a variety of differentiated cell types and attempted to organize into complex structures. In addition, when injected into the unincubated stage X blastoderm, the ESCs can be found in numerous somatic tissues and the germ line. The potential give rise to somatic and germ line chimeras is highly dependent upon the culture conditions and decreases with passage. Likewise, PGC-derived embryonic germ cells (EGCs) can give rise to simple embryoid bodies and can undergo some differentiation in vitro. Interestingly, chicken EG cells contribute to somatic lineages when injected into the stage X blastoderm, but only germ line chimeras have resulted from EGCs injected into the vasculature of the stage 16 embryo. To date, no lines of transgenic chickens have been generated using ESCs or EGCs. Nevertheless, progress towards the culture of avian pluripotent stem cells has been significant. In the future, the answers to fundamental questions regarding segregation of the avian germ line and the molecular basis of pluripotency should foster the full use of avian pluripotent stem cells.