Identification, Culture, and Characterization of Germline Stem Cell-Like Cells in Chicken Testes1

Strategies for the Generation of Gene Modified Avian Models: Advancement in Avian Germline Transmission, Genome Editing, and Applications

Avian models are valuable for studies of development and reproduction and have important implications for food production. Rapid advances in genome-editing technologies have enabled the establishment of avian species as unique agricultural, industrial, disease-resistant, and pharmaceutical models. The direct introduction of genome-editing tools, such as the clustered regularly interspaced short palindromic repeats (CRISPR) system, into early embryos has been achieved in various animal taxa. However, in birds, the introduction of the CRISPR system into primordial germ cells (PGCs), a germline-competent stem cell, is considered a much more reliable approach for the development of genome-edited models. After genome editing, PGCs are transplanted into the embryo to establish germline chimera, which are crossed to produce genome-edited birds. In addition, various methods, including delivery by liposomal and viral vectors, have been employed for gene editing in vivo. Genome-edited birds have wide applications in bio-pharmaceutical production and as models for disease resistance and biological research. In conclusion, the application of the CRISPR system to avian PGCs is an efficient approach for the production of genome-edited birds and transgenic avian models.

Efficient gene transfer into zebra finch germline-competent stem cells using an adenoviral vector system

Zebra finch is a representative animal model for studying the molecular basis of human disorders of vocal development and communication. Accordingly, various functional studies of zebra finch have knocked down or introduced foreign genes in vivo; however, their germline transmission efficiency is remarkably low. The primordial germ cell (PGC)-mediated method is preferred for avian transgenic studies; however, use of this method is restricted in zebra finch due to the lack of an efficient gene transfer method for the germline. To target primary germ cells that are difficult to transfect and manipulate, an adenovirus-mediated gene transfer system with high efficiency in a wide range of cell types may be useful. Here, we isolated and characterized two types of primary germline-competent stem cells, PGCs and spermatogonial stem cells (SSCs), from embryonic and adult reproductive tissues of zebra finch and demonstrated that genes were most efficiently transferred into these cells using an adenovirus-mediated system. This system was successfully used to generate gene-edited PGCs in vitro. These results are expected to improve transgenic zebra finch production.

Improvement of in vitro proliferation of cockerel spermatogonial stem cells using different combinations of growth factors

1. This study examined whether in vitro proliferation and maintenance of cockerel spermatogonial stem cells (SSCs) could be improved by adding different combinations of growth factors (GFs), including glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF) or leukaemia inhibitory factor (LIF) into the culture medium. 2. The SSCs were isolated from the testes of immature cockerels. For short-term cultures, a medium supplemented with different combinations of GFs for 7 d in 5 replicates was used. The groups were classified as follows: without GF (control group); with GDNF (G group); with GDNF and bFGF (GF group); and with GDNF, bFGF and LIF (GFL group). The number of colonies and cells per colony, as well as the transcript abundance of STRA8 and OCT4 genes, was determined 7 d after the initial culturing. Immunofluorescence staining of SSEA-1, SSEA-3 and VASA protein markers, besides periodic acid-Schiff (PAS) staining, was carried out. 3. The number of colonies and cells per colony increased in the G, GF and GFL groups, compared to the control group (P < 0.01); however, the highest proliferation and colony formation were observed in the GFL group. The positive immunofluorescence staining of SSEA-1, SSEA-3 and VASA protein markers, as well as PAS staining, confirmed the self-renewal and colonisation of cockerel SSCs. The proliferation results were supported by the increased STRA8 and OCT4 transcript abundance in the treated groups (G, GF and GLF), compared to the control group. The SSC proliferation was associated with the higher transcript abundance of STAR8 and OCT4 genes in the GFL group, compared to the G and GF groups (P < 0.01). 4. The results showed that proliferation and colony-forming capacity of cockerel SSCs were positively improved by GDNF, bFGF and LIF. However, the most significant effect was observed when the medium was supplemented with LIF in combination with GDNF and bFGF.

Production of quail (Coturnix japonica) germline chimeras by transfer of Ficoll-enriched spermatogonial stem cells

Due to the absence of long-term in vitro germline competent stem cell maintenance systems and efficient methods for germline transmission, efforts to develop an effective transgenic system in quail has remained limited. To overcome this limitation, here we produced germline chimeric quails through transplantation of spermatogonial stem cells (SSCs) enriched by density gradient methods utilizing Ficoll-Paque PLUS (Ficoll), Percoll and sucrose solution as a practical strategy for germline transmission in quail. For all gradient methods, testicular cells were separated as two fractions, and the expression levels of SSC-specific genes (GFRA1, ITGA6, ITGB1) and pluripotency genes (NANOG, POUV) were examined. As a result, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and RNA probe hybridization analysis revealed that the upper fraction that was separated by Ficoll showed the highest expression of SSC-specific and pluripotency genes among all fractions. Cells in the upper Ficoll gradient fraction also displayed reduced heterochromatin distribution, as observed in differentiated spermatogonia using transmission electron microscopy (TEM). These results indicate that SSCs were enriched in the upper fraction by Ficoll density gradient centrifugation. Subsequent transplantation experiments revealed that the efficiency of germline transmission to donor-derived gametes in the germline chimeras with transplanted SSCs and whole testicular cells was 0-13.2% and 0-4.4%, respectively. Collectively, these results demonstrate that quail SSCs were easily enriched with a density gradient method and that this method is a feasible and practical way to preserve the germplasm of quail. Furthermore, we can expect to apply this method in research examining the production of transgenic quail and preservation of avian species.

Targeting lentiviral vectors to primordial germ cells (PGCs): An efficient strategy for generating transgenic chickens

Recent advances in avian transgenic studies highlight the possibility of utilizing lentiviral vectors as tools to generate transgenic chickens. However, low rates of gonadal chimerism and germ line transmission efficiency still limit the broad usage of this method in creating transgenic chickens. In this study, we implemented a simple strategy using modified lentiviral vectors targeted to chicken primordial germ cells (PGCs) to generate transgenic chickens. The lentiviral vectors were pseudotyped with a modified Sindbis virus envelope protein (termed M168) and conjugated with an antibody specific to PGC membrane proteins. We demonstrated that these optimized M168-pseudotyped lentiviral vectors conjugated with SSEA4 antibodies successfully targeted transduction of PGCs in vitro and in vivo. Compared with the control, 50.0%-66.7% of chicken embryos expressed green fluorescent protein (GFP) in gonads transduced by the M168-pseudotyped lentivirus. This improved the targeted transduction efficiency by 30.0%-46.7%. Efficient chimerism of exogenous genes was also observed. This targeting technology could improve the efficiency of germ line transmission and provide greater opportunities for transgenic poultry studies.

Effects of nano-selenium on mRNA expression of markers for spermatogonial stem cells in the testis of broiler breeder males

Fertility is one of the most important parameters in breeder farms and cockerels play an outstanding role in the fertility of eggs in broiler breeder farms. Todays, supplementation of chicken diet with additives such as organic selenium is used to increase fertility. The aim of this study was to evaluate the effects of different levels of nano-selenium (Nano-Se) on the expression of molecular markers of spermatogonial stem cells (SSCs) in the testis of broiler breeder males. A total of 30 roosters of 40 weeks of age were randomly divided into five groups. Groups were as follows: 1) control (normal diet) group, 2) diet supplemented with 0.30 mg kg^-1 sodium selenite, 3) diet supplemented with 0.15 mg kg^-1 Nano-Se, 4) diet supplemented with 0.30 mg kg^-1 Nano-Se, and 5) diet supplemented with 0.60 mg kg^-1 Nano-Se. At the end of the experimental period (5^th week), birds were autopsied and samples from testis of all birds were collected. The testis samples were used to examine the β1-integrin (CD29), thy-1 (CD90) and NANOG mRNA expression by real-time PCR. The results showed that testis of the groups fed with the diets supplemented with 0.60 mg kg^-1 and 0.15 mg kg^-1 of Nano-Se had the highest and lowest mRNA expression of SSCs markers, respectively. In conclusion, the present study indicated that Nano-Se had advantages over sodium selenite. Diet supplemented with 0.60 mg kg^-1 of Nano-Se may contribute to optimal fertility via increasing the mRNA expression of SSCs markers of roosters’ testis and could be used to delay the reduction of fertility caused by aging in broiler breeder males.

The evolution of chicken stem cell culture methods

1. The avian embryo is an excellent model for studying embryology and the production of pharmaceutical proteins in transgenic chickens. Furthermore, chicken stem cells have the potential for proliferation and differentiation and emerged as an attractive tool for various cell-based technologies. 2. The objective of these studies is the derivation and culture of these stem cells is the production of transgenic birds for recombinant biomaterials and vaccine manufacture, drug and cytotoxicity testing, as well as to gain insight into basic science, including cell tracking. 3. Despite similarities among the established chicken stem cell lines, fundamental differences have been reported between their culture conditions and applications. Recent conventional protocols used for expansion and culture of chicken stem cells mostly depend on feeder cells, serum-containing media and static culture. 4. Utilising chicken stem cells for generation of cell-based transgenic birds and a variety of vaccines requires large-scale cell production. However, scaling up the conventional adherent chicken stem cells is challenging and labour intensive. Development of a suspension cell culture process for chicken embryonic stem cells (cESCs), chicken primordial germ cells (PGCs) and chicken induced pluripotent stem cells (ciPSCs) will be an important advance for increasing the growth kinetics of these cells. 6. This review describes various approaches and suggestions to achieve optimal cell growth for defined chicken stem cells cultures and use in future manufacturing applications.

Germline-competent stem cell in avian species and its application

Germ cells are the only cell type in the body that can transfer genetic information to the next generation. Germline-competent stem cells can self-renew and contribute to the germ cell lineage giving rise to pluripotent stem cells under specific conditions. Hence far, studies on germline-competent stem cells have contributed to the generation of avian model systems and the conservation of avian genetic resources. In this review, we focus on previous studies on germline-competent stem cells from avian species, mainly chicken germline-competent stem cells, which have been well established and characterized. We discuss different sources of germline-competent stem cells and recent advances for the future applications in birds.

Chick stem cells: current progress and future prospects

Chick embryonic stem cells (cESCs) can be derived from cells obtained from stage X embryos (blastoderm stage); these have the ability to contribute to all somatic lineages in chimaeras, but not to the germ line. However, lines of stem cells that are able to contribute to the germ line can be established from chick primordial germ cells (cPGCs) and embryonic germ cells (cEGCs). This review provides information on avian stem cells, emphasizing different sources of cells and current methods for derivation and culture of pluripotent cells from chick embryos. We also review technologies for isolation and derivation of chicken germ cells and the production of transgenic birds.

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Chick embryonic stem cells (cESCs) can be derived from a variety of sources.

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cESCs can contribute to all somatic cell types but not to the germ line.

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germ cells can be isolated from early embryos, embryonic blood and gonads.

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germ cells can establish self-renewing lines and contribute to the germline.

Primordial germ cells (PGCs) as a tool for creating transgenic chickens

The transgenic chicken has great potential as a bioreactor for the production of valuable pharmaceutical proteins, notably in the oviduct/egg. Whereas conventional transgenic approaches have significant limitations in this species, an alternative approach employing primordial germ cells (PGCs), the progenitor cells to ova and spermatozoa, has now been successfully applied to the insertion of exogenous genes into birds. Recent developments in manipulating avian embryos make it possible to produce germline chimeras derived from transferred PGCs. In this review we describe the migration pathway of chicken PGCs during early development. We then summarize different methods for the isolation of PGCs and the diversity of techniques used to introduce genes into these cells. Finally, we describe an in vitro assay for testing tissue-specific vectors designed to express heterologous proteins in transgenic chickens.

Transgenic chimera quail production by microinjecting lentiviral vector into the blood vessel of the early embryo

In the past, several strategies have been used to generate transgenic birds. The most successful method has proven to be injection of lentiviral vector into the subgerminal cavity of the newly laid egg. In this study, we directly injected lentiviral vector into the blood vessel of HH13-15 quail embryos to produce transgenic chimeras. In the manipulated, hatched birds, the green fluorescent protein (GFP) gene driven by a cytomegalovirus (CMV) promoter was extensively expressed. All tissues analyzed were GFP-positive, and gonad cells from some of the manipulated embryos expressed GFP. The semen genome of 21.4% of mature male birds was determined to be GFP-positive by PCR, indicating these male birds were transgenic chimeras.

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.

Pluripotency of male germline stem cells

The ethical issues and public concerns regarding the use of embryonic stem (ES) cells in human therapy have motivated considerable research into the generation of pluripotent stem cell lines from non-embryonic sources. Numerous reports have shown that pluripotent cells can be generated and derived from germline stem cells (GSCs) in mouse and human testes during in vitro cultivation. The gene expression patterns of these cells are similar to those of ES cells and show the typical self-renewal and differentiation patterns of pluripotent cells in vivo and in vitro. However, the mechanisms underlying the spontaneous dedifferentiation of GSCs remain to be elucidated. Studies to identify master regulators in this reprogramming process are of critical importance for understanding the gene regulatory networks that sustain the cellular status of these cells. The results of such studies would provide a theoretical background for the practical use of these cells in regenerative medicine. Such studies would also help elucidate the molecular mechanisms underlying certain diseases, such as testicular germ cell tumors.

Structural and histological characterization of oviductal magnum and lectin-binding patterns in Gallus domesticus

BACKGROUND

Although chicken oviduct is a useful model and target tissue for reproductive biology and transgenesis, little is known because of the highly specific hormonal regulation and the lack of fundamental researches, including lectin-binding activities and glycobiology. Because lectin is attached to secreted glycoproteins, we hypothesized that lectin could be bound to secretory egg-white proteins, and played a crucial role in the generation of egg-white protein in the oviduct. Hence, the purpose of this study was to investigate the structural, histological and lectin-binding characteristics of the chicken oviductal magnum from juvenile and adult hens.

METHODS

The oviductal magnums from juvenile and adult hens were prepared for ultrastructural analysis, qRT-PCR and immunostaining. Immunohistochemistry of anti-ovalbumin, anti-ESR1 and anti-PGR, and mRNA expression of egg-white genes and steroid hormone receptor genes were evaluated. Lectin histochemical staining was also conducted in juvenile and adult oviductal magnum tissues.

RESULTS

The ultrastructural analysis showed that ciliated cells were rarely developed on luminal surface in juvenile magnum, but not tubular gland cells. In adult magnum, two types of epithelium and three types of tubular gland cells were observed. qRT-PCR analysis showed that egg-white genes were highly expressed in adult oviduct compared with the juvenile. However, mRNA expressions of ESR1 and PGR were considerably higher in juvenile oviduct than adult (P < 0.05). The immunohistochemical analysis showed that anti-ovalbumin antibody was detected in adult oviduct not in juvenile, unlikely anti-ESR1 and anti-PGR antibodies that were stained in both oviducts. In histological analysis, Toluidine blue was stained in juvenile and adult oviductal epithelia, and adult tubular glands located in the outer layer of oviductal magnum. In contrast, PAS was positive only in adult oviductal tubular gland. Lectins were selectively bound to oviductal epithelium, stroma, and tubular gland cells. Particularly, lectin-ConA and WGA were bound to electron-dense secretory granules in tubular gland.

CONCLUSIONS

The observation of ultrastructural analysis, mRNA expression, immunohistochemistry and lectin staining showed structural and physiological characterization of juvenile and adult oviductal magnum. Consequently, oviduct study could be helped to in vitro culture of chicken oviductal cells, to develop epithelial or tubular gland cell-specific markers, and to understand female reproductive biology and endocrinology.

The reversible developmental unipotency of germ cells in chicken

We recently developed bimodal germline chimera production approaches by transfer of primordial germ cells (PGCs) or embryonic germ cells (EGCs) into embryos and by transplantation of spermatogonial stem cells (SSCs) or germline stem cells (GSCs) into adult testes. This study was undertaken to investigate the reversible developmental unipotency of chicken germ cells using our established germline chimera production systems. First, we transferred freshly isolated SSCs from adult testis or in vitro cultured GSCs into stage X and stage 14-16 embryos, and we found that these transferred SSCs/GSCs could migrate to the recipient embryonic gonads. Of the 527 embryos that received SSCs or GSCs, 135 yielded hatchlings. Of 17 sexually mature males (35.3%), six were confirmed as germline chimeras through testcross analysis resulting in an average germline transmission efficiency of 1.3%. Second, PGCs/EGCs, germ cells isolated from embryonic gonads were transplanted into adult testes. The EGC transplantation induced germline transmission, whereas the PGC transplantation did not. The germline transmission efficiency was 12.5 fold higher (16.3 vs 1.3%) in EGC transplantation into testis (EGCs to adult testis) than that in SSC/GSC transfer into embryos (testicular germ cells to embryo stage). In conclusion, chicken germ cells from different developmental stages can (de)differentiate into gametes even after the germ cell developmental clock is set back or ahead. Use of germ cell reversible unipotency might improve the efficiency of germ cell-mediated germline transmission.

Derive and conquer: sourcing and differentiating stem cells for therapeutic applications

Although great progress has been made in the isolation and culture of stem cells, the future of stem-cell-based therapies and their productive use in drug discovery and regenerative medicine depends on two key factors: finding reliable sources of multipotent and pluripotent cells and the ability to control their differentiation to generate desired derivatives. It is essential for clinical applications to establish reliable sources of pathogen-free human embryonic stem cells (ESCs) and develop suitable differentiation techniques. Here, we address some of the problems associated with the sourcing of human ESCs and discuss the current status of stem-cell differentiation technology.

Testicular and ovarian gonocytes from 20-day incubated chicken embryos contribute to germline lineage after transfer into bloodstream of recipient embryos

The present study was conducted to elucidate whether testicular and ovarian gonocytes obtained from 20-day incubated chicken embryos (stage 45) have the ability to migrate to the germinal ridges and contribute to germline lineage after transfer into the bloodstream of recipient embryos. Testicular and ovarian gonocytes were first identified as relatively large cells in a population of gonadal cells. The proportions of testicular and ovarian gonocytes in the total gonadal cells were 0.94 and 0.75% respectively, recognised as chicken vasa homologue-positive cells. Then, the dissociated gonadal cells obtained from 20-day incubated embryos containing testicular or ovarian gonocytes, with or without transfection, were transferred into recipient embryos. Expression of the introduced GFP gene was observed in the gonads of 6.5-day cultured recipient embryos (stage 30) in males and females, suggesting that the transferred testicular and ovarian gonocytes have the ability to migrate to the germinal ridges and enter the gonads. Furthermore, the presence of the donor-derived DNA was detected in the gonads of 20-day cultured recipient embryos in males and females, and also in the sperm samples obtained from the hatched male putative chimaeric chickens, suggesting that the transferred testicular and ovarian gonocytes were incorporated into the germline of chimaeric embryos and chickens. It is concluded that testicular and ovarian gonocytes obtained from 20-day incubated embryos have the ability to migrate to the germinal ridges after transfer into the bloodstream of recipient embryos, enter the gonads and contribute to the germline lineage of chimaeric embryos and chickens.