Long-term in vitro culture and characterisation of avian embryonic stem cells with multiple morphogenetic potentialities

The Effect of Inhibiting the Wingless/Integrated (WNT) Signaling Pathway on the Early Embryonic Disc Cell Culture in Chickens

The utilization of chicken embryonic-derived pluripotent stem cell (PSC) lines is crucial in various fields, including growth and development, vaccine and protein production, and germplasm resource protection. However, the research foundation for chicken PSCs is relatively weak, and there are still challenges in establishing a stable and efficient PSC culture system. Therefore, this study aims to investigate the effects of the FGF2/ERK and WNT/β-catenin signaling pathways, as well as different feeder layers, on the derivation and maintenance of chicken embryonic-derived PSCs. The results of this study demonstrate that the use of STO cells as feeder layers, along with the addition of FGF2, IWR-1, and XAV-939 (FIX), allows for the efficient derivation of chicken PSC-like cells. Under the FIX culture conditions, chicken PSCs express key pluripotency genes, such as POUV, SOX2, and NANOG, as well as specific proteins SSEA-1, C-KIT, and SOX2, indicating their pluripotent nature. Additionally, the embryoid body experiment confirms that these PSC-like cells can differentiate into cells of three germ layers in vitro, highlighting their potential for multilineage differentiation. Furthermore, this study reveals that chicken Eyal-Giladi and Kochav stage X blastodermal cells express genes related to the primed state of PSCs, and the FIX culture system established in this research maintains the expression of these genes in vitro. These findings contribute significantly to the understanding and optimization of chicken PSC culture conditions and provide a foundation for further exploration of the biomedical research and biotechnological applications of chicken PSCs.

Reinforcement of repressive marks in the chicken primordial germ cell epigenetic signature: divergence from basal state resetting in mammals

BACKGROUND

In mammals, primordial germ cells (PGCs), the embryonic precursors of the germline, arise from embryonic or extra-embryonic cells upon induction by the surrounding tissues during gastrulation, according to mechanisms which are elucidated in mice but remain controversial in primates. They undergo genome-wide epigenetic reprogramming, consisting of extensive DNA demethylation and histone post-translational modification (PTM) changes, toward a basal, euchromatinized state. In contrast, chicken PGCs are specified by preformation before gastrulation based on maternally-inherited factors. They can be isolated from the bloodstream during their migration to the genital ridges. Our prior research highlighted differences in the global epigenetic profile of cultured chicken PGCs compared with chicken somatic cells and mammalian PGCs. This study investigates the acquisition and evolution of this profile during development.

RESULTS

Quantitative analysis of global DNA methylation and histone PTMs, including their distribution, during key stages of chicken early development revealed divergent PGC epigenetic changes compared with mammals. Unlike mammalian PGCs, chicken PGCs do not undergo genome-wide DNA demethylation or exhibit a decrease in histone H3 lysine 9 dimethylation. However, chicken PGCs show 5‑hydroxymethylcytosine loss, macroH2A redistribution, and chromatin decompaction, mirroring mammalian processes. Chicken PGCs initiate their epigenetic signature during migration, progressively accumulating high global levels of H3K9me3, with preferential enrichment in inactive genome regions. Despite apparent global chromatin decompaction, abundant heterochromatin marks, including repressive histone PTMs, HP1 variants, and DNA methylation, persists in chicken PGCs, contrasting with mammalian PGCs.

CONCLUSIONS

Chicken PGCs' epigenetic signature does not align with the basal chromatin state observed in mammals, suggesting a departure from extensive epigenetic reprogramming. Despite disparities in early PGC development, the persistence of several epigenetic features shared with mammals implies their involvement in chromatin-regulated germ cell properties, with the distinctive elevation of chicken-specific H3K9me3 potentially participating in these processes.

Wnt signaling blockade is essential for maintaining the pluripotency of chicken embryonic stem cells

Activation of Wnt/β-catenin signaling supports the self-renewal of mouse embryonic stem cells. We aimed to understand the effects of Wnt signaling activation or inhibition on chicken embryonic stem cells (chESCs), as these effects are largely unknown. When the glycogen synthase kinase-3 β inhibitor CHIR99021-which activates Wnt signaling-was added to chESC cultures, the colony shape flattened, and the expression levels of pluripotency-related (NANOG, SOX2, SOX3, OCT4, LIN28A, DNMT3B, and PRDM14) and germ cell (CVH and DAZL) markers showed a decreasing trend, and the growth of chESCs was inhibited after approximately 7 d. By contrast, when the Wnt signaling inhibitor XAV939 was added to the culture, dense and compact multipotent colonies (morphologically similar to mouse embryonic stem cell colonies) showing stable expression of pluripotency-related and germline markers were formed. The addition of XAV939 stabilized the proliferation of chESCs in the early stages of culture and promoted their establishment. Furthermore, these chESCs formed chimeras. In conclusion, functional chESCs can be stably cultured using Wnt signaling inhibitors. These findings suggest the importance of Wnt/β-catenin signaling in avian stem cells, offering valuable insights for applied research using chESCs.

From fertilised oocyte to cultivated meat - harnessing bovine embryonic stem cells in the cultivated meat industry

Global demand for animal protein is on the rise, but many practices common in conventional production are no longer scalable due to environmental impact, public health concerns, and fragility of food systems. For these reasons and more, a pressing need has arisen for sustainable, nutritious, and animal welfare-conscious sources of protein, spurring research dedicated to the production of cultivated meat. Meat mainly consists of muscle, fat, and connective tissue, all of which can be sourced and differentiated from pluripotent stem cells to resemble their nutritional values in muscle tissue. In this paper, we outline the approach that we took to derive bovine embryonic stem cell lines (bESCs) and to characterise them using FACS (fluorescence-activated cell sorting), real-time PCR and immunofluorescence staining. We show their cell growth profile and genetic stability and demonstrate their induced differentiation to mesoderm committed cells. In addition, we discuss our strategy for preparation of master and working cell banks, by which we can expand and grow cells in suspension in quantities suitable for mass production. Consequently, we demonstrate the potential benefits of harnessing bESCs in the production of cultivated meat.

A Bird's-Eye View of Endangered Species Conservation: Avian Genomics and Stem Cell Approaches for Green Peafowl (Pavo muticus)

Aves ranks among the top two classes for the highest number of endangered and extinct species in the kingdom Animalia. Notably, the IUCN Red List classified the green peafowl as endangered. This highlights promising strategies using genetics and reproductive technologies for avian wildlife conservation. These platforms provide the capacity to predict population trends and enable the practical breeding of such species. The conservation of endangered avian species is facilitated through the application of genomic data storage and analysis. Storing the sequence is a form of biobanking. An analysis of sequence can identify genetically distinct individuals for breeding. Here, we reviewed avian genomics and stem cell approaches which not only offer hope for saving endangered species, such as the green peafowl but also for other birds threatened with extinction.

An inducible germ cell ablation chicken model for high-grade germline chimeras

Chicken embryos are a powerful and widely used animal model in developmental biology studies. Since the development of CRISPR technology, gene-edited chickens have been generated by transferring primordial germ cells (PGCs) into recipients after genetic modifications. However, low inheritance caused by competition between host germ cells and the transferred cells is a common complication and greatly reduces production efficiency. Here, we generated a gene-edited chicken, in which germ cells can be ablated in a drug-dependent manner, as recipients for gene-edited PGC transfer. We used the nitroreductase/metronidazole (NTR/Mtz) system for cell ablation, in which nitroreductase produces cytotoxic alkylating agents from administered metronidazole, causing cell apoptosis. The chicken Vasa homolog (CVH) gene locus was used to drive the expression of the nitroreductase gene in a germ cell-specific manner. In addition, a fluorescent protein gene, mCherry, was also placed in the CVH locus to visualize the PGCs. We named this system 'germ cell-specific autonomous removal induction' (gSAMURAI). gSAMURAI chickens will be an ideal recipient to produce offspring derived from transplanted exogenous germ cells.

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.

Current Approaches to and the Application of Intracytoplasmic Sperm Injection (ICSI) for Avian Genome Editing

Poultry are one of the most valuable resources for human society. They are also recognized as a powerful experimental animal for basic research on embryogenesis. Demands for the supply of low-allergen eggs and bioreactors have increased with the development of programmable genome editing technology. The CRISPR/Cas9 system has recently been used to produce transgenic animals and various animals in the agricultural industry and has also been successfully adopted for the modification of chicken and quail genomes. In this review, we describe the successful establishment of genome-edited lines combined with germline chimera production systems mediated by primordial germ cells and by viral infection in poultry. The avian intracytoplasmic sperm injection (ICSI) system that we previously established and recent advances in ICSI for genome editing are also summarized.

Fate Decisions of Chicken Primordial Germ Cells (PGCs): Development, Integrity, Sex Determination, and Self-Renewal Mechanisms

Primordial germ cells (PGCs) are precursor cells of sperm and eggs. The fate decisions of chicken PGCs in terms of their development, integrity, and sex determination have unique features, thereby providing insights into evolutionary developmental biology. Additionally, fate decisions in the context of a self-renewal mechanism have been applied to establish culture protocols for chicken PGCs, enabling the production of genome-edited chickens and the conservation of genetic resources. Thus, studies on the fate decisions of chicken PGCs have significantly contributed to both academic and industrial development. Furthermore, studies on fate decisions have rapidly advanced owing to the recent development of essential research technologies, such as genome editing and RNA sequencing. Here, we reviewed the status of fate decisions of chicken PGCs and provided insight into other important research issues that require attention.

Chicken genome editing for investigating poultry pathogens

Major advances in pathogen identification, treatment, vaccine development, and avian immunology have enabled the enormous expansion in global poultry production over the last 50 years. Looking forward, climate change, reduced feed, reduced water access, new avian pathogens and restrictions on the use of antimicrobials threaten to hamper further gains in poultry productivity and health. The development of novel in vitro cell culture systems, coupled with new genetic tools to investigate gene function, will aid in developing novel interventions for existing and newly emerging poultry pathogens. Our growing capacity to cryopreserve and generate genome-edited chicken lines will also be useful for developing improved chicken breeds for poultry farmers and conserving chicken genetic resources.

Research Note: Development of a chicken experimental model platform for induced pluripotent stem cells by using CRISPR/Cas9-mediated NANOG knock-in reporter DF1 cells

NANOG, as a transcription factor, plays a key role in maintaining pluripotency in higher vertebrates. Thus, NANOG gene expression is a critical index for the transition from somatic cells to the pluripotent stage. Here, we established chicken knock-in DF1 cells in which the red fluorescent protein (RFP) gene was specifically inserted into the transcriptional start site of the NANOG gene through the CRISPR‒Cas9 (clustered regularly interspaced short palindromic repeat-CRISPR associated protein 9) technical platform. Subsequently, 4 transcription factors (Pou5f3, Sox2, Nanog, and Lin28A) were introduced into the NANOG-RFP DF1 cells, and finally, the induced pluripotent cells were established and examined by endogenous NANOG promoter-controlled RFP gene expression. The development of induced pluripotent stem cells (iPSCs) in avians would be useful for practical applications in the field of avian biotechnology, including biobanking genetic materials and restoring endangered species. In this study, a reporter cell line system was established to efficiently identify the induced pluripotent stage, and it will facilitate potential use for various purposes in the field of avian experimental models.

Avian Embryonic Culture: A Perspective of In Ovo to Ex Ovo and In Vitro Studies

The avian embryos growing outside the natural eggshell (ex ovo) were observed since the early 19th century, and since then chick embryonic structures have revealed reaching an in-depth view of external and internal anatomy, enabling us to understand conserved vertebrate development. However, the internal environment within an eggshell (in ovo) would still be the ideal place to perform various experiments to understand the nature of avian development and to apply other biotechnology techniques. With the advent of genetic manipulation and cell culture techniques, avian embryonic parts were dissected for explant culture to eventually generate expandable cell lines (in vitro cell culture). The expansion of embryonic cells allowed us to unravel the transcriptional network for understanding pluripotency and differentiation mechanism in the embryos and in combination with stem cell technology facilitated the applications of avian culture to the next levels in transgenesis and wildlife conservation. In this review, we provide a panoramic view of the relationship among different cultivation platforms from in ovo studies to ex ovo as well as in vitro culture of cell lines with recent advances in the stem cell fields.

Ascorbic acid and all-trans retinoic acid promote proliferation of chicken blastoderm cells (cBCs) by mediating DNA demethylation

Chicken blastoderm cells (cBCs) obtained from stage X (EG&K) embryos are easily available materials for the study of cell development. However, cBCs are not widely used because they are hard to maintain in long-term culture in vitro. To solve this problem, ascorbic acid (AA; also known as vitamin C (VC)) and all-trans retinoic acid (ATRA) were added into basic culture medium to promote cell growth. Results suggested that cultured cBCs possessed strongly proliferative activity and maintained their pluripotency on the support of chicken embryonic fibroblast (CEF) feeder. Moreover, when VC or/and ATRA was added, the number and area of cBC colonies increased significantly compared with the control group. The expression of pluripotency genes (Sox2 and Nanog) and cell cycle-regulated genes (CCND1 and CDK6) was upregulated obviously. Furthermore, results showed that 5hmC levels in VC and RA groups increased significantly by DNA dot blot and immunofluorescence staining. These results provide strong evidence that VC and ATRA induced DNA demethylation and enhanced 5hmC level. The level of H3K27me3 was raised, while the level of H3K9me2 was reduced by addition of VC and ATRA. Finally, the expression of Tet1 and Dnmt3b was upregulated remarkably. Therefore, these results indicated that VC and ATRA enhanced DNA demethylation and then promoted cBC survival and proliferation in vitro.

Chicken blastoderms and primordial germ cells possess a higher expression of DNA repair genes and lower expression of apoptosis genes to preserve their genome stability

DNA is susceptible to damage by various sources. When the DNA is damaged, the cell repairs the damage through an appropriate DNA repair pathway. When the cell fails to repair DNA damage, apoptosis is initiated. Although several genes are involved in five major DNA repair pathways and two major apoptosis pathways, a comprehensive understanding of those gene expression is not well-understood in chicken tissues. We performed whole-transcriptome sequencing (WTS) analysis in the chicken embryonic fibroblasts (CEFs), stage X blastoderms, and primordial germ cells (PGCs) to uncover this deficiency. Stage X blastoderms mostly consist of undifferentiated progenitor (pluripotent) cells that have the potency to differentiate into all cell types. PGCs are also undifferentiated progenitor cells that later differentiate into male and female germ cells. CEFs are differentiated and abundant somatic cells. Through WTS analysis, we identified that the DNA repair pathway genes were expressed more highly in blastoderms and high in PGCs than CEFs. Besides, the apoptosis pathway genes were expressed low in blastoderms and PGCs than CEFs. We have also examined the WTS-based expression profiling of candidate pluripotency regulating genes due to the conserved properties of blastoderms and PGCs. In the results, a limited number of pluripotency genes, especially the core transcriptional network, were detected higher in both blastoderms and PGCs than CEFs. Next, we treated the CEFs, blastoderm cells, and PGCs with hydrogen peroxide (H₂O₂) for 1 h to induce DNA damage. Then, the H₂O₂ treated cells were incubated in fresh media for 3–12 h to observe DNA repair. Subsequent analyses in treated cells found that blastoderm cells and PGCs were more likely to undergo apoptosis along with the loss of pluripotency and less likely to undergo DNA repair, contrasting with CEFs. These properties of blastoderms and PGCs should be necessary to preserve genome stability during the development of early embryos and germ cells, respectively.

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.

Cerebral organoids and their potential for studies of brain diseases in domestic animals

The brain is a complex organ and any model for studying it in its normal and pathological aspects becomes a tool of choice for neuroscientists. The mastering and dissemination of protocols allowing brain organoids development have paved the way for a whole range of new studies in the field of brain development, modeling of neurodegenerative or neurodevelopmental diseases, understanding tumors as well as infectious diseases that affect the brain. While studies are so far limited to the use of human cerebral organoids, there is a growing interest in having similar models in other species. This review presents what is currently developed in this field, with a particular focus on the potential of cerebral organoids for studying neuro-infectious diseases in human and domestic animals.

Successful cryopreservation and regeneration of a partridge colored Hungarian native chicken breed using primordial germ cells

Primordial germ cells (PGCs) are the precursors of germline cells that generate sperm and ova in adults. Thus, they are promising tools for gene editing and genetic preservation, especially in avian species. In this study, we established stable male and female PGC lines from 6Hungarian indigenous chicken breeds with derivation rates ranging from 37.5 to 50 percent. We characterized the PGCs for expression of the germ cell-specific markers during prolonged culture in vitro. An in vivo colonization test was performed on PGCs from four Hungarian chicken breeds and the colonization rates were between 76 and 100%. Cryopreserved PGCs of the donor breed (Partridge color Hungarian) were injected into Black Transylvanian Naked Neck host embryos to form chimeric progeny that, after backcrossing, would permit reconstitution of the donor breed. For 24 presumptive chimeras 13 were male and 11 were female. In the course of backcrossing, 340 chicks were hatched and 17 of them (5%) were pure Partridge colored. Based on the backcrossing 1 hen and 3 roosters of the 24 presumptive chimeras (16.6%) have proven to be germline chimeras. Therefore, it was proven that the original breed can be recovered from primordial germ cells which are stored in the gene bank. To our knowledge, our study is a first that applied feeder free culturing conditions for both male and female cell lines successfully and used multiple indigenous chicken breeds to create a gene bank representing a region (Carpathian Basin).

Liver organoids in domestic animals: an expected promise for metabolic studies

The liver is one of the most important organs, both in terms of the different metabolic processes (energy, lipid, ferric, uric, etc.) and of its central role in the processes of detoxification of substances of food origin or noxious substances (alcohol, drugs, antibiotics, etc.). The development of a relevant model that reproduces some of the functions of this tissue has become a challenge, in particular for human medicine. Thus, in recent years, most studies aimed at producing hepatocytes in vitro with the goal of developing hepatic 3D structures have been carried out in the human model. However, the tools and protocols developed using this unique model can also be considered to address physiological questions specific to this tissue in other species, such as the pig, chicken, and duck. Different strategies are presently being considered to carry out in vitro studies of the hepatic metabolism of these agronomic species.

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.

Differential transcriptional regulation of the NANOG gene in chicken primordial germ cells and embryonic stem cells

Background

NANOG is a core transcription factor (TF) in embryonic stem cells (ESCs) and primordial germ cells (PGCs). Regulation of the NANOG gene by TFs, epigenetic factors, and autoregulatory factors is well characterized in ESCs, and transcriptional regulation of NANOG is well established in these cells. Although NANOG plays a key role in germ cells, the molecular mechanism underlying its transcriptional regulation in PGCs has not been studied. Therefore, we investigated the mechanism that regulates transcription of the chicken NANOG (cNANOG) gene in PGCs and ESCs.

Results

We first identified the transcription start site of cNANOG by 5′-rapid amplification of cDNA ends PCR analysis. Then, we measured the promoter activity of various 5′ flanking regions of cNANOG in chicken PGCs and ESCs using the luciferase reporter assay. cNANOG expression required transcriptional regulatory elements, which were positively regulated by POU5F3 (OCT4) and SOX2 and negatively regulated by TP53 in PGCs. The proximal region of the cNANOG promoter contains a positive transcriptional regulatory element (CCAAT/enhancer-binding protein (CEBP)-binding site) in ESCs. Furthermore, small interfering RNA-mediated knockdown demonstrated that POU5F3, SOX2, and CEBP played a role in cell type-specific transcription of cNANOG.

Conclusions

We show for the first time that different trans-regulatory elements control transcription of cNANOG in a cell type-specific manner. This finding might help to elucidate the mechanism that regulates cNANOG expression in PGCs and ESCs.

Organoids in domestic animals: with which stem cells?

Organoids are three-dimensional structures that are derived from the self-organization of stem cells as they differentiate in vitro. The plasticity of stem cells is one of the major criteria for generating organoids most similar to the tissue structures they intend to mimic. Stem cells are cells with unique properties of self-renewal and differentiation. Depending on their origin, a distinction is made between pluripotent (embryonic) stem cells (PSCs), adult (or tissue) stem cells (ASCs), and those obtained by somatic reprogramming, so-called induced pluripotent stem cells (iPSCs). While most data since the 1980s have been acquired in the mouse model, and then from the late 1990s in humans, the process of somatic reprogammation has revolutionized the field of stem cell research. For domestic animals, numerous attempts have been made to obtain PSCs and iPSCs, an approach that makes it possible to omit the use of embryos to derive the cells. Even if the plasticity of the cells obtained is not always optimal, the recent progress in obtaining reprogrammed cells is encouraging. Along with PSCs and iPSCs, many organoid derivations in animal species are currently obtained from ASCs. In this study, we present state-of-the-art stem cell research according to their origins in the various animal models developed.

Primordial germ cells isolated from individual embryos of red junglefowl and indigenous pheasants of Thailand

Interspecific germline chimerism mediated by transplantation of primordial germ cells (PGCs) of wild species to domestic hosts promises the conservation of wild birds. Cryopreservation of avian eggs and embryos is impracticable, and currently only frozen PGCs enable conservation of both the male and female descendants. Purebred offspring have been obtained from germline chimeras of wild avian species, proving the feasibility of such technology. In vitro propagation has been optimized for avian PGCs of domestic species; however, evidence is rather limited for successful isolation as well as long-term culture from a single embryo of wild species. With accelerating biodiversity loss, we have committed to preserving current genetic resources by freezing PGCs isolated from individual embryos in addition to their genetic material. We have devised a reliable protocol for the isolation and proliferation of PGCs from wild fowls in the family Phasianidae that are conserved in captive breeding (red junglefowl, bar-tailed pheasant, kalij pheasant, Siamese fireback pheasant, and silver pheasant). We obtained individual isolates of cultured circulating PGCs (49.7%, 79/155) as well as tissue PGCs (92.9%, 144/155). The specific co-culture conditions of autologous embryonic cells, without additional growth factors, facilitated the proliferation of so-called tissue PGCs (the remaining PGCs in embryonic tissue following blood aspiration). Only circulating PGCs left in blood vessels and of PGCs migrating to developing gonads have been previously reported. However, the present study is the first to report on the harvest of ectopic PGCs. The defined conditions sustained continuous proliferation of tissue PGCs for at least six months and maintained PGC identity following cryopreservation. Cultured tissue PGCs of these wild species were extensively characterized for their expression of the germ cell-specific proteins, chicken vasa homolog (CVH) and deleted in azoospermia-like (DAZL), as well as the ability to colonize chicken embryonic gonads. The novel protocol is practical for generating enough PGCs for cryopreservation, transplantation, and additionally, it enables isolation of PGCs from both blood circulation and embryonic tissue simultaneously. For conservation purposes, this approach is potentially applicable more widely to other non-domestic birds than those in the family Phasianidae that were investigated in the present study.

Derivation and characterization of putative embryonic stem cells isolated from blastoderms of Taiwan Country chicken for the production of chimeric chickens

The conservation of Taiwan Country chicken (TCC) is important due to concerns for the local breed's adaptability to the area and disease resistance. Furthermore, the genetic resource base of native chickens can be used to improve egg and meat production efficiency in commercial TCC. As the embryonic stem cells (ESCs) hold great potential for regenerative medicine and species conservation, the aims of this study were to isolate and characterize ESCs of TCC. The blastodermal cells (BCs) were isolated from the zona pellucida of stage X chicken embryos and cultured in conditioned medium for the proliferation and maintenance of BCs in vitro. The quantitative real-time polymerase chain reaction (qPCR) results showed that POUV, SOX2 and NANOG were expressed in the putative ESCs. In addition, the expression of pluripotent markers, SSEA-1 and SSEA-4, was detected. The DiI-stained ESCs were injected into the dorsal aorta of the E3.5 recipient fetuses soon after staining and the injected embryos were continuously incubated and checked on day 7 of incubation. It was shown that some DiI-positive cells were found in the 7-d-old chimeric embryos. The results demonstrated that some pluripotent cells existed in the cultured BCs for the production of germline chimeric embryos from TCC.

Study on immortal conditions of chicken embryonic stem cells

In recent years, considerable attention has been paid to chicken embryonic stem cells (ESCs) studies in relation to extensive applications in gene therapy and regenerative medicine. However, the approaches used are still immature. In this study, we showed that the chicken ESCs clones with a clear border can express alkaline phosphatase and marker proteins such as SSEA-1, SOX2, and OCT4 stably. In addition, culture medium containing 10 μmol/L of vitamin C (VC) could significantly promote the proliferation of ESCs cells. Moreover, ESCs transfected with p:enhanced green fluorescent protein (pEGFP)-hTERT could be subcultured more than tenth generations in culture medium containing exogenous factors (mLIF + bFGF + hSCF) and VC, and these ESCs clone could still be regenerated following cryopreservation. Quantitative real-time polymerase chain reaction results showed that there was no significant difference between SSEA-1, SOX2, and OCT4 expression during ESCs immortalization and that the tenth generation of ESCs was still able to express marker proteins SSEA-1, SOX2, and OCT4. Our results showed that an immobilized system for ESCs was established, and the ESCs were cultured in vitro maintaining their pluripotency.

Platypus Induced Pluripotent Stem Cells: The Unique Pluripotency Signature of a Monotreme

The platypus (Ornithorhynchus anatinus) is an egg-laying monotreme mammal whose ancestors diverged ∼166 million years ago from the evolutionary pathway that eventually gave rise to both marsupial and eutherian mammals. Consequently, its genome is an extraordinary amalgam of both ancestral reptilian and derived mammalian features. To gain insight into the evolution of mammalian pluripotency, we have generated induced pluripotent stem cells from the platypus (piPSCs). Deep sequencing of the piPSC transcriptome revealed that piPSCs robustly express the core eutherian pluripotency factors POU5F1/OCT4, SOX2, and NANOG. Given the more extensive role of SOX3 over SOX2 in avian pluripotency, our data indicate that between 315 and 166 million years ago, primitive mammals replaced the role of SOX3 in the vertebrate pluripotency network with SOX2. DAX1/NR0B1 is not expressed in piPSCs and an analysis of the platypus DAX1 promoter revealed the absence of a proximal SOX2-binding DNA motif known to be critical for DAX1 expression in eutherian pluripotent stem cells, suggesting that the acquisition of SOX2 responsiveness by DAX1 has facilitated its recruitment into the pluripotency network of eutherians. Using the RNAseq data, we were also able to demonstrate that in both fibroblasts and piPSCs, the expression ratio of X chromosomes to autosomes (X_1-5 X_1-5:AA) is approximately equal to 1, indicating that there is no upregulation of X-linked genes. Finally, the RNAseq data also allowed us to explore the process of X-linked gene inactivation in the platypus, where we determined that for any given gene, there is no preference for silencing of the maternal or paternal allele; that is, within a population of cells, the silencing of X-linked genes is not imprinted.

NANOG Is Required for the Long-Term Establishment of Avian Somatic Reprogrammed Cells

Somatic reprogramming, which was first identified in rodents, remains poorly described in non-mammalian species. Here, we generated avian reprogrammed cells by reprogramming of chicken and duck primary embryonic fibroblasts. The efficient generation of long-term proliferating cells depends on the method of delivery of reprogramming factors and the addition of NANOG and LIN28 to the canonical OCT4, SOX2, KLF4, and c-MYC gene combination. The reprogrammed cells were positive for several key pluripotency-associated markers including alkaline phosphatase activity, telomerase activity, SSEA1 expression, and specific cell cycle and epigenetic markers. Upregulated endogenous pluripotency-associated genes included POU5F3 (POUV) and KLF4, whereas cells failed to upregulate NANOG and LIN28A. However, cells showed a tumorigenic propensity when injected into recipient embryos. In conclusion, although the somatic reprogramming process is active in avian primary cells, it needs to be optimized to obtain fully reprogrammed cells with similar properties to those of chicken embryonic stem cells.

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NANOG is required for avian somatic reprogramming

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NANOG is necessary for long-term establishment of avian reprogrammed cells

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Avian reprogrammed cells express pluripotency markers

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Avian cells are only partially reprogrammed

Identification and functional characterization, including cytokine production modulation, of the novel chicken Interleukin-11

Interleukin (IL)-11 plays an important role in the immune system. However, IL-11 has not yet been characterized in avian species, including chickens. This study is the first to clone and functionally characterize chicken IL-11 (chIL-11). Multiple alignments and phylogenetic tree comparisons of chIL-11 with IL-11 proteins from other species revealed high levels of conservation and a close relationship between chicken and Japanese quail IL-11. Our results demonstrate that chIL-11 was a functional ligand of IL-11RA and IL-6ST in chicken HD11 and OU2 cell lines, as well as activated and regulated JAK-STAT, NF-κB, PI3K/AKT, and MAPK signaling pathways in chicken cell lines. In addition, chIL-11 inhibited nitric oxide production, affected proliferation of both tested cell lines, inhibited Type 1 and 17 T helper (Th) cytokine and IL-26, IL-12, and IL-17A-induced interferon-γ production, and enhanced Th2 cytokine (IL-4 and IL-10) production. Taken together, functional analysis of chIL-11 revealed it bound to IL-11RA and IL-6ST and activated the JAK-STAT, NF-κB, and MAPK signaling pathways, which resulted in modulation of Th1/Th17 and Th2 cytokine production in chicken HD11 and OU2 cell lines. Overall, this indicates chIL-11 has a role in both the innate and adaptive immune system.

Three-dimensional culture of chicken primordial germ cells (cPGCs) in defined media containing the functional polymer FP003

Scalable production of avian cell lines exhibits a valuable potential on therapeutic application by producing recombinant proteins and as the substrate for virus growth due to the special glycosylation occurs in avian species. Chicken primordial germ cells (cPGCs), a germinal pluripotent avian cell type, present the ability of self-renewal, an anchorage-independent cell growth and the ability to be genetically modified. This cell type could be an interesting bioreactor system for industrial purposes. This study sought to establish an expandable culture system with defined components for three-dimensional (3D) culture of cPGCs. cPGCs were cultured in medium supplemented with the functional polymer FP003. Viscoelasticity was low in this medium but cPGCs did not sediment in culture and efficiencies of space and nutrient utilization were thus enhanced and consequently their expansion was improved. The total number of cPGCs increased by 17-fold after 1 week of culture in 3D-FAot medium, an aseric defined medium containing FP003 polymer, FGF2 and Activin A as growth factors and Ovotransferrin as protein. Moreover, cPGC cell lines stably expressed the germline-specific reporter VASA:tdTOMATO, as well as other markers of cPGCs, for more than 1 month upon culture in 3D-FAot medium, indicating that the characteristics of these cells are maintained. In summary, this novel 3D culture system can be used to efficiently expand cPGCs in suspension without mechanical stirring, which is available for long-term culture and no loss of cellular properties was found. This system provides a platform for large-scale culture of cPGCs.

An Alternative Method for Long-Term Culture of Chicken Embryonic Stem Cell In Vitro

Chicken embryonic stem cells (cESCs) obtained from stage X embryos provide a novel model for the study of avian embryonic development. A new way to maintain cESCs for a long period in vitro still remains unexplored. We found that the cESCs showed stem cell-like properties in vitro for a long term with the support of DF-1 feeder and basic culture medium supplemented with human basic fibroblast growth factor (hbFGF), mouse stem cell factor (mSCF), and human leukemia inhibitory factor (hLIF). During the long culture period, the cESCs showed typical ES cell morphology and expressed primitive stem cell markers with a relatively stable proliferation rate and high telomerase activity. These cells also exhibited the capability to differentiate into cardiac myocytes, smooth muscle cells, neural cells, osteoblast, and adipocyte in vitro. Chimera chickens were produced by cESCs cultured for 25 passages with this new culture system. The experiments showed that DF-1 was the optimal feeder and hbFGF was an important factor for maintaining the pluripotency of cESCs in vitro.

Effects of various culture conditions on pluripotent stem cell derivation from chick embryos

Pluripotent stem cell (PSC) lines derived from embryonated avian eggs are a convenient platform for production of various recombinant proteins and vaccines. In chicks, both embryonic stem cells (ESC) and embryonic germ cells (EGC) are considered to be pluripotent cells obtained from early blastodermal cells (stage X) and gonadal tissues (stage HH28), respectively. However, the establishment and long-term maintenance of avian PSC lines faces several challenges and differs in efficiency between chick strains. This study aims to determine the effects of PSC culture media, including serum-based and serum-free media as well as various feeder layers, growth factors, and small molecules on derivation and maintenance of avian embryonic derived-PSCs. Our results have shown that among the different culture conditions, N2B27 serum-free medium supplemented with PD0325901 and SB431542, MEK and TGFβ chemical inhibitors, named as R2i and cytokine leukemia inhibitory factor (LIF) improved PSC derivation from stages X- and HH28 embryos. The application of N2B27/R2i + LIF medium validates the effect of defined pluripotency supporting medium on efficient derivation of chick PSCs and facilitates the use of these cells in biotechnology and biobanking of valuable species.

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.

ESCDL-1, a new cell line derived from chicken embryonic stem cells, supports efficient replication of Mardiviruses

Marek’s disease virus is the etiological agent of a major lymphoproliferative disorder in poultry and the prototype of the Mardivirus genus. Primary avian somatic cells are currently used for virus replication and vaccine production, but they are largely refractory to any genetic modification compatible with the preservation of intact viral susceptibility. We explored the concept of induction of viral replication permissiveness in an established pluripotent chicken embryonic stem cell-line (cES) in order to derive a new fully susceptible cell-line. Chicken ES cells were not permissive for Mardivirus infection, but as soon as differentiation was triggered, replication of Marek’s disease virus was detected. From a panel of cyto-differentiating agents, hexamethylene bis (acetamide) (HMBA) was found to be the most efficient regarding the induction of permissiveness. These initial findings prompted us to analyse the effect of HMBA on gene expression, to derive a new mesenchymal cell line, the so-called ESCDL-1, and monitor its susceptibility for Mardivirus replication. All Mardiviruses tested so far replicated equally well on primary embryonic skin cells and on ESCDL-1, and the latter showed no variation related to its passage number in its permissiveness for virus infection. Viral morphogenesis studies confirmed efficient multiplication with, as in other in vitro models, no extra-cellular virus production. We could show that ESCDL-1 can be transfected to express a transgene and subsequently cloned without any loss in permissiveness. Consequently, ESCDL-1 was genetically modified to complement viral gene deletions thus yielding stable trans-complementing cell lines. We herein claim that derivation of stable differentiated cell-lines from cES cell lines might be an alternative solution to the cultivation of primary cells for virology studies.

CRISPR/Cas9 mediated chicken Stra8 gene knockout and inhibition of male germ cell differentiation

An efficient genome editing approach had been established to construct the stable transgenic cell lines in the domestic chicken (Gallus gallus domesticus) at present. Our objectives were to investigate gene function in the differentiation process of chicken embryonic stem cells (ESCs) into spermatogonial stem cells(SSCs). Three guides RNA (gRNAs) were designed to knockout the Stra8 gene, and knockout efficiency was evaluated in domestic chicken cells using cleavage activity of in vitro transcription of gRNA, Luciferase-SSA assay, T7 endonuclease I assay(T7E1) and TA clone sequence. In addition, the Cas9/gRNA plasmid was transfected into ESCs to confirm the function of Stra8. SSA assay results showed that luciferase activity of the vector expressing gRNA-1 and gRNA- 2 was higher than that of gRNA-3. TA clone sequencing showed that the knockdown efficiency was 25% (10/40) in DF-1 cells, the knockdown efficiency was 23% (9/40) in chicken ESCs. T7E1 assay indicated that there were cleavage activity for three individuals, and the knockdown efficiency was 12% (3/25). Cell morphology, qRT-PCR, immunostaining and FCS indicated that Cas9/gRNA not only resulted in the knockout of Stra8 gene, but also suggested that the generation of SSCs was blocked by the Stra8 gene knockdown in vitro. Taken together, our results indicate that the CRISPR/Cas9 system could mediate stable Stra8 gene knockdown in domestic chicken's cells and inhibit ECSs differentiation into SSCs.

Retinoic acid promotes expression of germline-specific genes in chicken blastoderm cells by stimulating Smad1/5 phosphorylation in a feeder-free culture system

BACKGROUND

Producing transgenic chickens with chicken blastodermal cells (cBCs) is inefficient due to the extremely low germline transmission capacity of cBCs. As chicken primordial germ cells (PGCs) have been reported as an efficient method for producing transgenic chickens, the inefficiency of cBCs could potentially be resolved by inducing them to differentiate into germ cells. However, whether chemical inducers are able to enhance cBCs germline competence in vitro is unknown and the molecular mechanisms of differentiation of chicken pluripotent cells into germ cells are poorly understood.

RESULTS

We cultured cBCs with a monolayer morphology in E8 medium, a xeno- and feeder-free medium. We showed that retinoic acid (RA) treatment increased expression of germ cell-specific genes in cBCs. Using western blot, we determined that RA stimulated Smad1/5 phosphorylation. Moreover, Smad1/5 activation regulates the expression of germ cell-specific genes, as co-treatment with a Smad1/5 phosphorylation inhibitor or activator alters expression of these genes. We also demonstrate that Smad1/5 is required for RA-induced differentiation by RNA interference knockdown.

CONCLUSION

Our results demonstrated that E8 medium is able to maintain cBC growth for weeks and RA treatment induced germ cell differentiation of cBCs through the BMP-Smad1/5 signaling pathway.

Avian Biotechnology

Primordial germ cells (PGCs) generate new individuals through differentiation, maturation and fertilization. This means that the manipulation of PGCs is directly linked to the manipulation of individuals, making PGCs attractive target cells in the animal biotechnology field. A unique biological property of avian PGCs is that they circulate temporarily in the vasculature during early development, and this allows us to access and manipulate avian germ lines. Following the development of a technique for transplantation, PGCs have become central to avian biotechnology, in contrast to the use of embryo manipulation and subsequent transfer to foster mothers, as in mammalian biotechnology. Today, avian PGC transplantation combined with recent advanced manipulation techniques, including cell purification, cryopreservation, depletion, and long-term culture in vitro, have enabled the establishment of genetically modified poultry lines and ex-situ conservation of poultry genetic resources. This chapter introduces the principles, history, and procedures of producing avian germline chimeras by transplantation of PGCs, and the current status of avian germline modification as well as germplasm cryopreservation. Other fundamental avian reproductive technologies are described, including artificial insemination and embryo culture, and perspectives of industrial applications in agriculture and pharmacy are considered, including poultry productivity improvement, egg modification, disease resistance impairment and poultry gene "pharming" as well as gene banking.

Regulation of Zygotic Genome and Cellular Pluripotency

Events, manifesting transition from maternal to zygotic period of development are studied for more than 100 years, but underlying mechanisms are not yet clear. We provide a brief historical overview of development of concepts and explain the specific terminology used in the field. We further discuss differences and similarities between the zygotic genome activation and in vitro reprogramming process. Finally, we envision the future research directions within the field, where biochemical methods will play increasingly important role.

Derivation of Porcine Embryonic Stem-Like Cells from In Vitro-Produced Blastocyst-Stage Embryos

Efficient isolation of embryonic stem (ES) cells from pre-implantation porcine embryos has remained a challenge. Here, we describe the derivation of porcine embryonic stem-like cells (pESLCs) by seeding the isolated inner cell mass (ICM) from in vitro-produced porcine blastocyst into α-MEM with basic fibroblast growth factor (bFGF). The pESL cells kept the normal karyotype and displayed flatten clones, similar in phenotype to human embryonic stem cells (hES cells) and rodent epiblast stem cells. These cells exhibited alkaline phosphatase (AP) activity and expressed pluripotency markers such as OCT4, NANOG, SOX2, SSEA-4, TRA-1-60, and TRA-1-81 as determined by both immunofluorescence and RT-PCR. Additionally, these cells formed embryoid body (EB), teratomas and also differentiated into 3 germ layers in vitro and in vivo. Microarray analysis showed the expression of the pluripotency markers, PODXL, REX1, SOX2, KLF5 and NR6A1, was significantly higher compared with porcine embryonic fibroblasts (PEF), but expression of OCT4, TBX3, REX1, LIN28A and DPPA5, was lower compared to the whole blastocysts or ICM of blastocyst. Our results showed that porcine embryonic stem-like cells can be established from in vitro-produced blastocyst-stage embryos, which promote porcine naive ES cells to be established.

Evolution and functions of Oct4 homologs in non-mammalian vertebrates

PouV class transcription factor Oct4/Pou5f1 is a central regulator of indefinite pluripotency in mammalian embryonic stem cells (ESCs) but also participates in cell lineage specification in mouse embryos and in differentiating cell cultures. The molecular basis for this versatility, which is shared between Oct4 and its non-mammalian homologs Pou5f1 and Pou5f3, is not yet completely understood. Here, I review the current understanding of the evolution of PouV class transcription factors and discuss equivalent and diverse roles of Oct4 homologs in pluripotency, differentiation, and cell behavior in different vertebrate embryos. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

Mitochondrial Remodeling in Chicken Induced Pluripotent Stem-Like Cells

Chicken pluripotent stem cells (PSCs), such as embryonic stem cells and blastoderm cells, have been used to study development and differentiation in chicken. However, chicken PSCs are not widely used because they are hard to maintain in long-term culture. Recent reports suggest that chicken somatic cells can be reprogrammed to pluripotent state by defined factors to form induced pluripotent stem cells (iPSCs). These chicken iPSCs showed pluripotent differentiation potential and could be maintained in long-term culture. However, intracytoplasmic remodeling during reprogramming of chicken cells remains largely unknown. In this study, we generated chicken iPS-like cells (ciPSLCs) from chicken embryonic fibroblasts using a retroviral expression system encoding human reprogramming factors. These ciPSLCs could be maintained for more than 10 passages and expressed the endogenous chicken pluripotency markers, cNonog and cSox2. Moreover, the ciPSLCs showed higher nucleus to cytoplasm ratio and contained globular mitochondria with immature cristae. This morphology was similar to that of mammalian PSCs, but different from that of avian somatic cells, which showed lower nucleus to cytoplasm ratio and mature mitochondria. These results suggest that intracytoplasmic organelles in differentiated somatic cells could be successfully remodeled into the pluripotent state during reprogramming in chicken.

Zygotic Genome Activators, Developmental Timing, and Pluripotency

The transcription factors Pou5f1, Sox2, and Nanog are central regulators of pluripotency in mammalian ES and iPS cells. In vertebrate embryos, Pou5f1/3, SoxB1, and Nanog control zygotic genome activation and participate in lineage decisions. We review the current knowledge of the roles of these genes in developing vertebrate embryos from fish to mammals and suggest a model for pluripotency gene regulatory network functions in early development.

Chicken embryonic stem cells and primordial germ cells display different heterochromatic histone marks than their mammalian counterparts

Background

Chromatin epigenetics participate in control of gene expression during metazoan development. DNA methylation and post-translational modifications (PTMs) of histones have been extensively characterised in cell types present in, or derived from, mouse embryos. In embryonic stem cells (ESCs) derived from blastocysts, factors involved in deposition of epigenetic marks regulate properties related to self-renewal and pluripotency. In the germ lineage, changes in histone PTMs and DNA demethylation occur during formation of the primordial germ cells (PGCs) to reset the epigenome of the future gametes. Trimethylation of histone H3 on lysine 27 (H3K27me3) by Polycomb group proteins is involved in several epigenome-remodelling steps, but it remains unclear whether these epigenetic features are conserved in non-mammalian vertebrates. To investigate this question, we compared the abundance and nuclear distribution of the main histone PTMs, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in chicken ESCs, PGCs and blastodermal cells (BCs) with differentiated chicken ESCs and embryonic fibroblasts. In addition, we analysed the expression of chromatin modifier genes to better understand the establishment and dynamics of chromatin epigenetic profiles.

Results

The nuclear distributions of most PTMs and 5hmC in chicken stem cells were similar to what has been described for mammalian cells. However, unlike mouse pericentric heterochromatin (PCH), chicken ESC PCH contained high levels of trimethylated histone H3 on lysine 27 (H3K27me3). In differentiated chicken cells, PCH was less enriched in H3K27me3 relative to chromatin overall. In PGCs, the H3K27me3 global level was greatly reduced, whereas the H3K9me3 level was elevated. Most chromatin modifier genes known in mammals were expressed in chicken ESCs, PGCs and BCs. Genes presumably involved in de novo DNA methylation were very highly expressed. DNMT3B and HELLS/SMARCA6 were highly expressed in chicken ESCs, PGCs and BCs compared to differentiated chicken ESCs and embryonic fibroblasts, and DNMT3A was strongly expressed in ESCs, differentiated ESCs and BCs.

Conclusions

Chicken ESCs and PGCs differ from their mammalian counterparts with respect to H3K27 methylation. High enrichment of H3K27me3 at PCH is specific to pluripotent cells in chicken. Our results demonstrate that the dynamics in chromatin constitution described during mouse development is not universal to all vertebrate species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0056-6) contains supplementary material, which is available to authorized users.

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.

Chicken stem cell factor enhances primordial germ cell proliferation cooperatively with fibroblast growth factor 2

An in vitro culture system of chicken primordial germ cells (PGCs) has been recently developed, but the growth factor involved in the proliferation of PGCs is largely unknown. In the present study, we investigated the growth effects of chicken stem cell factor (chSCF) on the in vitro proliferation of chicken PGCs. We established two feeder cell lines (buffalo rat liver cells; BRL cells) that stably express the putative secreted form of chSCF (chSCF1-BRL) and membrane bound form of chSCF (chSCF2-BRL). Cultured PGC lines were incubated on chSCF1 or chSCF2-BRL feeder cells with fibroblast growth factor 2 (FGF2), and growth effects of each chSCF isoform were investigated. The in vitro proliferation rate of the PGCs cultured on chSCF2-BRL at 20 days of culture was more than threefold higher than those cultured on chSCF1-BRL cells and more than fivefold higher than those cultured on normal BRL cells. Thus, use of chSCF2-BRL feeder layer was effective for in vitro proliferation of chicken PGCs. However, the acceleration of PGC proliferation on chSCF2-BRL was not observed without FGF2, suggesting that chSCF2 would act as a proliferation co-factor of FGF2. We transferred the PGCs cultured on chSCF2-BRL cells to recipient embryos, generated germline chimeric chickens and assessed the germline competency of cultured PGCs by progeny test. Donor-derived progenies were obtained, and the frequency of germline transmission was 3.39%. The results of this study demonstrate that chSCF2 induces hyperproliferation of chicken PGCs retaining germline competency in vitro in cooperation with FGF2.