Pluripotent genes in avian stem cells

Influence and Optimization of Diverse Culture Systems on Chicken Embryonic Stem Cell Culture

BACKGROUND

The importance of embryonic stem cells (ESCs) in chickens is undeniable, as they can be applied across various fields, including animal modeling, developmental biology, cell fate research, drug screening, toxicity testing, and gene function studies. However, a widely applicable culture system for chicken ESCs has yet to be developed.

OBJECTIVES

This study aimed to investigate the effects of different culture systems on the derivation and maintenance of chicken ESCs, with a focus on optimizing the selected culture conditions.

METHODS

To achieve this, we tested the effectiveness of various species-specific ESC media in the derivation and culture of chicken PGCs, while incorporating different small molecule compounds to optimize the process. The pluripotency and differentiation potential of the resulting ESC-like cells were also evaluated.

RESULTS

The combination of PD0325901, SB431542, and LIF (R2i+LIF system) was found to be effective in generating chicken ESC-like clones. Further experiments showed that enhancing the R2i+LIF system with cytokines such as SCF and FGF2 significantly extended the culture period and increased the passage number of chicken ESC-like cells. These ESC-like cells were characterized through positive alkaline phosphatase staining and the expression of pluripotency markers POUV, NANOG, and SOX2. Additionally, differentiation assays confirmed their ability to form the three germ layers.

CONCLUSIONS

The newly developed culture system provides suitable conditions for the short-term culture of chicken ESCs. However, further optimization is required to establish a system that can sustain long-term maintenance.

Avian iPSC Derivation to Recover Threatened Wild Species: A Comprehensive Review in Light of Well-Established Protocols

Induced pluripotent stem cells (iPSCs) were first generated by Yamanaka in 2006, revolutionizing research by overcoming limitations imposed by the use of embryonic stem cells. In terms of the conservation of endangered species, iPSC technology presents itself as a viable alternative for the manipulation of target genetics without compromising specimens. Although iPSCs have been successfully generated for various species, their application in nonmammalian species, particularly avian species, requires further in-depth investigation to cover the diversity of wild species at risk and their different protocol requirements. This study aims to provide an overview of the workflow for iPSC induction, comparing well-established protocols in humans and mice with the limited information available for avian species. Here, we discuss the somatic cell sources to be reprogrammed, genetic factors, delivery methods, enhancers, a brief history of achievements in avian iPSC derivation, the main approaches for iPSC characterization, and the future perspectives and challenges for the field. By examining the current protocols and state-of-the-art techniques employed in iPSC generation, we seek to contribute to the development of efficient and species-specific iPSC methodologies for at-risk avian species. The advancement of iPSC technology holds great promise for achieving in vitro germline competency and, consequently, addressing reproductive challenges in endangered species, providing valuable tools for basic research, bird genetic preservation and rescue, and the establishment of cryobanks for future conservation efforts.

Comparison of the biological and functional characteristics of mesenchymal stem cells from intrahepatic and identical bone marrow

In our privious work, our reseach group characterized a population of hepatic-sourced mesenchymal stem cells (MSCs) called MLpvNG2⁺ cells. In the present study, we compared the biological and functional characteristics of naïve MLpvNG2 cells with identical bone marrow-derived MSCs (niBM-MSCs) using in vitro (conditioned media) and in vivo (a well-set diethylnitrosamine (DEN)-induced liver fibrotic/cirrhotic murine model) procedures. The intrahepatic-sourced mesodermal MLpvNG2⁺ cells exhibited some biological characteristics (e.g., a set of surface markers) similar to those of extrahepatic niBM-MSCs. In responsed to signals of pathological conditions, such as singals of fibrotic/cirrhotic liver, MLpvNG2⁺ cells showed higher survival and favored differentiation into ALB(+) and G6Pc(+) hepatocytes, whereas niBM-MSCs predominantly differentiated into CK/KRT19(+) cholangiocytes. We identified C/EBPα/β expression as a biological characteristic differentiating these two populations of MSCs, wherein MLpvNG2⁺ cells are likely regulated by C/EBPβ transcriptional signaling, whereas niBM-MSCs are likely controlled by C/EBPα transcriptional signaling. Notably, although C/EBPα and C/EBPβ transcriptional signaling regulate hepatocyte and cholangiocyte fate, respectively, the expression of these proteins in MLpvNG2⁺ cells is, to our knowledge, reported for the first time in the present study. We used anti-C/EBP neutralizing antibodies (Abs) both in vitro and in vivo to determine the functional characteristics of these proteins. We conclude that the biological characteristics of these two populations of MSCs depend on their differential C/EBPα/β expression patterns.

Characterisation of the developing heart in a pressure overloaded model utilising RNA sequencing to direct functional analysis

Cardiogenesis is influenced by both environmental and genetic factors, with blood flow playing a critical role in cardiac remodelling. Perturbation of any of these factors could lead to abnormal heart development and hence the formation of congenital heart defects. Although abnormal blood flow has been associated with a number of heart defects, the effects of abnormal pressure load on the developing heart gene expression profile have to date not clearly been defined. To determine the heart transcriptional response to haemodynamic alteration during development, outflow tract (OFT) banding was employed in the chick embryo at Hamburger and Hamilton stage (HH) 21. Stereological and expression studies, including the use of global expression analysis by RNA sequencing with an optimised procedure for effective globin depletion, were subsequently performed on HH29 OFT-banded hearts and compared with sham control hearts, with further targeted expression investigations at HH35. The OFT-banded hearts were found to have an abnormal morphology with a rounded appearance and left-sided dilation in comparison with controls. Internal analysis showed they typically had a ventricular septal defect and reductions in the myocardial wall and trabeculae, with an increase in the lumen on the left side of the heart. There was also a significant reduction in apoptosis. The differentially expressed genes were found to be predominately involved in contraction, metabolism, apoptosis and neural development, suggesting a cardioprotective mechanism had been induced. Therefore, altered haemodynamics during development leads to left-sided dilation and differential expression of genes that may be associated with stress and maintaining cardiac output.

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

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.

Stem cells: their source, potency and use in regenerative therapies with focus on adipose-derived stem cells - a review

Stem cells can be defined as units of biological organization that are responsible for the development and the regeneration of organ and tissue systems. They are able to renew their populations and to differentiate into multiple cell lineages. Therefore, these cells have great potential in advanced tissue engineering and cell therapies. When seeded on synthetic or nature-derived scaffolds in vitro, stem cells can be differentiated towards the desired phenotype by an appropriate composition, by an appropriate architecture, and by appropriate physicochemical and mechanical properties of the scaffolds, particularly if the scaffold properties are combined with a suitable composition of cell culture media, and with suitable mechanical, electrical or magnetic stimulation. For cell therapy, stem cells can be injected directly into damaged tissues and organs in vivo. Since the regenerative effect of stem cells is based mainly on the autocrine production of growth factors, immunomodulators and other bioactive molecules stored in extracellular vesicles, these structures can be isolated and used instead of cells for a novel therapeutic approach called "stem cell-based cell-free therapy". There are four main sources of stem cells, i.e. embryonic tissues, fetal tissues, adult tissues and differentiated somatic cells after they have been genetically reprogrammed, which are referred to as induced pluripotent stem cells (iPSCs). Although adult stem cells have lower potency than the other three stem cell types, i.e. they are capable of differentiating into only a limited quantity of specific cell types, these cells are able to overcome the ethical and legal issues accompanying the application of embryonic and fetal stem cells and the mutational effects associated with iPSCs. Moreover, adult stem cells can be used in autogenous form. These cells are present in practically all tissues in the organism. However, adipose tissue seems to be the most advantageous tissue from which to isolate them, because of its abundancy, its subcutaneous location, and the need for less invasive techniques. Adipose tissue-derived stem cells (ASCs) are therefore considered highly promising in present-day regenerative medicine.

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.

Systematic analysis of transcription start sites in avian development

Cap Analysis of Gene Expression (CAGE) in combination with single-molecule sequencing technology allows precision mapping of transcription start sites (TSSs) and genome-wide capture of promoter activities in differentiated and steady state cell populations. Much less is known about whether TSS profiling can characterize diverse and non-steady state cell populations, such as the approximately 400 transitory and heterogeneous cell types that arise during ontogeny of vertebrate animals. To gain such insight, we used the chick model and performed CAGE-based TSS analysis on embryonic samples covering the full 3-week developmental period. In total, 31,863 robust TSS peaks (>1 tag per million [TPM]) were mapped to the latest chicken genome assembly, of which 34% to 46% were active in any given developmental stage. ZENBU, a web-based, open-source platform, was used for interactive data exploration. TSSs of genes critical for lineage differentiation could be precisely mapped and their activities tracked throughout development, suggesting that non-steady state and heterogeneous cell populations are amenable to CAGE-based transcriptional analysis. Our study also uncovered a large set of extremely stable housekeeping TSSs and many novel stage-specific ones. We furthermore demonstrated that TSS mapping could expedite motif-based promoter analysis for regulatory modules associated with stage-specific and housekeeping genes. Finally, using Brachyury as an example, we provide evidence that precise TSS mapping in combination with Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)-on technology enables us, for the first time, to efficiently target endogenous avian genes for transcriptional activation. Taken together, our results represent the first report of genome-wide TSS mapping in birds and the first systematic developmental TSS analysis in any amniote species (birds and mammals). By facilitating promoter-based molecular analysis and genetic manipulation, our work also underscores the value of avian models in unravelling the complex regulatory mechanism of cell lineage specification during amniote development.

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.

Characterization of the finch embryo supports evolutionary conservation of the naive stage of development in amniotes

Innate pluripotency of mouse embryos transits from naive to primed state as the inner cell mass differentiates into epiblast. In vitro, their counterparts are embryonic (ESCs) and epiblast stem cells (EpiSCs), respectively. Activation of the FGF signaling cascade results in mouse ESCs differentiating into mEpiSCs, indicative of its requirement in the shift between these states. However, only mouse ESCs correspond to the naive state; ESCs from other mammals and from chick show primed state characteristics. Thus, the significance of the naive state is unclear. In this study, we use zebra finch as a model for comparative ESC studies. The finch blastoderm has mESC-like properties, while chick blastoderm exhibits EpiSC features. In the absence of FGF signaling, finch cells retained expression of pluripotent markers, which were lost in cells from chick or aged finch epiblasts. Our data suggest that the naive state of pluripotency is evolutionarily conserved among amniotes.

Germline Modification and Engineering in Avian Species

Production of genome-edited animals using germline-competent cells and genetic modification tools has provided opportunities for investigation of biological mechanisms in various organisms. The recently reported programmed genome editing technology that can induce gene modification at a target locus in an efficient and precise manner facilitates establishment of animal models. In this regard, the demand for genome-edited avian species, which are some of the most suitable model animals due to their unique embryonic development, has also increased. Furthermore, germline chimera production through long-term culture of chicken primordial germ cells (PGCs) has facilitated research on production of genome-edited chickens. Thus, use of avian germline modification is promising for development of novel avian models for research of disease control and various biological mechanisms. Here, we discuss recent progress in genome modification technology in avian species and its applications and future strategies.

Reprogramming of the chick retinal pigmented epithelium after retinal injury

Background

One of the promises in regenerative medicine is to regenerate or replace damaged tissues. The embryonic chick can regenerate its retina by transdifferentiation of the retinal pigmented epithelium (RPE) and by activation of stem/progenitor cells present in the ciliary margin. These two ways of regeneration occur concomitantly when an external source of fibroblast growth factor 2 (FGF2) is present after injury (retinectomy). During the process of transdifferentiation, the RPE loses its pigmentation and is reprogrammed to become neuroepithelium, which differentiates to reconstitute the different cell types of the neural retina. Somatic mammalian cells can be reprogrammed to become induced pluripotent stem cells by ectopic expression of pluripotency-inducing factors such as Oct4, Sox2, Klf4, c-Myc and in some cases Nanog and Lin-28. However, there is limited information concerning the expression of these factors during natural regenerative processes. Organisms that are able to regenerate their organs could share similar mechanisms and factors with the reprogramming process of somatic cells. Herein, we investigate the expression of pluripotency-inducing factors in the RPE after retinectomy (injury) and during transdifferentiation in the presence of FGF2.

Results

We present evidence that upon injury, the quiescent (p27^Kip1+/BrdU-) RPE cells transiently dedifferentiate and express sox2, c-myc and klf4 along with eye field transcriptional factors and display a differential up-regulation of alternative splice variants of pax6. However, this transient process of dedifferentiation is not sustained unless FGF2 is present. We have identified lin-28 as a downstream target of FGF2 during the process of retina regeneration. Moreover, we show that overexpression of lin-28 after retinectomy was sufficient to induce transdifferentiation of the RPE in the absence of FGF2.

Conclusion

These findings delineate in detail the molecular changes that take place in the RPE during the process of transdifferentiation in the embryonic chick, and specifically identify Lin-28 as an important factor in this process. We propose a novel model in which injury signals initiate RPE dedifferentiation, while FGF2 up-regulates Lin-28, allowing for RPE transdifferentiation to proceed.