Bovine ICM derived cells express the Oct4 ortholog

Bovine Pluripotent Stem Cells: Current Status and Prospects

Pluripotent stem cells (PSCs) can differentiate into three germ layers and diverse autologous cell lines. Since cattle are the most commonly used large domesticated animals, an important food source, and bioreactors, great efforts have been made to establish bovine PSCs (bPSCs). bPSCs have great potential in bovine breeding and reproduction, modeling in vitro differentiation, imitating cancer development, and modeling diseases. Currently, bPSCs mainly include bovine embryonic stem cells (bESCs), bovine induced pluripotent stem cells (biPSCs), and bovine expanded potential stem cells (bEPSCs). Establishing stable bPSCs in vitro is a critical scientific challenge, and researchers have made numerous efforts to this end. In this review, the category of PSC pluripotency; the establishment of bESCs, biPSCs, and bEPSCs and its challenges; and the application outlook of bPSCs are discussed, aiming to provide references for future research.

Perspectives in Genome-Editing Techniques for Livestock

Genome editing of farm animals has undeniable practical applications. It helps to improve production traits, enhances the economic value of livestock, and increases disease resistance. Gene-modified animals are also used for biomedical research and drug production and demonstrate the potential to be used as xenograft donors for humans. The recent discovery of site-specific nucleases that allow precision genome editing of a single-cell embryo (or embryonic stem cells) and the development of new embryological delivery manipulations have revolutionized the transgenesis field. These relatively new approaches have already proven to be efficient and reliable for genome engineering and have wide potential for use in agriculture. A number of advanced methodologies have been tested in laboratory models and might be considered for application in livestock animals. At the same time, these methods must meet the requirements of safety, efficiency and availability of their application for a wide range of farm animals. This review aims at covering a brief history of livestock animal genome engineering and outlines possible future directions to design optimal and cost-effective tools for transgenesis in farm species.

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

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

Relative abundance of pluripotency-associated candidate genes in immature oocytes and in vitro-produced buffalo embryos (Bubalus bubalis)

The present study was undertaken to analyze the relative abundance (RA) of pluripotency-associated genes (NANOG, OCT4, SOX2, c-MYC, and FOXD3) in different grades of immature oocytes and various stages of in vitro-produced buffalo embryos using RT-qPCR. Results showed that the RA of NANOG, OCT4, and FOXD3 transcripts was significantly higher (P < 0.05) in A grade oocytes compared with the other grades of oocytes. The RA of the c-MYC transcript was significantly higher (P < 0.05) in A grade compared with the C and D grades of oocytes, but the values did not differ significantly from the B grade of oocytes. The RA of the SOX2 transcript was almost similar in all grades of the oocytes. The expression levels of NANOG (P > 0.05), OCT4 (P > 0.05), c-MYC (P > 0.05) and SOX2 (P < 0.05) were higher in the blastocysts compared with the other stages of the embryos. Markedly, FOXD3 expression was significantly higher (P < 0.05) in 8-16-cell embryos compared with the 2-cell and 4-cell embryos and blastocyst, but did not differ significantly from the morula stage of the embryos. In the study, the majority of pluripotency-associated genes showed higher expression in A grade immature oocytes. Therefore, it is concluded that the A grade oocytes appeared to be more developmental competent and are suitable candidates for nuclear cloning research in buffalo. In buffalo, NANOG, OCT4, SOX2, and c-MYC are highly expressed in blastocysts compared with the other stages of embryos.

Perspectives of pluripotent stem cells in livestock

The recent progress in derivation of pluripotent stem cells (PSCs) from farm animals opens new approaches not only for reproduction, genetic engineering, treatment and conservation of these species, but also for screening novel drugs for their efficacy and toxicity, and modelling of human diseases. Initial attempts to derive PSCs from the inner cell mass of blastocyst stages in farm animals were largely unsuccessful as either the cells survived for only a few passages, or lost their cellular potency; indicating that the protocols which allowed the derivation of murine or human embryonic stem (ES) cells were not sufficient to support the maintenance of ES cells from farm animals. This scenario changed by the innovation of induced pluripotency and by the development of the 3 inhibitor culture conditions to support naïve pluripotency in ES cells from livestock species. However, the long-term culture of livestock PSCs while maintaining the full pluripotency is still challenging, and requires further refinements. Here, we review the current achievements in the derivation of PSCs from farm animals, and discuss the potential application areas.

Livestock pluripotency is finally captured in vitro

Pluripotent stem cells (PSCs) have demonstrated great utility in improving our understanding of mammalian development and continue to revolutionise regenerative medicine. Thanks to the improved understanding of pluripotency in mice and humans, it has recently become feasible to generate stable livestock PSCs. Although it is unlikely that livestock PSCs will be used for similar applications as their murine and human counterparts, new exciting applications that could greatly advance animal agriculture are being developed, including the use of PSCs for complex genome editing, cellular agriculture, gamete generation and invitro breeding schemes.

Characterization of mesenchymal stem cells derived from adipose tissue of a cougar (Puma concolor)

Adipose derived mesenchymal stem cells (AMSCs) have been isolated from domestic and wild cats. For wild cats, the isolation of AMSCs has been reported in the black-footed cats (Felis nigripes) and guigna (Leopardus guigna). Stromal vascular fraction (SVF) isolated from cougar adipose tissue have been used to restore elbow functionality in the cougar (Puma concolor) but multipotent characteristics of these cells have not been described. The present study describes for the first time the isolation and characterization of mesenchymal stem cells derived from adipose tissue of cougar. AMSCs and fibroblasts from six months female cougar were isolated and cultured in DMEM/F12, supplemented with FBS 10% + 1% Antibiotic/Antifungal + 2.4 mM L-Glutamine + 2.4 mM pyruvate up to passage 5. Expression of pluripotent and surface marker genes was evaluated at mRNA level. Mesodermal differentiation (adipogenic, osteogenic and chondrogenic) was described. AMSCs expressed mRNA of pluripotent genes Oct4, Nanog, Sox2 and Klf4 and surface markers Cd44, Cd90, Cd105 and MHCII. Fibroblasts showed similar mRNA expression with the exception of Sox2. AMSCs obtained from cougar exhibit multipotency features similar to domestic cats MSC, nevertheless, other analyses are required. AMSCs from cougar could be a source of interest for treatment of individuals that remain in captivity or arrive to wildlife rehabilitation centers.

Bone morphogenetic protein 4 and retinoic acid trigger bovine VASA homolog expression in differentiating bovine induced pluripotent stem cells

Primordial germ cells (PGCs) are the earliest identifiable and completely committed progenitors of female and male gametes. They are obvious targets for genome editing because they assure the transmission of desirable or introduced traits to future generations. PGCs are established at the earliest stages of embryo development and are difficult to propagate in vitro--two characteristics that pose a problem for their practical application. One alternative method to enrich for PGCs in vitro is to differentiate them from pluripotent stem cells derived from adult tissues. Here, we establish a reporter system for germ cell identification in bovine pluripotent stem cells based on green fluorescent protein expression driven by the minimal essential promoter of the bovine Vasa homolog (BVH) gene, whose regulatory elements were identified by orthologous modelling of regulatory units. We then evaluated the potential of bovine induced pluripotent stem cell (biPSC) lines carrying the reporter construct to differentiate toward the germ cell lineage. Our results showed that biPSCs undergo differentiation as embryoid bodies, and a fraction of the differentiating cells expressed BVH. The rate of differentiation towards BVH-positive cells increased up to tenfold in the presence of bone morphogenetic protein 4 or retinoic acid. Finally, we determined that the expression of key PGC genes, such as BVH or SOX2, can be modified by pre-differentiation cell culture conditions, although this increase is not necessarily mirrored by an increase in the rate of differentiation.

Development, Characterization, and Pluripotency Analysis of Buffalo (Bubalus bubalis) Embryonic Stem Cell Lines Derived from In Vitro-Fertilized, Hand-Guided Cloned, and Parthenogenetic Embryos

We present the derivation, characterization, and pluripotency analysis of three buffalo embryonic stem cell (buESC) lines, from in vitro-fertilized, somatic cell nuclear-transferred, and parthenogenetic blastocysts. These cell lines were developed for later differentiation into germ lineage cells and elucidation of the signaling pathways involved. The cell lines were established from inner cell masses (ICMs) that were isolated manually from the in vitro-produced blastocysts. Most of the ICMs (45-55%) resulted in formation of primary colonies that were subcultured after 8-10 days, leading subsequently to the formation of three buESC lines, one from each blastocyst type. All the cell lines expressed stem cell markers, such as Alkaline Phosphatase, OCT4, NANOG, SSEA1, SSEA4, TRA-1-60, TRA-1-81, SOX2, REX1, CD-90, STAT3, and TELOMERASE. They differentiated into all three germ layers as determined by ectodermal, mesodermal, and endodermal RNA and protein markers. All of the cell lines showed equal expression of pluripotency markers as well as equivalent differentiation potential into all the three germ layers. The static suspension culture-derived embryoid bodies (EBs) showed greater expression of all the three germ layer markers as compared to hanging drop culture-derived EBs. When analyzed for germ layer marker expression, EBs derived from 15% fetal bovine serum (FBS)-based spontaneous differentiation medium showed greater differentiation across all the three germ layers as compared to those derived from Knock-Out Serum Replacement (KoSR)-based differentiation medium.

Extended in vitro maturation affects gene expression and DNA methylation in bovine oocytes

To mimic post-ovulatory ageing, we have extended the in vitro maturation (IVM) phase to 48 h and examined effects on (i) developmental potential, (ii) expression of a panel of developmentally important genes and (iii) gene-specific epigenetic marks. Results were compared with the 24 h IVM protocol (control) usually employed for bovine oocytes. Cleavage rates and blastocyst yields were significantly reduced in oocytes after extended IVM. No significant differences were observed in the methylation of entire alleles in oocytes for the genes bH19, bSNRPN, bZAR1, bOct4 and bDNMT3A. However, we found differentially methylated CpG sites in the bDNMT3Ls locus in oocytes after extended IVM and in embryos derived from them compared with controls. Moreover, embryos derived from the 48 h matured oocyte group were significantly less methylated at CpG5 and CpG7 compared with the 24 h group. CpG7 was significantly hypermethylated in embryos produced from the control oocytes, but not in oocytes matured for 48 h. Furthermore, methylation for CpG5-CpG8 of bDNMT3Ls was significantly lower in oocytes of the 24 h group compared with embryos derived therefrom, whereas no such difference was found for oocytes and embryos of the in vitro aged group. Expression of most of the selected genes was not affected by duration of IVM. However, transcript abundance for the imprinted gene bIGF2R was significantly reduced in oocytes analyzed after extended IVM compared with control oocytes. Transcript levels for bPRDX1, bDNMT3A and bBCLXL were significantly reduced in 4- to 8-cell embryos derived from in vitro aged oocytes. These results indicate that extended IVM leads to ageing-like alterations and demonstrate that epigenetic mechanisms are critically involved in ageing of bovine oocytes, which warrants further studies into epigenetic mechanisms involved in ageing of female germ cells, including humans.

In vitro culture of stem-like cells derived from somatic cell nuclear transfer bovine embryos of the Korean beef cattle species, HanWoo

We established and maintained somatic cell nuclear transfer embryo-derived stem-like cells (SCNT-eSLCs) from the traditional Korean beef cattle species, HanWoo (Bos taurus coreanae). Each SCNT blastocyst was placed individually on a feeder layer with culture medium containing three inhibitors of differentiation (3i). Primary colonies formed after 2-3 days of culture and the intact colonies were passaged every 5-6 days. The cells in each colony showed embryonic stem cell-like morphologies with a distinct boundary and were positive to alkaline phosphatase staining. Immunofluorescence and reverse transcription-polymerase chain reaction analyses also confirmed that these colonies expressed pluripotent markers. The colonies were maintained over 50 passages for more than 270 days. The cells showed normal karyotypes consisting of 60 chromosomes at Passage 50. Embryoid bodies were formed by suspension culture to analyse in vitro differentiation capability. Marker genes representing the differentiation into three germ layers were expressed. Typical embryonal carcinoma was generated after injecting cells under the testis capsule of nude mice, suggesting that the cultured cells may also have the potential of in vivo differentiation. In conclusion, we generated eSLCs from SCNT bovine embryos, using a 3i system that sustained stemness, normal karyotype and pluripotency, which was confirmed by in vitro and in vivo differentiation.

Strategies for the derivation of pluripotent cells from farm animals

Recent experiments demonstrated that forced expression of few critical genes drives conversion of a somatic into a pluripotent cell state. These induced pluripotent cells (iPS) were first generated from murine fibroblasts by Shinya Yamanaka's laboratory in 2006. By using retroviral vectors to express combinations of stemness genes, they identified Oct4, Sox2, Krueppel-like factor 4 and c-Myc as essential factors for reprogramming of somatic cells. Subsequent experiments applied this technology to human and rat fibroblasts, as well as other cell types and several groups showed that iPS can be generated by an even smaller number of transcription factors. The efficiency of conversion and maintenance of a pluripotent state can be supported by small molecules, such as valproic acid and specific pharmacological inhibitors. This technology is a milestone for a basic understanding of cell potency, cell fate and pathogenesis, as well as for development of cell therapies and potential applications in animal breeding.

Pluripotent cells in farm animals: state of the art and future perspectives

Pluripotent cells, such as embryonic stem (ES) cells, embryonic germ cells and embryonic carcinoma cells are a unique type of cell because they remain undifferentiated indefinitely in in vitro culture, show self-renewal and possess the ability to differentiate into derivatives of the three germ layers. These capabilities make them a unique in vitro model for studying development, differentiation and for targeted modification of the genome. True pluripotent ESCs have only been described in the laboratory mouse and rat. However, rodent physiology and anatomy differ substantially from that of humans, detracting from the value of the rodent model for studies of human diseases and the development of cellular therapies in regenerative medicine. Recently, progress in the isolation of pluripotent cells in farm animals has been made and new technologies for reprogramming of somatic cells into a pluripotent state have been developed. Prior to clinical application of therapeutic cells differentiated from pluripotent stem cells in human patients, their survival and the absence of tumourigenic potential must be assessed in suitable preclinical large animal models. The establishment of pluripotent cell lines in farm animals may provide new opportunities for the production of transgenic animals, would facilitate development and validation of large animal models for evaluating ESC-based therapies and would thus contribute to the improvement of human and animal health. This review summarises the recent progress in the derivation of pluripotent and reprogrammed cells from farm animals. We refer to our recent review on this area, to which this article is complementary.

Selection of appropriate isolation method based on morphology of blastocyst for efficient derivation of buffalo embryonic stem cells

The efficiency of embryonic stem cell (ESC) derivation from all species except for rodents and primates is very low. There are however, multiple interests in obtaining pluripotent cells from these animals with main expectations in the fields of transgenesis, cloning, regenerative medicine and tissue engineering. Researches are being carried out in laboratories throughout the world to increase the efficiency of ESC isolation for their downstream applications. Thus, the present study was undertaken to study the effect of different isolation methods based on the morphology of blastocyst for efficient derivation of buffalo ESCs. Embryos were produced in vitro through the procedures of maturation, fertilization and culture. Hatched blastocysts or isolated inner cell masses (ICMs) were seeded on mitomycin-C inactivated buffalo fetal fibroblast monolayer for the development of ESC colonies. The ESCs were analyzed for alkaline phosphatase activity, expression of pluripotency markers and karyotypic stability. Primary ESC colonies were obtained after 2-5 days of seeding hatched blastocysts or isolated ICMs on mitomycin-C inactivated feeder layer. Mechanically isolated ICMs attached and formed primary cell colonies more efficiently than ICMs isolated enzymatically. For derivation of ESCs from poorly defined ICMs intact hatched blastocyst culture was the most successful method. Results of this study implied that although ESCs can be obtained using all three methods used in this study, efficiency varies depending upon the morphology of blastocyst and isolation method used. So, appropriate isolation method must be selected depending on the quality of blastocyst for efficient derivation of ESCs.

Regulatory microRNA network identification in bovine blastocyst development

Mammalian blastocyst formation is characterized by two lineage segregations resulting in the formation of the trophectoderm, the hypoblast, and the epiblast cell lineages. Cell fate determination during these early lineage segregations is associated with changes in the expression of specific transcription factors. In addition to the transcription factor-based control, it has become clear that also microRNAs (miRNAs) play an important role in the post-transcriptional regulation of pluripotency and differentiation. To elucidate the role of miRNAs in early lineage segregation, we compared the miRNA expression in early bovine blastocysts with the more advanced stage of hatched blastocysts. Reverse transcription-quantitative PCR-based miRNA expression profiling revealed eight upregulated miRNAs (miR-127, miR-130a, miR-155, miR-196a, miR-203, miR-28, miR-29c, and miR-376a) and four downregulated miRNAs (miR-135a, miR-218, miR-335, and miR-449b) in hatched blastocysts. Through an integrative analysis of matching miRNA and mRNA expression data, candidate miRNA-mRNA interaction pairs were prioritized for validation. Using an in vitro luciferase reporter assay, we confirmed a direct interaction between miR-218 and CDH2, miR-218 and NANOG, and miR-449b and NOTCH1. By interfering with the FGF signaling pathway, we found functional evidence that miR-218, mainly expressed in the inner cell mass, regulates the NANOG expression in the bovine blastocyst in response to FGF signaling. The results of this study expand our knowledge about the miRNA signature of the bovine blastocyst and of the interactions between miRNAs and cell fate regulating transcription factors.

Monitoring bovine fetal fibroblast reprogramming utilizing a bovine NANOG promoter-driven EGFP reporter system

NANOG is an essential transcription factor involved in the proliferation and maintenance of embryonic stem cells (ESC) and reprogramming of somatic cells to a pluripotent state. Oct4 and Nanog promoter-driven enhanced green fluorescent protein (EGFP) reporters have been employed for establishing lines of induced pluripotent stem cells (iPSC) from mouse, human, and pig. In ruminants, including cattle, in which no fully validated ESC lines have been established, iPSC generated by reprogramming somatic cells to an ESC-like state may prove useful in the production of genetically modified livestock. In this study, utility of the bovine NANOG reporter was tested for use with cattle. Seven proximal bovine NANOG promoter fragments of different size were fused to the LUC gene, and were tested in mouse ESC lines using a dual-luciferase assay. Three of the bovine NANOG promoters, 315 bp (-134/+181), 446 bp (-265/+181), and 1,100 bp (-919/+181), were fused to a nuclear localized signal EGFP reporter gene. The fidelity of these constructs was analyzed by transfection into mouse ESC and bovine fetal fibroblasts (bFFs), and subsequent reprogramming of the bFF. Fusion of the transgenic bFF with human teratocarcinoma (NTERA2) cells induced nuclear expression of the EGFP reporter. Similarly, bFF-derived somatic cell nuclear transfer (SCNT) embryos expressed EGFP in a stage- and location-appropriate manner. Following reprogramming of transgenic bFFs for 10 days with an Oct4-Sox2-Klf4-cMyc vector, iPSC expressed EGFP and alkaline phosphatase. These results indicate that NANOG reporters can be used to monitor nuclear reprogramming of bFFs and to distinguish cell allocation in SCNT-derived embryos.

Twenty years of embryonic stem cell research in farm animals

Notable distinctions between an embryonic stem cell (ESC) and somatic cell are that an ESC can maintain an undifferentiated state indefinitely, self-renew, and is pluripotent, meaning that the ESC can potentially generate cells representing all the three primordial germ layers and contribute to the terminally differentiated cells of a conceptus. These attributes make the ESC an ideal source for genome editing for both agricultural and biomedical applications. Although, ESC lines have been successfully established from rodents and primates, authentic ungulate stem cell lines on the contrary are still not available. Outstanding issues including but not limited to differences in pluripotency characteristics among the existing ESC lines, pre-implantation embryo development, pluripotency pathways, and culture conditions plague our efforts to establish authentic ESC lines from farm animals. In this review, we highlight some of these issues and discuss how the recent derivation of induced pluripotent stem cells (iPSCs) might augur the establishment of robust authentic ESC lines from farm animals.

Pluripotency network in porcine embryos and derived cell lines

Huge amounts of work have been dedicated to the establishment of embryonic stem cell lines from farm animal species since the successful isolation of embryonic stem cells from the mouse and from the human. However, no conclusive results have been obtained so far, and validated lines have yet to be established in domestic animals. Many limiting factors have been suggested and need to be studied further to isolate truly pluripotent cell lines from livestock. In this review, we will discuss the difficulties in deriving and maintaining embryonic stem cell lines from farm animal embryos and how can this lack of success be explained. We will summarize results obtained in our laboratory regarding derivation of pluripotent cells in the pigs. Problems related to the identification of standard methods for derivation, maintenance and characterization of cell lines will also be examined. We will focus our attention on the need for appropriate stemness-related marker molecules that can be used to reliably investigate pluripotency in domestic species. Finally, we will review data presently available on functional key pluripotency-maintaining pathways in farm animals.

Ectopic expression of human telomerase RNA component results in increased telomerase activity and elongated telomeres in bovine blastocysts

Telomeres play an important role in aging, and are critical for the regenerative capacity of mammalian cells. The holoenzyme telomerase rebuilds telomeres and is composed of two components, the catalytic protein telomerase reverse transcriptase (TERT) and the telomerase RNA (TERC). TERC is ubiquitously expressed in somatic cells and is thought to have no regulatory effects on telomerase activity. Transgenic expression of human TERT (hTERT) in bovine somatic and embryonic cells extends telomere length and enhances telomerase activity. To obtain further insight into the regulatory capacity of the two telomerase components, we have studied the ability of hTERC and hTERT to increase telomerase activity and telomere length in bovine embryos. Expression plasmids for the human RNA component (hTERC) and/or the catalytic subunit of human telomerase (hTERT), respectively, were injected into the cytoplasm of in vitro-produced bovine zygotes. Ectopic expression of hTERC increased telomerase activity and telomere length in bovine blastocysts. Coexpression of hTERT and hTERC did not result in further telomere elongation when compared to the hTERC group. These data indicate that TERC is one of the limiting factors of telomerase activity in bovine blastocysts, and further establish bovine preimplantation embryos as a useful model to modulate telomere length with impact for basic embryology and derivation of pluripotent cells.

Culture, characterization and differentiation of cells from buffalo (Bubalus bubalis) amnion

Stem cells present an important tool in livestock assisted reproduction and veterinary therapeutic field such as tissue engineering. We report for the first time isolation of pluripotent stem cell-like cells expressing pluripotency markers (alkaline phospahatase, OCT-4, NANOG and SOX-2) from the amnion of water buffalo (Bubalus bubalis). The cells showed no apparent abnormalities in their chromosomal profiles before and after cryopreservation. The cytochemical staining revealed that pluripotent cells were capable of undergoing directed differentiation in vitro into osteocytes. It could be inferred that amnion-derived pluripotent stem cell-like cells can be isolated, cultured for many passages and differentiated into mesoderm lineage, and may be an alternative source to mesenchymal stem cells. These cells can have applications in assisted reproduction, developmental biological and regenerative medicine.

Equivalency of buffalo (Bubalus bubalis) embryonic stem cells derived from fertilized, parthenogenetic, and hand-made cloned embryos

This study was aimed at establishing buffalo embryonic stem cells (ESCs) from in vitro fertilized (IVF), parthenogenetic, and hand-made cloned (HMC) embryos and to check their equivalency in terms of stem cell marker expression, longevity, proliferation, and differentiation pattern. ESCs derived from all three sources were found by immunofluorescence to express the pluripotency markers SSEA-4, TRA-1-60, TRA-1-81, OCT4, and SOX2 and were able to form embryoid bodies containing cells expressing genes specific to endoderm (AFP, HNF4, and GATA4), mesoderm (MSX1, BMP4, and ASA), and ectoderm (cytokeratin 8 and NF68). Reverse transcriptase PCR (RT-PCR) showed cells from all sources to be positive for pluripotency markers OCT4, SOX2, NANOG, STAT3, REX1, FOXD3, NUCLEOSTEMIN, and TELOMERASE. Pluripotency markers OCT4, SOX2, NANOG, and c-MYC were also analyzed by real-time PCR. No significant differences were observed among ESCs from all three sources for all these genes except NANOG, whose expression was higher (p<0.05) in HMC-derived ESCs (6.897±2.3) compared to that in parthenogenesis- and IVF-derived cells (1.603±0.315 and 1±0, respectively). Pluripotent, stable buffalo ESC lines derived from IVF, parthenogenesis, and HMC embryos may be genetically manipulated to provide a powerful tool for studies involving embryonic development, genomic imprinting, gene targeting, cloning, chimera formation, and transgenic animal production.

The state of the art for pluripotent stem cells derivation in domestic ungulates

Since the successful isolation, characterization and long-term culture of embryonic stem cells (ESCs) from mice in the early 1980s and from humans a decade later, considerable effort has been made to establish ESCs lines from livestock. The derivation of validated ESCs lines is a necessary step if the generation of economically relevant transgenic animals is to be achieved. However, this is still elusive, as the isolation of true ESCs lines for livestock has not been accomplished to date. It has been demonstrated that by forced expression of a defined set of transcription factors, it is possible to reprogram somatic cells to cells that closely resemble an ES-like state. These cells were termed induced pluripotent stem cells (iPSCs). We introduce the basic concepts relating to stem cell biology and give an overview of the various attempts to isolate and generate pluripotent stem cells (PSCs) from species relevant to livestock production. Further, we point out the issues to be addressed and hurdles to be overcome to realize the promise of stem cells in agriculture.

Isolation and characterization of embryonic stem cell-like cells from in vitro produced goat (Capra hircus) embryos

The aim of the present study was to isolate and characterize goat embryonic stem cell-like cells from in vitro produced goat embryos. Inner cell mass (ICM) cells were isolated either mechanically or by enzymatic digestion from 150 blastocysts and 35 hatched blastocysts whereas 100 morulae were used for blastomeres isolation mechanically. The ICM derived cells or blastomeres were cultured on a feeder layer. The primary colony formation was significantly higher (P < 0.01) for hatched blastocysts (77.14%) than early/expanded blastocysts (54%) or morula (14%). When ICMs were isolated mechanically the primary colony formation for hatched blastocysts (90%) as well as blastocysts (66%) were significantly more than when ICMs were isolated by enzymatic digestion (60% and 30%, respectively). The colonies were disaggregated either mechanically or by enzymatic digestion for further subculture. When mechanical method was followed, the colonies remained undifferentiated up to 15 passages and three ES cell-like cell lines were produced (gES-1, gES-2, and gES-3). However, enzymatic disaggregation resulted in differentiation. The undifferentiated cells showed stem cell like morphological features, normal karyotype, and expressed stem cell specific surface markers like alkaline phosphatase, TRA-1-61, TRA-1-81, and intracellular markers Oct4, Sox2, and Nanog. Following prolonged culture of the ES cell-like cells were differentiated into several types of cells including neuron like and epithelium-like cells. In conclusion, goat embryonic stem cell-like cells can be isolated from in vitro produced goat embryos and can be maintained for long periods in culture.

In vitro culture of bovine embryos in murine ES cell conditioned media negatively affects expression of pluripotency-related markers OCT4, SOX2 and SSEA1

Despite extensive efforts, establishment of bovine embryonic stem (ES) cell lines has not been successful. We hypothesized that culture conditions for in vitro-produced (IVP) embryos, the most used source of inner cell mass (ICM) to obtain ES cells, might affect their undifferentiated state. Therefore, the aim of this work was to improve pluripotency of IVP blastocysts to produce suitable ICM for further culturing. We tested KSR and foetal calf serum (FCS) supplements in SOF medium and ES cell conditioned medium (CM) on IVC (groups: KSR, KSR CM, FCS and FCS CM). Cleavage and blastocyst rates were similar between all groups. Also, embryonic quality, assessed by apoptosis rates (TUNEL assay), total cell number and ICM percentage did not differ between experimental groups. However, expression of pluripotency-related markers was affected. We detected down-regulation of OCT3/4, SOX2 and SSEA1 in ICM of FCS CM blastocysts (p < 0.05). SOX2 gene expression revealed lower levels (p < 0.05) on KSR CM blastocysts and a remarkable variation in SOX2 mRNA levels on FCS-supplemented blastocysts. In conclusion, pluripotency-related markers tend to decrease after supplementation with ES cell CM, suggesting different mechanisms regulating mouse and bovine pluripotency. KSR supplementation did not differ from FCS, but FCS replacement by KSR may produce blastocysts with stable SOX2 gene expression levels.

Pluripotent stem cells and reprogrammed cells in farm animals

Pluripotent cells are unique because of their ability to differentiate into the cell lineages forming the entire organism. True pluripotent stem cells with germ line contribution have been reported for mice and rats. Human pluripotent cells share numerous features of pluripotentiality, but confirmation of their in vivo capacity for germ line contribution is impossible due to ethical and legal restrictions. Progress toward derivation of embryonic stem cells from domestic species has been made, but the derived cells were not able to produce germ line chimeras and thus are termed embryonic stem-like cells. However, domestic animals, in particular the domestic pig (Sus scrofa), are excellent large animals models, in which the clinical potential of stem cell therapies can be studied. Reprogramming technologies for somatic cells, including somatic cell nuclear transfer, cell fusion, in vitro culture in the presence of cell extracts, in vitro conversion of adult unipotent spermatogonial stem cells into germ line derived pluripotent stem cells, and transduction with reprogramming factors have been developed with the goal of obtaining pluripotent, germ line competent stem cells from domestic animals. This review summarizes the present state of the art in the derivation and maintenance of pluripotent stem cells in domestic animals.

Derivation of buffalo embryonic stem-like cells from in vitro-produced blastocysts on homologous and heterologous feeder cells

PURPOSE

The aim of the present study is to compare the ability of homologous and heterologous embryonic fibroblast feeder layers to support isolation and proliferation of buffalo ES-like cells generated from hatched and expanded blastocysts produced by in vitro fertilization and characterization of derived cells through expression of pluripotent markers.

METHODS

Embryonic stem cells were derived from hatched and expanded blastocysts through intact blastocyst culture and enzymatic method respectively and compared for proliferation rate on homologous (buffalo) and heterologous feeder layers (goat and sheep).

RESULTS

A total of 69 hatched and 83 expanded blastocysts were used for isolation of inner cell masses which were seeded on buffalo, goat and sheep embryonic feeder layers. Following seeding, attachment rate, primary colony formation rate and survival to maximum number of passages were observed to be higher on homologous feeder layers.

CONCLUSIONS

Upon comparison of different feeder layer cells for derivation and maintenance of buffalo ES-like cells from hatched and expanded blastocysts, buffalo embryonic fibroblast cells were able to provide a better environment for maintaining pluripotency in culture conditions.

Changes in the expression of pluripotency-associated genes during preimplantation and peri-implantation stages in bovine cloned and in vitro produced embryos

In cattle, embryos elongate before implantation and after hatching. Changes in gene expression during this transition are not well studied. Especially important are variations in the expression of pluripotency-associated genes as a result of assisted reproductive biotechnologies, such as cloning and in vitro fertilization (IVF). We hypothesize that there will be a decline in the expression of key pluripotency-associated genes and an increase in the expression of IFN-tau in elongated embryos when compared with day-7 blastocysts. To test this we generated cloned and IVF bovine day-7 blastocyst and day-17 elongated embryos (day 0 = day of nucleus transfer or IVF). Gene expression in all embryos was assessed via RT-qPCR. OCT4 was overexpressed (p < 0.05) in the cloned blastocysts when compared with IVF. No differences in gene expression at this stage between cloned and IVF embryos were found for EOMES, NANOG and FGF4. At elongation EOMES, NANOG and FGF4 were upregulated in IVF embryos (p < 0.05). IFN-tau and OCT4 were expressed at similar levels. There were changes in the expression levels for all transcripts between blastogenesis and elongation. NANOG, IFN-tau and EOMES were overexpressed in all the elongated embryos (p < 0.05), FGF4 was underexpressed in both treatments. OCT4 dropped drastically in the cloned elongated embryos, but not in the IVF. Interestingly only adult donor cells (but not fetal) from which the cloned embryos originated also expressed high levels of OCT4. Our findings might help to understand the shift of gene expression during elongation and to identify key markers of embryonic development useful for embryo screening purposes.

Cytoplasmic injection of circular plasmids allows targeted expression in mammalian embryos

Injection of linearized DNA constructs into the pronuclei of fertilized mammalian eggs is a standard method for producing transgenic embryos and animals. Here, we show that injection of covalently closed circular (ccc) plasmids into the cytoplasm of fertilized bovine and murine eggs is a highly efficient and simple alternative for ectopic expression of foreign DNA in embryos. A broad range of plasmids could be successfully expressed in preimplantation stages, including plasmids and minicircles with a scaffold/matrix attachment region (S/MAR), conventional plasmids, and bacterial artificial chromosomes (BACs). Although the foreign DNA plasmids are mainly maintained as episomal entities during preimplantation development, they accurately behave like nuclear DNA. Onset of transcription of an Oct4 promoter-controlled marker gene coincided with the species-specific time points of major embryonic genome activation, and could be modulated by in vitro DNA-methylation. This approach allows an experimental access to reprogramming events in early mammalian embryos.

Differential gene expression in bovine elongated (Day 17) embryos produced by somatic cell nucleus transfer and in vitro fertilization

Somatic cloning in cattle is associated with impaired embryo development, caused by inappropriate epigenetic reprogramming during embryogenesis; however, there is a paucity of data regarding gene expression at the critical elongation and peri-implantation stages. The objective of the present study was to identify genes differentially expressed in bovine cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or IVF). Day 7 blastocysts (Hand Made Cloned or IVP) were transferred to recipient cattle and collected at Day 17. The efficiency of recovery of elongated embryos was similar, however cloned embryos elongated less than IVP embryos (91.8+/-45.8 vs. 174+/-50mm) and fewer had embryonic discs (63 vs. 83%). Qualitative and quantitative PCR detected expression of OCT4, NANOG, IFNtau, EOMES, FGF4, SOX2, and CDX2 in all IVP embryos. In most cloned embryos, NANOG and FGF4 were absent (verified by qPCR); NANOG, EOMES, and FGF4 were underexpressed, whereas IFNtau was overexpressed in cloned embryos. Based on qPCRs, other genes, i.e., SPARC, SNRB1, and CBPP22, were down-regulated in cloned embryos, whereas HSP70 and TDKP1 were overexpressed. In bovine microarrays, 47 genes (3.6%) were deregulated in cloned embryos, including several involved in trophoblast growth and differentiation. In conclusion, we inferred that these data were indicative of incomplete epigenetic reprogramming after cloning; this could lead to aberrant gene expression and subsequently early pregnancy loss. There was an apparent association between incomplete morphological elongation and aberrant reprogramming of a subset of genes critical for early embryonic development.

Blastocyst elongation, trophoblastic differentiation, and embryonic pattern formation

The molecular basis of ungulate and non-rodent conceptus elongation and gastrulation remains poorly understood; however, use of state-of-the-art genomic technologies is beginning to elucidate the mechanisms regulating these complicated processes. For instance, transcriptome analysis of elongating porcine concepti indicates that protein synthesis and trafficking, cell growth and proliferation, and cellular morphology are major regulated processes. Furthermore, potential autocrine roles of estrogen and interleukin-1-β in regulating porcine conceptus growth and remodeling and metabolism have become evident. The importance of estrogen in pig is emphasized by the altered expression of essential steroidogenic and trophoblast factors in lagging ovoid concepti. In ruminants, the characteristic mononucleate trophoblast cells differentiate into a second lineage important for implantation, the binucleate trophoblast, and transcriptome profiling of bovine concepti has revealed a gene cluster associated with rapid trophoblast proliferation and differentiation. Gene cluster analysis has also provided evidence of correlated spatiotemporal expression and emphasized the significance of the bovine trophoblast cell lineage and the regulatory mechanism of trophoblast function. As a part of the gastrulation process in the mammalian conceptus, specification of the germ layers and hence definitive body axes occur in advance of primitive streak formation. Processing of the transforming growth factor-β-signaling molecules nodal and BMP4 by specific proteases is emerging as a decisive step in the initial patterning of the pre-gastrulation embryo. The topography of expression of these and other secreted molecules with reference to embryonic and extraembryonic tissues determines their local interaction potential. Their ensuing signaling leads to the specification of axial epiblast and hypoblast compartments through cellular migration and differentiation and, in particular, the specification of the early germ layer tissues in the epiblast via gene expression characteristic of endoderm and mesoderm precursor cells.

Single-cell duplex RT-LATE-PCR reveals Oct4 and Xist RNA gradients in 8-cell embryos

BACKGROUND

The formation of two distinctive cell lineages in preimplantation mouse embryos is characterized by differential gene expression. The cells of the inner cell mass are pluripotent and express high levels of Oct4 mRNA, which is down-regulated in the surrounding trophectoderm. In contrast, the trophectoderm of female embryos contains Xist mRNA, which is absent from cells of the inner mass. Prior to blastocyst formation, all blastomeres of female embryos still express both of these RNAs. We, thus, postulated that simultaneous quantification of Oct4 and Xist transcripts in individual blastomeres at the 8-cell stage could be informative as to their subsequent fate. Testing this hypothesis, however, presented numerous technical challenges. We overcame these difficulties by combining PurAmp, a single-tube method for RNA preparation and quantification, with LATE-PCR, an advanced form of asymmetric PCR.

RESULTS

We constructed a duplex RT-LATE-PCR assay for real-time measurement of Oct4 and Xist templates and confirmed its specificity and quantitative accuracy with different methods. We then undertook analysis of sets of blastomeres isolated from embryos at the 8-cell stage. At this stage, all cells in the embryo are still pluripotent and morphologically equivalent. Our results demonstrate, however, that both Oct4 and Xist RNA levels vary in individual blastomeres comprising the same embryo, with some cells having particularly elevated levels of either transcript. Analysis of multiple embryos also shows that Xist and Oct4 expression levels are not correlated at the 8-cell stage, although transcription of both genes is up-regulated at this time in development. In addition, comparison of data from males and females allowed us to determine that the efficiency of the Oct4/Xist assay is unaffected by sex-related differences in gene expression.

CONCLUSION

This paper describes the first example of multiplex RT-LATE-PCR and its utility, when combined with PurAmp sample preparation, for quantitative analysis of transcript levels in single cells. With this technique, copy numbers of different RNAs can be accurately measured independently from their relative abundance in a cell, a goal that cannot be achieved using symmetric PCR. The technique illustrated in this work is relevant to a wide array of applications, such as stem cell and cancer cell analysis and preimplantation genetic diagnostics.

Porcine embryonic stem cells: Facts, challenges and hopes

Embryonic stem cells (ESCs) represent a promising tool for cell therapy, regenerative medicine and tissue repair. At the same time they constitute an invaluable model for basic investigations in developmental biology, nuclear reprogramming and differentiation process. ESCs are very unique due to their unlimited self-renewal ability and high plasticity that allow them to differentiate into all embryonic tissues. However, these properties have been so far only demonstrated in the mouse and, to a lesser extent, in man. Assessment of ESC capabilities in species different from the mouse is an ongoing topic of interest and is crucial in view of their potential use as experimental models in pre-clinical applications. The mouse model is not adequate when long-term effects of cell replacement need to be evaluated. The pig has been considered for a long time among the best models for pre-clinical development of therapeutic approaches and represents an innovative model due to its morphological and functional affinity with man; therefore, pig ESCs are attracting renewed interest. However, a number of open questions need to be addressed since no validated protocols for the derivation and maintenance of pig ESCs have yet been established. In the present paper data from the literature will be presented together with experimental evidence recently obtained in our laboratory. We will discuss aspects related to the timing of isolation, the initiation of primary cultures, the use of different culture conditions and cytokines. The identification of pluripotency-related molecular markers in the pig will also be examined. Finally, the ability to respond to specifically formulated medium with spontaneous as well as induced differentiation will be assessed.

Parent-of-origin dependent gene-specific knock down in mouse embryos

In mice hemizygous for the Oct4-GFP transgene, the F1 embryos show parent-of-origin dependent expression of the marker gene. F1 embryos with a maternally derived OG2 allele (OG2(mat)/-) express GFP in the oocyte and during preimplantation development until the blastocyst stage indicating a maternal and embryonic expression pattern. F1-embryos with a paternally inherited OG2 allele (OG2(pat)/-) express GFP from the 4- to 8-cell stage onwards showing only embryonic expression. This allows to study allele specific knock down of GFP expression. RNA interference (RNAi) was highly efficient in embryos with the paternally inherited GFP allele, whereas embryos with the maternally inherited GFP allele showed a delayed and less stringent suppression, indicating that the initial levels of the target transcript and the half life of the protein affect RNAi efficacy. RT-PCR analysis revealed only minimum of GFP mRNA. These results have implications for studies of gene silencing in mammalian embryos.

Isolation and characterization of embryonic stem cell-like cells from in vitro-produced buffalo (Bubalus bubalis) embryos

This study was carried out to isolate and characterize buffalo embryonic stem (ES) cell-like cells from in vitro-produced embryos. Inner cell mass (ICM) cells were isolated either mechanically or by enzymatic digestion from 120 blastocysts whereas 28 morulae were used for the isolation of blastomeres mechanically. The ICM cells/ blastomeres were cultured on mitomycin-C-treated feeder layer. Primary cell colony formation was higher (P < 0.05) for hatched blastocysts (73.1%, 30/41) than that for early/expanded blastocysts (25.3%, 20/79). However, no primary cell colonies were formed when blastomeres obtained from morulae were cultured. Primary colonies were formed in 14.1% (12/85) of intact blastocyst culture, which was significantly lower (P < 0.05) than that of 41.6% for ICM culture. These colonies were separated by enzymatic or mechanical disaggregation. Using mechanical disaggregation method, the cells remained undifferentiated and two buffalo ES cell-like cell lines (bES1, bES2) continued to grow in culture up to eight passages. However, disassociation through enzymatic method resulted in differentiation. Undifferentiated cells exhibited stem cell morphological features, normal chromosomal morphology, and expressed specific markers such as alkaline phosphatase (AP) and Oct-4. Cells formed embryoid bodies (EBs) in suspension culture; extended culture of EBs resulted in formation of cystic EBs. Following prolonged in vitro culture, these cells differentiated into several types of cells including neuron-like and epithelium-like cells. Furthermore, the vitrified-thawed ES cell-like cells also exhibited typical stem cell characteristics. In conclusion, buffalo ES cell-like cells could be isolated from in vitro-produced blastocysts and maintained in vitro for prolonged periods of time.

Transgenic farm animals: an update

The first transgenic livestock species were reported in 1985. Since then microinjection of foreign DNA into pronuclei of zygotes has been the method of choice. It is now being replaced by more efficient protocols based on somatic nuclear transfer that also permit targeted genetic modifications. Lentiviral vectors and small interfering ribonucleic acid (siRNA) technology are also becoming important tools for transgenesis. In 2006 the European Medicines Agency (EMEA) gave green light for the commercialistion of the first recombinant protein produced in the milk of transgenic animals. Recombinant antithrombin III will be launched as ATryn for prophylactic treatment of patients with congenital antithrombin deficiency. This important milestone will boost the research activities in farm animal transgenesis. Recent developments in transgenic techniques of farm animals are discussed in this review.

Challenges and prospects for the establishment of embryonic stem cell lines of domesticated ungulates

Embryonic stem (ES) cell lines provide an invaluable research tool for genetic engineering, developmental biology and disease models. These cells can be maintained indefinitely in culture and yet maintain competence to produce all the cells within a fetus. While mouse ES cell lines were first established over two decades ago and primate ES cells in the 1990 s, validated ES cell lines have yet to be established in ungulates. Why competent, pluripotent ES cells can be established from certain strains of mice and from primates, and not from cows, sheep, goats or pigs is an on-going topic of interest to animal reproduction scientists. The identification of appropriate stem cell markers, functional cytokine pathways, and key pluripotency-maintaining factors along with the release of more comprehensive bovine and porcine genomes, provide encouragement for establishment of ungulate ES cell lines in the near future.