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

NG2 proteoglycan-expressing microglia as multipotent neural progenitors in normal and pathologic brains

Rat primary microglia (MG) acquired a multipotent property to give rise to neuroectodermal cells through two-step culture in 10 and 70% serum-supplemented media for 5 days. Such multipotent MG, called promicroglioblasts (ProMGBs), formed cell aggregates, which generated cells with neuroectodermal phenotypes shortly after their transfer into serum-free medium. As revealed by immunohistochemistry, there were a few MG expressing NG2 chondroitin sulfate proteoglycan (NG2) in the neonatal rat brain. Primary culture from the neonatal brain contained NG2+ MG, which appeared to be the source of NG2+ ProMGB aggregates. The aggregates were MG marker+/NG2+/GFAP+/NCAM+/S-100beta- and had alkaline phosphatase activity. The marked accumulation of NG2+ MG was observed close to stab wounds made in the mature rat brain. The accumulated NG2+ MG in the wound gradually decreased in number, but the cells persisted up to 150 days postlesioning. In addition, GFAP immunoreactivity increased markedly around the wound. The NG2+ MG in the wounds separated with trypsin-EDTA formed NG2+ aggregates in 70% serum-supplemented medium and then transformed into cells with neuroectodermal phenotypes in serum-free medium. Although it is difficult to separate viable neurons from mature brains, cells from stab wounds generated process-bearing beta-tubulin III+ cells in vitro easily. These data suggest that NG2+ MG in normal developing or pathologic brains are involved in the genesis or regeneration of the brain.

Avian Germplasm Preservation: Embryonic Stem Cells or Primordial Germ Cells?

Presently, avian genetic resources are best maintained as living collections of birds. Unfortunately, these stocks have been under constant pressure to be destroyed because of the decline in the number of Poultry Science Departments and pressures to cut costs at land grant institutions. Cryopreservation of semen is often suggested as a means to bank avian germplasm. However, this is only applicable for single-gene traits and does not allow for full reconstitution of the genetics of the original line. Over the last 15 yr, advances in the manipulation of the early chick embryo, manipulation of primordial germ cells (PGC), and the culture of embryonic stem cells (ESC) suggests that cryopreservation of blastodermal cells, ESC, or PGC might offer a means to preserve the entire genome of highly selected, specialized stocks of poultry. Freezing each of these cell types is possible with varying degrees of efficiency. Similarly, the effectiveness of generating germ line chimeras using blastodermal cells, ESC, or PGC also varies greatly. Other factors that must be considered include the choice of the recipient lines to develop the germ line chimeras and the number of individuals needed to reconstitute the line. Finally, the low efficiency rate of reconstitution and the high cost associated with current technologies makes these approaches prohibitive. Significant challenges remain to be overcome before the entire genome of poultry stocks can be routinely cryoperserved and reconstituted.

High-grade transgenic somatic chimeras from chicken embryonic stem cells

Male and female embryonic stem (ES) cell lines were derived from the area pellucidae of Stage X (EG&K) chicken embryos. These ES cell lines were grown in culture for extended periods of time and the majority of the cells retained a diploid karyotype. When reintroduced into Stage VI-X (EG&K) recipient embryos, the cES cells were able to contribute to all somatic tissues. By combining irradiation of the recipient embryo with exposure of the cES cells to the embryonic environment in diapause, a high frequency and extent of chimerism was obtained. High-grade chimeras, indistinguishable from the donor phenotype by feather pigmentation, were produced. A transgene encoding GFP was incorporated into the genome of cES cells under control of the ubiquitous promoter CX and GFP was widely expressed in somatic tissues. Although cES cells made extensive contributions to the somatic tissues, contribution to the germline was not observed.

Production of human monoclonal antibody in eggs of chimeric chickens

The tubular gland of the chicken oviduct is an attractive system for protein expression as large quantities of proteins are deposited in the egg, the production of eggs is easily scalable and good manufacturing practices for therapeutics from eggs have been established. Here we examined the ability of upstream and downstream DNA sequences of ovalbumin, a protein produced exclusively in very high quantities in chicken egg white, to drive tissue-specific expression of human mAb in chicken eggs. To accommodate these large regulatory regions, we established and transfected lines of chicken embryonic stem (cES) cells and formed chimeras that express mAb from cES cell-derived tubular gland cells. Eggs from high-grade chimeras contained up to 3 mg of mAb that possesses enhanced antibody-dependent cellular cytotoxicity (ADCC), nonantigenic glycosylation, acceptable half-life, excellent antigen recognition and good rates of internalization.

The molecular repertoire of the 'almighty' stem cell

Stem cells share the defining characteristics of self-renewal, which maintains or expands the stem-cell pool, and multi-lineage differentiation, which generates and regenerates tissues. Stem-cell self-renewal and differentiation are influenced by the convergence of intrinsic cellular signals and extrinsic microenvironmental cues from the surrounding stem-cell niche, but the specific signals involved are poorly understood. Recently, several studies have sought to identify the genetic mechanisms that underlie the stem-cell phenotype. Such a molecular road map of stem-cell function should lead to an understanding of the true potential of stem cells.

Increased reactivity of cultured chicken blastodermal cells to anti-stage-specific embryonic antigen-1 antibody after exposure to bone morphogenetic proteins

We evaluated whether bone morphogenetic proteins (BMPs) increased the reactivity of chicken stage X blastodermal cells to the germ cell marker, anti-stage-specific embryonic antigen (SSEA)-1 antibody. In Experiment 1, blastodermal cells cultured on a feeder layer of SIM mouse embryo-derived thioguanine and ouabain resistant (STO) cells were treated with different doses of BMP-2 and/or BMP-4, and the anti-SSEA-1 antibody reactivity of cultured cells was examined 48 h later. A significant (P < 0.05) increase in the number of anti-SSEA-1 antibody-positive cells was detected after the addition of 75 or 100 ng/ml BMP-2. Neither 0-20 ng/ml BMP-4 nor the combined addition of 75 ng/ml BMP-2 with either 10 or 15 ng/ml BMP-4 increased reactivity more than that induced by 75 ng/ml BMP-2 alone. Results of the qualification and quantification of BMP receptor kinase (BRK)-1, BRK-2, and BRK-3 using RT-PCR and real-time PCR showed that all three receptors were detected in blastodermal cells treated with BMPs, intact stage X embryos and 5.5-day-old embryonic gonads, but no expression was detected in STO feeder cells. In Experiment 2, the treatment of stage X embryos with different doses of BMP-2 (0.15-3 ng/embryo) or BMP-4 (0.02-0.4 ng/embryo) did not affect the reactivity of 5.5-day-old embryonic gonadal cells to the anti-SSEA-1 antibody. BRK-1 expression was selectively increased in stage X embryos after the infusion of 3ng BMP-2 than after no infusion, but no changes in other BRKs' expression were detected. In conclusion, the addition of BMP-2 to culture medium in the presence of STO feeder cells promoted the reactivity of blastodermal cells to anti-SSEA-1 antibody, which might contribute to the generation of chicken primordial germ cell precursor or germ cell-like cells. The relationship between BMP action and BRK expression was further discussed.

Development of Novel Markers for the Characterization of Chicken Primordial Germ Cells

This study was undertaken to develop novel markers for chicken primordial germ cells (PGCs), which are of potentially enormous value in transgenic research. Gonadal cells collected from 5.5-day-old chicken embryos were cultured in a Dulbecco's minimal essential medium and the PGC colonies formed during the primary culture period were subcultured three times. Characterization of the PGCs with the candidate marker reagents was performed on the mixed cell population 2 hours after seeding, after the primary culture period (day 10), and after the third passage (day 40). Mouse embryonic stem (ES) cells were used as controls. The cytochemical reagents investigated included periodic acid-Schiff (PAS) stain, antibodies to stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), antibody to epithelial membrane antigen (EMA)-1, antibodies to integrins alpha6 and beta1, several lectins (Solanum tuberosum agglutinin [STA], Dolichos biflorus agglutinin [DBA], concanavalin A agglutinin [ConA], and wheat germ agglutinin [WGA]), and double staining with antibodies to SSEA-1, SSEA-3, SSEA-4, integrin alpha6, or integrin beta1 and then with the lectin STA. Densitometric quantification was used to identify PGC-specific markers. The results showed that chicken PGCs were stained selectively by PAS and by antibodies to SSEA-1, SSEA-3, SSEA-4, EMA-1, integrin alpha6, and integrin beta1. The control mouse ES cells reacted with PAS, anti-SSEA-1, and anti-EMA-1 antibodies, as well as with antibodies to integrins alpha6 and beta1, but not with antibodies to SSEA-3 and SSEA-4. Chicken PGCs reacted with the lectins STA and DBA, but mouse ES cells reacted with STA and WGA. The results of double staining of PGC colonies subcultured three times showed that the intensity of staining was not altered by concomitant use of the marker reagents. This study demonstrated that, in addition to PAS and antibodies to SSEA-1 and EMA-1, new specific markers of chicken PGCs are recognized by the lectins STA and DBA and by antibodies to SSEA-3 and SSEA-4 and integrins alpha6 and beta1. Double staining using these newly developed markers might be the method of choice for rapid characterization of chicken PGCs.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Isolation of chicken primordial germ cells using fluorescence-activated cell sorting

Presently, it is difficult to undertake germ line modification of the chicken with primordial germ cells (PGC) because it has been difficult to efficiently fractionate the PGC from the total somatic cell population. The objective of this study was to develop a method that allows isolation of an enriched population of viable PGC from embryonic blood and embryonic gonadal tissue. Blood was harvested from early chick embryos (stages 13 to 15), and cells were liberated from the gonads of stage 27 chick embryos. Subsequently, viable PGC were labeled with anti-stage-specific embryonic antigen-1 (SSEA-1), which was detected with goat-anti-mouse IgM-fluorescein isothiocyanate. Fluorescently labeled cells were sorted from the unlabeled cells using fluorescence-activated cell sorting (FACS), and the identities of the PGC were confirmed using periodic acid-Schiff (PAS) staining or anti-embryonic mouse antigen-1 (EMA-1) staining followed by microscopic evaluation. Finally, PGC were sorted from somatic cells of sex-identified embryos. Less than 0.1% of the blood cell population was collected as SSEA-1-positive cells. Similarly, approximately 2% of the gonadal cell population were collected as SSEA-1-positive cells. Therefore, fewer (-1,000 to 9,000) PGC were recovered from each isolate. Placing the sorted SSEA-1-positive cells on a glass slide from a microcentrifuge tube resulted in a recovery rate of 53 to 73% relative to the number detected by FACS. Furthermore, the proportions of sorted cells that stained with PAS or anti-EMA-1 following sorting were 92+/-4% PAS positive and 94+/-1% anti-EMA-1 positive. Finally, the sorted SSEA-1-positive cells were maintained in vitro to demonstrate their viability after sorting. It was demonstrated that it is possible to label blood and gonadal chicken PGC with SSEA-1 and subsequently to sort viable SSEA-1-positive PGC from somatic cells.

Generation and characterization of pluripotent stem cells from cloned bovine embryos

Bovine embryonic stem (ES) cell lines reported to date vary in morphology and marker expression (e.g., alkaline phosphatase [ALPL], stage-specific embryonic antigen 4 [SSEA4], and OCT4) that normally are associated with the undifferentiated, pluripotent state. These observations suggest that the proper experimental conditions for consistently producing bovine ES cells have not been identified. Here, we report three bovine ES cell lines, one from in vitro-fertilized and two from nuclear transfer embryos. These bovine ES cells grew in large, multicellular colonies resembling the mouse ES and embryonic germ (EG) cells and human EG cells. Throughout the culture period, most of the cells within the colonies stained positive for ALPL and the cell surface markers SSEA4 and OCT4. The staining patterns of nuclear transfer ES cells were identical to those of the blastocysts generated in vitro yet different from most previously reported bovine ES cell lines, which were either negative or not detected. After undifferentiated culture for more than 1 yr, these cells maintained the ability to differentiate into embryoid bodies and derivatives of all three EG layers, thus demonstrating their pluripotency. However, unlike the mouse and human ES cells, following treatment with trypsin, type IV collagenase, or protease E, our bovine ES cells failed to self-renew and became spontaneously differentiated. Presumably, this resulted from an interruption of the self-renewal pathway. In summary, we generated pluripotent bovine ES cells with morphology similar to those of established ES cells in humans and mice as well as marker-staining patterns identical to those of the bovine blastocysts.

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

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

Isolation, culture, and characterization of embryonic cell lines from vitrified sheep blastocysts

This study was conducted to isolate, to culture, and to characterize embryonic cell lines from in vitro produced vitrified sheep blastocysts. Embryos were produced and vitrified at the expanded blastocyst stage. Ten inner cell masses arising from day 6-7 blastocysts were isolated by immunosurgery, disaggregated, and cultured onto mitomocin-C-inactivated mouse STO fibroblasts (MIF). After 5 or 6 days of culture the primary cell colonies were disaggregated, seeded in a new MIF, and cultured for 3 or 4 days to form new colonies called Passage 1. These cells were then disaggregated and cultured for other two passages. The primary cell colonies and Passage 2 colonies expressed stage specific embryonic markers SSEA-1, SSEA-3, and SSEA-4, and were alkaline phosphatase positive. In the absence of feeder layer and human leukemia inhibitory factor (LIF), these cells differentiated into variety of cell types and formed embryoid bodies. When cultured for an extended period of time, embryoid bodies differentiated into derivatives of three embryonic germ (EG) layers. These were characterized by detection of specific markers for differentiation such early mesoderm (FE-C6), embryonic myosin (F1-652), neural precursor (FORSE-1), and endoderm (anti-cytokeratin 18). To our knowledge, this is the first time that embryonic cell lines from in vitro produced and vitrified ovine blastocysts have been isolated and examined for detection of SSEA markers, and embryoid bodies have been cultured and examined for specific cell surface markers for differentiation.

Characterization and expression analysis of the chicken interleukin-11 receptor alpha chain

Interleukin-11 (IL-11) is a multifunctional cytokine involved in various pathways in blood cells, their precursors and many other cell types in vitro and in vivo. The effects of IL-11 are largely mediated by the IL-11 receptor alpha-chain (IL-11Ralpha). In this study, a putative cDNA sequence encoding the 414 amino acid propeptide of chicken IL-11R (chIL-11R) was identified. The predicted 414 amino acid sequence showed 42-43% sequence identity with mammalian homologues. In a domain search of the molecule, two fibronectin (FN) type-III domains were identified in the C- terminal portion. On comparison with mammalian IL-11R, 4 conserved cysteine residues and a WSXWS motif were observed within the FN type-III domains. Expression analysis revealed that chIL-11Ralpha is strongly expressed in brain, heart, lung, liver, glandular stomach, kidney, the immature testis, ovary and chicken blastodermal cells (CBCs) after 1-day-cultivation. These findings strongly indicate that the identified chicken cDNA sequence encodes chIL-11R alpha-chain homologue.

Potential of embryonic and adult stem cells in vitro

Recent developments in the field of stem cell research indicate their enormous potential as a source of tissue for regenerative therapies. The success of such applications will depend on the precise properties and potentials of stem cells isolated either from embryonic, fetal or adult tissues. Embryonic stem cells established from the inner cell mass of early mouse embryos are characterized by nearly unlimited proliferation, and the capacity to differentiate into derivatives of essentially all lineages. The recent isolation and culture of human embryonic stem cell lines presents new opportunities for reconstructive medicine. However, important problems remain; first, the derivation of human embryonic stem cells from in vitro fertilized blastocysts creates ethical problems, and second, the current techniques for the directed differentiation into somatic cell populations yield impure products with tumorigenic potential. Recent studies have also suggested an unexpectedly wide developmental potential of adult tissue-specific stem cells. Here too, many questions remain concerning the nature and status of adult stem cells both in vivo and in vitro and their proliferation and differentiation/transdifferentiation capacity. This review focuses on those issues of embryonic and adult stem cell biology most relevant to their in vitro propagation and differentiation. Questions and problems related to the use of human embryonic and adult stem cells in tissue regeneration and transplantation are discussed.

Status of transgenic chicken models for developmental biology

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

An interclass nuclear transfer between fowl and mammal: In vitro development of chicken-to-cattle interclass embryos and the detection of chicken genetic complements

An attempt was made to develop an interclass somatic cell nuclear transfer method as an alternative means of establishing chicken embryonic stem cells. Chicken-to-cattle interclass embryos that activated calcium ionophore, cycloheximide, and cytochalasin D were developed into blastocysts, and the developing interclass embryos had chicken genetic complements.

Avian pluripotent stem cells

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

Prospects for transgenesis in the chick

Research to develop a useful method for genetic modification of the chick has been on-going since the first demonstrations in the mouse in the 1980s that genetic modification is an invaluable tool for the study of gene function. Manipulation of the chick zygote is possible but inefficient. Considerable progress has been made in developing potentially pluripotent embryo stem cells and their contribution to somatic chimeric birds well-established. Germ line transmission of gametes derived from genetically modified embryo cells has not been described. Transfer of primordial germ cells from a donor embryo to a recipient and production of functional gametes from the donor-derived cells is possible. Genetic modification of primordial germ cells before transfer and their recovery through the germ line has not been achieved. The first transgenic birds described were generated using retroviral vectors. The use of lentiviral vectors may make this approach a feasible method for transgenic production, although there are limitations to the applications of these vectors. It is likely that a method will be developed in the next few years that will enable the use of transgenesis as a tool in the study of development in the chick and for many other applications in basic research and biotechnology.

Establishment and in vitro differentiation of a new embryonic stem cell line from human blastocyst

Embryonic stem cells have the ability to remain undifferentiated and proliferate indefinitely in vitro while maintaining the potential to differentiate into derivatives of all three embryonic germ layers. These cells have, therefore, potential for in vitro differentiation studies, gene function, and so on. The aim of this study was to produce a human embryonic stem cell line. An inner cell mass of a human blastocyst was separated and cultured on mouse embryonic fibroblasts in embryonic stem cell medium with related additives. The established line was evaluated by morphology; passaging; freezing and thawing; alkaline phosphatase; Oct-4 expression; anti-surface markers including Tra-1-60 and Tra-1-81; and karyotype and spontaneous differentiation. Differentiated cardiomyocytes and neurons were evaluated by transmission electron microscopy and immunocytochemistry. Here, we report the derivation of a new embryonic stem cell line (Royan H1) from a human blastocyst that remains undifferentiated in morphology during continuous passaging for more than 30 passages, maintains a normal XX karyotype, is viable after freezing and thawing, and expresses alkaline phosphatase, Oct-4, Tra-1-60, and Tra-1-81. These cells remain undifferentiated when grown on mouse embryonic fibroblast feeder layers in the presence or absence of recombinant human leukemia inhibitory factor. Royan H1 cells can differentiate in vitro in the absence of feeder cells and can produce embryoid bodies that can further differentiate into beating cardiomyocytes as well as neurons. These results define Royan H1 cells as a new human embryonic stem cell line.

Chicken Leukemia Inhibitory Factor Maintains Chicken Embryonic Stem Cells in the Undifferentiated State

Mouse embryonic stem (ES) cells can be maintained in an undifferentiated state in the presence of leukemia inhibitory factor (LIF), a member of the interleukin-6 cytokine family. In other mammals, this is not possible with LIF alone. Chicken ES-like cells (blastodermal cells) have only been cultured with mouse LIF because chicken LIF was not available. However the culture system is imperfect and chicken ES-like cells equivalent to mouse ES cells were not observed. In the present study, we cloned the cDNA-encoding chicken LIF using mRNA subtraction and RACE methodology. The chicken LIF cDNA encodes a protein with approximately 40% sequence identity to mouse LIF. It has 211 amino acids including a putative N-terminal signal peptide of 24 residues. Chicken blastodermal cells were cultured in the presence of bacterially expressed chicken LIF or mouse LIF. The expression of alkaline phosphatase and embryonal carcinoma cell monoclonal antibody-1 and stage-specific embryonic antigen-1 and the activation of STAT3 were examined, all of which are indices of the undifferentiated state. Exposure in the blastodermal cells to recombinant chicken LIF but not to mouse LIF maintained the expression of these various markers. After 9 days of incubation, the blastodermal cells formed cystic embryoid bodies in the presence of mouse LIF but not in the presence of recombinant chicken LIF. We conclude that chicken LIF is able to maintain chicken ES cell cultures in the undifferentiated state.

Green fluorescent protein gene-transfected peafowl somatic cells participate in the development of chicken embryos

This study was performed to investigate whether the embryonic somatic cells are capable of reconstituting and participating in the embryonic development of chickens to produce chimeras. In order to track the migration behavior of the donor cells, a cell line, originally isolated from an Indian peafowl embryo, was fluorescent-labeled by transfection of the cells with enhanced Green Fluorescent Protein (GFP) and Neomycin resistant (Neo) genes prior to injection into the stage X blastoderm of White Leghorn chickens. The injection was performed with a medium in the presence of 1-5% polyethylene glycol. The development of putative chimeric embryos between the stages three and 24 was examined for GFP expression under fluorescent light. To trace the peafowl cells in the developing chicken embryos, both a species-specific genetic marker originating from the mitochondrial DNA cytochrome b (cyt b) gene and a DNA fragment of GFP gene were used. Of the 185 fertile eggs manipulated, 173 developed into embryos. Fifty-five of them showed positive GFP patches in extra-embryonic tissues, and 15 expressed GFP in intra-embryonic tissues such as those of the head, heart, and gonad. PCR analysis revealed that PCR fragments for the peafowl mitochondrial DNA cyt b and GFP genes were detected in the samples of the GFP positive extra- and intra-embryonic tissues of the chimeras. The present results provide evidence that fluorescent-labeled peafowl embryonic cells carrying GFP and Neo genes are able to participate in the development of chicken embryos to generate chimeras.

Long-term culture and differentiation of rat embryonic stem cell-like cells into neuronal, glial, endothelial, and hepatic lineages

The in vitro differentiation of mouse embryonic stem cells into different somatic cell types such as neurons, endothelial cells, or myocytes is a well-established procedure. Long-term culture of rat embryonic stem cells is known to be hazardous, and attempts to differentiate these cells in vitro so far have been unsuccessful. We herein describe stable long-term culture of an alkaline phosphatase-positive rat embryonic stem cell-like cell line (RESC) and its differentiation into neuronal, endothelial, and hepatic lineages. RESCs were characterized by typical growth in single cells as well as in embryoid bodies when cultured in the presence of leukemia inhibitory factor. RESC expressed stage-specific-embryonic antigen-1 and the major histocompatibility complex class I molecule. For neuronal differentiation, cells were incubated with medium containing 10(-6) M retinoic acid for 14 days. For endothelial differentiation, RESCs were grown on Matrigel for 14 days, and for induction of hepatocyte-specific antigen expression, RESCs were grown in medium supplemented with fibroblast growth factor-4. Differentiated cells exhibited typical morphological changes and expressed neuronal (nestin, mitogen-activated protein-2, synaptophysin), glial (S100, glial fibrillary acid protein), endothelial (panendothelial antibody, CD31) and hepatocyte-specific (alpha-fetoprotein [alphaFP], albumin, alpha-1-antitrypsin, CK18) antigens. In addition, expression of hepatocyte-specific genes (alphaFP, transthyretin, carbamoyl-phosphate synthetase, and coagulation factor-2) was detected by reverse transcription polymerase chain reaction. We were able to culture RESCs under stable, long-term conditions and to initiate programmed differentiation of RESCs to endothelial, neuronal, glial, and hepatic lineages in the rat species.

Differential tissue development during embryogenesis and regeneration in an annelid

The fragmenting potworm Enchytraeus japonensis (Oligochaeta, Annelida) reproduces asexually by dividing the body into several fragments that then regenerate to complete individuals in 4-5 days. Such large-scale regeneration, however, occurs only in some invertebrates. To better our understanding of why regeneration is so limited in many animals, despite their ability to undergo embryonic development from the single cell of a fertilized egg, comparisons were made between regeneration and embryonic development of E. japonensis by using two methods: histochemistry for alkaline phosphatase (ALP) and immunohistochemistry with an antibody against acetylated tubulin that visualizes nervous system development. The analyses revealed that both ALP expression patterns and central nervous system development differ between embryogenesis and the regeneration, suggesting that regeneration is not a simple reiteration of embryogenesis but involves different regulatory mechanisms. The study provides a basis for the elucidation of mechanisms that are unique and crucial to regeneration.

Telomeres in the chicken: genome stability and chromosome ends

Telomeres are the complex nucleoprotein structures at the termini of linear chromosomes. Telomeric DNA consists of a highly conserved hexanucleotide arranged in tandem repeats. Telomerase, a ribonucleoprotein of the reverse transcriptase family, specifies the sequence of telomeric DNA and maintains telomere array length. Numerous studies in model organisms established the significance of telomere structure and function in regulating genome stability, cellular aging, and oncogenesis. Our overall research objectives are to understand the organization of the telomere arrays in chicken in the context of the unusual organization and specialized features of this higher vertebrate genome (which include a compact genome, numerous microchromosomes, and high recombination rate) and to elucidate the role telomeres play in genome stability impacting cell function and life span. Recent studies found that the chicken genome contains three overlapping size classes of telomere arrays that differ in location and age-related stability: Class I 0.5 to 10 kb, Class II 10 to 40 kb, and Class III 40 kb to 2 Mb. Some notable features of chicken telomere biology are that the chicken genome contains ten times more telomeric DNA than the human genome and the Class III telomere arrays are the largest described for any vertebrate species. In vivo, chicken telomeres (Class II) shorten in an age-related fashion and telomerase activity is high in early stage embryos and developing organs but down-regulates during late embryogenesis or postnatally in most somatic tissues. In vitro, chicken cells down-regulate telomerase activity unless transformed. Knowledge of chicken telomere biology contributes information relevant to present and future biotechnology applications of chickens in vivo and chicken cells in vitro.

Developmental fate of embryonic germ cells (EGCs), in vivo and in vitro

Embryonic germ cells (EGCs) derived from mouse primordial germ cells (PGCs) are known both to colonize all cell lineages of the fetus and to make tumors in vivo. When aggregated with eight-cell embryos, EGCs from a new EGC line expressing green fluorescent protein (GFP) were found to contribute preferentially to the epiblast but unexpectedly were also capable of colonizing primary endoderm. When injected under the kidney capsule, EGCs derived from 12.5 days post coitum (dpc) PGCs formed differentiated tumors. The ability of EGCs to differentiate in an organ culture system depends upon their partners in cell culture. When EGCs, marked with a LacZ transgene, were mixed with disaggregated and reaggregated mouse fetal lung in an organ culture system, they remained undifferentiated. In urogenital ridge reaggregates on the other hand, some EGCs were capable of differentiating to form small epithelial cysts.

The potential of stem cells

Although stem cells have held the fascination of scientists for years, the attention of the general public has recently been captured by the derivation of human embryonic stem cells. In this review we describe the historical experiments leading up to the isolation of human embryonic stem cells and discuss recent advances in our understanding of both embryonic and somatic stem cells. Select examples are used to illustrate the potential of stem cells, both in the sense of their ability to differentiate into specific cell types and in the sense of their power to treat various diseases and conditions. Also discussed are recent studies describing current progress toward the treatment of Parkinson disease, spinal cord injuries, diabetes, and cardiac disease.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to describe the various types of stem cells, outline potential clinical uses of stem cells, and summarize the somatic cell transdifferentiation debate.

Telomerase activity is widespread in adult somatic tissues of Xenopus

Chromosome ends, or telomeres, are maintained by telomerase. Work in selected vertebrates has implied that telomerase is often repressed in differentiated cells, and telomere erosion results in senescence of cultured cells. Tissues from mature Xenopus laevis frogs were examined for telomerase enzymatic activity with the TRAP (telomere repeat amplification protocol) assay. All tissues contained active telomerase, most abundantly in testis, spleen, liver, and embryos; activity was less abundant but still readily detectable with < 100 ng of protein extract from brain and muscle tissues. Activity in somatic tissues of the diploid Xenopus tropicalis suggests this condition is not limited to the polyploid members of the genus, and that extensive differentiation-linked telomerase repression does not occur in Xenopus.

Avian transgenesis: progress towards the promise

The hen has long held promise as a low cost, high-yield bioreactor for the production of human biopharmaceuticals in egg whites. A typical egg white contains 3.5-4.0 grams of protein, more than half of which comes from a single gene (ovalbumin). Harnessing the power of the gene to express a recombinant protein could yield up to a gram or more of the protein in the naturally sterile egg. Accordingly, a major effort has been underway for more than a decade to develop robust methods for modification of the chicken genome. This effort intensified in the mid-1990s when several avian transgenic companies entered the scene. Progress has been made in that time but much remains to be done.

Establishment of Feather Follicle Stem Cells as Potential Vehicles for Delivering Exogenous Genes in Birds

The present study was performed to develop a culture system for feather keratinocyte stem cells to enable the genetic manipulation of endangered avian species. The feather follicle cells were isolated from growing feathers of adult White Leghorn chicken. Leukemia inhibitory factor (LIF) was used to maintain the characterization of the keratinocyte colony-forming cells (KCFCs). The EGFPN1 plasmid DNA retroviral vector was used to deliver Green Fluorescent Protein (GFP) gene, which was introduced to the KCFCs by lipofection. After removal of the fibroblast-like cells, the feather KCFCs attached to the substrate within 24 h of seeding. The cells continued to proliferate for at least 30 days in the presence of LIF. The cell-adhesion molecules such as integrin beta1 and CD49c were immunocytochemically positive in the cells. The KCFCs differentiated into barbular cells and pennaceous feather vane in the LIF-free medium. The GFP gene-transfected KCFCs stably expressed GFP. The present results indicate that the KCFCs derived from feather follicles are closely related to multipotent stem cells. In addition, gene manipulation of such stem cells may be useful for the production of chimera in avian species.

Production of germline chimeras by transfer of chicken gonadal primordial germ cells maintained in vitro for an extended period

We previously reported that germline chimeras could be produced by transfer of chicken gonadal primordial germ cells (gPGCs) cultured for a short term (5 days). This study was subsequently undertaken to examine whether gPGCs maintained in vitro for an extended period could retain their specific characteristics to induce germline transmission. Chicken (White Leghorn, WL) gPGCs were retrieved from embryos at stage 28 (5.5 days of incubation) and continuously cultured for 2 months in modified Dulbecco's minimal essential medium without subpassage and changing of the feeder cell layer. After the identification of gPGC characteristics using Periodic acid-Shiff's (PAS) reaction and anti stage-specific embryonic antigen-1 (SSEA-1) antibody staining at the end of the culture, cultured gPGCs were injected into the dorsal aorta of Korean Ogol Chicken (KOC) recipient embryos at stage 17 (2.5 days of incubation). Nineteen chickens (13 males and 6 females) were hatched, grown to sexual maturity, and subsequently subjected to testcross analysis employing artificial insemination with adult KOC. Of these, four (three males and one female) hatched chickens with white coat color. The percentage of germline chimerism was 21% (4/19). The results of this study demonstrated that gPGCs could maintain their specific characteristics for up to 2 months in vitro, resulting in the birth of germline chimeras following transfer to recipient embryos.

Identification and evaluation of major histocompatibility complex antigens in chicken chimeras and their relationship to germline transmission

Chimeric chickens were evaluated as an intermediate for development of transgenic chickens. The transfer of Barred Plymouth Rock (BR) blastodermal cells into White Leghorn (WL) embryos results in BR-->WL chimeras, and some breeder males generate over 30% germline transmission of the BR genotype to offspring based on a feather-color trait. The objectives of the current study were to 1) identify the MHC (B haplotypes) in resident BR and WL lines, 2) establish that B antigens could be detected and quantified in red blood cells (RBC) of chimeras, 3) establish if there is a correlation in chimeras between percentage of RBC with donor B antigens and percentage germline transmission, and 4) evaluate if the MHC genotype influences chimera development. The RBC agglutination data indicated three B haplotypes were present in each line. The B*2-like, and B*19-like genes were unique to the WL line, and B*13-like and B-15-like genes were unique to the BR line, whereas a B*21-like gene was present in both lines. In adult BR-->WL chimeras, as well as 10- to 14 d-old WL-->WL chimeras, donor-type B antigens were detectable and quantifiable on RBC using flow cytometry. In BR-->WL chimeras, the percentage germline transmission was significantly correlated with the percentage of RBC with donor B antigen, as well as percentage of black feathers in the plumage. In a retrospective study using previously developed BR-->WL chimeras, the level of chimerism and germline transmission was higher in B*21/*21 type recipients, but this was not statistically significant in two prospective studies. It was concluded that MHC antigens on RBC can be used for identifying, quantifying, and selecting chicken chimeras developed by the transfer of blastodermal cells.

Pluripotent stem cells--model of embryonic development, tool for gene targeting, and basis of cell therapy

Embryonic stem (ES) cells are pluripotent cell lines with the capacity of self-renewal and a broad differentiation plasticity. They are derived from pre-implantation embryos and can be propagated as a homogeneous, uncommitted cell population for an almost unlimited period of time without losing their pluripotency and their stable karyotype. Murine ES cells are able to reintegrate fully into embryogenesis when returned into an early embryo, even after extensive genetic manipulation. In the resulting chimeric offspring produced by blastocyst injection or morula aggregation, ES cell descendants are represented among all cell types, including functional gametes. Therefore, mouse ES cells represent an important tool for genetic engineering, in particular via homologous recombination, to introduce gene knock-outs and other precise genomic modifications into the mouse germ line. Because of these properties ES cell technology is of high interest for other model organisms and for livestock species like cattle and pigs. However, in spite of tremendous research activities, no proven ES cells colonizing the germ line have yet been established for vertebrate species other than the mouse (Evans and Kaufman, 1981; Martin, 1981) and chicken (Pain et al., 1996). The in vitro differentiation capacity of ES cells provides unique opportunities for experimental analysis of gene regulation and function during cell commitment and differentiation in early embryogenesis. Recently, pluripotent stem cells were established from human embryos (Thomson et al., 1998) and early fetuses (Shamblott et al., 1998), opening new scenarios both for research in human developmental biology and for medical applications, i.e. cell replacement strategies. At about the same time, research activities focused on characteristics and differentiation potential of somatic stem cells, unravelling an unexpected plasticity of these cell types. Somatic stem cells are found in differentiated tissues and can renew themselves in addition to generating the specialized cell types of the tissue from which they originate. Additional to discoveries of somatic stem cells in tissues that were previously not thought to contain these kinds of cells, they also appear to be capable of developing into cell types of other tissues, but have a reduced differentiation potential as compared to embryo-derived stem cells. Therefore, somatic stem cells are referred to as multipotent rather than pluripotent. This review summarizes characteristics of pluripotent stem cells in the mouse and in selected livestock species, explains their use for genetic engineering and basic research on embryonic development, and evaluates their potential for cell therapy as compared to somatic stem cells.

Pluripotency of bovine embryonic cell line derived from precompacting embryos

We report herein the establishment of three bovine pluripotent embryonic cell lines derived from 8-16-cell precompacting embryos. Two cell lines were cultured for 10 passages and underwent spontaneous differentiation. One cell line (Z2) has been cultured continuously for over 3 years and has remained undifferentiated. These cells express cell surface markers that have been used routinely to characterize embryonic stem (ES) and embryonic germ (EG) cells in other species such as stage-specific embryonic antigens SSEA-1, SSEA-3, and SSEA-4, and c-Kit receptor. In the absence of a feeder layer, these cells differentiated into a variety of cell types and formed embryoid bodies (EBs). When cultured for an extended period of time, EBs differentiated into derivatives of three EG layers - mesoderm, ectoderm, and endoderm - which were characterized by detection of specific cell surface markers. Our results indicate that the Z2 cell line is pluripotent and resembles an ES cell line. To our knowledge, this is the first bovine embryonic cell line that has remained pluripotent in culture for more than 150 passages.

Embryonic stem cells provide a powerful and versatile model system

Embryonic stem (ES) cells are pluripotent stem cells that differentiate both in vitro and in vivo into cell types derived from each of the three embryonic germ layers. ES cells and their close relatives, embryonal carcinoma (EC) cells and embryonic germ (EG) cells, have been used extensively as model systems for studying early mammalian development. This work has led to important insights into the mechanisms that control embryogenesis at the molecular and cellular levels. This chapter focuses on the use of ES cells as an in vitro model system for studying cellular differentiation and reviews several areas where important progress has been made. Impressive progress has been made in the isolation and characterization of ES cells from many species, including humans. Significant progress has also been made in the development of culture conditions that help direct the differentiation of ES cells to specific cell types that form during myogenesis, angiogenesis, hematopoiesis, neurogenesis, and cardiogenesis. The ability to inactivate virtually any gene in ES cells by gene targeting has vastly improved our understanding of the roles played by specific genes at the cellular and organismic levels. Moreover, ES cells and EC cells have been used widely to investigate how specific genes are turned on and turned off in the course of differentiation. In this connection, DNA array technology has been used to identify genes regulated when ES cells differentiate. The final section of this chapter discusses how work with ES cells is shaping our understanding of stem cells, mammalian development, and cell replacement therapy.

Strain preference in donor and recipient for production of W-bearing sperm in mixed-sex germline chimeric chickens

To elucidate the strain preference in donor and recipient for the production of W-bearing sperm, mixed-sex germline chimeric chickens were produced. The combination of donor and recipient was White Leghorn (WL) and Barred Plymouth Rock (BPR), and vice versa. Four sets of mixed-sex chimeras that had the male phenotype at sexual maturity were subjected to analysis: group 1, a female WL donor and a male BPR recipient; group 2, a male WL donor and a female BPR recipient; group 3, a female BPR donor and a male WL recipient; group 4, a male BPR donor and a female WL recipient. The mean number of W-bearing sperm detected by in situ hybridization among 10000 sperm observed was 135, 158, 26 and 71 in groups 1, 2, 3 and 4, respectively. The number in group 1 was significantly higher than that of group 3 (P<0.05). And the number in group 2 was significantly higher than those of groups 3 and 4 (P<0.05). It is suggested that the combination of a WL donor and a BPR recipient produced W-bearing sperm more efficiently than the reverse combination.

Telomerase and differentiation in multicellular organisms: turn it off, turn it on, and turn it off again

Telomerase is a ribonucleoprotein complex that catalyses the addition of TTAGGG repeats onto telomeres, repetitive DNA structures found at the ends of linear chromosomes. The majority of human somatic tissues do not display telomerase activity and undergo telomeric shortening with consecutive divisions. This telomeric shortening results in replicative senescence in vitro and likely in vivo. Telomerase activity is present in the vast majority of tumors, preventing telomeric shortening and thereby enabling indefinite cell divisions. Telomerase activity is regulated throughout human development, undergoing silencing in almost all organ systems from embryogenesis onwards. However, regulated telomerase activity is seen in basal/stem cell compartments of highly regenerative tissues, such as those of the immune system, skin, and intestine. Avian species display telomerase repression and telomeric shortening similar to that seen in humans. However, rodents retain telomerase-competency throughout their lifespan and have not been shown to display division-dependent telomere shortening. The regulation of telomerase activity in plants is less well understood, although early indications suggest ubiquitous competency. The aim of this review is to present current data regarding developmental regulation of telomerase in humans, mice, chickens and flowering plants. Differentiation, quiescence and telomerase activity regulation will then be addressed in three human representative tissue systems; blood, skin, and intestine. We will also highlight similarities, differences and misconceptions in the developing field of telomere and telomerase biology.

Stem cells in regenerative biology and medicine

Embryonic stem cells of the mammalian blastocyst give rise to all the tissue lineages that begin to emerge at gastrulation. They are pluripotent cells and can be propagated in vitro without loss of pluripotency. Many adult tissues harbor cells that do not complete their differentiation program. These cells serve as self-renewing stem cells whose normal fate is to regenerate site-specific tissue, in response to either physiological cell turnover or damage inflicted by injury or disease. Neural, muscle, and bone marrow stem cells possess developmental potency far greater than their normal lineage-restricted fate. The understanding of the biology of stem cells is leading us into an era of regenerative medicine. The growth potential and pluripotency of embryonic stem cells and the developmental plasticity of adult stem cells, particularly those of bone marrow, make them potentially useful for replacing tissues, via transplantation or construction of bioartificial tissues, that either do not regenerate naturally or are damaged beyond their natural capability for regeneration. In addition to these two ways of replacing tissue, a third strategy of regenerative medicine is to stimulate regeneration in vivo from resident stem cells. Before these approaches become clinical reality, however, a number of basic research issues must be resolved, including the revision of our concept of a regeneration-competent cell.

Use of human gametes obtained from anonymous donors for the production of human embryonic stem cell lines

OBJECTIVE

To investigate the use of donated gametes for the production of human embryonic stem cell lines.

DESIGN

Basic research study.

SETTING

Assisted Reproductive Technology (ART) program at an academic institution.

PATIENT(S)

Consenting oocyte and sperm donors.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Oocytes were aspirated from oocyte donors (n = 12) and inseminated with frozen-thawed donor (n = 2) sperm followed by culture of embryos to day 5 or 6 in sequential media. The inner cell masses of expanded blastocysts were isolated using immunosurgery and cultured for 4-11 days on irradiated primary mouse embryonic fibroblasts (PMEFs). Viable cell colonies were passed every 7-10 days onto fresh PMEFs in the presence of leukemia inhibitory factor (0.1 microg/mL) and evaluated for appropriate cell surface markers.

RESULT(S)

Immunosurgery of 40 blastocysts resulted in the culture of 18 inner cell masses, which have produced three cell lines. One of these cell lines has been shown to stain positive for alkaline phosphatase and stage-specific embryonic antigen (SSEA)-4 and negative for SSEA-1, express telomerase activity, and produce hCG when allowed to differentiate.

CONCLUSION(S)

These findings demonstrate that the future production of human embryonic stem cell lines for therapeutic use is possible with the use of donated gametes. Many ethical issues were considered before the initiation of this study, and it was our goal to ensure that both oocyte and sperm donors understood the nature and purpose of the research before their participating in the study.

Molecular mechanism to maintain stem cell renewal of ES cells

Embryonic stem (ES) cells are pluripotent cells directly derived from early stage embryos that retain the ability to differentiate into all cell types. This unique feature is the basis of various applications of ES cell technology such as in vitro models of mammalian development, germline transgenesis to make knockout mice, and a generic source for cell therapy in regenerative medicine. To achieve success in these applications, the pluripotency of ES cells has to be kept stable during long-term culture in vitro, leading to the necessity of determining the molecular basis for maintaining ES self-renewal. This paper summarizes the recent progress in this area, focusing mainly on the LIF signaling pathway and the transcription factor Oct-3/4. Although it is still unclear how these components works together, a model is presented here that provides a plan to solve this problem.

Identification of a new gene family specifically expressed in chicken embryonic stem cells and early embryo

Chicken embryonic stem (CES) cells are pluripotent cells derived from chicken early blastoderm. In order to identify new genes specifically expressed in these pluripotent cells, we have used a gene trap strategy and cloned a novel gene family called cENS for chicken Embryonic Normal Stem cell gene. The cENS genes expression decreases after induction of CES cells differentiation in culture and is restricted in vivo to the very early embryo. We have characterized three different cENS genes. One, cENS-1, is composed of an open reading frame inserted between two terminal direct repeats which are the common point of the cENS genes. cENS-1 encodes a protein identical to cERNI, a recently described protein. cENS-2 is a truncated form of cENS-1. cENS-3 presents two adjacent open reading frames coding respectively for env and pol related proteins. The presence of conserved direct repeats, of retrovirus related genes and the absence of introns argue in favor of a retroviral origin of the cENS genes. In the cENS we identified a promoter region whose activity is strong in CES cells and decreases after induced differentiation showing a highly specific transcriptional activity specific of undifferentiated chicken embryonic stem cells.