Cell position regulates endodermal differentiation in embryonal carcinoma cell aggregates

It has been suggested that cell position regulates endodermal differentiation in mouse embryo inner cell masses and in aggregates of embryonal carcinoma (EC) cells. This hypothesis states that cells at the interface between the cell mass and blastocoel fluid or culture medium differentiate into endoderm, whereas internally located cells follow alternative developmental pathways. To test the cell position hypothesis, pluripotent PSA-1 cells were aggregated with hypoxanthine phosphoribosyltransferase-deficient, parietal-like, endodermal cells. The resulting aggregates consisted of cores of PSA-1 cells surrounded by endodermal cells. Autoradiography was used to distinguish between endodermal cells that were the products of EC cell differentiation and the exogenous endoderm. Alkaline phosphatase staining was used to distinguish EC cells from endodermal cells. As predicted by the cell position hypothesis, the PSA-1 EC cells, all of which were internally located, did not differentiate into endodermal cells. Nonspecific inhibition of differentiation did not account for the lack of PSA-1-derived endoderm since the PSA-1 cells in such aggregates did differentiate into columnar ectodermal-like cells. Similar experiments were also conducted with F9 cells. In this case, aggregation cultures contained retinoic acid to induce F9 cells to differentiate into visceral endoderm. In cultures containing F9 cells surrounded by parietal-like endodermal cells, no F9-derived endoderm was detected either autoradiographically or by assaying for alpha-fetoprotein production, a visceral endoderm marker. Thus, retinoic acid-induced endodermal differentiation was also regulated by cell position. Collectively, the above results provide strong evidence for the hypothesis that cell position regulates endodermal differentiation in aggregates of EC cells.     

An adhesion-defective variant of F9 embryonal carcinoma cells fails to differentiate into visceral endoderm

Adhesion-defective EC cells were isolated from a population of mutagenized F9 cells by serial transfer of cells that did not adhere to gelatin-coated dishes. The variant cells grew in suspension as multicellular clusters of loosely aggregated cells. The cells adhered to, but did not flatten on, fibroblast monolayers and extracellular matrix produced by parietal-like endoderm. Two different mutant cell lines exhibited increased sensitivity to the lectin abrin and decreased sensitivity to wheat germ agglutinin, suggesting that changes in cell surface glycosylation are associated with the mutant phenotype. These adhesion-defective mutants were used to study the relationship between cell-cell adhesion and endodermal differentiation. Unlike wild-type cells, when cultured with low concentrations of retinoic acid (RA) in suspension culture, the mutant cells did not form embryoid bodies but remained as loosely adhering strings of cells. Electron microscopic examination revealed that most of the differentiated variant cells resembled parietal endoderm, and this was confirmed by immunofluorescent staining for TROMA-3 marker. The levels of some of the markers that characterize the differentiative pathways were examined by immunoprecipitation and by enzyme-linked immunosorbent assay (ELISA). The variant line produced higher levels of laminin and type IV collagen compared to the wild-type cells. alpha-Fetoprotein (AFP) was produced at a significantly lower level by the variant compared to wild-type F9 cells during the differentiative process. The results show that variant cells differentiated toward parietal endoderm but have a very much restricted ability to differentiate to visceral endoderm. We conclude that aggregation and/or compaction provide some essential signals during the differentiation of F9 cells into epithelial layers of visceral endoderm.     

Isolation and characterization of peanut agglutinin-resistant embryonal carcinoma cell-surface variants

The isolation and characterization of variant embryonal carcinoma (EC) cells possessing altered cell-surface structures is described. The lectin peanut agglutinin (PNA), which binds to EC cells but not their differentiated derivatives, was used to select the variants. Clones resistant to the cytotoxic effect of PNA were isolated at a frequency of 4 × 10^–5 following mutagenesis. The resistant phenotype was stable in the absence of selection in all eight clones tested. The increased frequency of resistant clones following mutagenesis and the stability of the phenotype suggests a mutational origin. Somatic cell hybrids constructed between wild-type cells and two different PNA-resistant cell lines were sensitive to PNA; this suggests that the resistant phenotype is recessive. Binding assays demonstrated that resistant cells exhibited a twofold to fourfold reduction in the total amount of PNA bound. Together with the recessive behavior of the phenotype, this suggests that resistant cells are deficient for PNA receptors. The PNA-resistant cells also showed reduced binding of monoclonal antibody against stage-specific embryonic antigen 1 (SSEA–1) in indirect cytotoxicity tests. All eight PNA-resistant lines isolated were tumorigenic in syngeneic mice and gave rise to well-differentiated teratocarcinomas. The PNA-resistant cells behaved like their wild-type parents in a cell recognition assay; when incubated in suspension with endodermal cells, they sorted out to form simple embryoid bodies (a core of EC cells surrounded by an endodermal rind). Thus, EC cells can form tumors, differentiate, and recognize differentiated cells in a sorting assay despite a reduction in expression of the embryo-specific cell surface structures (s) that bind PNA and anti-SSEA-1 antibody.     

Differentiation in vitro of human-mouse teratocarcinoma hybrids.

The mouse embryonal carcinoma (EC) line, PCC4, was used to construct a series of somatic cell hybrids which contain a single or a few human chromosomes. The hybrids all retained the EC phenotype as determined by morphology, expression of SSEA-1, lack of cell surface H-2 antigen and cytokeratin filaments, high alkaline phosphatase levels, the ability to form EC tumors ectopically in nude mice, and the ability to differentiate in response to retinoic acid. Constitutively differentiated cloned lines were derived from retinoic acid-treated hybrid cultures. Several derived lines had a phenotype indistinguishable from that of parietal endoderm cells, which includes synthesis of large amounts of laminin, type IV procollagen, and plasminogen activator. One differentiated line showed a fibroblast-like morphology. The differentiated lines derived from two of the hybrids, MCP6 and GEOC4, stably maintained the sole human chromosomal component present in the EC progenitors. These EC hybrids therefore provide a system to study developmental regulation of the introduced and stably maintained human genetic material derived from a variety of cell types.     

Differentiation of EC cells in vitro by the fluorescent dye Hoechst 33342

The fluorescent dye Hoechst 33342 is able to differentiate F9 EC cells at low concentrations. This differentiation is accompanied by synthesis of large amounts of laminin, production of a well-developed cytoskeleton, disappearance of the SSEA-1 antigen, and synthesis of large amounts of fibronectin, all characteristics of the primitive endoderm. The dye immediately blocks the cells at the S/G2 phase of the cell cycle and produces a complete arrest in proliferation. This effect is not specific for the nullipotent F9 cell line, as multipotent EC cell lines like PCC3, P19, and PCC4 can also be easily differentiated into the same pathway by treatment with the Hoechst dye. In contrast, the dye has no remarkable effects on terminal differentiated, immortalized cells like NIH 3T3 or the parietal endoderm-like cell PYS-2.     

Modulation of lysosomal-associated membrane glycoproteins during retinoic acid-induced embryonal carcinoma cell differentiation

Differentiation of the murine embryonal carcinoma (EC) cell lines F-9 and PC-13, induced by beta-all transretinoic acid (RA) resulted in an increased level of two lysosomal-associated membrane glycoproteins (LAMP-1 and LAMP-2). After differentiation, the levels of both LAMPs in the EC cells were comparable to those found in visceral and parietal endoderm cell lines (PSA-5E and PYS-2, respectively). RA treatment of the EC cells also resulted in an increase in the apparent Mr of both LAMPs apparently due to increased glycosylation because the deglycosylated LAMP-1 from undifferentiated and from differentiated cells had a similar electrophoretic migration. Indeed, the binding of 125I-labeled L-phytohemagglutinin (L-PHA) to glycoproteins with Mr or 90,000-130,000 increased after differentiation and about 24 times more 125I-labeled L-PHA bound to LAMP-1 isolated by immunoprecipitation from extracts of RA-treated F-9 cells than to LAMP-1 from undifferentiated cells. The increased level of the LAMPs was detected in F-9 cells treated with greater than 10(-7) M RA and required greater than 48 h of treatment as did the increased expression of the B1 chain of laminin, an established marker for differentiation in this system. LAMP-1- and L-PHA-reactive glycoproteins were localized by fluorescence techniques to intracellular vesicles, presumably lysosomes, and to the cell surface and both increased after RA treatment. LAMP-2 was barely detectable intracellularly in undifferentiated cells but could be detected clearly after differentiation. In contrast, no LAMP-2 could be detected on the cell surface either before or after differentiation of F-9 cells. The increased level and glycosylation of both LAMP-1 and LAMP-2 was observed also in cells treated with a synthetic chalcone carboxylic acid analog of RA and by combination of either retinoid with dibutyryl cyclic AMP. These results demonstrate that differentiation of EC cells is accompanied by changes in the synthesis and glycosylation of LAMP glycoproteins and that these changes are specific for the cell type that results after differentiation.     

Stage-specific embryonic antigen 3 as a marker of visceral extraembryonic endoderm

The distribution of the stage-specific embryonic antigen SSEA-3 was studied immunohistochemically on postimplantation mouse embryos. This carbohydrate antigen, identified as an epitope of a globo-series ganglioside isolated from human teratocarcinoma cells (Kannagi et al., 1983, J. Biol. Chem.258, 8934–8942) was originally detected on the zygote and mouse early cleavage-stage embryos. It disappears on the early blastocyst and reappears on the primitive endoderm of the implanting blastocyst (Shevinsky et al., 1982, Cell30, 697–705). We now show in the early egg cylinder (on the sixth day of pregnancy) SSEA-3 is present in the entire visceral endoderm but not in any other part of the conceptus. From Day 7 of pregnancy onward, SSEA-3 is restricted to the extraembryonic visceral endoderm and the visceral yolk sac cells. Therefore, SSEA-3 is a useful marker for this endodermal cell lineage in midgestational mouse embryos.     

A pluripotent human stem-cell clone isolated from the TERA-2 teratocarcinoma line lacks antigens SSEA-3 and SSEA-4 in vitro, but expresses these antigens when grown as a xenograft tumor

Human embryonal carcinoma (EC) cells generally express the cell-surface, stage-specific embryonic antigens 3 and 4 (SSEA-3 and SSEA-4), the epitopes of which are defined by two monoclonal antibodies that recognize different portions of an extended globoseries oligosaccharide. To examine further the relationship between these epitopes and the human EC phenotype, we investigated the properties of two newly isolated clones from the human teratocarcinoma cell line, TERA-2. One clone expresses SSEA-3 and SSEA-4; the other does not. Nevertheless, these clones otherwise resemble one another, and based upon their morphology, their expression of other cell-surface antigens, and their ability to form xenograft tumors containing a variety of cell types, we conclude that both clones are composed of pluripotent human EC cells. When exposed to retinoic acid in vitro, neither clone differentiates as extensively as other clones that we have previously derived from TERA-2. These observations indicate heterogeneity among stem cells derived from a single human teratocarcinoma, and suggest that SSEA-3 and SSEA-4 are not necessarily integral features of the human EC phenotype. On the other hand, EC cells in xenograft tumors derived from the SSEA-3- and SSEA-4-negative clone re-express these epitopes. Further, this re-expression is stable, since EC cell lines that are SSEA-3- and SSEA-4-positive grow out when the tumors are explanted in vitro. We conclude that the expression of these globoseries epitopes can be modulated by environmental influences.     

Isolation and characterization of a near-diploid differentiated cell line from a murine teratocarcinoma that differentiates into muscle

Cell lines corresponding to various cell lineages of the mouse embryo have been isolated from murine teratocarcinomas. Embryonal carcinoma cell lines are developmentally equivalent to the embryonic ectoderm or inner cell mass. Most of these cell lines have a modal chromosome number equal or close to 40, the normal mouse complement. However, cell lines corresponding to more advanced cell lineages (e.g., endoderm) are tetraploid or hypotetraploid and display multiple chromosomal rearrangements. This paper describes the isolation of a near-diploid differentiated cell line (LT-D) from an LT teratocarcinoma. The modal chromosome number of LT-D is 40, and this number is stable during at least 12 mo of continuous culture. LT-D cells are morphologically distinct from embryonal carcinoma cells and no longer express the SSEA-1 cell surface antigen or high alkaline phosphatase activity characteristic of embryonal carcinoma cells. LT-D cells can be induced to fuse into structures resembling myotubes. The formation of these structures is accompanied by expression of the muscle-specific isozyme of creatine phosphokinase and desmin, a muscle-specific component of intermediate filaments. Lastly, LT-D cells do not form tumors in syngenetic mice.     

A gene sequence expressed only in undifferentiated EC, EK cells and testes.

A clone, EC1, has been isolated from a cDNA library prepared from 4-day embryoid bodies formed by suspension culture of PSMB EC cells. This clone has been used to screen a variety of RNA sources including adult tissues, embryonal carcinoma (EC), and endoderm cell lines. A 3-kb poly(A)+ RNA species was found to be present only in undifferentiated EC cells and adult mouse testes. This species was significantly reduced in testes of W/Wv mice compared with wild-type at this locus. Germ cells and their progeny are therefore implicated as the source of the RNA in testes. Hybrid-selected RNA from PSMB could be translated in vitro into a 35-kd protein, but no translatable message was evident in either PYS-2 (parietal), or PSA5-E (visceral) endoderm cell lines. DNA sequencing of the EC1 insert revealed that it is 744 bp in length, the 3' 460 bp of which are in open reading frame. Comparison with known sequences have shown no significant homology. EC1 subclones in M13 have been used to generate single-stranded probes for hybridisation to RNA in situ in tissue sections. Hybridisation of the strand complementary to RNA produces a signal limited to the central regions of embryoid bodies formed on suspension culture of embryo-derived EK cells coinciding with the presence of undifferentiated cells. Probing of a mouse genomic library and Southern blots of liver DNA with EC1 reveals that the gene is present as a single copy.     

Immunohistochemical localization of the early embryonic antigen (SSEA-1) in postimplantation mouse embryos and fetal and adult tissues

Distribution of the stage-specific embryonic antigen (SSEA-1) was studied in postimplantation murine embryos, fetuses, and adult mice by immunohistochemical techniques. SSEA-1 was also localized on the stem cells of differentiating solid teratocarcinomas and on the surface of core cells of solid embryoid bodies. At the egg cylinder stage the antigen is restricted to embryonic ectoderm and visceral endoderm. During subsequent development SSEA-1 becomes localized to portions of the brain and primordial germ cells. In addition some sites of the urogenital anlage are SSEA-1 positive. In adult mice, the epithelium of the oviduct, the endometrium, and the epididymis are the cells most reactive with the monoclonal antibody to SSEA-1; although some areas of the brain and kidney tubules are weakly positive. Study of this antigenic determinant might disclose some previously unexpected cell lineage relationships and/or might elucidate events necessary for reproduction.     

The Activin A-Dependent Proliferation of PCC3/A/1 Embryonal Carcinoma Cells in Serum-Free Medium

Examination of the growth requirements of murine embryonal carcinoma cells (EC cells) or embryonic stem cells (ES cells) in serum-free medium revealed that PCC3 EC cells required activin A to grow and/or survive in such medium. In the absence of activin A, PCC3 cells began to disintegrate within 3 days under any serum-free conditions examined. P19 and AT805 EC cells grew even in serum-free medium without activin A but their growth rates were slightly facilitated by its addition. F9 EC cells also grew in the medium without activin A and its addition somewhat inhibited their growth rate. Three independently isolated ES cell lines and feeder-dependent PSA-1 EC cells also grew in serum-free medium without activin A if leukemia inhibitory factor (LIF) was supplemented. The addition of activin A had little effect on their growth rates. These findings suggest that PCC3 EC cells are a sort of nutritional mutant requiring activin A, thus making them useful in stidies on the growth regulatory mechanisms of EC/ES cells and/or the action of activin on EC/ES cells.     

Autonomy of “nullipotent” and pluripotent embryonal carcinoma cells in differentiating aggregates

Previously it was observed that mixture cultures of “nullipotent” and pluripotent embryonal carcinoma (EC) cells failed to differentiate, suggesting that nullipotent cells might restrict the differentiation of pluripotent cells (M. J. Rosenstraus and A. J. Levine, 1979, Cell17, 337–346). This report shows, however, that the differentiation of mixed cultures is dependent on the relative growth rates of the two cell types and that nullipotent cells do not directly affect pluripotent cell development. When the growth rate of nullipotent cells was modulated by taking advantage of drug-resistance markers, mixed cultures, containing pluripotent PSA-1 cells and a genetically marked subclone of nullipotent F9 cells, exhibited extensive differentiation. The differentiated cells were PSA-1 derivatives, whereas, the F9 cells remained as undifferentiated EC cells. Similar results were obtained when a genetically marked PSA-1 subclone was cocultured with a second nullipotent cell line, Nulli SSC1. Thus nullipotent and pluripotent EC cells appear to express their developmental potential autonomously in mixed cultures. This implies that the nullipotent cell lines studied are intrinsically incapable of responding to the conditions that trigger in vitro differentiation of EC cells upon aggregation.     

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.     

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.     

Immunomagnetic isolation of primordial germ cells and the establishment of embryonic germ cell lines in the mouse

The stage-specific embryonic antigen 1 (SSEA-1) is a cell marker of primordial germ cells (PGCs). In the present study, it is shown that isolation and purification of PGCs from 8.5-11.5 days post coitum (dpc) embryos can be achieved by a immunomagnetic cell sorting method using SSEA-1 antibody-conjugated magnetic beads, and then the sorted PGCs can be used for long-term culture under strict culture conditions to derive embryonic germ (EG) cell lines. Five independent EG cell lines with male karyotypes have been established. They show both a strong alkaline phosphatase activity and expression of the SSEA-1 antigen, and are karyotypically stable with a modal number of chromosomes in more than 80% of the cells. One of the EG cell lines from 8.5-dpc embryos produced chimeras after injections of the cells into 8-cell host embryos. These procedures could provide a useful and simple method for isolation of undifferentiated cells from a heterogeneous cell population and for establishment of embryo-derived stem cell lines.     

Human teratocarcinoma stem cells: glycolipid antigen expression and modulation during differentiation

Teratocarcinomas are germ cell tumors in which pluripotent stem cells, embryonal carcinoma (EC) cells, undergo differentiation along the pathways resembling those occurring during early embryogenesis. Human EC cell lines established in vitro provide a model for studying embryonic cellular differentiation in a way that is pertinent to early human development. The predominant glycolipid antigens expressed by EC cells of both humans and mice have globoseries core structures; in humans they are terminally modified to yield the monoclonal antibody-defined stage-specific embryonic antigens SSEA-3 and SSEA-4, and also globo-ABH antigens; in the mouse terminal modification yields the Forssman antigen rather than SSEA-3 and -4. These observations focus attention on the possible role of the P-blood group system, which regulates synthesis of globoseries oligosaccharides, in the behavior of cells in the early embryo and in teratocarcinomas. Marked changes in the core structures of the cell surface glycolipids occur as the EC cells differentiate; thus globoseries structures rapidly diminish and are replaced by lactoseries and then by ganglioseries glycolipids. During differentiation of the NTERA-2 line of pluripotent human EC cells into neurons and other cell types, the various subsets of differentiated cells that arise are distinguished by their differential expression of new glycolipid antigens, particularly ganglioside GT3 (recognized by antibody A2B5), and ganglioside 9-0-acetyl GD3 (recognized by antibody ME311). Neurons are found among the A2B5+/ME311- cells.     

Isolation and characterization of a near-diploid differentiated cell line from a murine teratocarcinoma that differentiates into muscle

Summary Cell lines corresponding to various cell lineages of the mouse embryo have been isolated from murine teratocarcinomas. Embryonal carcinoma cell lines are developmentally equivalent to the embryonic ectoderm or inner cell mass. Most of these cell lines have a modal chromosome number equal or close to 40, the normal mouse complement. However, cell lines corresponding to more advanced cell lineages (e. g., endoderm) are tetraploid or hypotetraploid and display multiple chromosomal rearrangements. This paper describes the isolation of a near-diploid differentiated cell line (LT-D) from an LT teratocarcinoma. The modal chromosome number of LT-D is 40, and this number is stable during at least 12 mo of continuous culture. LT-D cells are morphologically distinct from embryonal carcinoma cells and no longer express the SSEA-1 cell surface antigen or high alkaline phosphatase activity characteristic of embryonal carcinoma cells. LT-D cells can be induced to fuse into structures resembling myotubes. The formation of these structures is accompanied by expression of the muscle-specific isozyme of creatine phosphokinase and desmin, a muscle-specific component of intermediate filaments. Lastly, LT-D cells do not form tumors in syngenetic mice. This work was supported in part by National Institutes of Health, Bethesda, MD, Grant CA-15823 and by a departmental gift from R. J. Reynolds Industries, Inc.     

Different patterns of glycolipid antigens are expressed following differentiation of TERA-2 human embryonal carcinoma cells induced by retinoic acid, hexamethylene bisacetamide (HMBA) or bromodeoxyuridine (BUdR)

NTERA-2 cl.D1 human embryonal carcinoma (EC) cells were induced to differentiate by either bromodeoxyuridine (BUdR) or hexamethylene bisacetamide (HMBA), and also by retinoic acid. Following exposure to each of these inducers, the globoseries glycolipid antigens stage-specific embryonic antigens -3 and -4 (SSEA-3 and -4) and the glycoprotein antigen TRA-1-60, all characteristic of the human EC cell surface, underwent a marked reduction in expression within about 7 days. At the same time, the lactoseries glycolipid antigen SSEA-1, and ganglioseries antigens A2B5 (GT3) and ME311 (9-0-acetyl GD3) were induced in BUdR- and retinoic acid-treated cells. However, these antigens did not appear during the first 7-14 days of HMBA-induced differentiation. The observations of cell surface antigen expression were paralleled by analysis of glycolipids isolated from the cells by thin-layer chromatography. This analysis, in which the new monoclonal antibodies VINIS-56 and VIN-2PB-22 were included, also revealed expression of gangliosides GD3 and GD2 in all differentiated cultures, albeit at much lower levels following HMBA exposure than following retinoic acid or BUdR-exposure. Further, disialylparagloboside was detected in retinoic acid and BUdR-induced, but not HMBA-induced, cultures. Taken with morphological observations, the results suggest that HMBA induces differentiation of NTERA-2 cl.D1 EC cells along a pathway distinct from the pathway(s) induced by retinoic acid and BUdR.