Differential expression of mouse Disabled 2 gene in retinoic acid-treated F9 embryonal carcinoma cells and early mouse embryos.

Using a differential display PCR, we identified a differentially expressed cDNA fragment which was detectable in retinoic acid (RA) treated F9 embryonal carcinoma (EC) cells but not in untreated F9 cells. A homology search of the Gene Bank indicated that the cDNA fragment is part of the mouse homolog of the Drosophila Disabled (mDab2) gene. Aggregate cultures of F9 EC cells grown in the presence of the RA differentiated into nonmalignant cells resembling the visceral endoderm of the mouse embryo. Upon induction of endodermal differentiation with 10(-7) M RA, the gene expression of mDab2 was increased gradually during the first 96 h. Neither undifferentiated F9 cells, nor the undifferentiated aggregate cells without RA expressed mDab2. Whole-mount in situ hybridization and quantitative RT-PCR also showed that the temporal expression pattern of the mDab2 gene coincides with the initiation pattern of RA synthesis that occurs during mouse embryogenesis. Also, two alternative splicing messages of mDab2 were detected in a tissue specific manner. All the data indicate that mDab2 may play an important role in RA-induced signal transduction during mouse development.     

Differentiation of F9 embryonal carcinoma cells

We found that monolayer cultures of F9 cells induced to differentiate with trans-retinoic acid (RA) contain two major subpopulations of cells. These two cell types can be distinguished by their cellular morphology, their pattern of laminin accumulation, and their ability to undergo further differentiation in response to N6-O2-dibutyryl adenosine 3':5' cyclic monophosphoric acid (dBcAMP). Furthermore, the developmental pathway induced by RA appears to lead to two alternative pathways, and differentiation at the branch point is either directly or indirectly controlled by cAMP. Differentiation along one branch of this pathway can be induced by 5-bromodeoxyuridine, whereas differentiation along an unrelated pathway is induced by N'-N'-dimethylacetamide. In all cases, differentiation is closely paralleled by suppression of the tumorigenic phenotype, indicating that these two processes are tightly linked and probably share a common step.     

Neuronal differentiation in F9 embryonal carcinoma cells

F9 line embryonal carcinoma cells were induced to differentiate into neural direction by long-term treatment of monolayer cultures with retinoic acid and dibutyryl cyclic AMP. Bi- and multi-polar cells appeared, expressing acetylcholinesterase and neurofilament proteins but not markers of glial differentiation including GFA-protein. Nerve growth factor combined with both retinoic acid and dibutyryl cyclic AMP greatly enhanced the development of neuron-like morphology and induced expression of immunoreactivity to tyrosine hydroxylase as well as to Leu-encephalin-like peptides. Similarly, serotonin-like immunofluorescence but not substance P-like immunoreactivity was demonstrable in such cultures. In addition, synaptic-like vesicles were often found in the processes. Analysis of matrix expression in neuronally differentiated F9 cells revealed marked increase in laminin production, as judged by immunofluorescence and immuno-electron microscopy, but no demonstrable intracellular staining for fibronectin or type IV collagen. The results with neuronal cells contrast with the expression of all the three matrix components in endodermally differentiating F9 cells in the same cultures.     

Retroviral vector gene expression in F9 embryonal carcinoma cells.

When F9 embryonal carcinoma (EC) cells are infected with retroviral vectors, the efficiency of expression of selectable genes is considerably lower than that in mouse fibroblasts infected with the same retroviral vectors. In this study, several retroviral vectors with regulatory sequences placed immediately 5' to a selectable gene were constructed, packaged, and used to infect mouse fibroblasts and F9 EC cells. With selection as an assay, there was a hierarchy of relative expression in F9 cells compared with that in mouse fibroblasts. These internally placed regulatory sequences are the source of the mRNAs detected in F9 EC cells, while both retroviral long-terminal-repeat promoters and internal promoters are the source of steady-state mRNAs in mouse fibroblasts. This effect was observable with both the internally placed herpes simplex virus thymidine kinase promoter and the Moloney murine leukemia virus promoter.     

Pluripotent differentiation of single F9 embryonal carcinoma cells

F9 embryonal carcinoma cells were induced to form a variety of differentiated cell types in monolayer culture. Cells with the morphological, histochemical and immunocytochemical properties of parietal and visceral endoderm, neurones and adipocytes were identified. Cells expressing Thy-1 antigen and large, multinucleated cells expressing cytoplasmic fibronectin were also observed. Various cell types were found together in colonies derived from individual F9 cells, allowing us to conclude that F9 cells are pluripotent in vitro.     

Retinoic acid-induced differentiation of F9 embryonal carcinoma cells

The ability of retinoic acid (RA) to induce differentiation in embryonal carcinoma (EC) cells was examined by growing mouse F9 cells in a medium containing 1 μM RA. The altered properties of the cells became apparent after a lag period of approx. 24 h and were fully expressed after 5 days. The RA-induced phenotype was characterized by changes in cell morphology, slowing of the rate of cell multiplication, reduced DNA and protein synthesis, altered pattern of polypeptide synthesis and changes in cell surface components. The slowing of cell multiplication and general reduction in the rate of protein synthesis was paralleled by changes in the relative rates at which different polypeptides were synthesized. Two-dimensional gel electrophoretic analysis of [³⁵S]methioninelabelled cell proteins showed an altered relative synthesis of at least fifty polypeptides. The relative rate of synthesis of two components of the cytoskeleton identified as vimentin and tropomyosin were shown to increase.     

F9 embryonal carcinoma cells can differentiate into endoderm-like cells

The mouse teratocarcinoma cell line, F9, has been used in many laboratories as the epitome of the “nullipotent” embryonal carcinoma cell line. However, careful inspection of F9 cultures reveals the presence of small numbers of cells which possess several properties of endoderm, particularly parietal endoderm, and which can be shown to derive from the embryonal carcinoma component. Furthermore, tumors of F9 cells include isolated patches of endoderm-like cells surrounded by a thick secretion resembling Reichert's membrane. The proportion of endoderm-like cells in F9 cultures can be increased to varying degrees by causing the cells to form aggregates and/or maintaining them at high density for several days, although the endoderm-like cells produced in these ways contribute very little to the formation of subcutaneous tumors from the resultant mixed cultures. Differentiated cell types other than endoderm are rarely observed in F9 monolayer or aggregate cultures, even after several weeks. Cloning studies support the view that most, if not all, F9 cells can differentiate, albeit at very low incidence.     

Comparison of polysaccharide synthesis between preimplantation stage mouse embryos and F9 embryonal carcinoma cells

Polysaccharide synthesis was compared between preimplantation stage mouse embryos and F9 embryonal carcinoma cells. When cells were labelled with [3H]fucose, elution profiles of the pronase digest from a Sephacryl S-200 column were similar for the two cell types and both had characteristic large polysaccharides of the same size (Mr 20-500K), although embryos contained less large polysaccharide than F9 cells, and embryonic polysaccharides were less acidic, suggesting poor sialosylation. A significant proportion of [3H]mannose was incorporated into complex-type glycopeptides in F9 cells, whereas in the case of embryonic cells most glycopeptides remained as high mannose-type. The most striking difference was observed when cells were labelled with galactose. In the case of embryonic cells, 90% of the radioactivity was incorporated into glycogen, whereas only 0.1% of the incorporated galactose occurred in this molecule in F9 cells. These observations indicate that carbohydrate metabolism of morula-stage embryos is very different from that of F9 cells.     

Calcitonin-responsive adenylate cyclase in cultured F9 embryonal carcinoma cells

Hormonal responsiveness of the adenylate cyclase system of cultured F9 teratocarcinoma cells was investigated. Of numerous hormones tested only calcitonin, (−)isoproterenol, and prostaglandin E₁, stimulate F9 adenylate cyclase activity. Of the active hormones, calcitonin is the most potent stimulator of cAMP formation. Treatment of intact F9 cells with calcitonin results in a time- and hormone concentration-dependent increase in the intracellular concentration of cAMP. cAMP accumulation is enhanced within 5 min after addition of 60 nM synthetic salmon calcitonin to intact F9 cells. These results raise the possibility that calcitonin may play a regulatory role in early embryonic development.