Immortalization of early embryonic cell derivatives after the transfer of the early region of simian virus 40 into F9 teratocarcinoma cells.

F9 embryonal carcinoma (EC) cells were transformed using a recombinant plasmid carrying simian virus 40 (SV40) early genes linked to the promoter-enhancer region of the early transcription unit 1A (E1A) of adenovirus type 5. One clone of transformed cells, F9-K4B2, contained several integrated copies of the plasmid and expressed SV40 early genes (T antigens) only when it was induced to differentiate in vitro by the addition of retinoic acid and dibutyryl-cAMP. From the cell population positive for T antigen, it is possible to isolate permanent cell lines with high efficiency. Most of these cells exhibit stable traits that are characteristic of parietal endoderm. We also obtained another cell type which did not express the specific markers of either undifferentiated EC cells or endoderm cells; this type might represent a different stage of commitment in the differentiation of F9 cells. All clones are tumorigenic when injected into irradiated syngeneic mice, and they maintain their phenotype after successive passages in vivo as well as in vitro. The introduction of SV40 early genes into other EC cell lines and early mouse embryos appears to be a promising approach for the immortalization of early embryonic cells.