Abstract
F9 teratocarcinoma stem cells differentiate into parietal endoderm‐like cells when given retinoic acid (RA) and dibutyryl cyclic adenosine monophosphate (DB‐cAMP). It is generally accepted that the stem cells are resistant to the action of cAMP alone and need to be primed by RA in order to respond to cAMP. In this report, we demonstrate that F9 stem cells differentiate into parietal endoderm‐like cells in the absence of exogenous RA when treated with cholera toxin and 1‐methyl,3‐isobutyl xanthine (CT/MIX) or 8‐bromo‐cAMP/MIX (8B^2^‐cAMP/MIX). Cells treated with CT/MIX or 8B^2^‐cAMP/MIX were morphologically similar to parietal endoderm‐like cells, produced high amounts of plasminogen activator, and synthesized both type IV collagen and laminin mRNA. Conversely, markers made in abundance by stem cells such as stage‐specific embryonic antigen (SSEA‐1) and an mRNA species of 6.8 kb (pST6‐135) were markedly reduced in CT/MIX‐treated cells. To prove that cAMP alone could induce differentiation Lipidex‐1000, a hydrophobio gel, was used to remove 80–;90% of the endogenous serum retinoids. F9 cells grown in this retinoid‐depleted serum and treated with 8B^2^‐cAMP/MIX differentiated to parietal endoderm‐like cells as shown by both dramatic changes in morphology and induction of type IV collagen mRNA. Our results indicate that the differentiation of F9 to parietal endoderm‐like cells can be induced by increased intracellular cAMP and is not strictly dependent on the addition of RA.