Activation of the β-catenin/Lef-Tcf pathway is obligate for formation of primitive endoderm by mouse F9 totipotent teratocarcinoma cells in response to retinoic acid

The morphogen retinoic acid promotes the formation of primitive endoderm in mouse F9 teratocarcinoma cells as does the stimulation of the Frizzled-1 pathway. We investigated whether the β-catenin/Lef-Tcf-sensitive transcriptional pathway activated by Frizzled-1 plays a role in the retinoic acid-induced pathway to primitive endoderm formation. An analysis of Lef-Tcf-sensitive transcription reveals increased transcription at 1 and 4 h post-treatment with retinoic acid. The stimulation of Lef-Tcf-sensitive transcription as well as the formation of primitive endoderm was accompanied by the stabilization of β-catenin as observed in activation of the Frizzled-1 pathway. Transient transfection of F9 cells with an expression vector harboring a dominant-negative mutant of Tcf4 resulted in the attenuation of both the increase in Lef-Tcf-sensitive transcription and formation of primitive endoderm in response to the morphogen. Clones stably transfected to express the dominant-negative Tcf4 displayed a block in retinoic acid-induced activation of Lef-Tcf-sensitive transcription and primitive endoderm formation. These data reveal the obligate role of the β-catenin/Lef-Tcf transcriptional pathway in the action of the morphogen retinoic acid.