FIG. 7.

Constitutive activation of Mek induced primitive endoderm differentiation and repressed Nanog transcription. (A) Afp-GFP ES cells were transfected with Mek mutants with or without PD98059 (25 μM) and selected with hygromycin (100 μg/ml) for 10 days. Images of representative colonies were shown using phase contrast (upper panel) and GFP filters (lower panel). Bars, 100 μm. (B) Nanog β-geo ES cells transfected with Mek mutants with or without PD98059 (25 μM) and selected with hygromycin (100 μg/ml) for 10 days. Phase-contrast images were captured after X-Gal staining (blue). Bars, 100 μm.