Fig. 4. Dose-dependent induction of NKX2.1 and albumin by FGF1. Induction of NKX2.1 or albumin protein (I) or gene (R) expression in ventral endoderm treated with recombinant FGF1, at designated concentrations, within 2 hours of isolation. Double-immunostaining (A-H) or RT-PCR analysis (J) of explants performed after 1-2 days of culture. Arrow indicates focal positive expression. (G-I) Ventral endoderm treated with FGF8B, at similar concentrations, did not consistently induce NKX2.1 or albumin; adjacent section stained with FOXA2 as marker of ventral endoderm. (K) Number of positive explants/total tested, at indicated concentration of FGF1.