Fig. 7.

The Gata4 G4 early endoderm enhancer is dependent on its conserved Forkhead (Fox) site for activity in vivo. Wild type and mutant versions of the Gata4-G4-lacZ transgene were used to generate transgenic embryos. Lateral (A, B) and frontal view (C, D) of X-gal stained transgenic embryos at E8.5 are shown. The wild type construct reproducibly directed expression to the definitive endoderm (A, C). Mutation of the Gata4 G4 Forkhead site completely abolished transgene expression in each of three independently-generated F₀ transgenic embryos analyzed (B, D). Arrowheads mark the definitive endoderm in all four panels.