Fig. 5. BMP4 inhibits early Nkx2.5 expression but not cardiogenesis: injected Gata4 elevates endogenous Gata4 and Gata5 mRNA levels. (A) Nkx2.5 and Nkx2.3 are present in uninjected animal caps (stage 16). BMP4 leads to the disappearance of these transcripts in the presence of ectopic GATA4. (B) BMP4 does not prevent cardiogenesis induced by GATA4 in the presence of Dkk1 or the elevation of Nkx2.5 at tadpole stages (stage 37/38). (C) Injected Gata4 induces endogenous Gata4 and Gata5 mRNA at the tadpole stage, along with cardiac markers. Both endogenous Gata4 and Gata5 mRNAs were detectable in uninjected explants at gastrula and neurula stages, at levels that were not significantly changed by ectopic GATA4 (data not shown).