Fig. 1. GATA4 induces cardiac-specific genes in the absence of skeletal muscle. (A) RNase protection assay showing induction by GATA4 of three cardiac markers, as well as the gut marker IFABP (intestinal fatty acid binding protein). Note that MEF2D induces only MLC2 and not the complete cardiogenic programme. (B,C) Absence of myogenic factor MYOD at stage 18, as well as skeletal muscle marker MLC1 (myosin light chain 1), in Gata4-injected animal pole explants. A wide range of Gata4 mRNA doses were injected to rule out concentration-dependent effect on MLC1 expression. (D) Eomesodermin is induced by GATA4 at stage 10.5. (E) GATA4 and GATA5 are efficient inducers of cardiac tissue, whereas GATA6 is more efficient in inducing LFABP (liver fatty acid binding protein). (F) Mixer and GATA4 induce gut tissue (IFABP), whereas only GATA4 additionally induces cardiac tissue. GATA4 induces IFABP in some, but not all experiments where cardiac markers were induced (data not shown). GATA1 does not induce cardiac tissue (G), whereas both GATA1 and GATA4 induce blood marker globin (H). Samples for RNA expression analysis were collected at stage 37/38. (EF1: elongation factor 1 ; t: transfer RNA control; u: uninjected animal caps; E: embryo control.)