Fig. 1. Wnt/β-catenin-mediated inhibition of cardiogenesis in Xenopus is via GATA4/6 function. Gene expression analysis at stage 32 by RT-PCR of animal cap explants, injected with RNA encoding Activin (Act, 50 fg) to induce cardiogenesis (A), dorsal marginal zone (DMZ) explants (B) and whole embryos (C), which were injected with β-cateninGR (βGR, 50 pg), GATA4GR (G4GR, 200 pg) or GATA6GR (G6GR, 200 pg), as indicated, and were cultured with dexamethasone from stages 8, 10 or 18 where indicated. Activation of β-catenin abolishes activin-induced (A) and endogenous (B) expression of GATA4 and GATA6, as well as cardiogenesis, as monitored by marker gene expression. (C) In whole embryo analysis, activation of β-catenin abolishes heart muscle-specific differentiation markers (MLC2, TnIc), but causes only a relatively weak reduction of markers that are not exclusively heart specific (GATA4, GATA6, Wnt11, Nkx2-5). However, β-catenin-mediated inhibition of cardiogenic marker gene expression is rescued by concomitant activation of GATA4GR or GATA6GR in all three assays. N/D, not determined; VMZ, ventral marginal zone explant.