Fig. 7. A model of the action of GATA4 in ectodermal explants. (A) GATA4 converts embryonic ectoderm to both endodermal and cardiomyocyte fates. Endoderm and WNT/ß-catenin antagonise cardiac tissue formation. (B) The dominant-negative Sox17 construct and the WNT antagonist Dkk1 each promote cardiomyocyte fate at the expense of endodermal fate. Sox17ßEnR could inhibit the endoderm-inducing activity and promote the cardiogenic activity of GATA4 directly (1), and/or prevent the maintenance of endoderm (2), and/or convert endoderm to cardiomyocytes (3). WNT/ß-catenin could interfere with cardiogenesis either directly or indirectly by promoting endoderm formation (Lickert et al., 2002).