Fig. 3. SOX17-dependent endoderm and canonical WNT signalling antagonise GATA4. (A) Expression of XWNT8 from the cytoskeletal actin promoter (CSKA) completely inhibits GATA4-mediated cardiogenesis. (B) SOX17ßEnR and the WNT antagonist DKK1 greatly synergise with GATA4 when the latter is activated either at stage 9 or at stage 13. (C) Cerberus, a tri-valent inhibitor of Nodal, BMP and WNT ligands also synergises with GATA4. (D) Chordin does not inhibit GATA4-mediated cardiac tissue formation, confirming that BMP is not required. (E) DKK1, Cerberus and GATA4 antagonise ß-catenin/TCF-dependent transcription in animal caps. The TOPFLASH reporter was co-injected with internal control TK-Renilla luciferase together with indicated RNA. Animal caps were collected at stage 13, and baseline level of normalised luciferase activity (TOPFLASH alone) was set at 100%. Data from three experiments were used. (F) No LFABP can be detected under conditions of efficient cardiac tissue induction. All samples were analysed for RNA expression at stage 37/8.