Fig. 6. Summary of findings about the required role of Tcf/Lef genes in Xenopus early mesoderm development. Tcf3 gene function is predominantly required in a transcriptional repressor role for mesoderm induction; while Tcf1 gene function is also required for mesoderm induction, but predominantly in a transcriptional activator role. However, Tcf1 gene function has another required role, also mainly as an activator, in ventrolateral mesoderm patterning, independent of its role in mesoderm induction. Lef1 gene function is also required as an activator for ventrolateral mesoderm patterning. Perturbing Tcf3 gene function also affects ventrolateral mesoderm induction, but only in a roundabout way, i.e. because ventrolateral mesoderm patterning is dependent on prior mesoderm induction, which is dependent of normal Tcf3 function.