Fig. 3. Diverse functions for Xenopus TCF/LEFs. Required roles for TCF/LEFs in early Xenopus development from fertilisation (left in figure) to gastrulation stages of development (right in figure). Maternal expression of Tcf genes is required for regulating dorsal axis induction, with TCF-3 expression being required for repressing transcription and TCF-1 expression being required for activating transcription. However, TCF-1 is also required in a repressing function and TCF-3 and TCF-4 function partially redundantly with TCF-1 in activating transcription of target genes of dorsal axis development (see Standley et al., 2006). Zygotic expression of Tcf/Lef genes is required for regulating mesoderm induction and subsequent mesoderm patterning, with TCF-3 required as a transcriptional repressor and TCF-1 required as a transcriptional activator for mesoderm induction and TCF-1 and LEF-1 required as transcriptional activators for mesoderm patterning (see Liu et al., 2005).