Functional diversity of Xenopus lymphoid enhancer factor/T-cell factor transcription factors relies on combinations of activating and repressing elements.
Lymphoid enhancer factor/T-cell factor (LEF/TCF) high mobility group box transcription factors are the nuclear transducers of the Wnt/beta-catenin signaling cascade. In Xenopus, three members of the LEF/TCF family, XLEF-1, XTCF-3, and XTCF-4, with distinct but partially overlapping expression patterns have been identified. The individual Xenopus LEF/TCF family members differ extremely in their properties of target gene regulation. We observed that in contrast to LEF-1, neither XTCF-3 nor XTCF-4 can induce secondary axis formation upon ventral overexpression in Xenopus embryos. To identify functional motifs within the LEF/TCF transcription factors responsible for target gene activation or repression, we created various mutants and a set of XLEF-1/XTCF-3 chimeras. In overexpression studies, we asked whether these constructs can mimic an activated Wnt/beta-catenin pathway and lead to the formation of a secondary body axis. In addition, we examined their capacity to rescue a loss-of-function phenotype given by dominant negative LEF-1 expression. We further analyzed their ability to directly activate target genes in reporter gene assays using the LEF/TCF target promoters, siamois and fibronectin. We found that a region homologous to exon IVa of human TCF-1 is an activating element. This is flanked by two small repressing motifs, LVPQ and SXXSS. Our findings implicate that the motifs identified here play an essential role in determining cell type-specific activity of LEF/TCF transcription factors.
Gradl
Dietmar
D
Abteilung Biochemie, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. dietmar.gradl@zi2.uni-karlsruhe.de
König
Alexander
A
Wedlich
Doris
D
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D005091:Exons; D005799:Genes, Dominant; D017930:Genes, Reporter; D024002:HMGB Proteins / Q000737:chemistry* / Q000502:physiology*; D006609:High Mobility Group Proteins / Q000737:chemistry* / Q000502:physiology*; D015151:Immunoblotting; D051821:Lymphoid Enhancer-Binding Factor 1; D051379:Mice; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051820:TCF Transcription Factors; D015534:Trans-Activators; D058127:Transcription Factor 3; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors / Q000737:chemistry* / Q000502:physiology*; D014162:Transfection; D051153:Wnt Proteins; D014981:Xenopus; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
C495266:CTNNB1 protein, Xenopus; C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D024002:HMGB Proteins; D006609:High Mobility Group Proteins; C116548:Lef1 protein, Xenopus; D051821:Lymphoid Enhancer-Binding Factor 1; D011518:Proto-Oncogene Proteins; D051820:TCF Transcription Factors; C544912:TCF7L1 protein, human; C544917:Tcf3 protein, Xenopus; C544913:Tcf7l1 protein, mouse; D015534:Trans-Activators; D058127:Transcription Factor 3; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D012313:RNA