Though the Wnt/β-catenin signaling pathway is known to play key roles during Xenopus axis specification, whether it signals exclusively through Lef/Tcf transcription factors in this process remains unclear. To investigate this issue, we generated transgenic frog embryos expressing green fluorescent protein (GFP) driven by a Lef/Tcf-dependent and Wnt/β-catenin-responsive promoter. This promoter is highly sensitive and even detects maternal β-catenin activity prior to the large-scale transcription of zygotic genes. Unexpectedly, GFP expression was observed only in some, but not all, known Wnt/β-catenin-positive territories in Xenopus early development. Furthermore, ubiquitous expression of dominant Lef-1 protein variants from transgenes revealed that zygotic Lef/Tcf activity is required for the ventroposterior development of Xenopus embryos. In summary, our results suggest that endogenous Wnt/β-catenin activity does not result in obligatory Lef/Tcf-dependent gene activation, and that the ventroposteriorizing activity of zygotic Wnt-8 signaling is mediated by Lef/Tcf proteins.
Bibliographical noteFunding Information:
The authors are grateful to Drs. R. Grosschedl, R. Kemmler and S. Hoppler for sharing plasmids. We thank Dr. W. Mei for discussion of the project. This work is supported by grants of the National Foundation of Natural Science (30170111, 30270650) and National Key Project for Basic Research of China (2001CB50991) to X.D.; L.X. was supported by a grant of the Human Frontiers of Science Program (RG0039/1999-M) to R.R., which was also used to support X.G.’s work at the Adolf-Butenandt-Institute. In addition, X.G. received a visitors fellowship from the Max-Planck-Society.
- Axis specification
- Restriction enzyme-mediated integration transgenesis