FGF8, Wnt8 and Myf5 are target genes of Tbx6 during anteroposterior specification in Xenopus embryo.

The T-box transcription factor Tbx6 is required for somite formation and loss-of-function or reduced activity of Tbx6 result in absence of posterior paraxial mesoderm or disorganized somites, but how it is involved in a regulatory hierarchy during Xenopus early development is not clear. We show here that Tbx6 is expressed in the lateral and ventral mesoderm of early gastrula, and it is necessary and sufficient to directly and indirectly regulate the expression of a subset of early mesodermal and endodermal genes. Ectopic expression of Tbx6 inhibits early neuroectodermal gene expression by strongly inducing the expression of posterior mesodermal genes, and expands the mesoderm territory at the expense of neuroectoderm.

Antagonistic interaction between IGF and Wnt/JNK signaling in convergent extension in Xenopus embryo.

The homeobox gene Otx2 is expressed during gastrulation in the anterior domain of the vertebrate embryo and is involved in neural and head induction during Xenopus early development. It also prevents convergent extension movements in trunk and posterior mesoderm. Insulin-like growth factors (IGFs) were shown to have similar function.

Identification of distinct genes with restricted expression in the somitic mesoderm in Xenopus embryo.

We have used whole-mount in situ hybridisation to identify genes expressed in the somitic mesoderm during Xenopus early development. We report here the analysis of eight genes whose expression pattern has not been described previously. They include the Xenopus homologues of eukaryotic initiation factor 2beta, methionine adenosyltransferase II, serine dehydratase, alpha-adducin, oxoglutarate dehydrogenase, fragile X mental retardation syndrome related protein 1, monocarboxylate transporter and voltage-dependent anion channel 1.

Frizzled receptor dimerization is sufficient to activate the Wnt/beta-catenin pathway.

Wnt signaling has an important role in cell-fate determination, tissue patterning and tumorigenesis. Wnt proteins signal through seven-pass transmembrane receptors of the frizzled family to activate beta-catenin-dependent transcription of target genes. Using early Xenopus embryos, we show that frizzled receptors can dimerize and that dimerization is correlated with activation of the Wnt/beta-catenin pathway.

Activation of Gbetagamma signaling downstream of Wnt-11/Xfz7 regulates Cdc42 activity during Xenopus gastrulation.

Wnt-11/Xfz7 signaling plays a major role in the regulation of convergent extension movements affecting the dorsal marginal zone (DMZ) of gastrulating Xenopus embryos. In order to provide data concerning the molecular targets of Wnt-11/Xfz7 signals, we have analyzed the regulation of the Rho GTPase Cdc42 by Wnt-11. In animal cap ectoderm, Cdc42 activity increases as a response to Wnt-11 expression.