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.

Zygotic Wnt/beta-catenin signaling preferentially regulates the expression of Myf5 gene in the mesoderm of Xenopus.

Zygotic Wnt signaling has been shown to be involved in dorsoventral mesodermal patterning in Xenopus embryos, but how it regulates different myogenic gene expression in the lateral mesodermal domains is not clear. Here, we use transient exposure of embryos or explants to lithium, which mimics Wnt/beta-catenin signaling, as a tool to regulate the activation of this pathway at different times and places during early development. We show that activation of Wnt/beta-catenin signaling at the early gastrula stage rapidly induces ectopic expression of XMyf5 in both the dorsal and ventral mesoderm.

Lithium induces dorsal-type migration of mesodermal cells in the entire marginal zone of urodele amphibian embryos.

The effect of lithium (Li) on gastrulation movements was investigated during the development of the urodele amphibianPleurodeles waltl. Attention was focused on mesodermal cell migration. Under conditions of Li treatment providing a maximal enhancement of dorsoanterior structures, it was found that the dorsoventral polarity of gastrulation was abolished.

A study of cell interactions involved in Pleurodeles waltlii epidermal differentiation.

A polyclonal antibody (SP-2) has been produced, which recognizes antigens expressed in epidermal cells of Pleurodeles waltlii embryos. The antigens appear first at the end of gastrulation in the external surface of the embryo and are selectively expressed in ectodermally derived epidermal structures. Ectodermal commitment was investigated using cell cultures and blastocoel graft experiments.

Expression of Three Gastrula Cell Surface Glycoproteins during Embryonic and Larval Development in the Amphibian Pleurodeles waltlii: (amphibian/antibodies/cell surface glycoproteins/development).

We have previously reported the identification of cell surface glycoproteins in Pleurodeles waltlii gastrulae. In an attempt to study the expression of three of these cell surface glycoproteins (proteins referred to 1, 11 and 14), we have produced monoclonal and polyclonal antibodies by immunizing mice with the spots of the three selected glycoproteins excised from 2D-gels. Expression of the three glycoproteins was detected on the surfaces of all cells during embryonic development.

Synthesis of laminin-related polypeptides in oocytes, eggs and early embryos of the amphibian Pleurodeles waltlii.

In the amphibian Pleurodeles waltlii, lamininrelated polypeptides (amphibian-LN) are present in the extracellular matrix underlying the blastocoel roof of gastrulating embryos. Immunoprecipitation with affinity-purified anti-laminin antibodies demonstrated that amphibian-LN is synthesized in oocytes (from stage III onward), eggs and throughout early development. At the late blastula stage, when experiments were carried out with animal and vegetal halves, there were no regional differences in the pattern of amphibian-LN synthesis.

Binding of anti-fibronectin to early amphibian ectoderm does not result in inhibition of neural induction under in vitro conditions.

Antibodies directed to fibronectin (anti-FN) were injected into the blastocoel of late blastulae of Xenopus laevis. Two animal caps (ectoderm) were isolated, when control embryos reached the early gastrula stage, and were combined with untreated upper blastopore lip in the sandwich method. In two control series fibronectin or Holtfreter solution was injected into the blastocoel.