A dynamic requirement for community interactions during Xenopus myogenesis

The community effect is an interaction among a group of many nearby cells that is necessary for them to maintain tissue-specific gene expression and differentiate co-ordinately. A community interaction is required for the muscle precursor cells of the Xenopus embryo to develop into terminally differentiated muscle, but exactly when and where the community effect acts during myogenesis has not been determined. Here, we ask whether dependence on the community effect varies with the developmental age of the muscle precursor cells. We find that dependence on the community signal changes with time through the muscle precursor cell population. During neurulation muscle precursor cells that are still in the vicinity of the blastopore and that are fated to form posterior muscle continue to require interactions with their neighbours, while differentiation of the anterior paraxial mesoderm,which gastrulated earlier, is independent of cell contact at this time. Thus the time during which a particular sub-population of muscle precursor cells requires a community interaction is related to their final destination along the anterior-posterior axis. In addition we show that this later acting community interaction around the blastopore involves FGF signalling

Maternal XTcf1 and XTcf4 have distinct roles in regulating Wnt target genes

AbstractWnt signaling pathways have essential roles in developing embryos and adult tissue, and alterations in their function are implicated in many disease processes including cancers. The major nuclear transducers of Wnt signals are the Tcf/LEF family of transcription factors, which have binding sites for both the transcriptional co-repressor groucho, and the co-activator β-catenin. The early Xenopus embryo expresses three maternally inherited Tcf/LEF mRNAs, and their relative roles in regulating the expression of Wnt target genes are not understood. We have addressed this by using antisense oligonucleotides to deplete maternal XTcf1 and XTcf4 mRNAs in oocytes. We find that XTcf1 represses expression of Wnt target genes ventrally and laterally, and activates their expression dorsally. Double depletions of XTcf1 and XTcf3 suggest that they act cooperatively to repress Wnt target genes ventrally. In contrast, XTcf4 has no repressive role but is required to activate expression of Xnr3 and chordin in organizer cells at the gastrula stage. This work provides evidence for distinct roles for XTcfs in regulating Wnt target gene expression