One fundamental aspect of morphogenesis is the separation of cell groups from one another to form recognizable and functionally distinct tissues and organs. The long therm goal of this work is to understand the molecular basis of tissue segregation. Tissue segregation is assumed to be due to the differential expression of cell surface adhesion molecules. It is also assumed that the initiation of tissue segregation in the early embryo is controlled by the same intercellular inductive signals that specify areas of the embryo to differentiate along new lineage pathways. This investigation will test these hypotheses with reference to one particular adhesion system, the cadherin/catenin complex in early Xenopus embryos, specifically studying adhesive and signaling functions. Cadherins mediate homotypic cell-cell adhesion. Inside the cell, they are complexed to the catenins, (alpha, beta, gamma) that are thought to provide a link between cadherins and the cytoskeleton. Catenins may also play role in intercellular signaling pathways. EP cadherin is the first cadherine to be expressed in Xenopus embryos. Previous experiments showed that it is required for adhesion in the blastula. Overexpression of the same molecule leads to a loss of dorsal axial structures. This implicates the cadherin/catenin complex not only in adhesion, but also in signaling pathways int he embryo. This hypothesis was supported by preliminary experiments, where targeted destruction of beta catenin mRNA in oocytes, caused embryos to develop without dorsal axes. We will extend these studies by: 1. Distinguishing when and where during embryonic development beta catenin is required for dorsal axis formation. 2. Identifying the signaling pathway that is perturbed in beta catenin depleted embryos. 3. Identifying the role of alpha catenin. 4. Studying the roles of the cadherins and catenins in differential adhesion and tissue segregation. The principal approach to be used will be to cause the underexpression of the target molecule in developing embryos, by injecting specific antisense oligonucleotides into full-grown oocytes, and then fertilizing them. Whole embryos, dissected pieces, or disaggregated cells will be assayed for adhesive and signaling phenotypes. Our published results show that these techniques work. These results will greatly clarify our understanding of the role of the cadherin/catenin complex in tissue formation and provide an important link between adhesion and signaling systems. They will give us insight into how these interactions may break down during abnormal development and in metastasis.
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