The broad objective of this research is to determine how the morphogenetic movements of amphibian neurulation are controlled by tissue interactions. The specific objective is to test the hypothesis that the detailed shaping of the neural anlagen of the amphibian, Xenopus laevis is controlled by two tissue interactions: 1) an edgewise induction of the dorsal ectoderm by the dorsal axial mesoderm to produce simple lengthening (extension) and narrowing (convergence) of the neural plate; 2) a basal induction of the dorsal ecotderm by dorsal mesoderm to produce cell shape changes (columnarization and wedging) in the dorsal ectoderm. Furthermore, we predict that the type of dorsal mesoderm will determine what cell shape changes are induced. We have been able to obtain different morphogenetic reswponses from dorsal ecectoderm, depending on the type of mesoderm used as an inductor and whether it is placed edgewise to the ectoderm or beneath it. We will test the above two-inductor hypothesis by explanting dorsal, axial mesoderm, or parts of it, and placing it in edgewise or basal apposition to specific regions of the ectoderm. We will monitor the degrtee and pattern of extension and convergence with high resolution video-optical disk recordings and cell shape changes in cross-fractured material with SEM. By using these two inductive routes to call forth different morphogenetic components of neural plate morphogenesis, separately and together, we hope to characterize the role of each in the overall process. These results will be basic to our understanding of the early steps in neural development of vertebrates and the methods and concepts developed will be applicable to a variety of other apporaches to analysis of neurogenesis at the molecular and cellular levels.
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