The long term objective of this research is to determine the cellular and molecular mechanisms that pattern and shape the embryonic vertebrate nervous system, using the frog, Xenopus laevis. The current objective is to determine the mechanisms that cause the morphogenetic processes of convergence and extension of the neural plate in the early embryo.
The first aim i s to characterize regional variations of a type of cell motility that we have shown to be important in convergent extension. Explant of neural plates will be cultured with and without the underlying mesodermal tissues, which control the type of cell motility expressed by the neural plate cells. Video-microscopy of fluorescently labeled cells in these explants will reveal the different types of cell motility used in the extension of the neural plate. The forces contributed by each type of motility to the extension will be measured with a biomechanical measuring machine. The second specific aim is to determine the role of cell adhesion, mediated by the cell adhesion molecule, N-cadherin, in the process of extension of the neural plate. Cell adhesion will be increased by injecting RNAs encoding the normal cell adhesion molecule or decreased by injecting RNAs encoding a mutant form of the molecule, along with RNAs encoding green fluorescent protein (GFP), which will allow one to do fluorescence video-microscopy of the affected cells. Video recordings of the motility of the normal cells and of cells with increased or decreased adhesion will reveal the role of cell-cell adhesion and N-cadherin in the cell motility driving convergence and extension. Effects of changing cell adhesion on the stiffness of the neural plate and on its production of forces of extension will be measured with the biomechanical measuring machine. These measurements will reveal the role of cell adhesion in the mechanical properties of the neural plate that are essential for extension. The combined approach of manipulating adhesion, recording cell motility with video-microscopy, and direct measurement of mechanical properties and forces promise to solve some long standing problems in neural development.
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