The long-term goal of this research is to define the cell lineages, cell movements, and cell interactions that contribute to the patterning of the early amphibian embryo and its nervous system. The specific objective in this project is to determine if the expression domains of """"""""early patterning"""""""" genes define sets of cells with distinct lineages, or if individual cells are free to move into or out of the gene expression domains. We hypothesize that the gene expression domains are, in fact, more restricted than would be predicted by the cell lineages and cell movements. The proposed experiments will test the specific hypothesis that the gene expression domains do not delimit cell lineage domains. The experiments will employ the ability of microscopic Magnetic Resonance Imaging (uMRI) to create three- dimensional time lapse movies to better define key cell and tissue events during the embryonic development of the amphibian embryo. At present little is known about some of these because of the inability of light microscopy to follow cells below the surface of the embryo. In particular, the studies will: 1. Determine the normal lineages of cells that contribute to the frog nervous system, the axial mesoderm and the paraxial mesoderm, defining the stages at which founder cell groups for the different tissue types are established. 2. Determine the spatiotemporal relationships of the early cell lineages and founder cell groups to the domains of expression for genes thought to play central roles in embryonic patterning. 3. Test the commitment of cells to the fates implied by their gene expression, by challenging the system with grafting, UV irradiation, and micro-injection of molecules thought to be critical to embryonic patterning - uMRI will be used to better define the cell movements and lineages that bring about the widely studied duplications and alterations of the embryonic axis. The proposed studies will better define key events of early embryogenesis and test the degree to which molecular markers are truly predictive of tissue fates and embryonic patterns. As such, the experiments will perform one of the first tests of what has become a central dogma of developmental biology.
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