Paul Kulesa, California Institute of Technology
During the development of the vertebrate embryo, cell and tissue dynamics give rise to many segmented structures. The segmental units are often sites of specific cell differentiation or regions from which migrating cells emerge or move through. The segmentation process may involve the shaping of tissue, as is the case when the cylindrical cranial neural tube is formed into 7 repeated segments called rhombomeres. Or cells may be organized into spherical balls called somites, which form in pairs adjacent to and on either side of the neural tube. Although several separate mechanisms have been proposed for the formation of these structures, attempts to test these hypotheses or gain further insight into cellular mechanisms have been hampered by the lack of an assay system to culture a live vertebrate embryo and image cell and tissue dynamics during morphogenesis. We have developed a whole chick embryo explant culture system in order to study cell and tissue movements with time-lapse video microscopy. Individual cells and small populations of cells can be labeled by microinjections with fluorescent dyes and visualized with high resolution microscopy. Cellular activity is then studied through intravital microscopy of labeled cells. Generation of time-lapse recordings of the movements and differentiation of these cells will allow for insight into the underlying cellular mechanisms of rhombomere and somite formation as wells as a comparison of such segmented structures with genetic expression domains.