Early Events in Leech Embryogenesis

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Embryos of the glossiphoniid leech Helobdella triserialis are well suited for studying cellular events in early development, because they are large, hardy, and contain identifiable cells that are accessible for many sorts of experimental manipulations. These embryos exhibit many phenomena that are of general significance in the development of higher eukaryotes, including cytoplasmic determinants, directed movements of nuclei and mitotic spindles, distinct phases of cleavage and stem cell divisions, epiboly, separable instances of lineage dependent and position dependent fate determination, and epithelial interactions. The research proposed here would employ a variety of techniques, such as: the microinjectin of cell lineage tracers, photosensitizing dyes, drugs and radiochemicals; in situ hybridization; immunohistochemistry; gel electrophoresis; autoradiography; time lapse video recording; and low light fluorescence microscopy. From these studies, a more detailed description of various developmental processes and the mechanisms by which they operate should be generated. In addition, by examining a number of developmental processes in parallel in the same species, it is hoped that some understanding of the higher order mechanisms by which the basic cellular and developmental processes interact will emerge. For example, one part of this project would study the formation of specialized cytoplasmic domains prior to first cleavage and how they might influence the symmetry of the first cleavage. Another part would test the hypothesis that inherited RNAs regulate a change in cell division pattern. The question of how individual cells acquire their specific fates during early embryological development is a basic problem of developmental biology. Dr. Weisblat, using the leech as a model system, proposes a series of experiments to define what influences cell lineages of the embryo.