The long-term objective of this project is to fathom the processes by which the segmentally iterated, identified neurons of the nervous system of the leech Theromyzon rude acquire their identity in embryonic development. Experiments are designed to reveal whether the determination of the exact number of segments to be formed (32), and if the specific identity of each segment and its set of neurons, is attributable to information intrinsic to the segmental founder cell clones or to topographically fixed external cues. Other experiments will examine the extent to which the developmental decision between a neuronal and an epidermal fate among members of the segmental founder cell clones resembles the corresponding decision process known to occur in insects. Experimental methods will include intracellularly injected cell lineage tracers, indirect immunofluorescence, and specific cell ablations. This project addresses the mechanisms underlying normal and abnormal embryonic development in an animal whose relative simplicity, high degree of order and ready experimental accessibility make it an unusually favorable experimental material. Dr. Stent expects to obtain insights of general relevance for the understanding of developmental processes, including those governing human development, by studying the determination of cell fate in the leech embryo.
