ABSTRACT 9603851 BOOKER During development of an organism, more cells are formed than are needed for the final body plan. This excess cell formation is particularly noteworthy in the nervous system, where individual cells have unique roles. Programmed cell death (PCD) plays a central role in the elimination of excess cells and in sculpting developing systems. The biochemical regulation of PCD is complex, involving a number of different biochemical pathways. One such pathway, ubiquitin-dependent proteolysis, is believed to play a key role in the final phases of at least some PCD in most organisms. Ubiquitin is probably present in all cells of all or most organisms and is thought to be responsible for the degradation of many cellular proteins. Consistent with this hypothesis, some but not all cells undergoing PCD show a large increase in the expression of ubiquitin and other proteins associated with the ubiquitin proteolytic pathway. One of the best characterized examples of PCD is the death of both neurons and muscles during metamorphosis of the moth Manduca sexta. In the moth there is a dramatic increase in the expression of ubiquitin following the onset of PCD. This project involves a series of experiments designed to better define the role that ubiquitin proteolysis plays in PCD. Preliminary experiments have shown that inhibitors of ubiquitin proteolysis can selectively block some PCD in the developing moth. These results will be exploited in an attempt to determine whether the ubiquitin proteolytic pathway is involved solely in the rapid removal of dying cells, or if this pathway is also important in the regulation of the PCD process. In the moth, the pattern of gene expression in cells undergoing PCD is altered in a characteristic manner. If ubiquitin proteolysis is involved in the regulation of PCD, then disrupting this pathway should alter the normal pattern of gene expression observed during PCD. The investigators will address this question by determining whether the pattern of gene expression is altered following application of the inhibitors. The near universal distribution of ubiquitin suggests that it could play a role in the PCD observed in other organisms, including humans. For example, increases in the expression of ubiquitin are also seen in the PCD associated with many developing systems, including the spinal motor neurons of chicks and the developing eye of flies. These studies in the moth have the potential to lead to a better understanding of the cellular and molecular mechanisms underlying PCD in a wide variety of organisms
