Key questions about apoptosis remain to be answered. For example, neither the role nor the regulation of dynamin-related GTPases is fully understood. Experiments are proposed that address these questions in the worm Caenorhabditis elegans, an organism that has proven to be a powerful tool for apoptosis studies. Dynamin-related GTPases required for mitochondrial membrane dynamics have recently been implicated in apoptosis in worms and mammals. For example, the C. elegans dynamin-related protein DRP-1 is at least partially required for apoptosis and can be sufficient for apoptosis when ectopically expressed. How DRP-1 contributes to apoptosis is currently unclear. One model that has been proposed is that DRP-1 induces mitochondrial division thereby causing mitochondrial fragmentation;however this model remains to be tested. Furthermore, members of the family of Bcl-2-like proteins have been implicated in the regulation of dynamin-related GTPases in apoptotic cells. For example, in C. elegans, the Bcl-2 family members EGL-1 and CED-9 are required for DRP-1-mediated mitochondrial fragmentation in apoptotic cells. How EGL-1 and CED-9 regulate the activity of DRP-1 during apoptosis is currently unknown. However, our preliminary results suggest that CED-9 and DRP- 1 might physically interact in apoptotic cells. The goal of the proposed studies is to investigate the mechanisms through which DRP-1 contributes to apoptosis and to determine the role of the Bcl-2 family members EGL-1 and CED- 9 in the regulation of DRP-1 in apoptotic cells. To that end, we will use biochemical, cell- biological and genetic approaches and perform studies in C. elegans and in vitro. Deregulated apoptosis contributes to the development and manifestation of a number of diseases such as cancer, autoimmune diseases and neurodegenerative diseases. Key questions about the biology of apoptosis remain to be answered and the studies proposed address some of these questions. Therefore, results from the proposed studies will improve our knowledge of apoptosis and hence our ability to understand and treat various human disorders.