Genetic Analysis of the Timing , Morphology and Degradation of Cell

Programmed cell death is an important process during the development and life of multicellular organisms. The process by which many cell types undergo programmed cell death is morphologically and mechanistically similar and has been termed apoptosis. To understand how cells achieve this conserved cell-death fate, we have analyzed the genetic control of downstream events in the cell-death process in the nematode Caenorhabditis elegans. We have found that mutations in the gene ced-8 alter the kinetics of appearance of cell corpses during C. elegans embryogenesis and that ced-8 encodes a protein similar to human XK, a putative membrane transport protein that is implicated in a form of hereditary neuroacanthocytosis. We isolated loss-of-function mutations in a novel gene, ced-11, which alter the conserved morphology of programmed cell deaths. We found that CED-11 shares similarity with TRP calcium channels, suggesting that calcium signaling may be important for the downstream morphological events in apoptotic cells. To develop markers for studying downstream cell-death processes during programmed cell death, we developed methods to assay DNA degradation in C. elegans cell corpses. We examined the kinetics of DNA degradation in the wild type and in the DNA degradation-defective mutant nuc-1 and found that DNA degradation during programmed cell death involves multiple genetically-separable steps, not all of which are under the control of nuc-1. We found that NUC-1 is similar in sequence to mammalian DNase II, thus confirming a role for this endonuclease in the pathway for programmed cell death. Thesis Supervisor: H. Robert Horvitz Title: Professor of Biology