Developing Caenorhabditis elegans neurons may contain both cell-death protective and killer activities.

We developed a method for examining the effects of overexpressing cell-death-related genes in specific Caenorhabditis elegans neurons that normally live. Using this method, we demonstrated that the cell-death genes ced-3, ced-4, and ced-9 all can act cell autonomously to control programmed cell death. Our observations indicate further that not only the protective activity of ced-9 but also the killer activities of ced-3 and ced-4 are likely to be present in cells that normally live. We propose that both in C. elegans and in other organisms a competition between antagonistic protective and killer activities determines whether specific cells will live or die. Our results suggest a genetic pathway for programmed cell death in C. elegans in which ced-4 acts upstream of or in parallel to ced-3 and ced-9 negatively regulates the activity of ced-4.