PROGRAMMED CELL-DEATH IN DROSOPHILA

During Drosophila development, large numbers of cells undergo natural cell death. Even though the onset of these deaths is controlled by man y different signals, most of the dying cells undergo common morphologi cal and biochemical changes that are characteristic of apoptosis in ve rtebrates. We have surveyed a large fraction of the Drosophila genome for genes that are required for programmed cell death by examining the pattern of apoptosis in embryos homozygous for previously identified chromosomal deletions. A single region on the third chromosome (in pos ition 75C1,2) was found to be essential for all cell deaths that norma lly occur during Drosophila embryogenesis. We have cloned the correspo nding genomic DNA and isolated a gene, reaper, which is capable of res toring apoptosis when reintroduced into cell death defective deletions . The reaper gene is specifically expressed in cells that are doomed t o die, and its expression precedes the first morphological signs of ap optosis by 1-2 h. This gene is also rapidly induced upon X-ray irradia tion, and reaper deletions offer significant protection against radiat ion-induced apoptosis. Our results suggest that reaper represents a ke y regulatory switch for the activation of apoptosis in response to a v ariety of distinct signals.