Distinct cell killing properties of the Drosophila reaper, head involution defective, and grim genes.

The Drosophila reaper, head involution defective (hid), and grim genes play key roles in regulating the activation of programmed cell death. Two useful systems for studying the functions of these genes are the embryonic CNS midline and adult eye. In this study we use the Gal4/UAS targeted gene expression system to demonstrate that unlike reaper or hid, expression of grim alone is sufficient to induce ectopic CNS midline cell death. We also show that in both the midline and eye, grim-induced cell death is not blocked by the Drosophila anti-apoptosis protein Diap2, which does block both reaper- and hid-induced cell death. grim can also function synergistically with reaper or hid to induce higher levels of midline cell death than observed for any of the genes individually. Finally we analyzed the function of a truncated Reaper-C protein which lacks the NH2-terminal 14 amino acids that are conserved between Reaper, Hid, and Grim. Ectopic expression of Reaper-C revealed cell killing activities distinct from full length Reaper, and indicated that the conserved NH2-terminal domain acts in part to modulate Reaper activity.