THE HEAD INVOLUTION DEFECTIVE GENE OF DROSOPHILA-MELANOGASTER FUNCTIONS IN PROGRAMMED CELL-DEATH

Deletions of chromosomal region, 75C1,2 block virtually all programmed cell death (PCD) in the Drosophila embryo. We have identified a gene previously in this interval, reaper (rpr), which encodes an important regulator of PCD. Here we report the isolation of a second gene in thi s region, head involution defective (hid), which plays a similar role in PCD. hid mutant embryos have decreased levels of cell death and con tain extra cells in the head. We have cloned the hid gene and find tha t its expression is sufficient to induce PCD in cell death defective m utants. The hid gene appears to encode a novel 410-amino-acid protein, and its mRNA is expressed in regions of the embryo where cell death o ccurs. Ectopic expression of hid in the Drosophila retina results in e ye ablation. This phenotype can be suppressed completely by expression of the anti-apoptotic p35 protein from baculovirus, indicating that p 35 may act genetically downstream from hid.