Bcl-2 Function in Drosophila

Bcl-2 family members are pivotal regulators of programmed cell death (PCD). In mammals, pro-apoptotic Bcl-2 family members initiate early apoptotic signals by causing the release of cytochrome c from the mitochondria, a step necessary for the initiation of the caspase cascade. Worms and flies do not show a requirement for cytochrome c during apoptosis, but both model systems express pro- and anti-apoptotic Bcl-2 family members. Drosophila encodes two Bcl-2 family members, Debcl (pro-apoptotic) and Buffy (anti-apoptotic). To understand the role of Debcl in Drosophila apoptosis, we produced an authentic null allele at the Debcl locus. Although gross development and lifespans were unaffected, we found that debcl was required for pruning cells in the developing central nervous system. debcl genetically interacted with the ced-4/Apaf-1counterpart, dark, but was not required for killing by RPR proteins. Surprisingly, in a model of caspaseindependent cell death, we found that heterologous killing by Murine Bax required debcl to exert its pro-apoptotic activity. DebclKO mutants were also significantly affected for mitochondrial density. Taken together, these findings suggest that evolutionary functions impacting mitochondrial properties represent ancient activities which preceded the evolution of these proteins as central regulators of PCD.