A Genetic Screen Identifies New Regulators of Steroid-Triggered Programmed Cell Death in Drosophila

摘要

The steroid hormone ecdysone triggers the rapid and massive destruction of larval tissues throughntranscriptional cascades that culminate in rpr and hid expression and caspase activation. Here we describenthe use of genetic screens to further our understanding of this steroid-triggered programmed cell deathnresponse. Pupal lethal mutants were screened for specific defects in larval salivary gland destruction. A pilotnscreen using existing P-element collections resulted in the identification of mutations in known cell deathnregulators, E74 and hid, as well as multiple alleles in CBP (nejire) and dTrf2. A large-scale EMS mutagenesisnscreen on the third chromosome resulted in the recovery of 48 mutants. These include seven multiallelicncomplementation groups, at least five of which do not map to regions or genes previously associated with cellndeath. Five mutants display defects in the transcriptional induction of rpr and hid, and all display a penetrantnblock in caspase activation. Three were mapped to specific genes: CG5146, which encodes a protein ofnunknown function, Med24, which encodes a component of the RNA polymerase II mediator complex, andnCG7998, which encodes a putative mitochondrial malate dehydrogenase. These genetic screens provide newndirections for understanding the regulation of programmed cell death during development.