Regulation of programmed cell death in the development of the drosophila antenna and ovary

Abstract

Apoptosis, or programmed cell death, is a genetically controlled form of cell suicide used to rid an organism of superfluous or damaged cells and serves as one of the major mechanisms for patterning during the development of complex animal structures. The antenna and ovary of the fruitfly, Drosophila melanogaster, were chosen as model systems in which to examine the molecular mechanisms of developmental apoptosis. The caspases are a family of cysteine proteases required for the execution of cell death, while the inhibitor of apoptosis protein Diap-1 is responsible for repressing the function of caspases. Diap-1, also known as Thread, was discovered in 1922 with the isolation of thread^1, a homozygous viable mutant whose molecular nature is unknown. thread was given its name due to its branchless or thread-like arista, the featherlike structure at the tip of the antenna. thread^1 antennal imaginal discs show excessive cell death during a brief period of larval development, which corresponds to a significant decrease in levels of Thread protein. Caspase activity is found more broadly than apoptotic DNA fragmentation in thread1 imaginal discs, suggesting that the mutant fails to inhibit caspases in many cells, but only a fraction succumb to apoptosis. These findings point to a narrow window of development in which regulation of programmed cell death is essential to the formation of the arista. Additionally, a candidate mutation has been discovered in a transcriptional regulatory region of the thread gene. Proof that this mutation is responsible for the branchless aristal phenotype may have important implications for understanding tissue-specific gene regulation during organogenesis. In the ovary, apoptotic roles for the DP subunit of the E2F transcription factor and the actin binding protein Profilin were investigated. While mutants for DP affect the regulation of Cytochome c and caspase activity in nurse cells, Profilin mutants show milder effects. To further characterize the role of apoptosis in the ovary, an ethylmethane sulphonate (EMS) mutagenesis screen was conducted and has led to the identification of several new genes. Future study of the apoptotic pathway will assist in developing treatments for diseases associated with its misregulation.