| Programmed cell death (PCD) is critical for the development and homeostasis of multicellular organisms. This dissertation explores mediators of PCD within the developing Drosophila retina. Several core components of the cell death machinery have been identified in flies, including caspases and an Apaf-1 ortholog. A search of genomic databases revealed two Drosophila Bcl-2 family members---dBorg-1 and dBorg-2. Removal of dBorg-1 during embryonic development resulted in excess glial cells, demonstrating its pro-apoptotic function. dBorg-1 efficiently induced apoptosis in cell cultures but also demonstrated protective activity when death stimuli were introduced. Ectopic expression of dBorg-1 in the eye led to subtle defects that were strongly potentiated by ultraviolet (UV) irradiation, resulting in a dramatic loss of retinal cells.; UV light is absorbed by cellular proteins and DNA, promoting skin damage, aging and cancer. The Drosophila retina was used to explore additional mediators of the UV response. The pupal retina enters a period of heightened UV sensitivity, a stage closely associated with its period of normal developmental PCD. Irradiated cells underwent morphology changes and apoptotic cell death; these defects could be completely accounted for by DNA damage. Cell death---but not morphology changes---was blocked by the caspase inhibitor P35. Genetic screens were performed in order to identify regulators of the DNA damage response. This and subsequent biochemical and genetic analysis pointed to the central role of hid expression and Diap1 protein stability in controlling the UV response. Surprisingly, the Drosophila p53 ortholog Dmp53 was required to protect cells from UV-mediated cell death, an effect attributed to its role in DNA repair.; Normal developmental PCD was explored by looking at a detailed timecourse of pupal retinal cell death as well as characterizing PCD defective mutants. The timecourse revealed three periods of PCD including a previously undocumented early peak in cell death. Previous work had isolated mutations that dominantly modify the cell death phenotype of irreC-rst mutants. One such mutant, C134, failed to complement mutations in elongation initiation factor-4e (eif4e). Examination of eIF4E revealed it promoted PCD within the retina, an effect likely attributable to translation of pro-apoptotic genes. |
