Follicle cell actin dynamics and calcium bursts during nurse cell death in Drosophila melanogaster
Candelas, Pelagia Graciela
Cell death is a key component in development and for the continued renewal of tissues. Phagoptosis is a process in which phagocytes directly lead to the death of other cells. This process of cell death is significantly less characterized when compared to other mechanisms of cell death, such as apoptosis. In the Drosophila ovary, phagoptosis appears to play a key role in the developmental process of oogenesis. Recent studies have shown that genes associated with phagocytosis are required for the programmed death of nurse cells in the Drosophila ovary. Ovaries are made up of 15 nurse cells, a single oocyte, and a layer of follicle cells bordering them. During the process of egg chamber development, all of the nurse cells undergo programmed cell death. During late oogenesis, each nurse cell is surrounded by a group of follicle cells referred to as stretch follicle cells. These stretch follicle cells have recently been implicated as a main promoter of nurse cell phagoptosis. However, an exact mechanism to explain how these stretch follicle cells induce nurse cell death is not fully characterized. To achieve a more detailed understanding of this mechanism, we are examining the function of the cytoskeleton in this process via live imaging. We hypothesize that the follicle cell cytoskeleton plays a significant role in nurse death due to the importance of actin during phagocytosis. Further, we intend to use these live imaging studies to investigate the role of calcium before, during, and after clearance of the nurse cells. Previous studies have shown that calcium bursts within the cell are associated with the initiation of phagocytosis in macrophages, as well as other phagocytic cell types. Studies in this thesis were done by utilizing live imaging and have shown dynamic changes in follicle cell actin before and during the death of nurse cells. These confocal microscopy real time videos have revealed that follicle cell actin polymerizes towards the nurse cell immediately before acidification. Following acidification of the nurse cells, the follicle cell actin changes direction, moving towards the phagocytic follicle cell. Additionally, through live imaging we have observed calcium bursts in the follicle cells immediately before nurse cell death. Overall, this work has provided a more detailed understanding of nurse cell death.