The proper removal of unneeded or damaged cells is indispensable for the normal development and health of multicellular organisms. Cell death is executed in a controlled, or "programmed", manner and often triggered by widespread signals such as steroid hormones. However, it is not well understood why some cells die in response to these signals and others do not. Especially well suited for studying this basic problem is the death of entire organs during insect metamorphosis. The PI's laboratory found that steroid-induced death of the salivary glands of fruit fly (Drosophila) larvae requires prior loss of Fork head (Fkh), a protein that cooperates with steroid hormone in controlling gene expression. These results support the hypothesis that cells are singled out for steroid-induced death by prior elimination of an essential survival factor. The main objective of the project is to further test this hypothesis by determining whether loss of Fkh is not only required but also sufficient to specify a death response to steroid hormone, and by examining how target genes of Fkh mediate the effect of the protein on cell death. Special focus will be on two of these genes. One has been identified by the PI's laboratory as a novel target gene of Fkh whose steroid-induced expression foreshadows cell death. In vertebrates, the counterpart of this gene is strongly upregulated during muscle atrophy. The other gene appears to control changes in the cytoskeleton that are required for death. The project will not only characterize the role of Fkh in cell death but also in the process of autophagy, a 'self-digestion' of the cell's cytoplasm, which precedes salivary gland death and is used in other tissues as a survival rather than a killing mechanism. To achieve these objectives, the PI's laboratory will use modern techniques of molecular biology and take full advantage of the elaborate tools of Drosophila genetics.
Intellectual merit: A central, basically unanswered question in developmental biology is how cells and tissues are singled out for destruction during development. The signaling molecules that induce death usually act very broadly, often eliciting a whole array of cellular responses other than cell death. It is not known how they trigger death in a tissue-specific manner, and why they kill at a specific time but not earlier. Using insect metamorphosis as a model, the study will give a detailed account on how a specific tissue acquires the competence to respond to a systemic steroid signal with cell death. It will thus make an important contribution to our understanding of how specific cells are targeted for programmed death, an aspect of cell death control that is largely understudied. The unique combination of genetic tools available for Drosophila, including the ease of analyses in transgenic animals, will allow insights in a whole organism context that are difficult to obtain in other systems. Fkh as well as the basic biochemical machineries that control and execute death and autophagy are evolutionarily highly conserved. The results of the project will therefore be applicable to other metazoans including humans. Further, it is anticipated that the project will help to shed some light on the poorly understood relationship between cell death and autophagy.
Broader impacts: The PI of the project is actively involved in various teaching activities at the University of Arkansas, Fayetteville, an institution with a high percentage of undergraduate students and an active Honors College. The majority of the undergraduate and graduate students working in his laboratory are women. The project will provide a continued training opportunity for these students. It is especially well suited for teaching undergraduates, who will be heavily involved in the research activities. The PI has been, and will continue to be, actively involved in programs that are aimed at broadening the access of minorities and other underrepresented groups to careers in science (NSF EPSCoR Outreach Program and HHMI Undergraduate Science Education Program). The project will provide the next stepping-stone in the careers of students recruited through these programs.
