UBC Theses and Dissertations
A functional genomics approach identifies novel genes involved in steroid-hormove induced programmed cell death in Drosophila Chittaranjan, Suganthi
Programmed Cell death (PCD) is a highly conserved and genetically controlled event that plays important roles in animal development, homeostasis and disease. Our first objective was to discover and characterize new genes involved in PCD. Since many PCD genes are conserved in Drosophila, and steroid-induced PCD of larval salivary glands (SGs) is transcriptionally regulated with features of both apoptosis and autophagy, we used this exceptionally well-suited in vivo system and performed Serial Analysis of Gene Expression (SAGE) in three pre-death stages. SAGE identified 1244 expressed transcripts, including genes involved in autophagy, apoptosis, immunity, cytoskeleton remodeling, and proteolysis. Of the 1244 transcripts, 463 transcripts belonged to knownlpredicted genes and were 5-fold differentially expressed prior to cell death. Next, we investigated the role of differentially expressed genes from SAGE, in cell death or cell survival, by RNA interference (RNAi ) in l(2)mbn haemocyte Drosophila cells. l(2)mbn cells undergo morphological changes in response to ecdysone treatment, and ultimately undergo PCD. We used cell viability, cell morphology, and apoptosis assays to identify the death-related genes and determined their ecdysone dependency and function in cell death regulation. Our RNAi screen identified six new pro-death related genes, including SH3PXJ and Soxl4, and 21 new pro-survival genes including SoxN. Identification of Soxl4 as pro-death and SoxN as pro-survival suggests that these Sox box proteins may have opposing roles in ecdysone-mediated cell death. Our final objective was to elucidate the function of CG409], a Drosophila homologue of human TNF-alpha induced proteins 8 (TNFAIP8) we identified from SAGE. We created loss-of-function and overexpression mutants of CG4091 to study gene function in vivo and employed immunoprecipitation and mass-spectrometry assays to identify proteins interacting with CG409] in vitro. We identified two proteins that are involved in n-fatty acid oxidation and several cytoskeletal proteins as interaction partners. Immunofluorescence based assays in vivo and in vitro revealed that CG409] is necessary for cytoskeletal remodeling. Further, defects in CG4091 expression affect cellular functions such as autophagy and lipid metabolism/trafficking that require an intact cytoskeleton. Together, our studies provided new insights into the molecular mechanisms involved in Drosophila SG cell death.
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