Molecular Genetic Analysis of Drosophila tRNA Processing Endonuclease, dRNaseZ
The Drosophila RNase ZL (dRNaseZ) gene encodes a protein with homologs in all eukaryotes. All RNase ZL proteins tested so far possess in vitro endoribonuclease activity that removes the 3’ trailer from pre-tRNA. Mutations in ELAC2, the human ortholog of dRNaseZ, have been associated with predisposition to prostate cancer and infantile hypertrophic cardiomyopathy. However, knowing mutations that lead to pathophysiological conditions is not enough for understanding the development of the diseases or finding cures. Therefore in this dissertation, I used Drosophila as the live model organism and studied the in vivo function of dRNaseZ at the organismal, cellular, and molecular levels. I showed that dRNaseZ is an essential gene, as reduction of its activity results in a strong growth arrest and early larval lethality. Deletion or depletion of dRNaseZ activity blocks the maturation of both nuclear and mitochondrial tRNA, suggesting that it is the sole tRNA 3’-end ribonuclease encoded by the Drosophila genome. I then studied the cell-autonomous role of dRNaseZ, and found that different types of tissues have different requirements for dRNaseZ. In endoreplicating tissues, dRNaseZ controls organ size by supporting cell growth; while in mitotic tissues, dRNaseZ is essential for cell proliferation but not cell growth. I further explored the molecular networks that include dRNaseZ in cell growth and proliferation. Based on the data, we proposed two mechanisms. In endoreplicating tissues, dRNaseZ knockout blocks tRNA maturation, leads to the relocation of mature tRNAs into the nuclei causing a decrease in translation efficiency and an arrest in cell growth. In mitotic tissues, mitochondrial dRNaseZ knockout damages mitochondrial translational machinery, increases ROS production, which serves as a retrograde signal that induces a cell survival genotoxic stress response with a cell cycle delay allowing time for DNA repair. My dissertation identifies the essential roles of dRNaseZ in vivo and helps better illuminate the possible contribution of human ELAC2 to different human disease pathologies.
Xie, Xie, "Molecular Genetic Analysis of Drosophila tRNA Processing Endonuclease, dRNaseZ" (2015). ETD Collection for Fordham University. AAI10013405.