Investigation on cytoophidium function and filament-forming proteins

In 2010, three independent groups reported that cytidine-5'-triphosphate synthase could form a filamentous structure. The term "cytoophidium" was coined in recognition of its observed serpent-like structure in Drosophila cells. In the last seven years of study on cytoophidia, lots of models and hypotheses related to cytoophidia have been put forward. In 2014, three independent studies pointed out that the CTP synthase-based cytoophidium is a functionally inactive structure. These studies built models for the inhibition of the enzyme by filamentation; research on cytoophidia had transited from descriptions to mechanisms. In this thesis, I study the function of the cytoophidium from two major aspects. Firstly, I describe the effects of dimerization and tetramerization interphases of CTP synthase mutants on filament assembly in Drosophila melanogaster, suggesting that the cytoophidium is an enzymatically inactive structure. Secondly, through a genome-wide screening of filament-forming proteins in Saccharomyces cerevisiae, I identify nine novel filament-forming proteins and select one candidate, asparagine synthetase, for further study of the stress regulation of cytoophidia. Results show that heat shock, cold shock, osmotic stress and oxidative stress induce filament formation of asparagine synthetase. These results provide new insights into the function of cytoophidia, the components of cytoophidia and filamentation regulation, indicating new possibilities in cell biology and enzymology.