| dc.description.abstract | Balance between saturated and unsaturated fatty acids is a key factor for maintaining the property and function of cellular membranes. The enzyme fatty acid desaturase catalyzes the production of unsaturated fatty acids in cells. While metazoans carry multiple fatty acids desaturases, named Stearoyl CoA Desaturases (SCDs), the budding yeast Saccharomyces cerevisiae has only one SCD, encoded by OLE1. This enzyme is essential for cell viability of budding yeast. However, it is unclear how desaturase regulates cellular processes by controlling fatty acid desaturation. In my study, I attempt to gain insights into this question by systematically analyzing the phenotypes of temperature-sensitive ole1 mutants. I first used the real-time polymerase chain reaction to examine OLE1 gene expression, which showed a higher level of the OLE1 transcript in ole1 mutants than the wild type, consistent with the notion that deficiency in the fatty acid desaturation promotes OLE1 expression. Cycloheximide chase assay showed that Ole1 is a short-lived protein and that the mutant proteins are more unstable at the restrictive temperature, suggesting that the mutations may compromise protein folding and cause instability. The lipidomic analysis showed a reduced level of unsaturated fatty acids and an increase of short chain fatty acids in ole1 mutants. In addition, phosphatidic acid is dramatically increased in ole1 mutants and triacylglyceride is decreased. Fluorescence recovery after photobleaching assay for an endoplasmic reticulum membrane protein showed a reduced mobility in the ole1 mutant, indicating that unsaturated fatty acids contribute to a fluid membrane. Furthermore, I performed genome-wide transcriptome analysis to understand how cells respond to lipid saturation. Notably, the result showed an altered expression profile of genes involved in sphingolipid and sterol biosynthesis, indicating their interplay with lipid saturation. In summary, the results reveal a global remodeling of lipid and transcription profiles in response to lipid saturation. My study opens up new research directions in mechanistic understanding of how these changes impact on cellular physiology. | en_US |