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Functional characterization of gene regulation by nhr-49 Lee, Ka Young


Nuclear hormone receptors (NHRs) are transcription factors that regulate a wide variety of developmental and physiological processes. NHRs are targets of numerous drugs. However, due to limited knowledge on NHR specificity, many such drugs activate multiple biological pathways downstream of NHRs, leading to undesired side effects. To study NHR specificity in vivo, I used the model organism Caenorhabditis elegans. One C. elegans NHR is NHR-49, which regulates various aspects of lipid metabolism. Specifically, it activates genes involved in fatty acid desaturation and fatty acid β-oxidation by binding to a subunit of the Mediator multiprotein complex, MDT-15. Vice versa, NHR-49 represses genes involved in sphingolipid breakdown by heterodimerizing with another C. elegans NHR, NHR-66. Recently, three point mutations in nhr-49 were identified that promote fatty acid desaturation, but whether these alleles act specifically in this pathway or also affect other nhr-49 regulated processes is not clear. To test whether the mutated residues are linked to specific biological functions, I studied how they affect gene expression and protein-protein interactions by real time quantitative PCR and Yeast 2 Hybrid assays. I found that the three point mutations have different effects on nhr-49 dependent metabolic processes. While all three alleles broadly promoted nhr-49 dependent activation, only one allele affected nhr-49 dependent repression. This shows that the mutations and the corresponding amino acid residues have some association with specific nhr-49 dependent biological processes.

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