THESIS
2016
viii, 62 pages : illustrations (some color) ; 30 cm
Abstract
Lipid droplets (LDs) are conserved organelles for energy storage in cells. It contains a core of neutral lipids, i.e. triacylglycerols and sterol esters, surrounded by a phospholipid monolayer. Dysregulation of lipid storage in LDs leads to metabolic diseases in human, such as congenital generalized lipodystrophy, which is caused by mutations in the Seipin gene. Seipin homologs have been identified in S. cerevisiae, C. elegans and other mammals. It has a conserved central domain, with a loop connecting two transmembrane helices. The N- and C-termini of the Seipin protein are divergent in different species. Previous studies found that human Seipin localizes to the ER, whereas our lab found that worm Seipin forms tubular cage structures that surround enlarged LDs in C. elegans. Differenti...[
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Lipid droplets (LDs) are conserved organelles for energy storage in cells. It contains a core of neutral lipids, i.e. triacylglycerols and sterol esters, surrounded by a phospholipid monolayer. Dysregulation of lipid storage in LDs leads to metabolic diseases in human, such as congenital generalized lipodystrophy, which is caused by mutations in the Seipin gene. Seipin homologs have been identified in S. cerevisiae, C. elegans and other mammals. It has a conserved central domain, with a loop connecting two transmembrane helices. The N- and C-termini of the Seipin protein are divergent in different species. Previous studies found that human Seipin localizes to the ER, whereas our lab found that worm Seipin forms tubular cage structures that surround enlarged LDs in C. elegans. Differential targeting of worm and human Seipin raises an intriguing question: what are the factors in worm Seipin that contribute to its localization to tubular cages? To address this question, I made constructs expressing a series of human-worm chimeric Seipin and transfected them into COS7 cells. My results identified a region in worm Seipin that is necessary but not sufficient for its proper targeting. Thus, additional factors are involved in the targeting of worm Seipin. Moreover, worm Seipin was targeted to a subset of LDs when it was expressed in COS7 cells, suggesting a conserved mechanism for its proper targeting. To identify proteins that may function in recruiting Seipin to peri-LD cages, I established stable COS7 cell lines that constitutively express Venus-tagged worm Seipin. Additionally, expressing worm Seipin in yeast SEI1Δ strain partially rescued its mutant phenotype, indicating that worm Seipin shares, in part, conserved functions with human Seipin.
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