Increase in cellular triacylglycerol content and emergence of large ER-associated lipid droplets in the absence of CDP-DG synthase function.
Bottom Line: Using two species of fission yeast, we show that cycling cells deficient in the function of the ER-resident CDP-DG synthase Cds1 exhibit markedly increased triacylglycerol content and assemble large lipid droplets closely associated with the ER membranes.We demonstrate that these unusual structures recruit the triacylglycerol synthesis machinery and grow by expansion rather than by fusion.Our results suggest that interfering with the CDP-DG route of phosphatidic acid utilization rewires cellular metabolism to adopt a triacylglycerol-rich lifestyle reliant on the Kennedy pathway.
Affiliation: Temasek Life Sciences Laboratory, 117604 Singapore Department of Biological Sciences, National University of Singapore, 117543 Singapore.Show MeSH
Mentions: It was previously proposed that deficiency in the Cds1 function in budding yeast could lead to LD fusion and emergence of supersized LDs caused by a rise in intracellular PA levels (Fei et al., 2011). Strong enrichment of TG synthases at abnormal lipid droplets in cds1-9 cells, together with the fact that they were closely associated with the ER, raised a possibility that these structures arose as a result of progressive enlargement rather than fusion of the preexisting, normally sized LDs. To evaluate this possibility, we performed time-lapse imaging of cds1-9 cells expressing the LD marker Tgl4-GFP or the artificial luminal ER marker GFP-ADEL (Zhang et al., 2010). Cells were shifted to the restrictive temperature of 36°C, and imaging started 2 h after the shift. We observed emergence of highly refractile bodies that recruited Tgl4-GFP and expanded over time (Figure 8A; n = 3 cells). Imaging using GFP-ADEL showed initial clustering of the ER membranes, followed by their outward expansion and eventual formation of large, “bubble”-like structures (Figure 8B; n = 14 cells). Thus abnormally large LDs in cells lacking the ER-localized CDP-DG synthase activity form through continuous growth rather than fusion between the preexisting LDs.
Affiliation: Temasek Life Sciences Laboratory, 117604 Singapore Department of Biological Sciences, National University of Singapore, 117543 Singapore.