Abstract
In recent years, scientific studies on lipid droplets (LDs) have advanced far more than in the past. There is increasing evidence that LDs are not only intracellular storage organelles but also dynamic in nature. In addition, LDs are associated with pathological conditions such as obesity, atherosclerosis and diabetes mellitus. Therefore, this study focuses on elucidating the fundamental molecular mechanisms governing lipid droplet synthesis using yeast as a model system. CKB1 and CKB2 encode the β-subunits of the novel Casein Kinase 2 (CK2). Through a reverse genetic screen of the non-essential genes (EUROSCARF) collection, it was observed that the Δckb1 and Δckb2 single deletion mutants produced supersized LD phenotype. The expressions of Ckb1p and Ckb2p in the respective single deletion mutants which are restored to wild type phenotype indicate that CKB1 and CKB2 may play a role in LD morphology and lipid biosynthesis. A 40 % increase in triacylglycerol (TAG) content and a 30 % decrease in phosphatidylcholine (PC) and 10 % reduction in phosphatidylethanolamine (PE) were observed in Δckb1 and Δckb2 when compared to wild type (WT). The expression of genes regulating phospholipids synthesis was examined and CDS1 expression was found to be significantly decreased in Δckb1 and Δckb2 mutants. Overexpression of CDS1 in Δckb1 and Δckb2 restored wild type morphology of the LDs. Mass spectrometry analysis also showed an abnormally high level of phosphatidic acid (PA) content in the Δckb1 and Δckb2 mutants when compared to WT. This implies that CK2 protein kinase may be involved in maintaining lipid droplet size by regulating the PA level, probably through the transcription machinery where CDS1 mRNA expression is regulated. However, detailed biomolecular mechanisms governing its role have to be further studied.