The structural challenges faced by eukaryotic cells through the cell cycle are key for understanding cell viability and proliferation. We tested the hypothesis that the biosynthesis of structural lipids is linked to the cell cycle. If true, this would suggest that the cell's structure is important for progress through and perhaps even control of the cell cycle. Lipidomics (31P NMR and MS), proteomics (Western immunoblotting) and transcriptomics (RT-qPCR) techniques were used to profile the lipid fraction and characterise aspects of its metabolism at seven stages of the cell cycle of the model eukaryote, Desmodesmus quadricauda. We found considerable, transient increases in the abundance of phosphatidylethanolamine during the G1 phase (+35%, ethanolamine phosphate cytidylyltransferase increased 2·5×) and phosphatidylglycerol (+100%, phosphatidylglycerol synthase increased 22×) over the G1/pre-replication phase boundary. The relative abundance of phosphatidylcholine fell by ~35% during the G1. N-Methyl transferases for the conversion of phosphatidylethanolamine into phosphatidylcholine were not found in the de novo transcriptome profile, though a choline phosphate transferase was found, suggesting that the Kennedy pathway is the principal route for the synthesis of PC. The fatty acid profiles of the four most abundant lipids suggested that these lipids were not generally converted between one another. This study shows for the first time that there are considerable changes in the biosynthesis of the three most abundant phospholipid classes in the normal cell cycle of D. quadricauda, by margins large enough to elicit changes to the physical properties of membranes.

• Keywords
• Cell cycle, Cell division, Cell structure, Desmodesmus quadricauda, Green algae, Lipid composition, Lipid metabolism,
• MeSH
• Cell Cycle * MeSH
• Phosphatidylcholines metabolism   biosynthesis   MeSH
• Phosphatidylethanolamines metabolism   biosynthesis   MeSH
• Phospholipids * metabolism   biosynthesis   MeSH
• Lipidomics methods   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phosphatidylcholines MeSH
• Phosphatidylethanolamines MeSH
• Phospholipids * MeSH
• phosphatidylethanolamine MeSH Browser

Temperature is one of the key factors affecting growth and division of algal cells. High temperature inhibits the cell cycle in Chlamydomonas reinhardtii. At 39 °C, nuclear and cellular divisions in synchronized cultures were blocked completely, while DNA replication was partly affected. In contrast, growth (cell volume, dry matter, total protein, and RNA) remained unaffected, and starch accumulated at very high levels. The cell cycle arrest could be removed by transfer to 30 °C, but a full recovery occurred only in cultures cultivated up to 14 h at 39 °C. Thereafter, individual cell cycle processes began to be affected in sequence; daughter cell release, cell division, and DNA replication. Cell cycle arrest was accompanied by high mitotic cyclindependent kinase activity that decreased after completion of nuclear and cellular division following transfer to 30 °C. Cell cycle arrest was, therefore, not caused by a lack of cyclin-dependent kinase activity but rather a blockage in downstream processes.

• Keywords
• Chlamydomonas reinhardtii, DNA replication, cell cycle arrest, cell size, cyclin-dependent kinase, starch accumulation, supraoptimal temperature, synchronized cultures,
• MeSH
• Algal Proteins metabolism   MeSH
• Cell Culture Techniques methods   MeSH
• Chlamydomonas reinhardtii cytology   physiology   MeSH
• Cyclin-Dependent Kinases metabolism   MeSH
• Down-Regulation MeSH
• Stress, Physiological MeSH
• Cell Cycle Checkpoints * MeSH
• Gene Expression Regulation, Plant MeSH
• Hot Temperature MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Algal Proteins MeSH
• Cyclin-Dependent Kinases MeSH

DNA damage is a ubiquitous threat endangering DNA integrity in all living organisms. Responses to DNA damage include, among others, induction of DNA repair and blocking of cell cycle progression in order to prevent transmission of damaged DNA to daughter cells. Here, we tested the effect of the antibiotic zeocin, inducing double stranded DNA breaks, on the cell cycle of synchronized cultures of the green alga Chlamydomonas reinhardtii. After zeocin application, DNA replication partially occurred but nuclear and cellular divisions were completely blocked. Application of zeocin combined with caffeine, known to alleviate DNA checkpoints, decreased cell viability significantly. This was probably caused by a partial overcoming of the cell cycle progression block in such cells, leading to aberrant cell divisions. The cell cycle block was accompanied by high steady state levels of mitotic cyclin-dependent kinase activity. The data indicate that DNA damage response in C. reinhardtii is connected to the cell cycle block, accompanied by increased and stabilized mitotic cyclin-dependent kinase activity.

• Keywords
• Chlamydomonas reinhardtii, DNA damage, caffeine, cell cycle, cyclin-dependent kinase, double-stranded break, zeocin,
• MeSH
• Bleomycin toxicity   MeSH
• Chlamydomonas reinhardtii drug effects   genetics   MeSH
• Cyclin-Dependent Kinases metabolism   MeSH
• Cytostatic Agents toxicity   MeSH
• DNA, Plant drug effects   MeSH
• DNA Breaks, Double-Stranded MeSH
• Caffeine pharmacology   MeSH
• Cell Cycle Checkpoints MeSH
• Mutagens toxicity   MeSH
• DNA Replication MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bleomycin MeSH
• Cyclin-Dependent Kinases MeSH
• Cytostatic Agents MeSH
• DNA, Plant MeSH
• Caffeine MeSH
• Mutagens MeSH
• Zeocin MeSH Browser