The biosynthesis of phospholipids is linked to the cell cycle in a model eukaryote

Abstract

The structural challenges faced by eukaryotic cells through the cell cycle are key for understanding cell viability and proliferation. In this study, 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 would form part the 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 2.5x) and phosphatidylglycerol over the G1/pre-replication phase boundary (+100%, phosphatidylglycerol synthase increased 22x). 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. The relative abundance of both phosphatidylinositol and its synthase remained constant despite an eightfold increase in cell volume. We conclude that the biosynthesis of the three most abundant structural phospholipids is linked to the cell cycle in D. quadricauda.

A pipeline for making 31P NMR accessible for small- and large-scale lipidomics studies

“…These results suggest that a minimum of 4 mg of lipids from biological extracts is required for a reliable 31 P NMR sample of typical mixed lipids. Although this may be challenging for some human studies, this sample size is more achievable, even desirable, for small-scale studies [23,25].…”

“…A tailormade solvent mixture that maximizes solubility of phospholipids and gives good separation of resonances whilst limiting that of polar and non-polar material (such as sugars and triglycerides, respectively), has been developed for this purpose [18][19][20][21]. The availability of such a solvent system has led to 31 P NMR being used as the sole technique for acquiring lipidomics data for some low-and medium-throughput studies [22][23][24][25]. 31 P NMR is useful for providing a straightforward spectrum of lipid class abundance but can also be used to acquire data about the molecular structure of lipids and allows us to correct for different ionization efficiencies in in MS lipidomics data.…”

“…It can also be used to acquire all the lipidomics data required for studies in which only molar concentration is required, e.g. structural studies [25]. However, many of the lipidomics-specific aspects of 31 P NMR have not yet been described in detail and the technique is typically alien to users not already familiar with NMR.…”