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Plasma membrane lipid composition of Dictyostelium Discoideum during early development in aqueous suspension

University of British Columbia

Cell-cell contact must be made and maintained for normal development and eventual differentiation of D. discoideum to occur. Certain plasma membrane components are known to alter in activity or abundance during the organism's developmental cycle although no quantitative measurement of plasma membrane neutral lipid and phospholipid content has been reported to date. Optimal conditions for the extraction, separation and assay of lipid components were derived and tested by quantification of the neutral lipid and phospholipid components of intact cells of strain Ax-2. Development was initiated in D. discoideum populations suspended in aqueous buffer and plasma membrane fractions were purified from both exponentially growing and aggregation-phase cells by a modified procedure which minimized phospholipid degradation during the plasma membrane isolation. Neutral lipid and phospholipid compositions of the plasma membrane fractions PM1 and PM2 from exponentially growing cells and from those in early aggregation phase were determined. Exponential phase cells' plasma membranes contained large proportions of phosphatidylethanolamine, phosphatidylcholine and lysophosphatidylethanolamine. Lysophosphatidylcholine was absent. A significant quantity of phosphatidylinositol was detected and cardiolipin, phosphatidylglycerol, phosphatidic acid and lyso-phosphatidic acid were each present in small amounts. The presence of phosphatidylethanolamine plasmalogen was suspected but not proven. No acylglycerol components were detected, the major neutral lipid fraction being that of free sterol which largely comprised stigmast-22-en-3β-ol; sterol ester was present in extremely small quantities. An unidentified neutral lipid component of plasma membranes was detected by its characteristic absorption and fluorescence upon irradiation at ultraviolet wavelengths. After sixteen hours aggregation the phosphatidylcholine content of the plasma membranes was greatly reduced, a significant proportion of the phosphatidylethanolamine appeared to have been converted to lysophosphatidylethanolamine, and phosphatidylglycerol, phosphatidic acid and lysophosphatidic acid were all in greater abundance than in growing cells' membranes. The free sterol component remained relatively constant but sterol ester had increased dramatically (7 to 10-fold) and the fatty acid composition of the plasma membrane phospholipids was more saturated, primarily because of the accumulation of palmitate and stearate and a reduction of the octadeca-dienoic fatty acid components.

Text

2010-03-11

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http://hdl.handle.net/2429/21745

Microbiology and Immunology

University of British Columbia

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