Preferential incorporation of phospholipids into plasma membranes during cell aggregation of Dictyostelium discoideum.

Changes in phospholipids of plasma r .embranes and total particulate membranes of the cellular slime mold Dictyostelium discoideum were analyzed during development. The predominant classes of phospholipids in the plasma membrane were phosphatidylethanolamine and phosphatidylcholine, constituting approximately 50 and 25 molar per cent of phospholipid phosphorus, respectively. The relative amount of plasma membrane phospholipid increased by almost 30% and the relative proportion of the major phospholipid classes remained constant during the early phase of development. An induction in phospholipid synthesis occurred during cell aggregation, resulting in a 12% increase in the cellular phospholipid content. The relative rate of synthesis increased rapidly between 3 and 9 h of development and began to drop at the postaggregation stage. Plasma membranes isolated from cells at different developmental stages showed that plasma membrane phospholipids were preferentially labeled at 6 h, giving rise to a 20-fold increase in specific activity. The specific activity of plasma membrane phospholipids was 8to 10-fold higher than that of total particulate membranes at 6 h. The data suggest that the newly synthesized phospholipids inside the cell were preferentially incorporated into the plasma membrane at the onset of cell aggregation. Phospholipid synthesis was also examined in an aggregateless mutant strain WL3. An approximate 2-fold increase in the synthesis of phospholipids was observed, but there was no preferential transport of labeled phospholipids to the plasma membrane. These results suggest that the rapid incorporation of phospholipids into plasma membrane is coupled with chemotactic migration during differentiation. The possible role of phospholipids in cell-cell adhesion is also discussed.