Developmentally regulated changes in 1,2-diacylglycerol in Dictyostelium. Regulation by light and G proteins

We have measured 1,2-diacylglycerol (DG) mass during Dictyostelium development. DG levels are initially high in vegetative cells, decrease upon starvation, increase during aggregation, and rise dramatically during culmination, concomitant with SpiA (a spore cell-specific gene) expression. These results are consistent with DG being involved in culmination-stage morphological changes and cell-type differentiation. Mutant analysis shows that the rise in DG during aggregation requires cAMP signaling pathways but is not directly regulated through these processes but via developmental programs induced through cAMP. DG accumulation during aggregation is approximately 8-fold higher than would be expected from inositol lipid hydrolysis (1), suggesting that DG is produced from sources in addition to phosphatidylinositol 4,5-bisphosphate. Our data suggest that during aggregation, although some DG is formed through phospholipase D activity, other pathways (e.g. de novo synthesis) may be more important regulators of DG accumulation. During culmination, DG accumulation correlated with the formation of phosphatidic acid and phosphatidylethanol suggesting the activation of phospholipase D. During this time, the [3H]palmitate labeling of a number of phospholipids decreased rapidly, suggesting a rapid metabolism of phospholipids at this time. Exposure of slugs developed in the dark to light, which initiates culmination, causes rapid DG accumulation, suggesting the activation of phospholipid hydrolysis. The temporal pattern and level of DG accumulation is altered in G alpha 1 null and overexpressing strains, suggesting that G alpha 1 is upstream from DG formation during culmination. These results demonstrate that specific pathways of DG formation are under developmental control and suggest a possible link between light, the activation of DG production, and induction of culmination.