Role of phospholipase C in Dictyostelium: Formation of inositol 1,4,5-trisphosphate and normal development in cells lacking phospholipase C activity

The micro-organism Dictyostelium uses extracellular cAMP to induce chemotaxis and cell differentiation. Signals are transduced via surface receptors, which activate G proteins, to effector enzymes. The deduced protein sequence of Dictyostelium discoideum phosphabidylinositol-specific phospholipase C (PLC) shows strong homology with the mammalian PLC-delta isoforms. To study the role of PLC in Dictyostelium, a plc(-) mutant was constructed by disruption of the PLC gene. No basal or stimulated PLC activity could be measured during the whole developmental programme of the plc(-) cells. Loss of PLC activity did not result in a visible alteration of grow th or development. Further analysis showed that developmental gene regulation, cAMP-mediated chemotaxis and activation of guanylyl and adenylyl cyclase were normal. Although the cells lack PLC activity, inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] was present at only slightly lower concentrations compared with control cells. Mass analysis of inositol phosphates demonstrated the presence of a broad spectrum of inositol phosphates in Dictyostelium, which was unaltered in the plc(-) mutant. Cell labelling experiments with [H-3]inositol indicated that [H-3]Ins(1,4,5)P-3 was formed in a different manner in the mutant than in control cells