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 che motaxisand cell differentiation. Signals are transduced via surface re ceptors, whichactivate G proteins, to effector enzymes. The deduced pr otein sequence of Dictyostelium discoideum phosphabidylinositol-specif ic phospholipase C (PLC) shows strong homology with the mammalian PLC- delta isoforms. To study the role of PLC in Dictyostelium, a plc(-) mu tant was constructed by disruption of the PLC gene. No basal or stimul ated PLC activity could be measured during the whole developmental pro gramme of the plc(-) cells. Loss of PLC activity did not result in a v isible alteration of grow th or development. Further analysis showed t hat developmental gene regulation, cAMP-mediated chemotaxisand activat ion of guanylyl and adenylyl cyclase were normal. Although the cells l ack PLC activity, inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] was pre sent 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 unal tered in the plc(-) mutant. Cell labelling experiments with [H-3]inosi tol indicated that [H-3]Ins(1,4,5)P-3 was formed in a different manner in the mutant than in control cells.