Rapid kinetics of lipid second messengers controlled by a cGMP signalling network coordinates apical complex functions in Toxoplasma tachyzoites

Abstract

Host cell invasion and subsequent egress by Toxoplasma parasites is regulated by a network of cGMP, cAMP, and calcium signalling proteins. Such eukaryotic signalling networks typically involve lipid second messengers including phosphatidylinositol phosphates (PIPs), diacylglycerol (DAG) and phosphatidic acid (PA). However, the lipid signalling network in Toxoplasma is poorly defined. Here we present lipidomic analysis of a mutant of central flippase/guanylate cyclase TgGC in Toxoplasma, which we show has disrupted turnover of signalling lipids impacting phospholipid metabolism and membrane stability. The turnover of signalling lipids is extremely rapid in extracellular parasites and we track changes in PA and DAG to within 5 seconds, which are variably defective upon disruption of TgGC and other signalling proteins. We then identify the position of each protein in the signal chain relative to the central cGMP signalling protein TgGC and map the lipid signal network coordinating conoid extrusion and microneme secretion for egress and invasion.