Ca2+ signalling is not required for chemotaxis in Dictyostelium

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Abstract
Dictyostelium cells can move rapidly towards a source of cyclic‐AMP (cAMP). This chemoattractant is detected by G‐protein‐linked receptors, which trigger a signalling cascade including a rapid influx of Ca2+. We have disrupted an inositol 1,4,5‐trisphosphate (InsP3) receptor‐like gene, iplA , to produce null cells in which Ca2+ entry in response to chemoattractants is abolished, as is the normal increase in free cytosolic Ca2+ ([Ca2+]c) that follows chemotactic stimulation. However, the resting [Ca2+]c is similar to wild type. This mutant provides a test for the role of Ca2+ influx in both chemotaxis and the signalling cascade that controls it. The production of cyclic‐GMP and cAMP, and the activation of the MAP kinase, DdERK2, triggered from the cAMP receptor, are little perturbed in the mutant; mobilization of actin into the cytoskeleton also follows similar kinetics to wild type. Mutant cells chemotax efficiently towards cAMP or folic acid and their sensitivity to cAMP is similar to wild type. Finally, they move at similar speeds to wild‐type cells, with or without chemoattractant. We conclude that Ca2+ signalling is not necessary for chemotaxis to cAMP.