Genetic analysis of the role of G protein-coupled receptor signaling in electrotaxis

C ells display chemotaxis and electrotaxis by migrating directionally in gradients of specific chemicals or electrical potential. Chemotaxis in Dictyostelium discoideum is mediated by G protein-coupled receptors. The unique Gbeta is essential for all chemotactic responses, although different chemoattractants use different receptors and Galpha subunits. Dictyostelium amoebae show striking electrotaxis in an applied direct current electric field. Perhaps electrotaxis and chemotaxis share similar signaling mechanisms? Null mutation of Gbeta and cAMP receptor 1 and Galpha2 did not abolish electrotaxis, although Gbeta-null mutations showed suppressed electrotaxis. By contrast, G protein signaling plays an essential role in chemotaxis. G protein-coupled receptor signaling was monitored with PHcrac-green fluorescent protein, which translocates to inositol phospholipids at the leading edge of cells during chemotaxis. There was no intracellular gradient of this protein during electrotaxis. However, F-actin was polymerized at the leading edge of cells during electrotaxis. We conclude that reception and transduction of the electrotaxis signal are largely independent of G protein-coupled receptor signaling and that the pathways driving chemotaxis and electrotaxis intersect downstream of heterotrimeric G proteins to invoke cytoskeletal elements.