A large-scale screen reveals genes that mediate electrotaxis in Dictyostelium discoideum

A screen in Dictyostelium reveals that mTORC2 signaling participates in electrotaxis, as well as chemotaxis. Moving to that electric feel Cell movement can be guided by chemical gradients (chemotaxis) or by electrical fields (electrotaxis), both of which contribute to wound healing. Whereas the mechanisms that control chemotaxis are well characterized, those controlling electrotaxis are not. To identify genes required for electrotaxis in the slime mold Dictyostelium discoideum, a model organism that has been used in chemotaxis studies, Gao et al. developed a high-throughput screening method of analyzing electrotaxis in genetically modified Dictyostelium strains. Without components of the TORC2 pathway, a pathway involved in chemotaxis, these single-celled organisms had defective electrotaxis. This study sets the stage for identifying signaling pathways that are unique to each type of movement and those that are shared. Directional cell migration in an electric field, a phenomenon called galvanotaxis or electrotaxis, occurs in many types of cells, and may play an important role in wound healing and development. Small extracellular electric fields can guide the migration of amoeboid cells, and we established a large-scale screening approach to search for mutants with electrotaxis phenotypes from a collection of 563 Dictyostelium discoideum strains with morphological defects. We identified 28 strains that were defective in electrotaxis and 10 strains with a slightly higher directional response. Using plasmid rescue followed by gene disruption, we identified some of the mutated genes, including some previously implicated in chemotaxis. Among these, we studied PiaA, which encodes a critical component of TORC2, a kinase protein complex that transduces changes in motility by activating the kinase PKB (also known as Akt). Furthermore, we found that electrotaxis was decreased in mutants lacking gefA, rasC, rip3, lst8, or pkbR1, genes that encode other components of the TORC2-PKB pathway. Thus, we have developed a high-throughput screening technique that will be a useful tool to elucidate the molecular mechanisms of electrotaxis.