The effect of the disruption of a gene encoding a PI4 kinase on the developmental defect exhibited by Dictyostelium rasC− cells

Abstract

The disruption of the gene encoding the Dictyostelium Ras subfamily protein, RasC results in a strain that fails to aggregate with defects in both cAMP signal relay and chemotaxis. Restriction enzyme mediated integration disruption of a second gene in the rasC − strain resulted in cells that were capable of forming multicellular structures in plaques on bacterial lawns. The disrupted gene, designated pikD 1 , encodes a member of the phosphatidyl-inositol-4-kinase β subfamily. Although the rasC − / pikD 1 cells were capable of progressing through early development, when starved on a plastic surface under submerged conditions, they did not form aggregation streams or exhibit pulsatile motion. The rasC − / pikD 1 cells were extremely efficient in their ability to chemotax to cAMP in a spatial gradient, although the reduced phosphorylation of PKB in response to cAMP observed in rasC − cells, was unchanged. In addition, the activation of adenylyl cyclase, which was greatly reduced in the rasC − cells, was only minimally increased in the rasC − / pikD 1 strain. Thus, although the rasC − / pikD − cells were capable of associating to form multicellular structures, normal cell signaling was clearly not restored. The disruption of the pikD gene in a wild type background resulted in a strain that was delayed in aggregation and formed large aggregation streams, when starved on a plastic surface under submerged conditions. This strain also exhibited a slight defect in terminal development. In conclusion, disruption of the pikD gene in a rasC − strain resulted in cells that were capable of forming multicellular structures, but which did so in the absence of normal signaling and aggregation stream formation.