A Mutation That Separates the RasG Signals That Regulate Development and Cytoskeletal Function inDictyostelium

Abstract

The expression of an activatedRasG, RasG-G12T, in vegetative cells ofDictyostelium discoideiumproduced an alteration in cell morphology. Cells underwent a transition between an extensively flattened form that exhibited lateral membrane ruffling to a less flattened form that exhibited prominent dorsal membrane ruffling. TheserasG-G12T transformants exhibited a redistribution of F-actin at the cell periphery and did not undergo the rapid contraction upon refeeding that is characteristic of wild-type cells. These results suggest a role for RasG in regulating cytoskeletal rearrangement inD. discoideum.We had shown previously that expression ofrasG-G12T inhibited starvation induced aggregation (M. Khoslaet al.,1996,Mol. Cell. Biol.16, 4156–4162).rasG-G12T genes containing secondary mutations were transformed into cells to test whether the effects ofrasG-G12T were transmitted through a single downstream effector. Cells expressingrasG-G12T/T35S orrasG-G12T/Y40C (secondary mutations within the effector domain) exhibited normal morphology and underwent normal aggregation, suggesting that signaling through the effector domain was required for both the morphological and the development changes induced byrasG-G12T. In contrast, cells expressingrasG-G12T/T45Q (a secondary mutation in the effector distal flanking domain) exhibited normal aggregation but a morphology indistinguishable from that ofrasG-G12T transformants. This result suggests that RasG regulates developmental and cytoskeletal functions by direct interaction with more than one downstream effector.